2019 |
Abdulsamad, F., Revil, A., Ahmed, A. S., Coperey, A., Karaoulis, M., Nicais, S., et al. (2019). Induced polarization tomography applied to the detection and the monitoring of leaks in embankments. Engineering Geology, 254, 89–101.
Résumé: During an induced polarization survey, both electrical conductivity and chargeability can be imaged. Recent petrophysical models have been developed to provide a consistent picture of these two parameters in terms of water and clay contents of soils. We test the ability of this method at a test site in which a controlled artificial leakage can be generated in an embankment surrounding an experimental basin. 3D tomography of the conductivity and normalized chargeability are performed during such a controlled leakage. Conductivity and induced polarization measurements were also performed on a core sample from the site. The sample was also characterized in terms of porosity and cation exchange capacity. Combining the 3D survey and these laboratory measurements, a 3D tomogram of the relative variation in water content (before leakage and during leakage) was estimated. It clearly exhibits the ground water flow path through the embankment from the outlet of the tube used to generate the leak to the bottom of the embankment. In addition, a self-potential survey was performed over the zone of leakage. This survey evidences also the projection of the ground water flow path over the ground surface. Both methods are found to provide a consistent picture. A 2.5D time lapse tomography of the electrical conductivity and normalized chargeability was also performed and evidences the position of the preferential flow paths below the profile. These results confirm the ability and efficiency of induced polarization to provide reliable information pertaining to the detection of leakages in dams and embankments.
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Abdulsamad, F., Revil, A., Ghorbani, A., Toy, V., Kirilova, M., Coperey, A., et al. (2019). Complex Conductivity of Graphitic Schists and Sandstones. Journal Of Geophysical Research-Solid Earth, 124(8), 8223–8249.
Résumé: Spectral induced polarization spectra were carried out on three graphitic schists and two graphitic sandstones. The microstructural arrangement of graphite of two graphitic schists was studied with thin sections using transmitted and reflected light optical and electron microscopic methods. Chemical maps of selected areas confirm the presence of carbon. The complex conductivity spectra were measured in the frequency range 10 mHz to 45 kHz and in the temperature range +20 degrees C down to -15 degrees C. The measured spectra are fitted with a double Cole-Cole complex conductivity model with one component associated with the polarization of graphite and the second component associated with the Maxwell-Wagner polarization. The Cole-Cole exponent and the chargeability are observed to be almost independent of temperature including in freezing conditions. The conductivity and relaxation time are dependent on the temperature in a predictable way. As long as the temperature decreases, the electrical conductivity decreases and the relaxation time increases. A finite element model is able to reproduce the observed results. In this model, we consider an intragrain polarization mechanism for the graphite and a change of the conductivity of the background material modeled with an exponential freezing curve. One of the core sample (a black schist), very rich in graphite, appears to be characterized by a very high conductivity (approximately 30 S/m). Two induced polarization profiles are discussed in the area of Thorens. The model is applied to the chargeability data to map the volumetric content of graphite.
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Ahmed, A. S., Revil, A., Steck, B., Vergniault, C., Jardani, A., & Vinceslas, G. (2019). Self-potential signals associated with localized leaks in embankment dams and dikes. Engineering Geology, 253, 229–239.
Résumé: The self-potential method can be used to detect and monitor anomalous seepages in dams and embankments. In such a case, an electrical field of electrokinetic nature (i.e., associated with pore water flow) can be measured using a set of non-polarizable electrodes typically located at the ground surface or in some wells. This field can be in turn related to the pattern of groundwater flow. We built an experimental dam to investigate to which extent the self-potential method can help characterizing seepages in dams. We first use the finite element method to simulate the ground water flow in a heterogeneous porous and permeable material by solving the groundwater flow equation. The resulting groundwater flow solution is then used to compute the electrical potential distribution by solving the corresponding elliptic partial differential equation. In a preliminary experiment, we could not measure any self-potential anomaly associated with the infiltration of water in the dam. Our numerical simulations showed that the magnitudes of the self-potential anomalies were controlled by (1) the nature of the flow regime (viscous laminar versus inertial laminar flow regimes) and (2) the presence of insulating Polyvinyl Chloride (PVC) tubes located at the end of the preferential flow channels in the structure of the dam. Thanks to these numerical simulations, we added sand at the entrance of the infiltration area in order to reduce the effects of the PVC tubes and to restrain the flow regime to the viscous laminar flow regime. New experiments allowed for detecting a self-potential anomaly with an amplitude of around -9 mV consistent with that obtained through numerical modelling with a finite element simulator. This comparison was used to test the accuracy of the modelling approach and define the strengths and weaknesses of the self-potential method to determine preferential seepages in earth dam structures.
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Airaghi, L., Janots, E., Lanari, P., de Sigoyer, J., & Magnin, V. (2019). Allanite Petrochronology in Fresh and Retrogressed Garnet-Biotite Metapelites from the Longmen Shan (Eastern Tibet). Journal Of Petrology, 60(1), 151–176.
Résumé: Linking the timing of allanite growth to metamorphic conditions in metapelites is particularly challenging because of the large variety of allanite textures and chemical compositions. This study focuses on five garnet-biotite metapelites retrogressed to different extents, from the internal domain of the Longmen Shan (eastern Tibet) from which few petrochronological data documenting the metamorphic ages are available. Microstructural observations were combined with whole-rock compositions, detailed mineral characterization, phase equilibria modelling, and in situ U-Th/Pb allanite dating to gain insights into the allanite reactivity relative to other rock-forming minerals. All samples experienced similar peak temperatures of 560-600 degrees C. Allanite is the main rare earth element (REE)-bearing accessory mineral but it exhibits different textures, such as epidote rims with distinct REE contents as well as late inclusion-like dissolution features. Garnet is, along with allanite, critical to reconstruct the REE budget of these rocks. In the two samples where allanite is observed as inclusions in garnet, garnet shows no textural zoning and a low Y content (<90ppm). This is attributed to early Y fractionation in allanite and epidote rims with no further equilibration with garnet. This allanite is therefore pre-garnet (T<520 degrees C). In the sample where allanite is observed only in the matrix, both garnet and allanite-epidote rims exhibit more complex textural and compositional zoning, with a higher Y content in garnet. The Y incorporation in garnet is attributed to a series of reactions involving allanite, interpreted as syn- to post-garnet growth (T>520 degrees C). This relative chronology is confirmed by in situ U-Th/Pb allanite dating: pre-garnet allanite shows ages of c. 200Ma, whereas syn- to post-garnet allanite has ages of c. 180Ma. The timing of allanite appearance strongly correlates with the biotite-in reaction predicted by the models and observed in microstructures. In the two samples collected close to the major Wenchuan Shear Zonedeformed up to mylonitization and retrogressed under greenschist-facies conditions (3-4 +/- 1kbar, 350-400 degrees C)allanite still preserves the peak metamorphic ages (c. 200 and c. 180Ma). Allanite and its epidote rims, however, are fragmented and partly replaced by a retrograde assemblage of Qz + Pb-depleted (<100ppm) monazite, providing an age <90-100Ma. Our results allow different metamorphic stages for the studied transect in the central Longmen Shan to be refined: a prograde path at c. 200Ma, a thermal relaxation and exhumation from c. 180Ma, and a late greenschist overprint. This study also shows that when allanite is the principal phase in a mineral assemblage datable by U-Th/Pb, detailed observations of allanite textures may be highly informative in constraining the timing of its growth relative to other major mineral phases.
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Anjom, F. K., Teodor, D., Comina, C., Brossier, R., Virieux, J., & Socco, L. V. (2019). Full-waveform matching of VP and VS models from surface waves. Geophysical Journal International, 218(3), 1873–1891.
Résumé: The analysis of surface wave dispersion curves (DCs) is widely used for near-surface S-wave velocity (VS) reconstruction. However, a comprehensive characterization of the near-surface requires also the estimation of P-wave velocity (VP). We focus on the estimation of both VS and VP models from surface waves using a direct data transform approach. We estimate a relationship between the wavelength of the fundamental mode of surface waves and the investigation depth and we use it to directly transform the DCs into VS and VP models in laterally varying sites. We apply the workflow to a real data set acquired on a known test site. The accuracy of such reconstruction is validated by a waveform comparison between field data and synthetic data obtained by performing elastic numerical simulations on the estimated VP and VS models. The uncertainties on the estimated velocity models are also computed.
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Arosio, D., Longoni, L., Papini, M., Bievre, G., & Zanzi, L. (2019). Geological and geophysical investigations to analyse a lateral spreading phenomenon: the case study of <bold>Torrioni di Rialba</bold>, northern Italy. Landslides, 16(7), 1257–1271.
Résumé: We combined geological, geomechanical, geophysical and remote sensing investigations, including persistent scatterer interferometry and bathymetry, to study a slope where four conglomerate towers laterally spread over a shale layer. Electrical resistivity tomography surveys confirm a shale layer that underlies the rock towers with an attitude parallel to the slope. Field mapping reveals that the stability of the rock towers is threatened by weakly cemented conglomerate layers, large eroded zones and karstic weathering due to water circulation. We deem that the most probable failure mechanism would be the toppling of the southernmost tower, promoted primarily by the weak conglomerate layer in its lower section. The plastic shale layer underneath the rock cliff is very likely to promote lateral spreading that may have triggered the toppling of an additional former rock pillar, whose rock blocks were found in the lake during a bathymetric survey. Close- and long-range remote sensing of displacements provide no results that could be interpreted with confidence. Seismic noise recording sessions with 3C low-frequency velocimeters suggest that the dynamic conditions of the towers do not show appreciable variations across the recording sessions, especially considering the two rock towers featuring the most interesting spectral characteristics. However, both the resonance frequencies and the preferential oscillation directions estimated from the seismic noise datasets are consistent with the analytical relationships and will support the design of an effective monitoring strategy.
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Ars, J. - M., Tarits, P., Hautot, S., Bellanger, M., Coutant, O., & Maia, M. (2019). Joint inversion of gravity and surface wave data constrained by magnetotelluric: Application to deep geothermal exploration of crustal fault zone in felsic basement. Geothermics, 80, 56–68.
Résumé: Geophysical exploration in unconventional geothermal reservoir is challenging because of the lack of structures with specific geophysical signature such as a clay cap above volcanic geothermal reservoirs. The combination of several geophysical methods such as magnetotelluric (MT), gravity and seismic methods provides complementary insight into the geothermal reservoir. We present a joint inversion approach of ambient noise surface wave and gravity constrained by the 3D distribution of electrical resistivity. The method is applied to analyze the potential of unconventional deep geothermal resources in the French Massif Central (FMC). We coupled the resistivity, density and shear wave velocity with a linear correlation. We characterized the common properties in relation to the geological domains down to about 10-15 km. We validated the proposed approach on a synthetic model derived from models obtained from each independent geophysical method. The joint inversion limited the non-uniqueness of the gravity and the ambient noise tomography inversion and allow to recover the features of the synthetic models. We applied the method to real field data acquired in the Sioule Valley, Massif Central, France. The joint features observed in the geophysical models suggest a deep heat source associated with a possible shallow (similar to 6-8 km) brittle ductile transition. A large fault zone, the Pongibaud Fault zone, seems to become listric and connect the surface to this transition zone to possibly constitute a permeable path for water circulation.
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Askri, D., Cunin, V., Beal, D., Berthier, S., Chovelon, B., Arnaud, J., et al. (2019). Investigating the toxic effects induced by iron oxide nanoparticles on neuroblastoma cell line: an integrative study combining cytotoxic, genotoxic and proteomic tools. Nanotoxicology, 13(8), 1021–1040.
Résumé: Nanomaterials have gained much attention for their use and benefit in several fields. Iron Oxide Nanoparticles (IONPs) have been used in Biomedicine as contrast agents for imaging cancer cells. However, several studies reported the potential toxicity of those nanoparticles in different models, especially in cells. Therefore, in our present study, we investigated the effects of IONPs on the SH-SY5Y neuroblastoma cell line. We carried out cytotoxic and genotoxic studies to evaluate the phenotypic effects, and proteomic investigation to evaluate the molecular effects and the mechanisms by which this kind of NPs could induce toxicity. Our results showed that the use of three different sizes of IONPs (14, 22 and 30 nm) induced cell detachment, cell morphological changes, size, and concentration-dependent IONP internalization and cell mortality. IONPs induced slight genotoxic damage assayed by modified comet assay without affecting cell cycle, mitochondrial function, membrane integrity, intracellular calcium level, and without inducing ROS generation. All the studies were performed to compare also the effects of IONPs to the ferric iron by incubating cells with equivalent concentration of FeCl3. In all tests, the NPs exhibited more toxicity than the ferric iron. The proteomic analysis followed by gene ontology and pathway analysis evidenced the effects of IONPs on cytoskeleton, cell apoptosis, and cancer development. Our findings provided more information about IONP effects on human cells and especially on cancer cell line.
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Askri, D., Cunin, V., Ouni, S., Beal, D., Rachidi, W., Sakly, M., et al. (2019). Effects of Iron Oxide Nanoparticles (gamma-Fe2O3) on Liver, Lung and Brain Proteomes following Sub-Acute Intranasal Exposure: A New Toxicological Assessment in Rat Model Using iTRAQ-Based Quantitative Proteomics. International Journal Of Molecular Sciences, 20(20).
Résumé: Iron Oxide Nanoparticles (IONPs) present unique properties making them one of the most used NPs in the biomedical field. Nevertheless, for many years, growing production and use of IONPs are associated with risks that can affect human and the environment. Thus, it is essential to study the effects of these nanoparticles to better understand their mechanism of action and the molecular perturbations induced in the organism. In the present study, we investigated the toxicological effects of IONPs (gamma-Fe2O3) on liver, lung and brain proteomes in Wistar rats. Exposed rats received IONP solution during 7 consecutive days by intranasal instillation at a dose of 10 mg/kg body weight. An iTRAQ-based quantitative proteomics was used to study proteomic variations at the level of the three organs. Using this proteomic approach, we identified 1565; 1135 and 1161 proteins respectively in the brain, liver and lung. Amon them, we quantified 1541; 1125 and 1128 proteins respectively in the brain, liver and lung. Several proteins were dysregulated comparing treated samples to controls, particularly, proteins involved in cytoskeleton remodeling, cellular metabolism, immune system stimulation, inflammation process, response to oxidative stress, angiogenesis, and neurodegenerative diseases.
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Askri, D., Ouni, S., Galai, S., Chovelon, B., Arnaud, J., Sturm, N., et al. (2019). Nanoparticles in foods? A multiscale physiopathological investigation of iron oxide nanoparticle effects on rats after an acute oral exposure: Trace element biodistribution and cognitive capacities. Food And Chemical Toxicology, 127, 173–181.
Résumé: Iron Oxide Nanoparticles (IONPs) are used in several fields of application, mainly in the biomedical field for their magnetic properties and in food additive known as “E172” for their colour. In the present investigation, we focused on IONP effects on Wistar rat following acute oral exposure. We performed a multiscale physiopathological investigation in order to elucidate potential toxic effects linked to IONP ingestion, especially on cognitive capacities, trace element distribution, blood constituents, organ functions, organ structure and iron deposit. We demonstrated that oral exposure to IONPs induces disturbances of certain parameters depending on the dose. Interestingly, the histopathological examination evidenced inflammatory effects of IONPs in the liver with iron deposits in hepatocytes and Kuppfer cells. Neurobehavioral examination showed that oral exposure to IONPs did not affect nor rat emotions, exploration and locomotion capacities, nor spatial reference memory status. Furthermore, oral administration of IONPs did not disrupt the trace element homeostasis nor in the liver neither in the stomach. Altogether, our study evidenced low signs of toxicity, but some effects lead us to a careful use of these NPs. Thereby, their use in foods should be further studied to better evaluate the potential toxic risks of the oral exposure to IONPs.
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Aslan, G., Cakir, Z., Lasserre, C., & Renard, F. (2019). Investigating Subsidence in the Bursa Plain, Turkey, Using Ascending and Descending Sentinel-1 Satellite Data. Remote Sensing, 11(1).
Résumé: We characterize and monitor subsidence of the Bursa Plain (southern Marmara region of Turkey), which has been interpreted as resulting from tectonic motions in the region. We quantify the subsidence using Interferometric Synthetic Aperture Radar (InSAR) time-series analysis. The Stanford Method for Persistent Scatterers InSAR package (StaMPS) is employed to process series of Sentinel 1 A-B radar images acquired between 2014 and 2017 along both ascending and descending orbits. The vertical velocity field obtained after decomposition of line-of-sight velocity fields on the two tracks reveals that the Bursa plain is subsiding at rates up to 25 mm/yr. The most prominent subsidence signal in the basin forms an east-west elongated ellipse of deformation in the east, and is bounded by a Quaternary alluvial plain undergoing average vertical subsidence at similar to similar to 10 mm/yr. Another localized subsidence signal is located 5 km north of the city, following the Bursa alluvial fan, and is subsiding at velocities up to 25 mm/yr. The comparison between temporal variations of the subsiding surface displacements and variations of the water pressure head in the aquifer allows estimation of the compressibility of the aquifer, It falls in the range of0.tic5x10-6-2x10-6 Pa-1, which corresponds to typical values for clay and sand sediments. We find a clear correlation between subsidence patterns and the lithology, suggesting a strong lithological control over subsidence. In addition, the maximum rate of ground subsidence occurs where agricultural activity relies on groundwater exploitation. The InSAR time series within the observation period is well correlated with changes in the depth of the ground water. These observations indicate that the recent acceleration of subsidence is mainly due to anthropogenic activities rather than tectonic motion.
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Aslan, G., Lasserre, C., Cakir, Z., Ergintav, S., Ozarpaci, S., Dogan, U., et al. (2019). Shallow Creep Along the 1999 Izmit Earthquake Rupture (Turkey) From GPS and High Temporal Resolution Interferometric Synthetic Aperture Radar Data (2011-2017). Journal Of Geophysical Research-Solid Earth, 124(2), 2218–2236.
Résumé: Characterizing the spatiotemporal evolution of creep is essential to constrain fault slip budget and understand creep mechanism. Studies based on interferometric synthetic aperture radar and Global Positioning System (GPS) satellite observations until 2012 have shown that the central segment of the 17 August 1999 M-w 7.4 Izmit earthquake on the North Anatolian Fault began slipping aseismically following the event. In the present study, we combine new interferometric synthetic aperture radar time series, based on TerraSAR-X and Sentinel 1A/B radar images acquired over the period 2011-2017, with near-field GPS measurement campaigns performed every 6months from 2014 to 2016. The mean velocity fields reveal that creep on the central segment of the 1999 Izmit fault rupture continues to decay, more than 19years after the earthquake, in overall agreement with models of postseismic afterslip decaying logarithmically with time for a long period of time. Along the fault section that experienced supershear velocity rupture during the Izmit earthquake creep continues with a rate up to 8mm/year. A significant transient accelerating creep is detected in December 2016 on the Sentinel-1 time series, near the maximum creep rate location, associated with a total surface slip of 10mm released in 1month only. Additional analyses of the vertical velocity fields show a persistent subsidence on the hanging wall block of the Golcuk normal fault that also ruptured during the Izmit earthquake. Our results demonstrate that afterslip processes along the North Anatolian Fault east-southeast of Istanbul are more complex than previously proposed as they vary spatiotemporally along the fault.
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Asta, M. P., Wang, Y., Frutschi, M., Viacava, K., Loreggian, L., Le Pape, P., et al. (2019). Microbially Mediated Release of As from Mekong Delta Peat Sediments. Environmental Science & Technology, 53(17), 10208–10217.
Résumé: Peat layers within alluvial sediments are considered effective arsenic (As) sinks under reducing conditions due to the binding of As(III) to thiol groups in natural organic matter (NOM) and the formation of As-bearing sulfide phases. However, their possible role as sources of As for anoxic groundwaters remains unexplored. Here, we perform laboratory experiments to provide evidence for the role of a sediment peat layer in releasing As. Our results show that the peat layer, deposited about 8,000 years ago in a paleomangrove environment in the nascent Mekong Delta, could be a source of As to porewater under reducing conditions. X-ray absorption spectroscopy (XAS) analysis of the peat confirmed that As was bound to NOM thiol groups and incorporated into pyrite. Nitrate was detected in peat layer porewater, and flow-through and batch experiments evidenced the release of As from NOM and pyrite in the presence of nitrate. Based on poisoning experiments, we propose that the microbially mediated oxidation of arsenic-rich pyrite and organic matter coupled to nitrate reduction releases arsenic from this peat. Although peat layers have been proposed as As sinks in earlier studies, we show here their potential to release depositional- and/or diagenetically-accumulated As.
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Astorga, A. L., Gueguen, P., Riviere, J., Kashima, T., & Johnson, P. A. (2019). Recovery of the resonance frequency of buildings following strong seismic deformation as a proxy for structural health. Structural Health Monitoring-An International Journal, 18(5-6), 1966–1981.
Résumé: Elastic properties of civil engineering structures change when subjected to a dynamic excitation. The modal frequencies show a rapid decrease followed by a relaxation, or slow recovery, that is dependent on the level of damage. In this article, we analyze the slow recovery process applying three relaxation models to fit real earthquake data recorded in a Japanese building that shows variant structural state over 20 years. Despite the differences in conditions, the different scales and the complexity of a real-scale problem, the models originally developed for laboratory experiments are well adapted to real building data. The relaxation parameters (i.e. frequency variation, recovery slope, characteristic times and their amplitudes, and range of relaxation times) are able to characterize the structural state, given their clear connection to the degree of fracturing and mechanical damage to the building. The recovery process following strong seismic deformation, could, therefore, be a suitable proxy to monitor structural health.
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Aubry, G. J., & Roux, P. (2019). Topological Effects of a Vorticity Filament on the Coherent Backscattering Cone. Physical Review Letters, 123(3).
Résumé: In this Letter, we report on the effects of a vorticity filament on the coherent backscattering cone. Using ultrasonic waves in a strongly reverberating cavity, we experimentally show that the discrete number of loops of acoustic paths around a pointlike vortex located at the center of the cavity drives the cancellation and the potential rebirth of the coherent backscattering enhancement. The vorticity filament behaves, then, as a topological anomaly for wave propagation that provides some new insight between reciprocity and weak localization.
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Aulbach, S., & Arndt, N. T. (2019). Eclogites as palaeodynamic archives: Evidence for warm (not hot) and depleted (but heterogeneous) Archaean ambient mantle. Earth And Planetary Science Letters, 505, 162–172.
Résumé: Some high-Mg eclogite xenoliths, entrained by kimberlites from the mantle lithospheres of ancient continental cores, and rare orogenic eclogites and ophiolites, exhumed or obducted during the closure of palaeo-ocean basins, have elemental and isotopic compositions indicative of protoliths that formed as little-differentiated melts erupted in ancient ocean floors. Despite metamorphism and, in part, partial melt loss, these samples of ancient mid-ocean ridge basalt and picrite retain a memory of the chemical and physical state of their protoliths' ambient convecting mantle sources. Published data show that, when filtered to exclude specimens with cumulate protoliths or showing evidence for later enrichment (metasomatism), the samples lack Y or Al2O3 depletion relative to TiO2 and MgO. This indicates melt segregation of the protolith predominantly from a garnet-free peridotite source and implies intersection of the solidus at low pressures (<= 3 GPa). Given the dependence of melt composition and volume on source composition (assumed to be similar to modern depleted mantle) and mantle potential temperature (T-P), we calculate moderate average melt fractions F (similar to 0.22 +/- 0.01) from the Ti contents of the least differentiated samples in three sample suites with 2.6 to 2.9 Ga ages. This converts to T-P of similar to 1410 +/- 10 degrees C assuming a final pressure of melting of 0.5 GPa, melt productivity of 10%/GPa and mantle adiabat of 0.4 degrees C/km, and using a mantle solidus parameterisation. Though model-dependent, the results are in agreement with recent work advocating moderate Archaean mantle T-P. Estimates drop to F = 0.19 and T-P = 1380 degrees C at 1.9 Ga and F = 0.12 and T-P = 1310 at 0.6 Ga, corresponding to a decrease in T-P of only similar to 100 degrees C over the last 3 Ga. A less depleted mantle source yields higher F and T-P, but the above estimates are in better agreement with qualitative evidence from Al2O3 and Y, and with Nd-Hf and Sr isotope compositions of orogenic eclogite and granulite suites and mantle eclogites, respectively, which indicate that portions of the Meso- to Neoarchaean mantle were depleted. Moderate T-P supports early plate strengthening and a possible transition to plate tectonics in the Mesoarchaean if not earlier. Moreover, moderate temperatures in Archaean subduction zones may have facilitated deep recycling of volatiles that would otherwise have been lost from subducting slabs at shallow depths. (C) 2018 Elsevier B.V. All rights reserved.
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Aulbach, S., & Arndt, N. T. (2019). Origin of high-Mg bimineralic eclogite xenoliths in kimberlite – reply to comment from Claude Herzberg. Earth And Planetary Science Letters, 510, 234–237.
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Bablon, M., Quidelleur, X., Samaniego, P., Le Pennec, J. - L., Audin, L., Jomard, H., et al. (2019). Interactions between volcanism and geodynamics in the southern termination of the Ecuadorian arc. Tectonophysics, 751, 54–72.
Résumé: This study focuses on the construction and evolution through time of volcanic edifices located in the southern part of the Ecuadorian arc, with the objective to contribute to a better understanding of the interactions between magmatism, slab geometry and the activity of tectonic faults. Our new groundmass K-Ar ages obtained for a dozen volcanoes from the southern Quaternary arc are rather young, without ages older than 800 ka, and highlight an increasing volcanic activity between 300 and 100 ka. These new temporal constraints suggest that a southward migration of the Ecuadorian arc occurred during the last 600 ka. We interpret this evolution as the result of major and recent geodynamic reorganization in Ecuador related to the activation of lithospheric faults and to the flexure of the slab at depth, following the inland prolongation of the Grijalva fracture zone. Both phenomena could have been induced by the oblique subduction of the Nazca plate towards the convex margin of the South American continent, and the coupling of these two plates along the Wadati-Benioff zone, progressively intensified by the Carnegie ridge subduction. Southward migration of the slab flexure at depth could have changed pressure and temperature conditions, favoring the partial melting of the mantle wedge and magma genesis, thereby inducing a southward migration of the Ecuadorian arc volcanoes. These results contribute therefore to a better knowledge of the current arc dynamics in the Northern Andes, and provide insights into the use of geochronological data applied to volcanic rocks for studies of past tectonic activity in Ecuador.
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Bakker, E., Lanson, B., Findling, N., Wander, M. M., & Huber, F. (2019). Mineralogical differences in a temperate cultivated soil arising from different agronomic processes and plant K-uptake. Geoderma, 347, 210–219.
Résumé: Potassium (K) is an essential plant nutrient mainly present in the crystal structure of K-bearing soil minerals (K-feldspars, micas). To assess the evolution of (clay) mineralogy due to K+ release from these minerals in continuously cultivated soils, samples were collected from long-term (1904-2014) field experiments submitted to contrasting crop rotations and amendments, with and without fertilisation. Soil samples were size-fractionated and mineralogy of the silt fraction and of clay subfractions was determined quantitatively by modelling X-ray diffraction (XRD) patterns. Clay subfractions were also analysed for their cation exchange capacity (CEC). Mineralogical data indicate the stability of clay mineralogy and the increased abundance of the finest clay subfraction at the expense of coarser ones, regardless of agronomic practices or amount of K removed by plants. This increase is accompanied by an increase in the bulk clay CEC owing to the major contribution of the finest clay subfraction to this parameter. Mineral dissolution, rather than alteration of mineral phases from coarse clay subfractions, most likely supplements K for plant nutrition in this soil. Dissolution is favoured over cation exchange owing to the dioctahedral character of micas and to their fine-grained granulometry. The observed longterm mineralogical resilience also indicates that part of plant nutrition is obtained from subsoil in a non K-limited context, whereas K supply through K-feldspar dissolution appears marginal.
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Bakshi, M., Line, C., Bedolla, D. E., Stein, R. J., Kaegi, R., Sarret, G., et al. (2019). Assessing the impacts of sewage sludge amendment containing nano-TiO2 on tomato plants: A life cycle study. Journal Of Hazardous Materials, 369, 191–198.
Résumé: Increasing evidence indicates the presence of engineered nanoparticles (ENPs) in sewage sludge derived from wastewater treatment. Land application of sewage sludge is, therefore, considered as an important pathway for ENP transfer to the environment. The aim of this work was to understand the effects of sewage sludge containing nano-TiO2 on plants (tomato) when used as an amendment in agricultural soil. We assessed developmental parameters for the entire plant life cycle along with metabolic and bio-macromolecule changes and titanium accumulation in plants. The results suggest that the sewage sludge amendment containing nano-TiO2 increased plant growth (142% leaf biomass, 102% fruit yield), without causing changes in biochemical responses, except for a 43% decrease in leaf tannin concentration. Changes in elemental concentrations (mainly Fe, B, P, Na, and Mn) of plant stem, leaves and, to a lesser extent fruits were observed. Fourier-transformed infrared analysis showed maximum changes in plant leaves (decrease in tannins and lignins and increase in carbohydrates) but no change in fruits. No significant Ti enrichment was detected in tomato fruits. In conclusion, we evidenced no acute toxicity to plants and no major implication for food safety after one plant life cycle exposure.
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Barrois, O., Gillet, N., Aubert, J., Hammer, M. D., Finlay, C. C., Martin, Y., et al. (2019). 'Contributions to the geomagnetic secular variation from a reanalysis of core surface dynamics' and 'Assimilation of ground and satellite magnetic measurements: inference of core surface magnetic and velocity field changes' (vol 211, pg 50, 2018). Geophysical Journal International, 216(3), 2106–2113.
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Batanova, V. G., Thompson, J. M., Danyushevsky, L. V., Portnyagin, M. V., Garbe-Schoenberg, D., Hauri, E., et al. (2019). New Olivine Reference Material for In Situ Microanalysis. Geostandards And Geoanalytical Research, 43(3), 453–473.
Résumé: A new olivine reference material – MongOL Sh11-2 – for in situ analysis has been prepared from the central portion of a large (20 x 20 x 10 cm) mantle peridotite xenolith from a ~ 0.5 My old basaltic breccia at Shavaryn-Tsaram, Tariat region, central Mongolia. The xenolith is a fertile mantle lherzolite with minimal signs of alteration. Approximately 10 g of 0.5-2 mm gem quality olivine fragments were separated under binocular microscope and analysed by EPMA, LA-ICP-MS, SIMS and bulk analytical methods (ID-ICP-MS for Mg and Fe, XRF, ICP-MS) for major, minor and trace elements at six institutions world-wide. The results show that the olivine fragments are sufficiently homogeneous with respect to major (Mg, Fe, Si), minor and trace elements. Significant inhomogeneity was revealed only for phosphorus (homogeneity index of 12.4), whereas Li, Na, Al, Sc, Ti and Cr show minor inhomogeneity (homogeneity index of 1-2). The presence of some mineral and fluid-melt micro-inclusions may be responsible for the inconsistency in mass fractions obtained by in situ and bulk analytical methods for Al, Cu, Sr, Zr, Ga, Dy and Ho. Here we report reference and information values for twenty-seven major, minor and trace elements.
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Beauce, E., Frank, W. B., Paul, A., Campillo, M., & van der Hilst, R. D. (2019). Systematic Detection of Clustered Seismicity Beneath the Southwestern Alps. Journal Of Geophysical Research-Solid Earth, 124(11), 11531–11548.
Résumé: We present a new automated earthquake detection and location method based on beamforming (or back projection) and template matching and apply it to study the seismicity of the Southwestern Alps. We use beamforming with prior knowledge of the 3-D variations of seismic velocities as a first detection run to search for earthquakes that are used as templates in a subsequent matched-filter search. Template matching allows us to detect low signal-to-noise ratio events and thus to obtain a high spatiotemporal resolution of the seismicity in the Southwestern Alps. We describe how we address the problem of false positives in energy-based earthquake detection with supervised machine learning and how to best leverage template matching to iteratively refine the templates and the detection. We detected 18,754 earthquakes over 1 year (our catalog is available online) and observed temporal clustering of the earthquake occurrence in several regions. This statistical study of the collective behavior of earthquakes provides insights into the mechanisms of earthquake occurrence. Based on our observations, we infer the mechanisms responsible for the seismic activity in three regions of interest: the Ubaye valley, the Brianconnais, and the Dora Maira massif. Our conclusions point to the importance of fault interactions to explain the earthquake occurrence in the Brianconnais and the Dora Maira massif, whereas fluids seem to be the major driving mechanism in the Ubaye valley.
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Beck, C., Carrillo, E., Audemard, F., van Welden, A., & Disnar, J. - R. (2019). Tentative integration of paleoseismic data from lake sediments and from nearby trenches: the central section of the Bocono Fault (northern Venezuela). Journal Of South American Earth Sciences, 92, 646–657.
Résumé: The right-lateral strike slip Bocono Fault (Merida Andes, northern Venezuela) accommodates an important part of the South-American Plate northern transform boundary. Along its central portion, preserved post-LMG lake fills are intersected by two surface-reaching active traces which could be trenched just beside. Outcropping and cored lacustrine sedimentary archives are combined with trench data in order to achieve a Holocene paleoseismicity record for a 7 km-long segment. For lakes sediments, several types of sedimentary “events” were taken into account as co-seismic: mass wasting on deltaic foreset, liquefaction and slumping, reflected tsunami effects, re-suspension, abrupt change in sedimentary dynamics and sources, abrupt emptying and lake surface changes. Time coincidences between two lacustrine archives and two trenches can be proposed for the last 10 kyr BP. Among a total of 24 events, 13 events are detected in two sites, 3 events in 3 sites. 9 possible correlations concern separate traces while 4 concern the same trace; a relay between the activity of the two traces is also deduced. This combination of surveys both reinforces and completes the trenches results, leading to a better knowledge of local to regional seismic hazard. Nevertheless, the total information results probably incomplete and/or biased. The co-seismic origin of lacustrine fills disturbances evidenced but the associated archive is incomplete and/or biased due to: changing recording potential through time, possible impacts by strong distant earthquakes. Trenches data appear to fill lacustrine “gaps” but with a number of events possibly overestimated if all ruptures and associated C-14 data are considered as representing separated earthquakes.
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Bellahsen, N., Bayet, L., Denele, Y., Waldner, M., Airaghi, L., Rosenber, C., et al. (2019). Shortening of the axial zone, pyrenees: Shortening sequence, upper crustal mylonites and crustal strength. Tectonophysics, 766, 433–452.
Résumé: The strength of the lithosphere may be constrained qualitatively by field observations on localized vs distributed modes of deformation and by the mineral assemblages formed during deformation. The internal deformation of the Bielsa basement unit of the Pyrenean Axial zone is investigated through structural, microstructural and thermometric data. In this area, shortening is widely distributed as attested by the folded attitude of the interface between the basement and its sedimentary Triassic cover. Shortening is estimated around 1.7 km (13%) from a regional balanced cross-section and should be considered in pre-Pyrenean reconstructions. Shortening probably occurred before strain localization on crustal ramps as suggested by zircon fission-track analysis. Distributed shortening is characterized at small-scale by low-temperature mylonites and cataclasites. In thin-section, feldspar originally present in the magmatic protolith is partially to totally sericitized. This transformation led to significant weakening of the rock and took place in the 250-350 degrees C temperature range. Sericitization is ubiquitous, even in un-deformed granodiorites. This shows that the weakening effect of sericitization not only occurs in ultra-mylonites, ultra-cataclasites and phyllonites but also more generally in the upper crust early during the shortening history, with implications for the shortening style. Estimates of the geothermal gradient suggest that Inherited thermicity may also have influenced the style of shortening. We propose that the upper crust was very weak before or at the onset of its shortening due to high-thermal gradients and fluid circulation that induced large-scale sericitization in greenschist fades conditions. This has strong implications on the rheological evolution of the upper crust submitted to metamorphic alteration in the greenschist fades and below.
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Bernet, M., Piraquive, A., Uruena, C., Lopez-Isaza, J. A., Bermudez, M. A., Zuluaga, C., et al. (2019). Multidisciplinary petro-geo-thermochronological approach to ore deposit exploration. Ore Geology Reviews, 112.
Résumé: The continuous search for mineral resources such as gold, copper and base metals etc. requires a refined understanding of the thermal evolution and exhumation history of potential exploration targets, as only ore deposits can be exploited that have been exhumed to the surface or near to the surface. In order to better understand the exhumation history of the ore deposits a multidisciplinary approach using single grain geo- and thermochronology double/triple dating in combination with other geochemical, fluid inclusion and petrological analyses, can significantly support prospecting for such resources, particularly in frontier areas, where little geological information exists. Geo-thermochronology provides information on the timing of initial host rock crystallization, ore deposit formation and subsequent exhumation as the thermal history can be modelled and exhumation rates can be determined. Here we present a methodological outline on which single-grain double/triple-dating techniques can be used, what sampling strategies may be applied, and how the data may be interpreted.
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Biggs, J., & Annen, C. (2019). The lateral growth and coalesence of magma systems. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 377(2139).
Résumé: Thermal and mechanical models of magma reservoir growth need to be reconciled with deformation patterns and structural relationships observed at active magma systems. Geophysical observations provide a series of short time-scale snap-shots (10(0)-10(2) years) of the long-term growth of magmatic bodies (10(3)-10(6) years). In this paper, we first review evidence for the growth of magmatic systems along structural features and the associated deformation patterns. We then define three distinct growth stages, (1) aligned melt pockets, (2) coalesced reservoirs, (3) highly evolved systems, which can be distinguished using short-term surface observations. We use two-dimensional thermal models to provide first-order constraints on the time scales and conditions associated with coalescence of individual magma bodies into large-scale reservoirs. We find that closely spaced intrusions (less than 1 km apart) can develop combined viscoelastic shells over time scales of 10s kyr and form laterally extensive mush systems over time scales of 10-100 kyr. The highest temperatures and melt fractions occur during a period of thermal relaxation after melt injection has ceased, suggesting that caldera-forming eruptions may preferentially occur long after the main intrusive activity. The coalescence of eruptible melt-rich chambers only occurs for the highest melt supply rates and deepest systems. Thus, these models indicate that, in most cases, conductive heat transfer alone is not sufficient for a full coalescence of magma chambers and that other processes involving mechanical ruptures and mush mobilization are necessary; individual melt lenses can remain isolated for long periods within growing mush systems, and will only mix during eruption or other catastrophic events. The long-term history of the magmatic system is therefore critical in determining rheological structure and hence short-term behaviour. This framework for the development of magmatic systems in the continental crust provides a mechanical basis for the interpretation of unrest at the world's largest volcanoes. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.
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Bissardon, C., Proux, O., Bureau, S., Suess, E., Winkel, L. H. E., Conlan, R. S., et al. (2019). Sub-ppm level high energy resolution fluorescence detected X-ray absorption spectroscopy of selenium in articular cartilage. Analyst, 144(11), 3488–3493.
Résumé: The speciation of highly-diluted elements by X-ray absorption spectroscopy in a diverse range of materials is extremely challenging, especially in biological matrices such as articular cartilage. Here we show that using a high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) technique coupled to an array of crystal analyzers, selenium speciation down to 400 ppb (mu g kg(-1)) within articular cartilage can be demonstrated. This is a major advance in the speciation of highly-diluted elements through X-ray absorption spectroscopy and opens new possibilities to study the metabolic role of selenium and other elements in biological samples.
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Boccato, S., Torchio, R., D'Angelo, P., Trapananti, A., Kantor, I., Recoules, V., et al. (2019). Compression of liquid Ni and Co under extreme conditions explored by x-ray absorption spectroscopy. Physical Review B, 100(18).
Résumé: The compression of liquid nickel and cobalt has been investigated up to 102 and 83 GPa, respectively, by x-ray absorption spectroscopy at the Ni and Co K edges, using laser-heated diamond anvil cell. A shortening of about 8%-10% of the metal bond distances is observed in the pressure range considered and the experimental results are confirmed by theoretical calculations. Ab initio quantum molecular dynamics calculations have been performed, providing a model pair distribution function for cobalt, used as a starting model in the extended x-ray absorption fine structure analysis. The specific volume of the liquid has also been estimated and compared to calculations in the literature. This work sets the basis for x-ray absorption spectroscopy studies of liquid metals under extreme conditions with potentially important implications for the understanding of Earth and planetary interiors.
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Bochicchio, R. C., Lobayan, R. M., & del Valle, C. P. (2019). Donor-acceptor interactions: Transition metal carbonyl group ligand [TM(CO)(6)](q) complexes. A case study at correlated level from the topological density point of view. International Journal Of Quantum Chemistry, 119(9).
Résumé: The analysis of d(6) transition metal (TM)-ligand (L) interactions between one metallic atom and several carbonyl group ligands complexes [TM (CO)(6)](q) (q net ionic charge) for the transition metal isoelectronic series, TM = Ti, V, Cr, Mn, Fe is presented within the framework of the local and nonlocal topological analysis electron density point of view using its natural decomposition into pairing and unpairing contributions. The driving idea of this analysis is the relationship between the molecular orbital sigma-, pi-donation for the description of the rearrangement and the existence of complex binding interactions of two or four electron over three centers type, (2e-3c), (4e-3c). This study reveals the formation of (4e-3c) complex patterns for the CO-TM moieties which coexists with pi-donation carried out by the TM.
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Bonilla, L. F., Gueguen, P., & Ben-Zion, Y. (2019). Monitoring Coseismic Temporal Changes of Shallow Material during Strong Ground Motion with Interferometry and Autocorrelation. Bulletin Of The Seismological Society Of America, 109(1), 187–198.
Résumé: Temporal changes of seismic velocities generated at the subsurface by the 2011 M-w 9 Tohoku earthquake in Japan are analyzed using interferometry and autocorrelation of waveforms recorded by surface and borehole sensors at the KiK-net station IBRH16. Spectral ratios and interferometry of data recorded in moving time windows at the surface and a depth of 300 m exhibit clear time delays and reduction of the predominant frequency during the strong ground motion followed by partial recovery in the waveform coda. Converting the time-delay evolution to velocity changes implies about 30% velocity reduction in the structure between the two sensors. Calculating temporal evolution with autocorrelation of data at the surface sensor in the moving time window indicates about 50% velocity reduction, reflecting changes of shallower material below the station. Computing autocorrelations of data recorded by the surface sensor with the Stockwell transform allows monitoring temporal changes with higher resolution that approaches the sampling rate of the waveforms. Using this technique, we estimate about 60% drop of seismic velocity below the surface sensor during strong ground motion followed again by partial recovery in the coda. These results provide fundamental information on in situ dynamic properties of soils and damaged shallow rocks that complement laboratory measurements, with important implications for constitutive equations of material degradation and healing and nonlinear site effects.
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Bonnaud, P., Santenoise, P., Tisserand, D., Nourrisson, G., & Ranger, J. (2019). Impact of compaction on two sensitive forest soils in Lorraine (France) assessed by the changes occurring in the perched water table. Forest Ecology And Management, 437, 380–395.
Résumé: The mechanisation of forestry operations is too recent in France to have enough perspective and scientific knowledge of the effects on extensively managed soils. Two experimental sites on soils sensitive to compaction (silty acidic soils laying on top of a clayey subsoil) were set in Lorraine (France). A gentle and controlled compaction of these physically very analogous soils was carried out during spring 2007 at the Azerailles site (AZ) and during spring 2008 at the Clermont-en-Argonne site (CA). Immediate changes were observed for all ecosystem physical, chemical and biological functioning indicators. Soil restoration dynamics were followed using continuous monitoring of numerous parameters, including soil moisture and occurrence of a perched water table (PWT) (monitored at a daily time step) and PWT chemistry (monthly time step). Mid-term monitoring (7-8 years) results showed that both soils shifted towards a hydromorphic soil type attested by the increase in PWT frequency and duration, which invaded the soil upper layers, leading to characteristic Fe, Mn and S mobility and a change in organic compounds stability. Though soil types were very similar, the PWT characteristics varied notably between both sites. The mean residence time of the PWT was shown to be a major driver of its geochemistry, but with strong interaction with soil characteristics. A previous study made on both sites suggested that soil clay content and clay mineralogy controls the PWT dynamics through effects on aggregation. From a PWT perspective, seven years of monitoring were insufficient to observe any soil compaction recovery in the richer soil of AZ but a partial recovery was observed for the chemically poorer soil (CA). Compaction durably impacted the two studied soils and the probability that a new compaction event may occur before the complete recovery from the first disturbance must be considered in forest management.
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Bouligand, C., Hurwitz, S., Vandemeulebrouck, J., Byrdina, S., Kass, M. A., & Lewicki, J. L. (2019). Heat and Mass Transport in a Vapor-Dominated Hydrothermal Area in Yellowstone National Park, USA: Inferences From Magnetic, Electrical, Electromagnetic, Subsurface Temperature, and Diffuse CO2 Flux Measurements. Journal Of Geophysical Research-Solid Earth, 124(1), 291–309.
Résumé: Vapor-dominated hydrothermal systems are characterized by localized and elevated heat and gas flux. In these systems, steam and gas ascend from a boiling water reservoir, steam condenses beneath a low-permeability cap layer, and liquid water descends, driven by gravity (heat pipe model). We combine magnetic, electromagnetic, and geoelectrical methods and CO2 flux and subsurface temperature measurements in the Solfatara Plateau Thermal Area in the Yellowstone Caldera to address several fundamental questions: (1) What are the structural and/or lithological controls on heat and mass transport in vapor-dominated areas? (2) What is the geometry and size of convecting multiphase thermal plumes? (3) Are thermal plumes associated with subsurface rock alteration and demagnetization? Magnetic and electromagnetic data inversions suggest an asymmetric 50- to 100-m thick basin of glacial deposits with the thickest part adjacent to the margin of a rhyolite flow. The 3-D electrical conductivity model in the glacial basin reveals a narrow vertical conductor interpreted as a focused multiphase plume, which coincides at the ground surface with the heat and CO2 flux maxima. The magnetic data suggest that destruction of magnetic minerals due to rock alteration associated with the hydrothermal plume occurs mainly near the ground surface. We propose a model where the buoyant multiphase plume forms in response to decompression, boiling, and phase separation of pressurized thermal groundwater that discharges from the brecciated base of a rhyolite flow into the basin of glacial deposits. Results from multiphase groundwater flow and heat transport numerical simulations corroborate the first-order characteristics of this model.
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Bourdineaud, J. - P., Gonzalez-Rey, M., Rovezzi, M., Glatzel, P., Nagy, K. L., & Manceau, A. (2019). Divalent Mercury in Dissolved Organic Matter Is Bioavailable to Fish and Accumulates as Dithiolate and Tetrathiolate Complexes. Environmental Science & Technology, 53(9), 4880–4891.
Résumé: The freshwater cyprinid Tanichthys albonubes was used to assess the bioavailability of divalent mercury (Hg(II)) complexed in dissolved organic matter (DOM) to fish. The fish acquired 0.3 to 2.2 μg Hg/g dry weight after 8 weeks in aquaria containing DOM from a Carex peat with complexed mercury at initial concentrations of 14 nM to 724 nM. Changes in the relative proportions of dithiolate Hg(SR)(2) and nanoparticulate beta-HgS in the DOM, as quantified by high energy-resolution XANES (HR-XANES) spectroscopy, indicate that Hg(SR)(2) complexes either produced by microbially induced dissolution of nanoparticulate beta-HgS in the DOM or present in the original DOM were the forms of mercury that entered the fish. In the fish with 2.2 μg Hg/g, 84 +/- 8% of Hg(II) was bonded to two axial thiolate ligands and one or two equatorial N/O electron donors (Hg[(SR)(2)+(N/O)(1-2)] coordination), and 16% had a Hg(SR)(4) coordination, as determined by HR-XANES. For comparison, fish exposed to Hg2+ from 40 nM HgCl2 contained 10.4 μg Hg/g in the forms of dithiolate (20 +/- 10%) and tetrathiolate (23 +/- 10%) complexes, and also HgxSy clusters (57 +/- 15%) having a beta-HgS-type local structure and a dimension that exceeded the size of metallothionein clusters. There was no evidence of methylmercury in the fish or DOM within the 10% uncertainty of the HR-XANES. Together, the results indicate that inorganic Hg(II) bound to DOM is a source of mercury to biota with dithiolate Hg(SR)(2) complexes as the immediate species bioavailable to fish, and that these complexes transform in response to cellular processes.
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Brax, M., Albini, P., Beauval, C., Jomaa, R., & Sursock, A. (2019). An Earthquake Catalog for the Lebanese Region. Seismological Research Letters, 90(6), 2236–2249.
Résumé: The present work aims at establishing an earthquake catalog for seismic hazard assessment in Lebanon. This catalog includes two different parts: historical earthquakes and instrumental earthquakes. The first part of the article describes the work done on the period 31 B.C.E. to the end of the nineteenth century. Numerous studies published in the last 30 yr, devoted to pre-instrumental earthquakes in Lebanon, had not been included in any parametric earthquake catalog. A thorough and critical review of these studies was devised to check their respective interpretations of available earthquake records in terms of seismic parameters (date, location, and size) and to select for each earthquake the most reliable interpretation. The second part provides the details on the selection of instrumental solutions for the period 1900-2015 and for magnitudes >= 4. From global instrumental earthquake catalogs, we build a unified earthquake catalog for Lebanon and bordering regions. A selection scheme is applied for the choice of the best location and the best magnitude among solutions available. The number of events in the catalog is relatively small, and all earthquakes can be checked one by one. The earthquake catalog is homogenized in moment magnitude. For 89% of the events, an M-w proxy was calculated from the original magnitude, applying conversion equations. The merging of the historical and instrumental periods highlights a specificity of this zone: the instrumental seismicity (1900-2015) corresponds to a relatively quiet period for Lebanon. The historical part, covering 2000 yr, includes similar periods of quiescence, as well as much more active periods with destructive earthquakes.
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Brenguier, F., Baue, P., Ben-Zion, Y., Vernon, F., Johnson, C. W., Mordret, A., et al. (2019). Train Traffic as a Powerful Noise Source for Monitoring Active Faults With Seismic Interferometry. Geophysical Research Letters, 46(16), 9529–9536.
Résumé: Laboratory experiments report that detectable seismic velocity changes should occur in the vicinity of fault zones prior to earthquakes. However, operating permanent active seismic sources to monitor natural faults at seismogenic depth is found to be nearly impossible to achieve. We show that seismic noise generated by vehicle traffic, and especially heavy freight trains, can be turned into a powerful repetitive seismic source to continuously probe the Earth's crust at a few kilometers depth. Results of an exploratory seismic experiment in Southern California demonstrate that correlations of train-generated seismic signals allow daily reconstruction of direct P body waves probing the San Jacinto Fault down to 4-km depth. This new approach may facilitate monitoring most of the San Andreas Fault system using the railway and highway network of California. Plain Language Summary Even though laboratory experiments report that they should be preceded by detectable precursors, earthquakes remain unpredictable. Indeed, contrary to the lab, scanning natural faults at a few kilometers depth where earthquakes initiate requires operating high-energy seismic sources continuously in time, which is found to be nearly impossible. In this study, we show that large freight trains generate sufficient seismic energy to travel down to a few kilometers depth and be detected at tens of kilometers from railways. We demonstrate that we can turn this apparently random source of seismic signal into an impulsive virtual seismic source to monitor active faults. We finally estimate that this new approach can be used for monitoring most of the San Andreas Fault system using the railway and highway network of California.
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Brunet, F. (2019). Hydrothermal Production of H-2 and Magnetite From Steel Slags: A Geo-Inspired Approach Based on Olivine Serpentinization. Frontiers In Earth Science, 7.
Résumé: The interaction between ultramafic rocks and hot seawater at slow-spreading mid-oceanic ridges triggers hydrothermal redox reactions which are known to produce magnetite and H-2 under appropriate pressure and temperature conditions. Steel slags share some common properties with ultramafic rocks. They are composed of anhydrous and refractory minerals formed at temperatures exceeding 1,200. C and they contain ferrous iron in comparable amounts. Consequently, when submitted to hydrothermal conditions both types of materials, natural and anthropogenic, are prone to form magnetite and H-2 according to the simplified redox reaction: 3[FeO] + H2O => Fe3O4 + H-2 (1) where [FeO] is the ferrous iron component of the corresponding material that can be present under different mineralogical forms. Since H-2 and magnetite are two valuable products for applications in new technologies, the hydrothermal treatment of steel slags can be seen as a way to valorize a byproduct of the steel industry, a few tenths of a billion tons of which are produced yearly. The hydrothermal behavior of steel slags which arise from basic oxygen furnace (BOF) operations and that of olivine (Mg, Fe) 2SiO(4), the main mineral constituent of abyssal peridotites, are described here based on data from the literature. The thermochemical characteristics of Reaction 1 are reviewed for both types of materials in the perspective of optimizing a process that would valorize BOF steel slags for the production of nanomagnetite (and high-purity H-2). In particular, the kinetics effect of temperature, pH and solution-to-solid mass ratio on the hydrothermal oxidation of wustite (FeO), considered here as an analog of the ferrous-iron component of steel slags, are modeled. The possible role of additives (impurity) on the hydrothermal oxidation of wustite through the catalysis of the water-splitting reaction is discussed. Finally, the lack of kinetics constraints on nanomagnetite growth under hydrothermal conditions in a wide range of pH is identified as a major gapin the understanding of two important issues: (1) the catalysis of abiotic molecules in the course of serpentinization reactions, and (2) the tailoring of the size of the magnetite produced by hydrothermal treatment of BOF steel slags.
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Brunet, F., & Lanson, M. (2019). Effect of gold and magnetite on the decomposition kinetics of formic acid at 200 degrees C under hydrothermal conditions. Chemical Geology, 507, 1–8.
Résumé: Formic acid and formate ions are intermediate compounds in the water gas shift reaction as well as in the abiotic formation of organic molecules from dissolved CO2 and H-2 under hydrothermal conditions. The decomposition kinetics of a 0.1 M formic acid solution has been investigated using PTFE-lined reactors at 200 degrees C on the liquid-vapour equilibrium of water for calculated in-situ pH comprised between 2.8 and 3.6. Under these conditions, formic acid is the dominant aqueous species. Formic acid aqueous decomposition follows a first-order kinetics with a constant k (s(-1)) such that In(k) = -13.6 +/- 0.6 at 200 degrees C. The addition of gold chips in the reactor is found to promote formic acid decomposition and the kinetics constant of the reaction is a linear function of the exposed gold surface by unit volume of solution (Sly). Consequently, experiments run in gold tubes as those typically used in cold-seal vessels can be by more than two orders of magnitude faster than those performed in PTFE reactors under the same conditions. The addition in the PTFE-lined reactor, of particles of magnetite (Fe3O4) with sizes centred on 300 nm or the presence of aqueous Fe at the millimolal level does not catalyse the hydrothermal decomposition of formic acid at 200 degrees C.
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Brunet, F., Crouzet, C., Cretu, S., David, R., Courty, M., Demortiere, A., et al. (2019). Oxidative decomposition products of synthetic NaFePO4 maricite: nano-textural and electrochemical characterization. European Journal Of Mineralogy, 31(4), 837–842.
Résumé: Single-phase maricite, NaFePO4, was synthesized from a mixture of monosodium phosphate and iron oxalate at 750 degrees C and atmospheric pressure. Thermal treatment of synthetic maricite in air led to its oxidative decomposition into Na3Fe23+(PO4)(3) NASICON and alpha-Fe2O3, which started at temperatures slightly below 225 degrees C. Intergrowth of the two reaction products is found to occur at the nanoscale without identified crystallographic relationship with the maricite precursor. Electrochemical activity of the reaction product is confirmed with the reversible insertion of one Na at 2.55 V versus Na+/Na-0.
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Burgisser, A. (2019). Travel on thin air. Nature Geoscience, 12(5), 311–312.
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Burgisser, A., Bechon, T., Chevalier, L., Collombet, M., Arbaret, L., & Forien, M. (2019). Conduit processes during the February 11, 2010 Vulcanian eruption of Soufriere Hills, Montserrat. Journal Of Volcanology And Geothermal Research, 373, 23–35.
Résumé: We analyzed pumice from the February 11, 2010 Vulcanian explosion that immediately followed a large dome collapse at Soufriere Hills volcano. We obtained pre-explosive values of porosity, pressure, and depth by combining textural analyses and glass water content determinations. Our data suggest that the February 2010 explosion evacuated the upper 3 km of the conduit from the dense magma (<= 10 vol% porosity) it contained. The low porosity distribution in the volcanic conduit implies that the magma rising from the reservoir had time to extensively degas during emplacement. We use a conduit flow model to characterize the effects of permeability on ascent conditions. Model input parameters were fitted to match our pre-explosive porosity data, which yielded first-order constraints on conduit radius, mass flux, outgassing efficiency, and permeability. This parametric study suggests that efficient lateral gas escape is necessary to explain the low pre-explosive porosities. Steady-state solutions fitting the observed range of dome extrusion rate in the month preceding the February 11 event suggest permeabilities < 10(-13) m(2) deeper than 500 m, which are values typical of crack-supported permeability. Conversely, solutions with parameters consistent with bubble-supported permeability imply transient flow conditions prior to the February 11 event. The transient conditions imply that our data represent a snapshot of the porosity distribution within the conduit that does not preclude the temporary presence of much higher porosities in the conduit. Such unsteady conduit flow conditions are consistent with the irregular but active dome growth in the month prior to the February 11 event. (C) 2019 Elsevier B.V. All rights reserved.
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Canals, A., Van Driessche, A. E. S., Palero, F., & Garcia-Ruiz, J. M. (2019). The origin of large gypsum crystals in the Geode of Pulpi (Almeria, Spain). Geology, 47(12), 1161–1165.
Résumé: The Geode of Pulpi (Almeria, Spain) is an similar to 11 m(3) ovoid cavity, the walls of which are covered with meter-sized idiomorphic and highly transparent gypsum (CaSO4 center dot 2H(2)O) crystals. We performed a thorough study based on field work, and petrographic and geochemical data collection, which aimed to reconstruct the geological history leading to the formation of this geode. The geode is hosted in mineralized Triassic carbonate rocks with a discontinuous mineral sequence from iron-carbonates and barite to celestine and finally gypsum (microcrystalline and selenite). Data from fluid inclusions show that barite precipitated above 100 degrees C, celestine at -70 degrees C, and gypsum below 25 degrees C. All delta S-34 sulfate phases fall between Triassic and Tertiary evaporite values. Barite and gypsum, either microcrystalline or large selenite crystals, show variable delta S-34 and delta O-18 compositions, whereas celestine and centimetric selenite gypsum have homogeneous values. We propose that the growth of the large selenite crystals in the Geode of Pulpi was the result of a self- feeding mechanism consisting of isovolumetric anhydrite replacement by gypsum at a temperature of 20 +/- 5 degrees C, episodically contributed by a ripening process enhanced by temperature oscillations due to climatic change.
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Cao, K., Wang, G., Leloup, P. H., Maheo, G., Xu, Y., van der Beek, P. A., et al. (2019). Oligocene-Early Miocene Topographic Relief Generation of Southeastern Tibet Triggered by Thrusting. Tectonics, 38(1), 374–391.
Résumé: The timing and mechanisms of uplift in southeastern Tibet remain disputed. To address this debate, we conducted structural and morphological analyses of the Yulong thrust belt; we also reconstruct the cooling and exhumation history of the Jianchuan basin in the hanging wall of the thrust system using inverse thermal modeling of apatite fission-track and (U-Th)/He thermochronology data. Our results provide evidence for 2.3-3.2km of rapid exhumation in the Jianchuan basin between 28 and 20Ma, followed by limited exhumation of less than 0.2km since then. The magnitude of basin exhumation is consistent with the present-day topographic step of 1.8-2.4km across the Yulong and Chenghai thrust belts, as shown by morphometric analysis. We thus infer that the present-day morphology of the southeastern margin of Tibet results partly from thrusting along the Yulong thrust belt during the Late Oligocene-Early Miocene. This structure may be the southwest continuation of the Longmen Shan thrust belt, offset by the Xianshuihe fault in the Late Miocene. On a regional scale, the approximate synchronicity of exhumation in the hanging walls of the Yalong-Yulong and Longmen Shan thrust systems indicates that widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene-Early Miocene. Plain Language Summary The timing and mechanisms for the high-elevation, low-relief landscape in southeastern Tibet remain at the center of debate. Using apatite fission track and apatite (U-Th)/He thermochronology and thermal modeling, this study sheds new lights on this issue by reconstructing the cooling and exhumation history of the Jianchuan basin, western Yunnan. One major finding is that the Jianchuan basin experienced rapid exhumation during 28-20Ma at a rate of 0.57-0.80km/Myr, coinciding with the absence of coeval sedimentation within the basin. Furthermore, morphometric and structural analyses point out a reasonable causal link between production of the topographic relief in the SE Tibet, exhumation of the Jianchuan basin, and thrusting of the Yalong thrust belt. These results allow us to propose a regional-scale tectonic scenario of widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene-Early Miocene.
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Carocci, E., Marignac, C., Cathelineau, M., Truche, L., Lecomte, A., & Pinto, F. (2019). Rutile from Panasqueira (Central Portugal): An Excellent Pathfinder for Wolframite Deposition. Minerals, 9(1).
Résumé: Abundant W-rich rutile in the tourmalinized wall-rocks from the Panasqueira W-deposit appears to be a marker of the onset of the main wolframite depositing event. Rutile displays spectacular zoning, both sector (SZ) and oscillatory (OZ). An extensive set of compositional data obtained on crystals, beforehand studied using back-scattered electron images and X-ray maps, was used to address (i) the effects of SZ on differential trapping of minor elements, and (ii) the significance of the OZ in deciphering fluid sources and fluid circulation dynamics. Particular attention was paid to Sn, W (Nb, Ta) concentrations in rutile as pathfinders of the W deposition. Concerning the sector zoning, W is more incorporated than (Nb, Ta) onto more efficient faces, whereas Sn contents are nearly not impacted. The net effect of the sector zoning is thus a progressive increase of the relative weight of Sn from pyramid to prism faces, in combination with a less significant increase in the relative weight of Nb + Ta. The oscillatory zoning concerns most minor elements: W, Nb (Ta), Fe, V, Cr and Sn. In the frequent doublets, the clear bands are in general enriched in W relatively to the dark ones, whereas the inverse is true for Nb and Ta. The doublets may be viewed as the result of the successive influx of (i) a W-rich, Nb + Ta poor fluid, abruptly replaced by (or mixed to) (ii) a Nb + Ta-rich and W-poor fluid. The Nb + Ta-rich fluid could be in turn related to a rare-metal granite layer observed atop of the Panasqueira granite.
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Carrara, A., Burgisser, A., & Bergantz, G. W. (2019). Lubrication effects on magmatic mush dynamics. Journal Of Volcanology And Geothermal Research, 380, 19–30.
Résumé: Silicic magma bodies are formed by repeated injections of mobile magma and reside as a crystal-rich mush. Numerical studies of open-system events have revealed the complexity of mixing and rheological behavior. This is associated with the dilation of the crystal network and the possible occurrence of a lubricated regime. Lubrication forces are hydrodynamic interactions occurring when neighboring crystals have relative motion. The effect of such dissipative forces has not yet been explored in the case of magmatic mush. Here, we investigate the effects of lubrication on mush dynamics and on magma transport. First, we propose scaling relationships to assess the relative importance of the forces controlling the motion of one crystal within a mush by adding lubrication terms into the Basset-Boussinesq-Oseen equation that describes crystal motion in a viscous melt. We then investigate lubrication effects at the macroscopic scale with computational fluid dynamics with discrete element modeling (CFD-DEM) simulations that include these forces. We explore two cases: crystal mush sedimentation and the injection of a crystal-free magma inside a mush. We perform all simulations twice, with and without lubrication forces, and compare the results. At the grain scale, we show that three dimensionless numbers and the crystal content can describe the competition between viscous drag, buoyancy, and lubrication. Two of these numbers (Stokes and Froude numbers) have been previously employed in the context of dilute suspensions. The third is a new form of the Sommerfeld number that measures the importance of lubrication. At the macroscopic scale, simulation pairs (with and without lubrication forces) exhibit very similar behavior when in steady state. The duration of the transient regime preceding steady state, however, is increased when lubrication forces are included. Lubrication causes an apparent bulk strain hardening followed by softening at the initiation of the mush motion. Our results show that lubrication opposes dilation and the initiation of motion within the magmatic mush during this transient phase. Our results highlight the control that the crystal network exerts on magma transport and provide a novel way to evaluate when lubrication matters. (C) 2019 Elsevier B.V. All rights reserved.
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Carrara, A., Pinel, V., Bascou, P., Chaljub, E., & De la Cruz-Reyna, S. (2019). Post-emplacement dynamics of andesitic lava flows at Volcan de Colima, Mexico, revealed by radar and optical remote sensing data. Journal Of Volcanology And Geothermal Research, 381, 1–15.
Résumé: We used optical and radar remote sensing datasets to map, estimate the volume, and measure the surface displacements of lava flows emplaced on the flanks of Volcan de Colima, Mexico by extrusion of lava dome material from the end of 2014 to early 2016. Our main result is that the flow motion of the lava contributes significantly to the recorded displacements several months after its emplacement. First, we mapped the deposits and estimated their volumes using two Digital Elevation Models (DEM), one derived from radar data acquired before the peak of activity and one derived from optical images acquired just after this peak of activity. Coherence information derived from the radar dataset added some temporal constraints on the timing of emplacement of various deposits. We thus estimated a mean extrusion rate of 1-2 m(3)s(-1) between November 2014 and February 2015. We then used a new approach to reconstruct the 3D displacement field, taking advantage of images acquired by the same satellite, on both ascending and descending tracks, and using a physical a priori on the direction of horizontal displacements. Our results show that about 2 cm yr(-1) of horizontal motion is still recorded a few months after the emplacement on the SW lava flow, which is the only one covered by the two-acquisition geometries. In order to differentiate the potential causes of the observed displacements, we modeled the thermal contraction of the lava flow using a finite element numerical method. Removing the contribution of thermoelastic contraction from the measured displacements enable to infer both the viscoelastic loading and flow motion effects from the residuals. Results show that, thermal contraction, flow motion and viscoelastic loading contribute significantly to the displacements recorded. (C) 2019 Elsevier B.V. All rights reserved.
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Cassidy, M., Ebmeier, S. K., Helo, C., Watt, S. F. L., Caudron, C., Odell, A., et al. (2019). Explosive Eruptions With Little Warning: Experimental Petrology and Volcano Monitoring Observations From the 2014 Eruption of Kelud, Indonesia. Geochemistry Geophysics Geosystems, 20(8), 4218–4247.
Résumé: Explosive eruptions that occur with little or no precursory unrest (less than a month) pose the greatest hazards from volcanoes to nearby populations. Here we focus on the preeruptive conditions for these explosive events, their triggers and how these eruptions evolve. We concentrate on Kelud volcano, where we have conducted a set of petrological experiments to understand preeruptive storage conditions for several recent eruptions. For the 2014 explosive eruption, we combine this with an analysis of interferometric synthetic aperture radar measured deformation. Our data suggest that both explosive and effusive eruptions at Kelud are sourced from a magma storage system at 2-4 km. However, explosive eruptions are fed by magma stored under relatively cool (similar to 1000 degrees C) and water-saturated conditions, whereas effusive eruptions are fed by slightly hotter (similar to 1050 degrees C), water-undersaturated magmas. We propose that the initial phase of the 2014 eruption was triggered by volatile overpressure, which then fostered top-down decompression tapping discrete magma bodies. By compiling a global data set of monitoring signatures of explosive eruptions, we show that the onset of unrest rarely points to the shallow ascent of magma to the surface, as ascent mostly occurs in a matter of hours or minutes. We relate the timescale of preeruptive unrest to eruption triggering mechanisms, with yearly/decadal periods of unrest relating to magma injection events (which may or may not precede a magmatic eruption), whereas internal triggering (e.g., second boiling) of an already present, cooling magma body can lead to explosive eruptions with little warning.
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Caudron, C., Girona, T., Taisne, B., Suparjan, Gunawan, H., Kristianto, et al. (2019). Change in seismic attenuation as a long-term precursor of gas-driven eruptions. Geology, 47(7), 632–636.
Résumé: A large fraction of volcanic eruptions do not expel magma at the Earth's surface. Although less known than magmatic eruptions, gas-driven eruptions expel fragments of preexisting rocks, volcanic gases, and steam, causing substantial casualties. The destructive potential of these eruptions lies in the difficulty in identifying clear warning signals. Some gas-driven eruptions have been preceded by some physicochemical changes, but these were extremely short-term (from minutes to hours), and no long-term trends have been clearly evidenced so far. Here, we show that unheralded gas-driven eruptions can be forecast in the long term using seismic signals recorded at nearby active craters. In particular, we have found that the most recent gas-driven eruptions at Kawah Ijen (Indonesia) and Ruapehu and Tongariro (New Zealand) volcanoes were all preceded by a systematic relative increase in lower-frequency (4.5-8 Hz) seismic amplitude compared to higher frequencies (8-16 Hz) over time scales of months to years. We show that this precursory activity reflects significant increases in seismic attenuation affecting preferentially high-frequency travelling waves; this probably results from the accumulation of volatiles in the shallow crust, which increases pore pressure in small-scale rock heterogeneities and eventually leads to gas-driven eruptions. Our results highlight the feasibility of better constraining the onset and the end of an unrest episode, which is of paramount importance for agencies in charge of volcano monitoring.
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Cebron, D., Laguerre, R., Noir, J., & Schaeffer, N. (2019). Precessing spherical shells: flows, dissipation, dynamo and the lunar core. Geophysical Journal International, 219, S34–S57.
Résumé: Precession of planets or moons affects internal liquid layers by driving flows, instabilities and possibly dynamos. The energy dissipated by these phenomena can influence orbital parameters such as the planet's spin rate. However, there is no systematic study of these flows in the spherical shell geometry relevant for planets, and the lack of scaling law prevents convincing extrapolation to celestial bodies. We have run more than 900 simulations of fluid spherical shells affected by precession, to systematically study basic flows, instabilities, turbulence and magnetic field generation. We observe no significant effects of the inner core on the onset of the instabilities. We obtain an analytical estimate of the viscous dissipation, mostly due to boundary layer friction in our simulations. We propose theoretical onsets for hydrodynamic instabilities, and document the intensity of turbulent fluctuations. We extend previous precession dynamo studies towards lower viscosities, at the limits of today's computers. In the low viscosity regime, precession dynamos rely on the presence of large-scale vortices, and the surface magnetic fields are dominated by small scales. Interestingly, intermittent and self-killing dynamos are observed. Our results suggest that large-scale planetary magnetic fields are unlikely to be produced by a precession-driven dynamo in a spherical core. But this question remains open as planetary cores are not exactly spherical, and thus the coupling between the fluid and the boundary does not vanish in the relevant limit of small viscosity. Moreover, the fully turbulent dissipation regime has not yet been reached in simulations. Our results suggest that the melted lunar core has been in a turbulent state throughout its history. Furthermore, in the view of recent experimental results, we propose updated formulas predicting the fluid mean rotation vector and the associated dissipation in both the laminar and the turbulent regimes.
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Celerier, S., Hurand, S., Garnero, C., Morisset, S., Benchakar, M., Habrioux, A., et al. (2019). Hydration of Ti3C2Tx MXene: An Interstratification Process with Major Implications on Physical Properties. Chemistry Of Materials, 31(2), 454–461.
Résumé: The MXenes, among which Ti3C2Tx is the most studied, are a large family of two-dimensional materials with proven potential in a variety of application fields (e.g., energy storage and conversion, water purification, electromagnetic interference shielding, humidity sensor, etc.). For most of these applications, the properties of MXenes depend, at least partly, on their water sorption ability and on the induced structural swelling, which is commonly considered a stepwise process, like in claylike materials. In the present study, we rather evidence the systematic coexistence of different hydrates in MXene interstratified crystals. Hydration heterogeneity and related structure disorder are described from the quantitative analysis of X-ray diffraction data. This specific methodological approach allows disentangling the complex interstratification and rationalizing the prediction of MXene electrical properties. The widespread use of this approach paves the way for a systematic and thorough determination of MXene structure, including order-disorder, and thus for grasping the influence of structural disorder (hydration heterogeneity) on a large number of MXene physical properties (e.g., optical transparency, capacitance). Deciphering this complex structural disorder is also essential in the design of new MXene-based materials for a variety of applications (supercapacitors, batteries, water treatment, etc.).
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Chandra, J., & Gueguen, P. (2019). Nonlinear Response of Soil?Structure Systems using Dynamic Centrifuge Experiments. Journal Of Earthquake Engineering, 23(10), 1719–1741.
Résumé: This study presents centrifuge tests analysis of nonlinear soil?structure interactions and the reciprocal influence of the soil and the structure. Weak and strong motions were considered and applied to several centrifuge setups, implemented ?with? or ?without? buildings. For each setup, the response of the site was analyzed using arrays of accelerometers located in the soil and buildings, using time and frequency domain methods. We conclude that the presence of buildings may strongly modify the nonlinear soil response in the free field and the simplified relationships linking the contribution of each motion to the overall soil?structure system response were discussed.
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Chauvire, B., & Rondeau, B. (2019). Constraints on gem opal formation: a case study of Ethiopian opals.
Résumé: Unlike other gems like diamond and corundum, opal is not forged in the heat and pressure of the earth, but at the surface. Composed of silica, which is by far the most abundant constituent in the earth's crust (and other terrestrial planets), the opal's specific microstructure is the origin of its striking beauty. The alteration of silicate by aqueous fluid releases the constituting silica, which is then transported by fluids until physical or chemical changes induce the precipitation into opal. Identifying the exact source of silica and the physical and chemical conditions required for gem opal formation remains challenging. Using the case of Wegel Tena, we demonstrate how to identify the process involved in gem opal formation. Petrological examination of opal host-rocks provides significant hints to understand the context for opal precipitation. Geochemical signatures of opal inform on the silica source and chemical conditions during fluid transportation. An improved genetic classification of gem opal is also proposed.
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Chauvire, B., & Thomas, P. S. (2019). DSC of natural opal: insights into the incorporation of crystallisable water in the opal microstructure. Journal Of Thermal Analysis And Calorimetry, .
Résumé: Low-temperature DSC on a wide range of opal-A and opal-CT samples was carried out to estimate the proportion of crystallisable water and to determine the size of water-filled cavities. A wide range of crystallisable water contents in the range 4.9 to 41.9% of the water contained in opals were observed, although the proportion of crystallisable water did not correlate with structure. Pore size and pore size distribution were estimated from the melt temperature depression and heat flow data, respectively. Opal-CT was observed to have smaller water-filled pores (radii < 2 nm) than opal-A (radii from 2.5 to 4.9 nm), suggesting that molecular water may be contained between nanograins in the microstructural units (spheres or lepispheres). A narrower pore size distribution was calculated for opal-CT, and no melting of the crystallisable water was observed where bulk water would be expected to melt, suggesting the absence of larger voids. The melting peaks for opal-A, on the other hand, transitioned into the melting of bulk water suggesting the presence of significantly larger water-filled pores, an observation consistent with the microstructure observed in SEM micrographs.
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Cherubini, A., Garcia, B., Cerepi, A., & Revil, A. (2019). Influence of CO2 on the Electrical Conductivity and Streaming Potential of Carbonate Rocks. Journal Of Geophysical Research-Solid Earth, 124(10), 10056–10073.
Résumé: Minimally intrusive geophysical methods are required to monitor CO2 leakages from underground storage reservoirs. We investigate the impact of gaseous CO2 on both electrical conductivity and electrokinetic properties of two limestones during their drainage. These data are contrasted with measurements performed on one clay-free sandstone. The initial NaCl brine concentrations before drainage (from 8.5 to 17.1 mMol/L) correspond to the limit between freshwater and slightly brackish water. These values are representative to saturated brine formations inside which CO2 can be stored. Using these water salinities, the surface conductivity of the samples represents less than 5% of the overall electrical conductivity. A CO2 release leads to an increase of the electrical conductivity of the rock during drainage in limestones and no change in sandstone. This increase in the electrical conductivity is due to the dissolution of calcite with the concomitant release of Ca2+ and HCO3- in the pore water. It is not due to the CO2 dissociation in the pore water in the pore pressure range 0-0.5 MPa and at a temperature of T = 20 degrees C. The measurements of the streaming potential show a substantial decrease of the streaming potential coupling coefficient and zeta potential magnitudes after a CO2 release in carbonates. This observation is explained by the increase of the ionic strength of the pore water in the course of the experiment. This change can be used, in turn, to determine calcite dissolution rates from the measurement of the electrokinetic properties.
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Chevalier, M. - L., & Replumaz, A. (2019). Deciphering old moraine age distributions in SE Tibet showing bimodal climatic signal for glaciations: Marine Isotope Stages 2 and 6. Earth And Planetary Science Letters, 507, 105–118.
Résumé: Determining the timing and extent of past glaciations in Tibet is essential to reconstruct regional paleoclimate and understand how atmospheric circulation varies due to the high altitude low latitude Tibetan Plateau. In SE Tibet, geomorphological field observation of glacial deposits shows two main imbricated moraines. We apply statistical analyses to a compilation of eight new Be-10 cosmogenic exposure ages from two moraine crests at GMX site and 128 previously published but recalculated exposure ages from 30 additional crests in the region. The results show that ages from the sharpest inner moraines range from 14-25 ka, corresponding to the full range of Marine oxygen Isotope Stage (MIS)-2 (i.e., Last Glacial Maximum, LGM) with less than 2% of older outliers. The outer moraines have a fundamentally different distribution with scattered ages from 10 to 200 ka, obtained using the same method of sampling, dating, and age modeling proven robust for dating the LGM inner moraines, therefore excluding a methodologic artifact. This large scatter prevents the application of any statistical analysis to the age distribution. At a site with well-developed and preserved imbricated moraines (Cuopu), the outer moraine's oldest ages are MIS-6, with the oldest one being at the MIS-6/MIS-7 limit, identical to what is observed in the regional compilation. Following our observations for the LGM moraines where <2% of older outliers are present, the outer moraines in SE Tibet could not be younger than MIS-6. This implies that no glacial advance occurred during MIS-3 which is surprising because MIS-3 moraines have been reported to be the most extensive elsewhere in the Himalayan-Tibetan orogen. Indeed, glaciers are sensitive to both precipitation increase and temperature decrease but whether one factor is prevalent remains debated especially on the Tibetan Plateau. Considering negligible erosion of the boulders, as observed in the field at Cuopu, the most conservative interpretation of our observations is that the true emplacement age of the outer moraines external to the LGM moraines is MIS-6. In that case, glacial advances in SE Tibet correlate with the two coldest periods of the Northern Hemisphere cooling cycles, MIS-2 and MIS-6, indicating that these glaciers are mostly sensitive to a decrease in temperature. (C) 2018 Elsevier B.V. All rights reserved.
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Chmiel, M., Mordret, A., Boue, P., Brenguier, F., Lecocq, T., Courbis, R., et al. (2019). Ambient noise multimode Rayleigh and Love wave tomography to determine the shear velocity structure above the Groningen gas field. Geophysical Journal International, 218(3), 1781–1795.
Résumé: The Groningen gas field is one of the largest gas fields in Europe. The continuous gas extraction led to an induced seismic activity in the area. In order to monitor the seismic activity and study the gas field many permanent and temporary seismic arrays were deployed. In particular, the extraction of the shear wave velocity model is crucial in seismic hazard assessment. Local S-wave velocity-depth profiles allow us the estimation of a potential amplification due to soft sediments. Ambient seismic noise tomography is an interesting alternative to traditional methods that were used in modelling the S-wave velocity. The ambient noise field consists mostly of surface waves, which are sensitive to the S wave and if inverted, they reveal the corresponding S-wave structures. In this study, we present results of a depth inversion of surface waves obtained from the cross-correlation of 1 month of ambient noise data from four flexible networks located in the Groningen area. Each block consisted of about 400 3-C stations. We compute group velocity maps of Rayleigh and Love waves using a straight-ray surface wave tomography. We also extract clear higher modes of Love and Rayleigh waves. The S-wave velocity model is obtained with a joint inversion of Love and Rayleigh waves using the Neighbourhood Algorithm. In order to improve the depth inversion, we use the mean phase velocity curves and the higher modes of Rayleigh and Love waves. Moreover, we use the depth of the base of the North Sea formation as a hard constraint. This information provides an additional constraint for depth inversion, which reduces the S-wave velocity uncertainties. The final S-wave velocity models reflect the geological structures up to 1 km depth and in perspective can be used in seismic risk modelling.
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Chmiel, M., Roux, P., & Bardainne, T. (2019). High-sensitivity microseismic monitoring: Automatic detection and localization of subsurface noise sources using matched-field processing and dense patch arrays. Geophysics, 84(6), KS211–KS223.
Résumé: Recent advancements in seismic data acquisition and computational power have enhanced the deployment of dense seismic monitoring networks. The growing volume of recorded data requires the development of automated techniques to monitor and image zones of seismicity. We have developed an automatic detection and localization method that demands minimal a priori information for retrieval of the spatial distribution of subsurface noise sources (including, but not limited to, microseismic activity), in a reservoir and in the near vicinity during a hydraulic fracturing treatment. This method is based on matched-field processing (MFP), which takes advantage of the phase coherence that is recorded at dense arrays of sensors to localize noise sources. MFP is applied with a distributed set of patch arrays in the context of geophysics exploration. The MFP approach is applied to ambient noise recordings, and it provides results that are consistent with the classic localization methods applied to high-amplitude microseismic signals (in particular, using the relative template-based method). Furthermore, MFP provides enhanced sensitivity of detection and spatially extended information about structural heterogeneities. MFP opens a route to continuous, automatic, statistics-based, and high-sensitivity reservoir monitoring and imaging for geophysics exploration. Potential applications can also be envisaged for seismic monitoring of volcanic and geyser activities, and for other types of hydrothermal activity.
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Coltice, N., Husson, L., Faccenna, C., & Arnould, M. (2019). What drives tectonic plates? Science Advances, 5(10).
Résumé: Does Earth's mantle drive plates, or do plates drive mantle flow? This long-standing question may be ill posed, however, as both the lithosphere and mantle belong to a single self-organizing system. Alternatively, this question is better recast as follows: Does the dynamic balance between plates and mantle change over long-term tectonic reorganizations, and at what spatial wavelengths are those processes operating? A hurdle in answering this question is in designing dynamic models of mantle convection with realistic tectonic behavior evolving over supercontinent cycles. By devising these models, we find that slabs pull plates at rapid rates and tear continents apart, with keels of continents only slowing down their drift when they are not attached to a subducting plate. Our models show that the tectonic tessellation varies at a higher degree than mantle flow, which partly unlocks the conceptualization of plate tectonics and mantle convection as a unique, self-consistent system.
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Coperey, A., Revil, A., Abdulsamad, F., Stutz, B., Duvillard, P. A., & Ravanel, L. (2019). Low-Frequency Induced Polarization of Porous Media Undergoing Freezing: Preliminary Observations and Modeling. Journal Of Geophysical Research-Solid Earth, 124(5), 4523–4544.
Résumé: We investigate the thermal dependence of the complex conductivity of nine porous materials in the temperature range +20 degrees C to -10 or -15 degrees C. The selected samples include three soils, two granites, three clay-sands mixes, and one graphitic tight sandstone. A total of 12 experiments is conducted with one sample tested at three different salinities. Our goal is to use this database to extend the dynamic Stern layer polarization model in freezing conditions. We observe two polarization mechanisms, one associated with the effect of the change in the liquid water content and its salinity upon the polarization of the porous material. A second mechanism, at higher frequencies (>10 Hz), is likely associated with the polarization of ice. At low frequencies and above the freezing point, the in-phase and quadrature conductivities depend on temperature in a predictable way. This dependence is due to the dependence of the mobility of the charge carriers with temperature. Below the freezing point, the in-phase and quadrature conductivity follow a brutal decay with temperature. This dependence is modeled through an exponential freezing curve function. We were also able to determine how the (apparent) formation factor and surface conductivity change with temperature and water content below the freezing point. Our model is able to replicate the data at low frequencies and predicts correctly the fact that the ratio between the normalized chargeability and the surface conductivity is independent of the water content and temperature and equals a well-defined dimensionless number R.
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Coperey, A., Revil, A., & Stutz, B. (2019). Electrical Conductivity Versus Temperature in Freezing Conditions: A Field Experiment Using a Basket Geothermal Heat Exchanger. Geophysical Research Letters, 46(24), 14531–14538.
Résumé: We use a basket geothermal heat exchanger during 518 hr to freeze a portion of soil. This field experiment is monitored using time lapse electrical conductivity tomography and a set of 47 in situ temperature sensors. A frozen soil core characterized by negative temperatures and low conductivity values (<10(-3) S/m) develops over time. A petrophysical model describing the temperature dependence of the electrical conductivity in freezing conditions is applied to the field data and compared to two laboratory experiments performed with two core samples from the test site. The results show that this petrophysical model can be used to interpret field measurements bridging electrical conductivity to temperature and liquid water content.
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Cordonnier, B., Pluymakers, A., Tengattini, A., Marti, S., Kaestner, A., Fusseis, F., et al. (2019). Neutron Imaging of Cadmium Sorption and Transport in Porous Rocks. Frontiers In Earth Science, 7.
Résumé: Understanding fluid flow in rocks is crucial to quantify many natural processes such as ground water flow and naturally triggered seismicity, as well as engineering questions such as displacement of contaminants, the eligibility of subsurface waste storage, geothermal energy usage, oil and gas recovery and artificially induced seismicity. Two key parameters that control the variability of fluid flow and the movement of dissolved chemical species are (i) the local hydraulic conductivity, and (ii) the local sorption properties of the dissolved chemical species by the solid matrix. These parameters can be constrained through tomography imaging of rock samples subjected to fluid injection under constrained flow rate and pressure. The neutron imaging technique is ideal to explore fluid localization in porous materials due to the high but variable sensitivity of neutrons to the different hydrogen isotopes. However, until recently, this technique was underused in geology because of its large acquisition time. With the improved acquisition times of newly set-up neutron beamlines, it has become easier to study fluid flow. In the current set of experiments, we demonstrate the feasibility of in-situ 2D and 3D time-lapse neutron imaging of fluid and pollutant percolation in rocks, in particular that of cadmium salt. Cadmium is a hazardous compound that is found in many electronic devices, including batteries and is a common contaminant in soil and groundwater. It also exhibits higher contrast in neutron attenuation with respect to heavy water, and is therefore an ideal tracer. Time-lapse 2D radiographies and 3D neutron tomographies of the samples were acquired on two neutron beamlines (ILL, France and SINQ, Switzerland). We performed two sets of experiments, imbibition and injection experiments, where we imaged in-situ flow properties, such as local permeability and interactions between cadmium and the solid rock matrix. Our results indicate that even within these cm-scale porous rocks, cadmium transport follows preferential pathways, and locally interacts within the limestone samples. Our results demonstrate that the use of neutron imaging provides additional insights on subsurface transport of pollutants.
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Cortes, G., Carniel, R., Angeles Mendoza, M., & Lesage, P. (2019). Standardization of Noisy Volcanoseismic Waveforms as a Key Step toward Station-Independent, Robust Automatic Recognition. Seismological Research Letters, 90(2), 581–590.
Résumé: This article addresses the automatic volcanoseismic recognition (VSR) in a noisy scenario studying the robustness of a classifier based on hidden Markov models (HMMs). The system learns recognition models analyzing signals recorded in 1995 to automatically detect and classify noisy events of 2009. Both datasets were acquired in different locations at Deception Island and with a different type of sensor showing a variety of site effects and noises. To deal with the inherent waveform variability of this setup, we propose to reconstruct the seismograms to achieve both modeling standardization and noise reduction goals. We analyze a set of empirical mode decomposition (EMD) algorithms jointly with static and dynamic reconstruction criteria to evaluate their impact on the robustness of the recognition process. This machine-learning focus on real time, continuous, unsupervised VSR paradigm is able to increase by 16% the global VSR accuracy using an adaptive reconstruction compared to the scores obtained without any standardization.
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Crouzet, C., Wilhelm, B., Sabatier, P., Demory, F., Thouveny, N., Pignol, C., et al. (2019). Palaeomagnetism for chronologies of recent alpine lake sediments: successes and limits. Journal Of Paleolimnology, 62(3), 259–278.
Résumé: Chronologies of lake-sediment records covering the last centuries to millennia are usually based on both short-lived radionuclides and radiocarbon dating. However, beyond the range of short-lived radionuclides, age model accuracy often suffers from large radiocarbon uncertainties. For high-altitude records, this issue is even more prominent as terrestrial plant fragments for radiocarbon dating are often lacking due to the sparse vegetation in such environments. In this study, we evaluate the potential of the geomagnetic field secular variations as a complementary tool to establish more robust age-depth relationships. Our palaeomagnetic study, applied to five high-altitude lakes from the western European Alps, first shows that recent unconsolidated sediments can carry stable remanent magnetization. The analysis of the magnetic parameters indicates that low-coercivity pseudo-single domain magnetite grains carry the natural magnetization. Nevertheless, the quality of palaeomagnetic secular variation records varies from one lake to another. This quality can be illustrated through the calculation of the declination/inclination maximum angular variations and their comparison to the expected value. Compared with available models, the declination variations are usually too large and the inclination too high. We discuss the validity of palaeosecular variation (PSV) of the Earth's magnetic field regarding rock magnetism, magnetization processes and possible deformation during coring. From a magnetic point of view, the quality of data is variable, but the characteristic remanent magnetization direction is consistent at site level between neighbouring lakes and with the reference curve, suggesting that geomagnetic field secular variations are approximately recorded. Finally, we attempt to correlate the declination/inclination variations of the characteristic remanent magnetization measured in the five records to the reference geomagnetic model to provide additional chronological markers for age-depth modelling. These stratigraphic chrono-markers appear in systematic agreement with our previous chronological data and enable a reduction of dating uncertainties up to 30% when including these chrono-markers in the age-depth modelling. This agreement supports the interpretation that PSV may have been recorded more or less accurately depending on the studied lake. Therefore, coupled with a comprehensive understanding through other analysis (sedimentology, dating, geochemistry), PSV can be used to improve the age models in the more favourable cases.
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Cruz-Hernandez, P., Carrero, S., Perez-Lopez, R., Fernandez-Martinez, A., Lindsay, M. B. J., Dejoie, C., et al. (2019). Influence of As(V) on precipitation and transformation of schwertmannite in acid mine drainage-impacted waters. European Journal Of Mineralogy, 31(2), 237–245.
Résumé: Iron-rich sediments commonly cover riverbeds affected by acid mine drainage (AMD). Initial precipitates are often dominated by schwertmannite, which has an exceptionally high capacity to sequester As and other toxic elements. This poorly crystalline Fe oxyhydroxysulfate rapidly recrystallizes to goethite; however, the influence of trace elements on ageing rates and products is poorly understood. This study examined the influence of As(V) concentrations on the kinetics of schwertmannite precipitation and transformation. Schwertmannite was synthesized in the presence of various initial dissolved As concentrations (i.e., 0-2 mNI) and subsequently aged at 40, 60 or 85 degrees C for 1 h to 300 d. The initial As concentration had a profound impact on schwertmannite precipitation and transformation. Schwertmannite precipitation was inhibited at higher initial As concentrations in favor of pseudo-amorphous Fe-hydroxyarsenate formation. Schwertmannite transformation to goethite was accompanied by sulfate release and, over longer time, As release. Pair distribution function (PDF) analysis of high-energy X-ray diffraction (HEXD) patterns revealed that increasing initial As concentration produced structural defects in associated precipitates. Schwertmannite precipitation exerts an important control on As mobility in AMD-impacted waters; however, this study has demonstrated that the long-term stability of schwertmannite and associated precipitates should be considered when designing AMD remediation strategies and AMD treatment systems.
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Curry, M. E., van der Beek, P., Huisrnans, R. S., Wolf, S. G., & Munoz, J. - A. (2019). Evolving paleotopography and lithospheric flexure of the Pyrenean Orogen from 3D flexural modeling and basin analysis. Earth And Planetary Science Letters, 515, 26–37.
Résumé: We present the results of a numerical modeling study of the Pyrenees Mountains investigating the spatio-temporal variation in lithospheric flexure in response to the developing orogen, with the aim of setting constraints on paleotopography. We employ a finite-element method to model the 3D flexural deformation of the lithosphere beneath the Pyrenean orogen since the onset of convergence in the Late Cretaceous. Using subsurface and structural data, we describe the evolving geometry of both the northern Aquitaine and southern Ebro foreland basins at the Paleocene (early orogenic phase), the end-and mid-Eocene (peak orogenic phase), the Oligocene (late orogenic phase), and the present (post-orogenic phase). The flexural modeling provides insight into how both the rigidity of the lithosphere and the paleotopographic load have varied over the course of orogenesis to shape the basin geometry. Employing a 3D continuous-plate model, we find that the overriding European plate has slightly higher rigidity than the underthrusting Iberian plate. The best-fit model results for the modern setting produce a root mean -square error (RMSE) of 458 m using effective elastic thickness (T-e) values of 23 and 16 km for the European and Iberian plates, respectively. We also test a broken-plate model, which produces a similar RMSE but predicts higher T-e (32 km for the European plate and 26 km for the Iberian plate). The broken plate model results indicate minimal vertical plate-boundary forces are necessary to reproduce the observed basin geometry. Flexural modeling results suggest that the topographic load doubled from the Paleocene to the Oligocene, and achieved modern topography by the end of the Eocene. The topography remained relatively stable throughout the Oligocene and Neogene, with only limited growth and decay. These results have implications for surface processes and foreland-basin development of the Pyrenean Orogen, tectonic inheritance, and the geodynamic evolution of Western Europe. (C) 2019 Elsevier B.V. All rights reserved.
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D'Amato, J. (2019). Contribution of a rockfall database obtained by laser scanner to the characterization of failure conditions and associated processes. Bulletin Of Engineering Geology And The Environment, 78(1), 653–668.
Résumé: Using laser scanner data, an exhaustive rockfall database has been established for a rockwall located near the town of Grenoble (France). The study site is a long double cliff, on the eastern border of the Chartreuse Massif. The two cliffs consist respectively of thinly bedded and massive limestone, which show different structures, morphologies and rockfall activities. The 3D point clouds obtained by laser scanner allow to detect and model the fallen compartments in 3D. Information about cliff surface, and localization, dimensions, failure mechanism for each compartment were obtained and analyzed in order to characterize the morphological evolutions of the cliffs. It appears that the morphology and the slope of the lower cliff is related to fracturing and torrential erosion which occurs in the marls below the cliff, showing a rockfall frequency 22 times higher than for the upper cliff. These results show that the erosion process in the lower cliff is in a transient state, whereas it could be in a steady state in the upper cliff. Rockfalls have been dated by a near-continuous photographic survey (1 photo each 10mn) and a monthly survey during 2.5years. The analysis of the two data bases shows that the rockfall frequency is 7 times higher during freeze-thaw episodes than without meteorological event, and 4.5 times higher during rainfall episodes. Moreover, it becomes 26 times higher when the mean rainfall intensity is higher than 5mm/h. Based on these results, a 3-level hazard scale has been proposed for hazard prediction.
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Dansereau, V., Demery, V., Berthier, E., Weiss, J., & Ponson, L. (2019). Collective Damage Growth Controls Fault Orientation in Quasibrittle Compressive Failure. Physical Review Letters, 122(8).
Résumé: The Mohr-Coulomb criterion is widely used in geosciences and solid mechanics to relate the state of stress at failure to the observed orientation of the resulting faults. This relation is based on the assumption that macroscopic failure takes place along the plane that maximizes the Coulomb stress. Here, this hypothesis is assessed by simulating compressive tests on an elastodamageable material that follows the Mohr-Coulomb criterion at the mesoscopic scale. We find that the macroscopic fault orientation is not given by the Mohr-Coulomb criterion. Instead, for a weakly disordered material, it corresponds to the most unstable mode of damage growth, which we determine through a linear stability analysis of its homogeneously damaged state. Our study reveals that compressive failure emerges from the coalescence of damaged clusters within the material and that this collective process is suitably described at the continuum scale by introducing an elastic kernel that describes the interactions between these clusters.
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Dawelbeit, A., Jaillard, E., & Eisawi, A. (2019). Sedimentary and paleobiological records of the latest Pleistocene-Holocene climate evolution in the Kordofan region, Sudan. Journal Of African Earth Sciences, 160, 103605.
Résumé: The study of the Quaternary sediments of the Kordofan region, Sudan, allowed to decipher the succession of environments in this area, since about 13 kyr. The oldest sediments ( > 13 to 10.5 kyr BP) are mainly aeolian deposits, except in the southern areas. The “African Humid Period” is recorded by scattered palustrine and lacustrine carbonates dated at 10.5-6.5 kyr BP in the center and North, respectively, by fluvial deposits in the South, and by the pedogenesis of previous deposits in all areas. Fluvial activity may be responsible for the erosion of the previous aeolian sands in the southern areas. Between 6.5 and 3.3 kyr BP, the evolution from aquatic to terrestrial gastropod fauna, and from tropical to arid pollen assemblages points to the shift toward an arid climate. This aridification phase culminated between 3.3 and 1.1 kyr BP, with a period of strong aeolian activity and erosion. Aeolian deposition resumed after 1.1 kyr BP under conditions comparable to those of today. This evolution is consistent with that recorded in Saharan areas, although the period of strong aeolian erosion (approximate to 3.3-1.1 kyr BP) may have been underestimated so far.
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De Barros, L., Baques, M., Godano, M., Helmstetter, A., Deschamps, A., Larroque, C., et al. (2019). Fluid-Induced Swarms and Coseismic Stress Transfer: A Dual Process Highlighted in the Aftershock Sequence of the 7 April 2014 Earthquake (Ml 4.8, Ubaye, France). Journal Of Geophysical Research-Solid Earth, 124(4), 3918–3932.
Résumé: The upper part of the Ubaye Valley (French Alps) is characterized by alternating mainshock-aftershock sequences and swarms. Particularly, during the 2012-2015 crisis, four mainshocks with Ml>3.5 occurred. We here focus on the aftershocks of the largest one (Ml=4.8, 7 April 2014), in order to better understand the involved processes behind this peculiar seismic behavior. We use template matching detection, waveform classification, and double-difference relocations to analyze this seismicity, on average and at the scale of the clusters that compose it. Most event sources are aligned along a plane consistent with the mainshock fault (N165, 65 degrees W), but occurred on conjugate structures. A few clusters of seismicity are also observed far from the mainshock source. Our analysis shows that distinct, spatially separated processes are at play. While coseismic stress transfer explains the seismicity close to the mainshock source, fluid-pressure diffusion and distant stress triggering are required to generate events farther away. The overall distributions in time and magnitude followed a slow Omori's decay and a Gutenberg-Richter relationship, respectively. However, these classical responses arise from the superposition of very different behaviors, associated with different processes at depth. Plain Language Summary Earthquakes have regularly shaken the upper part of the Ubaye valley, near the town of Barcelonnette in the Southwestern French Alps, for nearly 20years. The earthquake behavior is peculiar, as swarms of numerous low magnitude events alternate with larger earthquakes, such as the Ml 4.8 one occurring on 7 April 2014. To understand this dual behavior, we performed an in-depth analysis of the aftershock of this event. The seismicity mainly aligns on a plane consistent with the mainshock fault (N165, 65 degrees W). However, most of the events occurred on branching structures, belonging to the damaged zone of this fault, or on some other small faults far away. While the average behavior of this aftershock sequence is close to a standard one, we show that two different processes occurred at depth. Events occurring close to the mainshock are triggered by coseismic stress transfer, while fluid-pressure diffusion are likely required to explain the seismicity further away. Such dual process should be considered for seismic hazard assessment.
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De Barros, L., Cappa, F., Guglielmi, Y., Duboeuf, L., & Grasso, J. - R. (2019). Energy of injection-induced seismicity predicted from in-situ experiments. Scientific Reports, 9.
Résumé: The ability to predict the magnitude of an earthquake caused by deep fluid injections is an important factor for assessing the safety of the reservoir storage and the seismic hazard. Here, we propose a new approach to evaluate the seismic energy released during fluid injection by integrating injection parameters, induced aseismic deformation, and the distance of earthquake sources from injection. We use data from ten injection experiments performed at a decameter scale into fault zones in limestone and shale formations. We observe that the seismic energy and the hydraulic energy similarly depend on the injected fluid volume (V), as they both scale as V-3/2. They show, however, a large discrepancy, partly related to a large aseismic deformation. Therefore, to accurately predict the released seismic energy, aseismic deformation should be considered in the budget through the residual deformation measured at the injection. Alternatively, the minimal hypocentral distance from injection points and the critical fluid pressure for fault reactivation can be used for a better prediction of the seismic moment in the total compilation of earthquakes observed during these experiments. Complementary to the prediction based only on the injected fluid volume, our approach opens the possibility of using alternative monitoring parameters to improve traffic-light protocols for induced earthquakes and the regulation of operational injection activities.
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de Plaen, R. S. M., Cannata, A., Cannavo, F., Caudron, C., Lecocq, T., & Francis, O. (2019). Temporal Changes of Seismic Velocity Caused by Volcanic Activity at Mt. Etna Revealed by the Autocorrelation of Ambient Seismic Noise. Frontiers In Earth Science, 6.
Résumé: On active volcanoes, ambient noise-based seismic interferometry can be a very useful monitoring tool as it allows to detect very slight variations in seismic velocity associated with magma transported toward the surface. However, the classical cross-station approach occasionally fails to detect seismic velocity changes related to eruptive activity, even on very active, well-instrumented volcanoes such as Mt. Etna. In this work, we explored an improved ambient noise-based monitoring strategy by performing the autocorrelation of seismic noise recorded at Mt. Etna volcano, by three stations located close to the active summit craters, during April 2013-October 2014. Such an interval was chosen because of the number and variety of eruptions. In place of the classical cross-correlation, we implemented the phase cross-correlation of each component with itself, which does not require normalization of the signals. The detected seismic velocity variations were very consistent for all three stations throughout the study period, mainly ranging between 0.3 and -0.2%, and were time-related to both sequences of paroxysmal eruptions and more effusive activities. In particular, we observed seismic velocity decreases accompanying paroxysmal eruptions, suggesting an intense pressurization within the plumbing system, which created an area of extensional strain with crack openings. In addition, seismic velocity variations over time were analyzed in the light of ground deformation data recorded by GPS stations and volcanic tremor centroid locations and displayed a particularly strong correlation with the former. Finally, we showed that, although the investigated frequency band (1-2 Hz) contained most of the volcanic tremor energy, our results did not indicate a particular contamination of seismic velocity variation measurements by variations of tremor sources. Ultimately, our investigation highlights a better way to implement noise-based seismic monitoring techniques. The near-field sensitivity of the autocorrelation helped improve our understanding of the relationship between variations of seismic velocity, ground deformation and the pressurization dynamics of volcanic plumbing systems which, in turn, allows for better monitoring implementations of seismic interferometry on other volcanoes.
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DeFelipe, I., Pedreira, D., Pulgar, J. A., van der Beek, P. A., Bernet, M., & Pik, R. (2019). Unraveling the Mesozoic and Cenozoic Tectonothermal Evolution of the Eastern Basque-Cantabrian Zone-Western Pyrenees by Low-Temperature Thermochronology. Tectonics, 38(9), 3436–3461.
Résumé: Low-temperature thermochronology studies have increased our knowledge of the orogenic processes along the Pyrenean-Cantabrian mountain belt by placing time constraints on the exhumation history of its rocks. However, a significant gap in the data existed between the western Pyrenees and the central Cantabrian Mountains, hampering a comprehensive view of the tectonothermal evolution along the belt. We present a new apatite fission track and zircon (U-Th)/He (ZHe) data set for the eastern Basque-Cantabrian zone-western Pyrenees. Apatite fission track central ages cluster in the Eocene-Oligocene. ZHe samples can be separated into two groups: Group 1 depicts clustered ZHe ages-eU concentration (Cinco Villas massif) and Group 2 depicts dispersed ZHe ages-eU concentration (Alduides massif and a Paleozoic rock pinned along the Leiza thrust). A sample from the Oroz-Betelu massif shows intermediate behavior. Inverse modeling suggests that samples from Group 1 reached 240-280 degrees C in the Late Cretaceous, implying deep sedimentary burial of the Cinco Villas massif before its major exhumation phase, most probably in the early to middle Eocene, postdating the phase of rapid exhumation of the western part of the Leiza thrust. The sample from the Oroz-Betelu massif, far from the Mesozoic exhumed mantle domain, experienced maximum temperatures close to 200 degrees C by burial beneath the Jaca-Pamplona basin. It was later exhumed in the hanging wall of the Gavarnie thrust in the Bartonian-Priabonian. This work provides new insights into the tectonothermal evolution of the Basque massifs and the inversion of a hyperextended margin.
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Desrues, M., Lacroix, P., & Brenguier, O. (2019). Satellite Pre-Failure Detection and In Situ Monitoring of the Landslide of the Tunnel du Chambon, French Alps. Geosciences, 9(7).
Résumé: Recent studies using satellite data have shown a growing interest in detecting and anticipating landslide failures. However, their value for an actual landslide prediction has shown variable results. Therefore, the use of satellite images for that purpose still requires additional attention. Here, we study the landslide of the Tunnel du Chambon in the French Alps that ruptured in July 2015, generating major impacts on economic activity and infrastructures. To evaluate the contribution of very high-resolution optical satellite images to characterize and potentially anticipate the landslide failure, we conduct here a retro analysis of its evolution. Two time periods are analyzed: September 2012 to September 2014, and May to July 2015. We combine Pleiades optical images analysis and geodetic measurements from in situ topographic monitoring. Satellite images were correlated to detect pre-failure motions, showing 1.4-m of displacement between September 2012 and September 2014. In situ geodetic measures were used to analyze motions during the main activity of the landslide in June and July 2015. Topographic measurements highlight different areas of deformations and two periods of strong activity, related to the last stage of the tertiary creep and to anthropic massive purges of unstable masses. The law of acceleration toward the rupture observed in June and July 2015 over the topographic targets also fits well the satellite observation between 2012 and 2014, showing that the landslide probably already entered into tertiary creep 2.5 years before its failure.
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Di Rosa, M., Meneghini, F., Marroni, M., Hobbs, N., & Vidal, O. (2019). The Exhumation of Continental Crust in Collisional Belts: Insights from the Deep Structure of Alpine Corsica in the Cima Pedani Area. Journal Of Geology, 127(3), 263–288.
Résumé: In northern Corsica, the Cima Pedani area is characterized by a stack of continental and oceanic units belonging to Alpine Corsica. The base of the unit stack consists of three metamorphic continental units (Canavaggia, Pedani, and Scoltola) that are overthrust by the Schistes Lustres Complex, represented by oceanic units. The continental units are metamorphic fragments of the European continental margin. They include a Paleozoic basement intruded by Permo-Carboniferous metagranitoids covered by Permian metavolcanites and a Triassic-Jurassic metacarbonatic sequence, unconformably covered by metabreccias and metasandstones of Eocene age. These units are affected by a polyphased tectonometamorphic history acquired in a time frame from the Priabonian to the Aquitanian. The reconstructed pressure-temperature (P-T) paths and the related deformations describe a retrograde history acquired during their progressive exhumation, whereas no trace of the older prograde history has been preserved. In all the reconstructed P-T paths, the P peak (1.04-1.35 GPa) corresponds to the maximum depth reached by these units, whereas the subsequent history includes a progressive P decrease associated with a coeval T increase. The deformation history related to exhumation includes three deformation phases. In particular, the D2 phase is characterized by noncoaxial ductile structures parallel to the boundaries of the units observed in the Cima Pedani tectonic window. The sense of shear of these shear zones is generally top-to-the-W (i.e., toward the Alpine foreland). The collected data provide evidence that the continental units were deformed and metamorphosed during the exhumation following their ascent path along the plate boundary interface. The geodynamic mechanism we propose for the exhumation of the Cima Pedani units is the subduction channel, in which high-pressure units arise between the down-going plate and the former accretionary wedge built up during the oceanic subduction, represented by the Schistes Lustres Complex.
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Dif, H., Zendagui, D., & Bard, P. - Y. (2019). Implementing effects of site conditions in damage estimated at urban scale. Bulletin Of Earthquake Engineering, 17(3), 1185–1219.
Résumé: Local site effects due to geotechnical conditions modify seismic motions on surface. This implies that during a given earthquake, buildings located on soft sites may experience a higher damage than similar buildings resting on nearby rock sites. The aim of this study is to provide an estimation of the influence of site conditions on the buildings damage distribution. We combine an approach adapted from the Hazus methodology for the assessment of building damage, with the Borcherdt non linear site amplification factors, that enable to characterize the high and low frequency amplification as a function of V-S30 (the average shear wave velocity in the upper 30m) and ground motion levels. Analysis of obtained results indicates that, seismic damage expressed by the normalized mean damage index depends not only on seismic shaking level and building typology but also on site conditions through the shear wave velocity proxy. A regression relationship is established between the seismic damage and both shaking levels and site conditions, aiming at presenting a simple, rapid tool for estimating this damage at urban areas. An index, the damage increase ratio, is proposed to quantify the increase of damage resulting from site effects, and its dependence on loading level and site conditions are quantified and discussed for the main building typologies present in Algeria. Depending on the building typology, the overall damage may vary within a range of 2-5 for moderate shaking (0.1g) between hard rock and very soft soil, and within a range 1-1.5 for strong shaking (0.5g). The reduction of the impact of site conditions with increasing shaking level is directly linked with the nonlinear soil behavior.
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Domingos, J., Pais, M. A., Jault, D., & Mandea, M. (2019). Temporal resolution of internal magnetic field modes from satellite data. Earth Planets And Space, 71.
Résumé: We aim to obtain a modal decomposition of the internal geomagnetic field. In order to do so, we perform a principal component analysis of two virtual observatory datasets, with 4-month sampling time, from the CHAMP (2001-2009) and Swarm (2014-2017) satellite records. The spatial patterns of well-resolved modes calculated from the three field components all have internal origin as expected for these datasets, except for one Swarm mode. For both datasets, we find that the modes with the shortest timescales have also the smallest length scales as expected from a physical standpoint. Also, the energy ordering of the modes is from the least to the most variable, in agreement with independent results on the main field data spectrum. This is not achieved in regularised inversions of geomagnetic field data into time-varying spherical harmonic decomposition, where the highest degree terms have also the poorest time resolution. The improved accuracy of Swarm data is reflected in the lower level of the noise variance.
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Donaldson, C., Winder, T., Caudron, C., & White, R. S. (2019). Crustal seismic velocity responds to a magmatic intrusion and seasonal loading in Iceland's Northern Volcanic Zone. Science Advances, 5(11).
Résumé: Seismic noise interferometry is an exciting technique for studying volcanoes, providing a continuous measurement of seismic velocity changes (dv/v), which are sensitive to magmatic processes that affect the surrounding crust. However, understanding the exact mechanisms causing changes in dv/v is often difficult. We present dv/v measurements over 10 years in central Iceland, measured using single-station cross-component correlation functions from 51 instruments across a range of frequency bands. We observe a linear correlation between changes in dv/v and volumetric strain at stations in regions of both compression and dilatation associated with the 2014 Baroarbunga-Holuhraun dike intrusion. Furthermore, a clear seasonal cycle in dv/v is modeled as resulting from elastic and poroelastic responses to changing snow thickness, atmospheric pressure, and groundwater level. This study comprehensively explains variations in dv/v arising from diverse crustal stresses and highlights the importance of deformation modeling when interpreting dv/v, with implications for volcano and environmental monitoring worldwide.
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Donze, F. - V., Tsopela, A., Guglielmi, Y., Henry, P., & Gout, C. (2019). Pressurized fluid flow within the mechanical stability domain of fault zones in shale (Vol. 98).
Résumé: Fracture interaction mechanisms and reactivation of natural discontinuities under fluid pressurization conditions inside fault zone can represent critical issues in risk assessment of caprock integrity. A field injection test, carried out in a damage fault zone at the decameter scale i.e. mesoscale, has been studied using a Distinct Element Model. Considering the complex structural nature of a fault zone, the contribution of fracture sets on the bulk permeability has been investigated during a hydraulic injection. It has been shown that their orientation for a given in-situ stress field plays a major role. However, if homogeneous properties are assigned to the fracture planes in the model, the limited irreversible displacements cannot be reproduced. Despite these limited displacements (40 μm maximum), the transmissivity increased by a factor of 10-100. These results provide insights in fracture controlled permeability of fault zones depending on the geometrical properties of the fractures and their resulting hydro-mechanical behavior for a given in-situ stress field.
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Dundas, C. M., Mellon, M. T., Conway, S. J., & Gastineau, R. (2019). Active Boulder Movement at High Martian Latitudes. Geophysical Research Letters, 46(10), 5075–5082.
Résumé: Lobate stony landforms occur on steep slopes at high latitudes on Mars. We demonstrate active boulder movement at seven such sites. Submeter-scale boulders frequently move distances of a few meters. The movement is concentrated in the vicinity of the lobate landforms but also occurs on other slopes. This provides evidence for a newly discovered, common style of activity on Mars, which may play an important role in slope degradation. It also opens the possibility that the lobate features are currently forming in the absence of significant volumes of liquid water. Plain Language Summary Tongue-shaped lobes of boulders occur on steep slopes at high latitudes on Mars. Boulders in those lobes, as well as on nearby slopes, commonly move short distances. Several processes could contribute to moving the boulders, but liquid water is probably not involved. This is a new type of active surface process on Mars and may be an important contributor to forming the lobes or changing steep slopes.
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Durr-Auster, T., Wiggenhauser, M., Zeder, C., Schulin, R., Weiss, D. J., & Frossard, E. (2019). The Use of Q-ICPMS to Apply Enriched Zinc Stable Isotope Source Tracing for Organic Fertilizers. Frontiers In Plant Science, 10.
Résumé: Organic fertilizer applications can contribute to Zinc (Zn) biofortification of crops. An enriched stable isotope source tracing approach is a central tool to further determine the potential of this biofortification measure. Here, we assessed the use of the widely available quadrupole single-collector ICPMS (Q-ICPMS, analytical error = 1% relative standard deviation) and the less accessible but more precise multicollector ICPMS as reference instrument (MC-ICPMS, analytical error = 0.01% relative standard deviation) to measure enriched Zn stable isotope ratios in soil-fertilizer-plant systems. The isotope label was either applied to the fertilizer (direct method) or to the soil available Zn pool that was determined by isotope ratios measurements of the shoots that grew on labeled soils without fertilizer addition (indirect method). The latter approach is used to trace Zn that was added to soils with complex insoluble organic fertilizers that are difficult to label homogeneously. To reduce isobaric interferences during Zn isotope measurements, ion exchange chromatography was used to separate the Zn from the sample matrix. The Zn-67:Zn-66 isotope ratios altered from 0.148 at natural abundance to 1.561 in the fertilizer of the direct method and 0.218 to 0.305 in soil available Zn of the indirect method. Analysis of the difference (Bland-Altman) between the two analytical instruments revealed that the variation between Zn-67:Zn-66 isotope ratios measured with Q-ICPMS and MC-ICPMS were on average 0.08% [95% confidence interval (CI) = 0.68%]. The fractions of Zn derived from the fertilizer in the plant were on average 0.16% higher (CI = 0.49%) when analyzed with Q- compared to MC-ICPMS. The sample matrix had a larger impact on isotope measurements than the choice of analytical instrument, as non-purified samples resulted on average 5.79% (CI = 9.47%) higher isotope ratios than purified samples. Furthermore, the gain in analytical precision using MC-ICPMS instead of Q-ICPMS was small compared to the experimental precision. Thus, Zn isotope measurements of purified samples measured with Q-ICPMS is a valid method to trace Zn sources in soil-fertilizer-plant systems. For the indirect source tracing approach, we outlined strategies to sufficiently enrich the soil with Zn isotopes without significantly altering the soil available Zn pool.
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El Haber, E., Cornou, C., Jongmans, D., Abdelmassih, D. Y., Lopez-Caballero, F., & AL-Bittar, T. (2019). Influence of 2D heterogeneous elastic soil properties on surface ground motion spatial variability. Soil Dynamics And Earthquake Engineering, 123, 75–90.
Résumé: Spatial variability of earthquake ground motion (SVEGM) refers to the differences in amplitude and phase between recordings of the same earthquake at different locations. In the near-surface, geological processes (sedimentation, erosion) and anthropogenic activities can lead to small scale spatial heterogeneities of soil mechanical properties, which may affect SVEGM. In this paper, the effect of shallow 2D spatial variability of the shear wave velocity (Vs) on the surface ground motion is assessed through a set of numerical experiments, using a simple 2D velocity structure (a sedimentary layer over a half-space). Non-linearity or damping are not considered in the wave propagation calculation in order to solely focus on the effects of soil elastic property variability. Vs is modeled as a random field using the EOLE method (Expansion Optimal Linear Estimation) and considering three statistical parameters: the coefficient of variation, and the horizontal and vertical auto correlation distances. Seismic ground motions are numerically simulated for a plane wave excitation with SV polarization. Modeling results clearly highlight the scattering of surface waves by ground heterogeneities, leading to large spatial variations in surface ground motion. We computed surface ground motion indicators (resonance frequency, spectral amplification, Arias intensity and duration) and we showed that their spatial variability is mainly controlled by the Vs coefficient of variation. A comparison between 2D and 1D ground motion probabilistic modeling shows that the 1D probabilistic approach may correctly reproduce average fundamental resonance frequencies and corresponding amplification. However, the 1D approach significantly under-predicts both ground motion amplification at higher frequencies and related variabilities, as well as Arias intensities and inferred durations, which are all controlled by the generation of locally diffracted surface waves.
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Ellis, A., DeMets, C., McCaffrey, R., Briole, P., Muralles, B. C., Flores, O., et al. (2019). GPS constraints on deformation in northern Central America from 1999 to 2017, Part 2: Block rotations and fault slip rates, fault locking and distributed deformation. Geophysical Journal International, 218(2), 729–754.
Résumé: We describe a new elastic-kinematic model for the present tectonics of northern Central America and southern Mexico, where the Motagua-Polochic fault zone, Middle America subduction zone and faults in the Central America volcanic arc pose significant seismic hazards. The new model, which consists of the angular velocities for eight plates and blocks, interseismic locking solutions for some of the block-bounding faults and strain-rate tensors for three blocks with significant internal deformation, optimizes the fit to regional fault azimuths and earthquake slip directions and a new 200+ station GPS velocity field that has been corrected for the coseismic and post-seismic effects of three large regional earthquakes in 2009 and 2012. From our new observations and modelling thereof, we find evidence for the following: (1) 13 +/- 1 mm yr(-1) of approximate to E-W stretching between undeformed Caribbean plate in central Honduras and a location approximate to 50 km west of the Guatemala City graben; (2) accommodation of the above extension via slow W-to-WNW motions of newly defined Chortis and Ipala blocks and distributed ENE-WSW stretching within both blocks; (3) 80 per cent of Chortis-North America platemotion in eastern Guatemala occurs on the Motagua fault versus only 20 per cent on the Polochic fault; (4) Motagua fault slip rates that decrease westwards from 14 +/- 1.5 mm yr(-1) to 9-10 +/- 2 mm yr(-1) to less than 2 mm yr(-1) in eastern Guatemala, central Guatemala and west of the Guatemala City graben, respectively; (5) Slip rates along Central America volcanic arc faults that decrease from 12.5 +/- 1.0 mm yr(-1) in Nicaragua to 10 +/- 1.3 mm yr(-1) in central El Salvador to 7.6 +/- 2.1 mm yr(-1) on the Jalpatagua fault of southern Guatemala to 2-3 mm yr(-1) or less across the volcanic arc west of Guatemala City; (6) a transition near the Mexico-Guatemala border from moderate-to-high locking of the subduction interface offshore from southern Mexico to low locking below the Central America forearc sliver; (7) Subduction of the Cocos plate beneath the Central America forearc sliver up to 10 mm yr(-1) faster than and 7-8. clockwise from all previous estimates; (8) 12 +/- 6 mm yr(-1) of E-W extension across the newly defined Fonseca block. A pattern of misfits to the velocities of sites in northern Guatemala and southern Mexico may be caused by distributed deformation in this region or shortcomings with our model and/or assumptions. The primary factors that control the regional deformation appear to include the arcuate geometry of the Motagua fault, low locking of the Middle America subduction interface, slow-to-no motion between the leading edge of the Central America forearc sliver and North America plate and a rheologically weak volcanic arc.
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Erdos, Z., Huismans, R. S., & van der Beek, P. (2019). Control of increased sedimentation on orogenic fold-and-thrust belt structure – insights into the evolution of the Western Alps. Solid Earth, 10(2), 391–404.
Résumé: We use two-dimensional thermomechanical models to investigate the potential role of rapid filling of foreland basins in the development of orogenic foreland fold-and-thrust belts. We focus on the extensively studied example of the Western European Alps, where a sudden increase in foreland sedimentation rate during the mid-Oligocene is well documented. Our model results indicate that such an increase in sedimentation rate will temporarily disrupt the formation of an otherwise regular, outward-propagating basement thrust-sheet sequence. The frontal basement thrust active at the time of a sudden increase in sedimentation rate remains active for a longer time and accommodates more shortening than the previous thrusts. As the propagation of deformation into the foreland fold-and-thrust belt is strongly connected to basement deformation, this transient phase appears as a period of slow migration of the distal edge of foreland deformation. The predicted pattern of foreland-basin and basement thrust-front propagation is strikingly similar to that observed in the North Alpine Foreland Basin and provides an explanation for the coeval mid-Oligocene filling of the Swiss Molasse Basin, due to increased sediment input from the Alpine orogen, and a marked decrease in thrustfront propagation rate. We also compare our results to predictions from critical-taper theory, and we conclude that they are broadly consistent even though critical-taper theory cannot be used to predict the timing and location of the formation of new basement thrusts when sedimentation is included. The evolution scenario explored here is common in orogenic foreland basins; hence, our results have broad implications for orogenic belts other than the Western Alps.
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Fargier, Y., Ananfouet, Y., Lopes, S. P., Saussaye, L., Dore, L., Jodry, C., et al. (2019). Quality Assessment of a Cut-Off Wall Dike Reinforcement by 2D-ERI. Journal Of Environmental And Engineering Geophysics, 24(3), 451–463.
Résumé: Each year hydraulic structures such as levees and earth dams are hit by disorders that can lead to their collapse. A dike reinforcement method such as the deep soil mixing gets interest for its reinforcement capacity at moderate cost. We report on the use of a non-destructive technique to effectively assess the proper achievement of these structures and their evolution in time. More particularly, 2D-electrical resistivity imaging (2D-ERI) was used to assess a cut-off wall. We evaluate the benefits and limitations of three acquisition techniques (longitudinal, transversal and cross-hole). To complete the interpretation, we performed a comprehensive geotechnical study to make a diagnosis of the structure. Each inversion result is combined with numerical modelling that enlightens limitations of the acquisition techniques and improve the interpretation. Results show that 2D-ERI can present a real benefit for the assessment of cut-off walls even if the dimensions of the cut-off wall limit the detectability of deep heterogeneities.
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Ferreira, J., Mattioli, E., Sucheras-Marx, B., Giraud, F., Duarte, L. V., Pittet, B., et al. (2019). Western Tethys Early and Middle Jurassic calcareous nannofossil biostratigraphy. Earth-Science Reviews, 197.
Résumé: An exhaustive biostratigraphic study based on the calcareous nannofossil content from Lower and Middle Jurassic Lusitanian Basin sections in Portugal is here presented. Located at the strategic intersection of important Jurassic water masses during a period of drastic environmental changes, the Lusitanian Basin conveyed mixed phytoplanktonic communities in its surface waters. Approximately 800 m of exceptionally continuous Lower and Middle Jurassic series bearing detailed ammonite biostratigraphy and two Global Stratotype Section and Point are studied. Vertical and lateral ubiquity of calcareous nannofossils in marine sediments and rapid evolutionary rate and radiation make this fossil group a remarkable biostratigraphic tool. Nearly 100 bioevents are acknowledged in similar to 24 Myr time span this work refers to, bridging 11 nannofossil zones and 29 subzones. A thorough revision of the existing literature referring to Early and Middle Jurassic calcareous nannofossil biostratigraphy is presented, and causes and implications for zonal marker discrepancies discussed under a palaeoceanographic and Jurassic nannofossil evolution angle. In order to create a solid biostratigraphic frame and to compare it with C and O stable isotopic trends, brachiopod calcite shells were analysed for geochemistry. This work yields for the first time a very detailed and inclusive biostratigraphic scheme for the Early and Middle Jurassic epochs.
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Francescone, F., Lauretano, V., Bouligand, C., Moretti, M., Sabatino, N., Schrader, C., et al. (2019). A 9 million-year-long astrochronological record of the early-middle Eocene corroborated by seafloor spreading rates. Geological Society Of America Bulletin, 131(3-4), 499–520.
Résumé: The early-middle Eocene (ca. 56-41 Ma) is recorded in the pelagic Scaglia Rossa and Variegata Formations of the Umbria-Marche Basin (central Italy). Geochemical and magnetostratigraphic alignment between the Bottaccione section (Gubbio, central Italy) and the Smirra core (Cagli, central Italy) allows us to generate a continuous and well-preserved new record that, combined with previously published data from the same area, creates a continuous high-resolution record from the Paleocene-Eocene thermal maximum (ca. 56 Ma) to the lower part of chron C21n. Comparison with carbon isotope records from Ocean Drilling Program Sites 1258 and 1263 reveals a satisfactory match, providing further evidence of the global significance of the long-term trend and superposed perturbations captured by the delta C-13 records. The identification of astronomically forced geochemical cycles allows us to develop a 405 k.y. tuned age model, thereby extending the astrochronology from ca. 56.0 to ca. 47.5 Ma. Marine magnetic anomaly profiles from major oceanic basins characterized by high seafloor spreading rates were used to independently test the astronomical polarity time scale associated with our tuning, as well as other polarity time scales. Our age model suggests the existence of periods of relatively constant seafloor spreading rates separated by rapid changes, while the other time scales generate more gradual variations and also include large and short-term deviations in spreading rates that occur simultaneously in different oceanic basins, implying errors in polarity reversal ages. The Umbria-Marche age model further contributes to the closure of the middle Eocene gap in the astronomical time scale.
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Fritschi, E. J. C., Juillot, F., Dublet, G., Fonteneau, L., Fandeur, D., Martin, E., et al. (2019). An alternative model for the formation of hydrous Mg/Ni layer silicates (“deweylite”/“garnierite”) in faulted peridotites of New Caledonia: II. Petrography and chemistry of white and green clay infillings. European Journal Of Mineralogy, 31(5-6), 945–962.
Résumé: This study, which complements a first mineralogical work, presents detailed petrographic and chemical data on the sequences of clay infillings commonly found in serpentine veins of reactivated faults from the New Caledonian peridotite formation. Chemical trends and transfers established from the outer serpentine fringe to the inner clay infilling, as well as from the white (deweylite) to the greenish (garnierite) parts of the veins, enable us to decipher the processes and conditions involved in the redistribution of Mg and Ni along reactivated faults. As commonly reported from studies of peridotite formations worldwide, two main chemical trends are distinguished. In New Caledonia, these trends belong to distinct periods of tectonic activities associated with the dislocation and early alteration of the ophiolite nappe. They result from two kinds of Ni-ore-forming processes and reveal a significant decrease in the mobility of Ni over time. The first process relates the step-by-step alteration of serpentine species into talclike (TL) minerals to the sequential leaching of Mg and Fe, together with their local replacement by Ni in octahedral sites of the newly formed TL minerals. The TL minerals are thus considered as the main Ni-bearing phases (pimelite) of the ore. The large-scale redistribution of Mg and Ni during a first period of tectonic activity and alteration leads to the differentiation of white (Ni-free) and olive-green (Ni-rich) clay infillings along the reactivated faults. The second process belongs to a second period of tectonic activity and alteration where most of the serpentine species have been converted into TL minerals without major Ni enrichment (formation of a second sequence of milky white and turquoise clay infillings). Redistribution of Mg and Ni occurs over shorter distances from the transition of Mg-rich to Ni-rich clay infillings (or breccias). It results from oscillatory phenomena and self-organised precipitation processes leading to cyclic and inverse Mg and Ni variations in alternating bands of contrasted optical anisotropy. The early redistribution of Ni and the significant decrease in the mobility of this element from the first to the second period of tectonic activity provide better constraints on an alternative model for the genesis of the Ni-silicate ore.
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Gailler, L., Kauahikaua, J., Lenat, J. - F., Revil, A., Gresse, M., Ahmed, A. S., et al. (2019). 3D electrical conductivity imaging of Halema'uma'u lava lake (Kilauea volcano). Journal Of Volcanology And Geothermal Research, 381, 185–192.
Résumé: Before the 2018 collapse of the summit of Kilauea volcano, a ca. 200 m in diameter lava lake inside of Halema'uma'u crater was embedded in a very active hydrothermal system. In 2015, we carried out an electrical conductivity survey and the data were inverted in 3D. The lack of conductivity contrast precludes distinguishing the lava column from the surrounding hydrothermal zones. Laboratory measurements on samples from the lava lake show that the conductivity of magma is significantly lower than that of hydrothermal zones but the high vesicularity of the upper part of the lava lake may decrease its macroscopic conductivity. Based on the 3D conductivity model, we distinguish at least two types of hydrothermal circulations: 1) one guided by the collapse faults of Halema'uma'u crater and by the magmatic column of the lava lake, and 2) another guided by previous caldera faults and fractures related to intrusions. We observe that the location of the faults formed during the 2018 collapse of the summit was greatly influenced by the hydrothermally altered zones. (C) 2019 Elsevier B.V. All rights reserved.
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Garambois, S., Voisin, C., Guzman, M. A. R., Brito, D., Guillier, B., & Refloch, A. (2019). Analysis of ballistic waves in seismic noise monitoring of water table variations in a water field site: added value from numerical modelling to data understanding. Geophysical Journal International, 219(3), 1636–1647.
Résumé: Passive seismic interferometry allows to track continuously the weak seismic velocity changes in any medium by correlating the ambient seismic noise between two points to reconstruct the Green's function. The ballistic surface waves of the reconstructed Green's functions are used to monitor the changes of water table induced by a controlled experiment in the Crepieux-Charmy (France) exploitation field. Viscoelastic numerical modelling of the monitoring experiment reproduces quite satisfactorily the sensitivity of the surface waves to the water table previously observed with seismic noise data. This numerical approach points out that this sensitivity is controlled by mode mixing of Rayleigh waves. It also made it possible to identify the refracted P wave and to extract its anticorrelated sensitivity to water table variations. Depending on the offset between receivers, it was observed numerically that the interferences between the different waves (with different velocities) composing the seismic wavefield slightly affect the quantitative sensitivity to water table changes. This suggests the use of an optimal spatial and temporal observation window for which wave interference is minor and does not blur the quantitative response to water table variations. We were thus able to determine the relationship between velocity and water table variations for all waves involved. From numerical computations, we identify a weak signal-to-noise ratio phase in the noise correlograms, with a anticorrelated sensitivity to the water table: the reconstructed refracted waves.
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Garcia-Delgado, H., Villamizar, N., & Bernet, M. (2019). Recent tectonic activity along the Bucaramanga Fault System (Chicamocha River Canyon, Eastern Cordillera of Colombia): a geomorphological approach. Zeitschrift Fur Geomorphologie, 62(3), 199–215.
Résumé: Tectonic geomorphology and geomorphic indices are nowadays one of the most used tools to quantify landscape response to recent tectonic activity and thus to study active faulting in orogens around the world. Based on this, a tectonic geomorphology study was conducted on the Bucaramanga Fault System (BFS) at the Chicamocha Canyon, which is structurally controlled by the Bucaramanga fault along a 36 km long section. The Chicamocha Canyon is one of the most striking landforms in the Colombian Andes, and its local environmental conditions, i.e., semi-arid climate and poorly vegetated slopes make it an outstanding laboratory to study Earth surface processes avoiding typical humid conditions. In this work, several geomorphic indices like the Hypsometric Integral (HI), the Asymmetry Factor (AF), the Ratio of Valley Floor to Valley Height (Vf), the Drainage Basin Shape index (Bs), and the Normalized Concavity Steepness (ksn) in 27 drainage basins of the Chicamocha Basin as well as channel width and slope measurements along the Chicamocha River are presented. From these indices, it was observed that drainage basins on the upthrown fault block of the Bucaramanga Fault, especially those located in southern segments between Cepita and Ricaurte, show recent tectonic surface uplift characterized by high HI, low Vf, and high ksn values. Tectonic-induced rejuvenation in some drainage basins like the Perchiquez, Guaca and Negro rivers, formed several geomorphic features such as deep V-shaped valleys, deflected drainages, barbed drainages and a regional tilting towards the NW. Besides this, threshold hillslopes reached after tectonic uplift in some drainage basins are expressed by intense landsliding in the form of debris and rock-slides, debris avalanches and debris flows, which in turn have modified the landscape of the Chicamocha canyon. Geomorphic indices obtained on the western block of the BFS hint at relatively low tectonic activity, even so recent surface uplift within three drainage basins in the San Miguel area seems to be associated with a Riedel-type structure of the Bucaramanga Fault. This work proposes a fault segmentation of the Bucaramanga Fault along the Chicamocha canyon, thus providing new evidence for the recent tectonic activity of this fault system.
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Gardonio, B., Campillo, M., Marsan, D., Lecointre, A., Bouchon, M., & Letort, J. (2019). Seismic Activity Preceding the 2011 Mw9.0 Tohoku Earthquake, Japan, Analyzed With Multidimensional Template Matching. Journal Of Geophysical Research-Solid Earth, 124(7), 6815–6831.
Résumé: The observation of a transient slip 1month before the rupture of the 2011 Tohoku earthquake is a conandrum since the area was supposedly fully coupled. A better understanding of the mechanisms at work during the preseismic phase is thus fundamental. However, the configuration of the Pacific plate and the location of the Tohoku rupture zone 200km from the coast make it difficult to detect microseismic events. In this study, we use a multidimensional template matching (MDTM) technique to detect earthquakes that are hidden in the noise. The temporal distribution of these 395 newly detected earthquakes provides new insights on the slip history of the megathrust earthquake epicentral zone. The detected events can be separated into two groups: 187 low-frequency detections (below 5Hz) that well recorded the episodes of earthquake migration prior to the Tohoku earthquake and 208 high-frequency detections (above 10Hz) that occurred close to the rupture zones of the M >= 4.8-6 earthquakes that struck between the 9 March 2011 M7.3 foreshock and the 30 November 2010 Tohoku-Oki earthquake. The seismic rate of these high frequency detection events starts to increase on 30 November 2010 until the Tohoku earthquake.
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Garenne, A., Beck, P., Montes-Hernandez, G., Bonal, L., Quirico, E., Proux, O., et al. (2019). The iron record of asteroidal processes in carbonaceous chondrites. Meteoritics & Planetary Science, 54(11), 2652–2665.
Résumé: The valence of iron has been used in terrestrial studies to trace the hydrolysis of primary silicate rocks. Here, we use a similar approach to characterize the secondary processes, namely thermal metamorphism and aqueous alteration, that have affected carbonaceous chondrites. X-ray absorption near-edge structure spectroscopy at the Fe-K-edge was performed on a series of 36 CM, 9 CR, 10 CV, and 2 CI chondrites. While previous studies have focused on the relative distribution of Fe-0 with respect to oxidized iron (Fe-ox = Fe2+ + Fe3+) or the iron distribution in some specific phases (e.g., Urey-Craig diagram; Urey and Craig 1953), our measurements enable us to assess the fractions of iron in each of its three oxidation states: Fe-0, Fe2+, and Fe3+. Among the four carbonaceous chondrites groups studied, a correlation between the iron oxidation index (IOI = [2(Fe2+) + 3(Fe3+)]/[Fe-TOT]) and the hydrogen content is observed. However, within the CM group, for which a progressive alteration sequence has been defined, a conversion of Fe3+ to Fe2+ is observed with increasing degree of aqueous alteration. This reduction of iron can be explained by an evolution in the mineralogy of the secondary phases. In the case of the few CM chondrites that experienced some thermal metamorphism, in addition to aqueous alteration, a redox memory of the aqueous alteration is present: a significant fraction of Fe3+ is present, together with Fe2+ and sometimes Fe-0. From our data set, the CR chondrites show a wider range of IOI from 1.5 to 2.5. In all considered CR chondrites, the three oxidation states of iron coexist. Even in the least-altered CR chondrites, the fraction of Fe3+ can be high (30% for MET 00426). This observation confirms that oxidized iron has been integrated during formation of fine-grained amorphous material in the matrix (Le Guillou and Brearley 2014; Le Guillou et al. 2015; Hopp and Vollmer 2018). Last, the IOI of CV chondrites does not reflect the reduced/oxidized classification based on metal and magnetite proportions, but is strongly correlated with petrographic types. The valence of iron in CV chondrites therefore appears to be most closely related to thermal history, rather than aqueous alteration, even if these processes can occur together (Krot et al. 2004; Brearley and Krot 2013).
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Gassner, T., Gumberidze, A., Trassinelli, M., Hess, R., Spillmann, U., Banas, D., et al. (2019). High-resolution wavelength-dispersive spectroscopy of K-shell transitions in hydrogen-like gold. X-Ray Spectrometry, , XRS3098.
Résumé: We present a measurement of K-shell transitions in H-like gold (Au78+) using specially developed transmission type crystal spectrometers combined with Ge(i) microstrip detectors. The experiment has been carried out at the Experimental Storage Ring at GSI in Darmstadt. This is a first high-resolution wavelength-dispersive measurement of a K-shell transition in a high-Z H-like ion, thus representing an important milestone in this field. Ideas on possible future improvements are discussed as well.
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Gautam, P., Huyghe, P., Mugnier, J. - L., & Regmi, K. R. (2019). Magneto-chemical signature of the Lower-to-Middle Siwaliks transition in the Karnali River section (Western Nepal): Implications for Himalayan tectonics and climate. Geological Journal, .
Résumé: Fluviatile sediments comprising a 600-m-thick sequence of the Lower and Middle Siwaliks in the Karnali area in Nepal exhibit a distinct zonation revealed by magnetic and geochemical properties. Four magneto-chemical zones (MCZ1-MCZ4), each about 150 m thick and 400 kyr in duration, provide new insights into Himalayan tectono-climatic events during the Tortonian (Miocene) stage. They exhibit contrasting magnetic susceptibility and isothermal remanence due to differences in magnetic mineral types (magnetite, haematite, and goethite) and concentrations. Odd-numbered zones with higher goethite/(goethite + haematite) ratio, a moisture proxy, indicate wetter conditions in the source area, while the even-numbered zones, virtually without goethite, suggest drier conditions. Chemical indices of alteration/weathering and proxies for hydraulic sorting and mobility derived from the major element compositions also reveal contrasts among these zones. The middle of the MCZ2-MCZ3 zone, with a transitional magneto-chemical signature, is the best candidate for the Lower-to-Middle Siwaliks contact, rather than the field-based boundary placed 18 m up-section at the base of the thick salt-and-pepper sandstone bed. The transition records an increase in river energy and associated accelerated erosion of the Himalayan gneiss zone as the source of coarse-grained material. We suggest a scenario, whereby climate change from drier to wetter (with higher precipitation) conditions affects erosional processes (i.e., weathering, disaggregation and particle transport on the hillslope) prevailing in a large catchment and influencing the depositional modes.
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Gervilla, F., Asta, M. P., Fanlo, l., Grolimund, D., Ferreira-Sanchez, D., Samson, V. A., et al. (2019). Diffusion pathways of Fe2+ and Fe3+ during the formation of ferrian chromite: a μXANES study. Contributions To Mineralogy And Petrology, 174(8).
Résumé: The alteration of chromian spinel is a key process during serpentinization and metamorphism of ultramafic rocks controlled by oxygen fugacity (fO(2)) and Fe2+<-> Fe3+ exchange during fluid-rock interaction. Chromian spinel alteration is better recorded in less permeable chromitite than in peridotites where extensive fluid-rock interaction frequently overprints the record of earlier stages of alteration. To shed light on that process we have studied the distribution of Fe2+ and Fe3+ in variably altered chromian spinel grains from a set of chromitite samples from the same mining district using synchrotron-based microscopic chemical imaging and spatially resolved X-ray absorption near edge structure spectroscopy. Our results show that early stages of alteration do not involve changes in Cr3+ and Fe2+ contents or in Fe speciation but only depletion in Al3+ and Mg2+ resulting in the formation of porous chromite. With ongoing alteration Fe3+ migrates into porous chromite mainly along fracture walls and fracture zones as well as along grain boundaries. Sheared-type chromitites record the maximum rates of fluid-rock interaction because in these chromitite-types the accommodation of deformation on porous chromite allowed higher rates of diffusion of Fe3+ and Fe2+ (a magnetite component with Fe3+/Fe-total=0.66) into the newly formed neoblasts. In porous chromite-type texture (all the original chromite grains fully transformed to porous chromite) the deformation and accompanying diffusion processes result in the formation of homogenous ferrian chromite grains. In contrast, in partly altered-type texture (chromite grains with original cores surrounded by porous chromite), such processes are only restricted to the porous rims, giving rise to zoned chromian spinel-ferrian chromite grains.
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Ghazoui, Z., Bertrand, S., Vanneste, K., Yokoyama, Y., Nomade, J., Gajurel, A. P., et al. (2019). Potentially large post-1505 AD earthquakes in western Nepal revealed by a lake sediment record. Nature Communications, 10.
Résumé: According to paleoseismological studies, the last earthquake that ruptured the Main Frontal Thrust in western Nepal occurred in 1505 AD. No evidence of large earthquakes has been documented since, giving rise to the concept of a seismic gap in the central Himalaya. Here, we report on a new record of earthquake-triggered turbidites from Lake Rara, western Nepal. Our lake-sediment record contains eight possibly moderate-to-large earthquake-triggered turbidites during the last 800 years, three of which overlap in age with previously reported M-w >= 7 events in western Nepal. Shaking intensity modelling, together with instrumental records, suggests that near-field earthquakes (<= 15 km) should have a minimum M-w 5.6, and regional earthquakes (<= 80 km) a M-w > similar to 6.5, to trigger turbidites. We present a likely scenario that western Nepal may be as seismically active as central Nepal; however, more data are needed to revaluate the seismic risk in the central Himalaya.
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Giachetti, T., Gonnermann, H. M., Gardner, J. E., Burgisser, A., Hajimirza, S., Earley, T. C., et al. (2019). Bubble Coalescence and Percolation Threshold in Expanding Rhyolitic Magma. Geochemistry Geophysics Geosystems, 20(2), 1054–1074.
Résumé: Coalescence during bubble nucleation and growth in crystal-free rhyolitic melt was experimentally investigated, and the percolation threshold, defined as the porosity at which the vesicular melt first becomes permeable, was estimated. Experiments with bubble number densities between 10(14) and 10(15)m(-3) were compared to four suites of rhyolitic Plinian pumices, which have approximately equal bubble number densities. At the same total porosity, Plinian samples have a higher percentage of coalesced bubbles compared to their experimental counterparts. Percolation modeling of the experimental samples indicates that all of them are impermeable and have percolation thresholds of approximately 80-90%, irrespective of their porosity. Percolation modeling of the Plinian pumices, all of which have been shown to be permeable, gives a percolation threshold of approximately 60%. The experimental samples fall on a distinct trend in terms of connected versus total porosity relative to the Plinian samples, which also have a greater melt-bubble structural complexity. The same holds true for experimental samples of lower bubble number densities. We interpret the comparatively higher coalescence within the Plinian samples to be a consequence of shear deformation of the erupting magma, together with an inherently greater structural complexity resulting from a more complex nucleation process.
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Gillet, N., Huder, L., & Aubert, J. (2019). A reduced stochastic model of core surface dynamics based on geodynamo simulations. Geophysical Journal International, 219(1), 522–539.
Résumé: We make use of recent geodynamo simulations to propose a reduced stochastic model of the dynamics at the surface of Earth's core. On decadal and longer periods, this model replicates the most energetic eigen directions of the geodynamo computation. Towards shorter timescales, it proposes a compensation for weaknesses of these simulations. This model furthermore accounts for the signature, in the geomagnetic secular variation, of errors of representativeness associated with unresolved processes. We incorporate the reduced stochastic model into a geomagnetic data assimilation algorithm-an augmented state ensemble Kalman filter- and apply it to re-analyse magnetic field changes over the period 1880-2015. Errors of representativeness appear to be responsible for an important fraction of the observed changes in the secular variation, as it is the case in the dynamo simulation. Recovered core surface motions are primarily symmetric with respect to the equator. We observe the persistence of the eccentric westward gyre over the whole studied era and vortices that partly follow isocontours of the radial magnetic field at the core surface. Our flow models provide a good fit to decadal changes in the length-of-day and predict its interannual variations over the period 1940-2005. The largest core flow acceleration patterns are found in an equatorial belt below 10 degrees in latitude and are associated with non-axisymmetric features. No systematic longitudinal drift of acceleration patterns is found, even over the past decades where satellite data are available. The acceleration of the high-latitude westward jet in the Pacific hemisphere is, during the satellite era, a factor 5 smaller than previously reported and its structure shows some evidence for equatorial asymmetry. The era of continuous satellite records provides enhanced contrast on the rapid core flow variations. The proposed assimilation algorithm offers the prospect of evaluating Earth-likeness of geodynamo simulations.
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Girona, T., Caudron, C., & Huber, C. (2019). Origin of Shallow Volcanic Tremor: The Dynamics of Gas Pockets Trapped Beneath Thin Permeable Media. Journal Of Geophysical Research-Solid Earth, 124(5), 4831–4861.
Résumé: Linking volcano-seismic signals with subsurface processes is crucial to improve the forecasting of volcanic eruptions. One of the most enigmatic signals is shallow volcanic tremor, a highly periodic ground vibration that is typically sourced beneath the crater of active volcanoes, is long lasting (from minutes to years), appears during unrest periods, and frequently precedes eruptions. In this paper, we demonstrate that shallow tremor can be produced by periodic pressure oscillations emerging spontaneously beneath permeable media (e.g., fractured magma caps). These pressure oscillations are the result of three concurrent processes: (a) the transient porous flow of gases through the permeable cap; (b) the temporary accumulation of these gases beneath the cap, forming a gas pocket; and (c) the random supply of volatiles from deeper levels. For highly permeable media (>= 10(-12) m(2); realistic for shallow volcanic edifices), the pressure in subsurface gas pockets is governed by the equation of a linear oscillator; hence, under proper conditions, periodic pressure oscillations emerge during the transfer of gases from the Earth's interior to the surface. Our model is consistent with geophysical data showing that the tremor source is localized at a fixed region and can explain the main characteristics of ground vibrations, including frequency gliding, variations of seismic amplitude prior to eruptions, and the different types of tremor observed. For thin permeable caps (<100 m), we find that different eruption mechanisms (e.g., magma ascent vs. cap sealing) leave distinct footprints in the tremor properties, thus opening new perspectives to forecast the type and style of impending eruptions.
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Giudicepietro, F., Chiodini, G., Caliro, S., De Cesare, W., Esposito, A. M., Galluzzo, D., et al. (2019). Insight Into Campi Flegrei Caldera Unrest Through Seismic Tremor Measurements at Pisciarelli Fumarolic Field. Geochemistry Geophysics Geosystems, 20(11), 5544–5555.
Résumé: Within a general volcanic unrest in the densely urbanized area of Campi Flegrei caldera (Italy) an increase in the activity of Pisciarelli hydrothermal area is occurring. The seismic amplitude of Pisciarelli fumarolic tremor is a proxy for the fluid emission rate of the entire Solfatara-Pisciarelli hydrothermal system. The long-term analysis indicates a significant increase, by a factor of 3 of the fumarolic tremor amplitude since May 2017. This increment matches with the trend of geochemical and seismic parameters observed in Campi Flegrei, therefore highlighting that Pisciarelli is a key site to monitor the volcanic unrest underway in this high-risk caldera. The analysis of data from three closely spaced seismic stations provided new clues about the source mechanism of the tremor. Analyzing the fumarolic tremor amplitude we could also identify an episode of enlargement of the emission area close to the main fumarole of Pisciarelli. We propose a monitoring system based on the fumarolic tremor analysis, which provides real-time information on the Pisciarelli hydrothermal activity and therefore on the current unrest in Campi Flegrei caldera.
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Goberna-Ferron, S., Fernandez-Martinez, A., Charlet, L., & Greneche, J. - M. (2019). Surface chemistry of silica-coated magnetic nanoparticles. Abstracts Of Papers Of The American Chemical Society, 257.
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Gombert, B., Duputel, Z., Shabani, E., Rivera, L., Jolivet, R., & Hollingsworth, J. (2019). Impulsive Source of the 2017 M-W=7.3 Ezgeleh, Iran, Earthquake. Geophysical Research Letters, 46(10), 5207–5216.
Résumé: On 12 November 2017, a M-W = 7.3 earthquake struck near the Iranian town of Ezgeleh, at the Iran-Iraq border. This event was located within the Zagros fold and thrust belt which delimits the continental collision between the Arabian and Eurasian Plates. Despite a high seismic risk, the seismogenic behavior of the complex network of active faults is not well documented in this area due to the long recurrence interval of large earthquakes. In this study, we jointly invert interferometric synthetic aperture radar and near-field strong motions to infer a kinematic slip model of the rupture. The incorporation of these near-field observations enables a fine resolution of the kinematic rupture process. It reveals an impulsive seismic source with a strong southward rupture directivity, consistent with significant damage south of the epicenter. We also show that the slip direction does not match plate convergence, implying that some of the accumulated strain must be partitioned onto other faults. Plain Language Summary Iran is a very seismically active region. However, the 2017 Ezgeleh earthquake of magnitude 7.3 occurred in a region where large earthquakes have not been documented for several centuries. Our knowledge of fault locations, geometries, and seismic behaviors is therefore limited in this region. We use near-field seismological and satellite geodetic data to retrieve the spatial and temporal distribution of slip occurring on the fault during the Ezgeleh earthquake. We show that the high slip rate and Southward directivity of the rupture may have worsened the damage south of the epicenter. We also observe that tectonic motion is partitioned between different types of faults. Although the Ezgeleh earthquake did release a significant part of that strain, other seismogenic faults in the region could represent an important hazard for the nearby population.
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Gorszczyk, A., Operto, S., Schenini, L., & Yamada, Y. (2019). Crustal-scale depth imaging via joint full-waveform inversion of ocean-bottom seismometer data and pre-stack depth migration of multichannel seismic data: a case study from the eastern Nankai Trough. Solid Earth, 10(3), 765–784.
Résumé: Imaging via pre-stack depth migration (PSDM) of reflection towed-streamer multichannel seismic (MCS) data at the scale of the whole crust is inherently difficult. This is because the depth penetration of the seismic wavefield is controlled, firstly, by the acquisition design, such as streamer length and air-gun source configuration, and secondly by the complexity of the crustal structure. Indeed, the limited length of the streamer makes the estimation of velocities from deep targets challenging due to the velocity-depth ambiguity. This problem is even more pronounced when processing 2-D seismic data due to the lack of multi-azimuthal coverage. Therefore, in order to broaden our knowledge about the deep crust using seismic methods, we present the development of specific imaging workflows that integrate different seismic data. Here we propose the combination of velocity model building using (i) first-arrival tomography (FAT) and full-waveform inversion (FWI) of wide-angle, long-offset data collected by stationary ocean-bottom seismometers (OBSs) and (ii) PSDM of short-spread towed-streamer MCS data for reflectivity imaging, with the former velocity model as a background model. We present an application of such a workflow to seismic data collected by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and the Institut Francais de Recherche pour l'Exploitation de la Mer (IFREMER) in the eastern Nankai Trough (Tokai area) during the 2000-2001 Seize France Japan (SFJ) experiment. We show that the FWI model, although derived from OBS data, provides an acceptable background velocity field for the PSDM of the MCS data. From the initial PSDM, we refine the FWI background velocity model by minimizing the residual move-outs (RMOs) picked in the pre-stack-migrated volume through slope tomography (ST), from which we generate a better-focused migrated image Such integration of different seismic datasets and leading-edge imaging techniques led to greatly improved imaging at different scales. That is, large to intermediate crustal units identified in the high-resolution FWI velocity model extensively complement the short-wavelength reflectivity inferred from the MCS data to better constrain the structural factors controlling the geodynamics of the Nankai Trough.
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Got, J. - L., Amitrano, D., Stefanou, I., Brothelande, E., & Peltier, A. (2019). Damage and Strain Localization Around a Pressurized Shallow-Level Magma Reservoir. Journal Of Geophysical Research-Solid Earth, 124(2), 1443–1458.
Résumé: Structures developing above long-term growing shallow-level magma reservoirs, such as resurgent domes, may contain information on the reservoir itself. To understand the formation of such tectonic features, we have investigated the deformation process around a shallow pressurized magma reservoir embedded in a damaging elastic volcanic edifice. Our model allows evidencing the effect of the progressive damage in producing the fault pattern associated to tectonic surface deformation. Damage is first isotropic around the cavity and constitutes a damaged zone. Then the free-surface effect appears, and an anisotropic shear strain develops from the boundary of the damaged zone; it localizes on reverse faults that propagate upward to the surface. When the surface deformation is sufficient, normal faulting appears. Finally, the complete structure shows an undeformed wedge above the damaged zone. This structure is similar to those found by analog modeling and from field geologic observations. From this model, we found a relation to estimate the reservoir radius and depth from the graben and dome widths. From limit analysis, we deduced an analytical expression of the magma reservoir pressure which provides a better understanding of the magma pressure buildup during doming. The dip of reverse faults limiting the dome can be inferred from the minimal pressure required to rupture the crust around the reservoir. Finally, the magma reservoir overpressure, the dip of the faults, the reservoir depth, and the damaged zone radius are inferred from three parameters: the ratio (R) computed from the dome and graben widths, the cohesion, and the friction angle.
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Gourlan, A. T., Douay, G., & Telouk, P. (2019). Copper isotopes as possible neoplasia biomarkers in captive wild felids. Zoo Biology, 38(4), 371–383.
Résumé: The longevity of zoo animals is increasing due to continuous improvement in husbandry and veterinary medicine. However, increasing age is correlated to a higher prevalence of neoplasia. Despite tremendous improvement in diagnoses and monitoring capacities, cancers are still a challenge for veterinarians within the global zoo community. The recent use of copper isotopes as biomarkers for neoplasia in both human and veterinary medicine is a promising and cost-effective diagnostic tool. Two hundred and twenty-nine serum samples from 10 different species of wild felids under human care were processed through mass spectrometry to determine the ratio of heavy and light copper isotopes (Cu-65/Cu-63). The results of this preliminary study exhibit an important variability between felid species, with a ratio ranging between -1.71 and 0.63. Additionally, copper isotopes seem to be a promising diagnostic tool in monitoring cancer in wild animals, as in human medicine, where the isotopic ratio decreases significantly with time in the presence of a tumor.
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Gradon, C., Moreau, L., Roux, P., & Ben-Zion, Y. (2019). Analysis of surface and seismic sources in dense array data with match field processing and Markov chain Monte Carlo sampling. Geophysical Journal International, 218(2), 1044–1056.
Résumé: We introduce a methodology based on array processing to detect and locate weak seismic events in a complex fault zone environment. The method is illustrated using data recorded by a dense array of 1108 vertical component geophones in a 600 m x 600 m area on the Clark branch of the San Jacinto Fault. Because surface and atmospheric sources affect weak ground motion, it is necessary to discriminate them from weak seismic sources at depth. Source epicentral positions and associated apparent velocities are extracted from continuous seismic waveforms using Match Field Processing (MFP). We implement MFP at specific frequencies targeting surface and subsurface sources, using for computational efficiency a forward model of acoustic source in a homogenous medium and Markov Chain Monte Carlo sampling. Surface sources such as Betsy gun shots and a moving vehicle are successfully located. Weak seismic events are also detected outside of the array, and their backazimuth angle is retrieved and found to be consistent with the fault geometry. We also show that the homogeneous acoustic model does not yield satisfying results when extracting microseismic event depth, because of the ambiguity between depth and the apparent velocity based on surface data.
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Grangeon, J., & Lesage, P. (2019). A robust, low-cost and well-calibrated infrasound sensor for volcano monitoring. Journal Of Volcanology And Geothermal Research, 387.
Résumé: Volcano acoustic signals contain valuable information on shallow magmatic and hydrothermal processes. In some cases, the detection of acoustic waves is the only clear evidence of the occurrence of volcanic explosions. Their study is thus complementary to that of seismic signals. For this reason, acoustic sensors are more and more frequently integrated in volcano monitoring systems as well as in temporary instrumental deployments. We have developed a broadband, robust and low-cost infrasound sensor designed for the detection and analysis of acoustic waves on volcanoes. It is based on a microelectromechanical differential pressure transducer (MEMS). The reference pressure is balanced with the atmospheric pressure through a pneumatic high-pass filter. Its low corner frequency, usually set to 60 mHz, can be adjusted from a few to tens of mHz. Its amplitude range is +/- 240 Pa and its sensitivity is 20 mV Pa-1, with a noise level <0.05 Pa RMS. The power consumption is 42 mW (3.5 mA with 12 V voltage). A direct output of the MEMS also provides a signal with sensitivity of about 500 μV Pa-1 and range +/- 1245 Pa. This sensor is not sensitive to mechanical vibrations. The instrumental response of each infrasound sensor is carefully measured from 1 mHz to >100 Hz using two specially designed calibration systems which deliver sinusoidal pressure variations. The mechanical elements of the sensor are produced by 3D printer and filled with epoxy resin which guarantees high robustness in the aggressive environment of most volcanoes. The sensor dimensions (26x45x80 mm) and weight (100 g) makes it very easy to handle and install. (C) 2019 Elsevier B.V. All rights reserved.
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Grasso, J. - R., Amorese, D., & Karimov, A. (2019). Anthropogenic seismicity as aftershocks for geo-resource production? Implications for M-max estimates (reservoir impoundment cases). Geophysical Journal International, 219(2), 958–967.
Résumé: Developing a model for anthropogenic seismic hazard remains an open challenge whatever the geo-resource production. We analyse the (M-max) largest reported magnitude on each site where (RTS) Reservoir Triggered Seismicity in documented (37 events, 1933-2008), for aftershocks of reservoir impoundment loading. We relate each reservoir impoundment to its magnitude-equivalent M*(reservoir) = M*(L-r). We use (Lr) the reservoir length as a proxy for a rupture length of the reservoir main shock-equivallent. This latter is derived from the empirical relationship that exists for tectonic earthquake among magnitude and rupture length. We resolve (i) M-max for RTS are bounded by M*(reservoir) at a 95 per cent confidence level; (ii) in average M-max are smaller than M*(reservoir) by 2.2 units (iii) 50 per cent of the M-max occurrence is within 2 +/- 1 yr from the reservoir impoundment. These triggering patterns support the signature of fluid driven seismicity during the slow reservoir impoundment emerges as a weaker efficiency (larger Delta M = M*(reservoir) – M-max) to trigger M-max events than from earthquake interactions.
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Guedron, S., Tolu, J., Brisset, E., Sabatier, P., Perrot, V., Bouchet, S., et al. (2019). Late Holocene volcanic and anthropogenic mercury deposition in the western Central Andes (Lake Chungara, Chile). Science Of The Total Environment, 662, 903–914.
Résumé: Volcanismis one of the major natural processes emitting mercury (Hg) to the atmosphere, representing a significant component of the global Hg budget. The importance of volcanic eruptions for local-scale Hg deposition was investigated using analyses of Hg, inorganic elemental tracers, and organic biomarkers in a sediment sequence from Lake Chungara (4520 m a.s.l.). Environmental change and Hg deposition in the immediate vicinity of the Parinacota volcano were reconstructed over the last 2700 years, encompassing the pre-anthropogenic and anthropogenic periods. Twenty eruptions delivering large amounts of Hg (1 to 457 μg Hg m(-2) yr(-1) deposited at the timescale of the event) were locally recorded. Peaks of Hg concentration recorded after most of the eruptions were attributed to a decrease in sedimentation rate together with the rapid re-oxidation of gaseous elemental Hg and deposition with fine particles and incorporation into lake primary producers. Over the study period, the contribution of volcanic emissions has been estimated as 32% of the total Hg input to the lake. Sharp depletions in primary production occurred at each eruption, likely resulting from massive volcaniclastic inputs and changes in the lake-water physico-chemistry. Excluding the volcanic deposition periods, Hg accumulation rates rose from natural background values (1.9 +/- 0.5 μg m(-2) yr(-1)) by a factor of 2.3 during the pre-colonial mining period (1400-900 yr cal. BP), and by a factor of 6 and 7.6, respectively, during the Hispanic colonial epoch (400-150 yr cal. BP) and the industrial era (similar to 140 yr cal. BP to present). Altogether, the dataset indicates that lake primary production has been the main, but not limiting, carrier for Hg to the sediment. Volcanic activity and climate change are only secondary drivers of local Hg deposition relative to the magnitude of regional and global anthropogenic emissions. (C) 2019 Elsevier B.V. All rights reserved.
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Gueguen, P., Mercerat, E. D., & Alarcon, F. (2019). Parametric Study on the Interpretation of Wave Velocity Obtained by Seismic Interferometry in Beam-Like Buildings. Bulletin Of The Seismological Society Of America, 109(5), 1829–1842.
Résumé: In this article, we propose an interpretation of the propagation velocities of the pulse wave obtained in vertical structures through seismic interferometry by deconvolution. The novelty of this article is to propose a parametric study applied to canonical finite-element models of fixed-base buildings from pure-shear to pure-bending beam-like buildings, adjusted to equivalent Timoshenko beam-like structures. For given input seismic motions, the time histories of the horizontal displacement at each floor are obtained and used to estimate the propagation velocity of the pulse wave by deconvolution. A frequency-wavenumber technique is used to highlight the dispersive characteristics of the pulse wave. The obtained velocity is compared with the theoretical dispersion curve of the Timoshenko beam-like structure and interpreted according to the nature of the structure. We propose a corrective coefficient to link the first resonance frequency of the building to the velocity obtained by deconvolution, according to the shear-to-bending ratio. Finally, we compare specific Timoshenko beam models with a number of previously published studies on the experimental interpretation of velocity in real-case buildings for which soil-structure interaction conditions are different from the fixed-base conditions of the Timoshenko beam-like structure.
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Gueguen, P., Mercerat, E. D., Singaucho, J. C., Aubert, C., Barros, J. G., Bonilla, L. F., et al. (2019). METACity-Quito: A Semi-Dense Urban Seismic Network Deployed to Analyze the Concept of Metamaterial for the Future Design of Seismic-Proof Cities. Seismological Research Letters, 90(6), 2318–2326.
Résumé: The presence of multiscale interactions means that the complex urban wavefield must be observed and analyzed in order to understand seismic ground motion in urban environments. Originally called site-city interaction, the interactions between soil and structures, structures and soil, and between structures contribute to the modification of urban seismic ground motion. This may affect the lateral variability of the ground motion observed in relation to earthquake damage, the characterization of site effects in urban areas, and also the response of civil engineering structures designed without consideration of the immediate urban environment. The METACity-Quito experiment was designed to take accurate measurements of the effects of the resonator array formed by structures in the seismic wavefield, in the manner of an urban metamaterial. Current applications in the fields of physics, acoustics and, more recently, geophysics have shown the existence of forbidden bands, that is, frequencies at which seismic energy vanishes. This concept could help to understand the heterogeneous distribution of damage in urban areas as well as to imagine the future design of seismic-proof cities.
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Guervilly, C., Cardin, P., & Schaeffer, N. (2019). Turbulent convective length scale in planetary cores. Nature, 570(7761), 368–+.
Résumé: Convection is a fundamental physical process in the fluid cores of planets. It is the primary transport mechanism for heat and chemical species and the primary energy source for planetary magnetic fields. Key properties of convection-such as the characteristic flow velocity and length scale-are poorly quantified in planetary cores owing to the strong dependence of these properties on planetary rotation, buoyancy driving and magnetic fields, all of which are difficult to model using realistic conditions. In the absence of strong magnetic fields, the convective flows of the core are expected to be in a regime of rapidly rotating turbulence(1), which remains largely unexplored. Here we use a combination of non-magnetic numerical models designed to explore this regime to show that the convective length scale becomes independent of the viscosity when realistic parameter values are approached and is entirely determined by the flow velocity and the planetary rotation. The velocity decreases very rapidly at smaller scales, so this turbulent convective length scale is a lower limit for the energy-carrying length scales in the flow. Using this approach, we can model realistically the dynamics of small non-magnetic cores such as the Moon. Although modelling the conditions of larger planetary cores remains out of reach, the fact that the turbulent convective length scale is independent of the viscosity allows a reliable extrapolation to these objects. For the Earth's core conditions, we find that the turbulent convective length scale in the absence of magnetic fields would be about 30 kilometres, which is orders of magnitude larger than the ten-metre viscous length scale. The need to resolve the numerically inaccessible viscous scale could therefore be relaxed in future more realistic geodynamo simulations, at least in weakly magnetized regions.
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Guillot, S., Agbossoumonde, Y., Bascou, J., Berger, J., Duclaux, G., Hilairet, N., et al. (2019). Transition from subduction to collision recorded in the Pan-African arc complexes (Mali to Ghana). Precambrian Research, 320, 261–280.
Résumé: The 1000 km-long suture zone of the Dahomeyide belt, exposed from Southeast Ghana to South Mali, corresponds to a narrow and lithologically diverse area with symptomatic coronitic HP granulitic massifs. Based on a review of published petrological, geochemical and geochronological data along the Dahomeyide belt we propose a global scenario for the closure of the Pharusian ocean between the West African craton (WAC) and the Benino-Nigerian shield during the end of the Neoproterozoic. The onset of a long-lived oceanic subduction by 800-780 Ma is recorded by early magmatism in the Amalaoulaou intra-oceanic arc in Mali, contemporary to the Gourma and Adrar des Iforas to the North, and in Brazil to the South. The first occurrence of tonalitic plutons dated at 720 Ma, and the development of a forearc system around 650 Ma mark the onset of active margin subduction beneath the Benino-Nigerain shield and its northward prolongation in Mali. Oceanic subduction beneath the active margin ended between 640 and 630 Ma with the onset of subduction of the WAC continental margin while subduction related magmatism continues till ca. 600 Ma on the upper plate. During a short period between 620 and 610 Ma, the forearc system and the tip of the active continental margin were buried synchronously. The positive Bouguer anomaly observed to the East of the suture zone, in Benin, and not beneath the suture zone itself supports the occurrence of a massive mafic body at the base of the crust that could correspond to the underplated buried forearc. Ultimately, the exhumation and partial amphibolitization of the suture zone and a shift from a calc-alkaline magmatism to anatectic magmatism along with the onset of strike-slip faulting in the upper plate marks the transition from continental subduction to continental collision between 610 and 580 Ma. This work highlights the importance of the Pharusian suture zone s.l. To our knowledge, it represents a unique example in the world in where the forearc system is buried and partly exhumed at the transition from subduction to collision.
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Guillot, S., Goussin, F., Airaghi, L., Replumaz, A., de Sigoyer, J., & Cordier, C. (2019). How and When Did the Tibetan Plateau Grow? Russian Geology And Geophysics, 60(9), 957–977.
Résumé: Due to its size and high altitude, the growth of the Tibetan Plateau remains an enigma. Based on a synthesis of anterior collisions, paleoaltimetric data, geochemistry of ultrapotassic lava and their rare mantle enclaves, combined with a reinterpretation of tomographic data, we suppose that Tibet's growth took take place in two main stages. Initially, the accretion of Gondwana terranes to the margin of South Asia, especially during the Early Triassic-Cretaceous period, resulted in the first episode of plateau growth, which affected an area of about 2/3 of the current plateau. We suppose that during the Late Cretaceous, the Tibetan crust reached a thickness of about 50-55 km, which is equivalent to an altitude of about 2500 to 3000 m, with local landforms that could have exceeded 4000 m. Another important consequence of these successive accretions was a strong metasomatism and a softening of the upper part of the Tibetan cover. The P wave low-velocity anomaly currently observed under the central part of Tibet would correspond not to a temperature anomaly but to a composition anomaly. From 50 Ma onwards, the convergence between India and Asia, estimated at about 1000 km on the Tibetan side, led to a shortening of the plateau by about 40%. We suppose that this additional shortening, which has led to the current thickness of the Earth's crust of about 70 km and an average altitude of 4800 m, has been compensated by the reactivation of the continental slabs along the previous sutures and by the homogeneous shortening of the crust.
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Hajji, S., Montes-Hernandez, G., Sarret, G., Tordo, A., Morin, G., Ona-Nguema, G., et al. (2019). Arsenite and chromate sequestration onto ferrihydrite, siderite and goethite nanostructured minerals: Isotherms from flow-through reactor experiments and XAS measurements. Journal Of Hazardous Materials, 362, 358–367.
Résumé: Sorption isotherms remain a major tool to describe and predict the mobility of pollutants in natural and anthropogenic environments, but they are typically determined by independent batch experiments. In the present study, the sequestration of As(III), Cr(VI) and competitive As(III)-Cr(VI) on/in 6L-ferrihydrite, siderite and goethite nanostructured minerals was reinvestigated using stirred flow-through reactor experiments. Herein, sorption isotherms were particularly determined from breakthrough curves for inert and reactive tracers monitored simultaneously in a single percolation experiment. In complement, X-ray absorption spectroscopy (XAS) was used to identify As sorption sites on 6L-ferrihydrite and goethite. As expected, the minerals have high potential to remove As and Cr from water (siderite = ferrihydrite (about 60 mg/g) > goethite (20 mg/g)). As and Cr sorption isotherms were modelled with a Langmuir model, and with a sigmoidal Hill model in the case of the competitive sorption. XAS measurements have revealed that As(III) was partially oxidized (up to 22%) in the competitive system with chromate oxyanion Cr(VI). As(III) sorbed on ferrihydrite and goethite adopted edge sharing and corner sharing complex geometries. Nowadays, a new class of adsorbing phases is being developed for wastewater treatment, including engineered nanostructured materials and nanocomposites. The use of flow through reactor experiments as a high throughput method, combined with XAS, should be considered as efficient screening methods to test their sorbing properties on various contaminants.
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Hawkins, R., Bodin, T., Sambridge, M., Choblet, G., & Husson, L. (2019). Trans-Dimensional Surface Reconstruction With Different Classes of Parameterization. Geochemistry Geophysics Geosystems, 20(1), 505–529.
Résumé: The use of Bayesian trans-dimensional sampling in 2-D and 3-D imaging problems has recently become widespread in geophysical inversion. Its benefits include its spatial adaptability to the level of information present in the data and the ability to produce uncertainty estimates. The most used parameterization in Bayesian trans-dimensional inversions is Voronoi cells. Here we introduce a general software, TransTessellate2D, that allows 2-D trans-dimensional inference with Voronoi cells and two alternative underlying parameterizations, Delaunay triangulation with linear interpolation and Clough-Tocher interpolation, which utilize the same algorithm but result in either C-0 or C-1 continuity. We demonstrate that these alternatives are better suited to the recovery of smooth models, and show that the posterior probability solution is less susceptible to multimodalities which can complicate the interpretation of model parameter uncertainties.
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Hawkins, R., Husson, L., Choblet, G., Bodin, T., & Pfeffer, J. (2019). Virtual Tide Gauges for Predicting Relative Sea Level Rise. Journal Of Geophysical Research-Solid Earth, .
Résumé: We present a Bayesian method to map contemporary rates of relative sea level change using a joint inversion of vertical trends from tide gauges, GPS time series, and satellite radar altimetry measurements. Tide gauge measurements constrain rates of relative sea level change on decadal to secular time scales at a few hundred sites sparsely distributed along coastlines. Predicting the rates of relative sea level change from historical tide gauge measurements is difficult due to the paucity and uneven distribution of sites with high quality records. Since the late twentieth century, deployments of GPS stations have enabled accurate determination of the rates of vertical land motion. A series of satellite radar altimetry missions provide continuous and global monitoring of geocentric sea level changes since the launch of TOPEX/Poseidon in 1992. By combining these three observations types into a single Bayesian inversion, we construct continuous maps of rates of relative sea level change, geocentric sea level change, and vertical land motion assuming linear trends, with robust estimates of uncertainties at regional scales. Cross-validation tests show that reliable predictions of relative sea level changes are still provided where only GPS and satellite altimetry data are used, suggesting this method is viable for studying potential sea level risk for communities where historical tide gauge data are not available. Our results provide spatially and temporally consistent estimates of the various contributions to relative sea level changes.
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He, W., Brossier, R., Metivier, L., & Plessix, R. - E. (2019). Land seismic multiparameter full waveform inversion in elastic VTI media by simultaneously interpreting body waves and surface waves with an optimal transport based objective function. Geophysical Journal International, 219(3), 1970–1988.
Résumé: Land seismic multiparameter full waveform inversion in anisotropic media is challenging because of high medium contrasts and surface waves. With a data-residual least-squares objective function, the surface wave energy usually masks the body waves and the gradient of the objective function exhibits high values in the very shallow depths preventing from recovering the deeper part of the earth model parameters. The optimal transport objective function, coupled with a Gaussian time-windowing strategy, allows to overcome this issue by more focusing on phase shifts and by balancing the contributions of the different events in the adjoint-source and the gradients. We first illustrate the advantages of the optimal transport function with respect to the least-squares one, with two realistic examples. We then discuss a vertical transverse isotropic (VTI) example starting from a quasi 1-D isotropic initial model. Despite some cycle-skipping issues in the initial model, the inversion based on the windowed optimal transport approach converges. Both the near-surface complexities and the variations at depth are recovered.
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Hedjazian, N., Bodin, T., & Metivier, L. (2019). An optimal transport approach to linearized inversion of receiver functions. Geophysical Journal International, 216(1), 130–147.
Résumé: Receiver function analysis is widely used to make quantitative inferences about the structure below a seismic station. As these observables are mainly sensitive to traveltimes of phases converted and reflected at seismic discontinuities, the resulting inverse problem is highly non-linear, the solution non-unique, and there are strong trade-offs between the depth of discontinuities and absolute velocities. To overcome this difficulty, we propose to measure the misfit between the predicted and observed data with an optimal transport distance instead of the conventional least-squares distance, a strategy that has shown its assets in the context of full waveform inversion. This approach views a seismogram as a distribution of 'mass'. The optimal transport distance between two waveforms is the minimal cost of transporting one waveform onto the other. We test the optimal transport approach on the inversion of a radial P-wave receiver function. We also show how it can be applied to measure the cross-convolution distance between the radial and vertical components, thus avoiding the need for deconvolution associated with the calculation of the receiver function. The resulting misfit function is minimized with a local optimization algorithm to constrain the receiver-side structure. The benefits of this methodology are studied in simple synthetic tests and with real data. In particular, we show that with its increased sensibility to time-shifts, the optimal transport distance reduces the number of local minima in the misfit function, which, in the case of a linearized inversion, significantly reduces the dependency to the starting model and results in a better convergence towards the solution model. A joint inversion of the P-wave receiver function and surface wave dispersion curves is performed at the Hyderabad station in India.
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Hellel, M., Oubaiche, E. H., Chatelain, J. - L., Bensalem, R., Amarni, N., Boukhrouf, M., et al. (2019). Efficiency of ambient vibration HVSR investigations in soil engineering studies: backfill study in the Algiers (Algeria) harbor container terminal. Bulletin Of Engineering Geology And The Environment, 78(7), 4989–5000.
Résumé: This paper deals with the contribution of the ambient vibration horizontal-to-vertical spectral ratio (HVSR) method in soil engineering studies, particularly in backfill compactness assessment. The study is based on 60 ambient vibration recordings performed in 2015 at the container terminal of Algiers harbor, subjected a year before to a geotechnical study based on 23 boreholes and 13 cone penetration tests (CPT) for backfill improvement. To highlight the contribution of the HVSR method, the results of the geotechnical and HVSR studies are first analyzed separately and then in combination. The HVSR method provides a compactness zonation map based on peak amplitude variation. Both methods define the same pattern: a southern section where the backfill is more compact, and a northern section where the backfill is less compact. This shows that the HVSR peak amplitudes are sensitive to compactness variations, which may be sufficient for qualitative zonation. In addition, with the combination of the two methods, rough estimations of shear-wave velocity and thickness of the backfill can be retrieved. This study shows that the HVSR method can be a very useful investigative tool in soil engineering studies. When the HVSR method is deployed before any conventional technique, a geotechnical investigation campaign can be significantly optimized. Moreover the combined interpretation brings complementary quantitative soil information.
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Hentschel, F., Trepmann, C. A., & Janots, E. (2019). Deformation of feldspar at greenschist facies conditions – the record of mylonitic pegmatites from the Pfunderer Mountains, Eastern Alps. Solid Earth, 10(1), 95–116.
Résumé: Deformation microstructures of albitic plagioclase and K-feldspar were investigated in mylonitic pegmatites from the Austroalpine basement south of the western Tauern Window by polarized light microscopy, electron microscopy and electron backscatter diffraction to evaluate feldspar deformation mechanisms at greenschist facies conditions. The main mylonitic characteristics are alternating almost monophase quartz and albite layers, surrounding porphyroclasts of deformed feldspar and tourmaline. The dominant deformation microstructures of K-feldspar porphyroclasts are intragranular fractures at a high angle to the stretching lineation. The fractures are healed or sealed by polyphase aggregates of albite, K-feldspar, quartz and mica, which also occur along intragranular fractures of tourmaline and strain shadows around other porphyroclasts. These polyphase aggregates indicate dissolution-precipitation creep. K-feldspar porphyroclasts are partly replaced by albite characterized by a cuspate interface. This replacement is interpreted to take place by interface-coupled dissolution-precipitation driven by a solubility difference between K-feldspar and albite. Albite porphyroclasts are replaced at boundaries parallel to the foliation by fine-grained monophase albite aggregates of small strain-free new grains mixed with deformed fragments. Dislocation glide is indicated by bent and twinned albite porphyroclasts with internal misorientation. An indication of effective dislocation climb with dynamic recovery, for example, by the presence of subgrains, is systematically missing. We interpret the grain size reduction of albite to be the result of coupled dislocation glide and fracturing (low temperature plasticity). Subsequent growth is by a combination of strain-induced grain boundary migration and formation of growth rims, resulting in an aspect ratio of albite with the long axis within the foliation. This strain-induced replacement by nucleation (associated dislocation glide and microfracturing) and subsequent growth is suggested to result in the observed monophase albite layers, probably together with granular flow. The associated quartz layers show characteristics of dislocation creep by the presence of subgrains, undulatory extinction and sutured grain boundaries. We identified two endmember matrix microstructures: (i) alternating layers of a few hundred micrometres' width, with isometric, fine-grained feldspar (on average 15 μm in diameter) and coarse-grained quartz (a few hundred micrometres in diameter), representing lower strain compared to (ii) alternating thin layers of some tens of micrometres' width composed of fine-grained quartz (<20 μm in diameter) and coarse elongated albite grains (long axis of a few tens of micrometres) defining the foliation, respectively. Our observations indicate that grain size reduction by strain-induced replacement of albite (associated dislocation glide and microfracturing) followed by growth and granular flow simultaneous with dislocation creep of quartz are playing the dominating role in formation of the mylonitic microstructure.
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Hernandez-Laguna, A., Perez del Valle, C., Hernandez-Haro, N., Ortega-Castro, J., Munoz-Santiburcio, D., Vidal, I., et al. (2019). Compressibility of 2M(1) muscovite-phlogopite series minerals. Journal Of Molecular Modeling, 25(11).
Résumé: Muscovite (Ms) and phlogopite (Phl) belong to the 2:1 dioctahedral and trioctahedral layer silicates, respectively, and are the end members of Ms-Phl series minerals. This series was studied in the 2M(1) polytype and modeled by the substitution of three Mg2+ cations in the Phl octahedral sites by two Al3+ and one vacancy, increasing the substitution up to reach the Ms. The series was computationally examined at DFT level as a function of pressure to 9 GPa. Cell parameters as a function of pressure and composition, and bulk moduli as a function of the composition agrees with the existing experimental results. The mixing Gibbs free energy was calculated as a function of composition. From these data, approximated solvi were calculated at increasing pressure. A gap of solubility is found, decreasing the gap of solubility at high pressure.
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Hillers, G., Campillo, M., Brenguier, F., Moreau, L., Agnew, D. C., & Ben-Zion, Y. (2019). Seismic Velocity Change Patterns Along the San Jacinto Fault Zone Following the 2010 M7.2 El Mayor-Cucapah and M5.4 Collins Valley Earthquakes. Journal Of Geophysical Research-Solid Earth, 124(7), 7171–7192.
Résumé: We study temporal changes of seismic velocity (dv/v) in the crust around the central section of the San Jacinto fault zone (SJFZ), Southern California. Focusing on a 200-day-long period around April 2010, our analysis resolves two tens-of-days-long successive episodes of reduced velocities that are compatible with signals from the long base strainmeter at the Pinon Flat Observatory. The imaged dv/v sequences are proxies for evolving material properties in the crust surrounding the SJFZ. The temporal and the spatial coincidence of the observed dv/v patterns with the occurrence of two proposed creep episodes suggest that the relative velocity changes reflect the response to deep creep events that follow the M7.2 El Mayor-Cucapah earthquake and the M5.4 Collins Valley earthquake that occurred 94days later on the San Jacinto fault. The main slip during the creep events was proposed to occur below 10-km depth. Wavefield properties suggest sensitivity to medium changes above this source zone, in the top 10km. The distribution of the obtained dv/v reductions shows a strong difference between large values to the west of the SJFZ and significantly smaller amplitudes to the east. The similarity to the seasonal velocity change pattern implies that the results are likely controlled by the contrast of mechanical properties across the fault, such as fault-perpendicular shear modulus variations. Our analysis extends the spectrum of methods that can be used to study earthquake interaction, fault zone rheology and dynamics, triggering, and the interplay between creep episodes and earthquakes. Plain Language Summary Motion along geologic fault zones not only occurs during small and large potentially devastating earthquakes. Some faults creep aseismically, which means the slip motion is too slow to generate earthquake waves. To develop a more complete understanding of fault behavior, it is important to detect and locate such creep transients. A particularly interesting problem is how earthquakes and episodic creep events, which tend to occur in a zone below the earthquakes, interact with each other. Creep events are usually detected using satellite-based methods. In this study we applied the most modern ambient seismic wavefield analysis techniques to first detect and locate changes in the rock properties around a continental strike slip fault, the San Jacinto fault, Southern California, that are caused by two successive deep creep events along that fault. These results are supported by data from a colocated deformation meter that picked up signals from the same creep events that are thought to be triggered, initiated by the two earthquakes indicated in the title. The observed deformation patterns-they are not uniform along and across the fault-and their temporal evolution can help us better understand the processes that happen on and off faults in earthquake-prone regions.
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Hoevelmann, J., Stawski, T. M., Besselink, R., Freeman, H. M., Dietmann, K. M., Mayanna, S., et al. (2019). A template-free and low temperature method for the synthesis of mesoporous magnesium phosphate with uniform pore structure and high surface area. Nanoscale, 11(14), 6939–6951.
Résumé: Mesoporous phosphates are a group of nanostructured materials with promising applications, particularly in biomedicine and catalysis. However, their controlled synthesis via conventional template-based routes presents a number of challenges and limitations. Here, we show how to synthesize a mesoporous magnesium phosphate with a high surface area and a well-defined pore structure through thermal decomposition of a crystalline struvite (MgNH4PO4 center dot 6H(2)O) precursor. in a first step, struvite crystals with various morphologies and sizes, ranging from a few micrometers to several millimeters, had been synthesized from supersaturated aqueous solutions (saturation index (SI) between 0.5 and 4) at ambient pressure and temperature conditions. Afterwards, the crystals were thermally treated at 70 – 250 degrees C leading to the release of structurally bound water (H2O) and ammonia (NH3). By combining thermogravimetric analyses (TGA), scanning and transmission electron microscopy (SEM, TEM), N-2 sorption analyses and small- and wide-angle X-ray scattering (SAXS/WAXS) we show that this decomposition process results in a pseudomorphic transformation of the original struvite into an amorphous Mg-phosphate. Of particular importance is the fact that the final material is characterized by a very uniform mesoporous structure with 2-5 nm wide pore channels, a large specific surface area of up to 300 m(2) g(-1) and a total pore volume of up to 0.28 cm(3) g(-1). Our struvite decomposition method is well controllable and reproducible and can be easily extended to the synthesis of other mesoporous phosphates. in addition, the so produced mesoporous material is a prime candidate for use in biomedical applications considering that magnesium phosphate is a widely used, non-toxic substance that has already shown excellent biocompatibility and biodegradability.
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Hoevelmann, J., Stawski, T. M., Freeman, H. M., Besselink, R., Mayanna, S., Perez, J. P. H., et al. (2019). Struvite Crystallisation and the Effect of Co2+ Ions. Minerals, 9(9).
Résumé: The controlled crystallisation of struvite (MgNH4PO4 center dot 6H(2)O) is a viable means for the recovery and recycling of phosphorus (P) from municipal and industrial wastewaters. However, an efficient implementation of this recovery method in water treatment systems requires a fundamental understanding of struvite crystallisation mechanisms, including the behavior and effect of metal contaminants during struvite precipitation. Here, we studied the crystallisation pathways of struvite from aqueous solutions using a combination of ex situ and in situ time-resolved synthesis and characterization techniques, including synchrotron-based small- and wide-angle X-ray scattering (SAXS/WAXS) and cryogenic transmission electron microscopy (cryo-TEM). Struvite syntheses were performed both in the pure Mg-NH4-PO4 system as well as in the presence of cobalt (Co), which, among other metals, is typically present in waste streams targeted for P-recovery. Our results show that in the pure system and at Co concentrations < 0.5 mM, struvite crystals nucleate and grow directly from solution, much in accordance with the classical notion of crystal formation. In contrast, at Co concentrations >= 1 mM, crystallisation was preceded by the transient formation of an amorphous nanoparticulate phosphate phase. Depending on the aqueous Co/P ratio, this amorphous precursor was found to transform into either (i) Co-bearing struvite (at Co/P < 0.3) or (ii) cobalt phosphate octahydrate (at Co/P > 0.3). These amorphous-to-crystalline transformations were accompanied by a marked colour change from blue to pink, indicating a change in Co2+ coordination in the formed solid from tetrahedral to octahedral. Our findings have implications for the recovery of nutrients and metals during struvite crystallisation and contribute to the ongoing general discussion about the mechanisms of crystal formation.
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Huang, L., Baud, P., Cordonnier, B., Renard, F., Liu, L., & Wong, T. -fong. (2019). Synchrotron X-ray imaging in 4D: Multiscale failure and compaction localization in triaxially compressed porous limestone. Earth And Planetary Science Letters, 528.
Résumé: Understanding failure and strain localization in porous rock is of fundamental importance in rock physics. Confined compaction experiments on porous rocks have revealed a broad spectrum of failure modes. Techniques such as acoustic emission location and velocity tomography provide kinematic information on the partitioning of damage and localization of strain. Complementary observations on deformed samples using microscopy and microcomputed tomography (CT) can also be used to image microscale damage and its distribution. Only by synthesizing such measurements on multiple scales could one infer the multiscale dynamics of compaction localization and similar rock failure phenomena. Located at the European Synchrotron Radiation Facility, the HADES rig allows direct in situ 3D imaging of the whole rock sample as it is triaxially compressed. The μCT data provide an integrated perspective of the spatiotemporal evolution of damage and strain localization on scales ranging from grain to continuum. We conducted an experiment on Leitha limestone (initial porosity of similar to 22%) at a confining pressure of 20 MPa. With increasing differential stress, the sample strain hardened and two distinct yield points were identified in the stress-strain curve. The spatiotemporal evolution of local porosity and damage were analyzed at multiple scales. At a mesoscopic scale of 10 voxels (65 pm), the time-lapse μCT images reveal the strain partitioning associated with the first yield point and development of strain localization with the second. The latter development of five discrete compaction bands is the first unambiguous observation of such a bifurcation phenomenon in a porous carbonate rock, with geometric attributes comparable to compactions bands observed in porous sandstones. The μCT data on the voxel-scale elucidate in refined details the nucleation and propagation of discrete compaction bands under quasi static loading, as well as the micromechanical processes, which in the past could only be inferred from a synthesis of kinematic observations of acoustic emissions activity and post-mortem observations of microstructure and damage. (C) 2019 Elsevier B.V. All rights reserved.
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Huder, L., Gillet, N., & Thollard, F. (2019). pygeodyn 1.1.0: a Python package for geomagnetic data assimilation. Geoscientific Model Development, 12(8), 3795–3803.
Résumé: The pygeodyn package is a sequential geomagnetic data assimilation tool written in Python. It gives access to the core surface dynamics, controlled by geomagnetic observations, by means of a stochastic model anchored to geo-dynamo simulation statistics. The pygeodyn package aims to give access to a user-friendly and flexible data assimilation algorithm. It is designed to be tunable by the community by different means, including the following: the possibility to use embedded data and priors or to supply custom ones; tunable parameters through configuration files; and adapted documentation for several user profiles. In addition, output files are directly supported by the package webgeodyn that provides a set of visualization tools to explore the results of computations.
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Husson, L., Boucher, F. C., Sarr, A. - C., Sepulchre, P., & Cahyarini, S. Y. (2019). Evidence of Sundaland's subsidence requires revisiting its biogeography. Journal Of Biogeography, .
Résumé: It is widely accepted that sea level changes intermittently inundated the Sunda Shelf throughout the Pleistocene, separating Java, Sumatra and Borneo from the Malay Peninsula and from each other. On this basis, the dynamics of the biodiversity hotspot of Sundaland is consistently regarded as solely contingent on glacial sea level oscillations, with interglacial highstands creating intermittent dispersal barriers between disjunct landmasses. However, recent findings on the geomorphology of the currently submerged Sunda shelf suggest that it subsided during the Pleistocene and that, over the Late Pliocene and Quaternary, is was never submerged prior to Marine Isotope Stage 11 (MIS 11, 400 ka). This would have enabled the dispersal of terrestrial organisms regardless of sea level variations until 400 ka and hampered movements thereafter, at least during interglacial periods. Existing phylogeographic data for terrestrial organisms conform to this scenario: available divergence time estimates reveal an 8- to 9-fold increase in the rate of vicariance between landmasses of Sundaland after 400 ka, corresponding to the onset of episodic flooding of the Sunda shelf. These results highlight how reconsidering the paleogeographic setting of Sundaland challenges understanding the mechanisms generating Southeast Asian biodiversity.
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Husson, L., Guillaume, B., & Martinod, J. (2019). Multichronometer thermochronologic modeling of migrating spreading ridge subduction in southern Patagonia. Geology, 47(10), E483.
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Incel, S., Labrousse, L., Hilairet, N., John, T., Gasc, J., Shi, F., et al. (2019). Reaction-induced embrittlement of the lower continental crust. Geology, 47(3), 235–238.
Résumé: Field observations and geophysical data reveal a causal link between brittle seismic failure and eclogitization of the lower continental crust. We present results from experimental deformation of plagioclase-rich samples at eclogite-facies conditions and quantify the link between rock rheology and the kinetics of the eclogitization reactions. The deformation was ductile both in the absence of reaction and when the progress of eclogitization was fast compared to the imposed strain rate. However, when the reaction rate was relatively slow, the breakdown of plagioclase into nanocrystalline reaction products triggered embrittlement, highlighted by a high acoustic emission activity. Fluid-induced plagioclase breakdown under eclogite-facies conditions is an exothermic reaction accompanied by a negative change in solid volume. This is similar to other mineral transformations that are known to trigger transformational faulting. We demonstrate that mineral reactions lead to brittle deformation in situations where reaction rates are slow compared to the deformation rate.
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Incel, S., Schubnel, A., Renner, J., John, T., Labrousse, L., Hilairet, N., et al. (2019). Experimental evidence for wall-rock pulverization during dynamic rupture at ultra-high pressure conditions. Earth And Planetary Science Letters, 528.
Résumé: The mechanisms triggering intermediate and deep earthquakes have puzzled geologists for several decades. There is still no consensus concerning whether such earthquakes are triggered by brittle or ductile mechanisms. We performed a deformation experiment on a synthetic lawsonite-bearing blueschist at a confining pressure of 3 GPa and temperatures from 583 to 1,073 K. After deformation, the recovered sample reveals conjugated shear fractures. Garnet crystals are dissected and displaced along these narrow faults and reveal micro- and nanostructures that resemble natural pulverization structures as well as partial amorphization. Formation of such structures at low confining pressures is known to require high tensile stresses and strain rates and is explained by the propagation of a dynamic shear rupture. The absence of shearing in the pulverized wall rock is taken as evidence that these structures pre-date the subsequent heat-producing frictional slip. In analogy to observations at low pressure we infer that the garnet structures in our experiment result from rapid propagation of a shear fracture even at the high pressure exerted on the sample and thus suggest that brittle deformation is possible at lower crustal to upper mantle depths. (C) 2019 Elsevier B.V. All rights reserved.
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Jaboyedoff, M., Del Gaudio, V., Derron, M. - H., Grandjean, G., & Jongmans, D. (2019). Characterizing and monitoring landslide processes using remote sensing and geophysics Preface. Engineering Geology, 259.
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Jaillard, E., Al Yacoubi, L., Reboulet, S., Robert, E., Masrour, M., Bouchaou, L., et al. (2019). Late Barremian eustacy and tectonism in the western High Atlas (Essaouira-Agadir Basin), Morocco. Cretaceous Research, 93, 225–244.
Résumé: The Barremian-Aptian interval is considered a turning point in the extensional evolution of the passive Atlantic margin of Morocco. The biostratigraphy and sedimentology study of the coarse-grained clastic deposits of the Essaouira-Agadir Basin (Bouzergoun Fm) indicates that they are entirely late Barremian (Sartousiana p.p. to Sarasini p.p. Zones) and suggests that most of them were deposited in a shallow marine environment, locally impacted by substantial fluvial influences. Facies evolution and the identification of discontinuity surfaces subdivide the unit into seven depositional sequences, two of which are marked by coarse-grained deposits and numerous indications of synsedimentary instability, and are interpreted as tectonically enhanced. These late Barremian tectonic events are interpreted as related to the abrupt uplift of the West Moroccan Arch, a long-lived, NNE-trending positive structure, located east of the Essaouira-Agadir Basin. (C) 2018 Elsevier Ltd. All rights reserved.
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Jaillard, E., Kassab, W. H., Giraud, F., Robert, E., Masrour, M., Bouchaou, L., et al. (2019). Aptian-early Albian sedimentation in the Essaouira-Agadir basin, Western Morocco. Cretaceous Research, 102, 59–80.
Résumé: Aptian to early Albian times were marked by various geodynamic and paleoenvironmental events such as large igneous province volcanism, perturbations of climate and the carbon cycle, and sea-level changes. The Essaouira-Agadir basin (EAB), located on the Atlantic passive margin of Morocco, offers good and fossiliferous exposures of the Aptian-Albian sedimentary series. A detailed analysis of this succession made it possible to establish a biostratigraphic framework. The identification of discontinuities allowed to define eight depositional sequences. As most of them are correlatable with depositional sequences of other Tethyan areas, they suggest that eustacy was the main parameter controlling sedimentation. The analysis of sedimentary fades and nannofossil assemblages provides information on paleoenvironmental changes. Sedimentation in the EAB evolved from a very low energy, carbonate ramp in the early Aptian to a low energy, slightly deeper, mixed carbonate-clastic ramp in the early Albian. This change occurred along with an increase of clastic input, a change from oligotrophic to mesotrophic faunal assemblages, and a decrease of sea-surface temperatures. The occurrence of current sedimentary features, sporadic dysaerobic deposits and local phosphatic and glauconitic crusts suggests that upwelling currents were significant during this period. Paleogeographic and isopach maps support a transgressive trend in the late Aptian and early Albian, and unravel subsidence anomalies suggesting mild halokinetic movements during Aptian-early Albian times. (C) 2019 Elsevier Ltd. All rights reserved.
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Jamtveit, B., Petley-Ragan, A., Incel, S., Dunkel, K. G., Aupart, C., Austrheim, H., et al. (2019). The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust. Journal Of Geophysical Research-Solid Earth, 124(8), 7725–7755.
Résumé: Rock rheology and density have first-order effects on the lithosphere's response to plate tectonic forces at plate boundaries. Changes in these rock properties are controlled by metamorphic transformation processes that are critically dependent on the presence of fluids. At the onset of a continental collision, the lower crust is in most cases dry and strong. However, if exposed to internally produced or externally supplied fluids, the thickened crust will react and be converted into a mechanically weaker lithology by fluid-driven metamorphic reactions. Fluid introduction is often associated with deep crustal earthquakes. Microstructural evidence, suggest that in strong highly stressed rocks, seismic slip may be initiated by brittle deformation and that wall-rock damage caused by dynamic ruptures plays a very important role in allowing fluids to enter into contact with dry and highly reactive lower crustal rocks. The resulting metamorphism produces weaker rocks which subsequently deform by viscous creep. Volumes of weak rocks contained in a highly stressed environment of strong rocks may experience significant excursions toward higher pressure without any associated burial. Slow and highly localized creep processes in a velocity strengthening regime may produce mylonitic shear zones along faults initially characterized by earthquake-generated frictional melting and wall rock damage. However, stress pulses from earthquakes in the shallower brittle regime may kick start new episodes of seismic slip at velocity weakening conditions. These processes indicate that the evolution of the lower crust during continental collisions is controlled by the transient interplay between brittle deformation, fluid-rock interactions, and creep flow.
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Janots, E., Grand'Homme, A., Bernet, M., Guillaume, D., Gnos, E., Boiron, M. - C., et al. (2019). Geochronological and thermometric evidence of unusually hot fluids in an Alpine fissure of Lauziere granite (Belledonne, Western Alps). Solid Earth, 10(1), 211–223.
Résumé: A multi-method investigation into Lauziere granite, located in the external Belledonne massif of the French Alps, reveals unusually hot hydrothermal conditions in vertical open fractures (Alpine-type clefts). The host-rock granite shows sub-vertical mylonitic microstructures and partial retrogression at temperatures of <400 degrees C during Alpine tectonometamorphism. Novel zircon fission-track (ZFT) data in the granite give ages at 16.3 +/- 1.9 and 14.3 +/- 1.6 Ma, confirming that Alpine metamorphism was high enough to reset the pre-Alpine cooling ages and that the Lauziere granite had already cooled below 240-280 degrees C and was exhumed to < 10 km at that time. Novel microthermometric data and chemical compositions of fluid inclusions obtained on millimetric monazite and on quartz crystals from the same cleft indicate early precipitation of monazite from a hot fluid at T > 410 degrees C, followed by a main stage of quartz growth at 300-320 degrees C and 1.5-2.2 kbar. Previous Th-Pb dating of cleft monazite at 12.4 +/- 0.1 Ma clearly indicates that this hot fluid infiltration took place significantly later than the peak of the Alpine metamorphism. Advective heating due to the hot fluid flow caused resetting of fission tracks in zircon in the cleft hanging wall, with a ZFT age at 10.3 +/- 1.0 Ma. The results attest to the highly dynamic fluid pathways, allowing the circulation of deep mid-crustal fluids, 150-250 degrees C hotter than the host rock, which affect the thermal regime only at the wall rock of the Alpine-type cleft. Such advective heating may impact the ZFT data and represent a pitfall for exhumation rate reconstructions in areas affected by hydrothermal fluid flow.
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Jara, J., Sanchez-Reyes, H., Socquet, A., Cotton, F., Virieux, J., Maksymowicz, A., et al. (2019). Kinematic study of Iquique 2014 M-w 8.1 earthquake: Understanding the segmentation of the seismogenic zone (vol 503, pg 131, 2018). Earth And Planetary Science Letters, 506, 347.
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Jin, Y., Misra, S., Homan, D., Rasmus, J., & Revil, A. (2019). Mechanistic model of multi-frequency complex conductivity of porous media containing water-wet nonconductive and conductive particles at various water saturations. Advances In Water Resources, 130, 244–257.
Résumé: Electrically conducive particles, such as pyrites, and surface-charge-bearing nonconductive particles, such as clays, are commonly present in water-bearing subsurface formations. Under an external electric field generated by electromagnetic measurement tool, these particles give rise to interfacial polarization (IFP) effects, which causes frequency dispersion of effective conductivity and effective permittivity of the mixture containing such particles. The neglect of IFP effects can lead to inaccurate estimation of petrophysical properties of formations, especially in clay- and pyrite- rich formations. In this paper, we developed a mechanistic model that couples surface-conductance-assisted interfacial polarization (SCAIP) model with perfectly polarized interfacial polarization (PPIP) model to estimate effective conductivity and effective permittivity of homogeneous formations containing both nonconductive and conducive particles at various fluids saturations. The model is developed based on the Poisson-Nernst-Planck (PNP) equations for a dilute solution in a weak electrical field regime to calculate the dipolarizability of the representative volume comprising a single isolated spherical particle in an electrolyte host. Then the effective medium theory is used to determine effective complex conductivity of the whole mixture. The result shows that the conducive particles dominate the frequency dispersion of complex conductivity due to IFP effects compared to nonconductive particles.
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Jouanne, F., Gajurel, A., Mugnier, J. - L., Bollinger, L., Adhikari, L. B., Koirala, B., et al. (2019). Postseismic deformation following the April 25, 2015 Gorkha earthquake (Nepal): Afterslip versus viscous relaxation. Journal Of Asian Earth Sciences, 176, 105–119.
Résumé: The postseismic deformation consecutive to the April 25, 2015 Gorkha earthquake (Mw 7.9) is estimated in this paper based on a cGNSS network installed prior to the earthquake and supplemented by 6 cGNSS stations installed after the main shock. Postseismic displacement are obtained from daily time series corrected for interseismic deformation and seasonal variations. The maximum postseismic displacement is found north of the rupture area, where locally it reached 100 mm between the date of the earthquake and late 2016. The post-seismic deformation affects the northern part of the rupture area but not the southern part, along the southern part of the Main Himalayan Thrust (MHT). Three hypotheses for the mechanisms controlling postseismic deformation are tested through numerical simulations of the postseismic time series: (i) viscous relaxation, (ii) afterslip, or (iii) a combination of these two mechanisms. We can exclude postseismic deformation controlled by viscous relaxation of a thick deformation zone along the northern and lower flat of the MHT. However, it is impossible to discriminate between postseismic deformation controlled by either afterslip along the MHT (northern part of the rupture zone, crustal ramp, and lower flat of the MHT) or a combination of afterslip along the MHT (northern part of the rupture zone, crustal ramp) and viscous relaxation controlled by a thin (similar to 3-4 km thick) low-viscosity body centered on the lower flat of the MHT. The occurrence of afterslip along the northern part of the upper flat of the MHT and its longitudinal variations have been established thanks to the densification of GNSS network by our team presented in this paper.
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Kaduri, M., Gratier, J. - P., Lasserre, C., Cakir, Z., & Renard, F. (2019). Quantifying the Partition Between Seismic and Aseismic Deformation Along Creeping and Locked Sections of the North Anatolian Fault, Turkey. Pure And Applied Geophysics, 176(3), 1293–1321.
Résumé: Shallow aseismic creep is a key deformation component along plate boundaries that contributes to the energy budget during the seismic cycle. Several major active continental faults show spatial alternation of creeping and locked sections. The present study focuses on the evaluation of the aseismic part of the total displacement along the North Anatolian Fault in Turkey. Detailed microstructural analyses of finite strain were performed using various methods, based on change of length or angle, on six representative samples collected over 32 outcrops along locked and creeping sections of the fault. Chemical analyses were used to map mineral composition of fault rocks and to calculate relative volume changes associated with creep. The relationship between finite strain and volume change allowed quantifying the evolution of the penetrative pressure solution cleavage mechanism of creep. In volcanic and analogous creeping rocks, finite strain measurements revealed two spatial scales of strain that correspond to the alternation of two types of shear zones, with cleavages either oblique or sub-parallel to the fault displacement. Using geodetic and geologic data, cumulative aseismic displacement was calculated in the range 9-49% of the total 80-km displacement in the creping sections and was negligible in locked sections. The large uncertainty in the kilometer-width creeping sections was related to the difficulty of quantifying the high strain values associated with high shear displacement and for which measurement uncertainties are large. A promising way to improve such quantification would be to develop reliable statistical analysis of cleavage orientation in the field.
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Kandula, N., Cordonnier, B., Boller, E., Weiss, J., Dysthe, D. K., & Renard, F. (2019). Dynamics of Microscale Precursors During Brittle Compressive Failure in Carrara Marble. Journal Of Geophysical Research-Solid Earth, 124(6), 6121–6139.
Résumé: Microscale heterogeneities influence failure mechanisms in the crust. To track the microstructural changes in rock samples when loaded until failure, we employed a novel experimental technique that couples dynamic X-ray microtomography imaging with a triaxial deformation apparatus. We studied the brittle failure of Carrara marble under triaxial compression. Dynamic tomographic data revealed the spatial organization of microfractures and damage increments characterizing the precursory activity toward catastrophic failure. We quantified the emergence of scaling relationships between microstructural parameters, including total damage volume, incremental damage volume, the largest connected microfracture, and the applied differential stress. The total volume of microfractures accumulated from the beginning of the experiment as well as the incremental damage showed power law increase. The growth of the largest connected microfracture was related to differential stress as a power law with divergence at failure. The microfracture volume increments were distributed according to a power law with an upper cutoff that itself spanned the entire volume toward failure. These characteristic features of brittle failure in Carrara marble under compression are in agreement with theoretical models that consider failure as a critical phase transition. We also observed that, very close to failure, several power law relationships broke down, which we interpret to be related to the coalescence of the largest microfractures in a finite size volume. Scaling laws and associated exponents computed from our data are compared with predictions made from theoretical and numerical models. Our results show that precursors of macroscopic brittle failure in Carrara marble follow predictable trends.
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Kang, X., Shi, X., Revil, A., Cao, Z., Li, L., Lan, T., et al. (2019). Coupled hydrogeophysical inversion to identify non-Gaussian hydraulic conductivity field by jointly assimilating geochemical and time-lapse geophysical data. Journal Of Hydrology, 578.
Résumé: Reliable inversion of spatial heterogeneity of hydraulic conductivity is crucial to understand subsurface fluids migration. The Ensemble Smoother – Direct Sampling method (ES-DS) has proven to be an effective method to identify non-Gaussian hydraulic conductivity distributions by incorporating a variety of traditional hydrodynamic measurements, e.g., piezometric head. However, inversion problems for non-Gaussian parameters often suffer from a sparsity of the available data from direct sampling in boreholes. As a non-intrusive, cost-effective, and high sampling density method, time-lapse geophysical technique has not yet drawn much attention as a useful source of information for delineating the underlying non-Gaussian heterogeneity. In this study, we integrated coupled hydrogeophysical modeling and the ES-DS algorithm to estimate non-Gaussian hydraulic conductivity field by assimilating both geochemical and time-lapse geophysical datasets. Four synthetic Cases for a salt injection experiment, monitored by both sampling analysis and electrical resistivity tomography, are conducted to assess the ability of the proposed approach to characterize hydraulic properties by assimilating different types of data. Results show that using geochemical or geophysical data alone only allow a rough reconstruction of subsurface heterogeneity of aquifers but might lose the fine structure. By incorporating multi-source datasets, the main patterns of the non-Gaussian reference fields can be reflected with an improved resolution. The time-lapse geophysical methods open up new opportunities to accurately characterize non-Gaussian aquifers and monitor the dynamic processes of subsurface fluids.
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Karabulut, H., Paul, A., Ozbakir, A. D., Ergun, T., & Senturk, S. (2019). A new crustal model of the Anatolia-Aegean domain: evidence for the dominant role of isostasy in the support of the Anatolian plateau. Geophysical Journal International, 218(1), 57–73.
Résumé: The engines of surface deformation in the Anatolia-Aegean region are a matter of debate, including the origin of the high elevations of the Anatolian plateau. Recent publications based on geological and thermomechanical modelling emphasize the role of dynamic topography in the plateau uplift. However, quantitative estimates of the contribution of dynamic topography are affected by large uncertainties due to insufficient knowledge of the crustal structure, in particular crustal thickness and density. To reduce these uncertainties, we provide a new accurate crustal thickness map of the Anatolia-Aegean domain computed from a large volume of broadband seismic data. In addition, we display high-resolution seismic sections of the internal structure of the crust in Western and Central Anatolia. Density contrasts are derived from the same seismic data set and Bouguer gravity anomaly computed from the EGM2008 model. Our crustal thickness model is highly correlated with the topography suggesting that the Anatolian plateau is close to isostatic equilibrium. The average density difference between crust and upper mantle computed from our crustal model and Bouguer gravity anomaly is low compared to the global average, approximate to 0.315 x10(3)kgm(-3). The ratio of surface elevation to crustal thickness is lower than average, 1/9.4, which also indicates a low-density crust. Differences between isostatic topography and observed topography are overall small (<500m). The east-to-west gradients of crustal thickness and topography changes are nearly constant in between the Taurides and Pontides at the northern and southern borders of Anatolia. The observed constant crustal thickness gradient may indicate a low viscosity lower crust supported by the thin mantle lithosphere evidenced by seismic tomography beneath the Anatolian plateau. We propose that viscous flow in the lower crust has smoothed out lateral changes in the crustal structure expected for such a heterogeneous collage of continental fragments. This flow may originate from gravitational potential energy differences between Eastern Anatolia (thick crust, high elevations) and the Aegean Sea (thin crust, low elevations), suggesting that gravity plays an integral part in the westward escape of Anatolia.
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Karimi, K., Amitrano, D., & Weiss, jerome. (2019). From plastic flow to brittle fracture: Role of microscopic friction in amorphous solids. Physical Review E, 100(1).
Résumé: Plasticity in soft amorphous materials typically involves collective deformation patterns that emerge on intense shearing. The microscopic basis of amorphous plasticity has been commonly established through the notion of “Eshelby”-type events, localized abrupt rearrangements that induce flow in the surrounding material via nonlocal elastic-type interactions. This universal mechanism in flowing disordered solids has been proposed despite their diversity in terms of scales, microscopic constituents, or interactions. Using a numerical particle-based study, we argue that the presence of frictional interactions in granular solids alters the dynamics of flow by nucleating micro shear cracks that continually coalesce to build up system-spanning fracturelike formations on approach to failure. The plastic-to-brittle failure transition is controlled by the degree of frictional resistance which is in essence similar to the role of heterogeneities that separate the abrupt and smooth yielding regimes in glassy structures.
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Kelch, S. E., Ferrage, E., Lanson, B., Charlet, L., & Aristilde, L. (2019). Water Trapping Dynamics in Carbohydrate-Populated Smectite Interlayer Nanopores. Journal Of Physical Chemistry C, 123(47), 28816–28827.
Résumé: Smectite-type clays play a critical role in the trapping of fluids within soil and atmospheric nanoparticles. The hydrodynamics of cation-saturated smectite nanopores are well documented. However, little is known about the influence of small organic compounds. Here we investigate the effects of carbohydrates (glucose and cellobiose), representing an important class of organic compounds, on the hydration and nanopore structures of montmorillonite, a prototypical smectite. To achieve the same amount of adsorbed water, higher relative humidity was required in the presence of the adsorbed carbohydrates than with the clay alone. The decrease in the characteristic micropore water adsorption with the clay-carbohydrate aggregates implied that water adsorption was constrained within the clay nanopore regions. The presence of carbohydrates promoted water retention as a function of gradual decrease in moisture content. Moisture-dependent X-ray diffraction patterns determined that, relative to the mineral alone, greater nanopore sizes were preserved in the presence of the carbohydrates, despite severe dehydration that is expected to induce clay nanopore collapse. Fourier-transform infrared spectroscopy captured disruption in the population of exchangeable waters within the carbohydrate-populated clay nanopores, with some agreement with the measured water-desorption profiling. These new findings demonstrate that carbohydrates can restructure smectite interlayer nanopores and water trapping dynamics.
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Khorrami, F., Vernant, P., Masson, F., Nilfouroushan, F., Mousavi, Z., Nankali, H., et al. (2019). An up-to-date crustal deformation map of Iran using integrated campaign-mode and permanent GPS velocities. Geophysical Journal International, 217(2), 832–843.
Résumé: We present the most extensive and up-to-date unified GPS velocity field for Iran. We processed the data collected during 10 yr (2006-2015) from the Iranian Permanent GNSS Network (IPGN) and combined them with previously published velocity solutions from the GPS survey measurements during 1997-2013. We analysed this velocity field using a continuum approach to compute a new strain-rate map for this region and we designed a block model based on the main geological, morphological and seismic structures. Comparison between both approaches suggests similar results and allows us to present the first comprehensive first-order fault-slip-rate estimates for the whole of Iran. Our results confirm most of the results from previous geodetic studies. However, we also show a trade-off between the coupling ratio of the Iranian Makran subduction interface and the kinematics of the faults north of the Makran in the Jazmurian depression. Indeed, although too scarce to accurately estimate a coupling ratio, we show that coupling higher than 0.4 on the plate interface down to a depth of 25 km will induce extension on the E-W faults in the Jazmurian region. However, the sites close to the shoreline suggest a low coupling ratio; hence, the coupling on this plate interface is probably more complicated than previously described and the Iranian Makran subduction interface mechanical behaviour might be similar to that on the Hellenic subduction zone.
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Knoery, J., Cossa, D., Thomas, B., Gregory, G., & Rigaud, S. (2019). Susane, a device for sampling chemical gradients in the benthic water column. Limnology And Oceanography-Methods, 17(6), 331–342.
Résumé: In aquatic environments, the benthic water column exhibits strong concentration gradients of various substances. They result from transfers and chemical reactions that may occur both within this layer, and at the sediment-water interface (SWI). Characterization of these gradients yields important information for the quantification of such processes and transfers. However, it is difficult to actually sample these gradients in the field, since turbulence decreases their vertical scale. This article describes a sampler designed to collect simultaneously 16 discrete water column samples at a centimeter-scale vertical resolution. This small device (40 x 40 x 60 cm) is reliable, safe to handle, and easily deployed from a small boat using a cable or a Scuba diver. It is made of materials compatible with trace element and dissolved gases work, and simultaneously draws samples from various heights above the SWI into 60 mL syringes. The altitude of the sample inlets is field-adjustable. Sampling artifacts are minimized by in situ flushing of tubing dead volumes, by rapid and simultaneous sample collection, and by sampling an undisturbed water-column. Thus, this device can contribute to the characterization of vertical concentration gradients in benthic water-columns. Such gradients of various compounds and metals from two coastal sites (Quiberon Bay and Berre Lagoon) are shown, illustrating the sampler's usefulness to describe and investigate processes in the benthic zone.
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Koishi, A., Fernandez-Martinez, A., Van Driessche, A. E. S., Michot, L. J., Pina, C. M., Pimentel, C., et al. (2019). Surface Wetting Controls Calcium Carbonate Crystallization Kinetics. Chemistry Of Materials, 31(9), 3340–3348.
Résumé: Because of the widespread presence of foreign substrates in natural settings, mineral precipitation usually occurs via heterogeneous nucleation. This process is controlled by the interplay between the fluid supersaturation and interfacial energies present between the fluid, nucleus, and substrate. Among a number of physicochemical parameters, the surface wetting properties have been shown to be a key parameter controlling heterogeneous nucleation. The present study aims at elucidating the pathway and kinetics of CaCO3 heterogeneous nucleation on a set of phlogopite micas with and without fluorine/hydroxyl substitutions, yielding substrates with contrasting hydrophilicity. Our results show that, irrespective of surface wetting properties, amorphous calcium carbonate (ACC) is formed during the early stages. The surface wetting properties have a strong effect on the crystallization kinetics: ACC precipitates persist longer on the hydrophilic (hydroxylated) surface than on the less hydrophilic (fluorinated) one. We show that this stabilization could have a thermodynamic origin because of the lower interfacial free energy between the hydrated amorphous precursor and the hydrophilic substrate. These results are highly relevant for biomineralization studies, where differences in wetting properties of organic moieties present in calcifying organisms could be used to accelerate or decelerate the crystallization of the initially formed amorphous precursor phase.
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Koishi, A., Lee, S. S., Fenter, P., Fernandez-Martinez, A., Michot, L., & Bourg, I. (2019). Surface hydrophobicity and energetics at Mica-water interfaces. Abstracts Of Papers Of The American Chemical Society, 257.
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Kristek, J., Moczo, P., Chaljub, E., & Kristekova, M. (2019). A discrete representation of a heterogeneous viscoelastic medium for the finite-difference modelling of seismic wave propagation. Geophysical Journal International, 217(3), 2021–2034.
Résumé: The accuracy and efficiency of numerical simulations of seismic wave propagation and earthquake ground motion in realistic models strongly depend on discrete grid representation of the material heterogeneity and attenuation. We present a generalization of the orthorhombic representation of the elastic medium to the viscoelastic medium to make it possible to account for a realistic attenuation in a heterogeneous viscoelastic medium with material interfaces. An interface is represented by an averaged orthorhombic medium with rheology of the Generalized Maxwell body (GMB-EK, equivalent to the Generalized Zener body). The representation is important for the possibility of applying one explicit finite-difference scheme to all interior grid points (points not lying on a grid border) no matter what their positions are with respect to the material interface. This is one of the key factors of the computational efficiency of the finite-difference modelling. Smooth or discontinuous heterogeneity of the medium is accounted for only by values of the effective (i.e. representing reasonably averaged medium) grid moduli and densities. Accuracy of modelling thus very much depends on how the medium heterogeneity is represented/averaged. We numerically demonstrate accuracy of the developed orthorhombic representation. The orthorhombic representation neither changes the structure of calculating stress-tensor components nor increases the number of arithmetic operations compared to a smooth weakly heterogeneous viscoelastic medium. It is applicable to the velocity-stress, displacement-stress and displacement FD schemes on staggered, partly staggered, Lebedev and collocated grids. We also present an optimal procedure for a joint determination of the relaxation frequencies and anelastic coefficients.
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Kuo, Y. - T., Wang, Y., Hollingsworth, J., Huang, S. - Y., Chuang, R. Y., Lu, C. - H., et al. (2019). Shallow Fault Rupture of the Milun Fault in the 2018 M-w 6.4 Hualien Earthquake: A High-Resolution Approach from Optical Correlation of Pleiades Satellite Imagery. Seismological Research Letters, 90(1), 97–107.
Résumé: We use high-resolution Pleiades optical satellite imagery to study the distribution and magnitude of fault slip along the Milun fault surface rupture, which broke during the 2018 Hualien earthquake (M-w 6.4) in eastern Taiwan. Correlation of pre- and postearthquake stereo Pleiades images reveals detailed 3D surface displacements along the 8-km-long Milun fault, with maximum similar to 1 m left-lateral offsets across the fault. Along the northern section of the Milun fault, our correlation results indicate a localized deformation zone, with offset values slightly larger than the maximum offsets reported in the field (similar to 77 cm). To the south, the left-lateral offsets become increasingly distributed, producing arctangent shapes in displacement profiles crossing the fault. In places, the deformation zone reaches widths of 200 + m and can be explained by a shallow east-dipping fault rupture extending from 2 to 3 km depth to 70-120 m below the surface. A very shallow coseismic rupture on the Milun fault is consistent with a shallow locking depth interpreted from previous geodetic analyses from the interseismic period. Despite a few highly discontinuous and irregular surface ruptures reported along the southern section of the fault, our results suggest the main fault slip (up to 1 m) stopped at very shallow depths below the surface, in which similar to 60% of the deformation may be accommodated as off-fault deformation (OFD). In this upper similar to 100 m of the crust, OFD may be promoted by a significant change in material strength, as the fault crosses from bedrock and/or consolidated sediments into weaker, water-rich, poorly consolidated alluvial sediments.
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Lachaud, C., Marsan, D., Montagnat, M., Weiss, J., Moreau, L., & Gimbert, F. (2019). Micro-Seismic Monitoring of a Shear Fault within a Floating Ice Plate. Journal Of Geophysical Research-Solid Earth, 124(10), 10444–10467.
Résumé: The deformation of a circular fault in a thin floating ice plate imposed by a slow rotational displacement is investigated. Temporal changes in shear strength, as a proxy for the resistance of the fault as a whole, are monitored by the torque required to impose a constant displacement rate. Micro-seismic monitoring is used to study the relationship between fault average resistance (torque) and micro-ruptures. The size distribution of ruptures follows a power-law scaling characterized by an unusually high exponent (b similar or equal to 3), characteristic of a deformation driven by small ruptures. In strong contrast to the typical brittle dynamics of crustal faults, an 'apparently aseismic' deformation regime is observed in which small undetected seismic ruptures, below the detection level of the monitoring system, control the slip budget. Most (similar or equal to 71%) of the detected ruptures are organized in bursts with highly similar waveforms, suggesting that these ruptures are only a passive by-product of apparently aseismic slip events. The seismic signature of this deformation regime has strong similarities with crustal faulting in settings characterized by high temperature and with non-volcanic tremors.
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Lacroix, P., Araujo, G., Hollingsworth, J., & Taipe, E. (2019). Self-Entrainment Motion of a Slow-Moving Landslide Inferred From Landsat-8 Time Series. Journal Of Geophysical Research-Earth Surface, 124(5), 1201–1216.
Résumé: In mountainous environments, slow-moving landslides (velocities <100m/year) are a major concern for local populations. Rainfall is often the dominant forcing, and often result in major changes in kinematics which can mask smaller signals related to internal forcings. We focus here on a major (>40Mm(3)) slow-moving landslide in the desert of southern Peru and take advantage of this arid environment to study the internal processes affecting landslide kinematics. We first estimate the ground displacement from time series analysis of Landsat-8 images, spanning a 5.7-year period. Systematic artifacts in the optical time series are shown to correlate with topography, as well as vary seasonally. We apply a novel procedure for correcting these artifacts, which significantly reduces noise in the resulting time series, thereby allowing us to precisely resolve landslide displacements. We find landslide velocities of up to 35m/year, with complex nonlinear interannual pattern, including a period of rapid acceleration. We validate our optically derived time series using Global Navigation Satellite System field measurements and find uncertainties (root-mean-square error) on the moving mass of 1.12 to 1.55m. Sudden acceleration of the landslide body after March 2016 may originate from a mass collapse due to retrogression of the headscarp. By coupling sparse 3-D Global Navigation Satellite System measurements with dense 2-D optical time series data, we show that the headscarp retrogression acts like a wedge, resulting in domino-like tilting of the downward blocks, and accelerates basal sliding over 2years. These observations reveal that the dynamics of this retrogressive landslide are predominantly controlled by sediment supply and that succession of retrogressive and advancing motions is a self-entrainment process.
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Lallement, R., Babusiaux, C., Vergely, J. L., Katz, D., Arenou, F., Valette, B., et al. (2019). Gaia-2MASS 3D maps of Galactic interstellar dust within 3 kpc. Astronomy & Astrophysics, 625.
Résumé: Gaia stellar measurements are currently revolutionizing our knowledge of the evolutionary history of the Milky Way. 3D maps of the interstellar dust provide complementary information and are a tool for a wide range of uses. We built 3D maps of the dust in the Local arm and surrounding regions. To do so, Gaia DR2 photometric data were combined with 2MASS measurements to derive extinction toward stars that possess accurate photometry and relative uncertainties on DR2 parallaxes smaller than 20%. We applied a new hierarchical inversion algorithm to the individual extinctions that is adapted to large datasets and to an inhomogeneous target distribution. Each step associates regularized Bayesian inversions in all radial directions and a subsequent inversion in 3D of all their results. Each inverted distribution serves as a prior for the subsequent step, and the spatial resolution is progressively increased. We present the resulting 3D distribution of the dust in a 6 x 6 x 0.8 kpc(3) volume around the Sun. Its main features are found to be elongated along different directions that vary from below to above the mid-plane. The outer part of Carina-Sagittarius, mainly located above the mid-plane, the Local arm/Cygnus Rift around and above the mid-plane, and the fragmented Perseus arm are oriented close to the direction of circular motion. The spur of more than 2 kpc length (nicknamed the split) that extends between the Local Arm and Carina-Sagittarius, the compact near side of Carina-Sagittarius, and the Cygnus Rift below the Plane are oriented along l similar to 40 to 55 degrees. Dust density images in vertical planes reveal a wavy pattern in some regions and show that the solar neighborhood within similar to 500 pc remains atypical by its extent above and below the Plane. We show several comparisons with the locations of molecular clouds, HII regions, O stars, and masers. The link between the dust concentration and these tracers is markedly different from one region to the other.
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Lamarca-Irisarri, D., Van Driessche, A. E. S., Jordan, G., Cappelli, C., & Huertas, F. J. (2019). The Role of pH, Temperature, and NH4+ during Mica Weathering. Acs Earth And Space Chemistry, 3(11), 2613–2622.
Résumé: Phyllosilicates are abundant materials both on Earth and Mars, and the weathering of these minerals is an essential part of a wide variety of geochemical cycles. Alteration mainly takes place at the solution-mineral interface and needs to be fully understood in order to correctly model global water-rock interactions. To directly link the physicochemical solution properties to the dominant surface processes controlling phyllosilicate alteration, we used a custom-built hydrothermal atomic force microscope to study in situ the surface reactivity of biotite, phlogopite, and muscovite in contact with aqueous solutions for a broad range of temperatures and pH values. On the basis of our microscopic observations correlated with previously obtained macroscopic dissolution rates, we have constructed a tentative weathering diagram for mica minerals connecting the dominant surface mechanisms and bulk dissolution behavior to the physicochemical solution properties (pH, T, and speciation). The resulting diagram can be divided into two main areas: low-grade weathering occurring at low temperatures and mildly acidic to neutral pH and high-grade weathering taking place at high temperatures and low pH, separated by a transition zone. Each of these areas is characterized by a series of chemical and physical surface processes, which can be related directly or indirectly to incongruent and congruent bulk dissolution. The transition temperatures and pH values depend on the type of mica, with biotite being the most reactive one and muscovite the least reactive one. It is noteworthy that for close to neutral pH conditions the presence of NH4+ shifts the transitions from low- to high-grade weathering to a significantly lower temperature.
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Laurent, G., Izart, C., Lechenard, B., Golfier, F., Marion, P., Collon, P., et al. (2019). Numerical modelling of column experiments to investigate in-situ bioleaching as an alternative mining technology. Hydrometallurgy, 188, 272–290.
Résumé: This publication investigates indirect in-situ bioleaching as an alternative mining technology for minimizing waste production, environmental impact, and chemical consumption. The process consists in injecting a leaching solution into a targeted ore body for dissolving base metal bearing minerals, while iron-oxidizing microorganisms regenerate the solution. In this contribution, we present laboratory column experiments that investigate the impact of grain size on the action of an acidic oxidizing solution in contact with ore samples crushed at different grain sizes. These results are used for developing a one-dimensional reactive transport model based on PhreeqC software. In this model, porous and fractured media are approached by a dual porosity reactive transport model where dissolution reactions are described by kinetics. Column experiments are used as a reference for calibrating the key parameters of the numerical models, which include the relative volume of mobile and immobile zones within the dual porosity medium and the exchange rate between these two volumes. This model is then adapted to in-situ conditions by considering the preferential flow of fluids through natural or artificial fractures of enhanced hydraulic conductivity. These models are used to discuss key elements affecting the feasibility of coupling bioleaching and in-situ recovery for improving the sustainability of mining, especially for deep and complex ore deposits.
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Le Bouteiller, P., Benjemaa, M., Metivier, L., & Virieux, J. (2019). A discontinuous Galerkin fast-sweeping eikonal solver for fast and accurate traveltime computation in 3D tilted anisotropic media. Geophysics, 84(2), C107–C118.
Résumé: We tackle the challenging problem of efficient and accurate seismic traveltime computation in 3D anisotropic media by applying the fast-sweeping method to a discontinuous Galerkin (DG)-based eikonal solver. Using this method leads to a stable and highly accurate scheme, which is faster than finite-difference schemes for a given precision, and with a low computational cost compared to the standard Runge-Kutta DG formulation. The integral formulation of the DG method also makes it easy to handle seismic anisotropy and complex topographies. Several numerical tests on complex models, such as the 3D SEG advanced modeling model, are given as illustration, highlighting the efficiency and the accuracy of this new approach. In the near future, these results will be used together with accurate solvers for seismic amplitude and take-off angle computation to revisit asymptotic inversion (traveltime/slope tomography) and imaging approaches (quantitative migration involving amplitudes and angles).
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Le Breton, M., Baillet, L., Larose, E., Rey, E., Benech, P., Jongmans, D., et al. (2019). Passive radio-frequency identification ranging, a dense and weather-robust technique for landslide displacement monitoring. Engineering Geology, 250, 1–10.
Résumé: Ground deformation monitoring at a local scale requires accuracy, along with dense spatio-temporal resolution. Radio-Frequency Identification (RFID) technology is proposed as an alternative to classical geodetic methods for monitoring displacements of a landslide. Passive RFID tags allow for a very dense resolution, both in time and space, at the scale of a 100-m-long surface. By deploying 19 passive RED tags on a landslide for 5 months, this study validates the technique by comparison with laser total station and wire extensometer data. The accuracy of the RFID technique was 1 cm during normal weather and up to 8 cm during snow events. The results demonstrate that RFID tag tracking can monitor landslide displacements with multiple sensors at low cost, providing dense spatio-temporal data. This technique could potentially be used for other applications such as monitoring volcanic activity, buildings, unstable rocks or snow cover.
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Le Roy, G., Helmstetter, A., Amitrano, D., Guyoton, F., & Le Roux-Mallouf, R. (2019). Seismic Analysis of the Detachment and Impact Phases of a Rockfall and Application for Estimating Rockfall Volume and Free-Fall Height. Journal Of Geophysical Research-Earth Surface, 124(11), 2602–2622.
Résumé: We analyzed 21 rockfalls that occurred in limestone cliffs of the Chartreuse Massif (French Alps). These rockfalls were detected both by Terrestrial Laser Scanning or photogrammetry and by a local seismological network. The combination of these methods allowed us to study relations between rockfall properties (location of detachment and impacts areas, volume, geometry, and propagation) and the induced seismic signal. We observed events with different propagation modes (sliding, mass flow, and free fall) that could be determined from digital elevation models. We focused on events that experienced a free fall after their detachment. We analyzed the first parts of the seismic signals corresponding to the detachment phase and to the first impact. The detachment phase has a smaller amplitude than the impact phase, and its amplitude and duration increases with rockfall volume. By measuring the time delay between the detachment phase and the first impact, we can estimate the free-fall height. We found a relation E-s = aE(p)(b) between the potential energy of a rockfall E-p and the seismic energy Es generated during an impact, with a = 10(-8) and b = 1.55 and with a correlation coefficient R-2 = 0.98. We can thus estimate both the potential energy of a block and its free-fall height from the seismic signals. By combining these results, we obtain an accurate estimate of the rockfall volume. The relation between the E-p and E-s was tested on different geological settings and for larger range of volumes using Yosemite, Mount Granier rockfalls, and with a data set of controlled releases of blocks (Hibert et al., 2017, https://doi.org/10.5194/esurf-5-283-2017, https://www.earth-surf-dynam.net/5/283/2017/).
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Ledevin, M., Arndt, N., Chauvel, C., Jaillard, E., & Simionovici, A. (2019). The Sedimentary Origin of Black and White Banded Cherts of the Buck Reef, Barberton, South Africa. Geosciences, 9(10).
Résumé: The Buck Reef is a 250-400 m thick sequence of banded black and white (B&W) cherts deposited ca. 3416 Ma ago in a shallow basin. We provide field, petrological and geochemical constraints on the chert-forming process and the origin of the banding. White layers consist of nearly pure microquartz, while black layers are mixed with detrital carbonaceous matter, quartz grains and carbonaceous microlaminae, interpreted as remnants of microbial mats. The circulation of Si-rich fluid is recorded by abundant chert veins and pervasive silicification. However, the high purity of the white layers, their lack of internal structures and extremely low Al, Ti and high-field-strength elements preclude an origin by silicification of sedimentary or volcanic precursors. Moreover, their reworking at the surface into slab conglomerates, and sediment-like contacts with black layers rule out a diagenetic origin. We propose a new model whereby the white layers were periodically deposited as precipitates of pure silica; and the micro-layering within the black layers formed by annual temperature fluctuations, favouring microbial activity in summer and inorganic silica precipitation in winter. Outcrop-scale alternation of B&W layers was associated with major, thousand-year-long climate events: white cherts represent massive silica precipitation resulting from changes in ocean circulation and temperature during cold intervals.
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Lehmann, B., Herman, F., Valla, P. G., King, G. E., & Biswas, R. H. (2019). Evaluating post-glacial bedrock erosion and surface exposure duration by coupling in situ optically stimulated luminescence and Be-10 dating. Earth Surface Dynamics, 7(3), 633–662.
Résumé: Assessing the impact of Quaternary glaciation at the Earth's surface implies an understanding of the long-term evolution of alpine landscapes. In particular, it requires simultaneous quantification of the impact of climate variability on past glacier fluctuations and on bedrock erosion. Here we present a new approach for evaluating post-glacial bedrock surface erosion in mountainous environments by combining terrestrial cosmogenic nuclide Be-10 (TCN) and optically stimulated luminescence (OSL) surface exposure dating. Using a numerical approach, we show how it is possible to simultaneously invert bedrock OSL signals and Be-10 concentrations into quantitative estimates of post-glacial exposure duration and bedrock surface erosion. By exploiting the fact that OSL and TCN data are integrated over different timescales, this approach can be used to estimate how bedrock erosion rates vary spatially and temporally since glacier retreat in an alpine environment.
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Lehmann, S. G., Seve, M., Vanwonterghem, L., Michelland, S., Cunin, V., Coll, J. - L., et al. (2019). A large scale proteome analysis of the gefitinib primary resistance overcome by KDAC inhibition in KRAS mutated adenocarcinoma cells overexpressing amphiregulin. Journal Of Proteomics, 195, 114–124.
Résumé: KDAC inhibitors (KDACi) overcome gefitinib primary resistance in non-small cell lung cancer (NSCLC) including mutant-KRAS lung adenocarcinoma. To identify which proteins are involved in the restoration of this sensitivity and to provide new therapeutic targets for mutant-KRAS lung adenocarcinoma, we performed an iTRAQ quantitative proteomic analysis after subcellular fractionation of H358-NSCLC treated with gefitinib and KDACi (TSA/NAM) versus gefitinib alone. The 86 proteins found to have been significantly dysregulated between the two conditions, were mainly involved in cellular metabolism and cell transcription processes. As expected, the pathway related to histone modifications was affected by the KDACi. Pathways known for controlling tumor development and (chemo)-resistance (miRNA biogenesis/glutathione metabolism) were affected by the KDACi/gefitinib treatment. Moreover, 57 dysregulated proteins were upstream of apoptosis (such as eEF1A2 and STAT1) and hence provide potential therapeutic targets. The inhibition by siRNA of eEF1A2 expression resulted in a slight decrease in H358-NSCLC viability. In addition, eEF1A2 and STAT1 siRNA transfections suggested that both STAT1 and eEF1A2 prevent AKT phosphorylation known for enhancing gefitinib resistance in NSCLC. Therefore, altogether our data provide new insights into proteome regulations in the context of overcoming the NSCLC resistance to gefitinib through KDACi in H358 KRAS mutated and amphiregulin-overexpressing NSCLC cells.
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Lehmann, S. G., Toybou, D., del Real, A. - E. P., Arndt, D., Tagmount, A., Viau, M., et al. (2019). Crumpling of silver nanowires by endolysosomes strongly reduces toxicity. Proceedings Of The National Academy Of Sciences Of The United States Of America, 116(30), 14893–14898.
Résumé: Fibrous particles interact with cells and organisms in complex ways that can lead to cellular dysfunction, cell death, inflammation, and disease. The development of conductive transparent networks (CTNs) composed of metallic silver nanowires (AgNWs) for flexible touchscreen displays raises new possibilities for the intimate contact between novel fibers and human skin. Here, we report that a material property, nanowire-bending stiffness that is a function of diameter, controls the cytotoxicity of AgNWs to nonimmune cells from humans, mice, and fish without deterioration of critical CTN performance parameters: electrical conductivity and optical transparency. Both 30- and 90-nm-diameter AgNWs are readily internalized by cells, but thinner NWs are mechanically crumpled by the forces imposed during or after endocytosis, while thicker nanowires puncture the enclosing membrane and release silver ions and lysosomal contents to the cytoplasm, thereby initiating oxidative stress. This finding extends the fiber pathology paradigm and will enable the manufacture of safer products incorporating AgNWs.
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Levy, L., Maurya, P. K., Byrdina, S., Vandemeulebrouck, J., Sigmundsson, F., Arnason, K., et al. (2019). Electrical resistivity tomography and time-domain induced polarization field investigations of geothermal areas at Krafla, Iceland: comparison to borehole and laboratory frequency-domain electrical observations. Geophysical Journal International, 218(3), 1469–1489.
Résumé: Interaction of H2S and basaltic rocks in volcanic geothermal areas can originate from natural up-flow of magmatic fluids or H2S artificial re-injection in relation to geothermal exploitation, both causing pyrite mineralization. We study the possibility to track these processes with electrical impedance field measurements. Electrical Resistivity Tomography (ERT) and TimeDomain Induced Polarization (TDIP) measurements were performed along thirteen 1.24 km long profiles, at three different sites around the eastern caldera rim of the Krafla caldera: (i) a 'cold altered' site affected by past hydrothermal circulations, (ii) a hot active site and (iii) a 'cold un-altered' site, unaffected by hydrothermal circulations. We present 2-D inversions of direct current (DC) resistivity, maximum phase angle of the electrical impedance (MPA) and relaxation time. The maximum depth of investigation for the MPA is 200 m, obtained in zones of high resistivity, corresponding to fresh and recent unaltered basalt. At the hot and cold altered sites, the field resistivities are compared to in situ borehole logs and laboratory complex resistivity measurements on rock samples from the boreholes. The laboratory complex resistivity was measured at six different pore water conductivities, ranging from 0.02 to 5 Sm-1, and frequency in the range 10(-2)-10(6) Hz. The time-range investigated in our field TDIP measurements was approximately 0.01-8 s. At the cold altered site, the inverted resistivity is consistent with both borehole observations and laboratory measurements. At the hot site, resistivity from field inversion and borehole logs are consistent. Comparing inversion results and borehole logs to laboratory resistivity measured on core samples at room temperature reveals that a correction coefficient for the effect of temperature on resistivity of 6 per cent per degrees C is appropriate at investigated depths. This exceptionally high temperature correction coefficient suggests a dominant influence of interface and interfoliar conduction, characteristic of smectite-rich rocks, compared to electrolyte conduction. High MPA is attributed to the presence of pyrite at the hot site and of iron-oxides at the cold unaltered site, through joint consideration of MPA together with DC resistivity and relaxation time. TDIP measurements offer the possibility to detect the presence of metallic minerals at shallow depth and distinguish between pyrite and iron-oxides. The abundance of highly conductive smectite in altered volcanic rocks represents a challenge for resolving IP parameters, because the low resistivity created by abundant smectite limits the data quality of the measured voltage discharge.
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Ling, C., Revil, A., Abdulsamad, F., Qi, Y., Ahmed, A. S., Shi, P., et al. (2019). Leakage detection of water reservoirs using a Mise-a-la-Masse approach. Journal Of Hydrology, 572, 51–65.
Résumé: Localizing leaks of water and fluids from storage tanks and water reservoirs with geomembranes is an important task for a variety of environmental applications and water resources applications. The minimally intrusive mise-a-la-masse method is used to detect leaks with the current injected inside the reservoir and a return current electrode located remotely. We test a new approach for the inversion of the voltage data using sandbox experiments and numerical modeling. A method similar to the self-potential inversion method is proposed to inverse the voltages recorded around the tank or reservoir. A global objective function with a data misfit term and regularization term is minimized to invert the voltages. In the inversion process, a depth-weighting matrix is used to strengthen the depth resolution of the current source, and the minimum support method is used to avoid oversmoothed results in terms of leak detection. The distributions of electrical current density on the walls of reservoir indicate the position of leaks. The results show that the inversion method with source compaction accurately identifies the location of single leaks. For two separated leaks, there is an obvious bias for the deeper hole and the bias increases with its depth. For three holes, the source compaction method generally identifies the location of the three leaks when their depth ranges are similar. When one of the leaks becomes deeper, localization of the deeper one becomes more difficult. The influence of the size of the leak on the inversion results is also investigated. The inversion algorithm overestimates the depth of small leaks while it slightly underestimates the depth of large leaks. For a leak having the form of a crack, the inversion results using the source compaction method agree with the position of the leak and its shape.
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Ling, C., Revil, A., Qi, Y., Abdulsamad, F., Shi, P., Nicaise, S., et al. (2019). Application of the Mise-a-la-Masse method to detect the bottom leakage of water reservoirs. Engineering Geology, 261.
Résumé: Leakages of reservoirs are responsible for the loss of water resources and the spread of contaminants. We develop a methodology to detect leaks located at the bottom side of a reservoir with the minimally invasive mise-a-la-masse method, which involves the potential electrodes located at the ground surface around the reservoir and the current source and sink placed in and out of the reservoir, respectively. This method allows localizing the secondary current distribution associated with leakage using the distribution of potential recorded on a set of electrodes during the mise-a-la-masse experiment. An initial model based on the distribution of root mean square values between the observation and the simulation data is first given to the inversion algorithm. The Tikhonov regularization, which includes a weighting matrix and a minimum support function, is used to strengthen the detection resolution of the leak. 29 sandbox experiments show that the proposed method and inversion algorithm can localize a single leak. For a leak with a crack shape, the inversion algorithm detects the location of the leak with a small bias. When the leak lasts, a conductive zone may occur below the leak due to the increase of water content or ionic strength of the pore water. The occurrence of such a conductive body could affect the localization of the leak because the conductivity distribution may not be well-resolved. The effect is analyzed using synthetic experiments. The results show that the bias between the real leak and inversion results increases with the position and size of the undetected conductive zone. Two small-scale field tests were conducted to test the performance of the mise-a-la-masse method. The two leaks are properly identified. This study provides an efficient approach to detect the bottom leakage of reservoirs.
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Lott, M., & Roux, P. (2019). Effective impedance of a locally resonant metasurface. Physical Review Materials, 3(6).
Résumé: We study here a mesoscopic metasurface made of a randomly distributed set of long vertical metallic rods attached to a thin elastic plate. The A(0) Lamb wave propagation is strongly affected by the local change in apparent stiffness of the plate induced by the low-quality factor resonance of the rods. At the resonance, the plate-plus-rods system is allowed to move freely, and plate waves can penetrate into the metamaterial. At the antiresonance, the plate behaves in terms of waves as if it was clamped by the rods in the metamaterial region, which induces large-frequency band gaps. Between the resonant and antiresonant frequencies, the continuous change in effective rigidity results in a continuous change in reflectivity. In the present paper, we aim at measuring the corresponding complex impedance of the metasurface in terms of amplitude and phase. Experimental data are presented to estimate the effective impedance of a locally resonant metasurface, in agreement with theoretical prediction and numerical simulation.
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Lozano, A., Ayora, C., & Fernandez-Martinez, A. (2019). Sorption of rare earth elements onto basaluminite: The role of sulfate and pH. Geochimica Et Cosmochimica Acta, 258, 50–62.
Résumé: Scandium, yttrium and lanthanides (REE) are critical raw materials in increasing demand for modern technology, so identifying and developing new sources of REE has become a pressing need. REE concentrations in acid mine drainage (AMD) are several orders of magnitude higher than those in natural water, and their recovery is of economic interest. Passive remediation systems designed to minimize AMD impact on the ecosystem retain REE in solid waste, where basaluminite, Al4SO4(OH)(10)center dot 5H(2)O, is the mineral responsible for the scavenge. However, no information about the retention mechanisms of REE is currently available in the literature. The objective of the present work is to study the adsorption of lanthanides, yttrium and scandium onto synthetic basaluminite over a pH range of 4-7 at room conditions. Since sulfate is ubiquitous in AMD, the adsorption has been investigated with variable sulfate concentrations. Experimental results show that sorption onto basaluminite is strongly dependent on pH, starting at pH 5 for lanthanides and yttrium and at pH 4 for scandium. At any given pH values, sorption increases with sulfate concentration. Distribution coefficients, defined as K-D = [REEsorbed]/[REEsolution], are higher for Sc, and across the lanthanide series, the distribution coefficients increase from La to Lu according to decreasing ionic radius, where yttrium is considered close to Ho. Experimental results were modeled using a sorption model that considers mass law equations where the strong sulfate aqueous complex, MSO4+, is adsorbed by exchanging a proton with the mineral surface. The dependence of the experimental results on pH suggests the formation of monodentate binding for Y and lanthanides. The bidentate complex for Sc is deduced by the two proton exchange per mol of Sc extracted from the experiments. The thermodynamic constants for the surface complexation reactions were obtained from experiments with high sulfate concentration and were successfully applied to the experiment with low sulfate content and different solid-liquid ratios. Therefore, the model can be applied to interpret the REE geochemistry in natural systems with variable pH and sulfate concentrations. (C) 2019 Elsevier Ltd. All rights reserved.
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Lozano, A., Fernandez-Martinez, A., Ayora, C., Di Tommaso, D., Poulain, A., Rovezzi, M., et al. (2019). Solid and Aqueous Speciation of Yttrium in Passive Remediation Systems of Acid Mine Drainage. Environmental Science & Technology, 53(19), 11153–11161.
Résumé: Yttrium belongs to the rare earth elements (REEs) together with lanthanides and scandium. REEs are commonly used in modern technologies, and their limited supply has made it necessary to look for new alternative resources. Acid mine drainage (AMD) is a potential resource since it is moderately enriched in REEs. In fact, in passive remediation systems, which are implemented to minimize the environmental impacts of AMD, REEs are mainly retained in basaluminite, an aluminum hydroxysulfate precipitate. In this study, the solid and liquid speciation and the local structure of yttrium are studied in high-sulfate aqueous solutions, basaluminite standards, and samples from remediation columns using synchrotron-based techniques and molecular modeling. Pair distribution function (PDF) analyses and ab initio molecular dynamics density functional theory models of the yttrium sulfate solution show that the YSO4+ ion pair forms a monodentate inner-sphere complex. Extended X-ray absorption fine structure (EXAFS) and PDF analyses show that Y is retained by basaluminite, forming a monodentate inner-sphere surface complex on the aluminum hydroxide surface. EXAFS of the column samples shows that more than 72% of their signal is represented by the signal of basaluminite with which YSO4+ forms an inner-sphere complex. The atomic view of the REE configuration in AMD environments could facilitate a deeper research of REE recovery from waste generated in AMD remediation systems.
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L’Hôte, G., S. Cazottes, J. Lachambre, M. Montagant, P. Courtois, J. Weiss and S. Deschanel. (2019). Dislocation dynamics during cyclic loading in copper single crystal. Materialia, 8, 100501.
Résumé: In this paper, we study the effects of θ′-Al2Cu plate-like precipitates on the plasticity of Al-Cu micro-pillars, with a sample size allowing the precipitates to cross the entire micro-pillar. {100}-slip traces are identified for the first time in Al and Al alloys at room temperature. We investigate the underlying mechanisms of this unusual {100}-slip, and show that it operates along the coherent θ′-Al2Cu precipitate/α-Al matrix interface. A combination of molecular dynamics simulations and stress analysis indicates that screw dislocations can cross-slip from the {111} plane onto the {100} θ′-Al2Cu/α-Al interface, then move on it through a kink-pair mechanism, providing a reasonable explanation to the observed {100}-slips. The roles of the θ′-Al2Cu precipitate/α-Al matrix interface on the properties of interfacial dislocations are studied within the Peierls–Nabarro framework, showing that the interface can stabilize the {100} screw dislocations from the spreading of the core, and increases the Peierls stress. These results improve our understanding of the mechanical behavior of Al-Cu micro-pillars at room temperature, and imply an enhanced role of interfacial slip in Al-Cu based alloys at elevated temperature in consideration of the underlying kink-pair mechanism.
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Ma, B., Charlet, L., Fernandez-Martinez, A., Kang, M., & Made, B. (2019). A review of the retention mechanisms of redox-sensitive radionuclides in multi-barrier systems. Applied Geochemistry, 100, 414–431.
Résumé: The deep geological disposal concept is widely accepted by the scientific community for the storage of high activity level nuclear waste. It uses a multi-barrier system to isolate radioactive waste from the hydrosphere and biosphere for hundreds of centuries. The multiple barriers include, from the waste to near-and far-field: metal (e.g., iron or copper) and/or concrete canisters/casks containing the radioactive waste, cement, clay (e.g., smectites) buffer and/or backfill materials, and naturally occurring host rocks (e.g., claystone and granite). The mobility of radionuclides (RNs) is a key issue regarding the safety assessment of nuclear waste repositories, especially for the soluble and mobile RNs, such as I-129, Cl-36, (235,) U-238, Se-79, and Tc-99. Among them, U-235,U- 238, Se-79, Mo-99, and Sb-125 are some of the redox-sensitive RNs whose mobility largely depends on their speciation, i.e., their oxidation states. The interactions of these redox-sensitive RNs with the components of each of the barriers is complex, and it needs to be fully understood for a correct safety assessment. Much progress has been made in the recent years in getting a fundamental understanding of the migration of redox-sensitive RNs in geological media. Here, an overview of the major achievements is presented. In general, the electron donors in repositories can be steel (i.e., zero valent iron), steel reaction products when in contact with groundwater (producing H-2), steel corrosion products (e.g., magnetite, green rust, and ferrous oxyhydroxides), Fe(II)-sulfides (e.g., pyrite, chalcopyrite, and mackinawite), Fe(II)-bearing clays (e.g., Fe-bearing smectites) in claystone, or Fe (II)-bearing mica minerals (e.g., biotite) in granites. All these phases can sorb redox-sensitive RNs and drive reductive immobilization processes. For U and all the redox-sensitive RN oxyanions, the resulting reduced products are the most stable and least soluble phases, such as FeSe2 for Se or UO2 for U, which may be favorably formed in the presence of a high solubility of electron donors and fast reaction kinetics. However, with slow reaction kinetics, metastable reduced mixed species in intermediate oxidation states such as Se(0) and hyper-stoichiometric uranium oxides are produced. In order to characterize the RN-bearing phases and the uptake and reduction pathway, powerful molecular-scale tools such as X-ray photoelectron spectroscopy (XPS) or X-ray absorption spectroscopy (XAS) are commonly used. Here, we provide a comprehensive perspective on the studies addressing interactions of redox-sensitive RNs with the above-mentioned potential barrier.
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Maccaferri, F., Smittarello, D., Pinel, V., & Cayol, V. (2019). On the Propagation Path of Magma-Filled Dikes and Hydrofractures: The Competition Between External Stress, Internal Pressure, and Crack Length. Geochemistry Geophysics Geosystems, 20(4), 2064–2081.
Résumé: Mixed-mode fluid-filled cracks represent a common means of fluid transport within the Earth's crust. They often show complex propagation paths which may be due to interaction with crustal heterogeneities or heterogeneous crustal stress. Previous experimental and numerical studies focus on the interplay between fluid overpressure and external stress but neglect the effect of other crack parameters. In this study, we address the role of crack length on the propagation paths in the presence of an external heterogeneous stress field. We make use of numerical simulations of magmatic dike and hydrofracture propagation, carried out using a two-dimensional boundary element model, and analogue experiments of air-filled crack propagation into a transparent gelatin block. We use a 3-D finite element model to compute the stress field acting within the gelatin block and perform a quantitative comparison between 2-D numerical simulations and experiments. We show that, given the same ratio between external stress and fluid pressure, longer fluid-filled cracks are less sensitive to the background stress, and we quantify this effect on fluid-filled crack paths. Combining the magnitude of the external stress, the fluid pressure, and the crack length, we define a new parameter, which characterizes two end member scenarios for the propagation path of a fluid-filled fracture. Our results have important implications for volcanological studies which aim to address the problem of complex trajectories of magmatic dikes (i.e., to forecast scenarios of new vents opening at volcanoes) but also have implications for studies that address the growth and propagation of natural and induced hydrofractures. Plain Language Summary Fluids move within the Earth by means of different mechanisms. One of the most relevant mechanisms, particularly for magma transport within the lithosphere, is the propagation through fluid-filled fractures: the fluid (or magma) can create its own path through the crustal rocks by fracturing them. If the density of the fluid is lower than the density of the rocks, the fluid would be pushed upward by buoyancy (similarly to a gas bubble in water). However, the propagation path followed by these fluid-filled fractures may be complex. This may be due to several factors, including the forces (stresses) acting within the crust because of plate tectonic or because of remarkable topographic features. Here we make use of computer simulations and laboratory experiments to test how fluid-filled fractures interact with such crustal stresses. We quantify how the competition between (i) crustal stresses, (ii) fluid (or magma) pressure, and (iii) the length of a fluid-filled fracture may affect its direction of propagation. We define a critical range of values for a parameter which may help identifying the path of a fluid-filled fracture propagating through the Earth crust. Our results may have important implications for volcanological studies which aim to forecast scenarios of new eruption locations.
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Machacca-Puma, R., Lesage, P., Larose, E., Lacroix, P., & Anccasi-Figueroa, R. M. (2019). Detection of pre-eruptive seismic velocity variations at an andesitic volcano using ambient noise correlation on 3-component stations: Ubinas volcano, Peru, 2014. Journal Of Volcanology And Geothermal Research, 381, 83–100.
Résumé: Volcano monitoring and eruption forecasting are based on the observation and joined interpretation of several precursory phenomena. It is thus important to detect new types of precursor and to study their relationship with forthcoming eruptions. In the last years, variations of seismic velocity have been observed in some volcanoes, mainly basaltic, before eruptions. In this paper, we look for velocity variations and waveform decorrelations before the 2014 eruptive sequence of the andesitic Ubinas volcano in Peru. We compute velocity changes by using seismic ambient noise cross-correlation (between pairs of stations) and cross-components correlation (between vertical and horizontal components of single stations), as well as coda wave interferometry of seismic multiplets. With these different approaches, we show that the major explosions that occurred from 13 to 19 April were preceded by a clear velocity decrease and waveform decorrelation. The amplitude of velocity change is generally larger on single-station cross-components correlation than on two-station cross-correlation in all the frequency ranges tested (between 0.1 and 8 Hz). We highlight an apparent anisotropy of velocity change in single station cross-components correlation, with larger amplitudes when correlating vertical and tangential components than using vertical and radial components with respect to the crater. The Mw = 8.1 Iquique earthquake on 1 April 2014 produced also a marked co-seismic velocity drop detected in a high frequency range(3-5 Hz) in both single-station cross-components correlation and cross-correlations. We locate in the horizontal plane and in depth the velocity perturbation and the structural change related with decorrelation. During the main phase of eruptive activity, the velocity decrease at low frequency (0.1-1 Hz) appears to affect the whole edifice mainly at depth of about 1 to 3 km below the surface. The structural perturbation is more concentrated on the south flank of the volcano, a zone that corresponds to an ancient collapse. We suggest that the observed velocity variations are due to the dilatation of the edifice and to microfracturation induced by magma pressurization. The structural change may be locally enhanced by a possible zone of material weakness in the southern sector. The co-seismic velocity perturbation is located mostly in the southeast flank, at depth smaller than 0.5 to 1 km, and may be related to the presence of the hydrothermal system of the volcano. (C) 2019 Elsevier B.V. All rights reserved.
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Mahaney, W. C., Somelar, P., West, A., Dirszowsky, R. W., Allen, C. C. R., Remmel, T. K., et al. (2019). Reconnaissance of the Hannibalic Route in the Upper Po Valley, Italy: Correlation with Biostratigraphic Historical Archaeological Evidence in the Upper Guil Valley, France. Archaeometry, 61(1), 242–258.
Résumé: Controversy over the alpine route taken by the Hannibalic Army from the Rhone Basin into Italia in 218 bc (2168 cal bp) has raged amongst classicists for over two millennia. Because Hannibal crossed the Alps, the significance for identifying the route taken by the Punic Army lies more in its potential for identifying sites of historical archaeological significance than a resolution of one of history's most enduring questions. While compelling stratigraphic, geochemical and microbiological evidence has been recovered from an alluvial floodplain mire in the upper Guil Valley, located below the Col de la Traversette (about 3000 masl) on the French-Italian border, it potentially identifies the invasion route as the one originally proposed by Sir Gavin de Beer in 1974. The dated layers in several sections, termed the MAD (mass animal deposition) beds based on disrupted/churned bedding and key/specialized biological components strongly supports de Beer's thesis that Hannibal chose the highest transit col into Italia. In addition to other physical evidence, we present here new physical, geomorphological and stratigraphic evidence, all calibrated by radiocarbon dating, that suggests Hannibal's imprint on the landscape exists in coalescing alluvial fans in the upper Po catchment of northern Italy.
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Mai Quyen Pham, Lacroix, P., & Doin, M. P. (2019). Sparsity Optimization Method for Slow-Moving Landslides Detection in Satellite Image Time-Series. Ieee Transactions On Geoscience And Remote Sensing, 57(4), 2133–2144.
Résumé: This paper presents a new method based on recent optimization technique to detect slow-moving landslides (<150m/year) in time series of displacement field generated by satellite images. Sparse optimization is applied simultaneously on the 3-D data set in space as well as in time. The proposed method takes into account the distinctive signal physical properties in space and time, by enforcing a sparse representation by blocks in space, but a continuing and monotonous representation in time of the landslides. As a result, we show that a mixed l(1,2)-norm is the most suitable norm for this detection problem, compared to pure l(1)-norm or l(2)-norm. Moreover, an outlier estimation step is included that sets apart the Gaussian noise from locally sparse processing errors in the data. The performance of this approach is tested by applying it both on synthetic data and on a time series of displacements fields over 16 dates in the Colca Valley, Peru. This detection presents commission and omission errors for landslides of 29% and 14%, respectively, using a medium resolution (10 m) data set of optical satellite images. It detects all important landslides, already known from field investigations. Moreover, it also points out other smaller or unknown landslides, increasing the existing slow-moving landslide inventory by +50%.
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Manceau, A. (2019). Comment on “Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles”. Acs Earth And Space Chemistry, 3(8), 1576–1580.
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Manceau, A., & Nagy, K. L. (2019). Thiols in Natural Organic Matter: Molecular Forms, Acidity, and Reactivity with Mercury(II) from First-Principles Calculations and High Energy-Resolution X-ray Absorption Near-Edge Structure Spectroscopy. Acs Earth And Space Chemistry, 3(12), 2795–2807.
Résumé: Thiol functional groups in natural organic matter form strong complexes with Hg(II) and other soft metal cations and therefore are an important component of sulfur and metal cycling in the environment. However, characterizing thiol reactivity is difficult because natural organic molecules are complex both in composition and molecular structure. Here, reactivity was assessed by calculating the Gibbs free energies of thiolation and thiol deprotonation reactions for model structures considered to form during abiotic sulfurization of natural organic matter. Gaussian calculations were performed at the CCSD(T) level of theory. Thiol addition is predicted to be faster by as much as 8 orders of magnitude on unsaturated cyclic structures rich in ketone and ether linkages than on open-chain carbonyl structures. The RIC, values of thiols added to carboxyl-rich alicyclic molecules are predicted to be above 10, whereas plc values of thiols bonded to lignin-derived polyhydroxyphenols are predicted to be between 2 and 6. Reactivity of thiols with Hg(II) was evaluated by monitoring the kinetics of transformation of Hg(SR)(2) complexes to nanoparticulate metacinnabar in dissolved organic matter with different chemical compositions under oxic conditions using high-energy-resolution X-ray absorption near-edge structure spectroscopy (HR-XANES). The most rapid transformation occurred in the material with the greatest quinone carbon (ketone) and polyphenol contents, consistent with the predicted low pK(a) values of thiolated ketones near phenolic hydroxyl groups. The slowest transformation occurred in the material with the least amount of cyclic ketone structures despite having the highest amount of thiols. These results indicate that the sulfur atoms in thiolated ketones are those that are most reactive and removed during the alkyl transfer reaction considered to nucleate metacinnabar and that the concentration of the low-pK(a) thiols controls the transformation rate.
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Manceau, A., Bustamante, P., Haouz, A., Bourdineaud, J. P., Gonzalez-Rey, M., Lemouchi, C., et al. (2019). Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy-Resolution XANES Spectroscopy. Chemistry-A European Journal, 25(4), 997–1009.
Résumé: Of all divalent metals, mercury (Hg-II) has the highest affinity for metallothioneins. Hg-II is considered to be enclosed in the alpha and beta domains as tetrahedral alpha-type Hg(4)Cys(11-12) and beta-type Hg(3)Cys(9) clusters similar to Cd-II and Zn-II. However, neither the four-fold coordination of Hg nor the existence of Hg-Hg atomic pairs have ever been demonstrated, and the Hg-II partitioning among the two protein domains is unknown. Using high energy-resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, evidence for the coexistence of two-coordinate Hg-thiolate complex and four-coordinate Hg-thiolate cluster with a metacinnabar-type (beta-HgS) structure in the alpha domain of separate metallothionein molecules from blue mussel under in vivo exposure is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the alpha domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster-forming motifs. Oligomerization is driven by metallophilic Hg center dot center dot center dot Hg interactions. Our results provide clues as to why Hg has higher affinity for the alpha than the beta domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.
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Mandic, O., Sant, K., Kallanxhi, M. - E., Coric, S., Theobalt, D., Grunert, P., et al. (2019). Integrated bio-magnetostratigraphy of the Badenian reference section Ugljevik in southern Pannonian Basin – implications for the Paratethys history (middle Miocene, Central Europe). Global And Planetary Change, 172, 374–395.
Résumé: The Central Paratethys was a large-scale Oligo-Miocene epicontinental sea located in Central and Eastern Europe. It was separated from the Mediterranean by the Alpine orogenic belt. The Paratethys progressively flooded the Pannonian back-arc basin that formed during the early to middle Miocene. Along the southern margin of the basin, the maximum extension of the Paratethys onto the flanks of the Dinarides Mountains occurred during the middle Miocene (Badenian). We have studied the most complete middle Miocene (BadenianSarmatian) Paratethys section located at this southern margin. It comprises a > 1.5 Myr long, continuous marine depositional sequence, which is highly relevant for our understanding of the interplay between global climatic and regional geodynamic perturbations in this semi-isolated epicontinental basin. The investigated record is particularly important to assess the impact of the Middle Miocene Climate Transition, the Langhian-Serravallian glacial Mi-3b event, the syn-rift climax of the Pannonian Basin and the Badenian Salinity Crisis. Moreover, we present the first high resolution age model for the regional Badenian stage based on integrated biomagnetostratigraphy. According to our age model, the marine flooding reached the area at similar to 14.15 Ma, during the regional Badenian stage. Open marine conditions persisted until similar to 12.6 Ma when the extinction of the fully marine fauna marks the beginning of the regional Sarmatian stage. Sea-level fluctuations are reflected in the section by four transgressive regressive cycles coinciding roughly with 400-kyr-eccentricity periods. The largest sea-level fall occurred after the first cycle and corresponds to the end of the Middle Miocene Climate Transition marked by glacial event Mi-3b. Elsewhere in the Pannonian Basin, this marked drop in base-level triggered deposition of evaporites during the Badenian Salinity Crisis. At Ugljevik however, there are no evaporites and the short-term Mi-3b regression was followed by a transgression and re-establishment of deeper marine conditions at 13.76 Ma, i.e. during the earliest Serravallian. Diversified planktonic and benthic assemblages suggest fully marine conditions with a persistent connection to the Mediterranean at this time. Such conditions prevailed until the mid Serravallian (latest Badenian) when sediment input increased and coastal environments prograded seawards. The Badenian/Sarmatian boundary roughly coincided with a 400-kyr-eccentricity as well as with a 1.2-Myr obliquity minimum.
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Mao, S., Campillo, M., van der Hilst, R. D., Brenguier, F., Stehly, L., & Hillers, G. (2019). High Temporal Resolution Monitoring of Small Variations in Crustal Strain by Dense Seismic Arrays. Geophysical Research Letters, 46(1), 128–137.
Résumé: We demonstrate the feasibility of detecting very weak deformation in the shallow crust with high temporal resolution by monitoring the relative changes in seismic wave velocity (dv/v) using dense arrays of seismometers. We show that the dv/v variations are consistent between independent measurements from two seismic arrays. Dominant peaks in the observed dv/v spectrum suggest that tides and temperature changes are the major causes of daily and subdaily velocity changes, in accordance with theoretical strain modeling. Our analysis illustrates that dv/v perturbations of the order of 10(-4), corresponding to crustal strain changes of the order of 10(-8), can be measured from ambient seismic noise with a temporal resolution of 1hr. This represents a low-cost technique for high precision and high time-resolution monitoring of crustal deformation that is complementary to existing geodetic measurements and is instrumental in both the detection and understanding of low-amplitude precursory processes of natural catastrophic events. Plain Language Summary Theoretical and laboratory studies have shown that the onset of earthquakes, landslides, and volcanic eruptions is often preceded by a so-called initiation phase. Detecting such a precursory phenomenon will help in the prediction, early warning, or assessment of catastrophic geological events. The time scale and amplitude of these precursory evolutions are not well known, however, and their detection and characterization require monitoring techniques with both high precision and high temporal resolution. We present here an approach to monitor the elastic properties of crustal rocks using continuous recordings of ambient seismic noise by networks of dense autonomous sensors. We show that this technique allows the monitoring at a temporal resolution of 1hr for crustal strain variations of the order of 10(-8), namely, the deformation associated with tides. This technique can be used in concert with existing geodetic techniques for understanding and detecting transient crustal deformation.
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Margerin, L., Bajaras, A., & Campillo, M. (2019). A scalar radiative transfer model including the coupling between surface and body waves. Geophysical Journal International, 219(2), 1092–1108.
Résumé: To describe the energy transport in the seismic coda, we introduce a system of radiative transfer equations for coupled surface and body waves in a scalar approximation. Our model is based on the Helmholtz equation in a half-space geometry with mixed boundary conditions. In this model, Green's function can be represented as a sum of body waves and surface waves, which mimics the situation on Earth. In a first step, we study the single-scattering problem for point-like objects in the Born approximation. Using the assumption that the phase of body waves is randomized by surface reflection or by interaction with the scatterers, we show that it becomes possible to define, in the usual manner, the cross-sections for surface-to-body and body-to-surface scattering. Adopting the independent scattering approximation, we then define the scattering mean free paths of body and surface waves including the coupling between the two types of waves. Using a phenomenological approach, we then derive a set of coupled transport equations satisfied by the specific energy density of surface and body waves in a medium containing a homogeneous distribution of point scatterers. In our model, the scattering mean free path of body waves is depth dependent as a consequence of the body-to-surface coupling. We demonstrate that an equipartition between surface and body waves is established at long lapse-time, with a ratio which is predicted by usual mode counting arguments. We derive a diffusion approximation from the set of transport equations and show that the diffusivity is both anisotropic and depth dependent. The physical origin of the two properties is discussed. Finally, we present Monte Carlo solutions of the transport equations which illustrate the convergence towards equipartition at long lapse-time as well as the importance of the coupling between surface and body waves in the generation of coda waves.
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Margirier, A., Braun, J., Gautheron, C., Carcaillet, J., Schwartz, S., Jamme, R. P., et al. (2019). Climate control on Early Cenozoic denudation of. the Namibian margin as deduced from new thermochronological constraints. Earth And Planetary Science Letters, 527.
Résumé: The processes that control long term landscape evolution in continental interiors and, in particular, along passive margins such as in southern Africa, are still the subject of much debate (e.g. Braun, 2018). Although today the Namibian margin is characterized by an arid climate, it has experienced climatic fluctuations during the Cenozoic and, yet, to date no study has documented the potential role of climate on its erosion history. In western Namibia, the Brandberg Massif, an erosional remnant or inselberg, provides a good opportunity to document the Cenozoic denudation history of the margin using the relationship between rock cooling or exhumation ages and their elevation. Here we provide new apatite (UThSm)/He dates on the Brandberg Inselberg that range from 151 +/- 12 to 30 +/- 2 Ma. Combined with existing apatite fission track data, they yield new constraints on the denudation history of the margin. These data document two main cooling phases since continental break-up 130 Myr ago, a rapid one (similar to 10 degrees C/Myr) following break-up and a slower one (similar to 12 degrees C/Myr) between 65 and 35 Ma. We interpret them respectively to be related to escarpment erosion following rifting and continental break-up and as a phase of enhanced denudation during the Early Eocene Climatic Optimum. We propose that during the Early Eocene Climatic Optimum chemical weathering was important and contributed significantly to the denudation of the Namibian margin and the formation of a pediplain around the Brandberg and enhanced valley incision within the massif. Additionally, aridification of the region since 35 Ma has resulted in negligible denudation rates since that time. (C) 2019 Elsevier B.V. All rights reserved.
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Marrocchi, Y., Euverte, R., Villeneuve, J., Batanova, V., Welsch, B., Ferriere, L., et al. (2019). Formation of CV chondrules by recycling of amoeboid olivine aggregate-like precursors. Geochimica Et Cosmochimica Acta, 247, 121–141.
Résumé: We have studied porphyritic olivine-rich chondrules of the carbonaceous chondrite Kaba (CV3) by combined high-resolution X-ray mapping, quantitative electron microprobe analyses, and oxygen isotopic analyses via secondary ion mass spectrometry. These chondrules contain smaller inner-chondrule olivine grains characterized by low refractory element (Ca, Al, Ti) contents, and larger outer-chondrule olivine crystals that are enriched in refractory elements and show complex Ti and Al oscillatory zonings. Our 0 isotopic survey revealed that many of the inner-chondrule olivines are O-16-richer than the relatively isotopically uniform outer-chondrule olivines. Inner-chondrule olivine crystals only a minority of which may be derived from earlier generations of chondrules are likely mostly inherited from nebular condensates similar to AOAs, as they share similar isotopic and chemical features and are thus interpreted as relict grains. Still, being O-16-poorer than most AOAs, they may have experienced significant exchange with a O-16-poor reservoir prior to chondrule formation (even if to a lesser degree than relicts in CM2 and ungrouped C2 chondrites). Subsequent incomplete melting of the relict grains produced Ca-Al-Ti-rich melts that engulfed the remaining relict olivine grains. The complex Ti and Al zoning patterns in outer chondrule (host) olivines, in particular the systematic dilution near the margin, seem to reflect gas-melt interactions (with e.g. SiO (g), Mg (g)) which also buffered the O isotopic composition of chondrule hosts. Together, these results demonstrate that important episodes of recycling of nebular condensates occurred in the solar protoplanetary disk. (C) 2018 Elsevier Ltd. All rights reserved.
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Marsan, D., Weiss, J., Moreau, L., Gimbert, F., Doble, M., Larose, E., et al. (2019). Characterizing horizontally-polarized shear and infragravity vibrational modes in the Arctic sea ice cover using correlation methods. Journal Of The Acoustical Society Of America, 145(3), 1600–1608.
Résumé: The deployment of three drifting seismic stations on the Arctic sea ice during the winter of 2014-2015 with station inter-spacing between 30 and 80 km enables the characterization of the coherent seismic wavefield at these scales through the use of array methods. Two distinct vibrational modes are observed, corresponding to the fast and non-dispersive horizontally-polarized shear (SH) mode and the slow and dispersive flexural, infragravity mode (ice swell). The excitation of these two modes is not synchronous. The activation of the infragravity mode is linked to the arrival of energetic, dispersive wavetrains that can be readily seen on individual spectrograms, and that, as previous studies have shown, are likely to have their origins in distant storms. In contrast, the SH mode is excited at other time intervals and cannot be isolated on the recording of single stations due to the broadband and emergent nature of these wavetrains; given the horizontal polarization of these waves, the authors hypothesize that SH waves are caused by episodes of rapid SH deformation along major leads located outside the station network. The existence of horizontally-polarized waves propagating over long distances opens the possibility of monitoring ice deformation at the scale of the Arctic basin with unprecedented time resolution. (C) 2019 Acoustical Society of America.
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Matoshko, A., Matoshko, A., & de Leeuw, A. (2019). The Plio-Pleistocene demise of the East Carpathian foreland fluvial system and arrival of the paleo-Danube to the Black Sea. Geologica Carpathica, 70(2), 91–+.
Résumé: This paper studies the Porat Formation (Fm.), which was deposited along the NE margin of the Dacian Basin part of the East Carpathian foreland (ECF) during the Pliocene and Early Pleistocene. We use a review of stratigraphic data in combination with lithofacies and sedimentary architecture analysis to interpret the Porat Fm. as a large sandy alluvial basin ilia with an aggradational structure, consisting of cyclic successions of shallow sandy high-energy braided rivers. Aggradation of the Porat Fan was governed by subsidence of the Dacian Basin, along with a northerly supply of water and sediment from the Carpathians. Along the southern margin of the area the fan entered the Reni lzmail-Trough, which formed the periodically active gateway between the Black Sea and Dacian basins. Along this trough, the Porat Fm. is developed in a different facies, discerned as the Dolynske Member (Mb.1), which accumulated in the channel of a large river interpreted as the paleo-Danube. According to mammal stratigraphy of the Porat Fm. this continental-scale river had reached the area by the Gelasian to early Calabrian. The Porat alluvial mull indicates a stable water supply from the Carpathians, which explains the ecologically mixed fauna in its deposits: moistened forested alluvial plain-valleys were present between the zonally semi-arid steppe interfluves. The Porat Fm. and the previously studied late Miocene Balta Fm. are key elements for further in-depth study of the terrestrial evolution (tectonic sedimentary relief) of the ECF and north-western Black Sea coastal regions.
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Mazza, S. E., Gazel, E., Bizimis, M., Moucha, R., Beguelin, P., Johnson, E. A., et al. (2019). Sampling the volatile-rich transition zone beneath Bermuda. Nature, 569(7756), 398–+.
Résumé: Intraplate magmatic provinces found away from plate boundaries provide direct sampling of the composition and heterogeneity of the Earth's mantle. The chemical heterogeneities that have been observed in the mantle are usually attributed to recycling during subduction(1-3), which allows for the addition of volatiles and incompatible elements into the mantle. Although many intraplate volcanoes sample deep-mantle reservoirs-possibly at the core-mantle boundary(4)-not all intraplate volcanoes are deep-rooted(5), and reservoirs in other, shallower boundary layers are likely to participate in magma generation. Here we present evidence that suggests Bermuda sampled a previously unknown mantle domain, characterized by silica-undersaturated melts that are substantially enriched in incompatible elements and volatiles, and a unique, extreme isotopic signature. To our knowledge, Bermuda records the most radiogenic Pb-206/Pb-204 isotopes that have been documented in an ocean basin (with Pb-206/Pb-204 ratios of 19.9-21.7) using high-precision methods. Together with low Pb-207/Pb-204 ratios (15.5-15.6) and relatively invariant Sr, Nd, and Hf isotopes, the data suggest that this source must be less than 650 million years old. We therefore interpret the Bermuda source as a previously unknown, transient mantle reservoir that resulted from the recycling and storage of incompatible elements and volatiles6-8 in the transition zone (between the upper and lower mantle), aided by the fractionation of lead in a mineral that is stable only in this boundary layer, such as K-hollandite(9,10). We suggest that recent recycling into the transition zone, related to subduction events during the formation of Pangea, is the reason why this reservoir has only been found in the Atlantic Ocean. Our geodynamic models suggest that this boundary layer was sampled by disturbances related to mantle flow. Seismic studies and diamond inclusions(6,7) have shown that recycled materials can be stored in the transition zone(11). For the first time, to our knowledge, we show geochemical evidence that this storage is key to the generation of extreme isotopic domains that were previously thought to be related only to deep recycling.
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Mazza, S. E., Gazel, E., Bizimis, M., Moucha, R., Beguelin, P., Johnson, E. A., et al. (2019). Sampling the volatile-rich transition zone beneath Bermuda (vol 569, pg 398, 2019). Nature, 571(7765), E9.
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McBeck, J., Cordonnier, B., Mair, K., & Renard, F. (2019). The evolving energy budget of experimental faults within continental crust: Insights from in situ dynamic X-ray microtomography. Journal Of Structural Geology, 123, 42–53.
Résumé: We investigate the evolving distribution of strain produced by a sliding fault within intact crystalline rock, and the energetics of deformation that occur both on- and off-fault. We slid precut faults of differing roughness oriented at 45 degrees to sigma(1) while acquiring in situ X-ray microtomograms. Digital volume correlation of tomograms provide estimates of the 3D displacement and strain fields. This characterization of the strain tensor field reveal that the differing fault roughness produced distinct slip behavior, degree of strain localization and accumulation, and energy budget partitioning. The rougher fault slipped more episodically, hosted a wider and more asymmetric damage zone, and accommodated less normal and shear strain. This fault consumed more energy in off-fault deformation (W-int) per volume and more energy in frictional slip (W-fric) as portions of the total energy input to the system (W-ext) than the smoother fault. In both experiments, W-fric consumed the largest portion of the energy budget (50-100%), while W-int consumed smaller percentages (5-20%). Tracking the temporal variability of energy partitioning revealed how evolving fault architecture determined the energetic dominance of particular deformational processes, and so highlighted the importance of tracking energy partitioning through time.
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McBeck, J., Kandula, N., Aiken, J. M., Cordonnier, B., & Renard, F. (2019). Isolating the Factors That Govern Fracture Development in Rocks Throughout Dynamic In Situ X-Ray Tomography Experiments. Geophysical Research Letters, 46(20), 11127–11135.
Résumé: Centuries of work have highlighted the importance of several characteristics on fracture propagation. However, the relative importance of each characteristic on the likelihood of propagation remains elusive. We rank this importance by performing dynamic X-ray microtomography experiments that provide unique access to characteristics of evolving fracture networks as rocks are triaxially compressed toward failure. We employed a machine learning technique based on logistic regression analysis to predict whether or not a fracture grows from 14 fracture geometry and network characteristics identified throughout four experiments on crystalline rocks in which thousands of fractures propagated. The characteristics that best predict fracture growth are the length, thickness, volume, and orientation of fractures with respect to the external stress field and the distance to the closest neighboring fracture. Growing fractures tend to be more clustered, shorter, thinner, volumetrically smaller, and dipping closer to 30-60 degrees from the maximum compression direction than closing fractures.
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McBeck, J., Mair, K., & Renard, F. (2019). How Porosity Controls Macroscopic Failure via Propagating Fractures and Percolating Force Chains in Porous Granular Rocks. Journal Of Geophysical Research-Solid Earth, 124(9), 9920–9939.
Résumé: This contribution aims to illuminate the micromechanisms that control the macroscopic failure of porous, granular, and cohesive rocks. With discrete element method simulations, we triaxially compress cohesive granular models composed of interlocking breakable grains, similar to sandstone and oolitic limestone. We track the morphology of the force network and the resulting spatiotemporal fracture distribution. To shed light on the varying applicability of the pore-emanated and Hertzian fracture models, we focus on differences in the micromechanics that develop between and within grains. For 5-20% porosity rocks, the cement between grains develops 10-50% higher mean forces than material within grains. Force chains that support the highest system-spanning forces are more localized prior to failure in 20% porosity rocks and are more diffusely spread in 5% porosity rocks. Confining stress reduces this localization, similar to the impact of confining stress on the macroscopic expression of brittle failure. The magnitude and rate of fracture development relative to the axial strain or axial stress increase toward failure, consistent with experimental observations. In contrast, the rate of fracture development relative to the amount of external work done on the system, W-ext, is approximately constant. Higher porosity rocks require lower inputs of W-ext to produce the same degree of fracturing. Decreasing the cement strength promotes fracture development within the cement, revealing the dominance of intergranular, pore-emanated fractures. These simulations provide predictions about how porosity controls the persistence of the stress field, with implications on the sequential development of deformation bands, and other deformational processes that modify porosity.
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McBeck, J., Mair, K., & Renard, F. (2019). Linking macroscopic failure with micromechanical processes in layered rocks: How layer orientation and roughness control macroscopic behavior. Tectonophysics, 750, 229–242.
Résumé: To constrain the impact of preexisting mechanical weaknesses on strain localization culminating in macroscopic shear failure, we simulate triaxial compression of layered sedimentary rock using three-dimensional discrete element method simulations. We develop a novel particle packing technique that builds layered rocks with preexisting weaknesses of varying orientations, roughness, and surface area available for slip. We quantify how the geomechanical behavior, characterized by internal friction coefficient, mu(o), and failure strength, sigma(F), vary as a function of layer orientation, theta, interface roughness, and total interface area. Failure of the simulated sedimentary rocks mirrors key observations from laboratory experiments on layered sedimentary rock, including minima sigma(F) and mu(o) for layers oriented at 30 degrees with respect to the maximum compressive stress, sigma(1), and maxima sigma(F), and mu(o) for layers oriented near 0 degrees and 90 degrees to sigma(1). The largest changes in sigma(F), (66%) and mu(o) (20%) occur in models with the smoothest interfaces and largest interface area. Within the parameter space tested, layer orientation exerts the most significant impact on sigma(F), and mu(o). These simulations allow directly linking micromechanical processes observed within the models to macroscopic failure behavior. The spatial distributions of nucleating microfractures, and the rate and degree of strain localization onto preexisting weaknesses, rather than the host rock, are systematically linked to the distribution of failure strengths. Preexisting weakness orientation more strongly controls the degree and rate of strain localization than the imposed confining stress within the explored parameter space. Using the upper and lower limits of mu(o) and sigma(F), obtained from the models, estimates of the Coulomb shear stress required for failure of intact rock within the upper seismogenic zone (7 km) indicates that a rotation of 30 degrees of sigma(1) relative to the weakness orientation may reduce the shear stress required for failure by up to 100 MPa.
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McBeck, J. A., Cordonnier, B., Vinciguerra, S., & Renard, F. (2019). Volumetric and Shear Strain Localization in Mt. Etna Basalt. Geophysical Research Letters, 46(5), 2425–2433.
Résumé: To examine the impact of preexisting weaknesses on fracture coalescence during volcanic edifice deformation, we triaxially compressed Mount Etna basalt while acquiring in situ dynamic X-ray microtomograms and calculated the internal strain tensor fields using image correlation. Contraction localization preceded dilation and shear strain localization into the protofault zone. This onset of strain localization preceded macroscopic yielding and coincided with increases in the magnitude and volume of rock experiencing dilation, and spatial clustering of the strain populations. The exploitation of weaknesses by propagating fractures enabled the dominant shear strain to switch senses as propagating fractures lengthened along 30-60 degrees from sigma(1). Scanning electron microscopy images reveal pore-emanated fractures, and fractures linking pores. These experiments provide evidence of internal contraction preceding dilation and shear, consistent with inferences from field and laboratory observations. The transition from contraction to dilation may provide a precursory signal of volcanic flank eruption. Plain language summary Directly observing how rocks break at seismogenic depths in natural settings is at present impossible. Here we used X-ray imaging techniques to view deforming, and then breaking, basaltic rocks at stress conditions equivalent to the flanks of the upper part of the Mount Etna volcano. We tracked how preexisting weaknesses, including pores and fractures produced during the fast cooling of the lava, controlled the growth and coalescence of new fractures and faults. At 50% of the stress at failure, shear and dilative strains began to concentrate in the volume that eventually developed the largest connected fracture network. The localization of contractive strains preceded this shear and dilation localization. These data sets provide observations of fracture growth within Etna basalt that previous studies could only infer, and thus constraints on how the volcanic edifice deforms under magmatic and tectonic stresses and eventually ruptures in flank eruptions.
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McNeill, L. C., Shillington, D. J., Carter, G. D. O., Everest, J. D., Gawthorpe, R. L., Miller, C., et al. (2019). High-resolution record reveals climate-driven environmental and sedimentary changes in an active rift (vol 9, 3116, 2019). Scientific Reports, 9.
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McNeill, L. C., Shillington, D. J., Carter, G. D. O., Everest, J. D., Gawthorpe, R. L., Miller, C., et al. (2019). High-resolution record reveals climate-driven environmental and sedimentary changes in an active rift. Scientific Reports, 9.
Résumé: Young rifts are shaped by combined tectonic and surface processes and climate, yet few records exist to evaluate the interplay of these processes over an extended period of early rift-basin development. Here, we present the longest and highest resolution record of sediment flux and paleoenvironmental changes when a young rift connects to the global oceans. New results from International Ocean Discovery Program (IODP) Expedition 381 in the Corinth Rift show 10s-100s of kyr cyclic variations in basin paleoenvironment as eustatic sea level fluctuated with respect to sills bounding this semi-isolated basin, and reveal substantial corresponding changes in the volume and character of sediment delivered into the rift. During interglacials, when the basin was marine, sedimentation rates were lower (excepting the Holocene), and bioturbation and organic carbon concentration higher. During glacials, the basin was isolated from the ocean, and sedimentation rates were higher (similar to 2-7 times those in interglacials). We infer that reduced vegetation cover during glacials drove higher sediment flux from the rift flanks. These orbital-timescale changes in rate and type of basin infill will likely influence early rift sedimentary and faulting processes, potentially including syn-rift stratigraphy, sediment burial rates, and organic carbon flux and preservation on deep continental margins worldwide.
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Meger, N., Rigotti, C., Pothier, C., Tuan Nguyen, Lodge, F., Gueguen, L., et al. (2019). Ranking evolution maps for Satellite Image Time Series exploration: application to crustal deformation and environmental monitoring. Data Mining And Knowledge Discovery, 33(1), 131–167.
Résumé: Satellite Image Time Series (SITS) are large datasets containing spatiotemporal information about the surface of the Earth. In order to exploit the potential of such series, SITS analysis techniques have been designed for various applications such as earthquake monitoring, urban expansion assessment or glacier dynamic analysis. In this paper, we present an unsupervised technique for browsing SITS in preliminary explorations, before deciding whether to start deeper and more time consuming analyses. Such methods are lacking in today's analyst toolbox, especially when it comes to stimulating the reuse of the ever growing list of available SITS. The method presented in this paper builds a summary of a SITS in the form of a set of maps depicting spatiotemporal phenomena. These maps are selected using an entropy-based ranking and a swap randomization technique. The approach is general and can handle either optical or radar SITS. As illustrated on both kinds of SITS, meaningful summaries capturing crustal deformation and environmental phenomena are produced. They can be computed on demand or precomputed once and stored together with the SITS for further usage.
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Merkulova, M., Mathon, O., Glatzel, P., Rovezzi, M., Batanova, V., Marion, P., et al. (2019). Revealing the Chemical Form of “Invisible” Gold in Natural Arsenian Pyrite and Arsenopyrite with High Energy-Resolution X-ray Absorption Spectroscopy. Acs Earth And Space Chemistry, 3(9), 1905–1914.
Résumé: The structural chemistry of gold in arsenian pyrite (FeS2) and arsenopyrite (FeAsS) is as yet unknown, despite the economic importance of this element and its potential recovery from low-grade ores and mine tailings. The systematic co-occurrence of Au and As poses a challenge for measuring the Au L-3-edge X-ray absorption spectra because the Au L alpha emission line is partly (pyrite) to totally (arsenopyrite) obscured by the intense As K alpha line. Utilizing a newly developed high luminosity multicrystal analyzer, in combination with the capabilities of a synchrotron-based microprobe, the Au L alpha and As K alpha lines were separated, and the Au L-3-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra of chemically bound Au in arsenian pyrite and arsenopyrite from gold deposits were measured for the first time. High energy-resolution XANES (HR-XANES) shows that gold has a formal oxidation state of 1+ in the two sulfides, but a distinct bonding environment. In arsenian pyrite with a point Au/As atomic ratio of 0.14 (0.37 wt ratio) and lacking geochemical correlation between the concentrations of Au and As, Au occupies the Fe site and is bonded to six S atoms at 2.41 angstrom, as determined by HR-EXAFS. In contrast, in arsenopyrite with a point Au/As atomic ratio of 7.1 x 10(-3) (0.02 wt ratio) and exhibiting a Au-As correlation, octahedrally coordinated Au is bonded only to As atoms at 2.52 angstrom. The results reveal the atomic-scale structure of gold and its intricate geochemical association with arsenic in auriferous Fe sulfides. This work demonstrates that high energy-resolution X-ray absorption spectroscopy on synchrotron X-ray microprobes can illuminate the structural chemistry of trace elements in chemically complex Earth and planetary materials.
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Merkulova, M., Murdzek, M., Mathon, O., Glatzel, P., Batanova, V., & Manceau, A. (2019). Evidence for syngenetic micro-inclusions of As3+- and As5+-containing Cu sulfides in hydrothermal pyrite. American Mineralogist, 104(2), 300–306.
Résumé: Most frequently arsenic is nominally monovalent (As1-) in pyrite (FeS2) and substituted for S. Nominally trivalent arsenic (As3+) has been reported previously in hydrothermal Peruvian pyrite and was considered to be substituted for Fe based on the negative correlation between the concentrations of the two elements. Here, we provide the first observation of the incorporation of As3+ in goldfieldite [Cu-12(As,Sb,Bi)(2)Te2S13] and As5+ in colusite [Cu26V2(As,Sb)(4)Sn2S32] inclusions in As1--pyrite from high-sulfidation deposits in Peru. This information was obtained by combining spatially resolved electron probe (EPMA), synchrotron-based X-ray fluorescence (SXRF), and absorption spectroscopy (micro-XANES and micro-EXAFS) with new high energy-resolution XANES spectroscopy (HR-XANES). The two Cu sulfide inclusions range from several to one hundred micrometers in size, and the As3+/As5+ concentration varies from a few parts per million (ppm) to a maximum of 17.33 wt% compared to a maximum of 50 ppm As1- in pyrite. They also contain variable amounts of Sn (18.47 wt% max), Te (15.91 wt% max), Sb (8.54 wt% max), Bi (5.53 wt% max), and V (3.25 wt% max). The occurrence of As3+/As5+-containing sulfosalts in As1--containing pyrite grains indicates that oxidizing hydrothermal conditions prevailed during the late stage of the mineralization process in the ore deposits from Peru. From an environmental perspective, high concentrations of potentially toxic As, contained in what appear to be non-As-bearing pyrite, may pose a heretofore unrecognized threat to ecosystems in acid mine drainage settings. More generally, the combination of techniques used in this study offers a new perspective on the mineralogy and crystal chemistry of hazardous elements in pyrite, such as highly toxic and little studied thallium.
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Metivier, L., Brossier, R., Merigot, Q., & Oudet, E. (2019). A graph space optimal transport distance as a generalization of L-p distances: application to a seismic imaging inverse problem. Inverse Problems, 35(8).
Résumé: Optimal transport distance is an appealing tool to measure the discrepancy between datasets in the frame of inverse problems, for its ability to perform global comparisons and its convexity with respect to shifted patterns in the compared quantities. However, solving inverse problems might require to compare signed quantities, while the optimal transport theory has been developed for the comparison of probability measures. In this study we propose to circumvent this difficulty by applying optimal transport to the comparison of the graph of the data rather than the data itself. We investigate this approach in the frame of seismic imaging, where each channel of the oscillatory data is interpreted as a discrete point cloud. We demonstrate that the corresponding misfit function can be computed through the solution of series of linear sum assignment problem (LSAP), while, based on the adjoint state technique, its gradient can be computed from the assignment solution of these LSAP. We illustrate how this approach yields a convex misfit function in the frame of seismic imaging using the full waveform. We show how an efficient strategy, based on a specific LSAP solver, the auction algorithm, can be designed. We illustrate the interest of the approach on a realistic 2D visco-acoustic seismic imaging problem. The proposed strategy relaxes the constraint on the accuracy of the initial model, outperforming the conventional least-squares approach and a previously proposed optimal transport based approach. The computational time increases by only a few percents compared with the least-squares approach, opening the way to applications to 3D field data in the near future.
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Molinari, A., & Perfettini, H. (2019). Fundamental aspects of a new micromechanical model of rate and state friction. Journal Of The Mechanics And Physics Of Solids, 124, 63–82.
Résumé: The foundations of a new micromechanical model of rate and state friction are established. Based on the assumption that the relative sliding of two material surfaces is accommodated by the viscoplastic deformation of junctions in their entire volume, the model parameters are characterized in terms of loading conditions, geometrical contact characteristics and rheological properties of the bulk material. A relationship is established between the state parameter of the friction law and the mean microscopic normal stress exerted on the real contact area. Original results are obtained for the transition from stable to unstable slip regimes and applications to geological faults are considered. (C) 2018 Elsevier Ltd. All rights reserved.
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Monville, R., Vidal, J., Cebron, D., & Schaeffer, N. (2019). Rotating double-diffusive convection in stably stratified planetary cores. Geophysical Journal International, 219, S195–S218.
Résumé: In planetary fluid cores, the density depends on temperature and chemical composition, which diffuse at very different rates. This leads to various instabilities, bearing the name of double-diffusive convection (DDC). We investigate rotating DDC (RDDC) in fluid spheres. We use the Boussinesq approximation with homogeneous internal thermal and compositional source terms. We focus on the finger regime, in which the thermal gradient is stabilizing whereas the compositional one is destabilizing. First, we perform a global linear stability analysis in spheres. The critical Rayleigh numbers drastically drop for stably stratified fluids, yielding large-scale convective motions where local analyses predict stability. We evidence the inviscid nature of this large-scale double-diffusive instability, enabling the determination of the marginal stability curve at realistic planetary regimes. In particular, we show that in stably stratified spheres, the Rayleigh numbers Ra at the onset evolve like Ra similar to Ek(-1), where Ek is the Ekman number. This differs from rotating convection in unstably stratified spheres, for which Ra similar to Ek(-4/3). The domain of existence of inviscid convection thus increases as Ek(-1/3). Secondly, we perform non-linear simulations. We find a transition between two regimes of RDDC, controlled by the strength of the stratification. Furthermore, far from the RDDC onset, we find a dominating equatorially antisymmetric, large-scale zonal flow slightly above the associated linear onset. Unexpectedly, a purely linear mechanism can explain this phenomenon, even far from the instability onset, yielding a symmetry breaking of the non-linear flow at saturation. For even stronger stable stratification, the flow becomes mainly equatorially symmetric and intense zonal jets develop. Finally, we apply our results to the early Earth core. Double diffusion can reduce the critical Rayleigh number by four decades for realistic core conditions. We suggest that the early Earth core was prone to turbulent RDDC, with large-scale zonal flows.
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Mordret, A., Roux, P., Boue, P., & Ben-Zion, Y. (2019). Shallow three-dimensional structure of the San Jacinto fault zone revealed from ambient noise imaging with a dense seismic array. Geophysical Journal International, 216(2), 896–905.
Résumé: We use 1 month of continuous seismic waveforms from a very dense seismic network to image with unprecedented resolution the shallow damage structure of the San Jacinto fault zone across the Clark fault strand. After calculating noise correlations, high apparent velocity arrivals coming from below the array are removed using a frequency-wavenumber filter. This is followed by a double-beamforming analysis on multiple pairs of subarrays to extract phase and group velocity information across the study area. The phase and group velocity dispersion curves are regionalized into phase and group velocity maps at different frequencies, and these maps are inverted using a neighbourhood algorithm to build a 3-D shear wave velocity model around the Clark fault down to approximate to 500m depth. The model reveals strong lateral variations across the fault strike with pronounced low-velocity zones corresponding to a local sedimentary basin and a fault zone trapping structure. The results complement previous earthquake- and seismic noise-based imaging of the fault zone at greater depth and clarify properties of structural features near the surface.
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Mukherjee, A., Gupta, S., Coomar, P., Fryar, A. E., Guillot, S., Verma, S., et al. (2019). Plate tectonics influence on geogenic arsenic cycling: From primary sources to global groundwater enrichment. Science Of The Total Environment, 683, 793–807.
Résumé: More than 100 million people around the world are endangered by geogenic arsenic (As) in groundwater, residing in sedimentary aquifers. However, not all sedimentary aquifers are groundwater As enriched, and the ultimate source of As in enriched aquifer sediments is yet-unknown, globally. A reconnaissance of the major aquifers suggests that major As enriched aquifers are predictably systematic on a global scale, existing in sedimentary foreland basins in the vicinity of modern or ancient orogenic systems. In conformity with the Principle of Uniformitarianism, we demonstrate that the groundwater As comes from magmatic arcs (primary source) in present (e.g. Andes) or ancient (e.g. Himalaya) continental convergent margins of some of the most prominent orogenic systems across the globe, and ends up in sediments (secondary source) in adjoining foreland or related basins that eventually act as aquifers. These arc magmas scavenge As while rising through the deep continental crust. Erosion of such orogens ultimately increases the bulk As content in sediments of adjoining basins, leading to groundwater As enrichment in downstream aquifers. Such As-polluted aquifers are eventually extensively used for groundwater exploitation, for drinking and other human purposes. Surface geological and biogeochemical processes, like redox reactions, are conducive to such groundwater As enrichment. We suggest this model by integrating our study of long-time observations in Himalayan and Andean basin aquifers, and generalizing 63 major aquifers across the globe, to demonstrate the source-to-sink transport of As, thereby delineating it's geogenic cycling in the subsurface. This work outlines the specifics of the mechanisms that would drive the processes of groundwater As enrichment across spatio-temporal scales, i.e. tectonic-scale taking place over millions of years on continental-scale and groundwater pollution taking place at human time-scales on village to household scale. Thus, in this work, we demonstrate a direct evidence of connectivity between global geological processes and individual human health. (C) 2019 Elsevier B.V. All rights reserved.
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Murray, K. E., Reiners, P. W., Thomson, S. N., Robert, X., & Whipple, K. X. (2019). The Thermochronologic Record Of Erosion And Magmatism In The Canyonlands Region Of The Colorado Plateau. American Journal Of Science, 319(5), 339–380.
Résumé: The Cenozoic history of crustal deformation, surface uplift, and erosion of the central Colorado Plateau (southwestern USA) is distinct from and relatively poorly understood compared with surrounding regions in the North American Cordillera, including the Grand Canyon region and the southwestern Plateau margin. Here, we present new apatite thermochronologic results from Paleozoic-Mesozoic sandstones sampled in the Canyonlands region-the interior of the Colorado Plateau in southeastern Utah. The apatite (U-Th-Sm)/He (He) ages are highly dispersed, with both positive-slope and negative-slope age-effective U (eU) trends. Samples with apatite He results suitable for thermal history modeling are from the Abajo and La Sal mountains intrusive complexes and the Permian, Triassic, and Jurassic rocks sampled near the Colorado River at Lees Ferry, Arizona, and Hite, Utah. Samples with the richest thermal history information have positive-slope apatite He age-[eU] trends, with ages ca. 10 to 5 Ma at [eU] < 10 ppm and ca. 25 to 20 Ma at [eU] > 60 ppm. Modeled thermal histories that best predict this pattern require two periods of rock cooling: one during the middle Cenozoic ca. 30 to 20 Ma and the other since the latest Miocene ca. 6 Ma. The most recent cooling documents the transition from a slowly eroding Miocene landscape to recent rapid erosion that likely postdates 6 Ma and the integration of the modern Colorado River. Middle Cenozoic rock cooling can be attributed to either similar to 1 km of erosion between ca. 25 and 15 Ma, as previous workers have suggested in other parts of the Colorado Plateau region, or relaxation of a geothermal gradient transiently doubled by magmatism associated with the vigorous magmatic flare-up that swept through the region ca. 34 to 20 Ma. The ambiguity of using middle Cenozoic rock cooling as a proxy for erosion in this region means that this event should be described using a nongenetic term: the Middle Cenozoic Cooling Event.
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Myagkiy, A., Golfier, F., Truche, L., & Cathelineau, M. (2019). Reactive Transport Modeling Applied to Ni Laterite Ore Deposits in New Caledonia: Role of Hydrodynamic Factors and Geological Structures in Ni Mineralization. Geochemistry Geophysics Geosystems, 20(3), 1425–1440.
Résumé: This study is devoted to understanding the impact of topography and hydrodynamics on the formation of high-grade supergene nickel deposits. The investigation proposes a new conceptual mineralization model that describes the formation of various exceptionally Ni-enriched hot spots observed in lateritic profiles. Numerical analysis of the effects of local hydrodynamics on deposits formation is performed by means of PHREEQC geochemical simulator and COMSOL Multiphysics software. These are coupled through an iCP Java interface that allows to code their level of interaction and facilitates the exchange of parameters. The model developed extends the currently existing geochemical formulation of nickeliferous laterite formation from peridotite carried out in 1-D and is additionally capable of simulating mass solute transport and geochemical processes within complex fractured-porous systems. The simulations improve our understanding of metal enrichment in saprolite and bedrock zones. It was shown that, although the initial development of nickel lateritic ores takes a few million years, they are prone to relatively quick leaching and subsequent redistribution of Ni when the topography changes in response to tectonic processes. The latter leads to the formation of rich nickel deposits at the bottom of the slope, mostly due to leaching of the saprolite material. In addition to the role of changes in topography, the critical impact of fractures and fracture networks on metal mobility and distribution was identified. The model developed provides significant insight into the distribution of mineral resources, in particular Ni deposits, and can be of great help for future mineral prospecting in industry.
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Narcisi, B., Petit, J. R., Delmonte, B., Batanova, V., & Savarino, J. (2019). Multiple sources for tephra from AD 1259 volcanic signal in Antarctic ice cores. Quaternary Science Reviews, 210, 164–174.
Résumé: Strong volcanic signals simultaneously recorded in polar ice sheets are commonly assigned to major low-latitude eruptions that dispersed large quantities of aerosols in the global atmosphere with the potential of inducing climate perturbations. Parent eruptions responsible for specific events are typically deduced from matching to a known volcanic eruption having coincidental date. However, more robust source linkage can be achieved only through geochemical characterisation of the airborne volcanic glass products (tephra) sometimes preserved in the polar strata. We analysed fine-grained tephra particles extracted from layers of the AD 1259 major bipolar volcanic signal in four East Antarctic ice cores drilled in different widely-spaced locations on the Antarctic Plateau. The very large database of glass-shard geochemistry combined with grain size analyses consistently indicate that the material was sourced from multiple distinct eruptions. These are the AD 1257 mega-eruption of Samalas volcano in Indonesia, recently proposed to be the single event responsible for the polar signal, as well as a newly-identified Antarctic eruption, which occurred in northern Victoria Land in AD 1259. Finally, a further eruption that took place somewhere outside of Antarctica has also contributed to tephra deposition. Our high-resolution, multiple-site approach was critical for revealing spatial heterogeneity of tephra at the continental scale. Evidence from ice-core tephra indicates recurrent explosive activity at the Antarctic volcanoes and could have implications for improved reconstruction of post-volcanic effects on climate from proxy polar records. (C) 2019 Elsevier Ltd. All rights reserved.
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Niane, B., Guedron, S., Feder, F., Legros, S., Ngom, P. M., & Moritz, R. (2019). Impact of recent artisanal small-scale gold mining in Senegal: Mercury and methylmercury contamination of terrestrial and aquatic ecosystems. Science Of The Total Environment, 669, 185–193.
Résumé: In Senegal, the environmental impact of artisanal small-scale gold mining (ASGM) using mercury (Hg) is poorly documented despite its intensification over the past two decades. We report here a complete dataset including the distribution and speciation of Hg in soil, sediment, and water in pristine and ASGM impacted sites of the Gambia River ecosystem (Kedougou region – eastern Senegal). Selective extraction showed that soils surrounding ASGM activities were contaminated with elemental Hg [Hg(0)] at concentrations up to 3.9 mg kg(-1). In the Gambia River, high total Hg (THg: 1.16 +/- 0.80 mg kg(-1)) and methylmercury (MeHg: 3.2 +/- 2.3 ng g(-1)) were also measured in sediment samples collected at ASGM sites. Along the stream, THg concentrations in sediment decrease with distance from the ASGM sites, while those of methylmercury increase downstream. The study of THg and MeHg partitioning between filtered surface water and suspended particles demonstrate that particulate transport is responsible for the downstream dissemination of the Hg contamination from ASGM sites. Sedimentation of fine particles enriched in Hg downstream ASGM sites likely favors MeHg production and accumulation in sediment. Although elemental Hg is weakly labile, surface soil erosion may also provide important and long-term Hg inputs to downstream aquatic ecosystems, where it can be oxidized and methylated. Finally, the dissemination of THg and MeHg downstream from the ASGM sites in the Gambia River may constitute a long-term source of contamination and can have a large scale impact on the aquatic ecosystem through biomagnification. (C) 2019 Elsevier B.V. All rights reserved.
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Nicoleau, L., Van Driessche, A. E. S., & Kellermeier, M. (2019). A kinetic analysis of the role of polymers in mineral nucleation. The example of gypsum. Cement And Concrete Research, 124.
Résumé: One of the major applications to be interested by the processes controlling the nucleation (and growth) of minerals are the concrete and the gypsum industries. The available theoretical framework, i.e. classical nucleation theory (CNT), has several shortcomings which limit its ability to describe the complex crystallisation pathways. To address the apparent contradiction rising from CNT in the presence of nucleation retarding polymers (i.e. increase of the interfacial energy vs. formation of emerging nucleus surface-polymer bonds), we have performed induction time experiments to study the effect of various polymers on the nucleation of gypsum (CaSO4 center dot 2H(2)O), and in parallel determined the interfacial energy between aqueous solutions of the same polymers and different faces of macroscopic gypsum crystals by means of contact angle measurements. Based on the collected data, we show that added polymers mainly alter the kinetics of the reaction and do not significantly affect the thermodynamic properties of the system.
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Nishiyama, R., Ariga, A., Ariga, T., Lechmann, A., Mair, D., Pistillo, C., et al. (2019). Bedrock sculpting under an active alpine glacier revealed from cosmic-ray muon radiography. Scientific Reports, 9.
Résumé: Mountain glaciers form landscapes with U-shaped valleys, roche moutonees and overdeepenings through bedrock erosion. However, little evidence for active glacial carving has been provided particularly for areas above the Equilibrium Line Altitude (ELA) where glaciers originate. This is mainly due to our lack of information about the shape of the bedrock underneath active glaciers in highly elevated areas. In the past years, the bedrock morphology underneath active glaciers has been studied by geophysical methods in order to infer the subglacial mechanisms of bedrock erosion. However, these comprise surveys on the glaciers' surface, from where it has been difficult to investigate the lateral boundary between the ice and the bedrock with sufficient resolution. Here we perform a muon-radiographic inspection of the Eiger glacier (Switzerland, European Alps) with the aid of cosmic-ray muon attenuation. We find a reach (600 x 300 m) within the accumulation area where strong lateral glacial erosion has cut nearly vertically into the underlying bedrock. This suggests that the Eiger glacier has profoundly sculpted its bedrock in its accumulation area. This also reveals that the cosmic-ray muon radiography is an ideal technology to reconstruct the shape of the bedrock underneath an active glacier.
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Obermann, A., Molinari, I., Metaxian, J. - P., Grigoli, F., Strauch, W., & Wiemer, S. (2019). Structure of Masaya and Momotombo volcano, Nicaragua, investigated with a temporary seismic network. Journal Of Volcanology And Geothermal Research, 379, 1–11.
Résumé: Since the end of 2013, the region around the two volcanoes Masaya and Momotombo, which includes the Nicaraguan capital Managua, has shown an unusually high seismic and volcanic activity. In December 2015, the Momotombo volcano erupted after 110 years of quiescence. Since mid-December 2015, the Masaya volcano has also shown gradually increasing activity, including the formation of a lava lake in its main crater. By adding 30 broadband stations, we had temporarily (December 2016-March 2017) densified the permanent Nicaraguan seismic network around these volcanoes to study the local seismicity and image the subsurface structure. During the observation period, we observed an overall low level of seismicity. Recorded events around Momotombo likely consist of aftershocks of the M5.5 earthquake that struck this area on September, 26th, 2016. At Masaya, we did not observe volcano-tectonic events. Using the continuous waveform recordings, we perform a 3D ambient seismic noise tomography that reveals a first image of the subsurface velocity structure below the Masaya and Momotombo volcanoes. While Momotombo shows a typical elongated low shear-wave velocity anomaly that reaches depths of about 8 km, Masaya does not show indications of a deep plumbing system. At Masaya, we have indications of a shallow (0-3 km) magmatic chamber, offset to the west and not directly below the active Santiago vent, where the crater lake is located At greater depth (3-8 km) a low velocity anomaly towards the northeast coincides in location with a modelled positive gravity anomaly and could indicate the presence of a former intrusive body. With this study we want to trigger further interest in the diverse tectonic and volcanic features of Nicaragua. Future, long-term seismic imaging and monitoring projects are of critical interest for the estimation of seismic and volcanic risks in Managua and the surroundings. (C) 2019 Elsevier B.V. All rights reserved.
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Obermann, A., Planes, T., Larose, E., & Campillo, M. (2019). 4-D Imaging of Subsurface Changes with Coda Waves: Numerical Studies of 3-D Combined Sensitivity Kernels and Applications to the Mw 7.9, 2008 Wenchuan Earthquake. Pure And Applied Geophysics, 176(3), 1243–1254.
Résumé: In the context of seismic monitoring, recent studies made successful use of seismic coda waves to image the lateral extent of medium changes. Locating the depth of the changes, however, remains a challenge. We use multiply scattered body- and surface-wave 3-D combined sensitivity kernels to address this problem. We show that we can locate velocity perturbations at depth with numerical data from elastic wave-field simulations in 3-D heterogeneous media. This procedure is then applied to assess the extent of the crustal damage due to the Mw 7.9, 2008 Wenchuan earthquake. We discuss the potential and limitations of our approach to retrieve the depth information of temporal changes occurring in heterogeneous structures.
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Olivier, G., Brenguier, F., Carey, R., Okubo, P., & Donaldson, C. (2019). Decrease in Seismic Velocity Observed Prior to the 2018 Eruption of Klauea Volcano With Ambient Seismic Noise Interferometry. Geophysical Research Letters, 46(7), 3734–3744.
Résumé: The 2018 Klauea eruption was a complex event that included deformation and eruption at the summit and along the East Rift Zone. We use ambient seismic noise interferometry to measure time-lapse changes in seismic velocity of the volcanic edifice prior to the lower East Rift Zone eruption. Our results show that seismic velocities increase in relation to gradual inflation of the edifice between 1 March and 20 April. In the 10 days prior to the 3 rd of May eruption onset, a rapid seismic velocity decrease occurs even though the summit is still inflating. We confirm that intereruptive velocity change is correlated with surface deformation, while the velocity decrease prior to eruption is likely due to accumulating damage induced by the pressure exerted by the magma reservoir on the edifice. The accumulating damage and subsequent decrease in bulk edifice strength may have facilitated increased transport of magma from the summit reservoir to the Middle East Rift Zone.
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Panahi, H., Kobchenko, M., Meakin, P., Dysthe, D. K., & Renard, F. (2019). Fluid expulsion and microfracturing during the pyrolysis of an organic rich shale. Fuel, 235, 1–16.
Résumé: During progressive burial, low permeability organic-rich shale rocks evolve chemically and physically as the temperature and stress increase and organic matter matures. The transformation of organic matter into hydrocarbon, followed by its expulsion into secondary migration pathways along which it is conveyed into reservoirs rocks, is a coupled process that involves chemical reactions, changes in volume and stress leading to the nucleation and growth of microfractures, the opening and closing of these microfractures, and fluid transport through them. Primary migration was studied using an experimental setup that was designed to measure changes in fluid pressure, which are correlated with organic matter maturation and hydrocarbon expulsion. The setup consisted of a pressurized autoclave which was externally heated. Shale samples were confined, under an initially low confining pressure and an applied differential stress (0.18 MPa), and heated to temperatures of 210-320 degrees C. Changes in temperature, static pressure (pressure measured using a linear response transducer) and dynamic fluid pressures (measured using a piezoelectric differential transducer) in the autoclave chamber were monitored and recorded during each experiment. In the higher part of the temperature range, fluid produced by kerogen maturation and the concomitant formation of microfractures increased volumetric expansion of the shale. Power spectral densities of the fluid pressure signals were calculated and a conceptual model is proposed to explain the dynamics of fluid expulsions. While a power law distribution of frequencies of pressure burst amplitudes was identified, the frequencies of time intervals between successive expulsion events (waiting times) decrease monotonically with increasing waiting time. Co-generation of gas and liquid hydrocarbon was evidenced. Several samples were imaged after kerogen maturation using X-ray microtomography, and the data confirm the existence of a percolating network of microfracture that controls the primary migration of hydro-carbons.
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Pastier, A. - M., Husson, L., Pedoja, K., Bezos, A., Authemayou, C., Arias-Ruiz, C., et al. (2019). Genesis and Architecture of Sequences of Quaternary Coral Reef Terraces: Insights From Numerical Models. Geochemistry Geophysics Geosystems, 20(8), 4248–4272.
Résumé: The variety of coral reefs morphologies highlights their sensitivities to several forcings; fossil reefs stack in sequences that are accordingly diverse. In order to understand their genesis and architectures, we devised a numerical approach, accounting for Quaternary sea level oscillations, vertical land motion, initial slope, wave erosion, and reef growth. We first test our model on the subsiding sequence of Hawaii and on the uplifting sequence of Wangi-Wangi (Sulawesi) that bears active barriers. We then construct a parametric study that we analyze based on a comprehensive yet compact description of sequences as barcodes, that depict the vertical distribution of a few geometrical characteristics (number, width, and height of the terraces and barriers). We find that geological factors suffice to explain the variety of architectures of reefal sequences at first order, regardless of additional ecosystemic processes. Vertical land motion and foundation slopes are the prime players, while reef growth rates only play a minor role. Barriers may develop both in uplift and subsidence mode, and their preservation attests for the erosional power. Last, we reappraise the genesis of sequences and find that sequences do not fingerprint discrete events of sea level oscillations but a continuous process harrowed by stochastic events: Major sea level fluctuations can be overrepresented by several terraces or conversely absent; reoccupations may yield composite terraces representing multiple events. Overall, sequences shall not be regarded as stacks of reef bodies forming during sea level highstands, which implies that the commonly assumed bijective relationship between sea level highstands and terraces shall be abandoned.
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Perfettini, H., Frank, W. B., Marsan, D., & Bouchon, M. (2019). Updip and Along-Strike Aftershock Migration Model Driven by Afterslip: Application to the 2011 Tohoku-Oki Aftershock Sequence. Journal Of Geophysical Research-Solid Earth, 124(3), 2653–2669.
Résumé: We present an analytical model based on the idea that afterslip drives seismicity: aftershocks occur when a given level of afterslip is reached in their vicinity. Afterslip is assumed to be governed by a resisting stress that increases as the logarithm of the sliding velocity. This model extends the aftershock migration model of Perfettini et al. (2018, ), limited to along-strike migration and the early postseismic phase, to any migration direction (in particular the along-dip migration) and any time of the postseismic phase. This model is able to capture most of the features of aftershock migration such as the increase of the aftershock region as the logarithm of time and the observed aftershock migration velocities. When applied to the aftershock sequence of the Tohoku-Oki earthquake, our model is able to describe the expansion of the aftershock region in both strike and dip directions together with the observed variations of migration velocities. Plain Language Summary Aftershocks are shown to migrate with time away from the rupture area of the mainshock. We present here a model based on the idea that afterslip drives aftershocks. The model is able to predict observed aftershock migrations both along the strike and dip directions of the fault. We show that the aftershock zone expand as the logarithm of time and predict apparent propagation velocities consistent with the observations. The model is able to explain most of the features of the aftershock sequence of the Tohoku-Oki earthquake.
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Perrot, V., Landing, W. M., Grubbs, R. D., & Salters, V. J. M. (2019). Mercury bioaccumulation in tilefish from the northeastern Gulf of Mexico 2 years after the Deepwater Horizon oil spill: Insights from Hg, C, N and S stable isotopes. Science Of The Total Environment, 666, 828–838.
Résumé: Mercury (Hg) concentration in fish of the Gulf of the Mexico (GoM) is a major concern due to the importance of the GoM for U.S. fisheries. The Deepwater Horizon (DWH) oil spill in April 2010 in the northern GoM resulted in large amounts of oil and dispersant released to the water column, which potentially modified Hg bioaccumulation patterns in affected areas. We measured Hg species (methylmercury (MMHg) and inorganic Hg (IHg)) concentrations, and light (C, N and S) and Hg stable isotopes in muscle and liver tissues from tilefish (Lopholatilus chamaleonticeps) sampled in 2012 and 2013 along the shelf break of the northeastern GoM. Fish located close to the mouth of the Mississippi River (MR) and northwest of the DWH well-head (47 km) showed significantly lower Hg levels in muscle and liver than fish located further northeast of the DWH (>109 km), where 98% of tilefish had Hg levels in the muscle above US consumption advisory thresholds (50% for tilefish close to the DWH). Differences in light and Hg stable isotopes signatures were observed between these two areas, showing higher delta N-15, and lower delta Hg-202, Delta Hg-199 and delta S-34 in fish close to the DWH/MR. This suggests that suspended particles from the MR reduces Hg bioavailability at the base of the GoM food chains. This phenomenon can be locally enhanced by the DWH that resulted in increased particles in the water column as evidenced by the marine snow layer in the sediments. On the other hand, freshly deposited Hg associated with organic matter in more oligotrophic marine waters enhanced Hg bioaccumulation in local food webs. Comparing Hg isotopic composition in liver and muscle of fish indicates specific metabolic response in fish having accumulated high levels of MMHg. (C) 2019 Published by Elsevier B.V.
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Petley-Ragan, A., Ben-Zion, Y., Austrheim, H., Ildefonse, B., Renard, F., & Jamtveit, B. (2019). Dynamic earthquake rupture in the lower crust. Science Advances, 5(7).
Résumé: Earthquakes in the continental crust commonly occur in the upper 15 to 20 km. Recent studies demonstrate that earthquakes also occur in the lower crust of collision zones and play a key role in metamorphic processes that modify its physical properties. However, details of the failure process and sequence of events that lead to seismic slip in the lower crust remain uncertain. Here, we present observations of a fault zone from the Bergen Arcs, western Norway, which constrain the deformation processes of lower crustal earthquakes. We show that seismic slip and associated melting are preceded by fracturing, asymmetric fragmentation, and comminution of the wall rock caused by a dynamically propagating rupture. The succession of deformation processes reported here emphasize brittle failure mechanisms in a portion of the crust that until recently was assumed to be characterized by ductile deformation.
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Phan, V. T. H., Bardelli, F., Le Pape, P., Couture, R. - M., Fernandez-Martinez, A., Tisserand, D., et al. (2019). Interplay of S and As in Mekong Delta sediments during redox oscillations. Geoscience Frontiers, 10(5), 1715–1729.
Résumé: The cumulative effects of periodic redox cycling on the mobility of As, Fe, and S from alluvial sediment to groundwater were investigated in bioreactor experiments. Two particular sediments from the alluvial floodplain of the Mekong Delta River were investigated: Matrix A (14 m deep) had a higher pyrite concentration than matrix B (7 m deep) sediments. Gypsum was present in matrix B but absent in matrix A. In the reactors, the sediment suspensions were supplemented with As(III) and SO42-, and were subjected to three full-redox cycles entailing phases of nitrogen/CO2, compressed air sparging, and cellobiose addition. Major differences in As concentration and speciation were observed upon redox cycling. Evidences support the fact that initial sediment composition is the main factor controlling arsenic release and its speciation during the redox cycles. Indeed, a high pyrite content associated with a low SO42- content resulted in an increase in dissolved As concentrations, mainly in the form of As(III), after anoxic half-cycles; whereas a decrease in As concentrations mainly in the form of As(V), was instead observed after oxic half-cycles. In addition, oxic conditions were found to be responsible for pyrite and arsenian pyrite oxidation, increasing the As pool available for mobilization. The same processes seem to occur in sediment with the presence of gypsum, but, in this case, dissolved As were sequestered by biotic or abiotic redox reactions occurring in the Fe-S system, and by specific physico-chemical condition (e.g. pH). The contrasting results obtained for two sediments sampled from the same core show that many complexes and entangled factors are at work, and further refinement is needed to explain the spatial and temporal variability of As release to groundwater of the Mekong River Delta (Vietnam). (C) 2019, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.
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Phan, V. T. H., Bernier-Latmani, R., Tisserand, D., Bardelli, F., Le Pape, P., Frutschi, M., et al. (2019). As release under the microbial sulfate reduction during redox oscillations in the upper Mekong delta aquifers, Vietnam: A mechanistic study. Science Of The Total Environment, 663, 718–730.
Résumé: The impact of seasonal fluctuations linked to monsoon and irrigation generates redox oscillations in the subsurface, influencing the release of arsenic (As) in aquifers. Here, the biogeochemical control on As mobility was investigated in batch experiments using redox cycling bioreactors and As- and SO42--amended sediment. Redox potential (E-h) oscillations between anoxic (-300-0 mV) and oxic condition (0-500 mV) were implemented by automatically modulating an admixture of N-2/CO2 or compressed air. A carbon source (cellobiose, a monomer of cellulose) was added at the beginning of each reducing cycle to stimulate the metabolism of the native microbial community. Results show that successive redox cycles can decrease arsenic mobility by up to 92% during reducing conditions. Anoxic conditions drive mainly the conversion of soluble As(V) to As(III) in contrast to oxic conditions. Phylogenetic analyses of 16S rRNA amplified from the sediments revealed the presence of sulfate and iron – reducing bacteria, confirming that sulfate and iron reduction are key factors for As immobilization from the aqueous phase. As and S K-edge X-ray absorption spectroscopy suggested the association of Fe-(oxyhydr)oxides and the importance of pyrite (FeS2(s)), rather than poorly ordered mackinawite (FeS(s)), for As sequestration under oxidizing and reducing conditions, respectively. Finally, these findings suggest a role for elemental sulfur in mediating aqueous thioarsenates formation in As-contaminated groundwater of the Mekong delta. (C) 2019 Elsevier B.V. All rights reserved.
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Phuong-Thu Trinh, Brossier, R., Metivier, L., Tavard, L., & Virieux, J. (2019). Efficient time-domain 3D elastic and viscoelastic full-waveform inversion using a spectral-element method on flexible Cartesian-based mesh. Geophysics, 84(1), R61–R83.
Résumé: Viscoelastic full-waveform inversion is recognized as a challenging task for current acquisition deployment at the crustal scale. We have developed an efficient formulation based on a time-domain spectral-element method on a flexible Cartesian-based mesh. We consider anisotropic elastic coefficients and isotropic attenuation. Complete gradient expressions including the attenuation contribution spread into those of elastic components are given in a consistent way. The influence of attenuation on the P-wave velocity reconstruction is illustrated through a toy configuration. The numerical implementation of the forward problem includes efficient matrix-vector products for solving second-order elastodynamic equations for 3D geometries: An original high-order integration for topography effects is performed at nearly no extra cost. Combined adjoint and forward field recomputation from the final state and previously saved boundary values allows the estimation of misfit gradients for density, elastic parameters, and attenuation factors with no I/O efforts. Two-level parallelism is implemented over the sources and domain decomposition, which is necessary for a realistic 3D configuration. The misfit gradient preconditioning is performed by a so-called Bessel filter using an efficient differential implementation based on finite-element ingredients on the forward mesh instead of the often-used, costly convolution approach. A 3D synthetic illustration is provided on a subset (2 x 7 x 3 km) of the SEG Advanced Modeling (SEAM) Phase II Foothills model with 4 lines of 20 sources. The structurally based Bessel filter and a simple data hierarchy strategy considering early body waves before all waves including surface waves allow a precise reconstruction of the P- and S-wavespeeds while keeping a smooth density description.
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Pilitsyna, A. V., Tretyakov, A. A., Degtyarev, K. E., Salnikova, E. B., Kotov, A. B., Kovach, V. P., et al. (2019). Early Palaeozoic metamorphism of Precambrian crust in the Zheltau terrane (Southern Kazakhstan; Central Asian Orogenic belt): P-T paths, protoliths, zircon dating and tectonic implications. Lithos, 324, 115–140.
Résumé: Palaeoproterozoic amphibole-biotite orthogneisses with a protolith age of similar to 1840 Ma and Neoproterozoic muscovite-chlorite orthogneisses with an estimated protolith age of similar to 790 Ma have been identified in the structure of the Zheltau terrane (Southern Kazakhstan; west Central Asian Orogenic belt). In addition, metasedimentary complexes represented by prevailing garnet-mica schists and subordinate muscovite-chlorite schists with obtained detrital zircon ages in the range of 604 – 2819 Ma (with two peaks at similar to 991 Ma and similar to 1082 Ma) also comprise the Zheltau terrane. In accordance with the Sm-Nd whole-rock isotopic compositions, the protolith of the observed Palaeoproterozoic orthogneisses formed as a result of a mixing of the Neoarchean crustal source with a juvenile source, whereas the formation of the Neoproterozoic orthogneisses protolith may have been related to the melting of Palaeoproterozoic crustal material. In turn, Late Mesoproterozoic – Early Neoproterozoic granitoids or felsic volcanic rocks, which formed as a result of the melting of Palaeoproterozoic continental crust, are considered as possible sources for the studied detrital zircons obtained from the schists. The terrigenous protolith of the schists from the Zheltau terrane accumulated in the range of similar to 600 to similar to 490 Ma, corresponding to the Ediacaran-Cambrian. Subduction processes in the Early Palaeozoic led to the burial of different horizons of the Zheltau terrane continental crust to significant depths; some of the complexes experienced high-pressure metamorphism at P 15 – 18 kbar; T 750 – 850 degrees C (high-pressure granulites), whereas most of the rocks were evidently metamorphosed at maximum amphibolite facies and avoided high-pressure re-equilibration. The spatial proximity of the studied metamagmatic and metasedimentary crustal complexes and similar metamorphic changes during the latest stages of retrogression imply their possible mutual exhumation from different levels during the period between 490 and 470 Ma and their following juxtaposition as a package of tectonic slices. (C) 2018 Elsevier B.V. All rights reserved.
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Plunian, F., Stepanov, R., & Verma, M. K. (2019). On uniqueness of transfer rates in magnetohydrodynamic turbulence. Journal Of Plasma Physics, 85(5).
Résumé: In hydrodynamic and MHD (magnetohydrodynamic) turbulence, formal expressions for the transfer rates rely on integrals over wavenumber triads (k, p, q) satisfying k + p + q = 0. As an example S-E(uu) (k vertical bar p, q) denotes the kinetic energy transfer rate to the mode k, from the two other modes in the triad, p and q. However as noted by Kraichnan (Phys. Rev., vol. 111, 1958, pp. 1747-1747), in S-E(uu) (k vertical bar p, q), what fraction of the energy transferred to the mode k originated from p and which from q is unknown. Such an expression is thus incongruent with the customary description of turbulence in terms of two-scale energy exchange. Notwithstanding this issue, Dar et al. (Physica D, vol. 157 (3), 2001, pp. 207-225) further decomposed these transfers into separate contributions from p-to-k and q-to-k, thus introducing the concept of mode-to-mode transfers that they applied to MHD turbulence. Doing so, they had to set aside additional transfers circulating within each triad, but failed to calculate them. In the present paper we explain how to derive the complete expressions of the mode-to-mode transfers, including the circulating transfers. We do it for kinetic energy and kinetic helicity in hydrodynamic turbulence, for kinetic energy, magnetic energy and magnetic helicity in MHD turbulence. We find that the degree of non-uniqueness of the energy transfers derived from the induction equation is a priori higher than the one derived from the Navier-Stokes equations. However, separating the contribution of magnetic advection from magnetic stretching, the energy mode-to-mode transfer rates involving the magnetic field become uniquely defined, in striking contrast to the hydrodynamic case. The magnetic helicity mode-to-mode transfer rate is also found to be uniquely defined, contrary to kinetic helicity in hydrodynamics. We find that shell-to-shell transfer rates have the same properties as mode-to-mode transfer rates. Finally calculating the fluxes, we show how the circulating transfers cancel in accordance with conservation laws.
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Poret, M., Finizola, A., Ricci, T., Ricciardi, G. P., Linde, N., Mauri, G., et al. (2019). The buried caldera boundary of the Vesuvius 1631 eruption revealed by present-day soil CO2 concentration. Journal Of Volcanology And Geothermal Research, 375, 43–56.
Résumé: Volcanic risk at Vesuvius is one of the highest in the world due to the similar to 670,000 inhabitants living in the Red Zone, the area exposed to both pyroclastic flows and tephra fallout, to be evacuated before renewal of any eruptive activity. The national emergency plan for Vesuvius builds its risk zonation on a scenario similar to the last sub-Plinian eruption, which occurred in 1631. This study aims at providing new insights on the geometry of the caldera associated with this historical eruption. The impact of past Vesuvius eruptions on present-day soil CO2 concentration has been investigated by means of an extended geochemical survey carried out for identifying the circulation pathways of hydrothermal fluids inside the volcano. We performed 4018 soil CO2 concentration measurements over the whole Somma-Vesuvius volcanic complex, covering an area of 50 km(2). Besides relatively low values, the results show a significant spatial CO2 concentration heterogeneity over Somma-Vesuvius ranging from the atmospheric value (similar to 400 ppm) up to similar to 24,140 ppm. The summit of Vesuvius shows an area with anomalous CO2 concentrations well matching the crater rim of the 1906 eruption. Along the cone flanks, secondary CO2 anomalies highlight a roughly circular preferential pathway detected along 8 radial profiles at distances between similar to 840 m and similar to 1150 m from the bottom of the present-day crater resulting from the last eruption in 1944. In depth review of the available literature highlights an agreement between this circle-like shaped anomaly and the 1631 sub-Plinian eruption caldera boundary. Indeed, based on the historical chronicles the depression produced by the 1631 eruption had a diameter of 1686 m, whereas the CO2 circular anomaly indicates a diameter of 1956 m. Finally, the results were compared with a 3-D density model obtained from a recent gravity survey that corroborates both the literature and the CO2 data in terms of potential buried structure at the base of the Vesuvius cone. (C) 2019 Elsevier B.V. All rights reserved.
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Protin, M., Schimmelpfennig, I., Mugnier, J. - L., Ravanel, L., Le Roy, M., Deline, P., et al. (2019). Climatic reconstruction for the Younger Dryas/Early Holocene transition and the Little Ice Age based on paleo-extents of Argentiere glacier (French Alps). Quaternary Science Reviews, 221.
Résumé: Investigation of Holocene extents of mountain glaciers along with the related naturally-driven climate conditions helps improve our understanding of glacier sensitivity to ongoing climate change. Here, we present the first Holocene glacial chronology in the Mont-Blanc massif (Argentiere glacier) in the French Alps, based on 25 in situ-produced cosmogenic Be-10 dates of moraines and glacial bedrocks. The obtained ages from mapped sequences of moraines at three locations reveal that the glacier retreated from its Lateglacial extent and oscillated several times between similar to 11.7 ka and similar to 10.4 ka, i.e. during the Younger Dryas/Early Holocene (YD/EH) transition, before substantially retreating at similar to 10.4 ka. Climate conditions corresponding to the past extents of Argentiere glacier during the YD/EH transition (similar to 11 ka) and the Little Ice Age (LIA) were modelled with two different approaches: by determining summer temperature differences from reconstructed ELA-rises and by using a Positive Degree Day (PDD) mass-balance model. The ELA-rise reconstructions yield a possible range of temperatures for the YD/EH transition that were lower by between 3.0 and 4.8 degrees C compared to the year 2008, depending on the choice of the ELA sensitivity to temperature. The results from the PDD model indicate temperatures lower by similar to 3.6-5.5 degrees C during the YD/EH transition than during the 1979-2002 period. For the LIA, our findings highlight the role of local precipitation changes, superimposed on the dominant temperature signal, in the detailed evolution of the glacier. Overall, this study highlights the challenge that remains in accurately inferring paleoclimate conditions from past glacier extents. (C) 2019 Elsevier Ltd. All rights reserved.
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Qi, Y., El-Kaliouby, H., Revil, A., Ahmed, A. S., Ghorbani, A., & Li, J. (2019). Three-dimensional modeling of frequency- and time-domain electromagnetic methods with induced polarization effects. Computers & Geosciences, 124, 85–92.
Résumé: Electrical conduction describes the ability of porous media to conduct electrical charges and induced polarization (IP) describes their ability to reversibly store electrical charges. An effective conductivity can be defined as a complex number with frequency-dependent components (i.e., the conductivity is also dispersive). Although IP effects have been observed in frequency- and time-domain electromagnetic (FDEM and TDEM, respectively) data for years, most FDEM and TDEM studies still treat the earth using the conductivity alone (therefore neglecting IP effects). Electromagnetic field data inversion and interpretation require a quantitative three-dimensional modeling with dispersive conductivities, which is still a challenging problem. Using the generic partial-differential-equation solver Comsol Multiphysics's application program interface (API) with Matlab, we have successfully developed three-dimensional FDEM and TDEM modeling with IP effects. Benchmarks are performed using analytical solutions and other numerical techniques. Results with and without IP effects are also compared and analyzed to illustrate the importance of taking IP effects into account. Our modeling could be of great importance in quantitatively studying IP effects in the FDEM and TDEM methods, in developing new field configurations, and also in educational purposes.
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Quesnel, B., Boiron, M. - C., Cathelineau, M., Truche, L., Rigaudier, T., Bardoux, G., et al. (2019). Nature and Origin of Mineralizing Fluids in Hyperextensional Systems: The Case of Cretaceous Mg Metasomatism in the Pyrenees. Geofluids, 2019.
Résumé: During the Albian, the hyperextension of the Pyrenean passive margin led to a hyperthinning of the continental crust and the subsequent subcontinental mantle exhumation. The giant Trimouns talc-chlorite deposit represents the most prominent occurrence of Albian metasomatism in the Pyrenees, with the occurrence of the largest talc deposit worldwide. Consequently, this deposit, which is located on a fault zone and a lithological contact, represents one of the major drains at the scale of the Pyrenees and one of the best geological targets in order to determine the origin(s) of the fluid(s) that circulated during this period. Talc-chlorite ore is characterized by the presence of brines trapped in dolomite, quartz, and calcite fluid inclusions in the vicinity of the talc-rich zone. Considered as being responsible for the formation of talc, these fluids may be interpreted in several ways: (i) primary brines expelled from Triassic evaporites, (ii) secondary brines produced through halite leaching by diagenetic/metamorphic fluids, and (iii) brines derived from seawater serpentinization of mantle rocks. Stable isotope analyses (delta C-13, delta O-18, delta D, and delta Cl-37) and Cl/Br ratio measurements in fluid inclusions and their host minerals were carried out in order to determine the origin of the fluid(s) involved in the formation of the ore deposit. The data are consistent with a primary brine origin for the mineralizing fluid, which could have been expelled from the Triassic levels. Other hypotheses have been tested, for example, the production of brines via the seawater concentration during serpentinization. The geochemical proxies used in this study provide equivocal results. The first hypothesis is by far the most realistic one considering the numerous occurrences of Trias formations nearby, their deformation during the extension, and the drainage of the expulsed brines as evidenced by the high-salinity fluid inclusions found all around the deposit. Alternatively, the exhumation of the mantle is considered as a major source of heat and stress that favored brine migration along the major shear zones. Our results fit well with brine circulation in a hyperextensional geodynamic context, which is related to the formation of the talc-chlorite ore, the thinning of the continental crust, and the exhumation of the subcontinental mantle, in accordance with recent works.
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Ramdhan, M., Widiyantoro, S., Nugraha, A. D., Metaxian, J. - P., Rawlinson, N., Saepuloh, A., et al. (2019). Detailed seismic imaging of Merapi volcano, Indonesia, from local earthquake travel-time tomography. Journal Of Asian Earth Sciences, 177, 134–145.
Résumé: Mt. Merapi, located in central Java, Indonesia, is one of the most active volcanoes in the world. It has been subjected to numerous studies using a variety of methods, including tomographic imaging, in an attempt to understand the structure and dynamics of its magmatic plumbing system. Results of previous seismic tomographic studies that include Mt. Merapi poorly constrain the location of its underlying magma source due to limited data coverage. In order to comprehensively understand the internal structure and magmatism of Mt. Merapi, a project called DOMERAPI was conducted, in which 53 broadband seismic stations were deployed around Mt. Merapi and its neighbourhood for approximately 18 months, from October 2013 to April 2015. In this study, we compare Vp, Vs, and Vp/Vs tomograms constructed using data obtained from local (DOMERAPI) and regional seismic networks with those obtained without DOMERAPI data. We demonstrate that the data from the DOMERAPI seismic network are crucial for resolving key features beneath the volcano, such as high Vp/Vs ratios beneath the Merapi summit at similar to 5 km and similar to 15 km depths, which we interpret as shallow and intermediate magma bodies, respectively. Furthermore, west-east vertical sections across Mt. Merapi, and a “dormant” (less active) volcano, Mt. Merbabu, exhibit high Vp/Vs and low Vp/Vs ratios, respectively, directly beneath their summits. This observation likely reflects the presence (for Mt. Merapi) and absence (for Mt. Merbabu) of shallow magma bodies near the surface.
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Ramdhan, M., Widiyantoro, S., Nugraha, A. D., Metaxian, J. - P., Saepuloh, A., & Daryono. (2019). Velocity Structure Beneath Merapi Volcano And Its Surroundings Based On Seismic Tomography Travel-Time Study. Riset Geologi Dan Pertambangan, 29(2), 227–238.
Résumé: The relatively short eruption period of Merapi volcano is the reason for many earth scientists to investigate the processes that occur both beneath the surface and at the top of the volcano. The DOMERAPI seismic network consisting of 53 seismic stations was installed to understand the characteristics of the main magma reservoir under the volcano with a period of data recording from October 2013 to mid-April 2015. A total of 464 earthquakes were detected by DOMERAPI seismic network with the majority of the earthquake occured outside the seismic network because the volcano was inactive at that time. The earthquakes are used to delineate the main magma reservoir beneath the volcano. The main magma reservoir was identified at a depth of 15 km below mean sea level (MSL,) which is characterized by high Vp, a high Vp/Vs ratio and low Vs. The existence of shallow magma reservoirs related to fluid percolation was also clearly identified in this study which was at a depth of less than 5 km below MSL which was characterized by low Vp, a high Vp/Vs ratio and low Vs. The existence of deep magma reservoir was not identified in this study because of the limited resolution of seismic data.
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Rat, J., Mouthereau, F., Brichau, S., Cremades, A., Bernet, M., Balvay, M., et al. (2019). Tectonothermal Evolution of the Cameros Basin: Implications for Tectonics of North Iberia. Tectonics, 38(2), 440–469.
Résumé: Constraining the way in which continental deformation is accommodated in time and space is essential to reconcile past plate movements with geological observations. Kinematic reconstructions of the Iberia-Europe plate boundary are still debated. Here we focus on an inverted Mesozoic rift basin, the Cameros basin, which is part of the Iberian chain. We use a combination of detrital low-temperature thermochronological techniques to define the time-temperature evolution of the basin from Mesozoic rifting to Cenozoic collision. Zircon fission-track analyses of Oligocene-Miocene sedimentary rocks yield two main age populations at 17010 and 10010Ma, reflecting (i) an Early Jurassic thermal event related to the Atlantic-Alpine Tethys opening and (ii) an Albo-Cenomanian thermal event related to the Bay of Biscay opening. Thermal modeling of combined zircon fission-track, apatite fission-track, and apatite (U-Th-Sm)/He data reveals that collision-related cooling of the Cameros basin started during the Paleocene (60Ma). A second cooling/exhumation phase of the basin is recorded from 35 to 25Ma. Initial cooling occurred after a protracted postrift period characterized by persistence of high geothermal gradients, a feature also recognized in the Pyrenees. Our results show that the Iberian chain shared the same Early to Late Jurassic tectonothermal evolution with the Atlantic-Alpine Tethyan rifted margins. From the Albian onward, the thermal evolution of the Cameros basin was very similar to that of the Pyrenees. This study shows that the preservation in mountain ranges of a succession of rifting events provide important clues for plate reconstructions.
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Reguzzoni, M., Rossi, L., Baldoncini, M., Callegari, I., Poli, P., Sampietro, D., et al. (2019). GIGJ: A Crustal Gravity Model of the Guangdong Province for Predicting the Geoneutrino Signal at the JUNO Experiment. Journal Of Geophysical Research-Solid Earth, 124(4), 4231–4249.
Résumé: Gravimetric methods are expected to play a decisive role in geophysical modeling of the regional crustal structure applied to geoneutrino studies. GIGJ (GOCE Inversion for Geoneutrinos at JUNO) is a 3-D numerical model constituted by 46x10(3) voxels of 50x50x0.1km, built by inverting GOCE (Gravity field and steady-state Ocean Circulation Explorer) gravimetric data over the 6 degrees x4 degrees area centered at the JUNO (Jiangmen Underground Neutrino Observatory) experiment, currently under construction in the Guangdong Province (China). The a priori modeling is based on the adoption of deep seismic sounding profiles, receiver functions, teleseismic P wave velocity models, and Moho depth maps, according to their own accuracy and spatial resolution. The inversion method allowed for integrating GOCE data with the a priori information and some regularization conditions through a Bayesian approach and a stochastic optimization. GIGJ fits the highly accurate and homogeneously distributed GOCE gravity data with a 1 mGal standard deviation of the residuals, compatible with the observation accuracy. GIGJ provides a site-specific subdivision of the crustal layers masses, of which uncertainties include estimation errors, associated to the gravimetric solution, and systematic uncertainties, related to the adoption of a fixed sedimentary layer. A consequence of this local rearrangement of the crustal layer thicknesses is a 21% reduction and a 24% increase of the middle and lower crust geoneutrino signal, respectively. The geophysical uncertainties of geoneutrino signals at JUNO produced by unitary uranium and thorium abundances distributed in the upper, middle, and lower crust are reduced by 77%, 55%, and 78%, respectively. The numerical model is available at this site (http://www.fe.infn.it/radioactivity/GIGJ).
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Renard, F., McBeck, J., Cordonnier, B., Zheng, X., Kandula, N., Sanchez, J. R., et al. (2019). Dynamic In Situ Three-Dimensional Imaging and Digital Volume Correlation Analysis to Quantify Strain Localization and Fracture Coalescence in Sandstone. Pure And Applied Geophysics, 176(3), 1083–1115.
Résumé: Advances in triaxial compression deformation apparatus design, dynamic X-ray microtomography imaging, data analysis techniques, and digital volume correlation analysis provide unparalleled access to the insitu four-dimensional distribution of developing strain within rocks. To demonstrate the power of these new techniques and acquire detailed information about the micromechanics of damage evolution, deformation, and failure of porous rocks, we deformed 3-cm-scale cylindrical specimens of low-porosity Fontainebleau sandstone in an X-ray-transparent triaxial compression apparatus, and repeatedly recorded three-dimensional tomograms of the specimens as the differential stress was increased until macroscopic failure occurred. Experiments were performed at room temperature with confining pressure in the range of 10-20MPa. Distinct grayscale subsets, indicative of density, enabled segmentation of the three-dimensional tomograms into intact rock matrix, pore space, and fractures. Digital volume correlation analysis of pairs of tomograms provided time series of three-dimensional incremental strain tensor fields throughout the experiments. After the yield stress was reached, the samples deformed first by dilatant opening and propagation of microfractures, and then by shear sliding via grain rotation and strain localization along faults. For two samples, damage and dilatancy occurred by grain boundary opening and then a sudden collapse of the granular rock framework at failure. For the third sample, a fault nucleated near the yield point and propagated in the sample through the development of transgranular microfractures. The results confirm findings of previous experimental studies on the same rock and provide new detailed quantifications of: (1) the proportion of shear versus dilatant strain in the sample, (2) the amount of dilatancy due to microfracture opening versus pore opening when a fault develops, and (3) the role of grain boundaries and pore walls in pinning microfracture propagation and slowing down the rate of damage accumulation as failure is approached. Our study demonstrates how the combination of high-resolution insitu dynamic X-ray microtomography imaging and digital volume image correlation analysis can be used to provide additional information to unravel brittle failure processes in rocks under stress conditions relevant to the upper crust.
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Renard, F., McBeck, J., Kandula, N., Cordonnier, B., Meakin, P., & Ben-Zion, Y. (2019). Volumetric and shear processes in crystalline rock approaching faulting. Proceedings Of The National Academy Of Sciences Of The United States Of America, 116(33), 16234–16239.
Résumé: Understanding the approach to faulting in continental rocks is critical for identifying processes leading to fracturing in geomaterials and the preparation process of large earthquakes. In situ dynamic X-ray imaging and digital volume correlation analysis of a crystalline rock core, under a constant confining pressure of 25 MPa, are used to elucidate the initiation, growth, and coalescence of microfractures leading to macroscopic failure as the axial compressive stress is increased. Following an initial elastic deformation, microfractures develop in the solid, and with increasing differential stress, the damage pervades the rock volume. The creation of new microfractures is accompanied by propagation, opening, and closing of existing microfractures, leading to the emergence of damage indices that increase as powers of the differential stress when approaching failure. A strong spatial correlation is observed between microscale zones with large positive and negative volumetric strains, microscale zones with shears of opposite senses, and microscale zones with high volumetric and shear strains. These correlations are attributed to microfracture interactions mediated by the heterogeneous stress field. The rock fails macroscopically as the microfractures coalesce and form a geometrically complex 3D volume that spans the rock sample. At the onset of failure, more than 70% of the damage volume is connected in a large fracture cluster that evolves into a fault zone. In the context of crustal faulting dynamics, these results suggest that evolving rock damage around existing locked or future main faults influences the localization process that culminates in large brittle rupture events.
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Renard, F., Royne, A., & Putnis, C. V. (2019). Timescales of interface-coupled dissolution-precipitation reactions on carbonates. Geoscience Frontiers, 10(1), 17–27.
Résumé: In the Earth's upper crust, where aqueous fluids can circulate freely, most mineral transformations are controlled by the coupling between the dissolution of a mineral that releases chemical species into the fluid and precipitation of new minerals that contain some of the released species in their crystal structure, the coupled process being driven by a reduction of the total free-energy of the system. Such coupled dissolution-precipitation processes occur at the fluid-mineral interface where the chemical gradients are highest and heterogeneous nucleation can be promoted, therefore controlling the growth kinetics of the new minerals. Time-lapse nanoscale imaging using Atomic Force Microscopy (AFM) can monitor the whole coupled process under in situ conditions and allow identifying the time scales involved and the controlling parameters. We have performed a series of experiments on carbonate minerals (calcite, siderite, dolomite and magnesite) where dissolution of the carbonate and precipitation of a new mineral was imaged and followed through time. In the presence of various species in the reacting fluid (e. g. antimony, selenium, arsenic, phosphate), the calcium released during calcite dissolution binds with these species to form new minerals that sequester these hazardous species in the form of a stable solid phase. For siderite, the coupling involves the release of Fe2+ ions that subsequently become oxidized and then precipitate in the form of Fe-III oxyhydroxides. For dolomite and magnesite, dissolution in the presence of pure water (undersaturated with any possible phase) results in the immediate precipitation of hydrated Mg-carbonate phases. In all these systems, dissolution and precipitation are coupled and occur directly in a boundary layer at the carbonate surface. Scaling arguments demonstrate that the thickness of this boundary layer is controlled by the rate of carbonate dissolution, the equilibrium concentration of the precipitates and the kinetics of diffusion of species in a boundary layer. From these parameters a characteristic time scale and a characteristic length scale of the boundary layer can be derived. This boundary layer grows with time and never reaches a steady state thickness as long as dissolution of the carbonate is faster than precipitation of the new mineral. At ambient temperature, the surface reactions of these dissolving carbonates occur on time-scales of the order of seconds to minutes, indicating the rapid surface rearrangement of carbonates in the presence of aqueous fluids. As a consequence, many carbonate-fluid reactions in low temperature environments are controlled by local thermodynamic equilibria rather than by the global equilibrium in the whole system. (C) 2018, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.
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Revi, A., Ghorbani, A., Mapeli, C., Livo, K., & Prasad, M. (2019). Differential pressure dependence of the complex conductivity of sandstones. Geophysical Journal International, 219(3), 2110–2124.
Résumé: An experimental work is undertaken to understand the effect of the differential pressure (in the range 3-20.7 MPa) upon the complex conductivity of sedimentary rocks. We use five sandstone core samples from outcrops and a sandstone analog built from sintered glass beads. The spectra were fitted with a Cole-Cole complex conductivity model and the four Cole-Cole parameters were plotted as a function of the differential stress (in the range 3-20.7 MPa). The Cole-Cole relaxation times are analysed in terms of the evolution of the pore size with the differential pressure. Neither the relaxation time nor the Cole-Cole exponent show a strong dependence with the differential pressure indicating that the distribution of the relaxation times remains here roughly the same when the differential stress increases. More specifically, the Cole-Cole exponent does not describe the entire distribution of relaxation times, but the broadness of this distribution. Since the relaxation times are related to the pore sizes, this means that the pore sizes do not depend on the differential pressure in this case. The chargeability is essentially independent of the differential pressure and close to the upper value that can be reached in rocks without metallic particles. This also means that the conductivity of these rocks is dominated by their surface conductivity contribution considering the low pore water salinity used in this work. These results are interpreted thanks to the Stern layer polarization model. The Stern layer denotes the inner part of the electrical double layer coating the surface of the grains. The predictions of this model are mostly consistent with the data.
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Revil, A., Qi, Y., Ghorbani, A., Coperey, A., Ahmed, A. S., Finizola, A., et al. (2019). Induced polarization of volcanic rocks. 3. Imaging clay cap properties in geothermal fields. Geophysical Journal International, 218(2), 1398–1427.
Résumé: Smectite-rich clay caps form permeability seals in geothermal systems. The presence of smectite is also responsible for a strong surface (interfacial) electrical conductivity and polarization due to their electrical double layer properties. We developed new complex conductivity models using both differential effective medium (DEM) and volume averaging theories accounting for both conduction and polarization of these high cation exchange capacity (CEC) materials. These models predict that the chargeability is also a non-linear function of the pore water conductivity reaching a constant value at pore water conductivity far above the so-called iso-conductivity point. The iso-conductivity point is characterized by the equality between the conductivity of the rock and the conductivity of the pore water. We apply the DEM conductivity model (which requires only two textural parameters) to smectite-rich volcanic and sedimentary rocks using data sets from the literature. When smectite is present in the volcanic rocks, the CEC of the rock is dominated by the CEC of smectite. The grain conductivity and the normalized chargeability are related to each other by a dimensionless number R = 0.10 (independent of temperature and saturation) and both are controlled by the excess of charge per unit pore volume QV, which can be determined from the CEC and porosity. Our petrophysical model is also able to predict the permeability of the rock as well from the CEC and the porosity. It is applied to a 3-D data set at Krafla volcano (Iceland). The porosity, the CEC, the percentage of smectite, and the permeability of the clay-cap are imaged by 3-D induced polarization tomography. Electrical conductivity tomography alone does not allow separation of the contribution of the bulk pore space from the interfacial properties related to alteration and therefore should be used with caution.
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Revil, A., Razdan, M., Julien, S., Coperey, A., Abdulsamad, F., Ghorbani, A., et al. (2019). Induced polarization response of porous media with metallic particles – Part 9: Influence of permafrost. Geophysics, 84(5), E337–E355.
Résumé: We consider a mixture made of dispersed metallic particles immersed into a background material saturated by an electrolyte. Below the freezing temperature (typically 0 degrees C to -4 degrees C), a fraction of the liquid water in the pore space is transformed into ice, whereas the salt remains segregated into the liquid-pore water solution. Our goal is to understand how freezing affects the complex conductivity (induced polarization) of such mixtures. Complex conductivity measurements (96 spectra) are performed in a temperature-controlled bath equipped with a high-precision impedance meter. We cover the temperature range from +20 degrees C to -15 degrees C to -18 degrees C and the frequency range from 10-2 Hz to 45 kHz. The spectra are fitted with a double Cole-Cole complex conductivity model. A finite-element model is used to further analyze the mechanisms of polarization by considering an intragrain polarization mechanism for the metallic particles and a change of the conductivity of the background material modeled with an exponential freezing curve. This curve is used to relate the liquid water content to the temperature. In the context of freezing, we test all the aspects of the intragrain polarization model developed in the previous papers of this series, at least for a weakly polarizable background material. The Cole-Cole exponent and the chargeability are observed to be essentially independent of temperature including in freezing conditions. This means that all the relaxation times of the system follow the same temperature dependence and that the chargeability is controlled by the volume fraction of metal. The instantaneous conductivity (high-frequency conductivity) and the relaxation times depend on the temperature in a predictable way, and their product can be considered to be essentially temperature independent. The analytical and numerical models can reproduce the inverse relationship between the relaxation time and the instantaneous conductivity.
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Riga, E., Hollender, F., Roumelioti, Z., Bard, P. - Y., & Pitilakis, K. (2019). Assessing the Applicability of Deconvolution of Borehole Records for Determining Near-Surface Shear-Wave Attenuation. Bulletin Of The Seismological Society Of America, 109(2), 621–635.
Résumé: The near-surface shear-wave attenuation characteristics of a site are crucial for the accurate prediction of seismic ground motion. However, attenuation is usually either approximated by means of empirical correlations or inferred based on limited laboratory data. An empirical method for the assessment of attenuation, which uses high-quality borehole earthquake data, has been proposed by Fukushima et al. (2016). The method is based on a deconvolution analysis of the seismogram recorded downhole and at the wellhead, which allows the separation of the incident and surface-reflected waves on the deconvolved time series. A frequency-dependent attenuation is then estimated from the transfer function between the incident and reflected waves. In this study, we use 1D synthetic wavefields to perform a sensitivity analysis to (a) test the effectiveness of the method in its original form, as well as with some methodological modifications; (b) examine the effect of different parameters involved in the methodology such as downhole sensor depth, existence of a high shear-wave velocity contrast, and input signal duration on the applicability of the method; and (c) explore the potential extension of the originally suggested application criteria with respect to the minimum depth of the borehole, which essentially originate from the capability of the method to separate the incident and reflected waves on the deconvolved time series. The applicability of the method is characterized by the frequency band for which the method results in satisfactory estimates of attenuation. The method is shown to be quite robust with respect to different parameters regarding both the inherent characteristics of the site under investigation and the available simulation alternatives. Results are promising for extending the application of the method to sites of relatively shallow borehole instrumentation.
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Rodriguez-Pascua, M. A., Benavente Escobar, C., Rosell Guevara, L., Grutzner, C., Audin, L., Walker, R., et al. (2019). Did earthquakes strike Machu Picchu? Journal Of Seismology, .
Résumé: The Historic Sanctuary of Machu Picchu (Cusco, Peru) is one of the most important archaeological monuments in Peru and worldwide. Machu Picchu is classified as a UNESCO World Heritage site and at risk from climatic change. However, the seismic centennial history of Peru reports large earthquakes generated both along the subduction zone (Mw8) and on active crustal faults along the Andean Cordillera (Mw7). It is therefore important to know if Machu Picchu is located in an area of seismic hazard and then to take measures to mitigate potential seismic hazards. Due to the short historical earthquake catalogue (< 500 years) and the absence of significant recent instrumental seismicity in the site's vicinity (radius of < 30 km), our knowledge about the seismic hazard in Machu Picchu is limited. The earthquakes of 1650 and 1950 affected Cusco city and surrounding areas, but without damage descriptions in Machu Picchu (80 km away) (Silgado Ferro 1978). In this study, we make the first attempt to use the analysis of earthquake archaeological effects (EAEs) and their differentiation from the effects generated by slope movements (creep) to investigate the past occurrence of strong earthquakes at the site. The application of geological structural analysis to the deformations observed in Machu Picchu shows two directions of the mean ground movement: N020 degrees E and N110 degrees E. Two earthquakes that affected Machu Picchu during its construction generated these directions. This kind of data should be used in the future to protect this important archaeological site.
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Rolland, Y., Bernet, M., van der Beek, P., Gautheron, C., Duclaux, G., Bascou, J., et al. (2019). Late Paleozoic Ice Age glaciers shaped East Antarctica landscape. Earth And Planetary Science Letters, 506, 123–133.
Résumé: The erosion history of Antarctica is fundamental to our understanding of interlinks between climate and glacier dynamics. However, because of the vast polar ice sheet covering more than 99% of Antarctica land mass, the continental surface response to glacial erosion remains largely unknown. Over the last decade the subglacial topography of Antarctica has been imaged by airborne radar surveys. These studies revealed high and complex sub-glacial relief in the core of the East Antarctic shield, interpreted as resulting from rifting episodes and low long-term erosion rates, or repeated large-scale glacial retreats and advances. In East Antarctica, thermochronology studies have revealed a spatially localized Cenozoic erosion starting after 34 Ma, with a maximum denudation of 2 km in the Lambert Trough. Low pre-glacial erosion rates before 34 Ma have been inferred since the Permian period, following a phase of significant (>2 km) erosion during the Late Paleozoic between 350 and 250 Ma. However, the exact extent, magnitude and significance of this Late-Paleozoic erosion phase remain elusive. Here we show that homogeneous exhumation occurred at the scale of the Terre Adelie margin of East Antarctica in response to major glacial erosion during the Late Paleozoic Ice Age (LPIA). Our data require homogeneous exhumation and >4 km erosion between 340 and 300 Ma, along a 600-km profile along the Terre Adelie-George V Land coast. The data are inconsistent with either exhumation during Permian rifting, or with significant (>1.5 km) Cenozoic glacial erosion, which requires LPIA glaciers to have been temperate, promoting glacial sliding, erosion and sediment transfer, even at high latitudes, unlike in the present situation. (C) 2018 Elsevier B.V. All rights reserved.
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Rousset, B., Burgmann, R., & Campillo, M. (2019). Slow slip events in the roots of the San Andreas fault. Science Advances, 5(2).
Résumé: Episodic tremor and accompanying slow slip are observed at the down-dip edge of subduction seismogenic zones. While tremors are the seismic signature of this phenomenon, they correspond to a small fraction of the moment released; thus, the associated fault slip can be quantified only by geodetic observations. On continental strike-slip faults, tremors have been observed in the roots of the Parkfield segment of the San Andreas fault. However, associated transient aseismic slip has never been detected. By making use of the timing of transient tremor activity and the dense Parkfield-area global positioning system network, we can detect deep slow slip events (SSEs) at 16-km depth on the Parkfield segment with an average moment equivalent to M-w 4.90 +/- 0.08. Characterization of transient SSEs below the Parkfield locked asperity, at the transition with the creeping section of the San Andreas fault, provides new constraints on the seismic cycle in this region.
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Saade, M., Araragi, K., Montagner, J. P., Kaminski, E., Roux, P., Aoki, Y., et al. (2019). Evidence of reactivation of a hydrothermal system from seismic anisotropy changes. Nature Communications, 10.
Résumé: Seismic velocity measurements have revealed that the Tohoku-Oki earthquake affected velocity structures of volcanic zones far from the epicenter. Using a seismological method based on ambient seismic noise interferometry, we monitored the anisotropy in the Mount Fuji area during the year 2011, in which the Tohoku-Oki earthquake occurred (M-w = 9.0). Here we show that even at 400 km from the epicenter, temporal variations of seismic anisotropy were observed. These variations can be explained by changes in the alignment of cracks or fluid inclusions beneath the volcanic area due to stress perturbations and the propagation of a hydrothermal fluid surge beneath the Hakone hydrothermal volcanic area. Our results demonstrate how a better understanding of the origin of anisotropy and its temporal changes beneath volcanoes and in the crust can provide insight into active processes, and can be used as part of a suite of volcanic monitoring and forecasting tools.
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Sadhukhan, S., Samue, R., Plunian, F., Stepanov, R., Samtaney, R., & Verma, M. K. (2019). Enstrophy transfers in helical turbulence. Physical Review Fluids, 4(8).
Résumé: In this paper we study the enstrophy transfers in helical turbulence using direct numerical simulation. We observe that the helicity injection does not have significant effects on the inertial-range energy and helicity spectra (similar to k(-5/3)) and fluxes (constants). We also calculate the separate contributions to enstrophy transfers via velocity-to-vorticity and vorticity-to-vorticity channels. There are four different enstrophy fluxes associated with the former channel or vorticity stretching, and one flux associated with the latter channel or vorticity advection. In the inertial range, the fluxes due to vorticity stretching are larger than that due to advection. These transfers too are insensitive to helicity injection.
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Sambolian, S., Operto, S., Ribodetti, A., Tavakoli, B. F., & Virieux, J. (2019). Parsimonious slope tomography based on eikonal solvers and the adjoint-state method. Geophysical Journal International, 218(1), 456–478.
Résumé: Velocity macromodel building is an essential step of the seismic imaging workflow. Indeed, obtaining acceptable results through migration or full waveform inversion is highly dependent on the kinematic accuracy of the background/initial velocity model. Two decades ago, stereotomography was proposed as an alternative to reflection traveltime tomography, the first relying on semi-automatic picking of locally coherent events associated with small reflection or diffraction segments tied to scatterers in depth by a pair of rays, while the latter on interpretive picking of laterally continuous reflections. The flexibility of stereotomography paved the way for many developments that have shown the efficiency of the method whilst emphasizing on the complementary information carried out by traveltimes and slopes of locally coherent events. A recent formulation recast stereotomography under a matrix-free formulation based on eikonal solvers and the adjoint-state method. In the latter, like in the previous works, the scatterer positions and the velocity field are updated jointly to tackle the ill-famed velocity-position coupling in reflection tomography. Following on from this adjoint-state formulation, we propose a new parsimonious formulation of slope tomography that offers the chance to restrain the problem to minimizing the residuals of a single data class being a slope, in search of a sole parameter class being the subsurface velocity field. This parsimonious formulation results from a variable projection, which is implemented by enforcing a consistency between the scatterer coordinates and the velocity macromodel through migration of kinematic attributes. We explain why the resulting reduced-parametrization inversion is more suitable for tomographic problems than the most common joint inversion strategy. We benchmark our method against the complex Marmousi model along with a validation through time domain full waveform inversion and then present the results of a field data case study.
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Sandikkaya, M. A., Akkar, S., & Bard, P. - Y. (2019). A probabilistic procedure to describe site amplification factors for seismic design codes. Soil Dynamics And Earthquake Engineering, 126.
Résumé: We introduce a site factor computation method for a region by extending the site-specific and probabilistic site amplification approach in Bazzuro and Cornell (2004). The site-factor exceedance probability is estimated from the exceedance probabilities of the reference rock ground motion and the soil amplification conditioned on the reference rock ground motion. The former probability is represented by regional hazard curves. The latter probability is computed from soil amplification models. The proposed method is capable of yielding site factors for a target exceedance probability. This property does not exist in the current code-based site factors. Given a site class, if the site factors and the reference rock spectrum possess the same exceedance probability the resulting spectrum would have the same probability of exceedance. The use of such probabilistically consistent earthquake demands would be more relevant for probability-based seismic design and assessment. Owing to the use of hazard curves, the proposed method can account for regional seismicity in the computation of site factors.
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Sanloup, C., Hudspeth, J. M., Afonina, V., Cochain, B., Konopkova, Z., Lelong, G., et al. (2019). Polymerized 4-Fold Coordinated Carbonate Melts in the Deep Mantle. Frontiers In Earth Science, 7.
Résumé: Our understanding of the deep carbon cycle has witnessed amazing advances in the last decade, including the discovery of tetrahedrally coordinated high pressure (P) carbonate phases. However, little is known about the physical properties of their molten counterpart at moderate depths, while their properties at lower mantle conditions remain unexplored. Here, we report the structure and density of FeCO3 melts and glasses from 44 to 110 GPa by means of in situ x-ray synchrotron diffraction, and ex situ Raman and x-ray Raman spectroscopies. Carbon is fully transformed to 4-fold coordination, a bond change recoverable at ambient P. While low P melts react with silica, resulting in the formation of silico-carbonate glasses, high P melts are not contaminated but still quench as glasses. Carbonatemelts are therefore polymerized, highly viscous and poorly reacting with silicates in the lower mantle, in stark opposition with their low P properties.
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Sanloup, C., Hudspeth, J. M., Afonina, V., Cochain, B., Konopkova, Z., Lelong, G., et al. (2019). Polymerized 4-Fold Coordinated Carbonate Melts in the Deep Mantle (vol 7, 72, 2019). Frontiers In Earth Science, 7.
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Sarr, A. - C., Husson, L., Sepulchre, P., Pastier, A. - M., Pedoja, K., Elliot, M., et al. (2019). Subsiding Sundaland. Geology, 47(2), 119–122.
Résumé: Sundaland is the currently partially drowned continental landmass that encompasses Borneo, Sumatra, Java, and the Malay Peninsula. It has episodically been reclaimed by the sea during successive Quaternary glaciations, and is commonly thought to be vertically stable. Combining geomorphological observations with numerical simulations of coral reef growth and shallow seismic stratigraphy, we show that the Sunda shelf is subsiding, and that the intermittent regime of transgressions only prevailed over the past 400,000 yr. Prior to that time, Sundaland was permanently exposed. We relate these drowning events to transient dynamic topography in the Indo-Australian subduction zone. Because the Sunda shelf is very shallow, these new data provide important insights into Pleistocene paleogeography, with implications on the interactions between the solid Earth and climate, oceanography, and dispersal of species, including hominids.
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Sarr, A. - C., Husson, L., Sepulchre, P., Pastier, A. - M., Pedoja, K., Elliot, M., et al. (2019). Subsiding Sundaland Reply. Geology, 47(7), E470.
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Sarr, A. - C., Mugnier, J. - L., Abrahami, R., Carcaillet, J., & Ravanel, L. (2019). Sidewall erosion: Insights from in situ-produced Be-10 concentrations measured on supraglacial clasts (Mont Blanc massif, France). Earth Surface Processes And Landforms, 44(10), 1930–1944.
Résumé: Sidewall erosion because of rockfalls is one of the most efficient erosional processes in the highest parts of mountain ranges; it is therefore important to quantify sidewall erosion to understand the long-term evolution of mountainous topography. In this study, we analyse how the Be-10 concentration of supraglacial debris can be used to quantify sidewall erosion in a glaciated catchment. We first analyse, in a glaciated catchment, the cascade of processes that move a rock from a rockwall to a supraglacial location and propose a quantitative estimate of the number of rockfalls statistically mixed in a supraglacial sand sample. This model incorporates the size of the rockwall, a power law distribution of the size of the rockfalls and the mean glacial transport velocity. In the case of the Bossons glacier catchment (Mont Blanc massif), the Be-10 concentrations obtained for supraglacial samples vary from 1.97 +/- 0.24 to 23.82 +/- 1.68 x 10(4) atoms g(-1). Our analysis suggests that part of the Be-10 concentration dispersion is related to an insufficient number of amalgamated rockfalls that does not erase the stochastic nature of the sidewall erosion. In the latter case, the concentration of several collected samples is averaged to increase the number of statistically amalgamated rockfalls. Variable and robust Be-10-derived rockwall retreat rates are obtained for three distinct rockfall zones in the Bossons catchment and are 0.19 +/- 0.08 mm year(-1), 0.54 +/- 0.1 mm year(-1) and 1.08 +/- 0.17 mm year(-1). The mean Be-10 retreat rate for the whole catchment (ca. 0.65 mm year(-1)) is close to the present-day erosion rate derived from other methods. (c) 2019 John Wiley & Sons, Ltd.
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Sarr, A. - C., Sepulchre, P., & Husson, L. (2019). Impact of the Sunda Shelf on the Climate of the Maritime Continent. Journal Of Geophysical Research-Atmospheres, 124(5), 2574–2588.
Résumé: Drastic paleogeography changes in the Indonesian archipelago over the Plio-Pleistocene, either in response to sea level oscillations or vertical land motion, enabled the periodic emergence of the Sunda shelf. When emerged, this wide continental platform in the heart of the Maritime Continent may have modified regional and global climate systems. We investigate the effect of the exposure of the Sunda shelf on climate dynamics using a set of numerical simulations with (i) atmosphere-land surface and (ii) fully coupled general circulation models. We first explore the impact of convection schemes on the rainfall regime simulated over the Maritime Continent and show how they could explain the discrepancies among previous studies. We further depict a robust and common mechanism that prevails. We show that diurnal heating of the surface of the continental platform enhances low-level convergence and local convection, and fosters local precipitations. This effect, to a second order, is modulated by the radiative effect and increased turbulent heat flux driven by vegetated surface properties such as albedo or roughness. Increasing precipitations over the exposed platform also impacts freshwater export into seawater, making salinity of the Indian Ocean and Indonesian Throughflow highly dependent on the routing scheme over the exposed shelf.
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Sarret, G., Guedron, S., Acha, D., Bureau, S., Arnaud-Godet, F., Tisserand, D., et al. (2019). Extreme Arsenic Bioaccumulation Factor Variability in Lake Titicaca, Bolivia. Scientific Reports, 9.
Résumé: Latin America, like other areas in the world, is faced with the problem of high arsenic (As) background in surface and groundwater, with impacts on human health. We studied As biogeochemical cycling by periphyton in Lake Titicaca and the mine-impacted Lake Uru Uru. As concentration was measured in water, sediment, totora plants (Schoenoplectus californicus) and periphyton growing on stems, and As speciation was determined by X-ray absorption spectroscopy in bulk and EDTA-extracted periphyton. Dissolved arsenic was between 5.0 and 15 μg L-1 in Lake Titicaca and reached 78.5 μg L-1 in Lake Uru Uru. As accumulation in periphyton was highly variable. We report the highest As bioaccumulation factors ever measured (BAFs(periphyton) up to 245,000) in one zone of Lake Titicaca, with As present as As(V) and monomethyl-As (MMA(V)). Non-accumulating periphyton found in the other sites presented BAFsperiphyton between 1281 and 11,962, with As present as As(III), As(V) and arsenosugars. DNA analysis evidenced several taxa possibly related to this phenomenon. Further screening of bacterial and algal isolates would be necessary to identify the organism(s) responsible for As hyperaccumulation. Impacts on the ecosystem and human health appear limited, but such organisms or consortia would be of great interest for the treatment of As contaminated water.
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Savidge, E., Nissen, E., Nemati, M., Karasozen, E., Hollingsworth, J., Talebian, M., et al. (2019). The December 2017 Hojedk (Iran) earthquake triplet-sequential rupture of shallow reverse faults in a strike-slip restraining bend. Geophysical Journal International, 217(2), 909–925.
Résumé: A triplet of M-w similar to 6 earthquakes on 2017 December 1-12 occurred similar to 50 km north of Kerman, Iran, in an area of mountainous topography where several major right-lateral strike-slip fault systems-the Gowk, Nayband, Lakar Kuh and Kuh Banan faults-converge. Here we assess their source parameters and surficial expression using regional and teleseismic waveforms and arrival times, synthetic aperture radar interferometry, optical satellite image correlation and field observations. All three main shocks occurred on shallow reverse faults associated with the southern termination of the Lakar Kuh right-lateral strike-slip fault. The first two main shocks on 1 December and 12 December (08: 43 UTC) likely ruptured and reruptured a previously unrecognized, blind, NE-dipping fault beneath the Mian Kuh range. Slip in both earthquakes extends much further along strike than down dip, hinting at structural or stratigraphic controls on rupture dimensions. The thirdmain shock on 12 December (21: 41 UTC) is perhaps the most interesting of the three events. It ruptured a conjugate SW-dipping thrust in the hangingwall of the first fault, generating a sinuous fault scarp in the alluvial plain north of the Mian Kuh range, consistent with its unusually shallow centroid depth of similar to 2 km. Its high ratio of net surface slip (average similar to 1.5 m and maximum similar to 2.5 m) to length (similar to 7 km) and its narrow down-dip width (similar to 6 km) implies a very high stress drop. The surface rupture aligns along-strike with larger scarps that contain uplifted and incised fan surfaces in their hangingwalls, but this subtle expression of active faulting had not been fully recognized prior to these earthquakes. The clustering in space and time of large, shallow earthquakes on hidden faults is of broad concern for seismic hazard assessment in mountainous parts of Iran and in other collisional settings.
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Scala, A., Serra, M., Festa, G., & Roux, P. (2019). Insight Into the Wave Scattering Properties of the Solfatara Volcano, Campi Flegrei, Italy. Frontiers In Earth Science, 7.
Résumé: Imaging methods able to discriminate type and content of fluids in volcanic areas and to track their migration with time are fundamental to get a picture of the volcanic structure and to constrain its shallow dynamics. In this study we provide an image of the Solfatara crater, located in the Campi Flegrei caldera, a volcanic area of Southern Italy, through a statistical description of the scatterers. We analyze active seismic data recorded in a 3D geometry during the first Repeated Induced Earthquake and Noise (RICEN) experiment, held in September 2013. After extraction of seismic sections, we evaluate the coherent and incoherent intensities, averaging over sources, and receivers sharing the same source-station distance. We thus compute the ratio between the two intensities for the direct surface wave, which is sensitive to the scattering mean free path in the area. We find that the intensity ratio in all the analyzed frequency bands exponentially decreases with distance, allowing for the computation of the scattering mean free path as a function of the frequency. We report that the scattering mean free path exhibits a small increase between 7.5 and 10 Hz from 50 to 60 m, and then it decreases down to about 10 m, at a frequency of 21.5 Hz. We thus model the scattering mean free path computing the backscattered field from a single scatterer of cylindrical shape in a homogeneous medium and we determine the model parameters through a fit with the mean free path inferred from data. We find that the best fit model is obtained for a size of the scatterer of about 10 m, with a small increase of the Rayleigh wave velocity inside the scatterer. The scatterers are here interpreted as regions richer in water with respect to the background and eventually due to the condensed steam running below the investigated area. The connection between the scattering mean free path and the type, and content of fluids retrieved here is of fundamental importance to image the volcanic structure. In addition, monitoring of this quantity with time can track fluid migration eventually related to magma injection and the unrest state of a volcano toward an eruption.
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Schreiber, M., Schaeffer, N., & Loft, R. (2019). Exponential integrators with parallel-in-time rational approximations for the shallow-water equations on the rotating sphere. Parallel Computing, 85, 56–65.
Résumé: High performance computing trends towards many-core systems are expected to continue over the next decade. As a result, parallel-in-time methods, mathematical formulations which exploit additional degrees of parallelism in the time dimension, have gained increasing interest in recent years. In this work we study a massively parallel rational approximation of exponential integrators (REXI). This method replaces a time integration of stiff linear oscillatory and diffusive systems by the sum of the solutions of many decoupled systems, which can be solved in parallel. Previous numerical studies showed that this reformulation allows taking arbitrarily long time steps for the linear oscillatory parts. The present work studies the non-linear shallow-water equations on the rotating sphere, a simplified system of equations used to study properties of space and time discretization methods in the context of atmospheric simulations. After introducing time integrators, we first compare the time step sizes to the errors in the simulation, discussing pros and cons of different formulations of REXI. Here, REXI already shows superior properties compared to explicit and implicit time stepping methods. Additionally, we present wallclock-time-to-error results revealing the sweet spots of REXI obtaining either an over 6 x higher accuracy within the same time frame or an about 3 x reduced time-to-solution for a similar error threshold. Our results motivate further explorations of REXI for operational weather/climate systems. (C) 2019 Elsevier B.V. All rights reserved.
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Seybold, L., Trepmann, C. A., & Janots, E. (2019). A ductile extensional shear zone at the contact area between HP-LT metamorphic units in the Talea Ori, central Crete, Greece: deformation during early stages of exhumation from peak metamorphic conditions. International Journal Of Earth Sciences, 108(1), 213–227.
Résumé: We report on an extensional ductile shear zone in central Crete at the contact area between the high-pressure low-temperature (HP-LT) metamorphic Phyllite-Quartzite unit sensu stricto (PQ s.str.) and the Talea Ori group (Plattenkalk unit). Mapping and microscopic analysis along the 20 km long contact reveal extensional shear bands, shear band cleavages (C'-type) and associated quartz veins in both units, occurring over a width of up to a kilometer. The shear offset along the shear bands is systematically perpendicular to the contact with the hanging block (PQ s.str.) being downfaulted. Abundant discordant quartz veins are associated to shear band boundaries, asymmetric boudinage and foliation boudinage, forming m-wide vein networks. These mesoscopic deformation structures together with related microstructures such as strain shadows, growth rims of albite porphyroblasts and stylolites indicate dissolution-precipitation creep as main deformation mechanism accompanied by vein formation. Temperatures during deformation are indicated to be close to peak metamorphic temperatures (>= 300-350 degrees C) by the growth rims of albite porphyroblasts and micas present in the shear band cleavages, which are consistent with quartz vein microstructures showing subgrains and sutured high angle grain boundaries. Peak metamorphic temperatures inferred by the degree of graphitization of carbonaceous material are similar in the hanging wall and the footwall of the shear zone, which is consistent with fast and nearly adiabatic exhumation. Our study demonstrates the importance of ductile shear zones with high strain rate dissolution-precipitation creep and vein formation in HP-LT metamorphic rocks for the early exhumation history.
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Shen, T., Wang, G., Bernet, M., Replumaz, A., Ai, K., Song, B., et al. (2019). Long-term exhumation history of the Gangdese magmatic arc: Implications for the evolution of the Kailas Basin, western Tibet. Geological Journal, .
Résumé: Constraining the long-term exhumation history of the Gangdese magmatic arc is critical for understanding the coupled evolution of orogenic exhumation and accumulation of basin sediments on the southern Tibetan Plateau. We present new zircon fission-track (ZFT) data from sandstones in the Mt. Kailas area, western Tibet, to decipher the relation between source rock exhumation and sediment deposition in the basin. Two sedimentary members were recognized in the Kailas Basin which are the Eocene conglomerates in the hanging wall of the Great Counter Thrust and the Oligocene-Miocene Kailas Formation in the footwall. The Eocene conglomerates were mostly derived from the Lhasa Terrane to the north with recycling of pre-Cenozoic sediments, containing zircons that experienced post-magmatic cooling after the Indian-Asian collision and buried deeply later by the Oligocene-Miocene Kailas Formation. The ZFT analysis from the Kailas Formation illustrates significant cooling during the Oligocene (ca. 32 Ma) in the source region, indicating that the Gangdese magmatic arc rocks were eroded rapidly during that time. The alternate increasing and decreasing of the southernmost Gangdese magmatic arc progresses are linked to dynamic topography deflection induced by the northward subduction of the Indian Plate since the Oligocene and subsequent southward overturning of the Indian mantle slab. Basin subsidence and formation of the Kailas Formation seems also be driven by dynamic topography since the Oligocene.
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Smittarello, D., Cayol, V., Pinel, V., Froger, J. - L., Peltier, A., & Dumont, Q. (2019). Combining InSAR and GNSS to Track Magma Transport at Basaltic Volcanoes. Remote Sensing, 11(19).
Résumé: The added value of combining InSAR and GNSS data, characterized by good spatial coverage and high temporal resolution, respectively, is evaluated based on a specific event: the propagation of the magma intrusion leading to the 26 May 2016 eruption at Piton de la Fournaise volcano (Reunion Island, France). Surface displacement is a non linear function of the geometry and location of the pressurized source of unrest, so inversions use a random search, based on a neighborhood algorithm, combined with a boundary element modeling method. We first invert InSAR and GNSS data spanning the whole event (propagation phase and eruption) to determine the final geometry of the intrusion. Random search conducted in the inversion results in two best-fit model families with similar data fits. Adding the same time-period GNSS dataset to the inversions does not significantly modify the results. Even when weighting data to provide even contributions, the fit is systematically better for descending than ascending interferograms, which might indicate an eastward flank motion. Then, we invert the GNSS time series in order to derive information on the propagation dynamics, validating our approach using a SAR image acquired during the propagation phase. We show that the GNSS time series can only be used to correctly track the magma propagation when the final intrusion geometry derived from InSAR and GNSS measurements is used as an a priori. A new method to extract part of a mesh, based on the representation of meshes as graphs, better explains the data and better accounts for the opening of the eruptive fissure than a method based on the projection of a circular pressure sources. Finally, we demonstrate that the temporal inversion of GNSS data strongly favors one family of models over an other for the final intrusion, removing the ambiguity inherent in the inversion of InSAR data.
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Smittarello, D., Cayol, V., Pinel, V., Peltier, A., Froger, J. - L., & Ferrazzini, V. (2019). Magma Propagation at Piton de la Fournaise From Joint Inversion of InSAR and GNSS. Journal Of Geophysical Research-Solid Earth, 124(2), 1361–1387.
Résumé: Magma propagation is an unsteady process controlled by magma-crust interaction. To provide information on its dynamics, we invert complementary ground deformation data spanning the 8hr preceding the 26 May 2016 eruption at Piton de la Fournaise (PdF) volcano (La Reunion, France). Data are inverted using 3-D boundary element models combined with a Monte Carlo inversion method. The final geometry of the displacement source is determined based on four interferograms spanning the whole propagation phase while the dynamics of the propagation is inferred from temporal inversion of continuous Global Navigation Satellite System (GNSS) data, using the final geometry as an a priori to constrain the source. The best modeled magma path consists in a 2,700-m-long sill located 800m above sea level and connected to the eruptive fissure by a subvertical dike. The quick opening of the horizontal part of the intrusion could have been favored by limited flank sliding during the early stage of propagation. The intrusion then stalled for approximate to 5hr, while pressure increased slightly, until final upward propagation and eruption. Volume budget suggests that the eruption was fed by a single batch of magma quickly disconnected from its source. The delay prior to the eruption may reflect a limited magma supply. Finally, two mechanisms, potentially acting together, might have favored the eruption: a driving role of magmatic gas and/or, as often observed at Piton de la Fournaise, an eastward flank slip. Plain Language Summary Basaltic magma stored beneath volcanoes reaches the surface by fracturing the Earth's crust. As experienced in May 2018 at Kilauea volcano (Hawaii, USA), magma can travel kilometers from the reservoir and fissure opening may threaten man-made structures. Anticipating where and when eruptive fissures open requires better understanding of the factors controlling magma propagation. During the 26 May 2016 eruption of Piton de la Fournaise, Reunion Island,the preeruptive crisis spanned 8hr25min from the first signal recorded by the observatory to the eruption onset.We determine the magma paths and propagation timing, which led to this eruption using complementary satellite data of ground surface displacement, combining radar interferometry, which provides high spatial resolution, with GPS, which provides high temporal resolution. We highlight complex magma propagation within the subareal volcano, showing two direction changes, an arrest and an acceleration. Flank slip and magma degassing seem to play a key role in controlling both the geometry and the timing. Based on this scenario, this event was close to turn into a failed eruption as there was a 5-hr pause in propagation before magma finally reached the surface. Understanding such unusual eruptions is a challenge for observatories as it may lead to repeated false alerts.
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Sobolev, A. V., Asafov, E. V., Gurenko, A. A., Arndt, N. T., Batanova, V. G., Portnyagin, M. V., et al. (2019). Deep hydrous mantle reservoir provides evidence for crustal recycling before 3.3 billion years ago. Nature, 571(7766), 555–+.
Résumé: Water strongly influences the physical properties of the mantle and enhances its ability to melt or convect. Its presence can also be used to trace recycling of surface reservoirs down to the deep mantle(1), which makes knowledge of the water content in the Earth's interior and its evolution crucial for understanding global geodynamics. Komatiites (MgO-rich ultramafic magmas) result from a high degree of mantle melting at high pressures(2) and thus are excellent probes of the chemical composition and water contents of the deep mantle. An excess of water over elements that show similar geochemical behaviour during mantle melting (for example, cerium) was recently found in melt inclusions in the most magnesiumrich olivine in 2.7-billion-year-old komatiites from Canada(3) and Zimbabwe(4). These data were taken as evidence for a deep hydrated mantle reservoir, probably the transition zone, in the Neoarchaean era (2.8 to 2.5 billion years ago). Here we confirm the mantle source of this water by measuring deuterium-to-hydrogen ratios in these melt inclusions and present similar data for 3.3-billion-year-old komatiites from the Barberton greenstone belt. From the hydrogen isotope ratios, we show that the mantle sources of these melts contained excess water, which implies that a deep hydrous mantle reservoir has been present in the Earth's interior since at least the Palaeoarchaean era (3.6 to 3.2 billion years ago). The reconstructed initial hydrogen isotope composition of komatiites is more depleted in deuterium than surface reservoirs or typical mantle but resembles that of oceanic crust that was initially altered by seawater and then dehydrated during subduction. Together with an excess of chlorine and depletion of lead in the mantle sources of komatiites, these results indicate that seawater-altered lithosphere recycling into the deep mantle, arguably by subduction, started before 3.3 billion years ago.
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Socquet, A., Hollingsworth, J., Pathier, E., & Bouchon, M. (2019). Evidence of supershear during the 2018 magnitude 7.5 Palu earthquake from space geodesy. Nature Geoscience, 12(3), 192–+.
Résumé: A magnitude 7.5 earthquake hit the city of Palu in Sulawesi, Indonesia on 28 September 2018 at 10:02:43 (coordinated universal time). It was followed a few minutes later by a 4-7-m-high tsunami. Palu is situated in a narrow pull-apart basin surrounded by high mountains of up to 2,000 m altitude. This morphology has been created by a releasing bend in the Palu-Koro fault, a rapidly moving left-lateral strike-slip fault. Here we present observations derived from optical and radar satellite imagery that constrain the ground surface displacements associated with the earthquake in great detail. Mapping of the main rupture and associated secondary structures shows that the slip initiated on a structurally complex and previously unknown fault to the north, extended southwards over 180 km and passed through two major releasing bends. The 30 km section of the rupture south of Palu city is extremely linear, and slightly offset from the mapped geological fault at the surface. This part of the rupture accommodates a large and smooth surface slip of 4-7 m, with no shallow slip deficit. Almost no aftershock seismicity was recorded from this section of the fault. As these characteristics are similar to those from known supershear segments, we conclude that the Palu earthquake probably ruptured this segment at supershear velocities.
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Soret, M., Agard, P., Ildefonse, B., Dubacq, B., Prigent, C., & Rosenberg, C. (2019). Deformation mechanisms in mafic amphibolites and granulites: record from the Semail metamorphic sole during subduction infancy. Solid Earth, 10(5), 1733–1755.
Résumé: This study sheds light on the deformation mechanisms of subducted mafic rocks metamorphosed at amphibolite and granulite facies conditions and on their importance for strain accommodation and localization at the top of the slab during subduction infancy. These rocks, namely metamorphic soles, are oceanic slivers stripped from the downgoing slab and accreted below the upper plate mantle wedge during the first million years of intraoceanic subduction, when the subduction interface is still warm. Their formation and intense deformation (i.e., shear strain >= 5) attest to a systematic and transient coupling between the plates over a restricted time span of similar to 1 Myr and specific rheological conditions. Combining microstructural analyses with mineral chemistry constrains grain-scale deformation mechanisms and the rheology of amphibole and amphibolites along the plate interface during early subduction dynamics, as well as the interplay between brittle and ductile deformation, water activity, mineral change, grain size reduction and phase mixing. Results indicate that increasing pressure and temperature conditions and slab dehydration (from amphibolite to granulite facies) lead to the nucleation of mechanically strong phases (garnet, clinopyroxene and amphibole) and rock hardening. Peak conditions (850 degrees C and 1 GPa) coincide with a pervasive stage of brittle deformation which enables strain localization in the top of the mafic slab, and therefore possibly the unit detachment from the slab. In contrast, during early exhumation and cooling (from similar to 850 down to similar to 700 degrees C and 0.7 GPa), the garnet-clinopyroxene-bearing amphibolite experiences extensive retrogression (and fluid ingression) and significant strain weakening essentially accommodated in the dissolution-precipitation creep regime including heterogeneous nucleation of fine-grained materials and the activation of grain boundary sliding processes. This deformation mechanism is closely assisted with continuous fluid-driven fracturing throughout the exhumed amphibolite, which contributes to fluid channelization within the amphibolites. These mechanical transitions, coeval with detachment and early exhumation of the high-temperature (HT) metamorphic soles, therefore controlled the viscosity contrast and mechanical coupling across the plate interface during subduction infancy, between the top of the slab and the overlying peridotites. Our findings may thus apply to other geodynamic environments where similar temperatures, lithologies, fluid circulation and mechanical coupling between mafic rocks and peridotites prevail, such as in mature warm subduction zones (e.g., Nankai, Cascadia), in lower continental crust shear zones and oceanic detachments.
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Soubestre, J., Seydoux, L., Shapiro, N. M., de Rosny, J., Droznin, D., V, Droznina, S. Y., et al. (2019). Depth Migration of Seismovolcanic Tremor Sources Below the Klyuchevskoy Volcanic Group (Kamchatka) Determined From a Network-Based Analysis. Geophysical Research Letters, 46(14), 8018–8030.
Résumé: We present a method for automatic location of dominant sources of seismovolcanic tremor in 3-D, based on the spatial coherence of the continuously recorded wavefield at a seismic network. We analyze 4.5 years of records from the seismic network at the Klyuchevskoy volcanic group in Kamchatka, Russia, when four volcanoes experienced tremor episodes. After enhancing the tremor signal with spectral whitening, we compute the daily cross-correlation functions related to the dominant tremor sources from the first eigenvector of the spectral covariance matrix and infer their daily positions in 3-D. We apply our technique to the tremors beneath Shiveluch, Klyuchevskoy, Tolbachik, and Kizimen volcanoes and observe the yearlong preeruptive volcanic tremor beneath Klyuchevskoy from deep to shallow parts of the plumbing system. This observation of deep volcanic tremor sources demonstrates that the cross-correlation-based method is a very powerful tool for volcano monitoring.
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Sparks, R. S. J., Annen, C., Blundy, J. D., Cashman, K. V., Rust, A. C., & Jackson, M. D. (2019). Formation and dynamics of magma reservoirs. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 377(2139).
Résumé: The emerging concept of a magma reservoir is one in which regions containing melt extend from the source of magma generation to the surface. The reservoir may contain regions of very low fraction intergranular melt, partially molten rock (mush) and melt lenses (or magma chambers) containing high melt fraction eruptible magma, as well as pockets of exsolved magmatic fluids. The various parts of the system may be separated by a sub-solidus rock or be connected and continuous. Magma reservoirs and their wall rocks span a vast array of rheological properties, covering as much as 25 orders of magnitude from high viscosity, sub-solidus crustal rocks to magmatic fluids. Time scales of processes within magma reservoirs range from very slow melt and fluid segregation within mush and magma chambers and deformation of surrounding host rocks to very rapid development of magma and fluid instability, transport and eruption. Developing a comprehensive model of these systems is a grand challenge that will require close collaboration between modellers, geophysicists, geochemists, geologists, volcanologists and petrologists. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.
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Stawski, T. M., Freeman, H. M., Van Driessche, A. E. S., Hoevelmann, J., Besselink, R., Wirth, R., et al. (2019). Particle-Mediated Nucleation Pathways Are Imprinted in the Internal Structure of Calcium Sulfate Single Crystals. Crystal Growth & Design, 19(7), 3714–3721.
Résumé: Calcium sulfate minerals are found in nature as three hydrates: gypsum (CaSO4 center dot 2H(2)O), bassanite (CaSO4 center dot 0.5H(2)O), and anhydrite (CaSO4). Due to their relevance in natural and industrial processes, the formation pathways of calcium sulfates from aqueous solution have been the subject of intensive research, and there is a growing body of literature, suggesting that calcium sulfates form through nonclassical nanoparticle-mediated crystallization processes. We showed earlier (Stawski et al. Nat. Commun. 2016, 7, 11177) that at the early stages in the precipitation reaction, calcium sulfate nanocrystals nucleate through the reorganization and coalescence of aggregates rather than through classical unit addition. Here, we used low-dose dark field (DF) transmission electron microscopy (TEM) and electron diffraction and document that these restructuring processes do not continue until a final near-perfectly homogeneous single crystal is obtained. Instead, we show that the growth process yields a final imperfect mesocrystal with an overall morphology resembling that of a single crystal, yet composed of smaller nanodomains. Our data reveal that organic-free calcium sulfate mesocrystals grown by a particle mediated-pathway may preserve in the final crystal structure a “memory” or “imprint” of their nonclassical nucleation process, something that has been overlooked until now. Furthermore, the nanoscale misalignment of the structural subunits within these crystals might propagate through the length-scales, which is potentially expressed macroscopically as misaligned zones/domains in large single crystals. This is akin to observations in some of the giant crystals from the Naica Mine, Chihuahua, Mexico.
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Stawski, T. M., van den Heuvel, D. B., Besselink, R., Tobler, D. J., & Benning, L. G. (2019). Mechanism of silica-lysozyme composite formation unravelled by in situ fast SAXS. Beilstein Journal Of Nanotechnology, 10, 182–197.
Résumé: A quantitative understanding of aggregation mechanisms leading to the formation of composites of inorganic nanoparticles (NPs) and proteins in aqueous media is of paramount interest for colloid chemistry. In particular, the interactions between silica (SiO2) NPs and lysozyme (LZM) have attracted attention, because LZM is well-known to adsorb strongly to silica NPs, while at the same time preserving its enzymatic activity. The inherent nature of the aggregation processes leading to NP-LZM composites involves structural changes at length scales from few to at least hundreds of nanometres but also time scales much smaller than one second. To unravel these we used in situ synchrotron-based small-angle X-ray scattering (SAXS) and followed the subtle interparticle interactions in solution at a time resolution of 50 ms/frame (20 fps). We show that if the size of silica NPs (ca. 5 nm diameter) is matched by the dimensions of LZM, the evolving scattering patterns contain a unique structure-factor contribution originating from the presence of LZM. We developed a scattering model and applied it to analyse this structure function, which allowed us to extract structural information on the deformation of lysozyme molecules during aggregation, as well as to derive the mechanisms of composite formation.
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Stawski, T. M., Van Driessche, A. E. S., Besselink, R., Byrne, E. H., Raiteri, P., Gale, J. D., et al. (2019). The Structure of CaSO4 Nanorods: The Precursor of Gypsum. Journal Of Physical Chemistry C, 123(37), 23151–23158.
Résumé: Understanding the gypsum (CaSO4 center dot 2H(2)O) formation pathway from aqueous solution has been the subject of intensive research in the past years. This interest stems from the fact that gypsum appears to fall into a broader category of crystalline materials whose formation does not follow classical nucleation and growth theories. The pathways involve transitory precursor cluster species, yet the actual structural properties of such clusters are not very well understood. Here, we show how in situ high-energy X-ray diffraction experiments and molecular dynamics (MD) simulations can be combined to derive the structure of small CaSO4 clusters, which are precursors of crystalline gypsum. We fitted several plausible structures to the derived pair distribution functions and explored their dynamic properties using unbiased MD simulations based on both rigid ion and polarizable force fields. Determination of the structure and (meta)stability of the primary species is important from both a fundamental and applied perspective; for example, this will allow for an improved design of additives for greater control of the nucleation pathway.
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Sternai, P., Sue, C., Husson, L., Serpelloni, E., Becker, T. W., Willett, S. D., et al. (2019). Present-day uplift of the European Alps: Evaluating mechanisms and models of their relative contributions. Earth-Science Reviews, 190, 589–604.
Résumé: Recent measurements of surface vertical displacements of the European Alps show a correlation between vertical velocities and topographic features, with widespread uplift at rates of up to similar to 2-2.5 mm/a in the North-Western and Central Alps, and 1 mm/a across a continuous region from the Eastern to the South-Western Alps. Such a rock uplift rate pattern is at odds with the horizontal velocity field, characterized by shortening and crustal thickening in the Eastern Alps and very limited deformation in the Central and Western Alps. Proposed mechanisms of rock uplift rate include isostatic response to the last deglaciation, long-term erosion, detachment of the Western Alpine slab, as well as lithospheric and surface deflection due to mantle convection. Here, we assess previous work and present new estimates of the contributions from these mechanisms. Given the large range of model estimates, the isostatic adjustment to deglaciation and erosion are sufficient to explain the full observed rate of uplift in the Eastern Alps, which, if correct, would preclude a contribution from horizontal shortening and crustal thickening. Alternatively, uplift is a partitioned response to a range of mechanisms. In the Central and Western Alps, the lithospheric adjustment to deglaciation and erosion likely accounts for roughly half of the rock uplift rate, which points to a noticeable contribution by mantle-related processes such as detachment of the European slab and/or asthenospheric upwelling. While it is difficult to independently constrain the patterns and magnitude of mantle contributions to ongoing Alpine vertical displacements at present, future data should provide additional insights. Regardless, interacting tectonic and surface mass redistribution processes, rather than an individual forcing, best explain ongoing Alpine elevation changes.
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Suarez, R. J., Ghiglione, M. C., Calderon, M., Sue, C., Martinod, J., Guillaume, B., et al. (2019). The metamorphic rocks of the Nunatak Viedma in the Southern Patagonian Andes: Provenance sources and implications for the early Mesozoic Patagonia-Antarctic Peninsula connection. Journal Of South American Earth Sciences, 90, 471–486.
Résumé: The Nunatak Viedma within the Southern Patagonian Icefield has been considered as a volcanic center based on its geomorphologic features, despite the fact that field explorations by Eric Shipton determined its metamorphic nature 70 years ago. We carried out fieldwork to characterize this isolated outcrop and performed the first U-Pb dating in detrital zircons from the basement rocks located inside the Southern Patagonian Icefield. We recognized very-low grade metamorphic rocks, corresponding principally to metapelites and metapsammites, and scarce metabasites. Detrital zircons in three metapsammitic samples (composite group of 240 grains) yielded prominent age population peaks at similar to 1090, similar to 960, similar to 630, similar to 520, similar to 480-460, similar to 380, similar to 290-260, similar to 235-225 Ma that are typical of Gondwanide affinity, and youngest grains at 208 Ma. Maximum depositional ages of 225, 223 and 212 Ma were calculated for each sample from the youngest cluster of ages. This distinctive and novelty Late Triassic age justifies differentiate the Nunatak Viedma Unit from the Devonian-early Carboniferous and Permian-Early Triassic (?) belts of the Eastern Andean Metamorphic Complex. Possible primary source areas for the detrital zircons are outcropping in southern Patagonia, the Antarctic Peninsula, and the Malvinas Islands. Additionally, secondary sources could be part of the erosion and recycling of metasediments from the Eastern Andean Metamorphic Complex. We propose that the cluster of Triassic ages is related to the volcanic arc emplaced along the Antarctic Peninsula and active at that time when was still attached to southern Patagonia during the Triassic. The dynamics of the early Mesozoic orogen is also discussed.
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Sucheras-Marx, B., Mattioli, E., Allemand, P., Giraud, F., Pittet, B., Plancq, J., et al. (2019). The colonization of the oceans by calcifying pelagic algae. Biogeosciences, 16(12), 2501–2510.
Résumé: The rise of calcareous nannoplankton in Mesozoic oceans has deeply impacted ocean chemistry and contributed to shaping modern oceans. Nevertheless, the calcareous nannoplankton colonization of past marine environments remains poorly understood. Based on an extensive compilation of published and unpublished data, we show that their accumulation rates in sediments increased from the Early Jurassic (similar to 200 Ma) to the Early Cretaceous (similar to 120 Ma), although these algae diversified up to the end of the Mesozoic (66 Ma). After the middle Eocene (similar to 45 Ma), a decoupling occurred between accumulation rates, diversity and coccolith size. The time series analyzed points toward a three-phase evolutionary dynamic. An invasion phase of the open-ocean realms was followed by a specialization phase occurring along with taxonomic diversification, ended by an establishment phase where a few small-sized species dominated. The current hegemony of calcareous nannoplankton in the world ocean results from a long-term and complex evolutionary history shaped by ecological interactions and abiotic forcing.
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Sun, W., Zhao, L., Malusa, M. G., Guillot, S., & Fu, L. - Y. (2019). 3-D Pn tomography reveals continental subduction at the boundaries of the Adriatic microplate in the absence of a precursor oceanic slab. Earth And Planetary Science Letters, 510, 131–141.
Résumé: Slab pull generated by subducting oceanic lithosphere is generally considered as a major trigger for the onset of continental subduction. However, this may be in conflict with the occurrence of UHP terranes bearing no evidence of oceanic lithospheric rocks involved in the exhumation cycle. Here, we image the uppermost mantle P velocity structure beneath the Central Mediterranean, suggesting the possibility that the initiation of continental subduction may not require a precursor oceanic slab. We combine (i) a three-step inverted 3-D Pn tomography model of the Adriatic microplate with (ii) available geologic constraints and palinspastic reconstructions of the Africa-Eurasia plate-boundary zone. Our Pn tomography model reveals elongated regions with Vp < 7.6 km/s around the Adriatic microplate, clearly connected with the slab structure inferred from teleseismic P wave tomography and supportive of continental subduction along the Dinaric, Alpine and Apenninic subduction zones. Contrasting styles of subduction are observed on the opposite sides of the Adriatic microplate: a laterally variable SW-dipping subduction is documented beneath the Apennines, continental to the north and oceanic to the south, where rollback is faster: a laterally continuous NE-dipping continental subduction is documented under the Dinarides. The lack of a precursor oceanic slab under the Dinarides demonstrates that the onset of continental subduction, in complex plate-boundary zones, can be controlled by plate-tectonic processes far away from the subduction initiation site, and may take place without the contribution of the negative buoyancy of an old oceanic lithosphere. (C) 2019 Elsevier B.V. All rights reserved.
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Sushchevskaya, N. M., Belyatsky, B. V., Leitchenkov, G. L., Batanova, V. G., & Sobolev, A. V. (2019). Geochemical Characteristics of Jurassic Plume Magmatism in Ahlmannryggen Massif (Queen Maud Land, East Antarctica). Doklady Earth Sciences, 486(1), 529–532.
Résumé: The Mesozoic dykes related to the distribution of Karoo plume on the territory of East Antarctica are studied. It is shown that magnesian high-Ti ferrobasalts are found in the area of Ahlmannryggen massif. Their formation is determined by melting of the mantle that contains pyroxenite. The isotope characteristics of the studied dolerites reflect the composition of a pyroxenite source, i.e., the ancient oceanic lithosphere (EMI) that subsided to the mantle depths of 150-170 km in the paleosubduction zone of the continent of Gondwana and was transformed to the pyroxenite melt 180 Ma ago during the interaction with mantle peridotite of the plume.
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Sushchevskaya, N. M., Belyatsky, B. V., Leitchenkov, G. L., Batanova, V. G., & Sobolev, A. V. (2019). The geochemical characteristics of the Jurassic plume magmatism within Ahlmannryggen massif (Queen Maud Land, East Antarctica). Doklady Akademii nauk, 486(1), 98–102.
Résumé: Mesozoic dikes associated with the Karoo plume were studied within the East Antarctica where at Queen Maud Land on the Almannryggen massif high-Ti magnesian Fe-basalts were found. It is assumed that such basalts originate by means of the pyroxenite-containing mantle melting. The isotopic characteristics of the studied dolerites reflect the composition of the pyroxenite source – the ancient oceanic lithosphere (ЕМI), submerged at the mantle depths of 150-170 km in the paleosubduction zone of the Gondwanian continent and transformed 180 m.y. ago into the pyroxenite melt when interacting with the plume mantle peridotite.
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Sushchevskaya, N. M., Shishkina, T. A., Portnyagin, M. V., Batanova, V. G., & Belyatsky, B. V. (2019). Long-Lasting Influence of the Discovery Plume on Tholeiitic Magmatism in the South Atlantic: Data on Basalts Recovered by Hole 513a, DSDP Leg 71. Geochemistry International, 57(2), 113–133.
Résumé: The paper presents the very first data on concentrations of major and trace elements; Sr, Nd, and Pb isotopic ratios of rocks; and the composition of olivine phenocrysts of 38-Ma basalts recovered by Hole 513a (DSDP Leg 71) in the South Atlantic. The bulk-rock samples and the chilled glasses are mildly magnesian (7-8 wt % MgO) and bear elevated FeO and low Na2O concentrations, as is typical of MORB of the TOR-1 type. Olivine phenocrysts (Fo(84.5-88)) in these rocks contain concentrations of trace elements (Ni, Mn, Cr, and Zn) that are typical of classic MORB, which are produced by partial melting of mantle peridotite. The rocks are strongly depleted in incompatible elements [(La/Sm)(n) similar to 0.6] but have elevated Ba/Nb, K/Nb, and Pb/Ce ratios and Cu, Ag, and Au concentrations that are 1.5-4 times higher than in typical depleted MORB (N-MORB) and in most rift basalts in the South Atlantic. Isotope compositions of the basalts (average ratios Pb-206/Pb-204 similar to 18.0; Pb-207/Pb-204 similar to 15.6, Pb-208/Pb-204 similar to 38.0, Nd-143/144Nd similar to 0.5130, and Sr-87/Sr-86 similar to 0.7040) are close to those in modern tholeiites from the southern MAR segment (SMAR) north of the Agulhas Fracture Zone. The data indicate that the magmas were derived from a strongly depleted mantle source that contained a minor (similar to 3%) admixture of an enriched component, which is discernible in the magmas of the Discovery hotspot. The composition of the source, which is more depleted than DM, and the high degrees of melting of this source explain why the basalts from DSDP Hole 513a are enriched in chalcophile elements. It is believed that spreading magmatism at 45 degrees-48 degrees S in SMAR as far back as 40 Ma was already affected by the Discovery hotspot. This hotspot might be related to the Tristan plume system, and its origin and long-lasting influence on spreading magmatism in the South Atlantic are regarded as evidence of the extensive effect of the Tristan plume.
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Sushchevskaya, N. M., Shishkina, T. A., Portnyagin, M. V., Batanova, V. G., & Belyatsky, B. V. (2019). Long-lasting influence of the Discovery plume on tholeiitic magmatism in the South Atlantic: data on basalts recovered by hole 513a, dsdp leg 71. Geokhimiya, 64(2), 107–127.
Résumé: The paper presents the very first data on concentrations of major and trace elements; Sr, Nd, and Pb isotopic ratios of rocks; and the composition of olivine phenocrysts of 38-Ma basalts recovered by Hole 513a (DSDP Leg 71) in the South Atlantic. The bulk-rock samples and the chilled glasses are mildly magnesian (7-8 wt % MgO) and bear elevated FeO and low Na2O concentrations, as is typical of MORB of the TOR-1 type. Olivine phenocrysts (Fo84.5-88) in these rocks contain concentrations of trace elements (Ni, Mn, Cr, and Zn) that are typical of classic MORB, which are produced by partial melting mantle peridotite. The rocks are strongly depleted in incompatible elements [(La/Sm)n ~ 0.6] but have elevated Ba/Nb, K/Nb, and Pb/Ce ratios and Cu, Ag, and Au concentrations that are 1.5-4 times higher than in typical depleted MORB (N-MORB) and in most rift basalts in the South Atlantic. Isotope compositions of the basalts (average ratios 206Pb/204Pb ~ 18.0; 207Pb/204Pb ~ 15.6, 208Pb/204Pb ~ 38.0, 143Nd/144 Nd ~ 0.5130, and 87Sr/86Sr ~ 0.7040) are close to those in modern tholeiites from the southern MAR segment (SMAR) north of the Agulhas Fracture Zone. The data indicate that the magmas were derived from a strongly depleted mantle source that contained a minor (~3%) admixture of an enriched component, which is discernible in the magmas of the Discovery hotspot. The composition of the source, which is more depleted than DM, and the high degrees of melting of this source explain why the basalts from DSDP Hole 513a are enriched in chalcophile elements. It is believed that spreading magmatism at 45°-48° S in SMAR as far back as 40 Ma was already affected by the Discovery hotspot. This hotspot might be related to the Tristan plume system, and its origin and long-lasting influence on spreading magmatism in the South Atlantic are regarded as evidence of the extensive effect of the Tristan plume.
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Syahbana, D. K., Kasbani, K., Suantika, G., Prambada, O., Andreas, A. S., Saing, U. B., et al. (2019). The 2017-19 activity at Mount Agung in Bali (Indonesia): Intense unrest, monitoring, crisis response, evacuation , and eruption. Scientific Reports, 9.
Résumé: After 53 years of quiescence, Mount Agung awoke in August 2017, with intense seismicity, measurable ground deformation, and thermal anomalies in the summit crater. Although the seismic unrest peaked in late September and early October, the volcano did not start erupting until 21 November. The most intense explosive eruptions with accompanying rapid lava effusion occurred between 25 and 29 November. Smaller infrequent explosions and extrusions continue through the present (June 2019). The delay between intense unrest and eruption caused considerable challenges to emergency responders, local and national governmental agencies, and the population of Bali near the volcano, including over 140,000 evacuees. This paper provides an overview of the volcanic activity at Mount Agung from the viewpoint of the volcano observatory and other scientists responding to the volcanic crisis. We discuss the volcanic activity as well as key data streams used to track it. We provide evidence that magma intruded into the mid-crust in early 2017, and again in August of that year, prior to intrusion of an inferred dike between Mount Agung and Batur Caldera that initiated an earthquake swarm in late September. We summarize efforts to forecast the behavior of the volcano, to quantify exclusion zones for evacuations, and to work with emergency responders and other government agencies to make decisions during a complex and tense volcanic crisis.
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Taral, S., Chakraborty, T., Huyghe, P., van der Beek, P., Vogeli, N., & Dupont-Nive, G. (2019). Shallow marine to fluvial transition in the Siwalik succession of the Kameng River section, Arunachal Himalaya and its implication for foreland basin evolution. Journal Of Asian Earth Sciences, 184.
Résumé: An understanding of the depositional environment and paleogeography of the Siwalik foreland basin are crucial in interpreting the basin configuration, sediment transport pathways and its evolutionary history. This study examines the sedimentology of the Siwalik succession of the Kameng River valley, Arunachal Himalaya, northeastern India. The facies characteristics of the fine-grained, well-sorted sediments of the Dafla Formation and its complex, polymodal paleocurrent pattern in this section, reveals deposition in a variety of open marine to deltaic environment. The overlying Subansiri Formation, characterized by coarse-grained, thick, multistoried sandstone, and showing more consistent SW-ward paleocurrent, indicate deposition from a large, axial braided river system. The proposed redefinition of the boundary between the Lower Siwalik Dafia and the Middle Siwalik Subansiri formations implies their transition at around 7.5 Ma, instead of 10.5 Ma, suggested earlier. The revised age of the transition is consistent with the age of arrival of the Transhimalayan sediments at 7 Ma and also denotes the time of marine to fluvial transition in this area. Presence of marine sediments in the Kameng section, with similar records further west, indicates the existence of an extensive seaway in the eastern Himalaya during the lower Siwalik time. The extant paleodrainage reconstructions have been recast on the basis of new data on the sedimentology and paleocurrent from this section. It is inferred that the changing sea level, uplifting Shillong Plateau and drainage evolution in the eastern Himalayan foreland during the middle Miocene time controlled the marine to fluvial transition in the basin.
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Tarantini, A., Wegner, K. D., Dussert, F., Sarret, G., Beal, D., Mattera, L., et al. (2019). Physicochemical alterations and toxicity of InP alloyed quantum dots aged in environmental conditions: A safer by design evaluation. Nanoimpact, 14.
Résumé: Due to their unique optical properties, quantum dots (QDs) are used in a number of optoelectronic devices and are forecasted to be used in the near future for biomedical applications. The most popular QD composition consists of cadmium selenide (CdSe) or cadmium telluride (CdTe), which has been shown to pose health risks due to the release of toxic cadmium (Cd) ions. Due to similar optical properties but lower intrinsic toxicity, indium phosphide (InP) QDs have been proposed as a safer alternative. Nevertheless, investigations regarding their safety and possible toxicological effects are still in their infancy. The fate and toxicity of seven different water-dispersible indium (In)-based QDs, either pristine or after ageing in a climatic chamber, was evaluated. The core of these QDs was composed of indium, zinc and phosphorus (InZnP) or indium, zinc, phosphorus and sulfur (InZnPS). They were assessed either as core-only or as core-shell QDs, for which the core was capped with a shell of zinc, selenium and sulfur (Zn(Se,S)). Their surface was functionalized using either penicillamine or glutathione. In their pristine form, these QDs showed essentially no cytotoxicity. The particular case of InZnPS QD showed that core-shell QDs were less cytotoxic than core-only QDs. Moreover, surface functionalization with either penicillamine or glutathione did not appreciably influence cytotoxicity but affected QD stability. These QDs did not lead to over-accumulation of reactive oxygen species in exposed cells, or to any oxidative damage to cellular DNA. However, accelerated weathering in a climatic chamber led to QD precipitation and degradation, together with significant cytotoxic effects. Ageing led to dissociation of In-P and Zn-S bonds, and to complexation of In and Zn ions with carboxylate and/or phosphate moieties. These results show that InZnP and InZnPS alloyed QDs are safer alternatives to CdSe QDs. They underline the necessity to preserve as much as possible the structural integrity of QDs, for instance by developing more robust shells, in order to ensure their safety for future applications.
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Tartrat, T., Revil, A., Abdulsamad, F., Ghorbani, A., Jougnot, D., Coperey, A., et al. (2019). Induced polarization response of porous media with metallic particles – Part 10: Influence of desiccation. Geophysics, 84(5), E357–E375.
Résumé: Desiccation influences the complex conductivity of porous media with disseminated metallic particles. We expand the mechanistic model developed in the previous papers of this series to include the effect of saturation upon the complex conductivity of mixtures of mineral grains, pyrite, and pore water. During desiccation, the salt is assumed to be segregated in the liquid pore water; therefore, the conductivity of the pore water increases when saturation decreases. We have performed 14 experiments corresponding to 91 complex conductivity spectra. In these experiments, the saturation of the water phase is changed over time by desiccation. The resulting spectra are fitted by a double Cole-Cole model used as the fitting model. We also developed a mechanistic model in which the chargeability and the relaxation time of the low-frequency polarization are expected to change with saturation in a predictable way. We first characterized the properties of the background material made by an illitic clay material. We determine how the Cole-Cole parameters depend on saturation. The Cole-Cole exponent is essentially independent on saturation. When the chargeability of the mixture is dominated by the presence of pyrite, it becomes independent of the saturation but a small effect on the chargeability is observed at low pyrite contents. The instantaneous conductivity of the background decreases with the saturation in a predictable way. The relaxation time depends on the inverse of the instantaneous conductivity and therefore on saturation. This dependence is well-explained through numerical simulations made with the finite-element method. Finally, we analyze the complex conductivity spectra of two clay-rock core samples from the Callovo-Oxfordian formation in the Paris Basin (France). The spectra are shown as a function of their desiccation and explained thanks to the newly developed model.
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Tavakoli, B. F., Operto, S., Ribodetti, A., & Virieux, J. (2019). Matrix-free anisotropic slope tomography: Theory and application. Geophysics, 84(1), R21–R43.
Résumé: Slope tomography uses traveltimes, source, and receiver slopes of locally coherent events to build subsurface velocity models. Locally coherent events by opposition to continuous reflections are suitable for semiautomatic and dense picking, which is conducive to better resolved tomographic models. These models can be further used as background/initial models for depth migration or full-waveform inversion. Slope tomography conventionally relies on ray tracing for traveltimes and slopes computation, where rays are traced from scatterers in depth to sources and receivers. The inverse problem relies on the explicit building of the sensitivity matrix to update the velocity model by local optimization. Alternatively, slope tomography can be implemented with eikonal solvers, which compute efficiently finely sampled traveltime maps from the sources and receivers, whereas slopes are estimated by finite differences of the traveltime maps. Moreover, a matrix-free inverse problem can be implemented with the adjoint-state method for the estimation of the data-misfit gradient. This new formulation of slope tomography is extended to tilted transverse isotropic (TTI) acoustic media, in which the model space is parameterized by four anisotropic parameters (e.g., vertical wave-speed, Thomson's parameter delta, is an element of,and tilt angle) and the coordinates of the scatterers. A toy synthetic example allows for a first assessment of the crosstalk between anisotropic parameters and scatterer coordinates. A more realistic synthetic example indicates the feasibility of the joint update of the vertical wavespeed and is an element of. The slope tomography is finally applied to real broadband towed-streamer data to build the vertical velocity and the scatterers, while anisotropic parameters is an element of and delta are used as background parameters. The velocity model quality is assessed through common-image gathers computed by TTI Kirchhoff prestack-depth migration.
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Taylor, G., Rost, S., Houseman, G. A., & Hillers, G. (2019). Near-surface structure of the North Anatolian Fault zone from Rayleigh and Love wave tomography using ambient seismic noise. Solid Earth, 10(2), 363–378.
Résumé: We use observations of surface waves in the ambient noise field recorded at a dense seismic array to image the North Anatolian Fault zone (NAFZ) in the region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip fault system extending similar to 1200 km across northern Turkey that poses a high level of seismic hazard, particularly to the city of Istanbul. We obtain maps of phase velocity variation using surface wave tomography applied to Rayleigh and Love waves and construct high-resolution images of S-wave velocity in the upper 10 km of a 70 x 30 km region around Lake Sapanca. We observe low S-wave velocities (< 2.5 km s(-1)) associated with the Adapazari and Pamukova sedimentary basins, as well as the northern branch of the NAFZ. In the Armutlu Block, between the two major branches of the NAFZ, we image higher velocities (> 3.2 km s(-1)) associated with a shallow crystalline basement. We measure azimuthal anisotropy in our phase velocity observations, with the fast direction seeming to align with the strike of the fault at periods shorter than 4 s. At longer periods up to 10 s, the fast direction aligns with the direction of maximum extension for the region (similar to 45 degrees). The signatures of both the northern and southern branches of the NAFZ are clearly associated with strong gradients in seismic velocity that also denote the boundaries of major tectonic units. Our results support the conclusion that the development of the NAFZ has exploited this pre-existing contrast in physical properties.
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Thery, R., Guillemot, A., Abraham, O., & Larose, E. (2019). Tracking fluids in multiple scattering and highly porous materials: Toward applications in non-destructive testing and seismic monitoring. Ultrasonics, 102, 106019.
Résumé: Seismic and ultrasonic waves are sometimes used to track fluid injections, propagation, infiltrations in complex material, including geological and civil engineered ones. In most cases, one use the acoustic velocity changes as a proxy for water content evolution. Here we propose to test an alternative seismic or acoustic observable: the waveform decorrelation. We use a sample of compacted millimetric sand as a model medium of highly porous multiple scattering materials. We fill iteratively the sample with water, and track changes in ultrasonic waveforms acquired for each water level. We take advantage of the high sensitivity of diffuse coda waves (late arrivals) to track small water elevation in the material. We demonstrate that in the mesoscopic regime where the wavelength, the grain size and the porosity are in the same order of magnitude, Coda Wave Decorrelation (waveform change) is more sensitive to fluid injection than Coda Wave Interferometry (apparent velocity change). This observation is crucial to interpret fluid infiltration in concrete with ultrasonic record changes, as well as fluid injection in volcanoes or snow melt infiltration in rocky glaciers. In these applications, Coda Wave Decorrelation might be an extremely interesting tool for damage assessment and alert systems.
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Thogersen, K., Sveinsson, H. A., Amundsen, D. S., Scheibert, J., Renard, F., & Malthe-Sorenssen, A. (2019). Minimal model for slow, sub-Rayleigh, supershear, and unsteady rupture propagation along homogeneously loaded frictional interfaces. Physical Review E, 100(4).
Résumé: In nature and experiments, a large variety of rupture speeds and front modes along frictional interfaces are observed. Here, we introduce a minimal model for the rupture of homogeneously loaded interfaces with velocity strengthening dynamic friction, containing only two dimensionless parameters; (tau) over bar, which governs the prestress, and (alpha) over bar, which is set by the interfacial viscosity. This model contains a large variety of front types, including slow fronts, sub-Rayleigh fronts, supershear fronts, slip pulses, cracks, arresting fronts, and fronts that alternate between arresting and propagating phases. Our results indicate that this wide range of front types is an inherent property of frictional systems with velocity strengthening branches.
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Thogersen, K., Sveinsson, H. A., Scheibert, J., Renard, F., & Malthe-Sorenssen, A. (2019). The Moment Duration Scaling Relation for Slow Rupture Arises From Transient Rupture Speeds. Geophysical Research Letters, 46(22), 12805–12814.
Résumé: The relation between seismic moment and earthquake duration for slow rupture follows a different power law exponent than subshear rupture. The origin of this difference in exponents remains unclear. Here, we introduce a minimal one-dimensional Burridge-Knopoff model which contains slow, subshear, and supershear rupture and demonstrate that different power law exponents occur because the rupture speed of slow events contains long-lived transients. Our findings suggest that there exists a continuum of slip modes between the slow and fast slip end-members but that the natural selection of stress on faults can cause less frequent events in the intermediate range. We find that slow events on one-dimensional faults follow M over bar 0,slow,1D proportional to T over bar 0.63 with transition to M over bar 0,slow,1D proportional to T over bar 32 for longer systems or larger prestress, while the subshear events follow M over bar 0,sub-shear,1D proportional to T over bar 2. The model also predicts a supershear scaling relation M over bar 0,super-shear,1D proportional to T over bar 3. Under the assumption of radial symmetry, the generalization to two-dimensional fault planes compares well with observations.
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Thurin, J., Brossier, R., & Metivier, L. (2019). Ensemble-based uncertainty estimation in full waveform inversion. Geophysical Journal International, 219(3), 1613–1635.
Résumé: Uncertainty estimation and quality control are critically missing in most geophysical tomographic applications. The few solutions to cope with that issue are often left out in practical applications when these ones grow in scale and involve complex modelling. We present a joint full waveform inversion and ensemble data assimilation scheme, allowing local Bayesian estimation of the solution that brings uncertainty estimation to the tomographic problem. This original methodology relies on a deterministic square root ensemble Kalman filter commonly used in the data assimilation community: the ensemble transform Kalman filter (ETKF). Combined with a 2-D visco-acoustic frequency domain full waveform inversion scheme, the resulting method allows to access a low-rank approximation of the posterior covariance matrix of the solution. It yields uncertainty information through an ensemble-representation, that can conveniently be mapped across the physical domain for visualization and interpretation. The combination of ETKF with full waveform inversion is discussed along with the scheme design and algorithmic details that lead to our mixed application. Both synthetic and field-data results are presented, along with the biases that are associated with the limited rank ensemble representation. Finally, we review the open questions and developments perspectives linked with data assimilation applications to the tomographic problem.
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Tigrine, Z., Nataf, H. - C., Schaeffer, N., Cardin, P., & Plunian, F. (2019). Torsional Alfven waves in a dipolar magnetic field: experiments and simulations. Geophysical Journal International, 219, S83–S100.
Résumé: The discovery of torsional Alfven waves (geostrophic Alfven waves) in the Earth's core (Gillet et al. 2010) calls for a better understanding of their properties. We present the first experimental observations of torsional Alfven waves, performed in the DTS-Omega set-up. In this set-up, 50 L of liquid sodium are confined between an inner sphere (r(i) = 74 mm) and an outer shell (r(o) = 210 mm). The inner sphere houses a permanent magnet, imposing a dipolar magnetic field (B-max = 345 mT). Both the inner sphere and the outer shell can rotate around the vertical axis. Alfven waves are triggered by a sudden jerk of the inner sphere. We study the propagation of these waves when the fluid is initially at rest, and when it spins at a rotation rate up to 15 Hz. We measure the azimuthal magnetic field of the wave at different radii inside the fluid with magnetometers installed in a sleeve. We also record the electric potential signature on the outer shell at several latitudes. Besides, we probe the associated azimuthal velocity field using ultrasound Doppler velocimetry. With a 15 Hz rotation rate, the dynamical regimes we achieve are characterized by dimensionless numbers in the following ranges: Lundquist number 0.5 < Lu < 12, Lehnert number 0.01 < Le < 0.26, Rossby number Ro similar to 0.1. We observe that the magnetic signal propagates away from the inner sphere, strongly damped by magnetic diffusion. Rotation affects the magnetic signature in a subtle way. Its effect is more pronounced on the surface electric potentials, which are sensitive to the actual fluid velocity of the wave. The ultrasound Doppler probes provide the first experimental measurement of the fluid velocity of an Alfven wave. To complement these observations, we ran numerical simulations, using the XSHELLS pseudospectral code with parameters as close as possible to the experimental ones. The synthetic magnetic and electric signals match our measurements. The meridional snapshots of the synthetic azimuthal velocity field reveal the formation of geostrophic cylinders expected for torsional Alfven waves. We establish scaling laws for the magnetic and kinetic energies of Alfven waves with and without rotation. In both cases, we find that the magnetic energy EM saturates at a level proportional to Rm(jerk)(2), where Rm(jerk) = U(jerk)r(o)/eta is the magnetic Reynolds number built with the maximum azimuthal velocity of the inner sphere during the jerk. The E-K(max)/E-M(max) ratio (where E-K(max) is the maximum kinetic energy), close to 1 for very quick jerks, increases linearly with the jerk duration.
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Tonazzi, D., Massi, F., Salipante, M., Baillet, L., & Berthier, Y. (2019). Estimation of the Normal Contact Stiffness for Frictional Interface in Sticking and Sliding Conditions. Lubricants, 7(7).
Résumé: Modeling of frictional contact systems with high accuracy needs the knowledge of several contact parameters, which are mainly related to the local phenomena at the contact interfaces and affect the complex dynamics of mechanical systems in a prominent way. This work presents a newer approach for identifying reliable values of the normal contact stiffness between surfaces in contact, in both sliding and sticking conditions. The combination of experimental tests, on a dedicated set-up, with finite element modeling, allowed for an indirect determination of the normal contact stiffness. The stiffness was found to increase with increasing contact pressure and decreasing roughness, while the evolution of surface topography and third-body rheology affected the contact stiffness when sliding.
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Toybou, D., Celle, C., Aude-Garcia, C., Rabilloud, T., & Simonato, J. - P. (2019). A toxicology-informed, safer by design approach for the fabrication of transparent electrodes based on silver nanowires. Environmental Science-Nano, 6(2), 684–694.
Résumé: Fabrication of silver nanowires (AgNWs) with fine and independent control of both the diameter (from 30 to 120 nm) and length (from 5 to 120 μm) by concomitant addition of co-nucleants and temperature control is demonstrated, and used for the preparation of size standards. Percolating random networks were fabricated using these standards and their optoelectronic properties were measured and compared with regard to the nanowire dimensions. The transparent electrodes appear suitable for various applications and exhibit excellent performances (e.g. 16 ohm sq(-1) at 93% transparency), with haze values varying from 1.6 to 26.2%. Besides, in vitro toxicological studies carried out on murine macrophages with the same size standards revealed that AgNWs are weakly toxic (no toxicity observed below 50 μg mL(-1) Ag), in particular compared to other silver nanoparticles. Short AgNWs (4 μm) appeared to be slightly more toxic than longer AgNWs (10 and 20 μm). Conversely, long AgNWs (20 μm) induced a more prolonged pro-inflammatory response in murine macrophages. These results contribute, in a safer by design approach, to promoting the use of short AgNWs. The global knowledge dealing with the combination of nanowire dimensions associated with optoelectronic performances and related toxicity should encourage the rational use of AgNWs, and guide the choice of the most adequate AgNW dimensions in an integrated approach.
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Toybou, D., Celle, C., Aude-Garcia, C., Rabilloud, T., & Simonato, J. - P. (2019). A toxicology-informed, safer by design approach for the fabrication of transparent electrodes based on silver nanowires (vol 6, pg 684, 2019). Environmental Science-Nano, 6(2), 695–696.
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Tretyakov, A. A., Pilitsyna, A. V., Degtyarev, K. E., Salnikova, E. B., Kovach, V. P., Lee, H. - Y., et al. (2019). Neoproterozoic granitoid magmatism and granulite metamorphism in the Chu-Kendyktas terrane (Southern Kazakhstan, Central Asian Orogenic Belt): Zircon dating, Nd isotopy and tectono-magmatic evolution. Precambrian Research, 332.
Résumé: Within the Chu-Kendyktas Precambrian terrane located in Southern Kazakhstan (in the western part of the Central Asian Orogenic Belt), medium- and high-grade metamorphic formations have been identified and attributed to the Aydaly and Shukyr Complexes. The Aydaly Complex is predominantly composed of orthogneisses with a Neoproterozoic protolith age of 790 Ma and subordinate high-temperature granulites comprising a succession of amphibolites, amphibole-rich granulites, mesocratic granulites, and melanocratic (clinopyroxene-rich) and leucocratic (melt-rich) granulites, which were evidently formed at moderate pressures of 6-9 kbar and high temperatures, increasing from 700 to 900 degrees C or more. The clinopyroxene-rich granulites of the Aydaly Complex contain detrital zircon grains of mainly Palaeoproterozoic (1790-2058 Ma) and, to a more limited extent, Neoarchean (similar to 2500 Ma) ages, with preserved magmatic zoning and indicating a sedimentary origin of the protolith via mafic greywackes that were subsequently metamorphosed to amphibolites. The age estimates of the leucocratic melt-rich granulites, which form veins or layers within the clinopyroxene-rich melanosome, correspond to the range 770-790 Ma and define the Neoproterozoic stage of magmatism and granulite metamorphism. Hence, the deposition of the sedimentary protolith for the Aydaly Complex granulites and its subsequent emplacement at mid-crustal levels occurred from the middle Palaeoproterozoic (similar to 1800 Ma) to the late Tonian (similar to 770-790 Ma). In turn, the Shukyr Complex consists of garnet-biotite schists, which are characterised by a significantly lower grade of metamorphism compared to the Aydaly Complex, at around T similar to 600 degrees C. The garnet-biotite schists are thought to represent moderate-temperature hornfels, located at the contact between the protolith (shales) and the Early Palaeozoic Ulken massif granitoids. The deposition of the Shukyr Complex protolith occurred during the Ediacaran-Cambrian, as a result of the erosion of mainly Mesoproterozoic (1000 Ma), and to a lesser extent Palaeoproterozoic (2460 Ma), rocks. The Sm-Nd whole-rock isotopic compositions suggest that the formation of the protoliths of the Aydaly and Shukyr Complexes was related to the reworking of Palaeoproterozoic continental crust.
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Truche, L., & Bazarkina, E. F. (2019). Natural hydrogen the fuel of the 21st century (Vol. 98).
Résumé: Much has been learned about natural hydrogen (H-2) seepages and accumulation, but present knowledge of hydrogen behavior in the crust is so limited that it is not yet possible to consider exploitation of this resources. Hydrogen targeting requires a shift in the long-standing paradigms that drive oil and gas exploration. This paper describes the foundation of an integrated source-to-sink view of the hydrogen cycle, and propose preliminary practical guidelines for hydrogen exploration.
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Tsopela, A., Donze, F. - V., Guglielmi, Y., Castilla, R., & Gout, C. (2019). Hydromechanical reactivation of natural discontinuities: mesoscale experimental observations and DEM modeling. Acta Geotechnica, 14(5), 1585–1603.
Résumé: Fracture interaction mechanisms and reactivation of natural discontinuities under fluid pressurization conditions can represent critical issues in risk assessment of caprock integrity. A field injection test, carried out in a damage fault zone at the decameter scale, i.e., mesoscale, has been studied using a distinct element model. Given the complex structural nature of the damage fault zone hydraulically loaded, the contribution of fracture sets on the bulk permeability has been investigated. It has been shown that their orientation for a given in situ stress field plays a major role. Based on these results, a simpler model with a fluid-driven fracture intersecting a second fracture has been set up to perform a sensitivity analysis. It is in presence of a minimum differential stress value with a minimum angle with the maximum principal stress that the second fracture could be both, hydraulically and mechanically reactivated. Results also showed that in the vicinity of the fluid-driven fracture, a natural fracture will offer contrasted hydromechanical responses on each side of the intersection depending on the stress conditions and its orientation with respect to the stress field. In this case, we show that a hydromechanical decoupling can occur along the same plane. These results provide insights into fracture-controlled permeability of fault zones depending on the properties of the fractures and their hydromechanical interactions for a given in situ stress field.
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Uber, M., Legout, C., Nord, G., Crouzet, C., Demory, F., & Poulenard, J. (2019). Comparing alternative tracing measurements and mixing models to fingerprint suspended sediment sources in a mesoscale Mediterranean catchment. Journal Of Soils And Sediments, 19(9), 3255–3273.
Résumé: Purpose Knowledge of suspended sediment provenance in mesoscale catchments is important for applying erosion control measures and best management practices as well as for understanding the processes controlling sediment transport in the critical zone. As suspended sediment fluxes are highly variable in time, particularly given the variability of soil and rainfall properties in mesoscale catchments, knowledge of sediment provenance at high temporal resolution is crucial. Materials and methods Suspended sediment fluxes were analyzed at the outlet of a 42-km(2) Mediterranean catchment belonging to the French critical zone observatory network (OZCAR). Spatial origins of the suspended sediments were analyzed at high temporal resolution using low-cost analytical approaches (color tracers, X-ray fluorescence, and magnetic susceptibility). As the measurements of magnetic susceptibility provide only one variable, they were used for cross-validation of the results obtained with the two alternative tracing methods. The comparison of the tracer sets and three mixing models (non-negative least squares, Bayesian mixing model SIMMR, and partial least squares regression) allowed us to estimate different sources of errors inherent in sediment fingerprinting studies and to assess the challenges and opportunities of using these fingerprinting methods. Results and discussion All tracer sets and mixing models could identify marly badlands as the main source of suspended sediments. However, the percentage of source contributions varied between the 11 flood events in the catchment. The mean contribution of the badlands varied between 74 and 84%; the topsoils on sedimentary geology ranged from 12 to 29% and the basaltic topsoils from 1 to 8%. While for some events the contribution remained constant, others showed a high within-event variability of the sediment provenance. Considerable differences in the predicted contributions were observed when different tracer sets (mean RMSE 19.9%) or mixing models (mean RMSE 10.1%) were used. Our result shows that the choice of the tracer set was more important than the choice of the mixing model. Conclusions These results highlighted the importance of using multi-tracer multi-model approaches for sediment fingerprinting in order to obtain reliable estimates of source contributions. As a given fingerprinting approach might be more sensitive to one type of error, i.e., source variability, particle size selectivity, multi-tracer ensemble predictions allow to detect and quantify these potential biases. High sampling resolution realized with low-cost methods is important to reveal within- and between-event dynamics of sediment fluxes and to obtain reliable information of main contributing sources.
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Vacher, L. G., Truche, L., Faure, F., Tissandier, L., Mosser-Ruck, R., & Marrocchi, Y. (2019). Deciphering the conditions of tochilinite and cronstedtite formation in CM chondrites from low temperature hydrothermal experiments. Meteoritics & Planetary Science, 54(8), 1870–1889.
Résumé: Tochilinite/cronstedtite intergrowths are commonly observed as alteration products in CM chondrite matrices, but the conditions under which they formed are still largely underconstrained due to their scarcity in terrestrial environments. Here, we report low temperature (80 degrees C) anoxic hydrothermal experiments using starting assemblages similar to the constituents of the matrices of the most pristine CM chondrite and S-rich and S-free fluids. Cronstedtite crystals formed only in S-free experiments under circumneutral conditions with the highest Fe/Si ratios. Fe-rich tochilinite with chemical and structural characteristics similar to chondritic tochilinite was observed in S-bearing experiments. We observed a positive correlation between the Mg content in the hydroxide layer of synthetic tochilinite and temperature, suggesting that the composition of tochilinite is a proxy for the alteration temperature in CM chondrites. Using this relation, we estimate the mean precipitation temperatures of tochilinite to be 120-160 degrees C for CM chondrites. Given the different temperature ranges of tochilinite and cronstedtite in our experiments, we propose that Fe-rich tochilinite crystals resulted from the alteration of metal beads under S-bearing alkaline conditions at T = 120-160 degrees C followed by cronstedtite crystals formed by the reaction of matrix amorphous silicates, metal beads, and water at a low temperature (50-120 degrees C).
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Valayer, P. J., Vidal, O., Wouters, N., & van Loosdrecht, M. C. M. (2019). The full energy cost of avoiding CO2: A clean-energy booking provision for a vigorous energy transition. Journal Of Cleaner Production, 237.
Résumé: Carbon tax, emission trading schemes and externality disclosures have not provided the incentive to replace fossil-carbon sourced energy as envisioned at the Paris Agreement 2015. Much of the enforcement of these schemes is outside the fossil hydrocarbon producer's control. As an alternate to these schemes, this paper proposes an inventive evaluation and accounting procedure, based on the energy penalty cost of decarbonizing fossil fuels. Such cost can be internalized within the producer's books, and provide the required incentives, including provisions for the deployment of carbon-free fuels. In the inspiring thermodynamics of hydrocarbon to hydrogen conversion in a closed system using hydrogen combustion to decompose the hydrocarbon, we find a penalty of 0.56J for each Joule available in the original hydrocarbon. Applying energy market price range of 150-500 $/t methane and molecular mass-conversion to CO2 equivalent, results in costs ranging from 60 to more than 200$/t CO2. They are well above current carbon tax or emission trading schemes prices. They quantify the required incentives to cleaner (C-free) production yielding prompt emission reduction in the producers' market. We show how similar penalties accrue from a broad spectrum of industrial hydrogen production processes using hydrocarbons. Among those, methane pyrolysis produces carbon-free energy from fossil fuels, with noncombustion promising applications for its carbon production. (C) 2019 Elsevier Ltd. All rights reserved.
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van Baarsel, T., Roux, P., Mars, J. I., Bonnel, J., Arrigoni, M., Kerampran, S., et al. (2019). Dynamic imaging of a capillary-gravity wave in shallow water using amplitude variations of eigenbeams. Journal Of The Acoustical Society Of America, 146(5), 3353–3361.
Résumé: Dynamic acoustic imaging of a surface wave propagating at an air-water interface is a complex task that is investigated here at the laboratory scale through an ultrasonic experiment in a shallow water waveguide. Using a double beamforming algorithm between two source-receiver arrays, the authors isolate and identify each multi-reverberated eigenbeam that interacts with the air-water and bottom interfaces. The waveguide transfer matrix is recorded 100 times per second while a low-amplitude gravity wave is generated by laser-induced breakdown at the middle of the waveguide, just above the water surface. The controlled, and therefore repeatable, breakdown results in a blast wave that interacts with the air-water interface, which creates ripples at the surface that propagate in both directions. The amplitude perturbations of each ultrasonic eigenbeam are measured during the propagation of the gravity-capillary wave. Inversion of the surface deformation is performed from the amplitude variations of the eigenbeams using a diffraction-based sensitivity kernel approach. The accurate ultrasonic imaging of the displacement of the air-water interface is compared to simultaneous measurements with an optical camera, which provides independent validation. (C) 2019 Acoustical Society of America.
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Van Driessche, A. E. S., Stawski, T. M., & Kellermeier, M. (2019). Calcium sulfate precipitation pathways in natural and engineered environments. Chemical Geology, 530.
Résumé: The solution-mediated formation of calcium sulfate minerals, i.e. gypsum, anhydrite and bassanite, is a common process in both natural and engineered settings. It plays a key role in the global sulfur cycle and serves as an indicator of past environmental conditions on Earth and Mars. Products relying on the crystallization of these minerals have been employed since antiquity, and today they are an essential part of a wide array of industrial applications. Accordingly, the fundamental aspects of calcium sulfate mineralization have been the focus of intensive research during the past century. However, a recent flurry of studies addressing alternative, i.e. nonclassical, nucleation and growth mechanisms has spurred a revisit of the precipitation pathway of the most common phase, gypsum. The newly obtained data sketch a far more complex picture of the mineralization process than previously assumed. This has important consequences for the interpretation of calcium sulfate deposits, both from a geochemical and industrial point of view. In order to shed light on this issue, we discuss in this review both recent and long-standing observations of abiotic formation routes of calcium sulfate minerals as a function of the physicochemical solution properties. By integrating both the classical and non-classical perspectives on crystallization we put forward a unified model for calcium sulfate crystallization. Using this model, we (re)-evaluate the phase stability and transformations taking place in the CaSO4-H2O system. Next, we look into the formation of calcium sulfate minerals occurring in close association with the biosphere. Employing the abiotic case scenario as a benchmarking tool, the possible influence and/or control exerted by biological activity (and its byproducts) on the precipitation pathway is critically reviewed. Finally, we point out the central issues that need to be resolved if we wish to fully understand, and control, the formation of calcium sulfate solids in natural and engineered environments.
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Verma, M. K., Stepanov, R., & Plunian, F. (2019). Energy Transfers In Mhd Turbulence And Its Applications To Dynamo. Magnetohydrodynamics, 55(1-2), 215–223.
Résumé: In this paper, we describe mode-to-mode energy transfers and energy fluxes of MHD turbulence. These energy transfers are very useful for understanding turbulence dynamics, as well as for applications, such as dynamo. We illustrate how the energy fluxes provide valuable insights into the mechanism of growth of large-scale magnetic energy in dynamo.
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Vidal, J., Cebron, D., Ud-Doula, A., & Alecian, E. (2019). Fossil field decay due to nonlinear tides in massive binaries. Astronomy & Astrophysics, 629.
Résumé: Context. Surface magnetic fields have been detected in 5-10% of isolated massive stars, hosting outer radiative envelopes. They are often thought to have a fossil origin, resulting from the stellar formation phase. Yet, magnetic massive stars are scarcer in (close) short-period binaries, as reported by the BinaMIcS (Binarity and Magnetic Interaction in various classes of Stars) Collaboration. Aims. Different physical conditions in the molecular clouds giving birth to isolated stars and binaries are commonly invoked. In addition, we propose that the observed lower magnetic incidence in close binaries may be due to nonlinear tides. Indeed, close binaries are probably prone to tidal instability, a fluid instability growing upon the equilibrium tidal flow via nonlinear effects. Yet, stratified effects have hitherto been largely overlooked. Methods. We theoretically and numerically investigate tidal instability in rapidly rotating, stably stratified fluids permeated by magnetic fields. We use the short-wavelength stability method to propose a comprehensive (local) theory of tidal instability at the linear onset, discussing damping effects. Then, we propose a mixing-length theory for the mixing generated by tidal instability in the nonlinear regime. We successfully assess our theoretical predictions against proof-of-concept, direct numerical simulations. Finally, we compare our predictions with the observations of short-period, double-lined spectroscopic binary systems. Results. Using new analytical results, cross-validated by a direct integration of the stability equations, we show that tidal instability can be generated by nonlinear couplings of inertia-gravity waves with the equilibrium tidal flow in short-period massive binaries, even against the Joule diffusion. In the nonlinear regime, a fossil magnetic field can be dissipated by the turbulent magnetic diffusion induced by the saturated tidal flows. Conclusions. We predict that the turbulent Joule diffusion of fossil fields would occur in a few million years for several short-period massive binaries. Therefore, turbulent tidal flows could explain the observed dearth of some short-period magnetic binaries.
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Vidal, O., Rostom, F. Z., Francois, C., & Giraud, G. (2019). Prey-Predator Long-Term Modeling of Copper Reserves, Production, Recycling, Price, and Cost of Production. Environmental Science & Technology, 53(19), 11323–11336.
Résumé: The dynamics of copper production is modeled with a prey-predator approach linking the evolution of reserves to that of industrial wealth. Our model differs from earlier approaches in that it does not require a priori knowledge of the initial stock of resources. The model variables and a long-term reference price are estimated from historical data, taking into account the combined effects on price and reserve of technological improvements and changes in ore grade. The business-as-usual scenarios invariably lead to a peak of primary production by the middle of the century. The peak of production is not the result of the complete exhaustion of exploitable copper but of the combination of (1) the deviation of growth of reserves from the exponential historical trend and (2) the incapacity of technological improvements to offset the increase in production costs. In the leveled-off-demand scenario for which future demand is simulated based on assumed evolutions of world population and gross domestic product per capita, no collapse of primary production is observed within the century for optimistic regeneration of reserves and a collection-recycling rate reaching 70% by 2100, at constant energy prices.
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Vigneresse, J. - L., Truche, L., & Richard, A. (2019). How do metals escape from magmas to form porphyry-type ore deposits? Ore Geology Reviews, 105, 310–336.
Résumé: Many precious and base metals (Cu, Au, Ag, Mo, W, Sn) in porphyry-type deposits are extracted from a granitic to granodioritic silicate melt and transported by magmatic-hydrothermal fluids to the site of ore deposition. Metals abundance increases from some ppb in the melt to % in ore bodies. Assuming a unique magmatic source for metals, it implies an exceptional combination of enrichment process acting over up to 4 orders of magnitude. Previous models of magma differentiation and hydrothermal circulations omitted to consider the role of metal segregation during magma chamber evolution. Models for the formation and evolution of intrusions have recently shifted from the so-called melting-storage-assimilation-homogenization (MASH) paradigm, basically steady state, to the mantle-melting-segregation-ascent-emplacement (m(M-SAE)) paradigm, dynamic and discontinuous in time. Successive magma injections of variable compositions progressively build the magma chamber. This is supported by field relations (e.g. cross-cutting dykes and stocks), textures (e.g. partially re-sorbed enclaves, or mineral fabrics), geochemistry (e.g. hybridization signatures), and age dating aswell as istopic studies. As melt crystallizes and forms a mush (> 50% crystals), volatiles also exsolve forming a magmatic volatile phase (MVP) while melt motion slows down. Metals partition between the three phases: melt; crystals; and MVP. They generally prefer the MVP owing to more favorable partition coefficients. This is indicated by metal content in coeval melt and fluid inclusions with homogenization temperatures above 600 degrees C, or in volcanic fumaroles. Here, by simulating the physical interactions between the three phases we suggest a model of fluid sparging, during which metals segregate towards the MVP by diffusion and are further transported by advection as metal complexes. The model also provides estimates of metal enrichment. An undimensional Peclet number rules the competition between diffusion and advection, basically scaling with respect to the inverse of the product of melt viscosity (eta) by metal diffusivity (D). The threshold value of the Peclet number between diffusion and advection is roughly 10(-9). Fast diffusive metals (Au, Cu, Ag, W) readily diffuse from silicate melt and towards bubbles of the MVP. To escape the mush through tubular structures, the MVP must overcome a critical gas saturation level (about 20% vol.) usually reached after several magma injections. Advection then takes over and transports the metal-enriched MVP towards the top of the magma chamber. This leads to nearly coeval (1) separation between a high salinity-liquid phase and a low-salinity vapor phase, (2) fluid-rock interactions resulting in potassic, advanced argillic and phyllic alterations and (3) metal deposition. The metal enrichment scales as the ratio between partition coefficient (i.e. related to the gradient in chemical potential), diffusivity (i.e. related to the gradient of concentration), and melt viscosity (i.e. related to the gradient of momentum). The rates at which all such gradients relax determe metals enrichment, inducing chemical and physical instabilities, leading to a cyclic process. The whole cycle also encompasses the case of a partial, non completed, full enrichment yielding to barren intrusions. A tentative model generalizes the sparging fluid model to other metal deposits linked to an intrusion. Such generalization should be interpreted as predicting metal enrichment by 3-4 orders of magnitude, rather than predicting an exact value.
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Villani, F., Civico, R., Pucci, S., Pizzimenti, L., Nappi, R., De Martini, P. M., et al. (2019). A database of the coseismic effects following the 30 October 2016 Norcia earthquake in Central Italy (vol 5, 180049, 2018). Scientific Data, 6.
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Vu, C. - C., Amitrano, D., Ple, O., & Weiss, J. (2019). Compressive Failure as a Critical Transition: Experimental Evidence and Mapping onto the Universality Class of Depinning. Physical Review Letters, 122(1).
Résumé: Acoustic emission (AE) measurements performed during the compressive loading of concrete samples with three different microstructures (aggregate sizes and porosity) and four sample sizes revealed that failure is preceded by an acceleration of the rate of fracturing events, power law distributions of AE energies and durations near failure, and a divergence of the fracturing correlation length and time towards failure. This argues for an interpretation of compressive failure of disordered materials as a critical transition between an intact and a failed state. The associated critical exponents were found to be independent of sample size and microstructural disorder and close to mean-field depinning values. Although compressive failure differs from classical depinning in several respects, including the nature of the elastic redistribution kernel, an analogy between the two processes allows deriving (finite-) sizing effects on strength that match our extensive data set. This critical interpretation of failure may have also important consequences in terms of natural hazards forecasting, such as volcanic eruptions, landslides, or cliff collapses.
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Wang, Q. - Y., Campillo, M., Brenguier, F., Lecointre, A., Takeda, T., & Hashima, A. (2019). Evidence of Changes of Seismic Properties in the Entire Crust Beneath Japan After the M-w 9.0, 2011 Tohoku-oki Earthquake. Journal Of Geophysical Research-Solid Earth, 124(8), 8924–8941.
Résumé: Studies of mechanical responses of the Earth crust to large earthquakes can provide us with unique insights into the processes of stress buildup and release. As a complement to geodetic methods that derive crustal strain dynamics from surface observations (e.g., GPS, InSAR), noise-based seismic velocity monitoring directly probes the mechanical state of the crust, at depth and continuously in time. We investigate the responses of the crust to the M-w 9.0, 2011 Tohoku-oki earthquake. In addition to the Hi-net short-period sensors, we use Hi-net tiltmeters as long-period seismometers (8-50 s) to sample the crust below 5 km in depth. The spatial distribution of the strong velocity decreases at short periods appears to be limited to the region of strong ground shaking induced by the 2011 Tohoku-oki earthquake, while the long-period velocity changes correlate well with the modeled static strain induced by viscoelastic relaxation and afterslip at depth. Amplitudes of coseismic velocity changes decrease with increasing depth. The temporal evolution of velocity changes in different period bands shows that the maximum drops in the velocity at long periods are delayed in time with respect to the occurrence of the Tohoku-oki earthquake. The inversion of seismic velocity changes at depth illustrates how S wave velocities evolve down to 40 km at a regional scale after a major earthquake.
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Wang, X., Peng, J., Liang, X., Zhu, M., Lanson, B., Wang, L., et al. (2019). Effects of Mn2+, Ni2+, and Cu2+ on the Formation and Transformation of Hydrosulfate Green Rust: Reaction Processes and Underlying Mechanisms. Acs Earth And Space Chemistry, 3(4), 519–530.
Résumé: Green rusts (GRs), which are important intermediate phases during Fe2+ oxidation, are commonly associated with various metal cations during their crystallization in soils and sediments, but the effects of these foreign metal cations on the formation of GRs and on their subsequent transformation to Fe (hydr)oxides remain unclear. In the present study, the effects of Mn2+, Ni2+, and Cu(2+)on the evolution processes of hydrosulfate green rust (GR2) are documented under various conditions and the mechanisms leading to cation incorporation in the reaction products are determined. The rates of GR2 formation and of its transformation to Fe (hydr)oxides both decrease in the order of Cu2+> Ni2+ > Mn2+ and increase with increasing metal cation concentration. During GR2 crystallization, a small fraction of foreign metal cations is structurally incorporated in GR2 by replacing Fe", and their amount in the mineral follows the order of Cu2+> Ni2+ > Mn2+. Under all conditions, the final reaction products are a mixture of lepidocrocite and goethite; a slow oxidation rate of mineral Fe' and a strong catalytic effect of surface Fe2+ both facilitate the goethite formation from GR2, reversely, favorable to lepidocrocite formation. Additionally, the three cations possess different speciation and distribution in lepidocrocite and goethite: Mn exists mainly as Mn(III) and probably minor Mn(II)-Mn(III) molecular clusters and occurs mainly in the mineral interior by isomorphic substitution or coated by the Fe (hydr)oxides crystals; Ni is present as Ni(II) and uniformly distributed in the newly formed minerals by either isomorphic substitution or surface adsorption; finally, Cu is mainly sorbed at the mineral surface as Cu(II) with minor Cu(I). These cations may thus be structurally incorporated in Fe oxides in the order of Mn(III) > Ni(II) > Cu(II). These new insights into the interaction between GR2 and trace metal cations improve our understanding of Fe oxide crystallization processes and of the environmental geochemical behavior of associated metal cations in redox alternating soils and sediments.
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Weaver, K. C., Doan, M. - L., Cox, S. C., Townend, J., & Holden, C. (2019). Tidal Behavior and Water-Level Changes in Gravel Aquifers in Response to Multiple Earthquakes: A Case Study From New Zealand. Water Resources Research, 55(2), 1263–1278.
Résumé: Earthquakes have been inferred to induce hydrological changes in aquifers on the basis of either changes to well water-levels or tidal behavior, but the relationship between these changes remains unclear. Here, changes in tidal behavior and water-levels are quantified using a hydrological network monitoring gravel aquifers in Canterbury, New Zealand, in response to nine earthquakes (of magnitudes M-w 5.4 to 7.8) that occurred between 2008 and 2015. Of the 161 wells analyzed, only 35 contain water-level fluctuations associated with Earth+Ocean (7) or Ocean (28) tides. Permeability reduction manifest as changes in tidal behavior and increased water-levels in the near field of the Canterbury earthquake sequence of 2010-2011 support the hypothesis of shear-induced consolidation. However, tidal behavior and water-level changes rarely occurred simultaneously (2%). Water-level changes that occurred with no change in tidal behavior reequilibrated at a new postseismic level more quickly (on timescales of 50min) than when a change in tidal behavior occurred (240min to 10days). Water-level changes were more than likely to occur above a peak dynamic stress of 50kPa and were more than likely to not occur below 10kPa. The minimum peak dynamic stress required for a tidal behavior change to occur was 0.2 to 100kPa.
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Weiss, J. (2019). Ice: the paradigm of wild plasticity. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 377(2146).
Résumé: Ice plasticity has been thoroughly studied, owing to its importance in glaciers and ice sheets dynamics. In particular, its anisotropy (easy basal slip) has been suspected for a long time, then fully characterized 40 years ago. More recently emerged the interest of ice as a model material to study some fundamental aspects of crystalline plasticity. An example is the nature of plastic fluctuations and collective dislocation dynamics. Twenty years ago, acoustic emission measurements performed during the deformation of ice single crystals revealed that plastic 'flow' proceeds through intermittent dislocation avalanches, power law distributed in size and energy. This means that most of ice plasticity takes place through few, very large avalanches, thus qualifying associated plastic fluctuations as 'wild'. This launched an intense research activity on plastic intermittency in the Material Science community. The interest of ice in this debate is reviewed, from a comparison with other crystalline materials. In this context, ice appears as an extreme case of plastic intermittency, characterized by scale-free fluctuations, complex space and time correlations as well as avalanche triggering. In other words, ice can be considered as the paradigm of wild plasticity. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.
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Weiss, J., Ben Rhouma, W., Deschanel, S., & Truskinovsky, L. (2019). Plastic intermittency during cyclic loading: From dislocation patterning to microcrack initiation. Physical Review Materials, 3(2).
Résumé: In metallic materials subjected to cyclic loading, strain hardening as well as fatigue crack initiation have been linked for a long time with the evolution of dislocation patterns and structures. In particular, the development of low-energy dislocation configurations such as persistent slip bands (PSBs) is considered as a precursor to crack initiation. However, the associated scenarios have been elaborated mainly from postmortem observations capturing only static pictures of dislocation patterns, while the dynamics of the problem has been somewhat overlooked. Here we analyze collective dislocation dynamics during cycling loading of aluminum using acoustic emission (AE). A strong link is revealed between dislocation patterning, cyclic hardening/softening, and the intermittency of plasticity: Plastic intermittency and dislocation avalanches rapidly decay during the initial hardening stage, in conjunction with the reduction of an internal length scale characterizing the dislocation structure. However, in nonannealed samples, a transient softening stage ensues, associated with a brutal reorganization of this structure. These initial stages of cyclic deformation illustrate the competition between two phenomena: collective dislocation dynamics, governed by long-ranged elastic interactions among dislocations, and the emergence of a self-organizing network controlled by short-range interactions and progressively inhibiting collective effects. Later on, the emergence of PSBs is accompanied by a reincrease of the AE intermittent activity. We propose that the associated AE bursts may be the signature of collective and coordinated dislocation motions along PSBs leading to the formation of incipient microcracks.
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Wellington, P., Brossier, R., & Virieux, J. (2019). Preconditioning full-waveform inversion with efficient local correlation operators. Geophysics, 84(3), R321–R332.
Résumé: Full-waveform inversion (FWI) is an iterative locally linearized data-fitting technique. The FWI method attempts to move from an initial low-wavenumber representation of earth parameters to a broader representation of the medium. An issue with the method is that FWI is an ill-posed problem, oversampled for the numerical forward discretization. The success of the model parameter reconstruction can often be greatly affected by external factors such as the presence of noise in the input field data or other artifacts arising from the imaging condition present in the FWI gradient computation. We have developed a strategy for mitigating against the influence of such external factors by preconditioning the discrete data gradient using an efficient differential approach instead of the often used integral formulation. Such an application of a smoothing correlation operator allows one to use prior information to locally filter along expected geological dips while being consistent with faults. The application of this preconditioning strategy to real and synthetic 2D data sets illustrates how this incremental additional step makes the FWI workflow less sensitive to noise and spatial aliasing artifacts. Nothing prevents a possible 3D acoustic extension, thanks to the small added computer cost for this local filter application. Three-dimensional elastic FWI may require this inexpensive filtering strategy due to the prohibitive forward-modeling costs that could be partially mitigated by using a coarse shot increment in conjunction with gradient preconditioning.
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Wiggenhauser, M., Bigalke, M., Imseng, M., Keller, A., Rehkamper, M., Wilcke, W., et al. (2019). Using isotopes to trace freshly applied cadmium through mineral phosphorus fertilization in soil-fertilizer-plant systems. Science Of The Total Environment, 648, 779–786.
Résumé: Applications of mineral phosphorus (P) fertilizer can lead to cadmium (Cd) accumulation in soils and can increase Cd concentrations in edible crop parts. To determine the fate of freshly applied Cd, a Cd source tracing experiment was conducted in three soil-fertilizer-wheat systems by using a mineral P fertilizer labeled with the radio isotope Cd-109 and by exploiting natural differences in Cd stable isotope compositions (delta Cd-114/110). Source tracing with stable isotopes overestimated the proportion of Cd in plants derived from the P fertilizer, because the isotope ratios of the sources were not sufficiently distinct from those of the soils. Despite indistinguishable extractable Cd pools between control and treatments, the addition of P fertilizer resulted in a more negative apparent isotope fractionation between soil and wheat. Overall, the radio isotope approach provided more robust results and revealed that 6.5 to 15% of the Cd in the shoot derived from the fertilizer. From the introduced Cd, a maximum of 22% reached the wheat shoots, whilst 97.8% remained in the roots and soils. The low recoveries of the fertilizer derived Cd suggest that continuous P fertilizer application in the past decades can lead to a build-up of a residual Cd pool in soils. (C) 2018 Elsevier B.V. All rights reserved.
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Wild, B., Daval, D., Micha, J. - S., Bourg, I. C., White, C. E., & Fernandez-Martinez, A. (2019). Physical Properties of Interfacial Layers Developed on Weathered Silicates: A Case Study Based on Labradorite Feldspar. Journal Of Physical Chemistry C, 123(40), 24520–24532.
Résumé: Amorphous silica-rich surface layers (ASSLs) formed at the interface between silicate materials and reacting fluids are known to strongly influence, at least in some cases, the dissolution rates of silicate phases including soil minerals, glasses, and cements. However, the factors governing the formation of these ASSLs remain largely unknown. Here, we outline a novel approach that uses recent developments in vertical scanning interferometry and in situ synchrotron-based X-ray reflectivity to directly follow the development of ASSLs and the evolution of their physical properties on a representative silicate, labradorite feldspar. Our approach enables independently probing the reactivities of the outer (bulk fluid/ASSL) interface and of the inner (ASSL/pristine mineral) interface in situ, providing a detailed picture of the temporal evolution of the fluid-mineral interface. We investigated the effects of pH, SiO2(aq) concentration, crystallographic orientation, and temperature on the layer thickness, density, and reactivity as well as on the dissolution rate of the primary mineral. The dissolution rate of labradorite crystals increased with temperature according to an apparent activation energy of similar to 57 kJ mol(-1) and showed no significant difference between crystallographic faces. Both labradorite and ASSL dissolution rates decreased as circum-neutral pH conditions were approached. High SiO2(aq) concentrations resulted in decreased apparent dissolution rates (even though far-from-equilibrium conditions with respect to labradorite were maintained in the bulk fluid) and in an increased ASSL density at least in some conditions (such as low temperature and close-to-neutral pH values). Our results highlight the importance of ASSLs and their complex impact on the dissolution process. In particular, our results provide evidence of a discrepancy between bulk fluid conditions, generally probed and reported, and those actually operating at the interface with the dissolving primary phase, which are of more direct relevance to the dissolution process but are still largely unknown.
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Wu, Z., Peacock, C. L., Lanson, B., Yin, H., Zheng, L., Chen, Z., et al. (2019). Transformation of Co-containing birnessite to todorokite: Effect of Co on the transformation and implications for Co mobility. Geochimica Et Cosmochimica Acta, 246, 21–40.
Résumé: The mobility and fate of bioessential transition metals, such as Ni and Co, are strongly controlled by their association with phyllomanganate minerals such as birnessite. These minerals however, can transform to tectomanganates such as todorokite during soil and sediment diagenesis, yet the mobility and fate of most metals during the transformation process remain largely unknown. Here this research investigates the effect of Co on, and the mobility and fate of Co during the transformation of birnessite into tunnel structure minerals. A range of Co-containing birnessite precursors with up to 16.9 % Co/(Co + Mn) molar ratios were synthesised, and subsequently transformed via a mild reflux procedure designed to mimic the diagenesis of these layered precursors into tunnel structures. The layered precursors and reflux products were characterized using a combination of mineralogical and geochemical techniques, including powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The results show that Co(III) is structurally incorporated into the layered precursors and reflux products, through the isomorphic substitution of Mn(III). The structural incorporation of Co(III) into the layered precursors leads to an overall reduction of Jahn-Teller distorted Mn(III) octahedra in these minerals, a key factor for their transformation to tunnel structures. As a consequence, the presence of such structural Co(III) disrupts the transformation of birnessite into todorokite, leading to the coexistence of 9.6 angstrom asbolane-like phyllomanganate and non-ideal 3 x n, or a-disordered, todorokite-like tectomanganates in the transformation products. Newly formed todorokite exhibits a wide range of 3 x n tunnel dimensions (n up to 13) and a plate-like morphology. Overall the structural incorporation of non Jahn-Teller distorted cations like Co(III) into birnessite might help explain the often observed predominance of phyllomanganates over tectomanganates in soils and sediments, and the persistence of phyllomanganates in ferromanganese deposits that can be many millions of years old. The results also indicate that Co(III) initially associated with birnessite is retained in the solid phase during transformation, and thus the mobility of Co(III) is limited. EXAFS data suggest that Co is mainly located in the octahedral layers of asbolane-like phyllomanganate and at non-edge sites in non-ideal todorokite. Overall the transformation of Co-containing birnessite into non-ideal todorokite and asbolane-like layered structures maintains the strong sequestration of Co by Mn oxides. (C) 2018 Elsevier Ltd. All rights reserved.
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Xue, Q., Larose, E., & Moreau, L. (2019). Locating structural changes in a multiple scattering domain with an irregular shape. Journal Of The Acoustical Society Of America, 146(1), 595–602.
Résumé: Locadiff is a method for imaging local structural changes in a random, heterogeneous medium. It relies on the combination of a forward model to calculate the sensitivity kernel of the source-receiver pairs, with an inversion method to determine the position of the changes. So far, the sensitivity kernel has been evaluated based on an analytical solution of the diffusion equation, which lacks the flexibility to handle problems where the domain has boundaries with an irregular shape. Moreover, the accuracy of the previous inversion method, based on linear algebra tools, was very sensitive to the values of the inversion parameters. This paper introduces a more generic approach to solve both these issues. The first problem is tackled by the implementation of a numerical method as an alternative for solving the diffusion equation. The second problem is tackled by the introduction of enhanced optimization algorithms to improve the stability of the inversion. This improved version of Locadiff is validated via both numerical examples and experimental data from an actual civil engineering problem. (C) 2019 Acoustical Society of America.
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Yates, A. S., Savage, M. K., Jolly, A. D., Caudron, C., & Hamling, I. J. (2019). Volcanic, Coseismic, and Seasonal Changes Detected at White Island (Whakaari) Volcano, New Zealand, Using Seismic Ambient Noise. Geophysical Research Letters, 46(1), 99–108.
Résumé: Ambient noise interferometry is becoming increasingly popular for studying seismic velocity changes. Such changes contain information on the structural and mechanical properties of Earth systems. Application to monitoring, however, is complicated by the large number of processes capable of inducing crustal velocity changes. We demonstrate this at White Island volcano over a 10-year period containing multiple well-documented eruptions. Using individual seismic stations, we detect velocity perturbations that we ascribe to volcanic activity, large earthquakes, and seasonality. Distant seismic stations capture widespread nonvolcanic changes that are also present at the volcano. Comparison between velocity changes recorded by distant and local stations then allows us to distinguish volcanic phenomena from seasonality. Through this, we resolve distinct features in ambient noise-derived velocity changes that relate to volcanic unrest and a phreatic eruption, illustrating the strength of the approach. Plain Language Summary Detecting small changes in physical properties at volcanoes is important toward effectively forecasting volcanic eruptions. One approach is to monitor the speed of seismic waves at the Earth's surface, which are sensitive to changes in the rock they pass through. At volcanoes, such changes may manifest through subsurface pressure increases preceding eruptions. Correctly interpreting these changes, however, is complicated. Many other, nonvolcanic, processes are also capable of producing similar wave speed perturbations. At White Island volcano, New Zealand, we detect changes associated with volcanic activity, large earthquakes, and weather-related processes using seismometers located on the volcano. We demonstrate that volcanic and nonvolcanic features can be distinguished by comparing changes recorded at the volcano with those recorded at large distances, where volcanic changes are not expected to be observed. Through this, we resolve distinct differences that can be related to volcanic activity, illustrating the strength of this approach.
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Zanetta, P. - M., Le Guillou, C., Leroux, H., Zanda, B., Hewins, R. H., Lewin, E., et al. (2019). Modal abundance, density and chemistry of micrometer-sized assemblages by advanced electron microscopy: Application to chondrites. Chemical Geology, 514, 27–41.
Résumé: Numerous geosciences samples display a multi-scale mineralogical heterogeneity for which it is challenging to obtain spatially resolved quantitative chemical data. It is the case for chondritic meteorites, which can contain up to 10 different phases with grain size ranging from the nanometer to the millimeter. We developed a method providing multiple physical and chemical information by advanced scanning electron microscopy (SEM), hyperspectral energy dispersive X-ray spectroscopy (EDX) and electron probe micro-analyses (EPMA). The method includes: i) infra-micrometric low-voltage EDX mapping and innovative post-acquisition hyperspectral data analysis (based on both clustering and multiple linear least square fitting) which allow phase mapping and quantification of the modal abundances; ii) EPMA of chemical end-members to upgrade the phase map into a quantified chemical map; iii) physical modeling of the EDX background, used as a proxy of the density. Density maps can be obtained with a precision of similar to 10%; iv) determination of the bulk sample composition by combining modal abundances, chemical analysis and density measurements. The approach is applied to three well-known chondrites (Murchison, Paris and Orgueil), showing heterogeneous grain sizes and mineralogy. Areas of similar to 250 (*) 250 μm(2) were mapped with a pixel size of 250 nm to determine the modal abundances, size distribution, circularity and densities of all phases, as well as the matrix bulk compositions. Taking bulk wet chemistry data as reference, ACADEMY leads to a better match than published defocused beam EPMA measurements. We demonstrate that choosing a Fe-rich, hydrated standard (a biotite) to quantify phyllosilicate by EPMA improves the quantification by up to 10%, and we ultimately retrieve the Mg/Si ratio with a 1% precision. We called this method ACADEMY for Analyzing the Composition, the modal Abundance and the Density using Electron MicroscopY. A code was developed and was made available online so that ACADEMY can be applied to other materials.
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Zhang, L., Nasika, C., Donze, F. - V., Zheng, X., Renard, F., & Scholtes, L. (2019). Modeling Porosity Evolution Throughout Reaction-Induced Fracturing in Rocks With Implications for Serpentinization. Journal Of Geophysical Research-Solid Earth, 124(6), 5708–5733.
Résumé: Numerical modeling based on the discrete element method was used to explore the kinetics and mechanics of fractures induced by mineral volumetric expansion during rock hydration. Two systems were considered: the hydration of periclase into brucite and the hydration of peridotite into serpentine. We modeled the coupling between mineral transformation, stress, volume increase, and deformation by simulating the volumetric growth of discrete elements based upon an Avrami-type kinetics equation. The model was implemented to consider the effects of stress and temperature on reaction kinetics as well as the alteration of material properties during hydration reactions. We were able to reproduce experimental evidences observed during the transformation of periclase into brucite, including volume growth, fracturing of periclase, formation of a porosity pulse, as well as the slow-down effect of effective stress on the kinetics of the transformation. The model was also applied to study the serpentinization process. We estimated a bell-shaped relationship between temperature and reaction rate of peridotite transformation following observations made during serpentinization experiments. For both periclase and peridotite systems, we characterized a relationship between the formation of a porosity pulse and the rate of fracture development within the medium. During serpentinization, the amplitude of the porosity pulse and the duration of this pulse depend on the reaction rate and, therefore, on the temperature. Our investigations provide geomechanical explanations on how native dihydrogen formed during serpentinization can be expelled and initiates its migration process.
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Zhang, P., J.J. Bian, C. Yang, J.Y. Zhang, G. Liu, J. Weiss and J. Sun. (2019). Plate-like precipitate effects on plasticity of Al-Cu micro-pillar: {100}-interfacial slip. Materialia, 7, 100416,.
Résumé: Crystalline plasticity can take place through numerous, small, uncorrelated dislocation motions (mild plasticity) or through collaborative events: dislocation avalanches (wild plasticity). Here, we study the correlation between dislocation patterning under cyclic loading and the nature of collective dislocation dynamics. The dislocation motion of a [110] oriented pure copper single crystal was dynamically followed using Acoustic Emission (AE) for different imposed stress amplitudes. The dislocation structure between each cyclic stress step was investigated using Electron BackScattered Diffraction (EBSD) and Rotational-Electron Channeling Contrast Imaging (R-ECCI) in a Scanning Electron Microscope (SEM). At low imposed stress, when the structure consists of dislocation cells, few dislocation avalanches are observed, while for a wall structure, at higher imposed stress, the contribution of avalanches is increased during the first cycles. For a given stress amplitude, the evolution of mild plasticity is synchronous with the plastic strain-rate, and rapidly vanishes after few cycles due to work hardening. The mean free path of the dislocations in this mild plasticity regime corresponds to the characteristic size of the dislocation structure (cell size, distance between walls). From one stress level to another, brutal rearrangements of the dislocation structure occur within a few numbers of cycles. Those rearrangements take place, at least partly, through dislocation avalanches. Upon reloading at a larger stress amplitude, dislocation avalanches can travel over distances much larger than the former dislocation mean free path. As the dislocation avalanches spread within the crystal, the memory of the previous dislocation structure is lost and a new dislocation structure emerges.
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Zhang, Y., Huang, W., Zhang, Y., Poujol, M., Guillot, S., Roperch, P., et al. (2019). Detrital zircon provenance comparison between the Paleocene-Eocene Nangqian-Xialaxiu and Gongjue basins: New insights for Cenozoic paleogeographic evolution of the eastern Tibetan Plateau. Palaeogeography Palaeoclimatology Palaeoecology, 533.
Résumé: Paleogeographic reconstructions of terranes can greatly benefit from the provenance analysis of sediments. A series of Cenozoic basins provide key sedimentary archives for investigating the growth of the Tibetan Plateau, yet the provenance of the sediments in these basins has never been constrained robustly. Here we report sedimentary petrological and detrital zircon geochronological data from the Paleocene-Eocene Nangqian-Xialaxiu and Gongjue basins. Sandstone detrital modes and zircon morphology suggest that the samples collected in these two basins were sourced from recycled orogen. Detrital zircon geochronology indicates that sediments in the Nangqian-Xialaxiu Basin are characterized by two distinct age populations at 220-280 Ma and 405-445 Ma. In contrast, three predominant age populations of 207-256 Ma, 423-445 Ma, and 1851-1868 Ma, and two subordinate age populations of similar to 50 Ma and similar to 2500 Ma, are recognized in the Gongjue Basin. Comparison with detrital zircon ages from the surrounding terranes suggests that sediments in the Nangqian-Xialaxiu Basin come from the neighboring thrust belts, whereas sediments from the Gongjue Basin are predominantly derived from the distant Songpan-Ganzi Terrane with minor contribution from the surrounding areas. A three-stage Cenozoic evolution of the eastern Tibetan Plateau is proposed. During the Paleocene, the Nangqian-Xialaxiu Basin appeared as a set of small intermontane sub-basins and received plentiful sediments from the neighboring mountain belts; during the Eocene, the Gongjue Basin kept a relatively low altitude and was a depression at the edge of a proto-Plateau; since the Oligocene, the Tibetan Plateau further uplifted and the marginal Gongjue Basin was involved in the Tibetan interior orogeny, indicating the eastward propagation of the Tibetan Plateau.
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Zheng, X., Cordonnier, B., McBeck, J., Boller, E., Jamtveit, B., Zhu, W., et al. (2019). Mixed-Mode Strain Localization Generated by Hydration Reaction at Crustal Conditions. Journal Of Geophysical Research-Solid Earth, 124(5), 4507–4522.
Résumé: Hydration reactions influence rock density and rheology. For example, volume increases produced in hydration reactions may generate sufficient tensile and shear stress to fracture both the rock undergoing the reaction and the surrounding host rock. We performed in situ dynamic X-ray synchrotron microtomography experiments to investigate reaction-induced fracturing. Two experiments on hydration of periclase were performed at 180 or 190 degrees C, under a confinement of 10 or 80 MPa, a pore fluid pressure of 5 or 75 MPa, and with or without differential stress. The sample assembly consists of a periclase cylinder inserted into a central hole within a serpentinite cylinder. The reaction from periclase to brucite results in a large volume increase (110%), pushing the periclase/brucite against the serpentinite and ultimately breaking it. Using time-resolved three-dimensional imaging, we quantify the spatial and temporal distribution of the reaction-induced fractures. We perform digital volume correlation analysis to obtain the incremental strain tensors throughout the hydration and fracturing process. We use numerical models to assess the distribution of stress within the serpentinite. The digital volume correlation results show mixed-mode strain localization. The von Mises strain, indicative of shear, increases by a larger percentage than the contractive or dilatative strain components as the reaction-induced fractures grow. The distribution of von Mises strain follows a power law relationship in the cumulative frequency-magnitude domain, indicative of long-range elastic stress interactions during fracturing. This experimental finding sheds insights on the mechanisms of microseismicity measured in areas undergoing active serpentinization.
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Zigone, D., Ben-Zion, Y., Lehujeur, M., Campillo, M., Hillers, G., & Vernon, F. L. (2019). Imaging subsurface structures in the San Jacinto fault zone with high-frequency noise recorded by dense linear arrays. Geophysical Journal International, 217(2), 879–893.
Résumé: Cross-correlations of 2-35 Hz ambient seismic noise recorded by three linear arrays across the San Jacinto Fault Zone (SJFZ) in Southern California are used to derive high-resolution shear wave velocity models for the top 50-90m of the crust at the array locations. Coherent Rayleigh surface waves are inverted to construct 2-D maps of group velocities in the range 0.2-0.6 km s(-1). These maps are inverted to shear wave velocities around the fault using a Markov Chain Monte Carlo approach. The results show marked low-velocity zones in the top 20-30 m with velocity reduction up to 35 per cent and shallow flower structures at depth shallower than 50 m. The derived velocities, location of low-velocity zone with respect to main surface traces and shape with depth are generally consistent with borehole measurements and previous imaging of deeper sections of the SJFZ at the same sites or nearby. The imaging technique requires only similar to 30 d of data (90 per cent of the signal-to-noise ratio is obtained in 15 d) and it bridges an observational gap between surface geology and typical tomography studies with no resolution in the top 100 m.
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