2020 |
Aben, F. M., Doan, M. L., & Mitchell, T. M. (2020). Variation of Hydraulic Properties Due to Dynamic Fracture Damage: Implications for Fault Zones. Journal Of Geophysical Research-Solid Earth, 125(4).
Résumé: High strain rate loading causes pervasive dynamic microfracturing in crystalline materials, with dynamic pulverization being the extreme end-member. Hydraulic properties (permeability, porosity, and storage capacity) are primarily controlled by fracture damage and will therefore change significantly by intense dynamic fracturing-by how much is currently unknown. Dynamic fracture damage observed in the damage zones of seismic faults is thought to originate from dynamic stresses near the earthquake rupture tip. This implies that during an earthquake, hydraulic properties in the damage zone change early. The immediate effect this has on fluid-driven coseismic slip processes following the rupture, and on postseismic and interseismic fault zone processes, is not yet clear. Here, we present hydraulic properties measured on the full range of dynamic fracture damage up to dynamic pulverization. Dynamic damage was induced in quartz-monzonite samples by performing uniaxial high strain rate (>10(0) s(-1)) experiments in compression using a split-Hopkinson pressure bar. Hydraulic properties were measured on samples subjected to single and successive loadings, the latter to simulate cumulative damage from repeated rupture events. We show that permeability increases by 6 orders of magnitude and porosity by 15% with dissipated energy up to dynamic pulverization, for both single and successive loadings. We present damage zone permeability profiles induced by earthquake rupture and how it evolves with repeated ruptures. We propose that the enhanced hydraulic properties measured for pulverized rock decrease the efficiency of thermal pressurization, when emplaced adjacent to the principal slip zone.
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Abramenkov, S., Shapiro, N. M., Koulakov, I., & Abkadyrov, I. (2020). Clustering of Long-Period Earthquakes Beneath Gorely Volcano (Kamchatka) during a Degassing Episode in 2013. Geosciences, 10(6).
Résumé: Gorely is one of the most active volcanoes in Kamchatka with a rich magmatic and eruptive history reflected in its composite structure. In 2013-2014, a temporary network of 20 seismic stations was installed on Gorely for one year. During the four months of its high degassing rate, seismic activity was mostly expressed in the form of a long-period (LP) seismic tremor. In this study, we have developed a workflow based on the combination of back-projection (BP), cluster analysis, and matched-filter (MF) methods. By applying it to continuous seismic records for the study period, we were able to identify discrete LP events within the tremor sequence automatically and individually investigate their properties. A catalog obtained using the BP detection algorithm consist of 1741 high-energy events. Cluster analysis revealed that the entire variety of LP earthquakes in this catalog could be grouped into five families, which are sequentially organized in time. Utilizing templates of these families in the MF search resulted in the complementary catalog of 80,615 low-energy events. The long-term occurrence of highly repetitive LP events in the same location may correspond to resonating conduits behaving in response to the high-pressure gases flowing from the decompressed magma chamber up to the volcano's crater.
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Agard, P., Prigent, C., Soret, M., Dubacq, B., Guillot, S., & Deldicque, D. (2020). Slabitization: Mechanisms controlling subduction development and viscous coupling. Earth-Science Reviews, 208.
Résumé: This contribution investigates mechanisms controlling subduction development and stabilization over time (coined as 'slabitization'), from a nascent slab to a mature slab viscously coupled to mantle convection, from grain scale to plate tectonics scale. Frozen-in, deep and warm portions of the subduction plate interface with both sides still preserved are found at the base of ophiolites in almost pristine state. Both sides record changes in the mineralogy, structure, fluid content and rheology due to devolatilization of subducting metamorphic rocks. They allow characterizing the evolution, shortly after subduction initiation (similar to 1-10 Ma), of interplate coupling, mantle resistance to slab penetration or incipient mantle wedge metasomatism, as well as transformations occurring at depth in warm or cold subduction zones today. This study combines structural field work, mineralogical and crystallographic data, detailed petrology, thermodynamic modelling and geochemistry from/on both sides of the plate interface, i.e. the base of the mantle wedge (basal ophiolitic peridotites) and crustal fragments from the slab (metamorphic soles). Data collected across the entire Semail ophiolite (Oman, UAE territory) and other similar settings worldwide (e.g., Canada, Turkey, New Caledonia) show a continuous evolution of the subduction plate interface from 1.2-0.9 GPa 900-750 degrees C to 0.7-0.5 GPa 750-600 degrees C, with progressive localization of strain and fluid transfer. Crystallization of neo-formed minerals, enrichment in fluid-mobile elements and their isotopic signature (e.g., for boron) indicate that metasomatism of the mantle base results from interaction with subduction fluids derived from the dehydrating metamorphic sole and slab tip, migrating at velocities similar to 1-10 m/a. Coeval deformation and metamorphic reactions in metabasalts of the downgoing slab reveal the importance of mineral changes (e.g., amphibole content) and deformation modes in controlling fluid delivery, stepwise detachment and accretion of successive slices from the downgoing slab (HTa, HTb and then LT soles) to the mylonitized mantle. This study demonstrates how the interplay between metamorphic reactions, fluid/melt transfer and deformation mechanisms, in particular dissolution-precipitation creep (DPC), controls the mechanical coupling state of the plate interface: (i) suppression of fluid transfer and DPC at depth triggers the onset of viscous coupling. This occurs near similar to 30 km depth during subduction infancy and HTa sole formation; (ii) with increased cooling and fluid availability, strain localization progressively develops downwards and unzips the subduction interface. The downward migration of viscous coupling triggers localized mantle wedge upwelling, potentially leading to short-lived suprasubduction ophiolite or forearc lithosphere formation; (iii) the locus of viscous coupling stabilizes near similar to 80-100 km in mature (and cold) subduction zones, and sets mantle counterflow. This is where and when plates get reattached and slabs become part of the mantle convection system. Recent geochronological data suggest that the duration from subduction nucleation to ophiolite formation is probably slower than suspected (similar to 5-10 Ma), and that another 5-10 Ma may be needed to reach mature subduction and profuse arc magmatism. These results refine our view of the subduction factory and have important implications for how, how much, and which sort of fluid is being fluxed into the mantle wedge at depths where serpentine is no longer stable.
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Airaghi, L., Bellahsen, N., Dubacq, B., Chew, D., Rosenberg, C., Janots, E., et al. (2020). Pre-orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central Pyrenees. Journal Of Metamorphic Geology, 38(2), 183–204.
Résumé: Pre-kinematic greenschist facies metamorphism is often observed in granites and basement units of mountain belts, but rarely dated and accounted for in orogenic cycle reconstructions. Studying pre-kinematic alteration is challenging because of its usual obliteration by subsequent syn-kinematic metamorphism often occurring at conditions typical of the brittle-ductile transition. It is, however, to be expected that pre-kinematic alteration has major implications for the rheology of the upper crust. In the 305 Ma-old Variscan basement of the Bielsa massif (located in the Axial Zone of the Pyrenees), successive fluid-rock interaction events are recorded in granites below 350 degrees C. Combined microstructural and petrographic analysis, low-T thermobarometry and in situ U-Th/Pb dating of anatase, titanite and monazite show extensive pre-orogenic (pre-Alpine) and pre-kinematic alteration related to feldspar sericitization and chloritization of biotite and amphibole at temperatures of 270-350 degrees C at 230-300 Ma. This event is followed by a second fluid-rock interaction stage marked by new crystallization of phyllosilicates at 200-280 degrees C and is associated with the formation of mylonitic shear zones and fractures parallel to the shear planes. U-Pb anatase and monazite ages as well as the microtextural relationships of accessory minerals suggest an age for this event at 40-70 Ma, consistent with independent regional geology constraints. The Variscan basement was therefore softened at late to post-Variscan time, at least 150-200 Ma before the main Alpine shortening while Alpine-age compression (c. 35-50 Ma) leads to the formation of a dense net of mylonites. The associated deformation, both distributed at the scale of the Bielsa massif and localized at decametric scale in mylonitic corridors, precedes the strain localization along the major thrusts of the Axial Zone. The Bielsa massif is a good example where inherited, pre-orogenic upper crustal softening controls the deformation patterns in granitic basement units through low-grade metamorphic reactions.
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Alboussiere, T., Drif, K., & Plunian, F. (2020). Dynamo action in sliding plates of anisotropic electrical conductivity. Physical Review E, 101(3).
Résumé: With materials of anisotropic electrical conductivity, it is possible to generate a dynamo with a simple velocity field, of the type precluded by Cowling's theorems with isotropic materials. Following a previous study by Ruderman and Ruzmaikin [M. S. Ruderman and A. A. Ruzmaikin, Magnetic field generation in an anisotropically conducting fluid, Geophys. Astrophys. Fluid Dyn. 28, 77 (1984)], who considered the dynamo effect induced by a uniform shear flow, we determine the conditions for the dynamo threshold when a solid plate is sliding over another one, both with anisotropic electrical conductivity. We obtain numerical solutions for a general class of anisotropy and obtain the conditions for the lowest magnetic Reynolds number, using a collocation Chebyshev method. In a particular geometry of anisotropy and wave number, we also derive an analytical solution, where the eigenvectors are just combinations of four exponential functions. An explicit analytical expression is obtained for the critical magnetic Reynolds number. Above the critical magnetic Reynolds number, we have also derived an analytical expression for the growth rate showing that this is a “very fast” dynamo, extrapolating on the “slow” and “fast” terminology introduced by Vainshtein and Zeldovich [S. I. Vainshtein and Y. B. Zeldovich, Reviews of topical problems: Origin of magnetic fields in astrophysics (turbulent “dynamo” mechanisms), Sov. Phys. Usp. 15, 159 (1972)].
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Allroggen, N., Garambois, S., Senechal, G., Rousset, D., & Tronicke, J. (2020). Crosshole reflection imaging with ground-penetrating radar data: Applications in near-surface sedimentary settings. Geophysics, 85(4), H61–H69.
Résumé: Crosshole ground-penetrating radar (GPR) is applied in areas that require a very detailed subsurface characterization. Analysis of such data typically relies on tomographic inversion approaches providing an image of subsurface parameters. We have developed an approach for processing the reflected energy in crosshole GPR data and applied it on GPR data acquired in different sedimentary settings. Our approach includes muting of the first arrivals, separating the up- and the downgoing wave-field components, and backpropagating the reflected energy by a generalized Kirchhoff migration scheme. We obtain a reflection image that contains information on the location of electromagnetic property contrasts, thus outlining subsurface architecture in the interborehole plane. In combination with velocity models derived from different tomographic approaches, these images allow for a more detailed interpretation of subsurface structures without the need to acquire additional field data. In particular, a combined interpretation of the reflection image and the tomographic velocity model improves the ability to locate layer boundaries and to distinguish different subsurface units. To support our interpretations of our field data examples, we compare our crosshole reflection results with independent information, including borehole logs and surface GPR data.
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Andrault, D., Morard, G., Garbarino, G., Mezouar, M., Bouhifd, M. A., & Kawamoto, T. (2020). Melting behavior of SiO2 up to 120 GPa. Physics And Chemistry Of Minerals, 47(2).
Résumé: The structure of liquid silicates is commonly described as a statistical mixture of various atomic entities with relative abundances that can vary with pressure, temperature, and composition. Unfortunately, this view remains largely theoretical due to scarce experimental reports on the silicate melt structure, in particular under pressure. We performed X-ray diffraction of the SiO2 end member to probe the melting curve up to 120 GPa and 7000 K, and the melt structure up to 80 GPa. We confirm the steep increase of the melting curve above 14 GPa when stishovite becomes stable over coesite in subsolidus conditions, with a slope of about 80 K/GPa. Then, around 45 GPa and 5400 K, the melting curve flattens significantly, an effect most likely reflecting the densification of the SiO2 melt structure. The signal of diffuse X-ray scattering is compatible with a change of the Si coordination number from 4 to 6 along the melting curve, in agreement with previous works reporting a similar evolution during the cold compression of SiO2 glass. Because of the limited pressure range (within 10 to 20 GPa) in which the melting curve changes its slope, we speculate a difficult coexistence of tetrahedral SiO4 and octahedral SiO6 units in SiO2 melt at high pressures.
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Angrand, P., Mouthereau, F., Masini, E., & Asti, R. (2020). A reconstruction of Iberia accounting for Western Tethys-North Atlantic kinematics since the late-Permian-Triassic. Solid Earth, 11(4), 1313–1332.
Résumé: The western European kinematic evolution results from the opening of the western Neotethys and the Atlantic oceans since the late Paleozoic and the Mesozoic. Geological evidence shows that the Iberian domain recorded the propagation of these two oceanic systems well and is therefore a key to significantly advancing our understanding of the regional plate reconstructions. The late-Permian-Triassic Iberian rift basins have accommodated extension, but this tectonic stage is often neglected in most plate kinematic models, leading to the overestimation of the movements between Iberia and Europe during the subsequent Mesozoic (Early Cretaceous) rift phase. By compiling existing seismic profiles and geological constraints along the North Atlantic margins, including well data over Iberia, as well as recently published kinematic and paleogeographic reconstructions, we propose a coherent kinematic model of Iberia that accounts for both the Neotethyan and Atlantic evolutions. Our model shows that the Europe-Iberia plate boundary was a domain of distributed and oblique extension made of two rift systems in the Pyrenees and in the Iberian intra-continental basins. It differs from standard models that consider left-lateral strike-slip movement localized only in the northern Pyrenees in introducing a significant strike-slip movement south of the Ebro block. At a larger scale it emphasizes the role played by the late-Permian-Triassic rift and magmatism, as well as strike-slip faulting in the evolution of the western Neotethys Ocean and their control on the development of the Atlantic rift.
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Asafov, E. V., Sobolev, A. V., Batanova, V. G., & Portnyagin, M. V. (2020). Chlorine in the Earth's Mantle as an Indicator of the Global Recycling of Oceanic Crust. Russian Geology And Geophysics, 61(9), 937–950.
Résumé: Homogenized melt inclusions in olivine were studied in Archean komatiites from the Barberton Greenstone Belt, Weltevreden Formation in South Africa (3.3 Ga), Abitibi Greenstone Belt in Canada (2.72 Ga), and the Belingwe Greenstone Belt in Zimbabwe (2.69 Ga). Contamination of the komatiite melts with crustal material enriched in Rb, Cl, and H2O during the crystallization of olivine is demonstrated. Uncontaminated melts have mantle Rb/Nb ratios but arc significantly enriched in Cl and H2O relative to K and Ce, respectively, exhibiting similar incompatibility during crystallization and partial mantle melting. These observations suggest the presence of a chlorine- and water-enriched mantle source before 3.3 Ga. The excess Cl and H2O contents in the komatiites are assumed to result from the interaction of partially molten mantle plumes with the mantle transition zone. The most likely source of Cl and H2O enriching the deep mantle is the oceanic lithosphere that endured a seafloor alteration. We conclude that the recycling of the altered oceanic lithosphere into the mantle, probably via subduction, began in the first billion years of the Earth's history. Delamination of the Archean crust could not cause transport of chlorine and water into the deep mantle.
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Asta, M. P., Fernandez-Martinez, A., Alonso, J., Charlet, L., Findling, N., Magnin, V., et al. (2020). Nanoscale Ion Dynamics Control on Amorphous Calcium Carbonate Crystallization: Precise Control of Calcite Crystal Sizes. Journal Of Physical Chemistry C, 124(46), 25645–25656.
Résumé: Amorphous calcium carbonate (ACC) is an essential component present during the early stages of biomineralization of many calcifying organisms, which is used as a precursor of crystalline calcium carbonate phases. Here, we performed X-ray photon correlation spectroscopy experiments on ACC which show that the amount of adsorbed water has a strong control over its diffusive dynamics. Results of crystallization experiments under conditions of controlled humidity indicate that the adsorbed water is enough to spark crystallization of calcite. A direct proportionality is found between the relative humidity of the environment and the final size of the calcite crystals. Different hypotheses are made to explain this result, with the confinement within the amorphous matrix being the main suspect of controlling the size of the crystallites. Control of water activity and water content is, therefore, a possible way to regulate biomineral crystallinity both in nature and for the design of functional biomimetic materials.
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Astorga, A., & Gueguen, P. (2020). Influence of seismic strain rates on the co- and post-seismic response of civil engineering buildings. Earthquake Engineering & Structural Dynamics, 49(15), 1758–1764.
Résumé: The elastic properties of buildings change during earthquakes. In particular, fundamental frequencies are observed to shift rapidly during the co-seismic phase and to recover slowly once the strong motion has finished. Although the frequency shift is usually correlated with loading amplitude, the co-seismic frequency variations observed in real structures are not only determined by the absolute amplitude of the strain value. In order to interpret the uncertainties of the prediction of engineering demand parameters for a given intensity measure, we analyze the influence of loading rates (i.e., strain rates) on resonance frequency variations in buildings with different structural states during the loading and unloading phases caused by seismic events. Our observations suggest the existence of a strain rate threshold that activates the nonlinear response of the structure, characterizing the activation of cracking and indicating a strong nexus between the elastic structural response, structural state, and the loading process.
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Astorga, A., Gueguen, P., Ghimire, S., & Kashima, T. (2020). NDE1.0: a new database of earthquake data recordings from buildings for engineering applications. Bulletin Of Earthquake Engineering, 18(4), 1321–1344.
Résumé: Over the last two decades, seismic ground motion prediction has been significantly improved thanks to the development of shared, open, worldwide databases (waveform and parametric values). Unlike seismic ground motion, earthquake data recorded in buildings are rarely shared. However, their contribution could be essential for evaluating the performance of structures. Increasing interest in deploying instrumentation in buildings gives hope for new observations, leading to better understanding of behavior. This manuscript presents a flat-file containing information on earthquake responses of instrumented buildings. Herein, we present the structure of the NDE1.0 flat-file containing structural response parameters (i.e. drift ratio, peak top values of acceleration, velocity and displacement, pre- and co-seismic fundamental frequencies) computed for several intensity measures characterizing ground motion (i.e. peak ground values of acceleration, velocity and displacement, spectral values, Arias intensity, strong motion duration, cumulative absolute velocity, destructive potential). The data are from real earthquake recordings collected in buildings over the years. Some building, site and earthquake characteristics are also included (i.e. structural design, shear wave velocity, magnitude, epicentral distance, etc.). This 1.0 version contains 8520 strong motion recordings that correspond to 118 buildings and 2737 events, providing useful information for analyses related to seismic hazard, variability of building responses, structural health monitoring, nonlinear studies, damage prediction, etc.
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Audemard, F. A., Reinoza, C., Lopez, R., Feaux, K., & Jouanne, F. (2020). Installation of continuously monitoring geodetic stations for geoscience research at the south Caribbean margin. Boletin De Geologia, 42(2), 15–29.
Résumé: Since 2015 six new continuous Global Positioning System (cGPS) and meteorological stations have been installed in Venezuela as part of the Continuously Operating Caribbean GPS Observational Network (COCONet) project (El Baul-CN41, Quebrada Arriba-CN39, Isla de Aves-CN49, Los Roques-CN42, Isla de Margarita-CN44, and Isla La Blanquilla-CN43). Almost simultaneously, in the framework of the VENCREEP project (ANR-France), a survey composed of two geodetic stations (Saucedo-SAU0 and La Pica Arriba de Catuaro-PAC0) and one creepmeter was installed to study the Pilar Fault. Also, new seven cGPS stations of fifteen planned were acquired through the Tsunami project (FONACIT 2013000361), aiming at densifying the current network. The whole set of stations will improve our knowledge about the local and regional geodynamics. We are sure that the results will have implications for seismic hazard studies.
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Baize, S., Audin, L., Alvarado, A., Jomard, H., Bablon, M., Champenois, J., et al. (2020). Active Tectonics and Earthquake Geology Along the Pallatanga Fault, Central Andes of Ecuador. Frontiers In Earth Science, 8.
Résumé: Based on new geological data and the analysis of a 4 m spatial resolution Digital Elevation Model (DEM), we provide a detailed and comprehensive description of section of the Chingual Cosanga Pallatanga Puna Fault System, a major active fault system in Ecuador. This work allows estimating new slip rates and large earthquakes parameters (displacement, recurrence) along a similar to 100 km-long section of the continental-scale dextral shear zone that accommodates the extrusion of the North Andean Sliver with respect to the South America continental Plate. We focus on the NE-SW Pallatanga strike-slip fault zone and related contractional and transcurrent features that extend to the north in the Inter-Andean valley and the Cordillera Real, respectively. The detailed analysis of the available DEM allowed mapping a series of lineaments at the regional scale and along the entire fault system. Field studies on key areas show valley deflections, aligned and elongated hills of Tertiary or Quaternary sediments, as well as faulted Holocene deposits and even preserved coseismic free-face ruptures in some places. Such morphological anomalies strongly suggest that those landscape scars represent long-living (Holocene to historical times) earthquake faults. Altogether, these new data confirm that very large crustal earthquakes (M similar to 7.5) have been generated along the fault system, probably during multiple segment ruptures. This conclusion agrees with reports of large earthquakes during historical times (post-1532 CE) in 1698, 1797, and 1949. They all occurred in the vicinity of the Pallatanga fault, causing catastrophic effects on environmental and cultural features. Based on new sample dating of both soils and volcanic series, we infer that the NE-SW dextral Pallatanga fault slips at rates ranging from similar to 2 to 6 mm/yr for southern and central strands of the studied area, respectively. Further north, surface faulting is distributed and the deformation appears to be partitioned between sub-meridian fault-related folds (similar to 2 mm/yr) and NE-SW strike-slip fault(s), like the similar to 1 mm/yr Pisayambo Fault that ruptured the surface in 2010. All this information offers the opportunity to size the earthquake sources for further seismic hazard analyses.
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Bajard, M., Poulenard, J., Sabatier, P., Bertrand, Y., Crouzet, C., Ficetola, G. F., et al. (2020). Pastoralism increased vulnerability of a subalpine catchment to flood hazard through changing soil properties. Palaeogeography Palaeoclimatology Palaeoecology, 538.
Résumé: Soil erosion is strongly linked to both precipitation patterns and land-use. We examine the effects of erosion and its drivers (i.e. human or/and climate) on soil evolution from the study of lacustrine archives in the northern French Alps. Multi-proxy analyses of the Lake Gers sediment sequence combined with the study of soils and rocks of its catchment allowed to reconstruct its evolution over the past 4.6 kyr. This included C-14 dating, short-lived radionuclides, geochemistry, loss on ignition, grain-size analyses, as well as plant and mammal DNA analyses. A total of 127 instantaneous deposits were identified among the continuous sedimentation in the lake and 93 were interpreted as flood deposits. Erosion was quantified for the whole catchment considering both the continuous sedimentation and the flood deposit thicknesses. The catchment is mainly formed by andesitic sandstones over which Andosols and Podzols can develop. However, low weathered materials from colluviation constitute the main input to the lake. Four main phases of changes in soil weathering were recorded by increases in K2O/TiO2 ratios, associated with an increase in both erosion and flood-frequency. Two phases were associated with climate cooling in the Western Alps, from 2.65 to 2.5 and from 1.45 to 1.3 cal kyr BP. The two others (1.9-1.75 and 0.9-0.4 cal kyr BP) were triggered with deforestation, with cow grazing during the Roman period, and with grazing of cows, sheep and goats during the Medieval period, amplified by the onset of the Little Ice Age. The increase in erosion and flood frequency after 950 cal yr BP indicates substantial damages to soils of the catchment including increase of their erodibility over the last millennia.
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Bard, P. Y., Bora, S. S., Hollender, F., Laurendeau, A., & Traversa, P. (2020). Are the Standard V-S-Kappa Host-to-Target Adjustments the Only Way to Get Consistent Hard-Rock Ground Motion Prediction? Pure And Applied Geophysics, 177(5), 2049–2068.
Résumé: Site-specific seismic hazard studies involving detailed account of the site response require the prior estimate of the hazard at the local reference bedrock level. As the real characteristics of such local bedrock often correspond to “hard-rock” with S-wave velocity exceeding 1.5 km/s, “standard rock” PSHA estimates should be adjusted in order to replace the effects of “standard-rock” characteristics by those corresponding to the local bedrock. The current practice involves the computation of scaling factors determined on the basis of V-S (S-wave velocity) and “kappa(0)” (site specific, high-frequency attenuation parameter) values, and generally predicts larger high-frequency motion on hard rock compared to standard rock. However, it also proves to be affected by large uncertainties (Biro and Renault, Proceedings of the 15th world conference on earthquake engineering, 24-28, 2012; Al Atik et al., Bull Seism Soc Am 104(1):336-346 2014), mainly attributed to (i) the measurement of host and target parameters, and (ii) the forward and inverse conversions from the response spectrum domain to the Fourier domain to apply the V-S and kappa(0) adjustments. Moreover, recent studies (Ktenidou and Abrahamson, Seismol Res Lett 87(6):1465-1478, 2016) question the appropriateness of current V-S – kappa(0) scaling factors, so that the significant amplification of high frequency content for hard-rock with respect to standard-rock seems overestimated. This paper discusses the key aspects of a few, recently proposed, alternatives to the standard approach. The calibration of GMPEs directly in the Fourier domain rather than in the response spectrum domain is one possibility (Bora et al., Bull Seism Soc Am 105(4):2192-2218, 2015, Bull Earthq Eng 15(11):4531-4561, 2017). Another possibility is the derivation of GMPEs which be valid also for hard-rock conditions (e.g. Laurendeau et al., Bull Earthq Eng 16(6):2253-2284, 2018). In this latter case the host site response is first removed using theoretical site response analyses (and site velocity profile), or generalized inversions techniques. A third possibility is to use existing hard rock surface recordings to derive purely empirical scaling models from standard rock to hard rock (Ktenidou et al., PEER Report, Pacific Earthquake Engineering Research Center, Berkeley, 2016). Finally, when a sufficient amount of records are available at a given site, generic GMPEs can be scaled to the site-specific ground motion using empirical site residual (delta(S2Ss)) (Kotha et al., Earthq Spectra 33(4):1433-1453, 2017; Ktenidou et al., Bulletin of Earthquake Engineering 16(6):2311-2336, 2018). Such alternative approaches present the advantage of a significant simplification with respect to the current practice (with thus a reduced number of uncertainty sources); their generalization calls however for high-quality recordings (including high-quality site metadata) for both host regions and target sites, especially for small to moderate magnitude events. Our answer to the question in the title is thus “No, alternative approaches exist and are promising; though, their routine implementation requires additional work regarding systematic site characterization (for the host regions) and high-quality site characterization/instrumentation (for the target site), and so do also the needed improvements of the existing HTTA procedure”.
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Barnes, C. J., Walczak, K., Janots, E., Schneider, D., & Majka, J. (2020). Timing of Paleozoic Exhumation and Deformation of the High-Pressure Vestgotabreen Complex at the Motalafjella Nunatak, Svalbard. Minerals, 10(2).
Résumé: The Vestgotabreen Complex exposed in the Southwestern Caledonian Basement Province of Svalbard comprises two Caledonian high-pressure units. In situ white mica 40Ar /39Ar and monazite Th-U-total Pb geochronology has resolved the timing of the tectonic evolution of the complex. Cooling of the Upper Unit during exhumation occurred at 476 2 Ma, shortly after eclogite-facies metamorphism. The two units were juxtaposed at 454 6 Ma. This was followed by subaerial exposure and deposition of Bullbreen Group sediments. A 430-400 Ma late Caledonian phase of thrusting associated with major sinistral shearing throughout Svalbard deformed both the complex and the overlying sediments. This phase of thrusting is prominently recorded in the LowerUnit, and is associated with a pervasive greenschist-facies metamorphic overprint of high-pressure lithologies. A c. 365-344 Ma geochronological record may represent an Ellesmerian tectonothermal overprint. Altogether, the geochronological evolution of the Vestgotabreen Complex, with previous petrological and structural studies, suggests that it may be a correlative to the high-pressure Tsakkok Lens in the Scandinavian Caledonides. It is suggested that the Vestgotabreen Complex escaped to the periphery of the orogen along the sinistral strike-slip shear zones prior to, or during the initial stages of continental collision between Baltica and Laurentia.
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Barnhart, W. D., Gold, R. D., & Hollingsworth, J. (2020). Localized fault-zone dilatancy and surface inelasticity of the 2019 Ridgecrest earthquakes. Nature Geoscience, 13(10), 699–+.
Résumé: Earthquakes produce a spectrum of elastic and inelastic deformation processes that are reflected across various length and time scales. While elasticity has long dominated research assumptions in active tectonics, increasing interest has focused on the inelastic characteristics of earthquakes, particularly those of the surface fault rupture zone itself, and how they relate to ground rupture hazard and the mechanics of damage zones. Here we present detailed co-seismic surface-strain analysis of the 2019 Ridgecrest, California, earthquakes. We derive three-dimensional high-resolution surface displacements from satellite optical imagery, which we then invert for the co-seismic surface-strain tensors. We show that fault-zone dilation is pervasive throughout these earthquakes and that inelastic failure is present but relatively localized (median width of 31 m). The width of the inelastic failure zone is not correlated to off-fault deformation, surface geology or displacement magnitude. Instead, the extent and kinematics of inelastic failure reflect active, mylonitic deformation of the fault damage zone that is influenced by rupture velocity and fault maturity. These results highlight how a single earthquake contributes to the long-term, permanent geologic record of faulting. Inelastic failure in the 2019 Ridgecrest earthquakes was localized and influenced by mylonitic deformation of the fault damage zone, according to an analysis of surface displacements derived from satellite images.
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Barre, G., Strzerzynski, P., Michels, R., Guillot, S., Cartigny, P., Thomassot, E., et al. (2020). Tectono-metamorphic evolution of an evaporitic decollement as recorded by mineral and fluid geochemistry: The “Nappe des Gypses” (Western Alps) case study. Lithos, 358.
Résumé: Evaporites play a major role on the structuration of collisional orogens especially when they act as decollement units. However, their exact pressure-temperature-deformation (P-T-d) paths are poorly documented. In this study, the first direct P-T-d constraints of the “Nappe des Gypses” formation (western French Alps) have been established. An innovative association of structural geology, petrography, crystallochemistry, and detailed study of both fluid inclusions and stable isotopes (C, O) analysis has been applied to this evaporitic facies. Geo-chemical analysis shows that the “Nappe des Gypses” formation has recorded the three typical metamorphic and deformational events of the Alps (namely D1, D2 and D3). These different constraints allow the determination of the first P-T path determination for this unit. Metamorphic peak conditions of the “Nappe des Gypses” are at 16.6 +/- 2.3 kbar and 431 degrees C +/- 28 degrees C. This formation was buried at similar conditions than the oceanic units. During the exhumation path, the D1-D2 transition is reached at 350 degrees C +/- 20 degrees C and 6.5 +/- 1.8 kbar and the D2D3 transition is assumed to be at 259 degrees C +/- 24 degrees C and 2.0 +/- 1.0 kbar (Strzerzynski et al., 2012). Peak P-T conditions overlap those of themedian Liguro-Piemontese units but are different fromthose of the Brianconnais units. It implies 1) an active and crucial role of the “Nappe des Gypses” during the exhumation of the Alpine oceanic complex, and 2) confirms the allochthonous and more distal origin of the European Tethyan passive margin of the “Nappe des Gypses” formation. Consideration of sulfates dehydration probably between 15.0 and 16.6 kbar and 200 and 300 degrees C, allows to discuss pore pressure excess and its mechanical consequences on the exhumation process. This process is very likely to amplify the “decollement” effect of the evaporites and allowthe nappe stack formation. This illustrates the role of this formation as a decollement surface. This difference of evolution highlights the major role of the evaporitic formations on the exhumation and structuration of a collisional chain. Suchmethodology could contribute to decipher the role of evaporites in the structural context of other collisional chains such as Himalaya, Pyrenees or Zagros. (C) 2020 Elsevier B.V. All rights reserved.
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Basile, C., Girault, I., Paquette, J. L., Agranier, A., Loncke, L., Heuret, A., et al. (2020). The Jurassic magmatism of the Demerara Plateau (offshore French Guiana) as a remnant of the Sierra Leone hotspot during the Atlantic rifting. Scientific Reports, 10(1).
Résumé: We report the discovery of 173.4Ma hotspot-related magmatic rocks in the basement of the Demerara Plateau, offshore French Guiana and Suriname. According to plate reconstructions, a single hotspot may be responsible for the magmatic formation of (1) both the Demerara Plateau (between 180 and 170Ma) and the Guinea Plateau (circa 165Ma) during the end of the Jurassic rifting of the Central Atlantic; (2) both Sierra Leone and Ceara Rises (mainly from 76 to 68Ma) during the upper Cretaceous oceanic spreading of the Equatorial Atlantic ocean; (3) the Bathymetrists seamount chain since the upper Cretaceous. The present-day location of the inferred Sierra Leone hotspot should be 100km west of the Knipovich Seamount.
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Beard, C. D., van Hinsberg, V. J., Stix, J., & Wilke, M. (2020). The effect of fluorine on clinopyroxene/melt trace-element partitioning. Contributions To Mineralogy And Petrology, 175(5).
Résumé: The impact of fluorine on phase relations and clinopyroxene-melt element partitioning has been explored experimentally to better understand the effect of this halogen on the residual enrichment of the REE and HFSE during crystallisation of alkaline and peralkaline magmas. Clinopyroxene was grown from three H2O-saturated synthetic glasses of tephriphonolite-to-phonolite composition in a rapid quench internally heated pressure vessel at 650-800 circle C and 200 MPa, with Delta log fO(2) fixed to ca. FMQ + 1. The fluorine content in the charges was varied and produced quenched melts from fluorine-free to 1.6 wt.% F. The experiments yield an assemblage of melt, fluid, sodic clinopyroxene, biotite, magnetite, +/- K-feldspar, +/- titanite, +/- fluorite, and +/- hiortdahlite (a Na-Ca-Ti-F sorosilicate). Addition of fluorine markedly increases the mode of biotite without significantly affecting the mode of clinopyroxene. Relative to fluorine-free compositions, experiments with 1.6 wt.% fluorine in the melt show a strong decrease in clinopyroxene-melt partition coefficients for the trivalent REE La-Dy and Y with a lesser decrease for the DHREE and DHFSE4+. The diminished uptake of these metals by clinopyroxene may reflect changes to their speciation in the melt phase, consistent with the formation of REE-F complexes and with modifications to the medium-range structural environment around HFSE4+ An increase in the fluorine content of the melt will thus make the REE and HFSE4+ progressively less compatible and, therefore, available for residual enrichment.
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Beauducel, F., Peltier, A., Villie, A., & Suryanto, W. (2020). Mechanical Imaging of a Volcano Plumbing System From GNSS Unsupervised Modeling. Geophysical Research Letters, 47(17).
Résumé: Identification of internal structures in an active volcano is mandatory to quantify the physical processes preceding eruptions. We propose a fully unsupervised Bayesian inversion method that uses the point compound dislocation model as a complex source of deformation, to dynamically identify the substructures activated during magma migration. We applied this method at Piton de la Fournaise. Using 7-day moving trends of Global Navigation Satellite System (GNSS) data preceding the June 2014 eruption, we compute a total of 15 inversion models of 2.5 million forward problems each, without a priori information. Obtained source shapes (dikes, prolate ellipsoids, or pipes) show magma migration from 7-8 km depth to the surface, drawing a mechanical “tomography” of the magma pathway. Our results also suggest source geometries compatible with observed eruptive fissures and seismicity distribution. In case of finite magma volume involved in final dike injection, source volume estimates from this method allow forecasting volumes of erupted lava.
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Beauval, C., Bard, P. Y., & Danciu, L. (2020). The influence of source- and ground-motion model choices on probabilistic seismic hazard levels at 6 sites in France. Bulletin Of Earthquake Engineering, 18(10), 4551–4580.
Résumé: In this study focused on France, we explore the uncertainties related to choices made while building a source model for hazard assessment and we quantify the impact on probabilistic hazard estimates. Earthquake recurrence models are initially built from the French Seismic CATalog (FCAT, Manchuel et al. in Bull Earthq Eng, 2018. 10.1007/s10518-017-0236-1). We set up a logic tree that includes two alternative seismogenic source models (ESHM13 and Baize et al. in Bull Soc Geol Fr 184(3):225-259, 2013), two versions of FCAT catalog, two alternative declustering algorithms, and three alternative minimum magnitudes for earthquake recurrence modeling. We calculate the hazard for six cities (i.e. Nantes, Lourdes, Clermont-Ferrand, Briancon, Nice and Strasbourg) that are located in source zones with a minimum amount of data to work with. Results are displayed for the PGA and spectral period 0.2 s, at return periods 475 and 5000 years. Exploration of the logic tree shows that the parameters with the most impact on hazard results are the minimum magnitude used in the recurrence modeling (up to 31%) and the selection of the seismogenic source model (up to 30%). We also use the SHARE European Earthquake Catalog (SHEEC, Woessner et al. in Bull Earthquake Eng, 2015. 10.1007/s10518-015-9795-1) to build earthquake recurrence models and compare hazard values obtained with the FCAT logic tree. Comparisons are limited because of the low number of events available in some sources in SHEEC; however, results show that, depending on the site considered, the earthquake catalog selection can also strongly impact the hazard estimates (up to 50%). The FCAT logic tree is combined with four ground-motion models (Bindi et al. in Bull Earthq Eng 12(1):391-430, 2014; Boore et al. in Earthq Spectra 30(3):1057-1085, 2014; Cauzzi et al. in Bull Earthq Eng 13(6):1587-1612, 2015. 10.1007/s10518-014-9685-y; Drouet and Cotton in Bull Seismol Soc Am 105(4):1883-1902, 2015) to account for the epistemic uncertainty on the prediction of ground-motion. Exploration of the logic tree shows that the contribution of ground-motion model uncertainties can be larger than, equivalent to, or lower than the contribution of the source-model uncertainties to the overall hazard variability. Which component controls overall uncertainty depends on the site, spectral period and return period. Finally, exploring the logic tree provides a distribution for the ratios between hazard levels at 5000 and 475 years return periods, revealing that the ratios only slightly depend on source-model uncertainties, vary strongly from site to site, and can take values between 3 and 5, which is significantly higher than what is commonly assumed in the engineering community.
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Belhadj, M., Tani, L. S. K., Medjati, N. D., Harek, Y., Sahi, M. D., Sun, Q., et al. (2020). Se Status Prediction by Food Intake as Compared to Circulating Biomarkers in a West Algerian Population. Nutrients, 12(12).
Résumé: Algeria is the largest country in Africa, located close to the Mediterranean coastal area, where nutrients consumption varies widely. Local data on selenium composition of foods are not available. We postulated a close correlation between selenium status predictions from food consumption analysis with a quantitative analysis of circulating biomarkers of selenium status. Population characteristics were recorded from 158 participants and dietary selenium intake was calculated by 24-h recall. The average total plasma selenium was 92.4 +/- 18.5 μg/L and the mean of selenium intake was 62.7 μg/day. The selenoprotein P concentration was 5.5 +/- 2.0 mg/L and glutathione peroxidase 3 activity was 247.3 +/- 41.5 U/L. A direct comparison of the dietary-derived selenium status to the circulating selenium biomarkers showed no significant interrelation. Based on absolute intakes of meat, potato and eggs, a model was deduced that outperforms the intake composition-based prediction from all food components significantly (DeLong's test, p = 0.029), yielding an area under the curve of 82%. Selenium status prediction from food intake remains a challenge. Imprecision of survey method or information on nutrient composition makes extrapolating selenium intake from food data providing incorrect insights into the nutritional status of a given population, and laboratory analyses are needed for reliable information.
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Bergemann, C. A., Gnos, E., Berger, A., Janots, E., & Whitehouse, M. J. (2020). Dating tectonic activity in the Lepontine Dome and Rhone-Simplon Fault regions through hydrothermal monazite-(Ce). Solid Earth, 11(1), 199–222.
Résumé: Zoned hydrothermal monazite-(Ce) from Alpine-type fissures and clefts is used to gain new insights into the tectonic history of the Lepontine Dome in the Central Alps and the timing of deformation along the Rhone-Simplon Fault zone on the dome's western end. Hydrothermal monazites-(Ce) (re)crystallization ages directly date deformation that induces changes in physicochemical conditions of the fissure or cleft fluid. A total of 480 secondary ion mass spectrometry (SIMS) spot analyses from 20 individual crystals, including co-type material of the monazite-(Nd) type locality, record ages for the time of similar to 19 to 2.7 Ma, with individual grains recording age ranges of 2 to 7.5 Myr. The combination of these age data with geometric considerations and spatial distribution across the Lepontine region gives a more precise young exhumation history for the area. At the northeastern and southwestern edges of the Lepontine Dome, units underwent hydrothermal monazite-(Ce) growth at 19-12.5 and 16.5-10.5 Ma, respectively, while crystallization of monazite-(Ce) in the eastern Lepontine Dome started later, at 15-10 Ma. Fissure monazite-(Ce) along the western limit of the dome reports younger ages of 13-7 Ma. A younger age group around 8-5 Ma is limited to fissures and clefts associated with the Simplon normal fault and related strike-slip faults such as the Rhone Fault. The data set shows that the monazite-(Ce) age record directly links the fluid-induced interaction between fissure mineral and host rock to the Lepontine Dome's evolution in space and time. A comparison between hydrothermal monazite-(Ce) and thermochronometric data suggest that hydrothermal monazite-(Ce) dating may allow us to identify areas of slow exhumation or cooling rates during ongoing tectonic activity.
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Bernard, A., Villacorte, E., Maussen, K., Caudron, C., Robic, J., Maximo, R., et al. (2020). Carbon Dioxide in Taal Volcanic Lake: A Simple Gasometer for Volcano Monitoring. Geophysical Research Letters, 47(24).
Résumé: We report here an increase in the amount of carbon dioxide in Taal lake during the year preceding the January 2020 eruption. Starting in February 2019, the CO2 emissions from the lake increased from background value (700 t day(-1)) to a flux close to 2,400 t day(-1) at the time of the eruption. We show that the lake acts as a highly sensitive gasometer where CO2 (aq) reflects the balance between CO2 supplied to the lake (by hot springs) and CO2 lost by diffusion at air-water interface. The lake waters are extremely enriched in dissolved carbon dioxide with pCO(2) values as high as 0.35 atm (350,000 ppmV) equivalent to a CO2 (aq) of 9.32 mmol l(-1). The residence time of CO2 in the lake is around 1 week which allows for fast detection of change in magma degassing and makes carbon dioxide a very promising tool for volcano monitoring. Plain Language Summary Volcanic gas fuels volcanic eruptions. Among the dominant species, sulfur dioxide is easily monitored using remote sensing and ground-based instruments. Carbon dioxide remains however challenging to detect and quantify due to its high background in the atmosphere. We have developed a new methodology for monitoring CO2 by using a volcanic lake in an innovative way. It allows to quantify CO2 emissions by the lake, thereby providing critical insights into the change in degassing magma at depth. Using this new methodology, we were able to detect the earlier precursory signs of the January 2020 eruption of Taal volcano in the Philippines which affected over 380,000 people from local communities. The Taal volcanic lake is a unique location to study CO2 emission with spectacular degassing from more than 500 subaqueous vents that were active for many years. The lake waters are extremely enriched in carbon dioxide, to our knowledge, the highest value ever recorded in a lake. Our method also provides the longest time series to date of continuous CO2 emission from a volcano.
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Bernet, M., Garcia, J. M., Chauvel, C., Londono, M. J. R., & Marin-Ceron, M. I. (2020). Thermochronological, petrographic and geochemical characteristics of the Combia Formation, Amaga basin, Colombia. Journal Of South American Earth Sciences, 104.
Résumé: The Amaga basin between the Western and Central Cordilleras of the Northern Andes of Colombia hosts the Neogene volcanic and volcaniclastic Combia Formation. Deposition of the Combia Formation in relation to Nazca plate subduction and arc volcanism is still a matter of debate. Therefore, the timing, petrography and geochemical characteristics of Combia Formation rocks were studied in the western and eastern parts of the Amaga basin, in order to gain more information on the type of magma generation and volcanic activity that led to the deposition of the Combia Formation. Apatite and zircon fission-track dating largely confirm a 12-6 Ma age for the deposition of the Combia Formation. Petrographic and major element analyses show that mainly trachy-andesite ignimbrites with a calcalkaline composition were deposited in the western Amaga basin, whereas the volcanic rocks of the eastern Amaga basin are lavas flow and fall-out deposits of basaltic andesites of tholeiitic affinity. Trace element and isotopic analyses show that slab dehydration and sediment melting/decarbonation were important in primary magma generation in the mantle wedge, but the primary magma was mixed with lower continental crustal melts (e.g. High-Pb radiogenic), resulting in characteristic isotope signatures in the western and eastern Amaga basin. Then, the hot-zone developed a high Pb-radiogenic, garnet-bearing lower continental crustal (LCC) level as a consequence of the quantity of dehydration of the subducting slab and of changes in the tectonic regime. An extensional pull-apart event (129 Ma), likely facilitated rapid magma ascend to the uppermost crust along a subvertical magma plumbing system throughout the Romeral Fault zone in the eastern Amaga basin, and calcalkaline magmas with adakite-like signature, which may indicate contractile tectonics that allow the formation of middle-to upper-crustal magma chambers with a garnet fractionation at depth and the evolution of silicate melts into the hot zone mainly related to the amount of water (>4 wt %) present.
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Bigalke, M., Imseng, M., Schneider, S., Schwab, L., Wiggenhauser, M., Keller, A., et al. (2020). Uranium Budget and Leaching in Swiss Agricultural Systems. Frontiers In Environmental Science, 8.
Résumé: Many mineral P fertilizers contain toxic uranium (U) in high concentrations. When the fertilizers are applied to agricultural sites, U can either accumulate in the soil or leach to ground and surface waters. We analyzed the U fluxes at three arable and three grassland agricultural sites on the Swiss plateau for 1 year. We calculated all inputs and outputs to the soils, modeled the speciation of U in the soil solution and investigated the possible leaching of U along preferential flow paths. We found that all sites showed positive U budgets (+0.9-6.6 g ha(-1)y(-1)), indicating an accumulation of U. However, the accumulation of U was low and a doubling of U concentration in the surface soil would need 850-2,660 years assuming today's U fluxes. Mineral P fertilizers were the quantitatively most important input, followed by manure application and mineral weathering (only important in the soils developed on limestone). While at sites with slightly acidic pH only little U (<0.01 μg L-1) was leached, the U leaching increased at neutral pH values, because of the formation of carbonato-U complexes. In all soil solutions, the U concentrations (<= 0.8 μg L-1) were below legal threshold values and comparable to local drinking and surface waters. We found no indication for enhanced U leaching along preferential flow paths.
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Bindi, D., & Kotha, S. R. (2020). Spectral decomposition of the Engineering Strong Motion (ESM) flat file: regional attenuation, source scaling and Arias stress drop. Bulletin Of Earthquake Engineering, 18(6), 2581–2606.
Résumé: We perform a spectral decomposition of the Fourier amplitude spectra disseminated along with the Engineering Strong Motion (ESM) flat file for Europe and Middle East. We apply a non-parametric inversion schema to isolate source, propagation and site effects, introducing a regionalization for the attenuation model into three domains. The obtained propagation and source components of the model are parametrized in terms of geometrical spreading, quality factor, seismic moment, and corner frequency assuming a omega(2) source model. The non-parametric spectral attenuation values show a faster decay for earthquakes in Italy than in the other regions. Once described in terms of geometrical spreading and frequency-dependent quality factor, slopes and breakpoint locations of the piece-wise linear model for the geometrical spreading show regional variations, confirming that the non-parametric models capture the effects of crustal heterogeneities and differences in the anelastic attenuation. Since they are derived in the framework of a single inversion, the source spectra of the largest events which have occurred in Europe in the last decades can be directly compared and the scaling of the extracted source parameters evaluated. The Brune stress drop varies over about 2 orders of magnitude (the 5th, 50th and 95th percentiles of the increment sigma distribution are 0.76, 2.94, and 13.07 MPa, respectively), with large events having larger stress drops. In particular, the 5th, 50th and 95th percentiles for M > 5.5 are 2.87, 6.02, and 23.5 MPa, respectively whereas, for M < 5.5, the same percentiles are 0.73, 2.84, and 12.43 MPa. If compared to the residual distributions associated to a ground motion prediction equation previously derived using the same Fourier amplitude spectra, the source parameter and the empirical site amplification effects correlate well with the inter-event and inter-station residuals, respectively. Finally, we calibrated both non-parametric and parametric attenuation models for estimating the stress drop from the ratio between Arias intensity and significant duration. The results confirm that computing the Arias stress drop is a suitable approach for complementing the seismic moment with information controlling the source radiation at high frequencies for rapid response applications.
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Blasco, M., Auque, L. F., Gimeno, M. J., Asta, M. P., & Mandado, J. (2020). Stable isotope characterisation of recent aragonite travertine deposits associated with the Fitero thermal waters (Spain). International Journal Of Earth Sciences, 109(3), 877–892.
Résumé: The travertines of the Fitero thermal springs, with more than 98% of aragonite in most of the samples, are studied in this paper. The main objective is to improve the general understanding of aragonite precipitation, since the deposits of almost pure aragonite are very scarce. This study presents a complete mineralogical and isotopic characterisation, including the evaluation of the delta O-18 and delta C-13 fractionation during precipitation, as valuable information for paleoclimate and paleoenvironmental studies. Samples of a laminated travertine deposit constituted by almost pure aragonite were taken from a pipe discharging water at 40 degrees C. Waters suffered an important CO2 outgassing, as suggested by the geochemical calculations and the delta C-13 values of travertines and waters. This outgassing triggers the oversaturation and precipitation of carbonate phases. Temperature seems to be the main factor controlling the precipitation of aragonite or calcite, as checked by studying another travertine sample with higher calcite content. Various delta O-18 isotope fractionation equations for aragonite and calcite were used. The results indicate that precipitation took place close to equilibrium according to some of these equations. The fact that the equilibrium is maintained in a natural system with an important CO2 loss is surprising. However, it can be explained by an HCO3--water oxygen isotopic equilibrium and a direct transfer of the HCO3- isotope signal to the carbonate without fractionation due to the fast CO2 loss and precipitation. Finally, considering other natural aragonite samples, a fractionation equation is defined for natural aragonite in the temperature range between 23 and 80 degrees C.
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Boccato, S., Torchio, R., Anzellini, S., Boulard, E., Guyot, F., Irifune, T., et al. (2020). Melting properties by X-ray absorption spectroscopy: common signatures in binary Fe-C, Fe-O, Fe-S and Fe-Si systems. Scientific Reports, 10(1).
Résumé: X-ray absorption spectroscopy (XAS) is a widely used technique to probe the local environment around specific atomic species. Applied to samples under extreme pressure and temperature conditions, XAS is sensitive to phase transitions, including melting, and allows gathering insights on compositional variations and electronic changes occurring during such transitions. These characteristics can be exploited for studies of prime interest in geophysics and fundamental high-pressure physics. Here, we investigated the melting curve and the eutectic composition of four geophysically relevant iron binary systems: Fe-C, Fe-O, Fe-S and Fe-Si. Our results show that all these systems present the same spectroscopic signatures upon melting, common to those observed for other pure late 3d transition metals. The presented melting criterion seems to be general for late 3d metals bearing systems. Additionally, we demonstrate the suitability of XAS to extract melt compositional information in situ, such as the evolution of the concentration of light elements with increasing temperature. Diagnostics presented in this work can be applied to studies over an even larger pressure range exploiting the upgraded synchrotron machines, and directly transferred to time-resolved extreme condition studies using dynamic compression (ns) or fast laser heating (ms).
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Bocci, M. G., Maviglia, R., Consalvo, L. M., Grieco, D. L., Montini, L., Mercurio, G., et al. (2020). Thromboelastography clot strength profiles and effect of systemic anticoagulation in COVID-19 acute respiratory distress syndrome: a prospective, observational study. European Review For Medical And Pharmacological Sciences, 24(23), 12466–12479.
Résumé: OBJECTIVE: Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2) infection may yield a hypercoagulable state with fibrinolysis impairment. We conducted a single-center observational study with the aim of analyzing the coagulation patterns of intensive care unit (ICU) COVID-19 patients with both standard laboratory and viscoelastic tests. The presence of coagulopathy at the onset of the infection and after seven days of systemic anticoagulant therapy was investigated. PATIENTS AND METHODS: Forty consecutive SARS-CoV-2 patients, admitted to the ICU of a University hospital in Italy between 29th February and 30th March 2020 were enrolled in the study, providing they fulfilled the acute respiratory distress syndrome criteria. They received full-dose anticoagulation, including Enoxaparin 0.5 mg-kg-1 subcutaneously twice a day, unfractionated Heparin 7500 units subcutaneously three times daily, or low-intensity Heparin infusion. Thromboelastographic (TEG) and laboratory parameters were measured at admission and after seven days. RESULTS: At baseline, patients showed elevated fibrinogen activity [rTEG-Ang 80.5 degrees (78.7 to 81.5); TEG-ACT 78.5 sec (69.2 to 87.9)] and an increase in the maximum amplitude of clot strength [FF-MA 42.2 mm (30.9 to 49.2)]. No alterations in time of the enzymatic phase of coagulation [CKH-K and CKH-R, 1.1 min (0.85 to 1.3) and 6.6 min (5.2 to 7.5), respectively] were observed. Absent lysis of the clot at 30 minutes (LY30) was observed in all the studied population. Standard coagulation parameters were within the physiological range: [INR 1.09 (1.01 to 1.20), aPTT 34.5 sec (29.7 to 42.2), antithrom bin 97.5% (89.5 to 115)]. However, plasma fibrinogen [512.5 mg.dl-1 (303.5 to 605)], and D-dimer levels [1752.5 ng.ml-1 (698.5 to 4434.5)], were persistently increased above the reference range. After seven days of full-dose anticoagulation, average TEG parameters were not different from baseline (rTEG-Ang p = 0.13, TEG-ACT p = 0.58, FF-MA p= 0.24, CK-R p = 0.19, CKH-R p = 0.35), and a persistent increase in white blood cell count, platelet count and D-dimer was observed (white blood cell count p < 0.01, neutrophil count p = 0.02, lymphocyte count p < 0.01, platelet count p = 0.13 < 0.01, D-dimer levels p= 0.02). CONCLUSIONS: SARS-CoV-2 patients with acute respiratory distress syndrome show elevated fibrinogen activity, high D-dimer levels and maximum amplitude of clot strength. Platelet count, fibrinogen, and standard coagulation tests do not indicate a disseminated intravascular coagulation. At seven days, thromboelastographic abnormalities persist despite full-dose anticoagulation.
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Bontemps, N., Lacroix, P., Larose, E., Jara, J., & Taipe, E. (2020). Rain and small earthquakes maintain a slow-moving landslide in a persistent critical state. Nature Communications, 11(1).
Résumé: In tectonically active mountain belts, landslides contribute significantly to erosion. Statistical analysis of regional inventories of earthquake-triggered-landslides after large earthquakes (Mw > 5.5) reveal a complex interaction between seismic shaking, landslide material, and rainfall. However, the contributions of each component have never been quantified due to a lack of in-situ data for active landslides. We exploited a 3-year geodetic and seismic dataset for a slow-moving landslide in Peru affected by local earthquakes and seasonal rainfalls. Here we show that in combination, they cause greater landslide motion than either force alone. We also show the rigidity of the landslide's bulk clearly decreasing during Ml >= 5 earthquakes. The recovery is affected by rainfall and small earthquakes (Ml < 3.6), which prevent the soil from healing, highlighting the importance of the timing between forcings. These new quantitative insights into the mechanics of landslides open new perspectives for the study of the mass balance of earthquakes.
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Bosse, L., Lilensten, J., Gillet, N., Rochat, S., Delboulbe, A., Curaba, S., et al. (2020). On the nightglow polarisation for space weather exploration. Journal Of Space Weather And Space Climate, 10.
Résumé: We present here observations of the polarisation of four auroral lines in the auroral oval and in the polar cusp using a new ground polarimeter calledPetit Cru. Our results confirm the already known polarisation of the red line, and show for the first time that the three other lines observed here (namely 557.7 nm, 391.4 nm and 427.8 nm) are polarised as well up to a few percent. We show that in several circumstances, this polarisation is linked to the local magnetic activity and to the state of the ionosphere through the electron density measured with EISCAT. However, we also show that the contribution of light pollution from nearby cities via scattering can not be ignored and can play an important role in polarisation measurements. This series of observations questions the geophysical origin of the polarisation. It also leaves open its relation to the magnetic field orientation and to the state of both the upper atmosphere and the troposphere.
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Bottelin, P., Baillet, L., Mathy, A., Garnier, L., Cadet, H., & Brenguier, O. (2020). Seismic study of soda straws exposed to nearby blasting vibrations. Journal Of Seismology, 24(3), 573–593.
Résumé: This research study has been developed to preserve a remarkable soda straw population from vibrations emitted by nearby rock blasting. The Choranche stalactite cave (Vercors, France) contains thousands of exceptionally long soda straws reaching a few meters in length for 0.5 cm in diameter. These slender speleothems are very vulnerable to vibrations not only because of their structural fragility but also because of their dynamic amplification. We found that soda straws' first natural frequencies lie within the frequency range emitted by nearby rock blasting works (ten to hundreds of Hz). We used in situ blast records, laboratory characterization, and a dynamic 2D finite element code to simulate the load experienced by the soda straw population. We show that induced loads may be increased by a factor 5 due to resonance. Consequently, short soda straws (0.1-1 m) were found more vulnerable to nearby blasting vibrations than longer speleothems (> 1 m), despite greater own weight and inertial forces for the latter. Simulations made on several blast tests yielded an admissible 2.4 mm/s peak particle velocity along the cave. Subsequent blasting works were carried out in compliance with this threshold with no harm done to the soda straw population. We also computed the dynamic response of soda straws exposed to a regional earthquake. In this case, longer speleothems (> 1 m) are primarily affected by resonance because of ground motion lower frequency content. We show that the omission of dynamic resonance or its simplification as made in previous studies may significantly underestimate the induced load in speleothems.
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Bouligand, C., Tivey, M. A., Finn, C. A., Morgan, L. A., Shanks, W. C. P., & Sohn, R. A. (2020). Geological and Thermal Control of the Hydrothermal System in Northern Yellowstone Lake: Inferences From High-Resolution Magnetic Surveys. Journal Of Geophysical Research-Solid Earth, 125(9).
Résumé: A multiscale magnetic survey of the northern basin of Yellowstone Lake was undertaken in 2016 as part of the Hydrothermal Dynamics of Yellowstone Lake Project (HD-YLAKE)-a broad research effort to characterize the cause-and-effect relationships between geologic and environmental processes and hydrothermal activity on the lake floor. The magnetic survey includes lake surface, regional aeromagnetic, and near-bottom autonomous underwater vehicle (AUV) data. The study reveals a strong contrast between the northeastern lake basin, characterized by a regional magnetic low punctuated by stronger local magnetic lows, many of which host hydrothermal vent activity, and the northwestern lake basin with higher-amplitude magnetic anomalies and no obvious hydrothermal activity or punctuated magnetic lows. The boundary between these two regions is marked by a steep gradient in heat flow and magnetic values, likely reflecting a significant structure within the currently active similar to 20-km-long Eagle Bay-Lake Hotel fault zone that may be related to the similar to 2.08-Ma Huckleberry Ridge caldera rim. Modeling suggests that the broad northeastern magnetic low reflects both a shallower Curie isotherm and widespread hydrothermal activity that has demagnetized the rock. Along the western lake shoreline are sinuous-shaped, high-amplitude magnetic anomaly highs, interpreted as lava flow fronts of upper units of the West Thumb rhyolite. The AUV magnetic survey shows decreased magnetization at the periphery of the active Deep Hole hydrothermal vent. We postulate that lower magnetization in the outer zone results from enhanced hydrothermal alteration of rhyolite by hydrothermal condensates while the vapor-dominated center of the vent is less altered.
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Bourdineaud, J. P., Durn, G., Rezun, B., Manceau, A., & Hrenovic, J. (2020). The chemical species of mercury accumulated by Pseudomonas idrijaensis, a bacterium from a rock of the Idrija mercury mine, Slovenia. Chemosphere, 248.
Résumé: A mercury-resistant bacterial strain has been isolated from a rock of the Idrija mercury mine in Slovenia. The rock had 19 g carbon and 2952 mg mercury (Hg) per kg. Mass spectrometry and DNA sequencing showed that the bacterium belongs to the Pseudomonas genus. It is called Pseudomonas idrijaensis. This bacterial strain is sensitive to methylmercury (MeHg) like the reference P. aeruginosa strain PAO1, and is resistant to divalent mercury (Hg(II)) in contrast to PAO1. This difference could be attributed to the presence of the mer operon yet deprived of the merB gene encoding the organomercurial lyase, on the basis of whole genome sequencing. The P. idrijaensis mer operon displays the RTPCADE organization and is contained in the Tn5041 transposon. This transposon identified here occurs in other Gram-negative Hg-resistant strains isolated from mercury ores, aquatic systems and soils, including Pseudomonas strains from 15,000 to 40,000 years old Siberian permafrost. When P. idrijaensis was exposed to mercury chloride, two intracellular Hg species were identified by high energy-resolution XANES spectroscopy, a dithiolate Hg(SR)(2) and a tetrathiolate Hg(SR)(4) complex. P. idrijaensis had a much higher [Hg(SR)2]/ Hg(SR)(4)] molar ratio than bacteria lacking the mer operon when exposed to 4 μg Hg-2(+)/L-resulting in an intracellular accumulation of 4.3 μg Hg/g dw. A higher amount of the Hg(SR)(2) complex provides a chemical signature for the expression of the dicysteinate Mer proteins in response to mercury toxicity. (C) 2020 Elsevier Ltd. All rights reserved.
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Breard, E. C. P., Dufek, J., Fullard, L., & Carrara, A. (2020). The Basal Friction Coefficient of Granular Flows With and Without Excess Pore Pressure: Implications for Pyroclastic Density Currents, Water-Rich Debris Flows, and Rock and Submarine Avalanches. Journal Of Geophysical Research-Solid Earth, 125(12).
Résumé: Numerous large-scale geophysical flows propagate with low-apparent basal friction coefficients, but the source of such phenomenology is poorly known. Motivated by scarce basal friction data from natural flows, we use numerical methods to investigate the interaction of granular flows with their substrate under idealized conditions. Here we investigate 3-D monodisperse and polydisperse fluid-particle granular flow rheology and flow-substrate interaction using discrete element modeling and coarse-graining techniques. This combination allows us to calculate the continuum fields of solid fraction, velocity, shear stress, and solid pressure and compare it with force measurements on the substrate. We show that the wall/basal friction coefficient is not constant. Instead, it is a function of the nondimensional slip defined as the ratio of the slip velocity over the slip velocity fluctuations. The scaling of the wall friction with nondimensional slip is independent of air viscosity and density and presence of excess pore pressure. Therefore, the reduction of the basal stress that must occur in mobile natural flows with excess pore pressure is not ascribed to the lowering of wall friction coefficient. Instead, lowering of the normal stress by fluid drag in flows with elevated pore fluid pressure justifies the definition of effective wall and internal friction coefficients to capture the geophysical flow rheology and the forcing on its substrate. These results are fundamental to understand the dynamics of geophysical mass flows including pyroclastic density currents, water-rich debris flows, and rock and submarine avalanches.
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Brenguier, F., Courbis, R., Mordret, A., Campman, X., Boue, P., Chmiel, M., et al. (2020). Noise-based ballistic wave passive seismic monitoring. Part 1: body waves. Geophysical Journal International, 221(1), 683–691.
Résumé: Unveiling the mechanisms of earthquake and volcanic eruption preparation requires improving our ability to monitor the rock mass response to transient stress perturbations at depth. The standard passive monitoring seismic interferometry technique based on coda waves is robust but recovering accurate and properly localized P- and S-wave velocity temporal anomalies at depth is intrinsically limited by the complexity of scattered, diffracted waves. In order to mitigate this limitation, we propose a complementary, novel, passive seismic monitoring approach based on detecting weak temporal changes of velocities of ballistic waves recovered from seismic noise correlations. This new technique requires dense arrays of seismic sensors in order to circumvent the bias linked to the intrinsic high sensitivity of ballistic waves recovered from noise correlations to changes in the noise source properties. In this work we use a dense network of 417 seismometers in the Groningen area of the Netherlands, one of Europe's largest gas fields. Over the course of 1 month our results show a 1.5 per cent apparent velocity increase of the P wave refracted at the basement of the 700-m-thick sedimentary cover. We interpret this unexpected high value of velocity increase for the refracted wave as being induced by a loading effect associated with rainfall activity and possibly canal drainage at surface. We also observe a 0.25 per cent velocity decrease for the direct P-wave travelling in the nearsurface sediments and conclude that it might be partially biased by changes in time in the noise source properties even though it appears to be consistent with complementary results based on ballistic surface waves presented in a companion paper and interpreted as a pore pressure diffusion effect following a strong rainfall episode. The perspective of applying this new technique to detect continuous localized variations of seismic velocity perturbations at a few kilometres depth paves the way for improved in situ earthquake, volcano and producing reservoir monitoring.
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Bruno, P. P., Festa, G., & Vandemeulebrouck, J. (2020). Editorial: Multidisciplinary Geophysical Imaging of Volcanoes. Frontiers In Earth Science, 8.
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Burgisser, A., Arbaret, L., Martel, C., Forien, M., & Colombier, M. (2020). The role of oxides in the shallow vesiculation of ascending magmas. Journal Of Volcanology And Geothermal Research, 406.
Résumé: Despite their generally low volume fraction, Fe\\Ti oxides have the potential to greatly influence the eruptive style because they lower the supersaturation pressure for heterogeneous bubble nucleation. Once nucleated, bubbles respond fast to pressure changes, fostering rapid expansion and explosive behavior. Yet, oxide microlite quantifications are often absent from data of explosive products. We used new, re-analyzed, and published data to build a compilation of oxide number densities (ONDs) and vesicle number densities (VNDs) of trachytic and calc-alkaline products. Four eruptive styles were selected: 1) Vulcanian explosions from Soufriere Hills volcano, Montserrat, Lascar volcano, Chile, and Kilian volcano, France, 2) blasts from Mt. Pelee volcano, Lesser Antilles, Mount St. Helens, USA, and Merapi volcano, Indonesia, 3) a sub-Plinian explosion from Merapi volcano, and 4) lava dome effusions with intermittent collapse from Soufriere Hills and Mt. Pelee volcanoes. Natural samples were separated into two groups according to the dominant texture of the products of each event: 1) vesicular pumice clasts from explosions with a strong vertical component and 2) dense clasts with diktytaxitic textures from dome collapse event and lateral blast. Group 1 samples are either distributed alongside the 1:1 trend be-tween VND and OND that spans from 1015 to 1017 m-3, or have a constant VND of 1016-16.5 m-3 regardless of OND. A large proportion of oxides (55-100%) touch vesicles. A more variable proportion of vesicles (16-72%) are in contact with oxides because of syn-explosive growth and coalescence. Group 2 samples have ONDs in the same broad range as group 1 samples. We also used new and published data to build a compilation of ONDs and VNDs of five series of experimental decompression of rhyolitic and phonolitic melts. In samples with OND approximate to VND, most bubbles are in contact with more than one oxide and 64-88% of the oxides are in contact with bubbles. Such high levels of connectivity suggest that the role of oxides in controlling bubble nucleation has been underestimated. When VND >= OND, nucleation densities of experimental vesicles can be reproduced by heterogeneous nucleation models, which we used to calculate syn-explosive decompression rates from VNDs at Merapi, Soufriere Hills, and Kilian. These rates and textural evidence suggest that the decompression front accompanying these Vulcanian and sub-Plinian explosions is responsible for syn-explosive bubble nucleation. We calculated the average pre-explosive ascent rates necessary to yield the observed ONDs at Soufriere Hills and Merapi volcanoes. The resulting rates, 0.005-20 m/s, overlap considerably with the range of critical ascent rate inferred for the effusive-explosive transition, supporting the hypothesis that this transition is primarily controlled by oxide microlites in the conduit because oxides are a primer for explosive behavior when present in sufficiently high number densities. Focusing on the older eruption of Kilian, for which no observation is available, we infer that pre-explosive ascent rates of >7 x 10(-3) m/s were necessary for explosive behavior to occur. (C) 2020 Elsevier B.V. All rights reserved.
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Burgisser, A., Carrara, A., & Annen, C. (2020). Numerical simulations of magmatic enclave deformation. Journal Of Volcanology And Geothermal Research, 392.
Résumé: Present in both plutonic and volcanic rocks, enclaves are inclusions of magma into a compositionally distinct magmatic host. Classical relationships between their shapes and the dynamical conditions that prevailed during their formation have been drawn from fluid-fluid analogies and from solid rock mechanics. Magmas, however, are hydrogranular suspensions with a rheology distinct from these two-end-members. This work presents results from computational fluid dynamics with discrete element modeling (CFD-DEM) aimed at deforming crystal-rich enclaves in pure shear. The CFD-DEM approach explicitly resolves solid-solid interactions such as contact and friction while taking into account fluid coupling. The first series of deformation involved only pure fluids to validate the setup. The second series comprised seven runs aimed at reproducing magmatic conditions. Enclaves were made of a cylindrical suspension of partides embedded into a host with different characteristics. In both media, particles and fluids had densities, viscosities, elastic characteristics, and sizes tailored to the geological constraints of the Adamello batholith, Italy. Each run corresponds to a temperature along the two respective crystallization paths and span crystal contents from 10 to 62 vol%. Results show that, to first order, deformation does not depend on differences in melt viscosities, crystal contents, or bulk viscosity contrast. This is due to the formation of force chains parallel to the main compression direction, which transmits stress across the enclave. A simple, first-order relationship could be fitted to our data to relate shear and enclave deformation, which we applied to the case of the Adamello pluton. There is a second-order dependence of deformation on the onset of particles contacts and force chains, which are both related to particle concentration. The main control of these second-order effects is the host crystal content. Enclave partides pack early, quickly erasing differences in initial content and building force chains parallel to the compression axis that transmit stresses to the host. Whether the host is able to transmit those stresses across its own volume is controlled by host crystal content. (C) 2020 Elsevier B.V. All rights reserved.
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Bussolesi, M., Grieco, G., Eslami, A., & Cavallo, A. (2020). Ophiolite Chromite Deposits as a New Source for the Production of Refractory Chromite Sands. Sustainability, 12(17).
Résumé: Chromite foundry sands, mixed with binding resins, are employed in the industry to form molds for high demanding casting of metals and steel. As there is no substitute, these sands highly contribute to placing chromium at the top value of the economic importance parameter in the EU classification of critical raw materials. Finding new sources to produce these sands can contribute to lowering its criticality. Chromite foundry sands must meet strict quality parameters, referred to as Cr(2)O(3)content, Fineness Index, SiO(2)content, and Acid Demand. The foundry chromite market is dominated by South Africa production deriving from layered intrusion chromite deposits. Chromite sands from ophiolite chromite deposits, normally used for the metallurgical-grade chromite market, were tested as an alternative starting raw material to produce chromite foundry sands. The study of the silicate impurities assemblage showed that its mineralogy strongly affects the result of the most crucial parameter, the Acid Demand. Ophiolite chromite with serpentine impurities should be depurated to a hardly affordable 0.31% SiO(2)content to meet Acid Demand quality threshold, due to high reactivity of this silicate with the acid environment of the test. Those with olivine impurities require to be depurated to a much more easily affordable 2.11% SiO(2)content. As a result, ophiolite chromite with an olivine dominated silicate assemblage can be used as an alternative source of chromite foundry sands.
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Cappelli, C., Cama, J., Van Driessche, A. E. S., & Huertas, F. J. (2020). Biotite reactivity in nitric and oxalic acid at low temperature and acid pH from surface and bulk dissolution measurements. Chemical Geology, 554.
Résumé: The dissolution of biotite, a trioctahedral mica, was investigated for a temperature range of 25-70 degrees C and a pH range of 1-3 in the presence of HNO3 (nitric acid) and H2C2O4 (oxalic acid) solutions. Single millimetric, cleaved flakes of biotite were reacted in batch and flow-through experiments to obtain kinetic information and elucidate the mechanisms that control the overall dissolution reaction under these conditions. The reacting basal surface was explored using in-situ laser confocal microscopy (LCM-DIM) and ex-situ scanning and phase shifting interferometry (VSI-PSI), while the release of tetrahedral (Al and Si), octahedral (Mg and Fe) and exchange (K) cations in solution was monitored over time. This experimental approach allowed us to calculate far-from-equilibrium dissolution rates associated with changes in topography of the (001) surface (horizontal retreat (R-step) and vertical retreat (R-vertical), etch pit formation and growth (R-pit) and the release of Si in solution, i.e., bulk dissolution (R-bulk,R-Si). In HNO3 solutions, a proton promoted reaction mechanism (PPRM), through proton adsorption on the biotite surface, was dominant. The variation of R-step, R-vertical and R-bulk,R-Si accounting for the dissolution of (hk0) surfaces at different temperature and pH was used to calculate the apparent activation energy (E-a) and the proton reaction order (n(H+)). The respective values decreased from 63 kJ mol(-1) at pH 1 to 31 kJ mol(-1) at pH 3 and increased from 0.46 at 25 degrees C to 0.77 at 70 degrees C. This variability was related to the variation of proton consumption with temperature. In H2C2O4 solutions, formation and growth of etch pits on the (001) surface occurred, yielding an increase in surface roughening. R-pit accounted for the rate of etch pit development which was observed to increase, as temperature increased. Based on R-pit, relatively high E-a values (121 kJ mol(-1) and 162 kJ mol(-1)) were associated with an early evolution of the basal etch pits, whereas lower values (36 kJ mol(-1) and 56 kJ mol(-1)) were calculated using R-bulk,R-Si. The present study contributes to the interpretation of the mechanisms involved in the biotite dissolution process at highly acidic pH, in the presence of inorganic and organic acid, and low temperature (T <= 80 degrees C). Furthermore, our results highlight the importance of combining surface and bulk analyses to assess the balance between the different reactions involving proton consumption during the dissolution and its dependency on temperature, pH and organic acids concentration.
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Carrara, A., Burgisser, A., & Bergantz, G. W. (2020). The architecture of intrusions in magmatic mush. Earth And Planetary Science Letters, 549.
Résumé: Magmatic reservoirs located in the upper crust have been shown to result from the repeated intrusions of new magmas, and spend much of the time as a crystal-rich mush. The geometry of the intrusion of new magmas may greatly affect the thermal and compositional evolution of the reservoir. Despite advances in our understanding of the physical processes that may occur in a magmatic reservoir, the resulting architecture of the composite system remains poorly constrained. Here we performed numerical simulations coupling a computational fluid dynamics and a discrete element method in order to illuminate the geometry and emplacement dynamics of a new intrusion into mush and the relevant physical parameters controlling it. Our results show that the geometry of the intrusion is to first order controlled by the density contrast that exists between the melt phases of the intrusion and resident mush rather than the bulk density contrast as is usually assumed. When the intruded melt is denser than the host melt, the intrusion pounds at the base of the mush and emplaced as a horizontal layer. The occurrence of Rayleigh-Taylor instability leading to the rapid ascent of the intruded material through the mush was observed when the intruded melt was lighter than the host one and was also unrelated to the bulk density contrast. In the absence of density contrasts between the two melt phases, the intrusion may fluidize the host crystal network and slowly ascend through the mush. The effect of the viscosity contrast between the intruded and host materials was found to have a lesser importance on the architecture of intrusions in a mush. Analyzing the eruptive sequence of well documented eruptions involving an intrusion as the trigger shows a good agreement with our modeling results, highlighting the importance of specifically considering granular dynamics when evaluating magmas and mush physical processes. (C) 2020 Elsevier B.V. All rights reserved.
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Castro, J., Asta, M. P., Galve, J. P., & Azanon, J. M. (2020). Formation of Clay-Rich Layers at The Slip Surface of Slope Instabilities: The Role of Groundwater. Water, 12(9).
Résumé: Some landslides around the world that have low-angle failure planes show exceptionally poor mechanical properties. In some cases, an extraordinarily pure clay layer has been detected on the rupture surface. In this work, a complex landslide, the so-called Diezma landslide, is investigated in a low- to moderate-relief region of Southeast Spain. In this landslide, movement was concentrated on several surfaces that developed on a centimeter-thick layer of smectite (montmorillonite-beidellite) clay-rich level. Since these clayey levels have a very low permeability, high plasticity, and low friction angle, they control the stability of the entire slide mass. Specifically, the triggering factor of this landslide seems to be linked to the infiltration of water from a karstic aquifer located in the head area. The circulation of water through old failure planes could have promoted the active hydrolysis of marly soils to produce new smectite clay minerals. Here, by using geophysical, mineralogical, and geochemical modelling methods, we reveal that the formation and dissolution of carbonates, sulfates, and clay minerals in the Diezma landslide could explain the elevated concentrations of highly plastic secondary clays in its slip surface. This study may help in the understanding of landslides that show secondary clay layers coinciding to their low-angle failure planes.
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Cathelineau, M., Boiron, M. C., Marignac, C., Dour, M., Dejean, M., Carocci, E., et al. (2020). High pressure and temperatures during the early stages of tungsten deposition at Panasqueira revealed by fluid inclusions in topaz. Ore Geology Reviews, 126.
Résumé: The Variscan vein-type Panasqueira W-Sn(Cu) deposit, one of the main tungsten deposits in Western Europe, has a long and complicated geological history. The first vein infillings, which consist of the quartz-wolframite association as well as the first generation of topaz, underwent significant deformation. As a consequence, most fluid inclusions of the earliest hydrothermal event are deformed and destroyed. Two preserved fluid inclusion assemblages are, however, found in the topaz overgrowth band and are dense aqueous-carbonic inclusions as well as dense CO2 dominated fluid inclusions. The P-T conditions of fluid trapping are constrained by using the intersection between isochores, as well as graphite-water equilibrium data and yield the following trapping conditions: 500 20 degrees C and 250 +/- 20 MPa. These P-T conditions are incompatible with fluid unmixing. Fluid chemistry results from water-graphite equilibrium, probably in metapelites, at two distinct temperatures: around 450-500 degrees C for the predominant aqueous-carbonic fluid, and higher temperatures of maximal550 degrees C for the CO(2)rich fluid enriched in N-2. These P-T estimates are consistent with deep crustal levels around 8-10 km depth and a high geothermal gradient around c. 60 degrees C/km(-1). The ascending non-magmatic fluids, enriched in volatiles, are essential in the ore genesis. The high thermal gradients may be related either to new magma pulse after the formation of the Panasqueira granite intrusion or to anomalous heat flux produced by the hot fluids ascending from migmatitic levels present at greater depth. This hypothesis necessitates to consider the role of a crustal weakness, which is attested both by the successive intrusions of several granitic magmas at the same place, and the presence of inherited quartz filled structures so-called Seixo-Bravo found only in the Panasqueira area.
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Caudron, C., Chardot, L., Girona, T., Aoki, Y., & Fournier, N. (2020). Editorial: Towards Improved Forecasting of Volcanic Eruptions. Frontiers In Earth Science, 8.
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Chauve, T., Scholtes, L., Donze, F. V., Mondol, N. H., & Renard, F. (2020). Layering in Shales Controls Microfracturing at the Onset of Primary Migration in Source Rocks. Journal Of Geophysical Research-Solid Earth, 125(5).
Résumé: The process of primary migration, which controls the transfer of hydrocarbons from source to reservoir rocks, necessitates the existence of fluid pathways in low permeability sedimentary formations. Primary migration starts with the maturation of organic matter which produces fluids that increase the effective stress locally. The interactions between local fluid production, microfracturing, stress conditions, and transport remain difficult to apprehend in shale source rocks. Here, we analyze these interactions using a coupled hydro-mechanical numerical model based on the discrete element method. The model is used to simulate the effects of fluid production emanating from kerogen patches contained within a shale rock alternating kerogen-poor and kerogen-rich layers. We identify two microfracturing mechanisms that control fluid migration: (i) propagation of hydraulically driven fractures induced by kerogen maturation in kerogen-rich layers and (ii) compression-induced fracturing in kerogen-poor layers caused by fluid overpressurization of the surrounding kerogen-rich layers. The relative importance of these two mechanisms is discussed considering different elastic properties contrasts between the shale layers, as well as various stress conditions encountered in sedimentary basins, from normal to reverse faulting regimes. The layering in shales causes local stress redistribution that controls the prevalence of each mechanism over the other and the onset of microfracturing during kerogen maturation. The approach is applied to the Draupne formation, a major source rock in the Norwegian continental shelf in the North Sea.
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Chauvire, B., & Thomas, P. S. (2020). DSC of natural opal: insights into the incorporation of crystallisable water in the opal microstructure. Journal Of Thermal Analysis And Calorimetry, 140(5), 2077–2085.
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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Chauvire, B., Houadria, M., Donini, A., Berger, B. T., Rondeau, B., Kritsky, G., et al. (2020). Arthropod entombment in weathering-formed opal: new horizons for recording life in rocks. Scientific Reports, 10(1).
Résumé: Animal fossils preserved in various geological materials, such as limestone, claystone, or amber, provide detailed information on extinct species that is indispensable for retracing the evolution of terrestrial life. Here, we present the first record of an animal fossil preserved in opal formed by weathering with such high-resolution details that even individual cuticle hairs are observed. The fossil consists of the exoskeleton of a nymphal insect belonging to the order Hemiptera and either the family Tettigarctidae or the Cicadidae. This identification is based on anatomical details such as the tibial and femoral morphology of the forelegs. The exoskeleton of the insect was primarily zeolitized during the alteration of the host rocks and later sealed in opal deposited by silica-rich fluids derived from the continental weathering of the volcanic host rocks. Organic matter is preserved in the form of amorphous carbon. This finding makes opal formed by rocks weathering a new, complementary source of animal fossils, offering new prospects for the search for ancient life in the early history of Earth and possibly other terrestrial planets such as Mars, where weathering-formed opal occurs.
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Chayka, I. F., Sobolev, A. V., Izokh, A. E., Batanova, V. G., Krasheninnikov, S. P., Chervyakovskaya, M. V., et al. (2020). Fingerprints of Kamafugite-Like Magmas in Mesozoic Lamproites of the Aldan Shield: Evidence from Olivine and Olivine-Hosted Inclusions. Minerals, 10(4).
Résumé: Mesozoic (125-135 Ma) cratonic low-Ti lamproites from the northern part of the Aldan Shield do not conform to typical classification schemes of ultrapotassic anorogenic rocks. Here we investigate their origins by analyzing olivine and olivine-hosted inclusions from the Ryabinoviy pipe, a well preserved lamproite intrusion within the Aldan Shield. Four types of olivine are identified: (1) zoned phenocrysts, (2) high-Mg, high-Ni homogeneous macrocrysts, (3) high-Ca and low-Ni olivine and (4) mantle xenocrysts. Olivine compositions are comparable to those from the Mediterranean Belt lamproites (Olivine-1 and -2), kamafugites (Olivine-3) and leucitites. Homogenized melt inclusions (MIs) within olivine-1 phenocrysts have lamproitic compositions and are similar to the host rocks, whereas kamafugite-like compositions are obtained for melt inclusions within olivine-3. Estimates of redox conditions indicate that “lamproitic” olivine crystallized from anomalously oxidized magma (NNO +3 to +4 log units.). Crystallization of “kamafugitic” olivine occurred under even more oxidized conditions, supported by low V/Sc ratios. We consider high-Ca olivine (3) to be a fingerprint of kamafugite-like magmatism, which also occurred during the Mesozoic and slightly preceded lamproitic magmatism. Our preliminary genetic model suggests that low-temperature, extension-triggered melting of mica- and carbonate-rich veined subcontitental lithospheric mantle (SCLM) generated the kamafugite-like melts. This process exhausted carbonate and affected the silicate assemblage of the veins. Subsequent and more extensive melting of the modified SCLM produced volumetrically larger lamproitic magmas. This newly recognized kamafugitic “fingerprint” further highlights similarities between the Aldan Shield potassic province and the Mediterranean Belt, and provides evidence of an overlap between “orogenic” and “anorogenic” varieties of low-Ti potassic magmatism. Moreover, our study also demonstrates that recycled subduction components are not an essential factor in the petrogenesis of low-Ti lamproites, kamafugites and leucitites.
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Chen, Y. C. E., Chen, K. H., Hu, J. C., & Lee, J. C. (2020). Probing the Variation in Aseismic Slip Behavior Around an Active Suture Zone: Observations of Repeating Earthquakes in Eastern Taiwan. Journal Of Geophysical Research-Solid Earth, 125(5).
Résumé: An examination of repeating earthquakes in eastern Taiwan revealed previously unrecognized quasiperiodic repetition of aseismic creep along two reverse faults in an active suture zone. Using 202 M-L 2.0 to 4.6 repeating earthquake sequences (RES) during the period from 2000 to 2011, we studied where and how certain faults creep. The RES were found to be highly concentrated in the southern segment of the Longitudinal Valley fault (LVF) and in the northern segment of the Central Range fault (CRF). They are mainly located at a depth of 10-25 km and show strong regional differences in creep behavior. Using the moment release rate of RES and geodetically derived long-term slip rate, we re-estimate the empirical relationship between deep creep and seismic moment for creeping sections in eastern Taiwan. For the 30-km-long LVF, the creep rate increased dramatically from 1.5 to 12.3 cm/year under the influence of the M-L 6.4 Chengkung earthquake of 2003. For the 80-km-long CRF, the high creep rate of 4.3 cm/year appears to have been stable over time and is descriptive of a previously unrecognized deep structure underneath the eastern flank of the Central Range. The quasiperiodic pulsing of the deep slip rate has a predominant interval of 1 year for both segments. After the M-L 6.4 event, the predominant interval for the creeping LVF halved in duration. The time-dependent aseismic slip showed a strong correlation with the creepmeter data, suggesting that the positing of a common mechanism is needed to connect the surface and deep creep variation.
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Cheng, Y. F., Ben-Zion, Y., Brenguier, F., Johnson, C. W., Li, Z. F., Share, P. E., et al. (2020). An Automated Method for Developing a Catalog of Small Earthquakes Using Data of a Dense Seismic Array and Nearby Stations. Seismological Research Letters, 91(5), 2862–2871.
Résumé: We propose a new automated procedure for using continuous seismic waveforms recorded by a dense array and its nearby regional stations for P-wave arrival identification, location, and magnitude estimation of small earthquakes. The method is illustrated with a one-day waveform dataset recorded by a dense array with 99 sensors near Anza, California, and 24 surrounding regional stations within 50 km of the dense array. We search a wide range of epicentral locations and apparent horizontal slowness values (0-15 s/km) in the 15-25 Hz range and time shift the dense array waveforms accordingly. For each location-slowness combination, the average neighboring station waveform similarity (avgCC) of station pairs <150 m apart is calculated for each nonoverlapping 0.5 s time window. Applying the local maximum detection algorithm gives 966 detections. Each detection has a best-fitting location-slowness combination with the largest avgCC. Of 331 detections with slowness < 0:4 s/ km, 324 (about six times the catalog events and 98% accuracy) are found to be earthquake P-wave arrivals. By associating the dense array P-wave arrivals and the P- and S-wave arrivals from the surrounding stations using a 1D velocity model, 197 detections (similar to 4 times of the catalog events) have well-estimated locations and magnitudes. Combining the small spacing of the array and the large aperture of the regional stations, the method achieves automated earthquake detection and location with high sensitivity in time and high resolution in space. Because no preknowledge of seismic-waveform features or local velocity model is required for the dense array, this automated algorithm can be robustly implemented in other locations.
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Chi, C., & Weiss, J. (2020). Asymmetric Damage Avalanche Shape in Quasibrittle Materials and Subavalanche (Aftershock) Clusters. Physical Review Letters, 125(10).
Résumé: Crackling dynamics is characterized by a release of incoming energy through intermittent avalanches. The shape, i.e., the internal temporal structure of these avalanches, gives insightful information about the physical processes involved. It was experimentally shown recently that progressive damage toward compressive failure of quasibrittle materials can be mapped onto the universality class of interface depinning when considering scaling relationships between the global characteristics of the microcracking avalanches. Here we show, for three concrete materials and from a detailed analysis of the acoustic emission waveforms generated by microcracking events, that the shape of these damage avalanches is strongly asymmetric, characterized by a very slow decay. This remarkable asymmetry, at odds with mean-field depinning predictions, could be explained, in these quasibrittle materials, by retardation effects induced by enhanced viscoelastic processes within a fracture process zone generated by the damage avalanche as it progresses. It is associated with clusters of subavalanches, or aftershocks, within the main avalanche.
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Colombier, M., Shea, T., Burgisser, A., Druitt, T. H., Gurioli, L., Muller, D., et al. (2020). Rheological change and degassing during a trachytic Vulcanian eruption at Kilian Volcano, Chaine des Puys, France. Bulletin Of Volcanology, 82(12).
Résumé: Magma ascent during silicic dome-forming eruptions is characterized by significant changes in magma viscosity, permeability, and gas overpressure in the conduit. These changes depend on a set of parameters such as ascent rate, outgassing and crystallization efficiency, and magma viscosity, which in turn may influence the prevailing conditions for effusive versus explosive activity. Here, we combine chemical and textural analyses of tephra with viscosity models to provide a better understanding of the effusive-explosive transitions during Vulcanian phases of the 9.4 ka eruption of Kilian Volcano, Chaine des Puys, France. Our results suggest that effusive activity at the onset of Vulcanian episodes at Kilian Volcano was promoted by (i) rapid ascent of initially crystal-poor and volatile-rich trachytic magma, (ii) a substantial bulk and melt viscosity increase driven by extensive volatile loss and crystallization, and (iii) efficient degassing/outgassing in a crystal-rich magma at shallow depths. Trachytic magma repeatedly replenished the upper conduit, and variations in the amount of decompression and cooling caused vertical textural stratification, leading to variable degrees of crystallization and outgassing. Outgassing promoted effusive dome growth and occurred via gas percolation through large interconnected vesicles, fractures, and tuffisite veins, fostering the formation of cristobalite in the carapace and talus regions. Build-up of overpressure was likely caused by closing of pore space (bubbles and fractures) in the dome through a combination of pore collapse, cristobalite formation, sintering in tuffisite veins, and limited pre-fragmentation coalescence in the dome or underlying hot vesicular magma. Sealing of the carapace may have caused a transition from open- to closed- system degassing and to renewed explosive activity. We generalize our findings to propose that the broad spectrum of eruptive styles for trachytic magmas may be inherited from a combination of characteristics of trachytic melts that include high water solubility and diffusivity, rapid microlite growth, and low melt viscosity compared to their more evolved subalkaline dacitic and rhyolitic equivalents. We show that trachytes may erupt with a similar style (e.g., Vulcanian) but at significantly higher ascent rates than their andesitic, dacitic, and rhyolitic counterparts. This suggests that the periodicity of effusive-explosive transitions at trachytic volcanoes may differ from that observed at the well-monitored andesitic, dacitic, and rhyolitic volcanoes, which has implications for hazard assessment associated with trachytic eruptions.
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Combey, A., Audin, L., Benavente, C., Bouysse-Cassagne, T., Marconato, L., & Rosell, L. (2020). Evidence of a large “prehistorical” earthquake during Inca times? New insights from an indigenous chronicle (Cusco, Peru). Journal Of Archaeological Science-Reports, 34.
Résumé: A colonial chronicle written by the indigenous Peruvian author Pachacuti Yamqui Salcamaygua ([1613?]) relates a legend of the sudden appearance of a huge animal – kilometres in length and approximately 4 m in width – and described as the Andean snake-like deity amaru. Pachacuti Yamqui alleged that this fantastic event occurred on the day that the sovereign Pachacuti Inca Yupanqui's eldest son was born around 1440 CE, and was named “Amaru”. We suggest that the underlying event was an earthquake, and that the propagation of the surface rupture across the landscape resembled a sudden appearance of a snake-like being wriggling over the mountains and leaving an undulating surface trace. The concordance between the snake's route and the layout of a major fault complex above Cusco, as well as several ethnographic testimonies, support this hypothesis. Although little is known about pre-1532 CE seismicity, the current tectonic settings of the Cusco area point to seismic awareness of the Incas (ca. 1300-1532 CE). Independent results from architectural and paleoseismological fields in the Cusco area corroborate a significant impact of large earthquakes on local societies. In Peru, without pre-Hispanic written sources, the oral folklore and traditions preserved in Spanish chronicles offer a relevant, but still underexploited resource for identifying paleo-extreme events. Combining multidisciplinary geomorphic observations, archaeological evidence and historical sources, we revisit this legendary episode and its possible implications.
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Cordier, C., Coin, K., Arndt, N. T., & Cartigny, P. (2020). The algliden Ni-Cu-Au deposit: magmatic sulfides in a subduction setting. Mineralium Deposita, 55(6), 1173–1196.
Résumé: The origin of most major sulfide Ni-Cu deposits is attributed to the segregation of immiscible sulfide liquids from intraplate silicate melts, in response to assimilation of siliceous or sulfur-bearing rocks. The algliden gabbroic dike in the Skellefte district (Sweden) contains Ni-Cu sulfide mineralization that is atypical because it formed in an arc setting and has a high Au content and low Ni/Cu ratio. This association led previously to a model in which the mineralization was linked to the assimilation of Cu-Au porphyry wall rocks. Based on new petrological, geochemical, and S isotope analyses of the dike and its wall rocks, we propose that assimilation of mineralized wall rocks was not instrumental in the formation of the deposit. Instead, we propose that the sulfides segregated during olivine crystallization from an evolved arc basalt and were injected into the dike in an olivine-rich crystal mush. This scenario explains the uniform dissemination of sulfide ores within norites, together with the high Au content and low Ni/Cu ratio of the ores. We propose that sulfide segregation from oxidized arc basalt was triggered by a decrease in the oxidation state of the melt, likely due to the cooling of the silicate melt or to the interaction with meta-sediments rich in organic matter, as proposed for other arc-related Cu-Ni sulfide deposits in Fennoscandia and elsewhere. At algliden, melt reduction would have occurred relatively late during magma evolution, leading to the formation of an uneconomic deposit consisting of low Ni ores and lacking massive sulfides.
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Cossa, D., & Tabard, A. M. (2020). Mercury in Marine Mussels from the St. Lawrence Estuary and Gulf (Canada): A Mussel Watch Survey Revisited after 40 Years. Applied Sciences-Basel, 10(21).
Résumé: Various species of marine mussels have been used, in the last 50 years, as sentinel organisms for monitoring metal contamination along marine coasts. There are two main reasons for this: these mollusks concentrate metals in their soft tissue and they are geographically widespread. In practice, trace metal concentrations in mussel soft tissue reveal (after some correction for biotic effects) the contamination level of their surrounding environment. We present the results of a mercury (Hg) survey in Mytilus spp. collected in the summers of 2016, 2018, and 2019 at 51 stations distributed along the coasts of the Estuary and Gulf of St. Lawrence. Mercury concentrations ranged from 0.063 to 0.507 μg g(-1) (dry weight, dw), with a grand mean of 0.173 +/- 0.076 μg g(-1) dw (+/- 1 standard deviation), and a median of 0.156 μg g(-1) dw for the 504 individuals analyzed. Mercury contents per individual mussel were significantly (p < 0.01) related to shell length and dry tissue weight, with the smaller individuals having the highest Hg concentrations. To take into account these biotic effects, we normalized Hg concentrations of the mussel soft tissue for constant shell length (L) and soft tissue weight (TW) based on the log-log relationships between Hg content and L or TW. The normalized Hg contents of mussels varied from 10.9 to 66.6 ng per virtual individual of 35 mm length and 0.17 g dry weight. A similar normalization procedure applied to 1977-1979 data, yielded a very similar range: 12 to 64 ng. This observation suggests that the Hg bioavailable to marine mussels in the study area did not change over a span of 40 years. Regional Hg distribution patterns indicate a gradual decrease of Hg content in mussels downstream from freshwater discharges to the St. Lawrence Estuary and the Baie des Chaleurs, suggesting that rivers constitute a significant Hg source in these estuarine systems. Atmospheric Hg deposition and concentration in marine waters of the Atlantic Ocean are known to have decreased in the last decades. However, in coastal environments, the response to these changes does not seem to be rapid, probably because of the long residence time of Hg in soils before being exported to coastal areas.
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Cossa, D., Knoery, J., Boye, M., Marusczak, N., Thomas, B., Courau, P., et al. (2020). Oceanic mercury concentrations on both sides of the Strait of Gibraltar decreased between 1989 and 2012. Anthropocene, 29.
Résumé: Mercury (Hg) is a toxic metal that threatens the health of aquatic ecosystems and fish consumers. Its natural cycle has been deeply perturbed by Anthropogenic Hg emissions have deeply perturbed its natural cycle, especially since the start of the Industrial Revolution circa 1850 CE. Anthropogenic Hg emissions from North America and Europe have decreased by a factor of two in the last decades following the implementation of strict regulations. The response of North Atlantic Ocean and Mediterranean waters to this decrease remains poorly documented by field observations. A comparison of results obtained between 1989 and 2012 shows a significant decrease of Hg concentrations in waters on both sides of the Strait of Gibraltar. West of Gibraltar, the Hg decrease ranges from similar to 35 % in the upper North East Atlantic Deep Water to similar to 50 % in the North East Atlantic Central Water. East of Gibraltar, the observed decrease is similar to 30 % in the Western Mediterranean Deep Water. No decrease is observed in the deep Atlantic Ocean layer that formed before the industrial era. These results strongly substantiate the effectiveness of global anti-pollution policies on Hg contamination in oceanic waters. A consequent decline of Hg bioaccumulation in Northeastern Atlantic and Western Mediterranean pelagic ecosystems still requires verification. (C) 2019 Elsevier Ltd. All rights reserved.
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Costa, C., Alvarado, A., Audemard, F., Audin, L., Benavente, C., Bezerra, F. H., et al. (2020). Hazardous faults of South America; compilation and overview. Journal Of South American Earth Sciences, 104.
Résumé: The heterogeneous South American geology has coined a wide variety of neotectonic settings where crustal seismogenic sources do occur. This fact has led to different approaches for mapping and inventory neotectonic structures. The South American Risk Assessment project promoted the discussion and update under uniform standards of the available information on neotectonic deformation, for its application in regional Probabilistic Seismic Hazard Assessments. As a result, 1533 hazardous faults have been inventoried onshore South America, 497 of them qualifying to feed the engine model driving probabilistic maps. Main hazardous structures are concentrated throughout the eastern boundary of the Northern Andean Sliver and along the foreland-facing Andean Thrust Front. Space geodesy and seismicity illuminate the seismogenic significance of these deformation belts, although few neotectonic surveys have been conducted to date in the latter region. The characteristics of the main structures or deformation zones are here outlined according to their filiation to neotectonic domains, which are dependant on the geologic, seismotectonic, or morphotectonic settings in Andean and extra-Andean regions. The knowledge accrued on the hazardous faults in South America here compiled, reinforces the fact that some of these structures constitute significant hazard sources for many urban areas and critical facilities and should be incorporated in seismic hazard assessments. However, the available fault data are insufficient in many cases or carry significant epistemic uncertainties for fault source characterization. This contribution aims to summarize the present knowledge on the South American hazardous faults as well as the main challenges for successful fault data incorporation into seismic hazard models.
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Cushing, E. M., Hollender, F., Moiriat, D., Guyonnet-Benaize, C., Theodoulidis, N., Pons-Branchu, E., et al. (2020). Building a three dimensional model of the active Plio-Quaternary basin of Argostoli (Cephalonia Island, Greece): An integrated geophysical and geological approach. Engineering Geology, 265.
Résumé: This work is a multidisciplinary approach from geological and geophysical surveys to build a 3D geological model of Argostoli Basin (Cephalonia Island, Greece) aiming to be used for computational 3D simulation of seismic motion. Cephalonia Island is located at the north-western end of the Aegean subduction frontal thrust that is linked to the dextral Cephalonia Transform Fault (west of Cephalonia) where the seismic hazard is high in terms of earthquake frequency and magnitude. The Plio-Quaternary Koutavos-Argostoli basin site was selected within the French Research Agency PIA SINAPS@ project (www.institut-seism.fr/projets/sinaps/ – last accessed on November 25th 2019) to host a vertical accelerometer array. The long-term goal is to validate three-dimensional nonlinear numerical simulation codes to assess the site-specific amplification and nonlinearity. Herein the geological and geophysical surveys carried out from 2011 to 2017 are presented and in particular the complementary investigations that led to the identification of the main stratigraphic units and their structures. In addition, coral debris sampled from the vertical array deep borehole cores were used for Th-230/U-234 measurements, which confirmed the Pleistocene age of the Koutavos basin. The characterization of the three-dimensional structure of the stratigraphic units was achieved by coupling geological cross-sections (i.e., depth geometry) and geophysical surveys based of surface wave analysis.
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D'Agostino, N., Metois, M., Koci, R., Duni, L., Kuka, N., Ganas, A., et al. (2020). Active crustal deformation and rotations in the southwestern Balkans from continuous GPS measurements. Earth And Planetary Science Letters, 539.
Résumé: The western limb of the Hellenic Arc defines the boundary of a large intracontinental active extensional domain covering the Aegean and the southwestern part of the Balkan peninsula. Along this boundary a transition from collision in the north to subduction in the south is associated with post-Miocene clockwise rotations of similar to 50 degrees. We present a new GPS velocity field that, with new permanent station velocities in Albania, Bulgaria, Kosovo, Montenegro, and Northern Macedonia, provides insights into previously unresolved aspects on the large-scale dynamics of continental lithosphere and on the relation between long and short-term kinematics. In particular we address (1) the kinematic description of the collision/subduction transition, (2) the relation between long-term finite rotations with geodetically-measured instantaneous rotations, (3) the forces maintaining and resisting the deformation of the extensional domain and (4) the extent of its northern boundary. We use the analogy of rigid elongate inclusions in the velocity field to predict the senses and approximate rates of rotation of crustal blocks in the deforming continental region. Across the collision/subduction transition zone a large rotational pattern in the velocity field is found whose spatial pattern and sense of rotation is compatible with the observed paleomagnetic rotations through the occurrence of fault-bounded block rotations. Geodetic observations show that clockwise vertical axis rotation of the western limb of the Hellenic margin is active today, with distribution and rates that are essentially the same as that defined by the paleomagnetic data for the last 5 Ma. The maximum rates of the rotational component of the velocity field is found along the wide arrangement of fault-bounded blocks in central Greece that accomodate the NE-SW dextral shear transferred from the northern Aegan trough. The northern limit of the rotating margin defines a hinge (Scutari-Pec transverse zone) that has remained stationary throughout the Middle Miocene (relative to the upper plate of the collision/subduction system) with important implications for the distribution of strength of the western margin of the Hellenic Arc. The distribution and style of deformation along the western boundary of the extensional domain is controlled by the relation between gravitational forces, driving the flow of crustal material towards the low-lying adjacent regions sea floor, and heterogeneous resistive forces along the collision/subduction boundary. (c) 2020 Elsevier B.V. All rights reserved.
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Dales, P., Pinzon-Ricon, L., Brenguier, F., Boue, P., Arndt, N., McBride, J., et al. (2020). Virtual Sources of Body Waves from Noise Correlations in a Mineral Exploration Context. Seismological Research Letters, 91(4), 2278–2286.
Résumé: The extraction of body waves from passive seismic recordings has great potential for monitoring and imaging applications. The low environmental impact, low cost, and high accessibility of passive techniques makes them especially attractive as replacement or complementary techniques to active-source exploration. There still, however, remain many challenges with body-wave extraction, mainly the strong dependence on local seismic sources necessary to create high-frequency body-wave energy. Here, we present the Marathon dataset collected in September 2018, which consists of 30 days of continuous recordings from a dense surface array of 1020 single vertical-component geophones deployed over a mineral exploration block. First, we use a cross-correlation beamforming technique to evaluate the wavefield each minute and discover that the local highway and railroad traffic are the primary sources of high-frequency body-wave energy. Next, we demonstrate how selective stacking of cross-correlation functions during periods where vehicles and trains are passing near the array reveals strong bodywave arrivals. Based on source station geometry and the estimated geologic structure, we interpret these arrivals as virtual refractions due to their high velocity and linear moveout. Finally, we demonstrate how the apparent velocity of these arrivals along the array contains information about the local geologic structure, mainly the major dipping layer. Although vehicle sources illuminating array in a narrow azimuth may not seem ideal for passive reflection imaging, we expect this case will be commonly encountered and should serve as a good dataset for the development of new techniques in this domain.
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Daout, S., Dini, B., Haeberli, W., Doin, M. P., & Parsons, B. (2020). Ice loss in the Northeastern Tibetan Plateau permafrost as seen by 16 yr of ESA SAR missions. Earth And Planetary Science Letters, 545.
Résumé: InSAR time series of surface deformation from 16 yr of Envisat (2003-2011) and Sentinel-1 (2014-2019) ESA satellite radar measurements have been constructed to characterise spatial and temporal dynamics of ground deformation over an 80,000 km(2) area in the permafrost of the northeastern Tibetan Plateau. The regional deformation maps encompass various types of periglacial landforms and show that seasonal thaw effects are controlled by the sediment type and local topography. High seasonal ground movements are concentrated on shallow slopes and poor-drainage areas in unconsolidated, frost-susceptible and fine-grained sediments within glacier outwash plains, braided stream plains, alluvial deposits or floodplains. Fast subsidence due to thaw settlement takes place during June/July while frost heave is intense during December/January when two-sided freezing of pore water under pressure causes prolonged ice segregation near the permafrost table. The analysis reveals pervasive subsidence of the ground of up to similar to 2 cm/yr, and increasing by a factor of 2 to 5 from 2003 to today, in high-relief and well-drained areas. The findings suggest that seasonal thaw increasingly affects ice-rich layers at the permafrost table, as well as high-rates of widespread mass movements of non-consolidated sediments, the latter amplified by an increase of effects from frost heave/thaw settlement. (C) 2020 Elsevier B.V. All rights reserved.
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de Gelder, G., Jara-Munoz, J., Melnick, D., Fernandez-Blanco, D., Rouby, H., Pedoja, K., et al. (2020). How do sea-level curves influence modeled marine terrace sequences? Quaternary Science Reviews, 229.
Résumé: Sequences of uplifted marine terraces are widespread and reflect the interaction between climatic and tectonic processes at multiple scales, yet their analysis is typically biased by the chosen sea-level (SL) curve. Here we explore the influence of Quaternary SL curves on the geometry of marine terrace sequences using landscape evolution models (LEMs). First, we modeled the young, rapidly uplifting sequence at Xylokastro (Corinth Rift; <240 ka; similar to 1.5 mm/yr), which allowed us to constrain terrace ages, model parameters, and best-fitting SL curves. Models that better reproduced the terraced topography used a glacio-isostatically adjusted SL curve based on coral data (for similar to 125 ka), and a eustatic SL curve based on ice-sheet models (for similar to 240 ka). Second, we explored the opposite end-member of older, slower uplifting sequences (2.6 Ma; 0.1-0.2 mm/yr). We find that cliff diffusion is important to model terrace sequence morphology, and that a hydraulic-model based SL curve reproduced observed terrace morphologies best. Third, we modeled the effect of SL noise with various amplitudes and wavelengths on our interpretations, finding that younger, faster uplifting sequences are less noise-sensitive and thus generally more promising for LEM studies. Our results emphasize the importance of testing a variety of SL-curves within marine terrace studies, and highlight that accurate modeling through LEMs may provide valuable insight on climatic and tectonic forcing to Quaternary coastal evolution. (C) 2019 Elsevier Ltd. All rights reserved.
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de Leeuw, A., Vincent, S. J., Matoshko, A., Matoshko, A., Stoica, M., & Nicoara, I. (2020). Late Miocene sediment delivery from the axial drainage system of the East Carpathian foreland basin to the Black Sea. Geology, 48(8), 761–765.
Résumé: We describe a late Miocene to early Pliocene axial drainage system in the East Carpathian foreland, which was an important sediment supplier to the Black Sea and the Dacian Basin. Its existence explains the striking progradation of the northwest Black Sea shelf prior to the onset of sediment supply from the continental-scale Danube River in the late Pliocene to Pleistocene. This axial drainage system evolved due to the diachronous along-strike evolution of the Carpathians and their foreland; continental collision, overfilling, slab breakoff, and subsequent exhumation of the foreland occurred earlier in the West Carpathians than in the East Carpathians. After overfilling of the western foreland, excess sediment was transferred along the basin axis, giving rise to a 300-km-wide by 800-km-long, southeast-prograding river-shelf-slope system with a sediment flux of similar to 12 x 103 km3/m.y. Such late-stage axial sedi-ment systems often develop in foreland basins, in particular, where orogenesis is diachronous along strike. Substantial lateral sediment transport thus needs to be taken into account, even though evidence of these axial systems is often eroded following slab breakoff and inversion of their foreland basins.
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de Vals, M., Gastineau, R., Perrier, A., Rubi, R., & Moretti, I. (2020). The stones of the Sanctuary of Delphi – Northern shore of the Corinth Gulf – Greece. Bsgf-Earth Sciences Bulletin, 191.
Résumé: The choice of stones by the ancient Greeks to build edifices remains an open question. If the use of local materials seems generalized, allochthonous stones are usually also present but lead to obvious extra costs. The current work aims to have an exhaustive view of the origins of the stones used in the Sanctuary of Delphi. Located on the Parnassus zone, on the hanging wall of a large normal fault related to the Corinth Rift, this Apollo Sanctuary is mainly built of limestones, breccia, marbles, as well as more recent poorly consolidated sediments generally called poros in the literature. To overpass this global view, the different lithologies employed in the archaeological site have been identified, as well as the local quarries, in order to find their origins. The different limestones are autochthons and come from the Upper Jurassic – Cretaceous carbonate platform of the Tethys Ocean involved in the Hellenides orogen. Those limestones of the Parnassus Massif constitute the majority of the rock volume in the site; a specific facies of Maastrichtian limestone called “Profitis Ilias limestone” has been used for the more prestigious edifices such as the Apollo Temple. The corresponding ancient quarry is located few kilometers west of the sanctuary. Then, slope breccia has been largely used in the sanctuary: it crops out in and around the site and is laying on top of the carbonates. Finally, the poros appear to be very variable and seven different facies have been documented, including travertine, oolitic grainstone, marine carbonates and coarse-grained sandstones. All these recent facies exist in the south-east shore of the Gulf of Corinth, although – except for the grainstone – the quarries are not yet known.
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Delgado, F., Zerathe, S., Audin, L., Schwartz, S., Benavente, C., Carcaillet, J., et al. (2020). Giant landslide triggerings and paleoprecipitations in the Central Western Andes: The aricota rockslide dam (South Peru). Geomorphology, 350.
Résumé: The central part of the Western Andes holds an exceptional concentration of giant paleolandslides involving very large volumes of rock material (v > km(3)). While those gravitational slope failures are interpreted consensually as an erosional response to the geodynamic activity of the Andes (relief formation and tectonic activity), the question of their triggering mechanisms remains enigmatic. To clarify the respective roles of climatic versus seismic forcing on the Andean landslides, new temporal constraints on paleo movements are essential. Here, we focus on one of those giant slope failures, the Aricota giant rockslide that damned the Locumba valley in southern Peru. We conducted fieldwork, high-resolution DEM analysis and cosmogenic nuclide dating to decipher its development history and failure mechanisms. Our results point to the occurrence of two successive events. A giant failure mobilizing a rock volume of ca. 2 km(3) first produced a dam at 17.9 +/- 0.7 ka. Considering its height of ca. 600 m, the Aricota rockslide dam is one of the three largest landslide dams worldwide. At 12.1 +/- 0.2 ka, a second event produced ca. 0.2 km(3) of material, and the rock-avalanche debris spread out over the dam. As the chronology of those two events is pointing to the two main paleoclimatic pluvial periods in this region (Heinrich Stadial 1a and Younger Dryas), we favor the interpretation of a climatic forcing. At a regional scale, the concomitant aggradation of alluvial terraces and fan systems along the nearby valleys highlights higher regional erosion, sediments supply and mass-wasting events during those paleoprecipitation events and strengthens this conclusion. (C) 2019 Elsevier B.V. All rights reserved.
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Delunel, R., Schlunegger, F., Valla, P. G., Dixon, J., Glotzbach, C., Hippe, K., et al. (2020). Late-Pleistocene catchment-wide denudation patterns across the European Alps. Earth-Science Reviews, 211.
Résumé: We compile detrital Be-10 concentrations of Alpine rivers, representing the denudation rates pattern for 375 catchments across the entire European Alps. Using a homogeneized framework, we employ state-of-the-art techniques for inverting in-situ Be-10 concentrations into denudation rates. From our compilation, we find that (i) while lithologic properties and precipitation/runoff do influence erosion mechanisms and rates at the scale of individual catchments and in some specific Alpine regions, such controls do not directly stand for the entire Alps, (ii) as also previously suggested, catchment-wide denudation rates across the entire European Alps closely follow first-order Alpine topographic metrics at the scale of individual catchments or selected Alpine sub-regions. However, in addition to previous local-scale studies conducted in the European Alps, our large-scale compilation highlights a functional relationship between catchment-wide denudation and mean catchment slope angle. Catchment-wide denudation positively correlates with mean catchment slope up to a threshold angle (25-30 degrees). Above this threshold, any correlation between catchment-wide denudation and slope as well as other catchment metrics breaks apart. We can reconcile these systematic patterns by proposing a regional erosion model based on diffusive-transport laws for catchments located below the slope threshold angle. In oversteepened catchments situated above-threshold slopes, erosion is stochastic in nature, as glacial carving likely caused a partial decoupling between hillslope and fluvial domains with complex topographic relationships and sediment connectivity patterns. Finally, we identify a first-order positive relationship between modern geodetic rock uplift and catchment wide denudation for the European Alps. The observed spatial pattern is highly variable and possibly reflects the surface response to deep geodynamic mechanisms prevailing in the different Alpine regions. We conclude that today's topography and geomorphic features of the entire Alps are the result of a millenial-scale geomorphic response to past glacial processes and active rock uplift, highlighting a link between external and internal drivers for mountain erosion.
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Derras, B., Bard, P. Y., Regnier, J., & Cadet, H. (2020). Non-linear modulation of site response: Sensitivity to various surface ground-motion intensity measures and site-condition proxies using a neural network approach. Engineering Geology, 269.
Résumé: The impact of non-linear soil behavior on site response may be described by the non-linear to linear site response ratio RSRNL introduced in Regnier et al. (2013). This ratio most often exhibits a typical shape with an amplitude above one below a site-specific frequency f(NL), and an amplitude below one beyond f(NL). This paper presents an investigation of the correlation between this RSRNL ratio and various parameters used to characterize the site (Site Condition Proxies: SCPs) and the seismic loading level (Ground Motion Intensity Measures: GMIMs). The data used in this analysis come from sites of the Japanese Kiban-Kyoshin (KiK-net) network, for which the nonlinear to linear site-response ratio (RSRNL) is obtained by comparing the surface/down-hole Fourier spectral ratio for strong events and for weak events. The five SCPs are Vs30, the minimum velocity of the soil profile(Vs(m)(in)), an index of the velocity gradient over the top 30 m (B-30), the fundamental frequency f(OHv), as measured from the H/V earthquake ratio, and the corresponding amplitude Amw. The seven GMIMs are PGA, PGV, PGV/V-s30 (peak strain proxy), I-A (Arias Intensity), CAV (Cumulative Absolute Velocity), a(rms), (Root Mean Square Acceleration) and Trifunac-Brady Duration (D-T). The original data set consists of a total of 2927 RSRNL derived from KiK-net recordings at 132 sites. To assign an equal weight to each site, and to avoid any bias linked to sites with many recordings, for each GMIM, this original data set is grouped in 15 different intervals corresponding to fixed fractiles of the statistical distribution of the considered GMIM (every 10% from F10 to F50, and every 5% from F55 to F100). In each group, the average RSRNL Gm for each site is computed. For each of these seven advanced data sets, a neural network approach is used to predict the behavior of RSRNL Gm as a function of the corresponding GMIM, and one or two SCPs. The performance of each model is quantified through the average variance reduction coefficient mu(Rc) in a fixed frequency range. This sensitivity study is performed in the normalized frequency (f/f NL ) domain to identify the best combinations (GMIM, SCPs) providing the largest variance reduction, and then in the absolute frequency domain for the final optimal combination. The optimal combinations [GMIM, two-SCPs] are triplets [PGV/V-s30, V-s30 f(0HV); mu(Rc) = 18.6%], [PGV/V-s30, V-s30 A(0HV); mu(Rc) = 18.16%], [PGV, V-s30 -f(0HV); mu(Rc) = 17.3%] and [PGA, B-30 -A(0HV); mu(Rc) = 17.2%]. The final absolute frequency model with the best triplet makes it possible to predict the non-linear response of a given site knowing its linear, weak-motion response, and two site proxy parameters, for wide ranges of the considered ground motion parameters.
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Dobretsov, N. L., Sobolev, A. V., Sobolev, N. V., Sobolev, S. V., & Touret, J. (2020). Geodynamics, Petrology, and Mineralogy: Global Problems, Experiments, and Key Cases. Russian Geology And Geophysics, 61(5-6), 495–501.
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Donze, F. V., Truche, L., Namin, P. S., Lefeuvre, N., & Bazarkina, E. F. (2020). Migration of Natural Hydrogen from Deep-Seated Sources in the Sao Francisco Basin, Brazil. Geosciences, 10(9).
Résumé: Hydrogen gas is seeping from the sedimentary basin of Sao Franciso, Brazil. The seepages of H(2)are accompanied by helium, whose isotopes reveal a strong crustal signature. Geophysical data indicates that this intra-cratonic basin is characterized by (i) a relatively high geothermal gradient, (ii) deep faults delineating a horst and graben structure and affecting the entire sedimentary sequence, (iii) archean to paleoproterozoic basements enriched in radiogenic elements and displaying mafic and ultramafic units, and (iv) a possible karstic reservoir located 400 m below the surface. The high geothermal gradient could be due to a thin lithosphere enriched in radiogenic elements, which can also contribute to a massive radiolysis process of water at depth, releasing a significant amount of H-2. Alternatively, ultramafic rocks that may have generated H(2)during their serpentinization are also documented in the basement. The seismic profiles show that the faults seen at the surface are deeply rooted in the basement, and can drain deep fluids to shallow depths in a short time scale. The carbonate reservoirs within the Bambui group which forms the main part of the sedimentary layers, are crossed by the fault system and represent good candidates for temporary H(2)accumulation zones. The formation by chemical dissolution of sinkholes located at 400 m depth might explain the presence of sub-circular depressions seen at the surface. These sinkholes might control the migration of gas from temporary storage reservoirs in the upper layer of the Bambui formation to the surface. The fluxes of H(2)escaping out of these structures, which have been recently documented, are discussed in light of the newly developed H(2)production model in the Precambrian continental crust.
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Dujardin, A., Hollender, F., Causse, M., Berge-Thierry, C., Delouis, B., Foundotos, L., et al. (2020). Optimization of a Simulation Code Coupling Extended Source (k(-2)) and Empirical Green's Functions: Application to the Case of the Middle Durance Fault. Pure And Applied Geophysics, 177(5), 2255–2279.
Résumé: We developed a ground-motion simulation code base on extended rupture modeling combined with the use of empirical Green's functions (EGFs), adapted for low-to-moderate seismicity regions (with a limited set of EGFs), and extended its range of applicability to the lowest source-to-site distances. This code is based on a kinematic source description of an extended fault and is designed to allow complex fault geometries and to generate a ground motion variability in agreement with that of the recorded databases. The code is developed to work with a sparse set of EGFs. Each available EGF is therefore used in several positions on the rupture area. To be used in positions different of their original position, we applied to the EGFs some adjustments. In addition to the classical adjustments (i.e. time delay correction, geometrical spreading correction and anelastic attenuation correction), we propose here a radiation pattern adjustment. The effectiveness of it is tested in a numerical application. We showed noticeable improvements at the lowest distances, and some limitations when approaching the nodal planes of the subevents the recording of which were used as EGFs. We took advantage of the development of this code, its ability to work with a sparse set of EGFs, its ability to take into account complex fault geometries and its ability to master the general variability, to perform a ground-motion simulation scenario on the Middle Durance Fault (MDF). We perform simulations for a hard rock site (V-S30 = 1800 m/s) and a sediment site (V-S30 = 440 m/s) of the CEA Nuclear Research Site of Cadarache (France), and compared the computed ground motion with several ground motion prediction equations (GMPEs). The GMPEs slightly underestimate the sediment site but strongly overestimate the ground motion amplitude on the hard rock site, even when using a specific correction factor which adapts GMPEs predictions from rock site to hard rock site. This general ascertainment confirms the need to continue efforts towards the establishment of consistent GMPEs applicable to hard-rock conditions.
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Edmund, E., Miozzi, F., Morard, G., Boulard, E., Clark, A., Decremps, F., et al. (2020). Axial Compressibility and Thermal Equation of State of Hcp Fe-5wt% Ni-5wt% Si. Minerals, 10(2).
Résumé: Knowledge of the elastic properties and equations of state of iron and iron alloys are of fundamental interest in Earth and planetary sciences as they are the main constituents of telluric planetary cores. Here, we present results of X-ray diffraction measurements on a ternary Fe-Ni-Si alloy with 5 wt% Ni and 5 wt% Si, quasi-hydrostatically compressed at ambient temperature up to 56 GPa, and under simultaneous high pressure and high temperature conditions, up to 74 GPa and 1750 K. The established pressure dependence of the c/a axial ratio at ambient temperature and the pressure-volume-temperature (P-V-T) equation of state are compared with previous work and literature studies. Our results show that Ni addition does not affect the compressibility and axial compressibility of Fe-Si alloys at ambient temperature, but we suggest that ternary Fe-Ni-Si alloys might have a reduced thermal expansion in respect to pure Fe and binary Fe-Si alloys. In particular, once the thermal equations of state are considered together with velocity measurements, we conclude that elements other than Si and Ni have to be present in the Earth's inner core to account for both density and seismic velocities.
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Elbaz-Poulichet, F., Guedron, S., Anne-Lise, D., Freydier, R., Perrot, V., Rossi, M., et al. (2020). A 10,000-year record of trace metal and metalloid (Cu, Hg, Sb, Pb) deposition in a western Alpine lake (Lake Robert, France): Deciphering local and regional mining contamination. Quaternary Science Reviews, 228.
Résumé: Concentrations of trace metals and metalloids (Cu, Hg, Sb, Pb), major elements, stable Pb and C isotope ratios, total organic carbon (TOC), C/N atomic ratios, were analyzed in two sediment cores encompassing 10,000 years of sedimentation sampled in Lake Robert (French Alps). The results showed that the establishment of a soil cover and vegetation during the Holocene climatic optimum increased Cu and Hg deposition in sediments. Results also enabled reconstruction of the history and local vs regional origins of pollution. During the Bronze Age (1800-1000 BC), Cu mining activities increased Hg and Sb accumulation rates (AR) by a factor of 7 (Hg) and 9 (Sb) compared to pre-Bronze Age values. The rise in Hg AR was equivalent to that of the industrial era highlighting a major local Hg point source not recorded in regional archives. During the Iron Age, Pb pollution was attributed to Sicilian ores whereas during the Roman Empire Pb pollution had the isotopic signature of Spanish Pb ores. During the Medieval period (ca. AD 1200), Pb and Hg pollution was due to the exploitation of the local Ag-Pb mines. Finally, during the industrial era, metal accumulations rates were 90 (Pb), 5 (Hg) and 20 (Sb) times higher than those in the pre-Bronze Age. The isotopic composition of Pb reflected mixed sources including industrial Pb and gasoline Pb. Synchronously, the increase in Sb and Hg pollution is attributed to global and regional atmospheric pollution. (C) 2019 Elsevier Ltd. All rights reserved.
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Elliott, A., Elliott, J., Hollingsworth, J., Kulikova, G., Parsons, B., & Walker, R. (2020). Satellite imaging of the 2015 M7.2 earthquake in the Central Pamir, Tajikistan, elucidates a sequence of shallow strike-slip ruptures of the Sarez-Karakul fault. Geophysical Journal International, 221(3), 1696–1718.
Résumé: On 7 December 2015, a shallow M-w 7.2 strike-slip earthquake struck the Murghab River Valley in the Central Pamirs of Tajikistan. Seismologically this event was similar to a large seismic event in 1911 whose causative fault has never been identified. We measure the displacement field of the 2015 event from satellite observations using Sentinel-1 radar interferometry, Landsat-8 optical pixel-tracking, and surface rupture mapping from high resolution SPOT-6/7 imagery to characterize the role this earthquake rupture plays in the accommodation of strain on its causative structure, the Sarez-Karakul fault. We present geomorphic mapping and interpretations o f other Quaternary-active reaches of this fault system, which highlight variable rupture history of the different sections. These sections appear to be separated by inherited bedrock structural boundaries. Significantly, the reaches of the fault northeast and southwest of the 2015 rupture exhibit the freshest morphology prior to 2015, indicative of a more recent rupture than elsewhere. Using new high resolution imagery we map fresh scarps at the northern and southern ends of the Sarez-Karakul fault which may represent this 1911 rupture. To test which of these reaches could have been the source of the elusive 1911 event, we compare synthetic seismograms from three plausible fault sources determined from geomorphology, with observed seismic traces from 1911 at early recording stations throughout Europe. We find that the best fitting fault source is in fact southwest of the 2015 rupture, meaning that we have a record of three distinct recent events on the Sarez-Karakul fault system-two of them instrumentally recorded. Our mapping of these separate events reveals a correlation between their boundaries and the active and inherited thrust and suture systems that intersect the northeast striking left-lateral fault, suggesting structural control over the extents of individual ruptures on the active strike-slip fault.
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Eslami, A., Kananian, A., Grieco, G., Gatta, G. D., & Rotiroti, N. (2020). Metallogeny of Serpentinite-hosted Magnetite Deposits: Hydrothermal Overgrowth on Chromite or Metamorphic Transformation of Chromite? Acta Geologica Sinica-English Edition, 94, 5.
Résumé: Peculiar and rare occurrences of serpentinite-hosted magnetite deposits with mineable sizes are found in the Mesozoic ophiolites of Greece (Skyros), Iran (Nain and Sabzevar) and Oman (Aniba). These deposits have diverse thickness (from a few centimeters up to 50 m) and length (2 to >500 m). Magnetite ores show variable textures, including massive, nodular and banded ores, veins, net and fine-grained disseminations in serpentinites. Intriguingly, the investigated magnetite deposits can be mistaken for chromitite pods. Serpentinite-hosted magnetite deposits show three modes of occurrences including: (i) boulders strewn across the serpentinites (i.e. Skyros Island); (ii) ore bodies along the nonconformity contacts between serpentinites and limestones (i.e. Aniba); (iii) irregular and discontinuous trails of massive and semi-massive ore bodies within highly sheared serpentinite masses (i.e. Nain; Sabzevar). In all of these magnetite ore bodies, relicts of chromian spinel grains are occasionally enclosed in magnetite crystals. The chemistry of Cr-spinel relics found in these magnetite bodies are comparable to those of accessory Cr-spinels in the surrounding serpentinized peridotites. BSE images and elemental mapping revealed that magnetite occurs as a nucleation on chromian spinels but not being involved in reaction either with chromite or ferritchromite. Low-grade metamorphic transformation of chromite into Fe-chromite is documented along the cracks and fractures of a few chromite grains. Generally, magnetite has typical hydrothermal compositions, characterized by low Cr, V and Ti and high Mg and Mn. It is crucial to note that a few magnetite grains with metamorphic origin are characterized by high Cr and low Ti and Ni. The potential source of iron is essentially the Fe-rich olivine. We believe that multi-episodic serpentinization of peridotite systems at high fluid-rock ratios is the main process responsible for precipitation of magnetite at ore levels whereas low-grade metamorphic transformation of chromite to magnetite has minor contribution. Cumulative factors in generation of these deposits are modal volume of mantle olivine, peridotite composition, fluid chemistry, fluid-rock ratio, mechanisms of transportation and precipitation, structural controls such as cracks and shear zones.
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Farge, G., Shapiro, N. M., & Frank, W. B. (2020). Moment-Duration Scaling of Low-Frequency Earthquakes in Guerrero, Mexico. Journal Of Geophysical Research-Solid Earth, 125(8).
Résumé: Low-frequency earthquakes (LFEs) are detected within tremor, as small, repetitive, impulsive low-frequency (1-8Hz) signals. While the mechanism causing this depletion of the high-frequency content of their signal is still debated, this feature may indicate that the source processes at the origin of LFEs are different from those for regular earthquakes. Key constraints on the LFE-generating physical mechanisms can be obtained by establishing scaling laws between their seismic moment and source durations. Here we apply a simple spectral analysis method to the S waveforms of LFEs from Guerrero, Mexico, to measure their seismic moments and corner frequencies, a proxy to source duration. We find characteristic values of M-0 similar to 3x10(12) N.m (M-w similar to 2.3 ) and f(c)similar to 3.0 Hz with the corner frequency very weakly dependent on the seismic moment. This moment-duration scaling observed for Mexican LFEs is similar to one previously reported in Cascadia and is very different from the established one for regular earthquakes. This suggests that they could be generated by sources of nearly constant size with strongly varying intensities. LFEs do not exhibit the self-similarity characteristic of regular earthquakes, suggesting that the physical mechanisms at their origin could be intrinsically different. Plain Language Summary Low-frequency earthquakes are unusual, small earthquakes that are detected on the deep end of plate boundary faults. They occur during periods of slow slip, when the plates start sliding against each other much slower than during earthquakes, but long enough to release the energy that might otherwise have caused large earthquakes. Thus, they carry precious information about the fault behavior while slow slip is active. In this study, we analyze a selection of low-frequency earthquakes from a slow slip zone of the Mexican subduction, beneath the state of Guerrero. We find that their magnitude is on average higher than in other regions where they have been detected (M(w)1.5 – 3). We also find that whatever the magnitude of these events, they always last about 0.3 s. On the contrary, regular earthquakes are known to last longer when they grow larger, and low-frequency earthquakes in Nankai (Japan) appear to behave similarly. We discuss a physical mechanism explaining such a discrepancy with regular earthquakes and such strong regional variations. The implication of crustal fluids circulating at extremely high pressure in between plates might be one of the key components of this mechanism, as it often is for slow slip processes.
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Fayjaloun, R., Causse, M., Cornou, C., Voisin, C., & SoNG, S. G. (2020). Sensitivity of High-Frequency Ground Motion to Kinematic Source Parameters. Pure And Applied Geophysics, 177(5), 1947–1967.
Résumé: Empirical ground motion prediction equations are calibrated from past earthquake seismic recordings. Although they are often used to predict Peak Ground Acceleration (PGA) and its variability, the use of these equations to predict near-fault PGA remains questionable due to the scarcity of near-fault recordings for large earthquakes (e.g. Mai Encyclopedia of complexity and systems science (pp. 4435-4474). New York: Springer. 10.1007/978-0-387-30440-3_263. 2009). The simulation of strong ground motion offers an attractive alternative for the assessment of near-fault seismic hazards, but the a priori choice of the source parameters used to describe the fault rupture process remains a complex issue. In order to better understand the effects of rupture parameters on surface ground motion and to capture the key source ingredients that impact ground motion variability, we simulated ground motions produced by various M7 strike-slip rupture earthquake scenarios on vertical faults. We computed ground motion up to 5 Hz using the far-field approximation as well as at the near-field stations located at 5 km, 25 km and 70 km from the fault (assuming a visco-elastic medium). The kinematic rupture parameters are modeled using a statistical rupture model generator as proposed by Song et al. Geophysical Journal International,196(3), 1770-1786 (2014). Our work demonstrates that PGA is mostly generated by abrupt changes in the rupture propagation (e.g. stopping phases at the fault boundaries or strong heterogeneities of rupture speed along the fault). We observed that PGA is mostly controlled by average rupture speed and average stress drop (in the far-field), and to a lesser extent by the standard deviation of the rupture speed. It is worth noting that for the set of stations in study, the correlation between source parameters and spatial correlation length does not affect average PGA and related variability significantly.
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Fernandez-Martinez, A., Tao, J. H., Wallace, A. F., Bourg, I. C., Johnson, M. R., De Yoreo, J. J., et al. (2020). Curvature-induced hydrophobicity at imogolite-water interfaces. Environmental Science-Nano, 7(9), 2759–2772.
Résumé: Imogolite, a nanotubular aluminosilicate mineral, is commonly found in volcanic soils, where it exerts a control on carbon dynamics. Synthetic imogolites are used for the removal of contaminants from industrial effluents and are considered for a range of other applications including gas adsorption and functionalised heterogeneous catalysts. In spite of their environmental and industrial relevance, the properties of imogolite-water interfaces remain poorly understood. Here, an experimental and computational study is presented in which the structure and energetics of water are characterized on the curved external surface of imogolite and the hydrophilicity of this surface is contrasted with that of gibbsite, its planar counterpart. Atomic force spectroscopy experiments show that in spite of their identical surface structure, imogolite has a lower hygroscopicity than gibbsite. Molecular dynamics simulations provide an explanation for this observation: the curvature of imogolite prevents the formation of in-plane H-bonds along the directions of the nanotube circumference, lowering the enthalpy of adsorption of water molecules. The different arrangement of surface H-bonds and the resulting differences in hydration properties also affects the acidity constants of surface hydroxyl groups. This 'nanotube effect' may be relevant to other nanotubular systems with high curvatures, potentially impacting their wetting properties, their colloidal stability and their affinity towards hydrophobic organic moieties.
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Fernandez-Martinez, A., Tao, J. H., Wallace, A. F., Bourg, I. C., Johnson, M. R., De Yoreo, J. J., et al. (2020). Curvature-induced hydrophobicity at imogolite-water interfaces (vol 7, pg 2759, 2020). Environmental Science-Nano, 7(10), 3201.
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Fiolleau, S., Jongmans, D., Bievre, G., Chambon, G., Baillet, L., & Vial, B. (2020). Seismic characterization of a clay-block rupture in Harmaliere landslide, French Western Alps. Geophysical Journal International, 221(3), 1777–1788.
Résumé: In late June 2016, the Harmaliere clayey landslide (located 30 km south of the city of Grenoble, French Alps) was dramatically reactivated at the headscarp after a 35-yr-long period of continuous but limited activity. The total involved volume, which moved as sliding blocks of various sizes, was estimated to be about 2 x 10(6) m(3). Two seismometers were installed at the rear of the main headscarp in August 2016, on both sides of a developing fracture delineating a block with a volume of a few hundred cubic metres. For 4 months, they continuously recorded seismic ambient vibrations and microcarthquakes until the block broke. Five seismic parameters were derived from the monitoring: the cumulative number of microearthquakes (CNe), the seismic energy (SE), the block resonance frequency (f(B)), the relative variation in Rayleigh wave velocity (dV/V) deduced from noise cross-correlations between the two sensors and the associated correlation coefficient (CC). All parameters showed a significant precursory signal before the rupture, but at very different times, which indicates the complexity of the rupture mechanism in this clay material.
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Flinders, A. F., Caudron, C., Johanson, I. A., Taira, T., Shiro, B., & Haney, M. (2020). Seismic velocity variations associated with the 2018 lower East Rift Zone eruption of Kilauea, HawaiModified Letter Turned Commai. Bulletin Of Volcanology, 82(6).
Résumé: The 2018 lower East Rift Zone eruption of Kilauea (Hawai'i) marked a dramatic change in the volcano's 35-year-long rift zone eruption. The collapse of the middle East Rift Zone vent Pu'u 'O'o was followed by one of the volcano's most voluminous eruptions in 500 years. Over the course of this 3-month eruption, the draining of summit-stored magma led to near-daily collapses of a portion of the caldera and ultimately up to 500 m of summit subsidence. While deformation data indicated that the summit and middle East Rift Zone were inflating for the previous several years, why Pu'u 'O'o collapsed and what initiated down-rift dike propagation remains unclear. Using ambient noise seismic interferometry, we show that a M(l)5.3 decollement earthquake beneath Kilauea's south flank in June 2017 induced a coseismic decrease of up to 0.30% in seismic velocity throughout the volcano. This velocity decrease may have been caused by dynamic stress-induced shallow crustal fracture, i.e., weakening to dilatant crack growth, and was greatest near Pu'u 'O'o. Additionally, we verify a pre-eruptive increase in seismic velocity, consistent with increasing pressurization in the volcano's shallow summit magma reservoir. This velocity increase occurred coincident with the first in a series of lower-crustal earthquake swarms, 6 days before a 2-month period of rapid summit and middle East Rift Zone inflation. The increase in up-rift magma-static pressure, combined with the pre-existing weakness from the June 2017 earthquake, may have facilitated down-rift dike propagation and the devastating 2018 eruption.
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Fondriest, M., Balsamo, F., Bistacchi, A., Clemenzi, L., Demurtas, M., Storti, F., et al. (2020). Structural Complexity and Mechanics of a Shallow Crustal Seismogenic Source (Vado di Corno Fault Zone, Italy). Journal Of Geophysical Research-Solid Earth, 125(9).
Résumé: The mechanics and seismogenic behavior of fault zones are strongly influenced by their internal structure. In this perspective, the internal structure of the extensional seismically active Vado di Corno Fault Zone (VCFZ, Central Apennines, Italy) was quantified by combining high-resolution structural mapping with 3-D fault network analysis over similar to 2 km along fault strike. The fault zone was exhumed from similar to 2 km depth in carbonate rocks, accommodated 1.5-2 km of extensional throw since Early Pleistocene, and cuts through the Pliocene Omo Morto Thrust Zone (OMTZ) with partial reactivation in extension. The exceptional exposure of the footwall block allowed us to reconstruct in detail the geometry of the OMTZ and quantify the spatial arrangement of master/subsidiary faults and fault zone rocks within the extensional VCFZ. The combination of the structural map and the 3-D fault network with kinematic and topological analyses pointed out the crucial role of the older thrust geometry (i.e., lateral ramps) in controlling the along-strike segmentation and slip distribution of the VCFZ. These observations were discussed in the framework of regional extension through a slip tendency analysis and a simplified mechanical model, which suggest the activation of oblique inherited structures during the lateral propagation of the VCFZ segments. The interaction of the VCFZ with the OMTZ generated along strike and possibly downdip mechanical asperities. Considering the exhumed VCFZ as an analog for the shallow structure of other seismic sources in the Central Apennines, similar settings could play first-order control on the spatio-temporal evolution and rupture heterogeneity of earthquakes in the region.
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Fondriest, M., Mecklenburgh, J., Passelegue, F. X., Artioli, G., Nestola, F., Spagnuolo, E., et al. (2020). Pseudotachylyte Alteration and the Rapid Fade of Earthquake Scars From the Geological Record. Geophysical Research Letters, 47(22).
Résumé: Tectonic pseudotachylytes are solidified frictional melts produced on faults during earthquakes and are robust markers of seismic slip events. Nonetheless, pseudotachylytes are apparently uncommon fault rocks, because they are either rarely produced or are easily lost from the geological record. To solve this conundrum, long-lasting (18-35 days) hydrothermal alteration tests were performed on fresh pseudotachylytes produced by sliding solid rock samples at seismic slip rates in the laboratory. After all tests, the pseudotachylytes were heavily altered with dissolution of the matrix and neo-formation of clay aggregates. Post-alteration products closely resemble natural altered pseudotachylytes and associated ultracataclasites (i.e., fault rocks affected by fracturing in the absence of melting), demonstrating that the preservation potential of original pseudotachylyte microstructures is very short, days to months, in the presence of hydrothermal fluids. As a consequence, pseudotachylytes might be significantly underrepresented in the geological record, and on-fault frictional melting during earthquakes is likely to occur more commonly than generally believed.
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Forest, M., Costa, L., Combey, A., Dorison, A., & Pereira, G. (2020). Testing Web Mapping and Active Learning to Approach Lidar Data. Advances In Archaeological Practice, 8(1), 25–39.
Résumé: After acquiring 91 km(2) of lidar data from the Zacapu region, West Mexico, we confronted a series of issues that most archaeologists using this technology face. These include the large volume of data available, the limited training of potential “analysts,” the difficult development of a collective mapping tool and protocol, and the reliability of desk-based interpretation of archaeological features. In this article, we present an initiative conducted in 2015 and 2017 as an attempt to answer these methodological and pedagogical issues. We developed a web mapping platform to collectively interpret archaeological features using lidar-derived imagery and to train volunteer students to participate in this desk-based web mapping within a crowdsourcing framework. After evaluating the results of this initiative, we discuss the potential and limitations of this method for both lidar-based research and future training.
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Fulbert, M. N. I., Sebastien, O., Boris, C. T., Justin, L., Bruno, L., & Emmanuel, E. G. (2020). Mineralogy and geochemistry of pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain monogenetic volcanoes in the central part of the Cameroon Volcanic Line. Acta Geochimica, 39(6), 830–861.
Résumé: Pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain, 3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line (the Tombel Plain, Bamileke Plateau, and Noun Plain), were explored in order to constrain their petrology and make some predictions on their pozzolanicity. The rocks in this study include alkaline and subalkaline basalts, trachy-basalts, and basanites. Most of these rocks present an overall composition that overlaps with primitive mantle, suggesting rapid ascent of magmas, limited crustal contamination and crystal fractionation of olivine, clinopyroxene, and feldspar. The pozzolans present enrichment of LREE relative to HREE and high chondrite normalized ratios of La/Yb and Tb/Yb, ranging between 7 and 20 and > 1.9 respectively, similar to those of Ocean Island Basalts. Like other nearby volcanoes, partial melting in a dominantly garnet-bearing mantle zone can be assumed. Quantitative mineralogy by X-ray diffraction revealed various mineral phases with dominantly plagioclase, augite, olivine, and Fe-Ti oxides. The samples contains important amorphous phase up to 23, 51, and 69 wt% in the Tombel Plain, Noun Plain, and Bamileke Plateau, respectively. This elevated amount of amorphous phases together with the sum of SiO2, Al2O3, and total Fe2O3 (SAI = 68.50-83.50 > 70 wt%) according to ASTM C 618 standard and the sum of CaO, FeO, and MgO (CIM = 14.5-30.52 wt% and 23.58-31.08 wt%) suggest interesting pozzolanicity character for the studied pozzolans.
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Furst, S., Chery, J., Peyret, M., & Mohammadi, B. (2020). Tiltmeter data inversion to characterize a strain tensor source at depth: application to reservoir monitoring. Journal Of Geodesy, 94(5).
Résumé: Surface deformation measured by geodetic data is the sum of single-strain sources deforming at depth. A combination of volume changes from several analytical models (e.g. a point source or dislocation along a plane) can be used to model the different sources. However, solving for the best fit of volume variations, dislocations, position and orientation parameters of all sources is a nonlinear problem, and its solution is generally non-unique. This problem can be converted into a linear one by assimilating the sum of sources to a simplified model formed by three orthogonal planes of dislocations at fixed position and orientation. This strain source model is equivalent to having all neighbouring deformation sources contained in a small size volume. The determination of the strain tensor components can be performed by inverting geodetic data. Because of their high resolution, tiltmeters are well adapted to survey shallow deformation of volcanoes and geological reservoirs. However, they are known to display unknown long-term drift. We propose an approach to jointly estimate the temporal evolution of the strain source and time-dependent instrumental parameters. We verify the approach using synthetic data, giving confidence intervals for each component of the strain tensor. Finally, we link geological information to the internal deformation by interpreting the strain tensor as principal directions of deformation. This approach seems promising for the identification of fracture onset and fault reactivation in geothermal, hydrocarbon exploitations or volcanic systems.
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Gaillot, A. C., Drits, V. A., & Lanson, B. (2020). Polymorph And Polytype Identification From Individual Mica Particles Using Selected Area Electron Diffraction. Clays And Clay Minerals, 68(4), 334–346.
Résumé: Dioctahedral micas are composed of two tetrahedral sheets and one octahedral sheet to form TOT or 2:1 layers. These minerals are widespread and occur with structures differing by (1) the layer stacking mode (polytypes), (2) the location of vacancies among non-equivalent octahedral sites (polymorphs), and (3) the charge-compensating interlayer cation and isomorphic substitutions. The purpose of the present study was to assess the potential of parallel-illumination electron diffraction (ED) to determine the polytype/polymorph of individual crystals of finely divided dioctahedral micas and to image their morphology. ED patterns were calculated along several zone axes close to thec*- andc-axes using the kinematical approximation fortrans- andcis-vacant varieties of the four common mica polytypes (1M, 2M(1), 2M(2), and 3T). When properly oriented, all ED patterns have similar geometry, but differ by their intensity distribution overhkreflections of the zero-order Laue zone. Differences are enhanced for ED patterns calculated along the [001] zone axis. Identification criteria were proposed for polytype/polymorph identification, based on the qualitative distribution of bright and weak reflections. A database of ED patterns calculated along other zone axes was provided in case the optimum [001] orientation could not be found. Various polytype/polymorphs may exhibit similar ED patterns depending on the zone axis considered.
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Galina, N. A., Shapiro, N. M., Droznin, D. V., Droznina, S. Y., Senyukov, S. L., & Chebrov, D. V. (2020). Recurrence of Deep Long-Period Earthquakes beneath the Klyuchevskoi Volcano Group, Kamchatka. Izvestiya-Physics Of The Solid Earth, 56(6), 749–761.
Résumé: Long-period earthquakes and tremors, on a par with volcano-tectonic earthquakes, are one of two main classes of volcano-seismic activity. It is believed that long-period volcanic seismicity is associated with pressure fluctuations in the magmatic and hydrothermal systems beneath volcanoes and can therefore be used as a precursor of the impending eruptions. At the same time, the physical mechanism of the long-period seismicity is still not fully understood. In this work, we have studied the long-period earthquakes that occur at the crust-mantle boundary beneath the Klyuchevskoi volcanic group in Kamchatka in order to establish their recurrence law-the relationship between the magnitude and frequency of occurrence of the events. In the region under study, the earthquakes pertaining to this type are most numerous and characterize the state of the deep magma reservoir located at the crust-mantle boundary. The changes in the seismic regime in this part of the magmatic system can be one of the early precursors of eruptions. For a more thorough characterization of the frequency-magnitude relationship of the discussed events, we compiled a new catalog of the deep long-period earthquakes based on the matched-filter processing of continuous seismograms recorded by the network stations of the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences in 2011-2012. For these earthquakes, we also used a magnitude determination method that provides the estimates close to the moment magnitude scale. The analysis of the obtained catalog containing more than 40 000 events shows that the frequency-magnitude relationships of the earthquakes markedly deviate from the Gutenberg-Richter power-law distribution, probably testifying to the seismicity mechanism and peculiarities of the sources that differ from the common tectonic earthquakes. It is shown that the magnitude distribution of the deep long-period earthquakes is, rather, described by the distributions with characteristic mean values such as the normal or gamma distribution.
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Gallach, X., Carcaillet, J., Ravanel, L., Deline, P., Ogier, C., Rossi, M., et al. (2020). Climatic and structural controls on Late-glacial and Holocene rockfall occurrence in high-elevated rock walls of the Mont Blanc massif (Western Alps). Earth Surface Processes And Landforms, 45(13), 3071–3091.
Résumé: In the Mont Blanc massif (European Western Alps), rockfalls are one of the main natural hazards for alpinists and infrastructure. Rockfall activity after the Little Ice Age is well documented. An increase in frequency during the last three decades is related to permafrost degradation caused by rising air temperatures. In order to understand whether climate exerts a long-term control on rockfall occurrence, a selection of paleo-rockfall scars was dated in the Glacier du Geant basin [>3200m above sea level (a.s.l.)] using terrestrial cosmogenic nuclides. Rockfall occurrence was compared to different climatic and glacial proxies. This study presents 55 new samples (including replicates) and 25 previously-published ages from nine sampling sites. In total, 62 dated rockfall events display ages ranging from 0.03 +/- 0.02ka to 88.40 +/- 7.60ka. Holocene ages and their uncertainties were used to perform a Kernel density function into a continuous dataset displaying rockfall probability per 100years. Results highlight four Holocene periods of enhanced rockfall occurrence: (i) c. 7-5.7ka, related to the Holocene Warm Periods; (ii) c. 4.5-4ka, related to the Sub-boreal Warm Period; (iii) c. 2.3-1.6ka, related to the Roman Warm Period; and (iv) c. 0.9-0.3ka, related to the Medieval Warm Period and beginning of the Little Ice Age. Laser and photogrammetric three-dimensional (3D) models of the rock walls were produced to reconstruct the detached volumes from the best-preserved rockfall scars (<= 0.91 +/- 0.12ka). A structural study was carried out at the scale of the Glacier du Geant basin using aerial photographs, and at the scale of four selected rock walls using the 3D models. Two main vertical and one horizontal fracture sets were identified. They correspond respectively to alpine shear zones and veins opened-up during long-term exhumation of the Mont Blanc massif. Our study confirms that climate primarily controls rockfall occurrence, and that structural settings, coincident at both the massif and the rock wall scales, control the rock-wall shapes as well as the geometry and volume of the rockfall events. (C) 2020 JohnWiley & Sons, Ltd.
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Gassner, T., Gumberidze, A., Trassinelli, M., Hess, R., Spillmann, U., Banas, D., et al. (2020). High-resolution wavelength-dispersive spectroscopy of K-shell transitions in hydrogen-like gold. X-Ray Spectrometry, 49(1), 204–208.
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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Gastineau, R., Conway, S. J., Johnsson, A., Eichel, J., Mangold, N., Grindrod, P. M., et al. (2020). Small-scale lobate hillslope features on Mars: A comparative 3D morphological study with terrestrial solifluction lobes and zebra stripe lobes. Icarus, 342.
Résumé: Small-scale lobes (SSL) observed at the surface of Mars are thought to be the result of solifluction. Hence, their existence has important implications for our understanding of recent climate history, the distribution of thaw liquids and its geomorphic effects, as water is believed not to have been recently stable at the martian surface. These small-scale lobes are limited to sloping terrains and often occur alongside polygonal patterned ground attesting to the presence of ice in the environment. In this study, we perform a comparative 3D morphometric analysis of the lobes on Mars with terrestrial analogues. We use data from High Resolution Imaging Science Experiment (HiRISE) camera in order to create Digital Terrain Models (DTMs) on Mars at 1 m/pix. For the terrestrial analogues, we use DTMs and orthophotos from five periglacial environments with solifluction lobes and from one site with lobate features found in the Atacama Desert. The lobate features in the Atacama Desert are found within features called “zebra stripes”, which are apparently unique to the Atacama and are now generally accepted to be the result of seismic shaking. We show that SSL on Mars overlap morphometrically with terrestrial solifluction lobes, and are less similar to zebra stripe lobes. The majority of martian SSL occur below the angle of repose which demonstrates that a dry fall mechanism cannot be responsible for their formation and that lubrication of the subsurface is required. We found that martian SSL only occur on slopes greater than similar to 10 degrees, a constraint not observed for terrestrial solifluction lobes nor zebra stripe lobes in Atacama. We hypothesise that this apparent constraint does not result from the lowered gravity on Mars, but instead from differing soil properties and/or thermal regime between Mars and Earth which affects the slope at which creep can initiate. We cannot rule out a role of CO2 sublimation in lobe-formation based on our terrestrial measurements.
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Gaunt, H. E., Burgisser, A., Mothes, P. A., Browning, J., Meredith, P. G., Criollo, E., et al. (2020). Triggering of the powerful 14 July 2013 Vulcanian explosion at Tungurahua Volcano, Ecuador. Journal Of Volcanology And Geothermal Research, 392.
Résumé: The 14 July 2013 Vulcanian explosion at Tungurahua occurred after two months of quiescence and was extremely powerful, generating some of the highest infrasound energies recorded worldwide. Here we report on how a combination of geophysical data, textural measurements, and physical and mechanical tests on eruptive products allowed us to determine the processes that led to the pressurization of the conduit and triggering of this large Vulcanian event. Two weeks prior to the 14 July event, daily seismic counts and radial tilt began to steadily increase, indicating the probable intrusion of a new batch of magma into the edifice. The 14 July explosion produced three different juvenile products that were each sampled for this study: airfall; juvenile, vesicular, pyroclastic density current material; and dense plug rocks in the form of ballistic ejecta. Feldspar microlite textures and vesicle size distributions were measured, and used jointly with a two-step recompression model to characterize the spatial distribution of gas in the conduit and the decompression histories of the erupted samples. Model results reveal a vertically stratified conduit with regards to porosity, crystallinity and volatile content prior to the explosion. Overall, our data suggests a complex sequence of events that led eventually to this powerful explosion. 1) Remnants of magma from the previous eruptive phase in May stalled in the shallow conduit, triggering crystallization which, coupled with efficient outgassing, formed a dense (< 2% porosity), highly crystalline plug. This plug had a very low matrix permeability (10(-17) to 10(-18) m(2)) and high tensile strength (9 to 13 MPa), forming an efficient rigid seal and preventing significant outgassing from the conduit. 2) Just below the plug, a high porosity zone (up to 50%) formed, acting as a gas storage zone, with pressurization occurring partly under closed-system degassing. 3) The shallow conduit became pressurized due to the combination of both gas accumulation and the resistance of the plug to magma column extrusion in response to a new influx of magma. 4) On the 14th of July a critical gas over-pressure was reached, overcoming the strength of the dense plug of magma, trigging extreme decompression and evacuation of the top two kilometres of the conduit. 5) The newly intruded magma was not directly involved in the explosion and continued to ascend during the week following the explosion. (C) 2020 Elsevier B.V. All rights reserved.
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Gautam, P., Huyghe, P., Mugnier, J. L., & Regmi, K. R. (2020). 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, 55(7), 4891–4904.
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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Gavira, J. A., Otalora, F., Gonzalez-Ramirez, L. A., Melero, E., van Driessche, A. E. S., & Garcia-Ruiz, J. M. (2020). On the Quality of Protein Crystals Grown under Diffusion Mass-transport Controlled Regime (I). Crystals, 10(2).
Résumé: It has been previously shown that the diffraction quality of protein crystals strongly depends on mass transport during their growth. In fact, several studies support the idea that the higher the contribution of the diffusion during mass transport, the better the diffraction quality of the crystals. In this work, we have compared the crystal quality of two model (thaumatin and insulin) and two target (HBII and HBII-III) proteins grown by two different methods to reduce/eliminate convective mass transport: crystal growth in agarose gels and crystal growth in solution under microgravity. In both cases, we used identical counterdiffusion crystallization setups and the same data collection protocols. Additionally, critical parameters such as reactor geometry, stock batches of proteins and other chemicals, temperature, and duration of the experiments were carefully monitored. The diffraction datasets have been analyzed using a principal component analysis (PCA) to determine possible trends in quality indicators. The relevant indicators show that, for the purpose of structural crystallography, there are no obvious differences between crystals grown under reduced convective flow in space and convection-free conditions in agarose gel, indicating that the key factor contributing to crystal quality is the reduced convection environment and not how this reduced convection is achieved. This means that the possible detrimental effect on crystal quality due to the incorporation of gel fibers into the protein crystals is insignificant compared to the positive impact of an optimal convection-free environment provided by gels. Moreover, our results confirm that the counterdiffusion technique optimizes protein crystal quality and validates both environments in order to deliver high quality protein crystals, although other considerations, such as protein/gel interactions, must be considered when defining the optimal crystallization setup.
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Gerick, F., Jault, D., Noir, J., & Vidal, J. (2020). Pressure torque of torsional Alfven modes acting on an ellipsoidal mantle. Geophysical Journal International, 222(1), 338–351.
Résumé: We investigate the pressure torque between the fluid core and the solid mantle arising from magnetohydrodynamic modes in a rapidly rotating planetary core. A 2-D reduced model of the core fluid dynamics is developed to account for the non-spherical core-mantle boundary. The simplification of such a quasi-geostrophic model rests on the assumption of invariance of the equatorial components of the fluid velocity along the rotation axis. We use this model to investigate and quantify the axial torques of linear modes, focusing on the torsional Alfven modes (TM) in an ellipsoid. We verify that the periods of these modes do not depend on the rotation frequency. Furthermore, they possess angular momentum resulting in a net pressure torque acting on the mantle. This torque scales linearly with the equatorial ellipticity. We estimate that for the TM calculated here topographic coupling to the mantle is too weak to account for the variations in the Earth's length-of-day.
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Ghannoum, M., Imtiaz, A., Grange, S., Causse, M., Cornou, C., & Baroth, J. (2020). Behavior of a RC Frame Under Differential Seismic Excitation. Journal Of Earthquake Engineering, 24(5), 705–726.
Résumé: Two very dense seismographic arrays were deployed in a seismically active area in Greece to incorporate the difference in amplitude and phase between two stations located within the dimension of a structure. The spatial variability in seismic ground motion is generally attributed to the wave passage effect, the incoherence effect, and the local site effect. It can cause severe damage on lifeline structures. This article studies the behavior of a reinforced concrete 2D frame structure subjected to differential seismic excitation at the supports. Both linear and nonlinear finite multifiber element models of the seismic behavior of this structure are used. The nonlinear behavior of the structure, under these different cases, displays different damage patterns and maximum displacements. This study allows evaluating the uncertainty that can be propagated through the finite element model, aiming at reducing variability for structural design purposes.
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Gordeev, E. I., Koulakov, I. Y., & Shapiro, N. M. (2020). The Magma Feeding System of the Klyuchevskaya Group of Volcanoes (Kamchatka). Doklady Earth Sciences, 493(2), 627–631.
Résumé: Using observations from a large-scale seismic station network, we built a seismic tomography model of velocity anomalies for longitudinal (P-wave) and transverse (S-wave) seismic waves beneath the Klyuchevskaya group of volcanoes. The observational network (about 150 km) and the number of seismic stations (about 200) made it possible to determine the velocity structure to depths of 150 km. A low-velocity anomaly is observed almost beneath all volcanoes in the Klyuchevskaya group of volcanoes at a depth of 50 km. Beneath the Shiveluch volcano, in the region where the subduction plate discontinues, an anomaly can be detected to depths of 150 km. Most likely, in this zone, there is a channel for the penetration of magmatic melts to the surface along the boundary of the submerging Pacific Plate ending. This is indirectly confirmed by the presence of a mantle plume to a depth of 1000 km, as previously shown by the seismic tomography studies and an anomalous heat flow at the junction of the Kuril-Kamchatka and Aleutian island arcs.
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Gourlan, A. T., Albarede, F., Achyuthan, H., & Campillo, S. (2020). The marine record of the onset of farming around the Arabian Sea at the dawn of the Bronze Age. Holocene, 30(6), 878–887.
Résumé: The rise and fall of human cultures are strongly modulated by the strong environmental changes taking place during the Holocene. Here, we use the sedimentological and geochemical records of a core taken in the Arabian Sea, west of Kerala, to identify potential factors that may reflect on-land history of local civilizations, in particular the Harappan culture which appeared and collapsed in the Indus Valley during the early and middle Bronze Age. The C-14 record highlights a fourfold increase in sedimentation rate at similar to 5380 cal. yr BP. The short duration of this event (similar to 220 years) suggests a steep regional increase in erosion at the beginning of the Bronze Age. Factor analysis of downcore changes in geochemistry identified two distinct detrital components dominated by silt and clay, respectively, and a component characteristic of chemical erosion. This interpretation is consistent with sediment mineralogy. Comparison with the known climatic record indicates that increased erosion rate at 5380 cal. yr BP around the Arabian Sea is because of the advent of farming. The development of tillage associated with both wheat and barley crops and animal husbandry was favored by trade between Mesopotamia and India. Human activities, therefore, were the trigger of major changes in the sedimentological and geochemical records at sea at the onset of the Bronze Age.
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Goussin, F., Riel, N., Cordier, C., Guillot, S., Boulvais, P., Roperch, P., et al. (2020). Carbonated Inheritance in the Eastern Tibetan Lithospheric Mantle: Petrological Evidences and Geodynamic Implications. Geochemistry Geophysics Geosystems, 21(2).
Résumé: The timing and mechanism of formation of the Tibet Plateau remain elusive, and even the present-day structure of the Tibetan lithosphere is hardly resolved, due to conflicting interpretations of the geophysical data. We show here that significant advances in our understanding of this orogeny could be achieved through a better assessment of the composition and rheological properties of the deepest parts of the Tibetan lithosphere, leading in particular to a reinterpretation of the global tomographic cross sections. We report mantle phlogopite xenocrysts and carbonate-bearing ultramafic cumulates preserved in Eocene potassic rocks from the Eastern Qiangtang terrane, which provide evidence that the lithospheric mantle in Central Tibet was enriched in H2O and CO2 prior to the India-Asia collision. Rheological calculations and numerical modeling suggest that (1) such metasomatized mantle would have been significantly weaker than a normal mantle but buoyant enough to prevent its sinking into the deep mantle; (2) the slow seismic anomalies beneath Central Tibet may image a weakened lithosphere of normal thickness rather than a lithosphere thinned and heated by the convective removal of its lower part; and (3) melting of such soft and fusible metasomatized mantle would have been possible during intracontinental subduction, supporting a subduction origin for the studied Eocene potassic magmatism. These results demonstrate that the inheritance a soft and buoyant precollisional Tibetan lithosphere may have conditioned the growth and the present-day structure of the Tibet Plateau. Plain Language Summary The Tibetan Plateau is the largest relief on the Earth's surface, but also one of the least understood geodynamic phenomena, due to the lack of constrain on its growth evolution and mechanism. Here we have discovered, enclosed in Eocene (35-Ma-old) lavas from Central Tibet, hydrous and carbonated minerals derived from the underlying upper mantle, which reveal an unsuspected abundance of water and CO2 in this upper mantle. We show that, consequently, the upper mantle beneath Central Tibet has been anomalously weak since before the collision of India with Asia. It was previously thought to have disappeared, foundered in a process called “delamination,” but we demonstrate here that this was an artifact: Most of the tibetan mantle is still there, but it is very weak and therefore does not appear on the seismic images. This implies that models expecting the Tibet Plateau to be a result of a delamination process are probably wrong; instead, we propose a model in which the weak upper mantle beneath our study area was easily indented by the strong adjacent continental block; this model manages to explain both Eocene magmatism and uplift in our study area.
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Govin, G., van der Beek, P., Najman, Y., Millar, I., Gemignani, L., Huyghe, P., et al. (2020). Early onset and late acceleration of rapid exhumation in the Namche Barwa syntaxis, eastern Himalaya. Geology, 48(12), 1139–1143.
Résumé: The Himalayan syntaxes, characterized by extreme rates of rock exhumation co-located with major trans-orogenic rivers, figure prominently in the debate on tectonic versus erosional forcing of exhumation. Both the mechanism and timing of rapid exhumation of the Namche Barwa massif in the eastern syntaxis remain controversial. It has been argued that coupling between crustal rock advection and surface erosion initiated in the late Miocene (8-10 Ma). Recent studies, in contrast, suggest a Quaternary onset of rapid exhumation linked to a purely tectonic mechanism. We report new multisystem detrital thermochronology data from the most proximal Neogene clastic sediments downstream of Namche Barwa and use a thermo-kinematic model constrained by new and published data to explore its exhumation history. Modeling results show that exhumation accelerated to similar to 4 km/m.y. at ca. 8 Ma and to similar to 9 km/m.y. after ca. 2 Ma. This three-stage history reconciles apparently contradictory evidence for early and late onset of rapid exhumation and suggests efficient coupling between tectonics and erosion since the late Miocene. Quaternary acceleration of exhumation is consistent with river-profile evolution and may be linked to a Quaternary river-capture event.
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Green, R. G., Sens-Schonfelder, C., Shapiro, N., Koulakov, I., Tilmann, F., Dreiling, J., et al. (2020). Magmatic and Sedimentary Structure beneath the Klyuchevskoy Volcanic Group, Kamchatka, From Ambient Noise Tomography. Journal Of Geophysical Research-Solid Earth, 125(3).
Résumé: The Klyuchevskoy Volcanic Group is a cluster of the world's most active subduction volcanoes, situated on the Kamchatka Peninsula, Russia. The volcanoes lie in an unusual off-arc position within the Central Kamchatka Depression (CKD), a large sedimentary basin whose origin is not fully understood. Many gaps also remain in the knowledge of the crustal magmatic plumbing system of these volcanoes. We conducted an ambient noise surface wave tomography, to image the 3-D shear wave velocity structure of the Klyuchevskoy Volcanic Group and CKD within the surrounding region. Vertical component cross correlations of the continuous seismic noise are used to measure interstation Rayleigh wave group and phase traveltimes. We perform a two-step surface wave tomography to model the 3-D Vsv velocity structure. For each inversion stage we use a transdimensional Bayesian Monte Carlo approach, with coupled uncertainty propagation. This ensures that our model provides a reliable 3-D velocity image of the upper 15 km of the crust, as well as a robust assessment of the uncertainty in the observed structure. Beneath the active volcanoes, we image small slow velocity anomalies at depths of 2-5 km but find no evidence for magma storage regions deeper than 5 km-noting the 15 km depth limit of the model. We also map two clearly defined sedimentary layers within the CKD, revealing an extensive 8 km deep sedimentary accumulation. This volume of sediments is consistent with the possibility that the CKD was formed as an Eocene-Pliocene fore-arc regime, rather than by recent (<2 Ma) back-arc extension. Plain Language Summary The Klyuchevskoy Volcanic Group is a cluster of 13 volcanoes on the Kamchatkan corner of the Pacific ring of fire. The volcanoes regularly produce large eruptions, but good knowledge of the magma plumbing system beneath the surface is still lacking. Why the Klyuchevskoy Volcanic Group volcanoes lie in the location they do, in a large low-lying depression, is also unexplained. We undertook a seismic experiment and used the data to produce a 3-D velocity image of the subsurface beneath the volcanoes and the depression. We found that small regions of slow seismic velocity are located beneath the active volcanoes, at 2-5 km depth below sea level. This slower velocity is probably caused by magma lying within the porous fracture spaces in this rock. The seismic velocities are much faster beneath the dormant volcanoes, suggesting they have no magma beneath them. With our velocity image, we also find that the Central Kamchatka Depression is very deep, filled with over 8 km of sediments. This supports an idea that the sediments accumulated as a fore-arc basin over many millions of years, since 40 Ma, when the active line of volcanoes was found 100 km to the west.
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Grieco, G., Bussolesi, M., Eslami, A., Gentile, A., Cavallo, A., Lian, D. Y., et al. (2020). Differential platinum group elements (PGE) re-mobilization at low fS(2) in Abdasht and Soghan mafic-ultramafic complexes (Southern Iran). Lithos, 366.
Résumé: The Abdasht and Soghan ultramafic complexes, Southern Iran, host major actively exploited chromitite bodies, variably enriched in PGE. The Platinum Group Minerals (PGM) – Base Metal Minerals (BMM) assemblage was studied in order to assess PGE remobilization during post-magmatic processes. Studied chromitites have variable textures: massive, banded, nodular and disseminated. Primary silicates are almost completely replaced by serpentine. Ferrian chromitization is present but not widespread. BMM are mostly found in the silicate matrix, while PGM are more common as inclusions within chromites. Primary BMM (pentlandite and bornite) within the silicate matrix are poorly preserved, while primary PGM (laurite) are more abundant. Secondary BMM (heazlewoodite, millerite and Ni-Fe alloys) and PGM (PGE-alloys) are the dominant mineralogical species. During serpentinization the pervasive percolation of low fS(2) fluids induced the desulfurization of the metallic assemblage. Primary sulfides were replaced by S-poor (heazlewoodite) or S-free (Ni-Fe alloys, PGE alloys, PGE-BM alloys) phases. Low fS(2) differentially mobilized PGE. The release of IPGE (fr, Os, Ru) into the fluids follows the order: Ru> > Os>Ir. PPGE (Pt, Pd, Rh) mobility is more difficult to assess, due to their small concentration, but the evidence suggests that Rh is more mobile than Ru, and that Pd and Pt were partially added to the system by fluids. A mass balance calculation on a polyphasic grain, showing differential stages of desulfurization, allowed a semi-quantitative analysis on the desulfurization degree of Abdasht and Soghan complexes, estimated, in the more serpentinized portions, between 75 and 100%. (C) 2020 Elsevier B.V. All rights reserved.
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Guedron, S., Acha, D., Bouchet, S., Point, D., Tessier, E., Heredia, C., et al. (2020). Accumulation of Methylmercury in the High-Altitude Lake Uru Uru (3686 m a.s.l, Bolivia) Controlled by Sediment Efflux and Photodegradation. Applied Sciences-Basel, 10(21).
Résumé: In shallow aquatic environments, sediment is a significant source of monomethylmercury (MMHg) for surface water (SW). High-altitude aquatic ecosystems are characterized by extreme hydro-climatic constraints (e.g., low oxygen and high UV radiation). We studied, during two seasons, the diel cycles of MMHg in SW and sediment porewaters (PW) of Lake Uru Uru (3686 m a.s.l, Bolivia) contaminated by urban and mining activities. Our results show that diel changes in SW MMHg concentrations (up to 1.8 ng L-1) overwhelm seasonal ones, with higher MMHg accumulation during the night-time and the dry season. The calculation of MMHg diffusive fluxes demonstrates that the sediment compartment was the primary source of MMHg to the SW. Most MMHg efflux occurred during the dry season (35.7 +/- 17.4 ng m(-2) day(-1)), when the lake was relatively shallow, more eutrophicated, and with the redoxcline located above the sediment-water interface (SWI). Changes in MMHg accumulation in the PWs were attributed to diel redox oscillations around the SWI driving both the bacterial sulfate reduction and bio-methylation. Finally, we highlight that although MMHg loading from the PW to the SW is large, MMHg photodegradation and demethylation by microorganisms control the net MMHg accumulation in the water column.
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Guedron, S., Audry, S., Acha, D., Bouchet, S., Point, D., Condom, T., et al. (2020). Diagenetic production, accumulation and sediment-water exchanges of methylmercury in contrasted sediment facies of Lake Titicaca (Bolivia). Science Of The Total Environment, 723.
Résumé: Monomethylmercury (MMHg) concentrations in aquatic biota from Lake Titicaca are elevated although the mercury (Hg) contamination level of the lake is low. The contribution of sediments to the lake MMHg pool remained however unclear. In this work, seven cores representative of the contrasted sediments and aquatic ecotopes of Lake Titicaca were sliced and analyzed for Hg and redox-sensitive elements (Mn, Fe, N and S) speciation in pore-water (PW) and sediment to document early diagenetic processes responsible for MMHg production and accumulation in PW during organic matter (OM) oxidation. The highest MMHg concentrations (up to 12.2 ng L-1 and 90% of THg) were found in subsurface PWs of the carbonate-rich sediments which cover 75% of the small basin and 20% of the large one. In other sediment facies, the larger content of OM restricted MMHg production and accumulation in PW by sequestering Hg in the solid phase and potentially also by decreasing its bioavailability in the PW. Diagenetically reduced S and Fe played a dual role either favoring or restricting the availability of Hg for biomethylation. The calculation of theoretical diffusive fluxes suggests that Lake Titicaca bottom sediments are a net source of MMHg, accounting for more than one third of the daily MMHg accumulated in the water column of the Lago Menor. We suggest that in the context of rising anthropogenic pressure, the enhancement of eutrophication in high altitude Altiplano lakes may increase these MMHg effluxes into the water column and favor its accumulation in water and biota. (C) 2020 Elsevier B.V. All rights reserved.
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Gueguen, P., Brossault, M. A., Roux, P., & Singaucho, J. C. (2020). Slow dynamics process observed in civil engineering structures to detect structural heterogeneities. Engineering Structures, 202.
Résumé: Under strong seismic excitation, the resonance frequencies of civil engineering structures rapidly decrease, followed by slow recovery back to their initial values if there is no damage. In this study, we show that as for laboratory trials with rock samples, the properties of the slow recovery characterise the level of heterogeneities, and in this case, the damage rate. First, we validate this concept with laboratory tests applied to continuous beam-like structures in damaged and undamaged states. One recent model is used to fit the observed recoveries, and we show that its parameters (i.e., frequency variation, recovery slope, characteristic times) change with the health of the equivalent structure. In a second step, this concept is applied to two civil engineering structures that experience earthquakes: the first (Factor Building, USA) without observed damage; and the second (Geophysics Institute building, Ecuador) that experienced a fore/ main/ after-shock sequence with apparent damage that was characterised by a permanent drop in resonance frequency. The efficiency of the proposed model is confirmed for monitoring and for the fit of the frequency recovery. We conclude that the recovery process is a clear proxy of the structural state, and that this could be helpful for seismic monitoring of structural health during earthquake sequences.
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Guerin, G., Rivet, D., Deschamps, A., Larroque, C., Mordret, A., Dessa, J. X., et al. (2020). High resolution ambient noise tomography of the Southwestern Alps and the Ligurian margin. Geophysical Journal International, 220(2), 806–820.
Résumé: The Southwestern Alps and the Ligurian margin is a region of moderate seismicity with a high rate of small to moderate events. Identifying the active faults in this very densely populated region is critical to better assess the hazard and mitigate the risk. An accurate 3-D velocity model of the shallow to middle crust is a fundamental step to better locate the seismicity, and hence, the faults from which it originates. We performed ambient noise surface-wave tomography based on all available continuous seismological data from the French and Italian permanent networks (RESIF, INGV, RSNI), and current and past temporary experiments (AlpArray, CASSAT, SISVAR, RISVAL). In addition to these available data, we deployed three more stations to improve the spatial resolution in a region with sparse seismic station coverage. Overall, we used 55 inland seismic stations, 5 oceans bottom seismometers and 2 offshore cabled site/sensors. Data span the 2014-2018 time period. Time series from all available components were cross-correlated to reconstruct both Rayleigh and Love-wave Green's functions. For each station-pair Rayleigh and Love group velocity dispersion curves were semi-automatically picked using a frequency-time analysis. Then we regionalize these group velocities to build 2-D Rayleigh and Love velocity-maps between 1.5 and 9 s period. Using a two-step inversion, we estimate the best 3-D shear wave velocity model. The first step is based on a Neighbourhood Algorithm to recover the best three layers' velocity model at each cell of the model. We then use this three-layer model as a starting model in a perturbational method based on finite elements. At periods up to 5 s, the spatial variation of the velocity is well correlated with the effective geology of the area. Lower velocities are observed in areas where the sedimentary cover is thicker, such as the Var and Paillon valley near Nice, or in the subalpine domain in the northwestern part of the region. Higher velocities are retrieved in areas where massifs are present, such as the Argentera-Mercantour massifs in the northeastern, or the Esterel massif in the southwestern part of the region.
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Guillemot, A., Helmstetter, A., Larose, E., Baillet, L., Garambois, S., Mayoraz, R., et al. (2020). Seismic monitoring in the Gugla rock glacier (Switzerland): ambient noise correlation, microseismicity and modelling. Geophysical Journal International, 221(3), 1719–1735.
Résumé: A network of seismometers has been installed on the Gugla rock glacier since October 2015 to estimate seismic velocity changes and detect microseismicity. These two processes are related to mechanical and structural variations occurring within the rock glacier. Seismic monitoring thus allows a better understanding of the dynamics of rock glaciers throughout the year. We observed seasonal variations in seismic wave velocity and microseismic activity over the 3 yr of the study. In the first part of our analysis, we used ambient noise correlations to compute daily changes of surface wave velocity. In winter, seismic wave velocities were higher, probably due to refreezing of the permafrost active layer and cooling of the uppermost permafrost layers, leading to increased overall rigidity of the medium. This assumption was verified using a seismic model of wave propagation that estimates the depth of P – and S-wave velocity changes from 0 down to 10 m. During melting periods, both a sudden velocity decrease and a decorrelation of the seismic responses were observed. These effects can probably be explained by the increased water content of the active layer. In the second part of our study, we focused on detecting microseismic signals generated in and around the rock glacier. This seismic activity (microquakes and rockfalls) also exhibits seasonal variations, with a maximum in spring and summer, which correlates principally with an exacerbated post-winter erosional phase of the front and a faster rock glacier displacement rate. In addition, we observed short bursts of microseismicity, both during snowfall and during rapid melting periods, probably due to pore pressure increase.
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Guren, M. G., Putnis, C. V., Montes-Hernandez, G., King, H. E., & Renard, F. (2020). Direct imaging of coupled dissolution-precipitation and growth processes on calcite exposed to chromium-rich fluids. Chemical Geology, 552.
Résumé: Recent increases in industrial activity have resulted in elevated chromium (Cr) pollution in the natural environment, from the degradation of concrete and the leakage of water from landfills or mine waste. The release of toxic chromate ions into the environment could have harmful consequences. Methods for Cr removal are therefore becoming increasingly important to control the release of this highly toxic metal into the environment. This study examines how chromate (CrO42-) can be incorporated into a new, stable solid phase at a dissolving calcite surface. To study the relationship between solutions containing chromate and calcite, we performed two series of time-lapse atomic force microscopy (AFM) experiments to identify calcite dissolution and growth rates in the presence of chromate. In addition, we conducted complementary experiments in a stirred flow-through reactor to determine the amount of Cr removal from solution. All experiments were performed at room temperature and under a constant initial pH in the range 6-12. During the AFM experiments, we observed calcite dissolution via etch pit formation and propagation. In the presence of chromate, nanoparticles of a new phase nucleated and grew at the calcite surface by a coupled dissolution-precipitation process. In experiments with concentrations above 10 ppm Cr or at pH 10 and higher, we observed many nanoparticle precipitates, while precipitates were rarely observed at lower concentrations of Cr. At pH 10.5, the precipitates covered the calcite surface. This partly passivated further calcite dissolution, an observation confirmed by the low amounts of Cr removal measured in the flow-through experiments. Scanning electron microscopy analysis demonstrated that Cr was associated with the precipitates, indicating that Cr could be captured from solution and trapped in solid nanoparticles in the presence of calcite. However, the passivation of the calcite surface by a new precipitate may eventually slow down Cr sequestration.
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Harrison, E. J., Brocard, G. Y., Gasparini, N. M., Lyons, N. J., & Willenbring, J. K. (2020). Seepage Erosion in the Luquillo Mountains, Puerto Rico, Relict Landscapes. Journal Of Geophysical Research-Earth Surface, 125(6).
Résumé: Seminal research into geomorphic shaping of landscapes by emerging groundwater suggest that the relationships governing channel form and incision rate are distinct from other fluvial systems (Howard, 1995; Dunne, 1980, 1990). While some recent work has connected these models to natural settings (Abrams et al., 2009; Petroff et al., 2011), other studies have shown that seepage erosion may be erroneously invoked in landscapes shaped by flooding and overland flow (Lamb et al., 2006, 2007). We investigate the impact of seepage erosion on the geomorphology of a tropical mountain watershed, the Rio Blanco in the Luquillo Mountains of northern Puerto Rico. We focus on a population of amphitheater-shaped channels that incise into deeply weathered saprolite profiles in the upland reaches of the watershed, where the river is disconnected from regional base-level lowering (Brocard et al., 2015, 2016). We measured high rates of baseflow from springs feeding these catchments, despite their small drainage areas. We constructed an empirical model relating baseflow discharge to catchment area within the watershed. We quantified long-term (103-104 yrs) catchment erosion from 10Be in sediment and measured the short-term volumetric flux of bedload transport at baseflow. Rates of transport and erosion in this group of channels scale linearly with the feeding drainage area and baseflow discharge. This finding supports a stream incision model proposed for groundwater-driven channels (Howard, 1995). We propose that deepening saprolite and coincident entrenchment of the subsurface water-routing system initiated seepage erosion and are actively expanding the headwaters in the Rio Blanco. Plain Language Summary The relationship between landforms and the processes that shape them on Earth can be used to identify the processes at work in places that can only be studied remotely, like the deep ocean or the surface of other planets. In the early 1980s, researchers recognized that river channels have different shapes depending on whether they are carved by water moving over the land surface or flowing underground. Early studies of groundwater erosion in sandbox models found that there is a unique relationship between erosion and the rate of groundwater flow into a channel that does not exist under other circumstances. However, this relationship has yet to be verified in natural landscapes. In this study, we measured the shape-properties, groundwater flow, and erosion rates over short (hours) and long (tens of thousands of years) timescales in the headwater channels of steep, mountain rivers in a tropical rainforest in Puerto Rico. We identified a distinctive population of streams with geometric properties and stream flow-to-erosion rate relationship that match predictions for channels carved by water flowing underground on both short and long timescales. This is the first study investigating groundwater-driven erosion using Be-10 as a direct geochemical tracer. Key Points Morphology of channels mimics theoretical expectations of groundwater-driven erosion Baseflow discharge from springs can transport the fluvial bedload Long-term erosion rates scale linearly with baseflow discharge rates
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Heap, M. J., Baud, P., McBeck, J. A., Renard, F., Carbillet, L., & Hall, S. A. (2020). Imaging strain localisation in porous andesite using digital volume correlation. Journal Of Volcanology And Geothermal Research, 404.
Résumé: Strain localisation structures, such as shear fractures and compaction bands, are of importance due to their influence on permeability and therefore outgassing, a factor thought to influence eruptive style. In this study, we aim to develop a better understanding of strain localisation in porous volcanic rocks using X-ray tomographic images of samples of porous andesite (porosity = 0.26) acquired before and after deformation in the brittle and ductile regimes. These 3D images have been first analysed to provide 3D images of the porosity structure within the undeformed andesite, which consists of a large, well-connected porosity backbone alongside many smaller pores that are either isolated or connected to the porosity backbone by thin microstructural elements (e.g., microcracks). Following deformation, porosity profiles of the samples show localised dilation (porosity increase) and compaction (porosity reduction) within the samples deformed in the brittle and ductile regimes, respectively. Digital volume correlation (DVC) of the images before and after triaxial deformation was used to quantify the tensor strain fields, and the incremental divergence (volumetric strain) and curl (used as an indicator of shear strain) of the displacement fields were calculated from the DVC. These fields show that strain localisation in the sample deformed in the brittle regime manifested as a similar to 1 mm-wide, dilatational shear fracture oriented at an angle of 40-45 degrees to the maximum principal stress. Pre- and post-deformation permeability measurements show that permeability of the sample deformed in the brittle regime increased from 3.9 x 10(-12) to 4.9 x 10(-12) m(2), which is presumed to be related to the shear fracture. For the sample deformed in the ductile regime, strain localised into similar to 1 mm-thick, undulating compaction bands orientated sub-perpendicular to the maximum principal stress with little evidence of shear. Taken together, our data suggest that these bands formed during large stress drops seen in the mechanical data, within high-porosity zones within the sample, and within the large, well-connected porosity backbone. Pre- and post-deformation permeability measurements indicate that inelastic compaction decreased the permeability of the sample by a factor of similar to 3. The data of this study assist in the understanding of strain localisation in porous volcanic rocks, its influence on permeability (and therefore volcanic outgassing), and highlight an important role for DVC in studying strain localisation in volcanic materials. (C) 2020 Elsevier B.V. All rights reserved.
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Hentschel, F., Janots, E., Trepmann, C. A., Magnin, V., & Lanari, P. (2020). Corona formation around monazite and xenotime during greenschist-facies metamorphism and deformation. European Journal Of Mineralogy, 32(5), 521–544.
Résumé: Epidote/allanite-fluorapatite coronae around monazite and xenotime are investigated in Permian pegmatites deformed under greenschist-facies conditions during Alpine tectonometamorphism in the Austroalpine basement, Eastern Alps. The aim was to evaluate the replacement reactions involved in the formation of a corona microstructure, its age and relation to deformation. In the corona core, monazite and xenotime single crystals show domains with different composition and age. Monazite (Mnz1) and xenotime (Xen1) dating by electron microprobe (EPM) reveals an age of 250-287 Ma, consistent with the Permian magmatic age of the pegmatites. These are partly replaced by secondary monazite (Mnz2) and xenotime (Xen2) compositions yielding younger Mesozoic (170-210 Ma) and Alpine (30-120 Ma) ages. The same crystallographic orientation of the primary and secondary monazite and xenotime indicates interface-coupled dissolution-precipitation reactions. Allanite U-Th-Pb dating by laser ablation inductively coupled mass spectrometry in the corona revealed an age of 60 +/- 6 Ma, interpreted as the age of corona formation. The coronae around monazite consist of an inner zone of equant fluorapatite grains surrounded by prismatic allanite, which are surrounded by epidote enriched in heavy rare earth elements (HREEs) and REE-poor epidote grains. Compared to coronae around monazite, fluorapatite has higher REE contents and no allanite occurs in the coronae surrounding the xenotime. General reactions for monazite and xenotime breakdown can be written as follows: Mnz1 + (Si, Ca, Al, Fe, F)fluid -> Mnz2 + LREE-Ap Aln HREE-Ep Ep (Th, U)O-2 + (Th, U)SiO4, Xenl + (Si, Ca, Al, Fe, F)fluid -> Xen2 + HREE-Ap + HREE-Ep + Ep + (Th,U)O-2. The amount of replacement (judged by the relative proportions of monazite and fluorapatite) is low for monazite included in tourmaline but high within the mylonitic foliation. This dependence on the degree of replacement on the local surrounding microfabric indicates that fluid availability along grain boundaries in the matrix and cracks controlled reaction advancement, allowing the elementary mass transfer required for corona formation (e.g. input of Ca, Al, Si, Fe, F). The oblate shape of the coronae aligned within the foliation of the pegmatites and the deflected foliation around the coronae, without an outer rim of prismatic epidote showing signs of deformation, indicate that the main stage of corona formation took place during deformation and reactions were still ongoing after the main stage of deformation. The corona microstructure documents replacement reactions of a single reactant into multiple distinct mineral growth zones by dissolution and precipitation processes at nonisostatic, greenschist-facies conditions, which prevailed in the area to the north of the Defereggen-Antholz-Vals shear zone between the middle Cretaceous and the Oligocene. These reactions ceased before being completed, and REE gradients within single grains within the corona and on the thin-section scale are preserved, which suggests restricted and/or episodic transport of REE in the fluid phase and/or availability of fluid.
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Hernandez, J. A., Morard, G., Guarguaglini, M., Alonso-Mori, R., Benuzzi-Mounaix, A., Bolis, R., et al. (2020). Direct Observation of Shock-Induced Disordering of Enstatite Below the Melting Temperature. Geophysical Research Letters, 47(15).
Résumé: We report in situ structural measurements of shock-compressed single crystal orthoenstatite up to 337 55 GPa on the Hugoniot, obtained by coupling ultrafast X-ray diffraction to laser-driven shock compression. Shock compression induces a disordering of the crystalline structure evidenced by the appearance of a diffuse X-ray diffraction signal at nanosecond timescales at 80 13 GPa on the Hugoniot, well below the equilibrium melting pressure (>170 GPa). The formation of bridgmanite and post-perovskite have been indirectly reported in microsecond-scale plate-impact experiments. Therefore, we interpret the high-pressure disordered state we observed at nanosecond scale as an intermediate structure from which bridgmanite and post-perovskite crystallize at longer timescales. This evidence of a disordered structure of MgSiO3 on the Hugoniot indicates that the degree of polymerization of silicates is a key parameter to constrain the actual thermodynamics of shocks in natural environments. Plain Language Summary The study of silicate materials at extreme pressures and temperatures provides insight on the evolution of planetary bodies evolution during solar system formation. During their accretion, rocky bodies have undergone several collisions and possibly planetary impacts that have transformed their minerals. The microscopic processes occurring during such events are not fully understood. In this study, we used high-power lasers to generate shock waves into MgSiO3 enstatite crystals, creating conditions comparable to the deepest part of the early Earth mantle and large planetary impacts. During the shock wave transit, within few nanoseconds, we probed the structure of shocked enstatite between 14 3 and 337 55 GPa using intense X-ray pulses from Linac Coherent Light Source X-ray free electron laser facility. We found that, when shocked between 80 +/- 13 GPa and the conditions of equilibrium melting (above 170 GPa), enstatite transforms into a disordered structure instead of forming bridgmanite or post-perovskite-the expected equilibrium phases. This disordered structure is similar to MgSiO3 glass or liquid and is observed up to 337 +/- 55 GPa. This study provides the first direct measurement of shocked enstatite structure and suggests that the observed disordered state is an intermediate phase on the transformation pathway of bridgmanite in natural impacts.
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Hirose, T., Nakahara, H., Nishimura, T., & Campillo, M. (2020). Locating Spatial Changes of Seismic Scattering Property by Sparse Modeling of Seismic Ambient Noise Cross-Correlation Functions: Application to the 2008 Iwate-Miyagi Nairiku (Mw 6.9), Japan, Earthquake. Journal Of Geophysical Research-Solid Earth, 125(6).
Résumé: Locating change regions of seismic velocities and seismic scattering properties associated with volcanic activities and earthquakes is important for structural monitoring. To increase such applications, we propose to use sparse modeling to estimate spatial distributions of seismic scattering property changes. The sparse modeling is an inversion technique that enables us to estimate model parameters from a small data set with sparsity condition such as l(1) norm regularization. We apply this technique to seismic ambient noise cross-correlation functions from 17 Hi-net stations around the epicenter of the 2008 Iwate-Miyagi Nairiku, Japan, earthquake (Mw=6.9). We compute waveform decoherences at the 0.5-1 Hz band and invert the waveform decoherences for the spatial distributions of seismic scattering property changes. Just after the main shock, the largest change occurred at the south of the epicenter, and the maximum change of the scattering coefficient in this region is estimated to be 0.032 km(-1). The result from an ordinary linear least squares inversion with the l(2) norm regularization is almost consistent with that from the sparse modeling. Moreover, we confirm the superiority of sparse modeling in imaging with smaller data sets. Only five seismic stations that are deployed near the epicenter so as to surround the change regions are necessary to retrieve the result from 17 stations. On the other hand, in the case of the l(2) norm regularization, we need at least 15 stations. The sparse modeling will be helpful to estimate the spatial distribution of seismic scattering property changes from a small data set.
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Hollender, F., Roumelioti, Z., Maufroy, E., Traversa, P., & Mariscal, A. (2020). Can We Trust High-Frequency Content in Strong-Motion Database Signals? Impact of Housing, Coupling, and Installation Depth of Seismic Sensors. Seismological Research Letters, 91(4), 2192–2205.
Résumé: Seismic hazard studies provide indicators of seismic motion that are expressed for “free-field,” that is, representative of the ground motion exactly at the free surface, without disturbances due to interactions between soil and buildings or other structures. Most of these studies are based on ground-motion prediction equations, which are, themselves, formulated to predict free-field motion, as they are derived from similarly free data. However, is this really the case? In this study, we use several examples to illustrate how small structures hosting permanent strong-motion stations (often anchored on small concrete slabs) generate soilstructure interaction effects that can amplify the high-frequency part of the earthquake signal (10 Hz) by up to a factor of 2-3 for stations on soils. We also show that the installation depth of a station, even if very shallow (i.e., a few meters), can change the recorded response, mainly by deamplifying the signal in high frequencies (> 10 Hz) by a factor up to 0.3. Such effects imply that there are actual differences between recorded and true free-field signals. Depending on the housing conditions, these effects can have significant impact on response spectra at high frequencies, and on measurements of the kappa parameter. It is, thus, becoming clear that such effects should be taken into account in studies involving high-frequency seismic motion. To do so, scientists need a detailed description of the conditions of installation and housing of seismological and accelerometric stations, which often lacks from the metadata distributed through the various, commonly used web services. Increasing such information and facilitating the access to it would allow the identification of stations that are problematic and of those that are truly close to free-field recording conditions. In a subsequent step, it would be important to quantify the modification curve of the response of stations that experience such effects.
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Hu, Y., Teng, F. Z., Plank, T., & Chauvel, C. (2020). Potassium isotopic heterogeneity in subducting oceanic plates. Science Advances, 6(49).
Résumé: Oceanic crust and sediments are the primary K sinks for seawater, and they deliver considerable amounts of K to the mantle via subduction. Historically, these crustal components were not studied for K isotopes because of the lack of analytical precision to differentiate terrestrial variations. Here, we report a high-precision dataset that reveals substantial variability in oceanic plates and provides further insights into the oceanic K cycle. Sixty-nine sediments worldwide yield a broad delta K-41 range from -1.3 to -0.02 parts per thousand. The unusually low values are indicative of release of heavy K during continental weathering and uptake of light K during submarine diagenetic alteration. Twenty samples of altered western Pacific crust from ODP Site 801 display delta K-41 from -0.60 to -0.05 parts per thousand, averaging at -0.32 parts per thousand. Our results indicate that submarine alteration of oceanic plates is essential for generating the high-delta K-41 signature of seawater. These regionally varying subducting components are heterogeneous K inputs to the mantle.
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Huder, L., Gillet, N., Finlay, C. C., Hammer, M. D., & Tchoungui, H. (2020). COV-OBS.x2: 180 years of geomagnetic field evolution from ground-based and satellite observations. Earth Planets And Space, 72(1).
Résumé: We present the geomagnetic field model COV-OBS.x2 that covers the period 1840-2020. It is primarily constrained by observatory series, satellite data, plus older surveys. Over the past two decades, we consider annual differences of 4-monthly means at ground-based stations (since 1996), and virtual observatory series derived from magnetic data of the satellite missions CHAMP (over 2001-2010) and Swarm (since 2013). A priori information is needed to complement the constraints carried by geomagnetic records and solve the ill-posed geomagnetic inverse problem. We use for this purpose temporal cross-covariances associated with auto-regressive stochastic processes of order 2, whose parameters are chosen so as to mimic the temporal power spectral density observed in paleomagnetic and observatory series. We aim this way to obtain as far as possible realistic posterior model uncertainties. These can be used to infer for instance the core dynamics through data assimilation algorithms, or an envelope for short-term magnetic field forecasts. We show that because of the projection onto splines, one needs to inflate the formal model error variances at the most recent epochs, in order to account for unmodeled high frequency core field changes. As a by-product of the core field model, we co-estimate the external magnetospheric dipole evolution on periods longer than 2 years. It is efficiently summarized as the sum of a damped oscillator (of period 10.5 years and decay rate 55 years), plus a short-memory (6 years) damped random walk.
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Husson, L., Boucher, F. C., Sarr, A. C., Sepulchre, P., & Cahyarini, S. Y. (2020). Evidence of Sundaland's subsidence requires revisiting its biogeography. Journal Of Biogeography, 47(4), 843–853.
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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Huyghe, P., Bernet, M., Galy, A., Naylor, M., Cruz, J., Gyawali, B. R., et al. (2020). Rapid exhumation since at least 13 Ma in the Himalaya recorded by detrital apatite fission-track dating of Bengal fan (IODP Expedition 354) and modern Himalayan river sediments. Earth And Planetary Science Letters, 534.
Résumé: Apatite fission-track analysis of middle Bengal fan sediments (IODP expedition 354) and modern Himalayan river sediments shows that most of the detrital apatites are very young compared to their depositional ages, independent of their uranium content. Bengal fan apatites display an average central age lag time as short as 2.26 +/- 1.6 Myr since at least similar to 13 Ma. Such lag times reflect a mean exhumation rate on the order of at least 1-3 km/Myr. The occurrence of detrital apatites with relatively short AFT lag times since at least 13 Ma indicates that there have always been areas of rapid erosional exhumation, supplying detrital apatites to the fluvial system and delivering them to the paleo-Ganges and/or -Brahmaputra plains and finally to the Bengal fan. It also supports that temporary storage of detrital apatites in the floodplains or delta has always been negligible since at least 13 Ma. Comparison of the AFT data of the Bengal fan with those of the Central and Eastern proximal Neogene Himalayan foreland basin shows that both paleo-Ganga and -Brahmaputra catchments provided apatites with similar short lag time to the distal Bengal Fan basin. In the modern drainage system of the Bengal fan, the apatites with young fission-track cooling ages are principally derived from areas where the topography has a sharp relief controlled by threshold hillslope processes and stream power resulting in landslide erosion as a coupled response to tectonic and fluvial forcing. By analogy with the modern erosion processes in the Himalayan range, we suggest that over the past 13 Ma, apatites were mainly derived from areas of sharp relief, where river stream power was high and hill slopes close to the threshold angle. As the exhumation signal is rather consistent since the late Miocene the detrital apatite fission-track data are either not sensitive enough to detect rapid climatically controlled changes in exhumation rates, or overall long-term erosion rates on the orogen scale are not strongly affected by climatic variations such as the variability of the Indian Summer Monsoon. Given the already rapid exhumation rates controlled by tectonics, the impact of climate variability on surface erosion rates cannot be detected with our data, especially in the case of erosion processes dominated by threshold hillslope model. (C) 2020 Elsevier B.V. All rights reserved.
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Inguaggiato, C., Pappaterra, S., Peiffer, L., Apollaro, C., Brusca, L., De Rosa, R., et al. (2020). Mobility of REE from a hyperacid brine to secondary minerals precipitated in a volcanic hydrothermal system: Kawah Ijen crater lake (Java, Indonesia). Science Of The Total Environment, 740.
Résumé: Rare Earth Elements (REE; lanthanides and yttrium) are elements with high economic interest because they are critical elements for modern technologies. This study mainly focuses on the geochemical behavior of REE in hyperacid sulphate brines in volcanic-hydrothermal systems, where the precipitation of sulphate minerals occurs. Kawah Ijen lake, a hyperacid brine hosted in the Ijen caldera (Indonesia), was used as natural laboratory. Sigma REE concentration in the lake water is high, ranging from 5.86 to 6.52 mg kg(-1). The REE pattern of lake waters normalized to the average local volcanic rock is flat, suggesting isochemical dissolution. Minerals spontaneously precipitated in laboratory at 25 degrees C from water samples of Kawah Ijen were identified by XRD as gypsum. Microprobe analyses and the chemical composition of major constituents allow to identify possible other minerals precipitated: jarosite, Al-sulphate and Sr, Ba-sulphate. Sigma REE concentration in minerals precipitated (mainly gypsum) range from 59.53 to 78.64 mg kg(-1). The REE patterns of minerals precipitated normalized to the average local magmatic rock show enrichment in LREE. The REE distribution coefficient (KD), obtained from a ratio of its concentration in the minerals precipitated (mainly gypsum) and the lake water, shows higher values for LREE than HREE. KD-LREE/KD-HREE increases in the studied samples when the concentrations of BaO, MgO, Fe2O3, Al2O3, Na2O and the sum of total oxides (except SO3 and CaO) decrease in the solid phase. The presence of secondary minerals different than gypsum can be the cause of the distribution coefficient variations. High concentrations of REE in Kawah Ijen volcanic lake have to enhance the interest on these environments as possible REE reservoir, stimulating future investigations. The comparison of the KD calculated for REE after mineral precipitation (mainly gypsum) from Kawah Ijen and Poas hyperacid volcanic lakes allow to generalize that the gypsum precipitation removes the LREE from water. (C) 2020 Elsevier B.V. All rights reserved.
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Jaafari, C., Bertrand, D., Guillot, T., Prudhomme, E., Tardif, N., Georgin, J. F., et al. (2020). Effect of early age drying shrinkage on the seismic response of RC structures. Materials And Structures, 53(6).
Résumé: Reinforced concrete (RC) damage over time can cause severe structural problems (e.g. Morandi Bridge in Italy). Many factors contribute to concrete deterioration (thermal conditions, chemical attacks, shrinkage, creep, carbonation, corrosion, etc). Reinforced concrete deterioration starts at early-age and continues with structure aging. Early-age shrinkage, creep and thermal conditions or initial cracks can have a significant impact on the dynamic behavior of concrete structures. The CEOS.fr National program for instance showed that the natural frequency of a RC beam subjected to early-age restrained shrinkage is highly affected. In order to quantify the impact of early-age drying shrinkage on the dynamic behavior of structures, the GEOMAS Lab at INSA Lyon has conducted a research project combining both numerical modeling and pseudo-dynamic tests on two types of RC portal frames. The first one was kept in endogenous conditions (by covering it using a plastic sheet to stop water exchange with the surrounding environment) during its early age period in a way to limit drying effects leading to cracks, while the second one was kept in non-endogenous conditions (water exchange was possible) similar to construction site conditions, which induced cracks apparition. Both RC portal frames were subjected after their early age period to the same seismic loading. The present paper focuses on the experimental part of the project based on the use of pseudodynamic tests in order to evaluate the behavior of such structures under a seismic loading. The portal frames were instrumented using optical fiber sensors, displacement and load sensors and velocimeters. Image correlation was also used in order to monitor the structures.
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Jault, D. (2020). Tangential stress at the core-mantle interface. Geophysical Journal International, 221(2), 951–967.
Résumé: Fluctuations in the rotation rate of the solid Earth over periods from 5 to 100 yr result from exchanges of angular momentum between the fluid outer core and the solid mantle. The coupling mechanism mediating angular momentum transfer is not clear yet. Here, I revisit local Cartesian models for the pressure stress on a bumpy core-mantle interface. One common approach consists in analysing forced magnetohydrodynamic modes arising from the interaction between a steady flow along the core-mantle interface and boundary topography. The wave amplitude scales as the height of corrugations and the pressure stress as zeta(2). As expected from Newton's third law, the tangential stress on the fluid is opposite to the tangential stress on the solid. It is exactly compensated by non-zero mean electromagnetic and Coriolis forces, which both result from interactions at infinity and not with the electrically insulating solid. Requiring zero net flux of mass and electrical current at infinity in order to better model closed systems necessitates to restore mean flow acceleration. This makes possible to investigate whether there is momentum transfer into the fluid interior or instead dissipation next to the boundary. Fluid stratification enhances the horizontal stress exerted by the pressure field on the core mantle boundary but we have yet to describe the mechanism to transport momentum from the boundary into the fluid.
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Jeong, D. H., Kvasnickova, A., Boutin, J. B., Cebron, D., & Sauret, A. (2020). Deposition of a particle-laden film on the inner wall of a tube. Physical Review Fluids, 5(11).
Résumé: The withdrawal of a liquid or the translation of a liquid slug in a capillary tube leads to the deposition of a thin film on the inner wall. When particles or contaminants are present in the liquid, they deposit and contaminate the tube if the liquid film is sufficiently thick. In this article, we experimentally investigate the condition under which particles are deposited during the air invasion in a capillary tube initially filled with a dilute suspension. We show that the entrainment of particles in the film is controlled by the ratio of the particle and the tube radii and the capillary number associated with the front velocity. We also develop a model which suggests optimal operating conditions to avoid contamination during the withdrawal of a suspension from a tube. This deposition mechanism can also be leveraged in coating processes by controlling the deposition of particles on the inner walls of channels.
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Jolly, A., Caudron, C., Girona, T., Christenson, B., & Carniel, R. (2020). 'Silent' Dome Emplacement into a Wet Volcano: Observations from an Effusive Eruption at White Island (Whakaari), New Zealand in Late 2012. Geosciences, 10(4).
Résumé: The 2012-2016 White Island (Whakaari) eruption sequence encompassed six small explosive events that included one steam driven and five explosive phreato-magmatic eruptions. More enigmatic, a dome was observed at the back of the vent and crater lake in November 2012. Its emplacement date could not be easily determined due to persistent steam from the evaporating crater lake and because of the very low levels of discrete volcanic earthquakes associated with its growth. During this period, seismicity also included persistent tremor with dominant frequencies in the 2-5 Hz range. Detailed assessment of the tremor reveals a very slow evolution of the spectral peaks from low to higher frequencies. These gliding spectral lines evolved over a three-month time period beginning in late September 2012 and persisting until early January 2013, when the tremor stabilised. As part of the dome emplacement episode, the crater lake progressively dried, leaving isolated pools which then promoted persistent mud/sulphur eruption activity starting in mid-January 2013. We interpret the emplacement of the dome as a non-explosive process where the hot, mostly degassed, magma intruded slowly through the hydrothermal system in late September 2012 and cooled in a relatively quiet state. The tremor evolution might reflect the slow contraction of subsurface resonant cavities, which increased the pitch of the peak resonant frequency through time. Alternatively, spectral evolution might reflect a 'comb function' due to clockwork beating of the slowly cooling dome, although direct evidence of clockwork beats is not seen in the waveform data. Finally, it might represent frothing of the hydrothermal system ahead of the slowly propagating magma.
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Jouanne, F., Munawar, N., Mugnier, J. L., Ahmed, A., Awan, A. A., Bascou, P., et al. (2020). Seismic Coupling Quantified on Inferred Decollements Beneath the Western Syntaxis of the Himalaya. Tectonics, 39(9).
Résumé: We used episodic GNSS measurements to quantify the present-day velocity field in the northwestern Himalaya from the Himalayan foreland to the Karakoram Range. We report a progressive N-S compressional velocity gradient with two noticeable exceptions: in the Salt Range, where important southward velocities are recorded, and in Nanga Parbat, where an asymmetrical E-W velocity gradient is recorded. A review of Quaternary slip along active thrusts both in and out of sequence allows us to propose a 14 mm/yr shortening rate. This constraint, together with a geometrical model of the Main Himalayan Thrust (MHT), allows us to propose estimations of the slip distributions along the active faults. The lower flat of the MHT is characterized by ductile slip, whereas the coupling increases along the crustal ramp and along the upper flat of the MHT. The basal thrust of the Potwar Plateau and Salt Range presents weak coupling, which is interpreted as the existence of a massive salt layer forming an excellent decollement. In the central part of the frontal Salt Range, the velocities suggest the existence of a southward horizontal flux in the massive salt layer. The simulations also suggest that the velocities recorded in Nanga Parbat can be explained by active westward thrusting along the fault that borders the massif to the west. Simulations suggest that the slip along this fault evolves with depth from 5 mm/yr ductile slip near the MHT to no slip along the upper part of the fault.
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Journeau, C., Shapiro, N. M., Seydoux, L., Soubestre, J., Ferrazzini, V., & Peltier, A. (2020). Detection, Classification, and Location of Seismovolcanic Signals with Multicomponent Seismic Data: Example from the Piton de La Fournaise Volcano (La Reunion, France). Journal Of Geophysical Research-Solid Earth, 125(8).
Résumé: We apply three different methods based on the analysis of the multicomponent seismic data to detect seismovolcanic tremors and other seismovolcanic signals, to propose an approach to classify them, and to locate their sources. We use continuous seismograms recorded during 1year by 21 stations at the Piton de la Fournaise volcano (La Reunion, France). The first method allows the detection of seismovolcanic signals based on stability in time of the intercomponent cross-correlation function. Two other methods based on the simultaneous analysis of the whole network can be used to detect seismovolcanic signals and to locate their sources. In the first network-based method, the seismic wavefield is analyzed by calculating the width of the network covariance matrix eigenvalue distribution.The second network-based method consists in performing the 3-D backprojection of the interstation cross correlations in order to calculate the network response function. Simultaneous analysis of the parameters measured by the three different methods can be used to classify different types of seismovolcanic tremors. Our results demonstrate that all three methods efficiently detect seismovolcanic tremors accompanying the 2010 eruptions and the preceding pre-eruptive seismic swarms. Furthermore, Methods 2 and 3 based on simultaneous analysis of the whole network detect a large number of volcanic earthquakes. Our location results show that each seismovolcanic tremor is located in a distinct regionof the volcano, close to the eruptive site at a shallow depth, and the preceding seismic crisis is located deeper at about the sea level under the summit crater.
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Kartal, M., Xia, F., Ralph, D., Rickard, W. D. A., Renard, F., & Li, W. (2020). Enhancing chalcopyrite leaching by tetrachloroethylene-assisted removal of sulphur passivation and the mechanism of jarosite formation. Hydrometallurgy, 191.
Résumé: Chalcopyrite (CuFeS2) is the primary ore mineral for copper, but leaching of this mineral under atmospheric conditions is slow due to the formation of surface passivating phases such as elemental sulphur and jarosite. Here, we studied chalcopyrite leaching in a sulphuric acid solution at 75 degrees C and 750 mV (relative to the standard hydrogen electrode), and found that after adding 20 vol% of tetrachloroethylene (TCE) into the leaching solution, elemental sulphur was dissolved from chalcopyrite and surface passivation was removed at the early stage of leaching. The removal of surface sulphur significantly enhanced the leaching rate by approximately 600% compared with TCE-free leaching. However, adding dimethyl sulfoxide (DMSO) did not improve the leaching rate. At the later stage of leaching, the increasing concentrations of Fe3+ from the dissolution of chalcopyrite and K+ possibly from the dissolution of minor amount of gangue minerals resulted in the precipitation of a potassium jarosite layer on the surface of chalcopyrite. The jarosite shell did not passivate TCE-free leaching due to its porous structure. However, in the case of leaching with TCE, elemental sulphur filled the pores, and the jarosite shell became nearly impermeable, resulting in passivation after 80% copper extraction. This study demonstrates a way for effective removal of sulphur passivation at the early stage of chalcopyrite leaching by adding sulphur dissolving solvent such as TCE, but to prevent jarosite formation at the later stage of leaching, it is necessary to keep the concentrations of Fe3+ and K+ at low levels.
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Kaviani, A., Paul, A., Moradi, A., Mai, P. M., Pilia, S., Boschi, L., et al. (2020). Crustal and uppermost mantle shear wave velocity structure beneath the Middle East from surface wave tomography. Geophysical Journal International, 221(2), 1349–1365.
Résumé: We have constructed a 3-D shear wave velocity (Vs) model for the crust and uppermost mantle beneath the Middle East using Rayleigh wave records obtained from ambient-noise cross-correlations and regional earthquakes. We combined one decade of data collected from 852 permanent and temporary broad-band stations in the region to calculate group-velocity dispersion curves. A compilation of >54000 ray paths provides reliable group-velocity measurements for periods between 2 and 150 s. Path-averaged group velocities calculated at different periods were inverted for 2-D group-velocity maps. To overcome the problem of heterogeneous ray coverage, we used an adaptive grid parametrization for the group-veloci tomographic inversion. We then sample the period-dependent group-velocity field at each cell of a predefined grid to generate 1-D group-velocity dispersion curves, which are subsequently inverted for 1-D Vs models beneath each cell and combined to approximate the 3-D Vs structure of the area. The Vs model shows low velocities at shallow depths (5-10 km) beneath the Mesopotamian foredeep, South Caspian Basin, eastern Mediterranean and the Black Sea, in coincidence with deep sedimentary basins. Shallow high-velocity anomalies are observed in regions such as the Arabian Shield, Anatolian Plateau and Central Iran, which are dominated by widespread magmatic exposures. In the 10-20 km depth range, we find evidence for a band of high velocities (>4.0 km s(-1)) along the southern Red Sea and Arabian Shield, indicating the presence of upper mantle rocks. Our 3-D velocity model exhibits high velocities in the depth range of 30-50 km beneath western Arabia, eastern Mediterranean, Central Iranian Block, South Caspian Basin and the Black Sea, possibly indicating a relatively thin crust. In contrast, the Zagros mountain range, the Sanandaj-Sirjan metamorphic zone in western central Iran, the easternmost Anatolian plateau and Lesser Caucasus are characterized by low velocities at these depths. Some of these anomalies may be related to thick crustal roots that support the high topography of these regions. In the upper mantle depth range, high-velocity anomalies are obtained beneath the Arabian Platform, southern Zagros, Persian Gulf and the eastern Mediterranean, in contrast to low velocities beneath the Red Sea, Arabian Shield, Afar depression, eastern Turkey and Lut Block in eastern Iran. Our Vs model may be used as a new reference crustal model for the Middle Fast in a broad range of future studies.
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Kazachkina, E., Kostoglodov, V., Cotte, N., Walpersdorf, A., Ramirez-Herrera, M. T., Gaidzik, K., et al. (2020). Active 650-km Long Fault System and Xolapa Sliver in Southern Mexico. Frontiers In Earth Science, 8.
Résumé: New estimates of long-term velocities of permanent GPS stations in Southern Mexico reveal that the geologically discernible similar to 650-km long shear zone, which strikes parallel to the Middle America trench, is active. This left-lateral strike-slip, La Venta-Chacalapa (LVC) fault system, is apparently associated with a motion of the Xolapa terrain and at the present time is the northern boundary of a similar to 110-160-km wide forearc sliver with a sinistral motion of 3-6 mm/year with respect to the North America plate. This sliver is the major tectonic feature in the Guerrero and Oaxaca regions, which accommodates most of the oblique component of the convergence between the Cocos and North America plates. Previous studies based purely on the moment tensor coseismic slips exceedingly overestimated the sliver inland extent and allocated its northern margin on or to the north of the Trans-Mexican Volcanic Belt. While the LVC fault system probably slips slowly over geologic scale time and there is not any historic evidence of large earthquakes on the fault so far, its seismic potential could be very high, assuming a feasible order of similar to 10(3)years recurrence cycle. A detailed analysis of long-term position time series of permanent GPS stations in the Guerrero and Oaxaca states, Southern Mexico discards previous models and provides clear evidence of an active LVC fault zone bounding the Xolapa forearc sliver. The southeastward motion of this sliver may have persisted for the last similar to 8-10 Million year and played an important role in the tectonic evolution of the region.
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Kotha, S. R., Weatherill, G., Bindi, D., & Cotton, F. (2020). A regionally-adaptable ground-motion model for shallow crustal earthquakes in Europe. Bulletin Of Earthquake Engineering, 18(9), 4091–4125.
Résumé: To complement the new European Strong-Motion dataset and the ongoing efforts to update the seismic hazard and risk assessment of Europe and Mediterranean regions, we propose a new regionally adaptable ground-motion model (GMM). We present here the GMM capable of predicting the 5% damped RotD50 of PGA, PGV, and SA(T=0.01-8s {T = 0.01 – 8\,{\text{s}}} \right) $$\end{document} from shallow crustal earthquakes of 3 <= MW <= 7.4 occurring 0<RJB <= 545km away from sites with 90 <= Vs30 <= 3000ms-1 90 \le V_{s30} \le 3000\,{\text{m}}\,{\text{s}}<^>{ – 1} $$\end{document} or 0.001 <= slope <= 1mm-1 0.001 \le slope \le 1\,{\text{m}}\,{\text{m}}<^>{ – 1} $$\end{document}. The extended applicability derived from thousands of new recordings, however, comes with an apparent increase in the aleatory variability (sigma). Firstly, anticipating contaminations and peculiarities in the dataset, we employed robust mixed-effect regressions to down weigh only, and not eliminate entirely, the influence of outliers on the GMM median and sigma. Secondly, we regionalised the attenuating path and localised the earthquake sources using the most recent models, to quantify region-specific anelastic attenuation and locality-specific earthquake characteristics as random-effects, respectively. Thirdly, using the mixed-effect variance-covariance structure, the GMM can be adapted to new regions, localities, and sites with specific datasets. Consequently, the sigma is curtailed to a 7% increase at T < 0.3 s, and a substantial 15% decrease at T >= 0.3 s, compared to the RESORCE based partially non-ergodic GMM. We provide the 46 attenuating region-, 56 earthquake localities-, and 1829 site-specific adjustments, demonstrate their usage, and present their robustness through a 10-fold cross-validation exercise.
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Koulakov, I., Shapiro, N. M., Sens-Schonfelder, C., Luehr, B. G., Gordeev, E. I., Jakovlev, A., et al. (2020). Mantle and Crustal Sources of Magmatic Activity of Klyuchevskoy and Surrounding Volcanoes in Kamchatka Inferred From Earthquake Tomography. Journal Of Geophysical Research-Solid Earth, 125(10).
Résumé: Klyuchevskoy and surrounding volcanoes in central Kamchatka form the Northern Group of Volcanoes (NGV), which is an area of particularly diverse and intensive Pleistocene-Holocene volcanism. In this study, we present a new seismic tomographic model of the crust and uppermost mantle beneath NGV based on local earthquake data recorded by several permanent and temporary seismic networks including a large-scale experiment that was conducted in 2015-2016 by an international scientific consortium. Having an unprecedented resolution for this part of Kamchatka, the new model reveals many features associated with the present and past volcanic activity within the NGV. In the upper crust, we found several prominent high-velocity anomalies interpreted as traces of large basaltic shield volcanoes, which were hidden by more recent volcanic structures and sediments. We interpret the mantle structure to reflect asthenospheric flow up through a slab window below the Kamchatka-Aleutian junction that feeds the entire NGV. The interaction of the hot asthenospheric material with fluids released from the slab determines the particular volcanic activity within the NGV. We argue that the eastern branch of the Central Kamchatka Depression, which is associated with a prominent low-velocity anomaly in the uppermost mantle, was formed as a recent rift zone separating the NGV from the Kamchatka Eastern Ranges.
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Kuehnert, J., Mangeney, A., Capdeville, Y., Metaxian, J. P., Bonilla, L. F., Stutzmann, E., et al. (2020). Simulation of Topography Effects on Rockfall-Generated Seismic Signals: Application to Piton de la Fournaise Volcano. Journal Of Geophysical Research-Solid Earth, 125(10).
Résumé: Seismic waves generated by rockfalls contain valuable information on the properties of these events. However, as rockfalls mainly occur in mountainous regions, the generated seismic waves can be affected by strong surface topography variations. We present a methodology for investigating the influence of topography using a Spectral-Element-based simulation of 3-D wave propagation in various geological media. This methodology is applied here to Dolomieu crater on the Piton de la Fournaise volcano, Reunion Island, but it can be used for other sites, taking into account local topography and medium properties. The complexity of wave fields generated by single-point forces is analyzed for different velocity models and topographies. Ground-motion amplification is studied relative to flat reference models, showing that Peak Ground Velocity (PGV) and total kinetic energy can be amplified by factors of up to 10 and 20, respectively. Simulations with Dolomieu-like crater shapes suggest that curvature variations are more influential than depth variations. Topographic effects on seismic signals from rockfalls at Dolomieu crater are revealed by interstation spectral ratios. Results suggest that propagation along the topography rather than source direction dominates the spectral ratios and that resulting radiation patterns can be neglected. The seismic signature of single rockfall impacts is studied. Using Hertz contact theory, impact force and duration are estimated and then used to scale simulations, achieving order-of-magnitude agreement with observed signal amplitudes and frequency thresholds. Our study shows that combining Hertz theory with high-frequency seismic wave simulations on real topography improves the quantitative analysis of rockfall seismic signals.
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Kuwayama, Y., Morard, G., Nakajima, Y., Hirose, K., Baron, A. Q. R., Kawaguchi, S. I., et al. (2020). Equation of State of Liquid Iron under Extreme Conditions. Physical Review Letters, 124(16).
Résumé: The density of liquid iron has been determined up to 116 GPa and 4350 K via static compression experiments following an innovative analysis of diffuse scattering from liquid. The longitudinal sound velocity was also obtained to 45 GPa and 2700 K based on inelastic x-ray scattering measurements. Combining these results with previous shock-wave data, we determine a thermal equation of state for liquid iron. It indicates that Earth's outer core exhibits 7.5%-7.6% density deficit, 3.7%-4.4% velocity excess, and an almost identical adiabatic bulk modulus, with respect to liquid iron.
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Lacroix, P., Dehecq, A., & Taipe, E. (2020). Irrigation-triggered landslides in a Peruvian desert caused by modern intensive farming. Nature Geoscience, 13(1), 56–+.
Résumé: Intensification of agriculture leads to stress on the environment and subsequently can have strong societal and ecological impacts. In deserts, areas of very high sensitivity to land-use changes, these local-scale impacts are not well documented. On the arid southwestern coast of Peru, several vast irrigation programmes were developed in the 1950s on the flat detritic plateau surrounding narrow valleys to supply new farming areas. We document the long-term effects of irrigation on the erosion of arid deserts in the Vitor and Siguas valleys, south Peru, using 40 yr of satellite data. We demonstrate that irrigation initiated very large slow-moving landslides, affecting one-third of the valleys. Their kinematics present periods of quiescence and short periods of rapid activity, corresponding to landslide destabilization by their headscarp retrogression. This analysis suggests that the landslide motion continues long after their initiation by irrigations. Those landslides affect the fertile valley floors, leading to the destruction of villages and agricultural areas. We conclude that modern intensive farming can strongly impact traditional agriculture in desert areas where water management is particularly critical.
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Laurent, L., Buoncristiani, J. F., Pohl, B., Zekollari, H., Farinotti, D., Huss, M., et al. (2020). The impact of climate change and glacier mass loss on the hydrology in the Mont-Blanc massif. Scientific Reports, 10(1).
Résumé: The Mont-Blanc massif, being iconic with its large glaciers and peaks of over 4,000 m, will experience a sharp increase in summer temperatures during the twenty-first century. By 2100, the impact of climate change on the cryosphere and hydrosphere in the Alps is expected to lead to a decrease in annual river discharge. In this work, we modelled the twenty-first century evolution of runoff in the Arve river, downstream of Mont-Blanc's French side. For the first time for this region, we have forced a hydrological model with output from an ice-dynamical glacier model and 16 downscaled climate projections, under RCP4.5 and RCP8.5 scenarios. By 2100, under RCP8.5 (high-emission scenario), the winter discharge of the Arve river remains low but is expected to increase by 80% when compared to the beginning of the century. By contrast, the summer season, currently the most important discharge period, will be marked by a runoff decrease of approximately 40%. These changes are almost similar according to a scenario with a lower warming (RCP4.5) and are mostly driven by glacier retreat. These shifts will have significant downstream impacts on water quantity and quality, affecting hydroelectric generation, agriculture, forestry, tourism and aquatic ecosystems.
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Lazarev, S., de Leeuw, A., Stoica, M., Mandic, O., van Baak, C. G. C., Vasiliev, I., et al. (2020). From Khersonian drying to Pontian “flooding”: late Miocene stratigraphy and palaeoenvironmental evolution of the Dacian Basin (Eastern Paratethys). Global And Planetary Change, 192.
Résumé: In the late Miocene, a large inland sea known as the Eastern Paratethys stretched out across the present-day Black Sea – Caspian Sea region. The basin was mostly endorheic and its water budget thus strongly dependent on regional climate. The basin was therefore prone to high-amplitude water-level fluctuations and associated turnovers in water chemistry and fauna. Profound palaeoenvironmental changes happened in the Eastern Paratethys during this time period. This article documents the evolution of the Dacian Basin of Romania, the westernmost branch of the Eastern Paratethys, during the time interval between 7.7 and 6.0 Ma. Our integrated study of sedimentary facies, micro- and macro fauna along the Slanicul de Buzau Section was constrained with a timeframe based on magnetostratigraphy. The remarkable 1.3 km-thick sedimentary record, high depositional rate (0.65-1.26 m/kyr) and abundance of fossils along this section provide a unique opportunity to study sedimentary and biotic turnovers in high detail. Our analyses reveal several marked water-level and salinity changes: A predominance of freshwater coastal plain environments, only occasionally flooded, indicates a low water-level in the Khersonian (similar to 7.7-7.63 Ma). The coastal plain deposits are overlain by offshore muds revealing a low mesohaline early Maeotian transgression, which was followed by the installation of littoral/ nearshore environments with freshwater molluscs in shallow settings and oligohaline ostracods in slightly deeper settings. Subsequent delta progradation and a prevalence of freshwater fauna in both marginal and more distal environments characterize the late Maeotian. This was followed by a remarkable freshwater transgression that started at 6.3 Ma and led to predominantly offshore deposition. The late Maeotian fossil record suggests brackish water pulses from Lake Pannon (Central Paratethys), followed by mass occurrences of Coelogonia novorossica. At 6.1 Ma, a short influx of meso- to polyhaline microfauna including benthic and planktonic foraminifera defines the “Pontian Salinity Incursion”. Molluscs, including Eupatorina littoralis, that biostratigraphically mark the onset of the Pontian arrived with a negligible delay of similar to 5 kyr after the microfauna influx. The onset of the Pontian at Slanicul de Buzau at 6.1 Ma (+/- 5 kyr), is thus synchronous with the onset in other Paratethys basins. Our integrated approach, placing the preserved fossil fauna in its respective sedimentary environment, allows for a detailed insight into the salinity of coeval marginal as well as basinal environments and could be more widely applied in the Paratethys realm and other semi-isolated basins with a deviant salinity.
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Lecocq, T., Hicks, S. P., Van Noten, K., van Wijk, K., Koelemeijer, P., De Plaen, R. S. M., et al. (2020). Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures. Science, 369(6509), 1338–1343.
Résumé: Human activity causes vibrations that propagate into the ground as high-frequency seismic waves. Measures to mitigate the coronavirus disease 2019 (COVID-19) pandemic caused widespread changes in human activity, leading to a months-long reduction in seismic noise of up to 50%. The 2020 seismic noise quiet period is the longest and most prominent global anthropogenic seismic noise reduction on record. Although the reduction is strongest at surface seismometers in populated areas, this seismic quiescence extends for many kilometers radially and hundreds of meters in depth. This quiet period provides an opportunity to detect subtle signals from subsurface seismic sources that would have been concealed in noisier times and to benchmark sources of anthropogenic noise. A strong correlation between seismic noise and independent measurements of human mobility suggests that seismology provides an absolute, real-time estimate of human activities.
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Lehmann, B., Herman, F., Valla, P. G., King, G. E., Biswas, R. H., Ivy-Ochs, S., et al. (2020). Postglacial erosion of bedrock surfaces and deglaciation timing: New insights from the Mont Blanc massif (western Alps). Geology, 48(2), 139–144.
Résumé: Since the Last Glacial Maximum, similar to 20 k.y. ago, Alpine glaciers have retreated and thinned. This transition exposed bare bedrock surfaces that could then be eroded by a combination of debuttressing or local frost cracking and weathering. Quantification of the respective contributions of these processes is necessary to understand the links between long-term climate and erosion in mountains. Here, we quantified the erosion histories of postglacial exposed bedrock in glacial valleys. Combining optically stimulated luminescence and terrestrial cosmogenic nuclide (TCN) surface exposure dating, we estimated the erosion rate of bedrock surfaces at time scales from 10(1) to 10(4) yr. Bedrock surfaces sampled from the flanks of the Mer de Glace (Mont Blanc massif, European Alps) revealed erosion rates that vary from 3.5 +/- 1.2 x 10(-1) mm/yr to 4.3 +/- 0.6 mm/yr over similar to 500 m of elevation, with a negative correlation between erosion rate and elevation. The observed spatial variation in erosion rates, and their high values, reflect morphometric (elevation and surface slope) and climatic (temperature and snow cover) controls. Furthermore, the derived erosion rates can be used to correct the timing of deglaciation based on TCN data, potentially suggesting very rapid ice thinning during the Gschnitz stadial.
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Lemelle, L., Bartolini, A., Simionovici, A., Tucoulou, R., De Nolf, W., Bassinot, F., et al. (2020). Nanoscale trace metal imprinting of biocalcification of planktic foraminifers by Toba's super-eruption. Scientific Reports, 10(1).
Résumé: Bioactive metal releases in ocean surface water, such as those by ash falls during volcanic super-eruptions, might have a potentially toxic impact on biocalcifier planktic microorganisms. Nano-XRF imaging with the cutting-edge synchrotron hard X-ray nano-analysis ID16B beamline (ESRF) revealed for the first time a specific Zn- and Mn-rich banding pattern in the test walls of Globorotalia menardii planktic foraminifers extracted from the Young Toba Tuff layer, and thus contemporaneous with Toba's super-eruption, 74,000 years ago. The intra-test correlation of Zn and Mn patterns at the nanoscale with the layered calcareous microarchitecture, indicates that the incorporation of these metals is syngenetic to the wall growth. The preferential Mn and Zn sequestration within the incipient stages of chamber formation suggests a selective incorporation mechanism providing a resilience strategy to metal pollution in the test building of planktic foraminifers.
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Lemelle, L., Simionovici, A., Colin, P., Knott, G., Bohic, S., Cloetens, P., et al. (2020). Nano-imaging trace elements at organelle levels in substantia nigra overexpressing alpha-synuclein to model Parkinson's disease. Communications Biology, 3(1).
Résumé: Sub-cellular trace element quantifications of nano-heterogeneities in brain tissues offer unprecedented ways to explore at elemental level the interplay between cellular compartments in neurodegenerative pathologies. We designed a quasi-correlative method for analytical nanoimaging of the substantia nigra, based on transmission electron microscopy and synchrotron X-ray fluorescence. It combines ultrastructural identifications of cellular compartments and trace element nanoimaging near detection limits, for increased signal-to-noise ratios. Elemental composition of different organelles is compared to cytoplasmic and nuclear compartments in dopaminergic neurons of rat substantia nigra. They exhibit 150-460 ppm of Fe, with P/Zn/Fe-rich nucleoli in a P/S-depleted nuclear matrix and Ca-rich rough endoplasmic reticula. Cytoplasm analysis displays sub-micron Fe/S-rich granules, including lipofuscin. Following AAV-mediated overexpression of alpha -synuclein protein associated with Parkinson's disease, these granules shift towards higher Fe concentrations. This effect advocates for metal (Fe) dyshomeostasis in discrete cytoplasmic regions, illustrating the use of this method to explore neuronal dysfunction in brain diseases. Lemelle et al. describe the use of TEM and synchrotron X-ray fluorescence for quasi-correlative nanoimaging and sub-cellular trace element quantification of rat brain tissue. They further observe elemental (iron and sulfur) dyshomeostasis in cytoplasmic granules when overexpressing alpha -synuclein protein associated with Parkinson's disease, demonstrating the usefulness of this method to further explore dysfunctions at organelle levels in brain diseases.
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Lemonnier, N., Homberg, C., Roche, V., Rocher, M., Boullier, A. M., & Schnyder, J. (2020). Microstructures of bedding-parallel faults under multistage deformation: Examples from the Southeast Basin of France. Journal Of Structural Geology, 140.
Résumé: We conducted a microstructural analysis of bedding-parallel faults (BPFs) in Mesozoic clay-rich layers of the Southeast Basin of France. Various microstructures are recognized in thin sections under a petrographic microscope and by cathodoluminescence. The microscale observations are combined with outcrop observations from previous studies to provide insight into the origin of the BPFs and their evolution during successive phases of deformation in a basin that had a polyphase tectonic history. The BPFs slipped while normal faults were formed during the Oligocene extension. Then, another phase of slip occurred later during the basin inversion. These two phases of deformation are expressed by recurrent crack-seal veins, pull-apart veins and stylolites. In addition, calcite veins with an elongate blocky morphology suggest an opening normal to bedding before the reactivation. The BPFs initiated in clay layers that were shallow dipping. Such conditions may appear mechanically unfavourable for an opening normal to bedding or a shearing parallel to bedding. We suggest that the role of rock anisotropy is critical. This study furthermore demonstrates that BPFs can be long-lived brittle structures that may record successive tectonic events.
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Levy, L., Fridriksson, T., Findling, N., Lanson, B., Fraisse, B., Marino, N., et al. (2020). Smectite quantification in hydrothermally altered volcanic rocks. Geothermics, 85.
Résumé: In volcanic environments, the presence of smectite may indicate recent hydrothermal circulations. Smectite is also responsible for enhanced rock electrical conductivity, as well as mechanical weakening. Therefore, quantifying smectite is important in geothermal exploration. Smectite identification requires X-ray diffraction (XRD) but quantification based on XRD is time-consuming and not always accurate. In the present study, we investigate the use of an optimized unbuffered Cation Exchange Capacity (CEC) determination, by back-titration of the Copper-triethylenetetramine(II) “Cu-trien” molecule, to quantify the smectite content of altered volcanic rock samples. We establish that a satisfying trade-off between the instrument uncertainty and an independant systematic error is theoretically reached for a fraction of reactants consumed of about 30% at the end of the exchange reaction. We suggest a modification to classical protocols to fall in that range. Finally, we show that optimized CEC determination by Cu-trien are a direct measure of the smectite weight fraction in altered volcanic samples, with an average CEC of pure smectite of 90 +/- 5 meq/100 g.
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Li, L., Bou, P., & Campillo, M. (2020). Observation and explanation of spurious seismic signals emerging in teleseismic noise correlations. Solid Earth, 11(1), 173–184.
Résumé: Deep body waves have been reconstructed from seismic noise correlations in recent studies. The authors note their great potential for deep-Earth imaging. In addition to the expected physical seismic phases, some spurious arrivals having no correspondence in earthquake seismograms are observed from the noise correlations. The origins of the noise-derived body waves have not been well understood. Traditionally, the reconstruction of seismic phases from inter-receiver noise correlations is attributed to the interference between waves from noise sources in the stationary-phase regions. The interfering waves emanating from a stationary-phase location have a common ray path from the source to the first receiver. The correlation operator cancels the common path and extracts a signal corresponding to the inter-receiver ray path. In this study, with seismic noise records from two networks at teleseismic distance, we show that noise-derived spurious seismic signals without correspondence in real seismograms can arise from the interference between waves without a common ray path or common slowness. These noise-derived signals cannot be explained by traditional stationary-phase arguments. Numerical experiments reproduce the observed spurious signals. These signals still emerge for uniformly distributed noise sources, and thus are not caused by localized sources. We interpret the presence of the spurious signals with a less restrictive condition of quasi-stationary phase: providing the time delays between interfering waves from spatially distributed noise sources are close enough, the stack of correlation functions over the distributed sources can still be constructive as an effect of finite frequencies, and thereby noise-derived signals emerge from the source averaging.
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Li, L., Boue, P., Retailleau, L., & Campillo, M. (2020). Spatiotemporal Correlation Analysis of Noise-Derived Seismic Body Waves With Ocean Wave Climate and Microseism Sources. Geochemistry Geophysics Geosystems, 21(9).
Résumé: Seismic signals can be extracted from ambient noise wavefields by the correlation technique. Recently, a prominentP-type phase was observed from teleseismic noise correlations in the secondary microseism period band. The phase is namedP(dmc)in this paper, corresponding to its origin from the interference between the directPwaves transmitting through the deep mantle and the core (PandPKPabwaves). We extract the phase by correlating noise records from two seismic networks in the Northern Hemisphere and locate the microseism sources that are efficient for theP(dmc)construction in the South Pacific. We investigate the spatiotemporal links of theP(dmc)signal with global oceanic waves and microseism sources. Interestingly, the correlation with wave height is higher in several regions surrounding the effective source region, rather than in the effective source region. TheP(dmc)amplitude is highly correlated with the power of the effective microseism sources. Also, it is apparently correlated with ineffective sources in the Southern Hemisphere and anticorrelated with sources in the Northern Hemisphere. We ascribe the correlation with the ineffective southern sources to the spatiotemporal interconnections of the southern sources. The anticorrelation with northern sources can be explained by the reverse seasonal patterns between the southern and northern sources and by that the northern sources impede the signal construction. The signal construction from noise correlations relies on the competition between the effective and ineffective sources, not just on the power of the effective sources. This principle should be valid in a general sense for noise-derived signals.
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Li, L., Tan, J. Q., Schwarz, B., Stanek, F., Poiata, N., Shi, P. D., et al. (2020). Recent Advances and Challenges of Waveform-Based Seismic Location Methods at Multiple Scales. Reviews Of Geophysics, 58(1).
Résumé: Source locations provide fundamental information on earthquakes and lay the foundation for seismic monitoring at all scales. Seismic source location as a classical inverse problem has experienced significant methodological progress during the past century. Unlike the conventional traveltime-based location methods that mainly utilize kinematic information, a new category of waveform-based methods, including partial waveform stacking, time reverse imaging, wavefront tomography, and full waveform inversion, adapted from migration or stacking techniques in exploration seismology has emerged. Waveform-based methods have shown promising results in characterizing weak seismic events at multiple scales, especially for abundant microearthquakes induced by hydraulic fracturing in unconventional and geothermal reservoirs or foreshock and aftershock activity potentially preceding tectonic earthquakes. This review presents a comprehensive summary of the current status of waveform-based location methods, through elaboration of the methodological principles, categorization, and connections, as well as illustration of the applications to natural and induced/triggered seismicity, ranging from laboratory acoustic emission to field hydraulic fracturing-induced seismicity, regional tectonic, and volcanic earthquakes. Taking into account recent developments in instrumentation and the increasing availability of more powerful computational resources, we highlight recent accomplishments and prevailing challenges of different waveform-based location methods and what they promise to offer in the near future. Plain language summary Earthquakes are a common physical phenomenon involving ground shaking and rupturing of the surface of the Earth. In addition to the well-known catastrophic tectonic earthquakes, similar vibration sources also appear at various scales in engineering fields, such as acoustic emissions resulting from microcracks in building walls and bridges, rock bursts in mines, microseismic events generated by mining and fluid injection/extraction, and microseisms caused by crustal activity. Seismic information provides a powerful tool for geophysical and engineering surveys. The source location describes the spatial and temporal extent of an earthquake and lays the foundation for seismic monitoring. Seismic location methods have made significant progress over the last century. Specifically, a category of new waveform-based location methods has emerged as a counterpart of conventional traveltime-based inversion. These methods directly utilize the notion of a wavefield and, very similar to an optical lens, aim at spatially focusing a source's emitted energy. Waveform-based methods have provided robust and effective source location results at various scales. We summarize the development history and current state of waveform-based location methods and discuss the advantages and challenges through their applications for seismic source location at multiple scales.
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Li, Y., Brossier, R., & Metivier, L. (2020). 3D frequency-domain elastic wave modeling with the spectral element method using a massively parallel direct solver. Geophysics, 85(2), T71–T88.
Résumé: Complex topography, the free-surface boundary condition, and anelastic properties of media should be accounted for in the frame of onshore geophysical prospecting imaging, such as full-waveform inversion (FWI). In this context, an accurate and efficient forward-modeling engine is mandatory. We have performed 3D frequency-domain anisotropic elastic wave modeling by using the highly accurate spectral element method and a sparse multifrontal direct solver. An efficient approach similar to computing the matrix-vector product in the time domain is used to build the matrix. We validate the numerical results by comparing with analytical solutions. A parallel direct solver, the sparse direct multifrontal massively parallel solver (MUMPS), is used to solve the linear system. We find that a hybrid implementation of message passing interface and open multiprocessing is more efficient in flops and memory cost. The influence of the deformed mesh, free-surface boundary condition, and heterogeneity of media on MUMPS performance is negligible. Complexity analysis suggests that the memory complexity of MUMPS agrees with the theoretical order O(N-4) (or O(N-3.5) with an efficient matrix reordering method) for an N-3 grid when nontrivial topography is considered. With the available resources, we conduct a moderate scale modeling with a subset of the SEAM Phase II Foothills model, where 60 wavelengths in the x-axis are propagated. Computing one gradient of FWI based on this model using the frequency-domain modeling is shown to require similar or fewer computational resources than what would be required for a time-domain solver, depending on the number of sources, while larger memory is necessary. An estimation of the increasing trend indicates that approximately 20 Tb of memory would be required for a 50 x 50 x 50 wavelength modeling. The limit of MUMPS scalability hinders the application to larger scale applications.
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Liang, X. R., Post, J. E., Lanson, B., Wang, X. M., Zhu, M. Q., Liu, F., et al. (2020). Coupled morphological and structural evolution of delta-MnO2 to alpha-MnO2 through multistage oriented assembly processes: the role of Mn(iii). Environmental Science-Nano, 7(1), 238–249.
Résumé: alpha-MnO2 is a typical tunneled Mn oxide (TMO) that is frequently associated with delta-MnO2 in the environment and exhibits strong adsorption and oxidation activity. The morphology of alpha-MnO2, which is controlled by an oriented attachment (OA) process, is one of the key factors affecting its reactivity. However, the detailed crystal growth process and coupling between morphology and structure of alpha-MnO2 during OA processes remain poorly understood. We propose that the transformation of layer-based delta-MnO2 to tunnel-based alpha-MnO2 occurs via a multistage OA process. In the initial stage, the produced delta-MnO2 nanoflakes are found to spontaneously self-assemble into a nanoribbon with a large number of lattice defects via edge-to-edge OA. The presence of lattice defects promotes the generation of oxygen vacancies, and the Mn(iv) ions in the [MnO6] octahedral layers of delta-MnO2 are reduced to Mn(iii)/Mn(ii). The reduced ions subsequently migrate from the [MnO6] octahedral layers to the interlayers during this process. The hydroxide which acts in coordination with the interlayer Mn(iii)/Mn(ii) and oxygen atoms coordination with adjacent nanoribbons attach to each other driven by hydrogen bonding and form primary nanorods through a face-to-face OA mechanism along the c-axis. Concomitantly, the bonding of [Mn(iii)O-6] octahedra in the interlayer of the nanoribbons with adjacent [MnO6] octahedral layers leads to the fabrication of a new alpha-MnO2 tunnel structure from the original delta-MnO2. These findings provide insights into both the transformation mechanisms of the layer-based to the tunnel-based nanoparticles and methods for the efficient and controlled synthesis of nanomaterials.
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Lobayan, R. M., Bochicchio, R. C., & del Valle, C. P. (2020). Topological population analysis and pairing/unpairing electron distribution evolution: Atomic B3(+) cluster bending mode, a case study. Journal Of Molecular Graphics & Modelling, 100.
Résumé: Local and non-local topological treatment of electronic distributions are applied to a simple out of equilibrium case of an electron-deficient three-atom cluster, B3(+). The bending movement is described in detail through the onset and disappearance of critical points defining two kinds of molecular structures, characterizing a transition state (TS) and predicting two stable equilibrium geometries. All points in this rich evolution and the structural change in the out of equilibrium conformations has been featured and distinguished by the behavior of the population magnitudes and of the paired and unpaired electron densities within the non-local and local points of view of the topological formalism. The unpaired or electron hole density appears as relevant in both versions, the non-local or integrated one, in which it is sometimes called free-valence and also for its complementary counterpart, the local one, to describe and to quantify the interatomic interactions. The stability of the cluster B3(+) is characterized in terms of a topologically defined ring structure and the highest total twoand three-center populations, thus showing the role of the geometry, the covalence, and the complex patterns. Consideration of the electron correlation effects constitutes the basement of the results gathered, thus displaying their influence in the formation and breaking of boron bonding interactions. (C) 2020 Elsevier Inc. All rights reserved.
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Loncke, L., Roest, W. R., Klingelhoefer, F., Basile, C., Graindorge, D., Heuret, A., et al. (2020). Transform Marginal Plateaus. Earth-Science Reviews, 203.
Résumé: Numerous submarine plateaus form highstanding bathymetric highs at continent to ocean transitions. Due to their proximity to continents, they have been frequently labelled “marginal plateaus”, although this term has not been clearly defined or associated with a specific geology or geodynamic process. Until now, these elevations have been interpreted as submerged thinned continental fragments detached from continents, basaltic buildups formed by hotspots, volcanic margins or oceanic plateaus. Many of these plateaus formed at transform margins connecting oceanic basins of contrasted ages. We propose for the first time to define and review a class of marginal plateaus related to a specific tectonic setting: “Transform Marginal Plateaus” (TMPs). Based on a compilation of 20 TMPs around the world, we show that most of them have a polyphased history and have undergone at least one major volcanic phase. Our review highlights in particular a hitherto unrecognized close link between hotspots, volcanic activity and transform margins. We also propose that, due to their polyphased history, TMPs may contain several successive basins and overlooked long-lived sedimentary archives. We finally highlight that, because these TMPs were transform plate boundaries perpendicular or oblique to surrounding rifts, many of them were close to last-contact points during final continental breakup and may have formed land bridges or bathymetric highs between continents. Therefore, we discuss broader scientific issues, such as the interest of TMPs in recording and studying the onset and variations of oceanic currents or past biodiversity growth, bio-connectivity and lineage evolution.
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Lott, M., Roux, P., Garambois, S., Gueguen, P., & Colombi, A. (2020). Evidence of metamaterial physics at the geophysics scale: the METAFORET experiment. Geophysical Journal International, 220(2), 1330–1339.
Résumé: The METAFORET experiment was designed to demonstrate that complex wave physics phenomena classically observed at the meso- and microscales in acoustics and in optics also apply at the geophysics scale. In particular, the experiment shows that a dense forest of trees can behave as a locally resonant metamaterial for seismic surface waves. The dense arrangement of trees anchored into the ground creates anomalous dispersion curves for surface waves, which highlight a large frequency band-gap around one resonant frequency of the trees, at similar to 45 Hz. This demonstration is carried out through the deployment of a dense seismic array of similar to 1000 autonomous geophones providing seismic recordings under vibrating source excitation at the transition between an open field and a forest. Additional geophysical equipment was deployed (e.g. ground-penetrating radar, velocimeters on trees) to provide essential complementary measurements. Insights and interpretations on the observed seismic wavefield, including the attenuation length, the intensity ratio between the field and the forest and the surface wave polarization, are validated with 2-D numerical simulations of trees over a layered half-space.
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Lott, M., Roux, P., Seydoux, L., Tallon, B., Pelat, A., Skipetrov, S., et al. (2020). Localized modes on a metasurface through multiwave interactions. Physical Review Materials, 4(6).
Résumé: In this paper, we describe the manifestation of localized states of a diffuse elastic wavefield inside a two- dimensional metamaterial made of a collection of vertical long beams glued to a thin plate. Through mesoscopic physics, we demonstrate that localized states arise due to multiwave interactions at the beam-plate attachment when the beams act as coupled resonators for both compressional and flexural resonances on the metasurface. In practice, when the compressional resonance of the beams clamps the plate on a large frequency band gap, thus preventing wave propagation inside the metamaterial area, the flexural resonance of the same beams permits evanescent waves to be diffused on a narrow frequency band between clusters of neighboring beams. This experiment physically highlights a tight-binding-like coupling in the localized regime for this two-dimensional metamaterial.
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Lozano, A., Ayora, C., & Fernandez-Martinez, A. (2020). Sorption of rare earth elements on schwertmannite and their mobility in acid mine drainage treatments. Applied Geochemistry, 113.
Résumé: Rare Earth Elements (REE) are nowadays considered critical raw materials due to their increasing use in modern industry and their shortage of supply. Acid mine drainage (AMD) contains REE concentrations several orders of magnitude higher than the rest of continental and marine waters, and the sludge from its treatment may become a supplementary source of REE. Schwertmannite, a Fe(III)-sulfate-hydroxide is the most common mineral precipitated from AMD and a main constituent of the neutralization sludge. The objective of this work is to study the mechanism of REE retention in synthetic schwertmannite and to predict the REE behavior in a column experiment mimicking an AMD passive remediation system. Suspensions of synthetic schwertmannite in sulfate solutions show that Y and the lanthanides are effectively sorbed at pH values higher than 4.5, and sorption is complete at pH values higher than 6.5. The experimental partition coefficients clearly show a preferential enrichment of heavy REE in the solid phase. Unlike the rest of the REE, Sc sorption occurred at a lower pH, from 3 to 5. The experimental results have been described with a non-electrostatic surface complexation model in which the aqueous complex MSO4+ exchanges with two H+ from the surface of schwertmannite, forming a bidentate surface complex, (XO)(2)MSO4-. Scandium sorption was also accurately predicted with the addition of a second bidentate surface complex, (XO)(2)MOH. The equilibrium constants for REE sorption on schwertmannite calculated in the present work, together with those for REE sorption on basaluminite (Lozano et al., 2019, GCA, 258, 50-62) were used to model the behavior of different REE observed in the pore water and solid of a column experiment. Schwertmannite and basaluminite were the main solid phases formed due to the progression of the neutralization. First schwertmannite precipitated at pH below 4 and then basaluminite precipitated at pH above 4. Both minerals can sorb REE in a similar pH range. However, since Y and the lanthanides sorbed at pH values higher than 5, their sorption only occurred on basaluminite. In contrast, the Sc sorption edge extended from pH 3 to 5 and Sc partially sorbed on schwertmannite. As a practical consequence, REE preferentially accumulated in the basaluminite residue of AMD neutralization systems, but a minor fraction of Sc can be retained in the schwertmannite waste.
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Lu, Y., Stehly, L., Brossier, R., & Paul, A. (2020). Imaging Alpine crust using ambient noise wave-equation tomography. Geophysical Journal International, 222(1), 69–85.
Résumé: We present an improved crustal Vs model and Moho depth map using ambient noise wave-equation tomography. The so-called 'ambient noise wave-equation tomography' is a method to invert seismic ambient noise phase dispersion data based on elastic waveform simulation, which accounts for 3-D and finite-frequency effects. We use cross-correlations of up to 4 yr of continuous vertical-component ambient seismic noise recordings from 304 high-quality broad-band stations in the Alpine region. We use model LSP_Eucrust1.0 obtained from traditional ambient noise tomography as initial model, and we iteratively improve the initial model by minimizing frequency-dependent phase traveltime differences between the observed and synthetic waveforms of Rayleigh waves in the period range 10-50 s. We obtain the final model after 15 iterations with similar to 65 percent total misfit reduction compared to the initial model. At crustal depth, the final model significantly enhances the amplitudes and adjusts the shapes of velocity anomalies. At Moho and upper-mantle depth, the final model corrects an obvious systematic velocity shift of the initial model. The resulting isovelocity Moho map confirms a Moho step along the external side of the external crystalline massifs of the northwestern Alps and reveals underplated gabbroic plutons in the lower most crust of the central and eastern Alps. Ambient noise wave-equation tomography turns out to be a useful tool to refine shear wave velocity models obtained by traditional ambient noise tomography based on ray theory.
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Lubbers, N., Agarwal, A., Chen, Y., Son, S., Mehana, M., Kang, Q. J., et al. (2020). Modeling and scale-bridging using machine learning: nanoconfinement effects in porous media. Scientific Reports, 10(1).
Résumé: Fine-scale models that represent first-principles physics are challenging to represent at larger scales of interest in many application areas. In nanoporous media such as tight-shale formations, where the typical pore size is less than 50 nm, confinement effects play a significant role in how fluids behave. At these scales, fluids are under confinement, affecting key properties such as density, viscosity, adsorption, etc. Pore-scale Lattice Boltzmann Methods (LBM) can simulate flow in complex pore structures relevant to predicting hydrocarbon production, but must be corrected to account for confinement effects. Molecular dynamics (MD) can model confinement effects but is computationally expensive in comparison. The hurdle to bridging MD with LBM is the computational expense of MD simulations needed to perform this correction. Here, we build a Machine Learning (ML) surrogate model that captures adsorption effects across a wide range of parameter space and bridges the MD and LBM scales using a relatively small number of MD calculations. The model computes upscaled adsorption parameters across varying density, temperature, and pore width. The ML model is 7 orders of magnitude faster than brute force MD. This workflow is agnostic to the physical system and could be generalized to further scale-bridging applications.
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Ma, B., Fernandez-Martinez, A., Kang, M. L., Wang, K. F., Lewis, A. R., Maffeis, T. G. G., et al. (2020). Influence of Surface Compositions on the Reactivity of Pyrite toward Aqueous U(VI). Environmental Science & Technology, 54(13), 8104–8114.
Résumé: Pyrite plays a significant role in governing the mobility of toxic uranium in an anaerobic environment via an oxidation-reduction process occurring at the mineral-water interface, but the factors influencing the reaction kinetics remain poorly understood. In this study, natural pyrites with different impurities (Pb, As, and Si) and different surface pretreatments were used to react with aqueous U(VI) from pH similar to 3.0 to similar to 9.5. Both aqueous and solid results indicated that freshly crushed pyrites, which do have more surface Fe2+/Fe3+ and S2- sites that were generated from breakage of Fe(S)-S bonds during ball milling, exhibited a much stronger reactivity than those treated with acid washing. Besides, U(VI) reduction which involves the possible intermediate U(V) and the formation of hyperstoichiometric UO2+x(s) was found to preferentially occur at Pb- and As-rich spots on the pyrite surface, suggesting that the incorporated impurities could act as reactive sites because of the generation of lattice defects and galena- and arsenopyrite-like local configurations. These reactive surface sites can be removed by acid washing, leaving a pyrite surface nearly inert toward aqueous U(VI). Thus, reactivity of pyrite toward U(VI) is largely governed by its surface compositions, which provides an insight into the chemical behavior of both pyrite and uranium in various environments.
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Ma, B., Fernandez-Martinez, A., Wang, K. F., Made, B., Henocq, P., Tisserand, D., et al. (2020). Selenite Sorption on Hydrated CEM-V/A Cement in the Presence of Steel Corrosion Products: Redox vs Nonredox Sorption. Environmental Science & Technology, 54(4), 2344–2352.
Résumé: Reinforced cementitious structures in nuclear waste repositories will act as barriers that limit the mobility of radionuclides (RNs) in case of eventual leakage. CEM-V/A cement, a ternary blended cement with blast furnace slag (BFS) and fly ash (FA), could be qualified and used in nuclear waste disposal. Chemical interactions between the cement and RNs are critical but not completely understood. Here, we combined wet chemistry methods, synchrotron-based X-ray techniques, and thermodynamic modeling to explore redox interactions and nonredox sorption processes in simulated steel-reinforced CEM-V/A hydration systems using selenite as a molecular probe. Among all of the steel corrosion products analyzed, only the addition of Fe-0 can obviously enhance the reducing ability of cement toward selenite. In comparison, steel corrosion products showed stronger reducing power in the absence of cement hydrates. Selenium K-edge X-ray absorption spectroscopy (XAS) revealed that selenite immobilization mechanisms included nonredox inner-/outer-sphere complexations and reductive precipitations of FeSe and/or Se(0). Importantly, the hydrated pristine cement showed a good reducing ability, driven by ferrous phases and (bi)sulfides (as shown by sulfur K-edge XAS) originated from BFS and FA. The overall redox potential imposed by hydrated CEM-V/A was determined, hinting to a redox shift in underground cementitious structures.
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Magen, Y., Ziv, A., Inbal, A., Baer, G., & Hollingsworth, J. (2020). Fault Rerupture during the July 2019 Ridgecrest Earthquake Pair from Joint Slip Inversion of InSAR, Optical Imagery, and GPS. Bull. Seismol. Soc. Amer., 110(4), 1627–1643.
Résumé: The Ridgecrest earthquake pair ruptured a previously unknown orthogonal fault system in the eastern California shear zone. The stronger of the two, an M-w 7.1 earthquake that occurred on 6 July 2019, was preceded by an M-w 6.4 foreshock that occurred 34 hr earlier. In this study, distinct final slip distributions for the two earthquakes are obtained via joint inversion of Interferometric Synthetic Aperture Radar (InSAR), optical imagery, and Global Positioning System (GPS) measurements. Special attention is paid to the merging of dense (e.g., InSAR and optical imagery) and sparse geodetic (e.g., GPS) datasets. In addition, a new approach is introduced for data and model discretization through intermittent model- and data-space reconditioning that stabilizes the inversion, thus ensuring that small changes in the data space do not cause disproportionate large changes to the model space. Although the coseismic slip of the M-w 6.4 earthquake was complex, involving three distinct asperities distributed among an intersecting orthogonal set of faults, the coseismic slip of the M-w 7.1 earthquake was limited to the main northwest-striking fault. In addition to the M-w 7.1 earthquake, that northwest-striking fault plane also hosted one of the M-w 6.4 asperities. Slip on this coplanar foreshock asperity increased the shear stress at the future site of the M-w 7.1 hypocenter, and triggered a vigorous aftershock activity on the main northwest fault that culminated in its rupture. This, in turn, reactivated the coplanar foreshock asperity. In addition to failing twice within 34 hr, we find that the reruptured asperity slipped about six times more during the M-w 7.1 than during the M-w 6.4 earthquake. This repeated failure is indicative of an incomplete stress drop and premature rupture arrest during the M-w 6.4 foreshock, requiring an efficient frictional strengthening and emphasizing the causal link between highly rate-dependent friction, dynamic frictional restrengthening, and partial stress drop that has been observed in numerical studies of frictional sliding.
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Magrani, F., Valla, P. G., Gribenski, N., & Serra, E. (2020). Glacial overdeepenings in the Swiss Alps and foreland: Spatial distribution and morphometrics. Quaternary Science Reviews, 243.
Résumé: Overdeepenings (ODs) are erosional features that have been excavated below the regional sea/fluvial base level to produce closed topographic basins. Accessing bedrock topography and OD volume is often challenging. Hence, despite constituting major landscape features and being widespread in (paleo-) glaciated regions, ODs have been overlooked and the subglacial processes involved in their evolution have remained debated. In the Swiss Alpine foreland and valleys, ODs are commonly found filled with water or large volumes of sediment. Using a GIS-Matlab approach based on topographic datasets and bedrock contour-curves, we mapped the spatial distribution of ODs in Switzerland and adjacent areas in the ice-free Alpine areas. The majority of the mapped ODs occurs in very-low bedrock erosional resistance, where ODs are larger, wider and shallower than in medium to high bedrock erosional resistance domains, evidencing a strong lithological control on OD geometry. Longitudinal asymmetry and hypsometric integral suggest a dominance of quarrying during OD evolution and, for selected glacial catchments, headward erosion propagation or high sediment evacuation efficiency. OD surface data (surface and length) can be tentatively used for extracting OD subsurface metrics (depths, nested valleys and first-order volume estimates). Our data seem to indicate that ODs may initiate as multiple small nested valleys and progress to a single and connected depression. Transversal cross-sections also suggest a negative feedback between the erosion potential for deep carving and the presence of low-resistance bedrock, where subglacial meltwater infiltration could have played a key role in OD evolution. Although insightful relationships have been evidenced for ODs in the Swiss Alps and foreland, we have also observed a high spatial variability in key OD metrics such as surface area and depth. This results in general (first-order) interpretations at regional scale, but currently prevent to quantitatively constrain physical subglacial processes at their origin. Comparisons with existing OD datasets under present-day ice (Greenland, Antarctica and modern Swiss glaciers) place our results in a broader context and allow a step forward in our understanding of the complex patterns and mechanisms of (sub-)glacial erosion and resulting landforms. (C) 2020 The Authors. Published by Elsevier Ltd.
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Makhoul, N., Navarro, C., Lee, J. S., & Gueguen, P. (2020). A comparative study of buried pipeline fragilities using the seismic damage to the Byblos wastewater network. International Journal Of Disaster Risk Reduction, 51.
Résumé: The seismic damage to buried pipelines could be disruptive in terms of safety, life quality, and socioeconomic impacts. In this paper, we investigate the extensive list of available buried pipelines fragilities: we select a series of typical and interesting fragilities in terms of different ground motions, diverse pipeline and soil types typologies and nature (i.e. empirical, analytical); and then we compare the seismic damage results. The aim is to have a palpable overview of the variability of damage results while using different selected buried pipelines fragilities, various ground motion parameters and different hazard scenarios. To achieve this comparative study, the buried pipeline wastewater network of Byblos, Lebanon, is used as a case study. The methodology used to assess damage to the waste-water network encompasses hazard assessment, wastewater network inventory, wastewater damage functions, and model development. The Ergo platform was especially updated by implementing the list of selected fragilities to achieve the damage to wastewater comparison in this article. Results: and recommendations are offered; first for a more adequate usage of those fragilities; second, for improvement of existing and future developed buried pipelines fragility functions; and third, for the Byblos wastewater pipelines network, allowing the establishment of a resilient earthquake preparedness strategy and recovery plan for infrastructure network in Byblos.
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Maldanis, L., Hickman-Lewis, K., Verezhak, M., Gueriau, P., Guizar-Sicairos, M., Jaqueto, P., et al. (2020). Nanoscale 3D quantitative imaging of 1.88 Ga Gunflint microfossils reveals novel insights into taphonomic and biogenic characters. Scientific Reports, 10(1).
Résumé: Precambrian cellular remains frequently have simple morphologies, micrometric dimensions and are poorly preserved, imposing severe analytical and interpretational challenges, especially for irrefutable attestations of biogenicity. The 1.88 Ga Gunflint biota is a Precambrian microfossil assemblage with different types and qualities of preservation across its numerous geological localities and provides important insights into the Proterozoic biosphere and taphonomic processes. Here we use synchrotron-based ptychographic X-ray computed tomography to investigate well-preserved carbonaceous microfossils from the Schreiber Beach locality as well as poorly-preserved, iron-replaced fossil filaments from the Mink Mountain locality, Gunflint Formation. 3D nanoscale imaging with contrast based on electron density allowed us to assess the morphology and carbonaceous composition of different specimens and identify the minerals associated with their preservation based on retrieved mass densities. In the Mink Mountain filaments, the identification of mature kerogen and maghemite rather than the ubiquitously described hematite indicates an influence from biogenic organics on the local maturation of iron oxides through diagenesis. This non-destructive 3D approach to microfossil composition at the nanoscale within their geological context represents a powerful approach to assess the taphonomy and biogenicity of challenging or poorly preserved traces of early microbial life, and may be applied effectively to extraterrestrial samples returned from upcoming space missions.
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Malvoisin, B., Austrheim, H., Hetenyi, G., Reynes, J., Hermann, J., Baumgartner, L. P., et al. (2020). Sustainable densification of the deep crust. Geology, 48(7), 673–677.
Résumé: The densification of the lower crust in collision and subduction zones plays a key role in shaping the Earth by modifying the buoyancy forces acting at convergent boundaries. It takes place through mineralogical reactions, which are kinetically favored by the presence of fluids. Earthquakes may generate faults serving as fluid pathways, but the influence of reactions on the generation of seismicity at depth is still poorly constrained. Here we present new petrological data and numerical models to show that in the presence of fluids, densification reactions can occur very fast, on the order of weeks, and consume fluids injected during an earthquake, which leads to porosity formation and fluid pressure drop by several hundreds of megapascals. This generates a mechanically highly unstable system subject to collapse and further seismic-wave emission during aftershocks. This mechanism creates new pathways for subsequently arriving fluids, and thus provides a route for self-sustained densification of the lower crust.
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Malvoisin, B., Zhang, C., Muntener, O., Baumgartner, L. P., & Kelemen, P. B. (2020). Measurement of Volume Change and Mass Transfer During Serpentinization: Insights From the Oman Drilling Project. Journal Of Geophysical Research-Solid Earth, 125(5).
Résumé: Serpentinization plays a key role on the evolution of the physicochemical properties of the mantle lithosphere. The rate of serpentinization reactions idiscontinuities in the platelet separating ?1-?m-long segments of clinopyroxene. The presence of traces of magnetite in the discontinuities and their orientation in parallel to other magnetite grains suggest that the discontinuities were formerly filled with magnetite, which reacted during serpentinizations controlled by the transport of fluid, which itself depends on volume change during reaction. Element transfer can strongly modify the magnitude and sign of volume change. Here, we measure solid volume change and element transport perpendicular to a serpentine vein in a serpentinized dunite collected at depth during the Oman Drilling Project. The sample is extensively replaced (extent of reaction > 80 %) by a serpentine/brucite mixture parallel to a main serpentine vein network. The Mg content of serpentine and brucite indicates reaction with a small amount of fluid at temperatures below 100 degrees C. Concentrations of fluid-mobile trace elements (Na, Ca, Sr, Rb, and Ba) decrease perpendicular to the main vein. Primary olivine contains parallel platelets of a clinopyroxene/magnetite symplectite. Tomography at the nanoscale reveals that these inclusions do not react during serpentinization but are cracked and displaced. We use these inert markers to measure a 59 % to 74 % positive volume change that is close to the 52 % expected for reaction in a closed system. Chemical data indicate no change in major element composition during reaction except for the addition of water. The initial olivine zoning in Al, Ti, V, Sc, and Cr is still preserved in serpentine and brucite. Serpentinization can thus be a local replacement process during which the solid volume homogeneously increases at the micrometer scale and the transport of aqueous species is limited.
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Manceau, A., Merkulova, M., Mathon, O., Glatzel, P., Murdzek, M., Batanova, V., et al. (2020). The Mode of Incorporation of As(-I) and Se(-I) in Natural Pyrite Revisited. Acs Earth And Space Chemistry, 4(3), 379–390.
Résumé: Pyrite (FeS2) from coal, sedimentary rocks, and hydrothermal ore deposits generally contains hazardous selenium (Se) and arsenic (As) that are released in natural waters through oxidative dissolution of the host. Knowing how As and Se are structurally incorporated into pyrite has important implications in controlling or preventing their release because trace metal(loid) substitution accelerates the dissolution of pyrite. Previous extended X-ray absorption fine structure (EXAFS) studies have reported that nominally monovalent arsenic clusters at the sulfur site form As-As pairs at 3.2 angstrom, whereas monovalent Se does not form Se-Se pairs at this distance for unknown reasons. Here, we revisit this question using As and Se K-edge X-ray absorption near-edge structure (XANES) and EXAFS spectroscopy complemented with atomistic calculations. We find that neither As nor Se atoms can be differentiated from a S atom at 3.2-3.3 angstrom with the cluster and dilute model-fits to As- and Se-EXAFS data yielding equivalent least-squares solutions. Thermodynamic calculations of Fe48As3S93 (3.8 wt % As) and Fe48Se3S93 (4.0 wt % Se) structures show that the formation of As-As pairs is energetically favorable and the formation of Se-Se pairs is unfavorable. Thus, the equilibrium distribution of As and Se predicted by calculation agrees with published EXAFS data. However, this agreement is incidental because EXAFS fits are ambiguous with the same EXAFS spectra being fit indifferently with a cluster and a dilute model. Regarding Se, the dilute model-fit is probably correct since Se-Se pairs are precluded thermodynamically. The situation is less clear for As. The lowest energy atomic arrangement of As in Fe48S93As3 is similar to the local structure of As in arsenopyrite (FeAsS), thus supporting the cluster model. However, the energy gain to total energy provided by the formation of As clusters decreases with decreasing As concentration, making them thermodynamically less favorable below 1.0 wt %.
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Manighetti, I., Perrin, C., Gaudemer, Y., Dominguez, S., Stewart, N., Malavieille, J., et al. (2020). Repeated giant earthquakes on the Wairarapa fault, New Zealand, revealed by Lidar-based paleoseismology. Scientific Reports, 10(1).
Résumé: The Mw 7.8 2016 Kaikoura earthquake ruptured the Kekerengu-Needle fault resulting in the loading of its eastern continuation, the Wairarapa fault. Since the most recent earthquake on Wairarapa occurred in 1855 and is one of the strongest continental earthquakes ever observed, it is critical to assess the seismic potential of the Wairarapa fault, which might be prone to break. Using Lidar data, we examine its bare-earth morphology and reveal similar to 650 mostly undiscovered offset geomorphic markers. Using a code we developed in earlier work, we automatically measure the lateral and vertical offsets of these markers providing more than 7000 well constrained measurements. The data document the lateral and vertical slip profiles of the 1855 earthquake for the first time and show its total slip reached similar to 20 m at surface. Modeling the entire offset dataset reveals 7 prior earthquakes ruptured the entire fault, each similarly producing 16.9 +/- 1.4 m dextral slip and similar to 0.6 m vertical slip at surface in the same central bend zone of the fault. Thus, the Wairarapa fault repeatedly produced giant earthquakes and is likely able to produce a similarly strong forthcoming event. The extreme large size of the Wairarapa earthquakes questions our understanding of earthquake physics.
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Mao, S. J., Mordret, A., Campillo, M., Fang, H. J., & van der Hilst, R. D. (2020). On the measurement of seismic traveltime changes in the time-frequency domain with wavelet cross-spectrum analysis. Geophysical Journal International, 221(1), 550–568.
Résumé: The spatial distribution of temporal variations in seismic wavespeed is key to understanding the sources and physical mechanisms of various geophysical processes. The imaging of wavespeed changes requires accurate measurements of traveltime delays with both high lapse-time and frequency resolutions. However, traditional methods for time-shift estimation suffer from their limited resolutions. In this paper we propose a new approach, the wavelet method, to measure the traveltime changes in the time-frequency domain. This method is based on wavelet cross-spectrum analysis, and can provide optimal time frequency joint resolution while being computationally efficient. It can deal not only with coda but also dispersive surface waves even in the presence of cycle skipping. Using synthetic coda, we show that the wavelet method can retrieve traveltime shifts more stably and accurately than traditional methods. An application at Salton Sea Geothermal Field indicates that the wavelet method is less affected by spectral smearing and better discriminates dv/v variations at different frequencies. Furthermore, upon investigations on synthetic coda, we illustrate that the bias on dv/v measurements due to changes in source frequency content is likely to be negligible, either with traditional methods or with the new wavelet method. The wavelet method sheds lights on applications of seismic interferometry that aim to locate changes in space.
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Margirier, A., Braun, J., Gautheron, C., Carcaillet, J., Schwartz, S., Jamme, R. P., et al. (2020). Climate control on Early Cenozoic denudation of the Namibian margin as deduced from new thermochronological constraints (vol 527, 115779, 2019). Earth And Planetary Science Letters, 531.
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Mariniere, J., Nocquet, J. M., Beauval, C., Champenois, J., Audin, L., Alvarado, A., et al. (2020). Geodetic evidence for shallow creep along the Quito fault, Ecuador. Geophysical Journal International, 220(3), 2039–2055.
Résumé: Quito, the capital city of Ecuador hosting similar to 2 million inhabitants, lies on the hanging wall of a similar to 60-km-long reverse fault offsetting the Inter-Andean Valley in the northern Andes. Such an active fault poses a significant risk, enhanced by the high density of population and overall poor building construction quality. Here, we constrain the present-day strain accumulation associated with the Quito fault with new Global Positioning System (GPS) data and Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) analysis. Far field GPS data indicate 3-5 mm yr(-1) of horizontal shortening accommodated across the fault system. In the central segment of the fault, both GPS and PS-InSAR results highlight a sharp velocity gradient, which attests for creep taking place along the shallowest portion of the fault. Smoother velocity gradients observed along the other segments indicate that the amount of shallow creep decreases north and south of the central segment. 2-D elastic models using GPS horizontal velocity indicate very shallow (<1 km) locking depth for the central segment, increasing to a few kilometres south and north of it. Including InSAR results in the inversion requires locking to vary both along dip and along strike. 3-D spatially variable locking models show that shallow creep occurs along the central 20-km-long segment. North and south of the central segment, the interseismic coupling is less resolved, and data still allows significant slip deficit to accumulate. Using the interseismic moment deficit buildup resulting from our inversions and the seismicity rate, we estimate recurrence time for magnitude 6.5 + earthquake to be between 200 and 1200 yr. Finally, PS-InSAR time-series identify a 2 cm transient deformation that occurred on a secondary thrust, east of the main Quito fault between 1995 and 1997.
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Marsan, D., & Tan, Y. J. (2020). Maximum Earthquake Size and Seismicity Rate from an ETAS Model with Slip Budget. Bulletin Of The Seismological Society Of America, 110(2), 874–885.
Résumé: We define a seismicity model based on (1) the epidemic-type aftershock sequence model that accounts for earthquake clustering, and (2) a closed slip budget at long timescale. This is achieved by not permitting an earthquake to have a seismic moment greater than the current seismic moment deficit. This causes the Gutenberg-Richter law to be modulated by a smooth upper cutoff, the location of which can be predicted from the model parameters. We investigate the various regimes of this model that more particularly include a regime in which the activity does not die off even with a vanishingly small spontaneous (i.e., background) earthquake rate and one that bears strong statistical similarities with repeating earthquake time series. Finally, this model relates the earthquake rate and the geodetic moment rate and, therefore, allows to make sense of this relationship in terms of fundamental empirical law (the Gutenberg-Richter law, the productivity law, and the Omori law) and physical parameters (seismic coupling, tectonic loading rate).
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Martinod, J., Gerault, M., Husson, L., & Regard, V. (2020). Widening of the Andes: An interplay between subduction dynamics and crustal wedge tectonics. Earth-Science Reviews, 204.
Résumé: Shortening of the continental lithosphere is generally accommodated by the growth of crustal wedges building above megathrusts in the mantle lithosphere. We show that the locus of shortening in the western margin of South America has largely been controlled by the geometry of the slab. Numerical models confirm that horizontal subduction favors compression far from the trench, above the asthenospheric wedge and steeply dipping segment of the subducting slab. As a result, a second crustal wedge grows in the hinterland of the continent, and widens the Andes. In the Bolivian orocline, this wedge corresponds to the Eastern Cordillera, whose growth was triggered by a major episode of horizontal subduction. When the slab returned to a steeper dip angle, shortening and uplift pursued, facilitated by the structural and thermo-chemical alteration of the continental lithosphere. We review the successive episodes of horizontal subduction that have occurred beneath South America at different latitudes and show that they explain the diachronic widening of the Andes. We infer that the present-day segmented physiography of the Andes results from the latitudinally variable, transient interplay between slab dynamics and upper plate tectonics over the Cenozoic. We emphasize that slab flattening, or absence thereof, is a major driving mechanism that sets the width of the Andes, at any latitude.
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Marty, N. C. M., Grangeon, S., Lassin, A., Made, B., Blanc, P., & Lanson, B. (2020). A quantitative and mechanistic model for the coupling between chemistry and clay hydration. Geochimica Et Cosmochimica Acta, 283, 124–135.
Résumé: It is proposed here to describe smectite water vapor desorption isotherms using an exchange formalism that quantitatively accounts for the different hydration states and thus different water contents. This approach makes it possible to reproduce both desorption isotherms and relative proportions of the different hydration states as determined by X-ray diffraction. The method is numerically robust and easy to implement in most reactive transport codes. The formalism is satisfactory from a phenomenological point of view and accounts for the influence of external parameters such as interlayer cation composition and solution cation composition and salinity on clay hydration. Furthermore, in contrast to most solid solution models, this approach focuses on the clay reactivity according to the charge and type of interlayer cation rather than on its solubility and therefore does not require the overall thermodynamic properties of the clay. In addition, such an explicit distinction of the hydration/cation exchange processes from the thermodynamic stability of smectite 2:1 layer allows the use of kinetics driving slow dissolution/precipitation rates if the number of exchange sites is related to the amount of clay minerals.
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Marty, N. C. M., Grangeon, S., Lassin, A., Made, B., Blanc, P., & Lanson, B. (2020). A quantitative and mechanistic model for the coupling between chemistry and clay hydration (vol 283, pg 124, 2020). Geochimica Et Cosmochimica Acta, 286, 462.
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Mathey, M., Walpersdorf, A., Sue, C., Baize, S., & Deprez, A. (2020). Seismogenic potential of the High Durance Fault constrained by 20 yr of GNSS measurements in the Western European Alps. Geophysical Journal International, 222(3), 2136–2146.
Résumé: Due to the steady moderate seismicity observed along the Briancon seismic arc, in the southwestern French Alps, three temporary GNSS (Global Navigation Satellite System) surveys took place in 1996, 2006 and 2011, across a similar to 50 x 60 km(2) wide area, to investigate the surface deformation field. The horizontal velocity field computed from these three surveys showed an east-west extension in the network. A fourth campaign was led in 2016, creating a 20 yr observation span, resulting in measurements which reach a sufficient accuracy to assess whether extension found within the Briancon network is localized onto any particular tectonic feature. Several faults in this area are known to be active normal faults. Assessing the localization of the deformation may lead to a better understanding of the active tectonics of the Alpine belt. To address this issue, a robust velocity field was computed from the combination of the different campaign and permanent GNSS data. Strain rate tensors were derived for the first time in this area on a 0.1 x 0.1 deg grid to assess the distribution of the deformation. The regional deformation appears localized in the Briancon area and reaches up to 20 +/- 5 nanostrain yr I in the centre of the network. The observed velocities were projected on a profile across the network and compared with modelled interseismic deformation to characterize the behaviour of the major active faults known in the study zone. While a two-fault model provides the best fit to the data, a single fault model has only marginally higher residuals, with parameters which are more consistent with the seismotectonics of the region. The localization of the single modelled fault is consistent with the location of the high Durance Fault (HDF). Therefore, we used the known geological location of this structure as a priori information in a block model to compute a fault slip rate at the interface between the two blocks. The velocities on the interface indicate 0.4-0.5 mm yr(-1) a of extension, and therefore strain accumulates along the HDF throughout the seismic cycle. The geodetically derived fault slip rate is converted into an equivalent seismic moment release rate, which is consistent within its uncertainty bounds with the known historical and instrumental seismicity of the Briancon area.
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McBeck, J., Aiken, J. M., Ben-Zion, Y., & Renard, F. (2020). Predicting the proximity to macroscopic failure using local strain populations from dynamic in situ X-ray tomography triaxial compression experiments on rocks. Earth And Planetary Science Letters, 543.
Résumé: Predicting the proximity of large-scale dynamic failure is a critical concern in the engineering and geophysical sciences. Here we use evolving contractive, dilatational, and shear strain deformation preceding failure in dynamic X-ray tomography experiments to examine which strain components best predict the proximity to failure. We develop machine learning models to predict the proximity to failure using time series of three-dimensional local incremental strain tensor fields acquired in rock deformation experiments under stress conditions of the upper crust. Three-dimensional scans acquired in situ throughout triaxial compression experiments provide a distribution of density contrasts from which we estimate the three-dimensional incremental strain that accumulates between each scan acquisition. Training machine learning models on multiple experiments of six rock types provides suites of feature importance that indicate the predictive power of each feature. Comparing the average importance of groups of features that include information about each strain component quantifies the ability of the contractive, dilatational and shear strain to predict the proximity of macroscopic failure. A total of 24 models of four machine learning algorithms with six rock types indicate that 1) the dilatational strain provides the best predictive power of the strain components, and 2) the intermediate values (25th-75th percentile) of the strain population provide the best predictive power of the statistics of the strain populations. In addition, the success of the predictions of models trained on one rock type and tested on other rock types quantifies the similarities and differences of the precursory strain accumulation process in the six rock types. These similarities suggest the potential existence of a unified theory of brittle rock deformation for a range of rock types. (C) 2020 Elsevier B.V. All rights reserved.
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McBeck, J., Ben-Zion, Y., & Renard, F. (2020). The mixology of precursory strain partitioning approaching brittle failure in rocks. Geophysical Journal International, 221(3), 1856–1872.
Résumé: We examine the strain accumulation and localization process throughout 12 triaxial compression experiments on six rock types deformed in an X-ray transparent apparatus. In each experiment, we acquire 50-100 tomograms of rock samples at differential stress steps during loading, revealing the evolving 3-D distribution of X-ray absorption contrasts, indicative of density. Using digital volume correlation (DVC) of pairs of tomograms, we build time-series of 3-D incremental strain tensor fields as the rocks are deformed towards failure. The Pearson correlation coefficients between components of the local incremental strain tensor at each stress step indicate that the correlation strength between pairs of local strain components, including dilation, contraction and shear strain, are moderate-strong in 11 of 12 experiments. In addition, changes in the local strain components from one DVC calculation to the next show differences in the correlations between pairs of strain components. In particular, the correlation of the local changes in dilation and shear strain tends to be stronger than the correlation of changes in dilation-contraction and contraction-shear strain. In 11 of 12 experiments, the most volumetrically frequent mode of strain accommodation includes a synchronized increase in multiple strain components. Early in loading, under lower differential stress, the most frequent strain accumulation mode involves the paired increase in dilation and contraction at neighbouring locations. Under higher differential stress, the most frequent mode is the paired increase in dilation and shear strain. This mode is also the first or second most frequent throughout each complete experiment. Tracking the mean values of the strain components in the sample and the volume of rock that each component occupies reveals fundamental differences in the nature of strain accumulation and localization between the volumetric and shear strain modes. As the dilative strain increases in magnitude throughout loading, it tends to occupy larger volumes within the rock sample and thus delocalizes. In contrast, the increasing shear strain components (left- or right-lateral) do not necessarily occupy larger volumes and so involve localization. Consistent with these evolutions, the correlation length of the dilatational strains tends to increase by the largest amounts of the strain components from lower to higher differential stress. In contrast, the correlation length of the shear strains does not consistently increase or decrease with increasing differential stress.
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McBeck, J., Cooke, M., & Renard, F. (2020). How the energy budget scales from the laboratory to the crust in accretionary wedges. Earth And Planetary Science Letters, 541.
Résumé: We investigate the scaling properties of the mechanical energy budget in accretionary prisms across five orders of magnitude, from the laboratory centimeter-scale to crustal kilometer-scale. We first develop numerical models that match the length scale, fault and material properties, surface topography, and fault geometries observed in scaled dry sand accretionary experiments. As we systematically increase the spatial dimensions of the numerical models by orders of magnitude, we calculate each component of the energy budget both before and after the first thrust fault pair develops. The increase of both the bulk stiffness and slip weakening distance from the laboratory-to crustal-scale produces a scale-invariant partitioning of the energy budget, relative to the total work done on the system. The components scale as power laws with exponents of three. Consequently, accurate laboratory simulations of the energetics of deformation within crustal accretionary wedges require careful scaling of the stiffness and slip weakening distance. Preceding thrust fault development at both the laboratory and crustal scale, the internal work consumes the largest portion of the budget (67-77%) and frictional work consumes the next largest portion (17-27%). Following thrusting, frictional work and internal work consume similar portions of the energy budget (38-50%). The sum of the remaining energy budget components, including gravitational work, seismic work, and the work of fracture propagation, consume <10-15% of the total energy budget preceding and following thrust fault development. (C) 2020 Elsevier B.V. All rights reserved.
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McBeck, J. A., Aiken, J. M., Mathiesen, J., Ben-Zion, Y., & Renard, F. (2020). Deformation Precursors to Catastrophic Failure in Rocks. Geophysical Research Letters, 47(24).
Résumé: Forecasting the timing of catastrophic failure, such as crustal earthquakes, has been a central concern for centuries. Such forecasting requires identifying signals that evolve or accelerate in the precursory phase leading to failure, and the subset of signals that may be detected in the crust. We develop machine learning models to predict the proximity of catastrophic failure in synchrotron X-ray tomography triaxial compression experiments on rocks using characteristics of evolving fracture networks. We then examine the characteristics that most strongly influence the model results, and thus may be considered the best predictors of the proximity of macroscopic failure. The resulting suite of predictive parameters underscores the importance of dilation in the precursory phase leading to catastrophic failure. The results indicate that the evolution of the strain energy density field may provide more robust predictions of the proximity of failure than other existing metrics of rock deformation. Plain Language Summary What controls the timing of large earthquakes? Estimating the conditions conducive to the next large earthquake can help mitigate seismic hazard and save significant societal and economic costs. A prerequisite for such estimates includes determining what measurable and detectable signals change in a systematic manner in rocks approaching catastrophic failure. Machine learning analyses of data acquired by synchrotron X-ray experiments on rocks provide robust means of identifying the evolving fault network characteristics that best predict the proximity of catastrophic failure of the rocks. Translating these fracture network characteristics to geophysical signals may help scientists detect such precursors within crustal fault systems preceding large earthquakes.
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Meijers, M. J. M., Brocard, G. Y., Whitney, D. L., & Mulch, A. (2020). Paleoenvironmental conditions and drainage evolution of the central Anatolian lake system (Turkey) during late Miocene to Pliocene surface uplift. Geosphere, 16(2), 490–509.
Résumé: Continued Africa-Eurasia convergence resulted in post-11 Ma surface uplift of the Central Anatolian Plateau (CAP) and the westward escape of the Anatolian microplate. Contemporaneously, a central Anatolian fluvio-lacustrine system developed that covered extensive parts of the rising CAP. Today, the semi-arid CAP interior-except for the Konya closed catchment-drains toward the Black Sea, the Mediterranean Sea, and the Persian Gulf. Lake connectivity and drainage patterns of the fluvio-lacustrine system in the evolving plateau region are, however, largely unknown. Here, we present sedimentological and stable isotopic (delta C-13 and delta O-18) data (N = 665) from 13 well-dated lake sections covering the former fluvio-lacustrine depocenters of the southern CAP. Persistently (>1 m.y.) stable paleoenvironmental and hydrological conditions suggest that a low-relief environment characterized the southern CAP during plateau uplift. Throughout the late Miocene, various open and closed lakes of the southern CAP drained into closed, terminal lakes within the plateau interior. Sedimentation east of the Tuz Golu fault ceased during the early Pliocene (ca. 5.3-3.6 Ma), when the eastern CAP became connected to marine base level as a result of river incision shortly after the switch from regional compression to extension. A final phase of lacustrine carbonate sedimentation characterizes most sampled basins, yet occurred asynchronously over the extent of the CAP. Therefore, the final episode of lacustrine sedimentation is unlikely to have been the result of a climatic event, consistent with the absence of a clear aridification trend in the lacustrine delta O-18 data. Rather, capping carbonates reflect the interplay of surface uplift and transition from inward- to outward-drained plateau regions and concomitant lake reorganization during the formation of the CAP and its margins.
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Melnik, O., Lyakhovsky, V., Shapiro, N. M., Galina, N., & Bergal-Kuvikas, O. (2020). Deep long period volcanic earthquakes generated by degassing of volatile-rich basaltic magmas. Nature Communications, 11(1).
Résumé: Deep long-period (DLP) earthquakes observed beneath active volcanoes are sometimes considered as precursors to eruptions. Their origin remains, however, unclear. Here, we present a possible DLP generating mechanism related to the rapid growth of gas bubbles in response to the slow decompression of over-saturated magma. For certain values of the gas and bubble content, the elastic deformation of surrounding rocks forced by the expanding bubbly magma can be fast enough to generate seismic waves. We show that amplitudes and frequencies of DLP earthquakes observed beneath the Klyuchevskoy volcano (Kamchatka, Russia) can be predicted by our model when considering pressure changes of similar to 10(7) Pa in a volume of similar to 10(3)-10(4) m(3) and realistic magma compositions. Our results show importance of the deep degassing in the generation of volcanic seismicity and suggest that the DLP swarms beneath active volcanoes might be related to the pulses of volatile-rich basaltic magmas rising from the mantle.
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Merkel, S., Lincot, A., & Petitgirard, S. (2020). Microstructural effects and mechanism of bcc-hcp-bcc transformations in polycrystalline iron. Physical Review B, 102(10).
Résumé: Cycling the alpha <-> epsilon transformation in polycrystalline Fe is investigated using in situ x-ray diffraction under quasihydrostatic conditions. The forward alpha -> epsilon transformation starts at 14 +/- 1 GPa and completes at 18 +/- 1 GPa while the reverse epsilon -> alpha transformation starts at 10.5 +/- 0.5 GPa and completes at 6 +/- 1 GPa. The anomalous evolution of c/a ratios of epsilon-Fe measured at the onset of the alpha -> epsilon transition in earlier studies is not observed. Microstructural features are consistent with a Burgers path for the transformation. The forward alpha -> epsilon transformation is sensitive to the average and intergranular stresses, inducing a strong variant selection with the c axes of the new epsilon phase preferentially aligned perpendicular to compression and concentrated into one single orientation. Partial texture memory is observed as the sample returns to the alpha phase but, as transformation cycles go on, irreversible changes occur in the microstructures that are later fully induced by the cycles of phase transformations.
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Mesalles, L., Lee, Y. H., & Bernet, M. (2020). Comment on Resentini et al., 2020: “Ongoing exhumation of the Taiwan orogenic wedge revealed by detrital apatite thermochronology: The impact of effective mineral fertility and zero-track grains”. Earth And Planetary Science Letters, 550.
Résumé: The interpretation of modern river apatite fission track (AFT) data of Taiwan by Resentini et al. (2020) presents some fundamental inaccuracies that call in question the main conclusions of the paper. The study aims at approximating source rock cooling histories by analysing erosional products, but ignores existing bedrock data in their maps and discussions. The allegedly “new” southern extension of the AFT reset zone is largely unconstrained by the presented data and ignores the local geology and stratigraphy of individual drainage basins. Notably, low grain counts (median=9) and catchment with various geological provinces, including orogenic derived sediments, question the significance of the dataset to characterise “single geological domains” as explained in the paper. Overall, the new data do not provide discriminating evidence for an earlier collision in the north of the island and thus do not support a southwardly propagation of collision. (C) 2020 Elsevier B.V. All rights reserved.
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Metaxian, J. P., Santoso, A. B., Caudron, C., Cholik, N., Labonne, C., Poiata, N., et al. (2020). Migration of seismic activity associated with phreatic eruption at Merapi volcano, Indonesia. Journal Of Volcanology And Geothermal Research, 396.
Résumé: Phreatic activity of Merapi started after nearly 2 years of quiescence following the October-November 2010 eruption which was the largest in more than 100 years. A dozen eruptions identified by visual andior seismic observations took place between August 2012 and April 2014. We present in this work the results of a detailed analysis of the April 20, 2014 phreatic eruption. We attempted to reconstruct the eruptive process, which lasted for over 30 min. To this end, we determined the wavefield composition by polarization analysis, located high-frequency earthquakes occurring in the initial part of the eruption process and then determined the seismic source migration of low-frequency part of the tremor-like signal [0.3-3 Hz] over time. Source depth of low-frequency signal was obtained by comparing the slowness vector calculated using 3 stations of the seismic antenna with a slowness vector model obtained by ray tracing in the structure, taking into account the topography and a 1D velocity model obtained by spatial auto-correlation analysis. The results allow to distinguish 3 different phases: 1) High-frequency transients interpreted as the result of a sudden decompression caused by the transition of the volcanic fluid to a gaseous phase that occurred approximately 1.5 km deep. This decompression process in the hydrothermal system generated a migration of the low-frequency seismic source from 900 m to 1800 m above sea level: 2) A second decompression process revealed by high-frequency micro-seismicity and associated to the migration of the low-frequency tremor source which is marked first by a descent phase, followed by a sharp ascent until reaching the surface. The evolution of the back-azimuth during the migration process indicates a slight inclination of the conduit, presumably in the orientation of the dome fracture, in the NW-SE direction. This direction is consistent with the alignment of regional tectonic structures and with the directivity of eruption deposits. 3) The seismic source then remains positioned at the altitude of the dome for over 10 min. This phase probably corresponds to the ash emission process. The average migration speed of the low-frequency seismic source from the starting eruptive process to ash emission is about 5 m/s. (C) 2020 Elsevier B.V. All rights reserved.
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Michaut, C., Pinel, V., & Maccaferri, F. (2020). Magma ascent at floor-fractured craters diagnoses the lithospheric stress state on the Moon. Earth And Planetary Science Letters, 530.
Résumé: On the Moon, floor-fractured craters (FFCs) present evidence of horizontal crater-centred magmatic intrusions. Crater floor uplift and moat formation indicate that these sill intrusions occur at shallow depths (< 10 km). While a recent study has demonstrated that magma ascent below FFCs and mare-filled craters was triggered by crater unloading, the mechanism leading to the emplacement of shallow sills is still poorly understood. Here we show that the local stress field due to crater unloading is also responsible for the horizontalisation of the magma flow leading to sill-like intrusions. On Earth, caldera formation has been shown to similarly affect magma trajectories, inducing the formation of a sill-shaped storage zone. Magma ascent to shallow depths below FFCs was however made possible because of a regional tensional stress caused by mare loading on the lunar lithosphere. We show that the tensional stress generated by elastic lithosphere deformation caused by mare loading combined to the local crater stress field can explain the distribution of FFCs on the Moon, with the smallest FFCs being located over a larger distance range from the mare. In particular, FFCs distribution around Oceanus Procellarum is consistent with an average load thickness of similar to 1 km. This study suggests that magma trajectory in the crust of terrestrial planets can provide a diagnostic of the lithospheric structure and state of stress. (C) 2019 Elsevier B.V. All rights reserved.
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Mietton, M., Gunnell, Y., Andriamitia, J., Crouzet, C., Montade, V., Jouannic, G., et al. (2020). Neotectonics and pastoralism: How they impact flood regimes in Madagascar's highlands. Science Of The Total Environment, 742.
Résumé: Sustainably maintaining the densely populated upland plains of Madagascar as operationally safe spaces for the food security of the nation and the urban growth of its capital city, Antananarivo, hinges critically on avoiding crop and infrastructure destruction by their through-flowing rivers. The flood regime, however, is also a function of two 'slow' variables hitherto undocumented: tectonic subsidence regime, and floodplain sedimentation rate. From a radiocarbon-dated chronostratigraphy and environmental history of the sediment sequences in three of Madagascar's semi-enclosed upland basins (Antananarivo, Arnbohibary, and Alaotra), we quantify and compare how the precarious equilibrium between the two variables entails differentials in accommodation space for sediment and floodwater. Results show that all these plains have been wetlands for at least 40,000 years, but that the Antananarivo Basin is the most vulnerable because the imbalance between sedimentation and subsidence is the largest. Although the tectonic regime and the endemic forms of gully erosion that occur in the catchments are beyond human control, we advocate that flood mitigation strategies should focus on the natural grassland savanna, which makes up most of the contributing areas to surface runoff in the watersheds. Pastoralists are persistently left out of rural development programmes, yet the rangelands could benefit from the introduction of multi-purpose grasses and legumes known to withstand high stocking rates on poor soils while combining the benefits of nutritiousness, fire and drought resistance, with good runoff-arrest and topsoil-retainment abilities. Future-proofing Madagascar's upland grainbaskets and population centres thus calls for joined-up action on the sediment cascade, focusing on soil and water sequestration through integrated watershed management rather than on hard-defence engineering against overflowing rivers on the plains, which has been the costly but ineffectual approach since the 17th century. (C) 2020 Elsevier B.V. All rights reserved.
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Migon, C., Heimburger-Boavida, L. E., Dufour, A., Chiffoleau, J. F., & Cossa, D. (2020). Temporal variability of dissolved trace metals at the DYFAMED time-series station, Northwestern Mediterranean. Marine Chemistry, 225.
Résumé: We present here results of an 18-month survey (July 2007-March 2009) of a suite of selected trace metals (TM: Co, Ni, Cu, Pb) in a 2350 m-deep offshore water column in the Ligurian Sea (Northwestern Mediterranean Sea). This low-nutrient low-chlorophyll region is characterised by a long stratification period (May-November) during which surface waters are depleted of macronutrients. Trace metals exhibit a range of biogeochemical behaviours from surface-enriched (scavenged-type) to surface-depleted (nutrient-like) with Co and Ni as representative cases. Cobalt (28-172 pM) distributions are governed by external inputs of aeolian dust deposition and removal by adsorption onto particles in surface, intermediate and deep waters as well. Nickel (3.57-5.52 nM) distributions are governed by internal biogeochemical cycles, together with physical mixing and circulation patterns. Nickel is primarily removed from surface waters with biogenic particles and then remineralised at depth. Copper (1.39-2.89 nM) distributions illustrate a mixture of the two typical behaviours mentioned above. Distributions of typically anthropogenic and particle-reactive Pb (82-235 pM) are in agreement with a Mediterranean flow source of Pb for the adjacent North Atlantic Ocean. The mechanisms controlling the biogeochemical cycling of TMs, such as atmospheric inputs, physical forcing, and interactions with primary production, are discussed according to the TM physico-chemical properties and biological importance.
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Miller, C. A., Christenson, B. W., Byrdina, S., Vandemeulebrouck, J., Brakenrig, T., Britten, K., et al. (2020). Snapshot of a magmatic/hydrothermal system from electrical resistivity tomography and fumarolic composition, Whakaari/White Island, New Zealand. Journal Of Volcanology And Geothermal Research, 400.
Résumé: Combined interpretation of Electrical Resistivity Tomography (ERT) data, with plume and fumarolic gas emissions provides a snapshot of the Whakaari/White Island hydrothermal system 11 months prior to an eruption on December 9,2019. Two and three dimensional inversion of the ERT data images the F0 fumarole as a low resistivity (2-5 Omega m) feature reflecting the two-phase zone surrounding the single phase vapour conduit. Crucially, interpretation of the inversion images is well constrained by a large existing dataset of rock electrical properties, including surface conductivity, porosity and intrinsic formation factor, alongside new measurements of liquid phase electrical conductivity taken from a range of hot-springs on the island. Pore-filling liquids are an order of magnitude more conductive than sea-water with their low to very low pH (3.4 to -03) contributing to their extremely conductive nature. An extensive low-resistivity feature (0.2 Omega m) at similar to 125 m depth is therefore interpreted as a liquid saturated layer exposed to hydrothermal alteration by acid fluids. The intersection of the F0 fumarole trace with this layer is coincident with a previously determined source of deformation, suggesting that heat transport inside the fumarole conduit pressurises surrounding liquid and vapour filled pore space, generating the deformation signal. The timeseries of fumarolic and plume emissions in the year prior to the ERT survey show that the gases transported by the fumarole are a mixture of high temperature magmatic vapour and lower temperature gas equilibrated within the hydrothermal environment. Interpretation of the gas data suggests that the snapshot captured by the ERT image shows the single-phase vapour and two-phase vapourliquid regions adjacent to the conduit were likely at close to their smallest extent, consisting of mostly hydrothermal derived gases. (C) 2020 Elsevier B.V. All rights reserved.
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Minetto, R., Montanari, D., Planes, T., Bonini, M., Del Ventisette, C., Antunes, V., et al. (2020). Tectonic and Anthropogenic Microseismic Activity While Drilling Toward Supercritical Conditions in the Larderello-Travale Geothermal Field, Italy. Journal Of Geophysical Research-Solid Earth, 125(2).
Résumé: This study investigates the seismic activity occurring at the Larderello-Travale geothermal field, central Italy, from June 2017 to January 2018. We deployed a network composed of nine broadband stations around the Venelle 2 well drilling for supercritical fluids. During the experiment, we recognize two types of seismic events (type 1 and type 2). Type-1 events have clear P and S wave arrivals and occur in clusters both above and below the K-horizon, which is a seismic reflector marking a debated transition zone at depth. The distribution and evolution of the seismic sequences suggest that the K-horizon could be interpreted as a fluid-rich region at near-lithostatic pressures. Type-2 events usually occur in swarms and show a periodic pattern, a narrow frequency band, and almost identical waveforms. Their source is estimated to be located near the well, and their occurrence ceases after about 3 weeks from the conclusion of the drilling. We propose a causal link with the drilling operations where pressure fronts inside the well may promote phase changes and fluid flow across the drilled formations. Our study sheds light on the fluid-driven tectonic and anthropogenic seismic activity at the Larderello-Travale geothermal field. More generally, we show that microseismic activity occurring during drilling in high-pressure and high-temperature conditions can remain at low magnitudes and that geothermal wells targeting geothermal fluids in such systems may be handled safely despite the critical conditions encountered at depth. The drilling of the Venelle 2 well is an encouraging example for the development of geothermal energy in critical conditions.
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Mishra, M., Besancon, G., Chambon, G., & Baillet, L. (2020). Observer design for state and parameter estimation in a landslide model (Vol. 53). Elsevier.
Résumé: This paper presents an observer-based state and parameter estimation for the extended sliding-consolidation model of a landslide. This system is described by a pair of coupled Ordinary Differential Equation (ODE) and Partial Differential Equation (PDE), with a mixed boundary condition for the PDE. The coupling appears both in the ODE and in the Neuman boundary condition of the PDE. The observer consists of a copy of the PDE part of the system and Kalman-like observer for the ODE. It is shown to ensure exponential convergence of the state and parameter estimates by means of Lyapunov tool. Finally, a simulation result of the extended sliding-consolidation model is presented to illustrate the effectiveness of the proposed observer. Copyright (C) 2020 The Authors.
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Mishra, M., Besancon, G., Chambon, G., & Baillet, L. (2020). Observer design for state and parameter estimation in a landslide model (Vol. 53). Elsevier.
Résumé: This paper presents an observer-based state and parameter estimation for the extended sliding-consolidation model of a landslide. This system is described by a pair of coupled Ordinary Differential Equation (ODE) and Partial Differential Equation (PDE), with a mixed boundary condition for the PDE. The coupling appears both in the ODE and in the Neuman boundary condition of the PDE. The observer consists of a copy of the PDE part of the system and Kalman-like observer for the ODE. It is shown to ensure exponential convergence of the state and parameter estimates by means of Lyapunov tool. Finally, a simulation result of the extended sliding-consolidation model is presented to illustrate the effectiveness of the proposed observer. Copyright (C) 2020 The Authors.
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Mishra, M., Besancon, G., Chambon, G., & Baillet, L. (2020). Observer design for state and parameter estimation in a landslide model (Vol. 53).
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Mishra, M., Besancon, G., Chambon, G., & Baillet, L. (2020). Optimal parameter estimation in a landslide motion model using the adjoint method.
Résumé: This work proposes an optimal approach for parameter estimation in a landslide motion, based on the so-called adjoint method. The system is described by an extended sliding-consolidation model composed of an ordinary differential equation and 1D parabolic partial differential equation that represents landslide motion and pore pressure evolution respectively. The key feature of this model is pore pressure feedback, which regulates landslide motion and leads to coupling between both differential equations. Parameters to be estimated include the friction and dilatancy angle of the material. The objective functional for the optimal estimation is composed of: i) a cost function defined as the least square error between measurements and related simulated values, and ii) a product of Lagrange variables and system dynamics. A variational approach is applied to get the gradients of the cost functional with respect to parameters to be estimated and adjoint model. The cost functional is optimized, employing the steepest descent method to estimate parameters. Finally, the presented optimal estimation method is validated on a simulated test case.
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Monasterio-Guillot, L., Alvarez-Lloret, P., Ibanez-Velasco, A., Fernandez-Martinez, A., Ruiz-Agudo, E., & Rodriguez-Navarro, C. (2020). CO2 sequestration and simultaneous zeolite production by carbonation of coal fly ash: Impact on the trapping of toxic elements. Journal Of Co2 Utilization, 40.
Résumé: Coal-fired power plants are main contributors to atmospheric CO2 emissions. They also produce huge amounts of coal fly ash (CFA) waste, which is typically landfilled, posing significant environmental risks due to its high content of potentially toxic elements (PTE). However, CFA is an alkaline aluminosilicate-rich waste, which offers the possibility of CO2 mineral capture and the production of economically-relevant mineral by-products such as zeolites. Yet, the combined carbonation and zeolite production from CFA resulting in PTE trapping has never been explored. Here we show that under mild hydrothermal conditions (150 degrees C) and depending of various process parameters such as pH and background alkali metal ion in (bi)carbonate solutions, a carbonation efficiency of up to 79 %, with a net CO2 mineral capture of 0.045 g/g CFA can be achieved, even when using a low Ca and Mg (3.72 wt% CaO, 1.74 wt%, MgO) Class F fly ash. Moreover, amorphous zeolitic precursors and different crystalline zeolites (yield up to 60 wt%) are simultaneously obtained, and PTE in CFA are effectively trapped into the newly formed calcite, zeolitic precursors, and zeolite phases. This is the first time that a combined study of carbonation, zeolitization and PTE trapping in newly formed phases has been developed. These results have important implications for carbon capture and storage, as well as for the safe reutilization and disposal of CFA waste.
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Montes-Hernandez, G. (2020). Synthesis of magnetite, ceria and magnetite-ceria materials by calcination of nanostructured precursor-minerals. Materials Letters, 276.
Résumé: The present short communication reports an original experimental calcination method to synthesize magnetic materials with high thermal stability such as magnetite (Fe3O4) with typical spinel and atypical crystal shape, sub-micrometric rounded crystals of ceria (CeO2) and magnetite-ceria composites with varied shape and size of crystals. Shape and size depending on the nature of mineral precursors (goethite, siderite or ferrihydrite). Herein, it was demonstrated that cooperative redox reactions and simple vacuum can be used to synthesize magnetic composite materials by calcination of nanostructured mineral precursors. In this way, bastnasite mineral (CeCO3F) is a powerful reducing agent to synthesize magnetite from reductive dehydration of ferric oxyhydroxides. (C) 2020 Elsevier B.V. All rights reserved.
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Montes-Hernandez, G., & Renard, F. (2020). Nucleation of Brushite and Hydroxyapatite from Amorphous Calcium Phosphate Phases Revealed by Dynamic In Situ Raman Spectroscopy. Journal Of Physical Chemistry C, 124(28), 15302–15311.
Résumé: Since the 1970s, it has been shown that calcium phosphate crystals nucleate from one or several early amorphous calcium phosphate phases into several in vivo and in vitro systems. However, the precise chemical composition, structure, and transformation mechanism of these amorphous phases remain controversial. Here, we characterize the reaction mechanism and kinetics of formation of two phosphate crystals, brushite and hydroxyapatite, by using in situ Raman spectroscopy in batch reactors at 25 degrees C. We investigate three pH regimes to control the phosphate speciation in solution and used solutions with or without citric acid, a complexing agent that may stabilize the amorphous phases. As expected, brushite (CaHPO4 center dot 2H(2)O) forms at pH < 9.8. Amorphous calcium phosphate (ACP: CaHPO4 center dot nH(2)O) with a short lifetime (<2 min) and octocalcium phosphate (OCP: Ca-8(HPO4)(2) (PO4)(4)center dot 5H(2)O) are the main transient phases prior to brushite nucleation that occurs after similar to 8 min. At pH > 11, hydroxyapatite (HAp: Ca-10(PO4)(6)(OH)(2)) nucleates after >35 min, depending on the experimental conditions. The reaction mechanism steps for hydroxyapatite are more complex compared to brushite. For hydroxyapatite formation, amorphous calcium phosphate phases with different chemical composition (Ca(HPO4)(1-x)(PO4)((2/3)x)center dot nH(2)O, with x in the range 0.2-1, and with different lifetime may form. Amorphous tricalcium phosphate (ATCP: Ca(PO4)(2/3)center dot n.H2O or Ca-3(PO4)(2)center dot nH(2)O when x = 1) is the most persistent phase which can either transform into OCP and then hydroxyapatite or directly evolve into hydroxyapatite at pH > 12.2. The presence of citric acid retards the transformation kinetics by increasing the nucleation times of brushite and hydroxyapatite but has little effect on the reaction mechanism steps. Finally, this study identifies new reactive pathways that characterize the formation of amorphous calcium phosphate phases and their transformation into brushite microcrystals or hydroxyapatite nanocrystals under abiotic conditions, relevant to a wide range of technological applications and natural environments.
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Montes-Hernandez, G., Bah, M., & Renard, F. (2020). Mechanism of formation of engineered magnesite: A useful mineral to mitigate CO2 industrial emissions. Journal Of Co2 Utilization, 35, 272–276.
Résumé: Magnesium carbonate production at the industrial scale is a realistic option to reduce the industrial emissions of CO2. Ultrabasic rocks and/or alkaline mine waste provide magnesium sources and are widely available in the Earth's crust. Here, we investigated the aqueous carbonation of magnesium hydroxide under moderate temperature (25-90 degrees C) and pressure (initial pressure of CO2 = 50 bar) using NaOH as the CO2 sequestering agent. From time-resolved Raman measurements, we demonstrate that the aqueous carbonation of magnesium hydroxide can be an effective engineered method to trap CO2 into a solid material and produce large amounts of magnesite MgCO3 (6 kg/m(3) h), or hydromagnesite Mg-5 (CO3)(4)(OH)(2)center dot 4H(2)O (120 kg/m(3)h) at 90 degrees C or nesquehonite MgCO3 center dot 3H(2)O (40 kg/m(3)h) at 25 degrees C. Higher production rates were measured for nesquehonite (at 25 degrees C) and hydromagnesite (at 60 and 90 degrees C). However, only the magnesite produced at 90 degrees C ensures a permanent CO2 storage because this mineral is the most stable Mg carbonate under Earth surface conditions, and it could be coused as construction material in roadbeds, bricks with fire-retarding property and granular fill. The use of specific organic additives can reduce the reaction temperature to precipitate magnesite. For example, ferric EDTA (ethylenediaminetetraacetic acid) reduces the temperature from 90 to 60 degrees C. However, more time is required to complete magnesite precipitation reaction at this lower temperature (15 h at 90 degrees C and 7 days at 60 degrees C). These results suggests that functionalized organic groups can reduce the energetic barriers during magnesite nucleation.
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Montes-Hernandez, G., Renard, F., Auzende, A. L., & Findling, N. (2020). Amorphous Calcium-Magnesium Carbonate (ACMC) Accelerates Dolomitization at Room Temperature under Abiotic Conditions. Crystal Growth & Design, 20(3), 1434–1441.
Résumé: The challenge to produce dolomite CaMg(CO3)(2) at low temperature (20-35 degrees C) over laboratory time scales so far has remained unsuccessful, which has led to long-lasting scientific debates in the last two <^> centuries. This mineral exerts a major control on the natural carbon dioxide sequestration into various sedimentary, basaltic, and mantellic rocks. The present study reports on specific abiotic conditions that allow the precipitation of disordered dolomite, high Mg calcite, and high Ca magnesite at room temperature over time scales of hours to days. Here we show that an amorphous calcium magnesium carbonate (ACMC) phase accelerates dolomitization at room temperature. ACMC is initially precipitated by mixing a carbonate (HCO3-/CO32- = 1; pH similar to 10.3 approximate to pK(a2)) alkaline solution with a Mg-Ca ionic solution (Mg molar fraction between 0 and 1). Then, time-resolved in situ Raman spectroscopy monitored the transformation of ACMC into Mg-rich carbonate minerals. The initial Mg molar fraction controlled both the reaction mechanism (e.g., nature of transient crystalline phases) and the kinetics. Nanosized crystallites with short-range order, called disordered dolomite CaMg(CO3)(2), precipitated following a complex reaction pathway. First, nesquehonite (MgCO3 center dot 3H(2)O: nucleation time 2.5 h) and then disordered dolomite (CaMg(CO3)(2): nucleation time 3.2 h) followed by monohydrocalcite (CaCO3 center dot H2O: nucleation time 3.4 h) formed from ACMC transformation. Nesquehonite and monohydrocalcite are transient phases that nourish the slow precipitation of disordered dolomite, which reached a spectral equilibrium after 7 days of reaction. The direct transformation of ACMC into disordered dolomite was also measured. Our experimental results demonstrate that disordered dolomite precipitates at room temperature when an ideal Mg/Ca ratio, high carbonate alkalinity, and high ionic concentration are reached in abiotic systems. This result suggests the possibility of a physicochemical rather than biotic control on the formation of disordered dolomite at low temperature in several geosystems.
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Morard, G., Hernandez, J. A., Guarguaglini, M., Bolis, R., Benuzzi-Mounaix, A., Vinci, T., et al. (2020). In situ X-ray diffraction of silicate liquids and glasses under dynamic and static compression to megabar pressures. Proceedings Of The National Academy Of Sciences Of The United States Of America, 117(22), 11981–11986.
Résumé: Properties of liquid silicates under high-pressure and high-temperature conditions are critical for modeling the dynamics and solidification mechanisms of the magma ocean in the early Earth, as well as for constraining entrainment of melts in the mantle and in the present-day core-mantle boundary. Here we present in situ structural measurements by X-ray diffraction of selected amorphous silicates compressed statically in diamond anvil cells (up to 157 GPa at room temperature) or dynamically by laser-generated shock compression (up to 130 GPa and 6,000 K along the MgSiO3 glass Hugoniot). The X-ray diffraction patterns of silicate glasses and liquids reveal similar characteristics over a wide pressure and temperature range. Beyond the increase in Si coordination observed at 20 GPa, we find no evidence for major structural changes occurring in the silicate melts studied up to pressures and temperatures exceeding Earth's core mantle boundary conditions. This result is supported by molecular dynamics calculations. Our findings reinforce the widely used assumption that the silicate glasses studies are appropriate structural analogs for understanding the atomic arrangement of silicate liquids at these high pressures.
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Mordret, A., Brenguier, F., Causse, M., Boue, P., Voisin, C., Dumont, I., et al. (2020). Seismic Stereometry Reveals Preparatory Behavior and Source Kinematics of Intermediate-Size Earthquakes. Geophysical Research Letters, 47(17).
Résumé: Although moderate-size earthquakes are poorly studied by lack of near-fault observations, they can provide key information about larger damaging earthquakes. Here we propose a new approach, inspired by double-difference relocation, that uses high-coherency waveforms recorded at neighboring sensors, to study the preparation phase and dynamics of moderate-size earthquakes. We validate this technique by analyzing the 2016,M(w)5.2 Borrego Springs earthquake in Southern California and find consistent rupture velocities of 2 km/s highlighting two main rupture asperities. The analysis of the 2019,Ml5.2 Le Teil earthquake in France reveals slow nucleation at depth that migrates to the surface and propagates northward with a velocity of similar to 2.8 km/s, highlighting two main rupture events also imaged by InSAR. By providing unprecedented resolution in our observation of the rupture dynamics, this approach will be useful in better understanding the preparation phase and rupture of both tectonic and induced earthquakes. Plain Language Summary Small and moderate-size earthquakes are much more numerous yet studied in much less detail than large and damaging earthquakes. This is because to study small earthquakes precisely, one needs seismometers very close to the rupture, which is rarely the case. It is still unclear if small and large earthquakes start the same way, thus studying more systematically small earthquakes could help to answer this question. Here we show that we can use two close-by seismometers, as we would do with 3-D glasses, to observe with a stereoscopic effect, the evolution of intermediate-size earthquakes when they rupture along a fault. We can retrieve the direction of rupture, the speed at which the fault breaks, and the length of the rupture, important parameters that help to characterize the earthquakes. Using this new method, we can sometimes also observe the behavior of the fault before the main rupture which will be useful to better understand how earthquakes start.
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Mordret, A., Courbis, R., Brenguier, F., Chmiel, M., Garambois, S., Mao, S. J., et al. (2020). Noise-based ballistic wave passive seismic monitoring – Part 2: surface waves. Geophysical Journal International, 221(1), 692–705.
Résumé: We develop a new method to monitor and locate seismic velocity changes in the subsurface using seismic noise interferometry. Contrary to most ambient noise monitoring techniques, we use the ballistic Rayleigh waves computed from 30 d records on a dense nodal array located above the Groningen gas field (the Netherlands), instead of their coda waves. We infer the daily relative phase velocity dispersion changes as a function of frequency and propagation distance with a cross-wavelet transform processing. Assuming a 1-D velocity change within the medium, the induced ballistic Rayleigh wave phase shift exhibits a linear trend as a function of the propagation distance. Measuring this trend for the fundamental mode and the first overtone of the Rayleigh waves for frequencies between 0.5 and 1.1 Hz enables us to invert for shear wave daily velocity changes in the first 1.5 km of the subsurface. The observed deep velocity changes (+/- 1.5 per cent) are difficult to interpret given the environmental factors information available. Most of the observed shallow changes seem associated with effective pressure variations. We observe a reduction of shear wave velocity (-0.2 per cent) at the time of a large rain event accompanied by a strong decrease in atmospheric pressure loading, followed by a migration at depth of the velocity decrease. Combined with P-wave velocity changes observations from a companion paper, we interpret the changes as caused by the diffusion of effective pressure variations at depth. As a new method, noise-based ballistic wave passive monitoring could be used on several dynamic (hydro-)geological targets and in particular, it could be used to estimate hydrological parameters such as the hydraulic conductivity and diffusivity.
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Moreau, L., Boue, P., Serripierri, A., Weiss, J., Hollis, D., Pondaven, I., et al. (2020). Sea Ice Thickness and Elastic Properties From the Analysis of Multimodal Guided Wave Propagation Measured With a Passive Seismic Array. Journal Of Geophysical Research-Oceans, 125(4).
Résumé: Field data are needed for a better understanding of sea ice decline in the context of climate change. The rapid technological and methodological advances of the last decade have led to a reconsideration of seismic methods in this matter. In particular, passive seismology has filled an important gap by removing the need to use active sources. We present a seismic experiment where an array of 247 geophones was deployed on sea ice, in the Van Mijen fjord near Sveagruva (Svalbard). The array is a mix of 1C and 3C stations with sampling frequencies of 500 and 1000 Hz. They recorded continuously the ambient seismic field in sea ice between 28 February and 26 March 2019. Data also include active acquisitions on 1 and 26 March with a radar antenna, a shaker unit, impulsive sources, and artificial sources of seismic noise. This data set is of unprecedented quality regarding sea ice seismic monitoring, as it also includes thousands of microseismic events recorded each day. By combining passive seismology approaches with specific array processing methods, we demonstrate that the multimodal dispersion curves of sea ice can be calculated without an active source and then used to infer sea ice properties. We calculated an ice thickness, Young's modulus, and Poisson's ratio with values h=543 cm, E=3.90.15 GPa, and nu=0.340.02 on 1 March, and h=583 cm, E=4.4 +/- 0.15 GPa, and nu=0.32 +/- 0.02 on 5 March. These values are consistent with in situ field measurements and observations.
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Moreau, L., Weiss, J., & Marsan, D. (2020). Accurate Estimations of Sea-Ice Thickness and Elastic Properties From Seismic Noise Recorded With a Minimal Number of Geophones: From Thin Landfast Ice to Thick Pack Ice. Journal Of Geophysical Research-Oceans, 125(11).
Résumé: Despite their high potential for accurate sea ice properties estimation, seismic methods are still limited by the difficulty of access and the challenging logistics of polar environments. Conventional seismic methods generally require tens of geophones together with active seismic sources for monitoring applications. While this is not an issue for mainland environment, it is restrictive for sea ice and prevents long-term monitoring. We introduce a method to estimate sea ice thickness and elastic properties from passive recordings of the ambient seismic field with a minimal number of geophones. In comparison with our previous work (Moreau et al., 2020; ) where about 50 sensors were used, the number of geophones is reduced by 1 order of magnitude, thanks to a new strategy of inversion of the passive seismic data. The method combines noise interferometry for estimating the elastic properties, with a Bayesian inversion of the dispersion in the waveforms of icequakes for inferring ice thickness, based on passive recordings from only 3-5 geophones, depending on the signal to noise ratio. We demonstrate its potential both on data recorded on thin landfast ice in Svalbard, and on data recorded on thick pack ice in the Arctic ocean.
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Myagkiy, A., Brunet, F., Popov, C., Kruger, R., Guimaraes, H., Sousa, R. S., et al. (2020). H-2 dynamics in the soil of a H-2-emitting zone (Sao Francisco Basin, Brazil): Microbial uptake quantification and reactive transport modelling. Applied Geochemistry, 112.
Résumé: Sandy kaolinite-rich soils, collected in a H-2-emitting circular depression (ca. 500 m in diameter), located in the Sao Francisco basin (Brazil), were exposed to H-2 gas concentrations in the 500-5000 ppm range for up to eight weeks. The samples were found to consume H-2 at a rate of approximately 0.05-0.1 mmol H-2/soil kg/day due to the microbial activity. DNA extraction from these soil samples before and after H-2 exposure, followed by Ribosomal Intergenic Spacer Analysis (RISA) and 16S rRNA gene amplicon sequencing, indicated that (i) the bacterial community is dominated by phyla that have been previously recognized to scavenge atmospheric H-2, and (ii) H-2 exposure leads to a significant modification of the bacterial community distribution. Measured H-2 uptake rates were fitted to the integrated form of the Michaelis-Menten equation and were further implemented in a 1-D reactive transport model. The model simulates gas-soil interactions in a 1-m vertical soil column, assuming homogeneous distribution of H-2-consuming bacteria. The evolution of the H-2 concentration in the unsaturated soil porosity along the column was simulated considering two different scenarios: a deep H-2 source (Case 1) and a biogenic surface source (Case 2). It was shown that, in the case of diffusion-dominated H-2 transport as considered in this study, bacterial activity will control the amplitude of the H-2 flux across the column. Moreover, we determined that bacterial activity can dramatically decrease the H-2 concentration in the soil porosity, by a factor of two compared to the source concentration. According to the simulation, the timeresolved concentration data collected in the Sao Francisco depression [Prinzhofer et al., 2019; International Journal of Hydrogen Energy] are consistent with the combination of a deep (Case 1) and a surficial biogenic (Case 2) H-2 source in this locality.
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Myagkiy, A., Moretti, I., & Brunet, F. (2020). Space and time distribution of subsurface H-2 concentration in so-called “fairy circles”: Insight from a conceptual 2-D transport model. Bsgf-Earth Sciences Bulletin, 191.
Résumé: Natural H-2 emissions from the ground have now been measured in many places worldwide. These emissions can be localized on faults or be more diffuse in some sedimentary basins, usually of Proterozoic age. In such a case, emanation zones are often visible from aerial images or on high-resolution topographic maps since they correspond to slight depressions of circular to elliptic shape. Furthermore, the rounded depressions are covered with a scrubby vegetation which often contrasts with the surrounding vegetation. Although the emission structure displays a very regular shape, the distribution of H-2 concentration in the first meter of soil in such a structure does show a clear pattern. For example, the maximum concentration is almost never measured in the center of the structure and the few time-resolved data show that the soil H-2 concentration is variable with time. Here, the time and space evolution of H-2 concentration is simulated using a 2-D advective-diffusive model of H-2 transport in porous media. Several parameters have been tested as the depth and periodicity of the H-2 point source (pulsed), bacterial H-2 consumption and permeability heterogeneities of the soil. The radius of the structure is linked to the time spent by the H-2 in the soil that depends on the soil permeability, the depth of the gas leakage point and the pressure of the bubble. To account for field observations, the case of a shaly, less permeable, heterogeneity in the center of the structures has been modeled. It resulted in an increase of the concentration toward the rim of the structure and a close to zero signal in its center. If the deep signal is periodic with a frequency smaller than a few hours, H-2 concentration within the soil is almost constant; in other cases, the near surface concentration wave reflects the concentration periodicity of the source with a delay (in the range of 12 h for 30 m of soil) and so the near surface H-2 concentration values will be highly dependent on the time at which the measurement is performed. H-2 monitoring through a sensor network is thus mandatory to characterize the H-2 dynamics in the soil of fairy circles.
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Naumenko-Dezes, M. O., Rolland, Y., Lamarque, G., Duclaux, G., Gallet, S., Bascou, J., et al. (2020). Petrochronology of the Terre Adelie Craton (East Antarctica) evidences a long-lasting Proterozoic (1.7-1.5 Ga) tectono-metamorphic evolution – Insights for the connections with the Gawler Craton and Laurentia. Gondwana Research, 81, 21–57.
Résumé: The Terre Adelie Craton displays superimposed strain fields related to the Neoarchean (2.6-2.4 Ga, M1) and Paleo-Mesoproterozoic (1.7-1.5 Ga, M2) metamorphic events. M1 is a regional granulite fades event, constrained by P-T modelling at -0.8-1.0 GPa – 800-850 et, followed by a decompressional retrogression in the upper amphibolite fades at -0.6 GPa – 750 degrees C. M2 Stage 1 P-T peak is constrained at 0.6-0.7 GPa – 670-700 degrees C, followed by a steep P-T path down to 0.3 GPa – 550 degrees C. Retrogression after M2 PT peak occurred in a context of dextral shearing along the Mertz Shear Zone along with thrust motions within the eastern Terre Adelie Craton. In this paper, we present a series of 63 new Ar-40/Ar-39 ages of biotite and amphibole pairs in mafic rocks from a complete traverse of the Terre Adelie Craton. Ar-40/Ar-39 Ar dating constrains M2 amphibolite facies metamorphism at a regional scale between 1700 and 1650 Ma, during stage 1 peak metamorphism. During retrogression, lower amphibolite fades recrystallization mainly occurred along vertical shear zones and mafic dykes between 1650 and 1600 Ma (Stage 2), followed by amphibolite to greenschist facies metamorphism until after 1500 Ma (Stage 3). At the scale of the Mawson continent, this event is related to the growth of an active margin above an oblique subduction zone. The supra-subduction model best explains opening of Dumont D'Urville and Hunter basins at 1.71 Ga followed by their rapid closure and metamorphism at 1.70 Ga. In this context, episodic shear zone reactivation and magmatic dyke emplacement led to a partial reequilibration of the Ar-40/Ar-39 system until <1500 Ma. This latter phase of mafic magmatism largely coincides with a hot spot event at the scale of the Gawler Craton and western Laurentia paleocontinent. (C) 2019 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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Nouira, D., Tonazzi, D., Meziane, A., Baillet, L., & Massi, F. (2020). Numerical and Experimental Analysis of Nonlinear Vibrational Response due to Pressure-Dependent Interface Stiffness. Lubricants, 8(7).
Résumé: Modelling interface interaction with wave propagation in a medium is a fundamental requirement for several types of application, such as structural diagnostic and quality control. In order to study the influence of a pressure-dependent interface stiffness on the nonlinear response of contact interfaces, two nonlinear contact laws are investigated. The study consists of a complementary numerical and experimental analysis of nonlinear vibrational responses due to the contact interface. The laws investigated here are based on an interface stiffness model, where the stiffness property is described as a nonlinear function of the nominal contact pressure. The results obtained by the proposed laws are compared with experimental results. The nonlinearity introduced by the interface is highlighted by analysing the second harmonic contribution and the vibrational time response. The analysis emphasizes the dependence of the system response, i.e., fundamental and second harmonic amplitudes and frequencies, on the contact parameters and in particular on contact stiffness. The study shows that the stiffness-pressure trend at lower pressures has a major effect on the nonlinear response of systems with contact interfaces.
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Omana-Sanz, B., Toybou, D., Lesven, L., Gaucher, V., Fadel, A., Addad, A., et al. (2020). An electrochemical method to rapidly assess the environmental risk of silver release from nanowire transparent conductive films. Nanoimpact, 18.
Résumé: Silver nanowires (AgNW) are new nanomaterials designed to be incorporated into transparent conductive films in electronics, microelectrodes, heated surfaces and others. Although in these films, the AgNW are generally protected by a coating material, a risk for release of silver at all stages of the nanoproduct life cycle does exist due to corrodibility of the metal. Since ionic and nanoparticulate Ag represent a toxicological risk for a large number of living cells, there is a need for quantifying the potential Ag release from these product components. We developed an electrochemical method to evaluate possible corrosion activity of silver in AgNW transparent conductive films (TCFs) and concomitant Ag+ release. A polysiloxane polymer was used as protective coating of AgNW TCFs. A consistent correlation is observed between the degree of corrosion and the coatings' characteristics, in particular the thicknesses. A major advantage of the new approach, compared to classical aging studies, is the short experimentation time: 20 min are sufficient for a diagnostic result. The method is an accelerated corrosion and release test. It is environmentally sound methodology with use of very low electric power and with no harmful reagents. A particularly attractive application could be in the field of environmental risk assessment of metals from portable electronics and biosensors.
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Opitz, P., Asta, M. P., Fernandez-Martinez, A., Panthofer, M., Kabelitz, A., Emmerling, F., et al. (2020). Monitoring a Mechanochemical Reaction Reveals the Formation of a New ACC Defect Variant Containing the HCO3- Anion Encapsulated by an Amorphous Matrix. Crystal Growth & Design, 20(10), 6831–6846.
Résumé: Amorphous calcium carbonate (ACC) is an important precursor in the biomineralization of crystalline CaCO3. In nature, it serves as a storage material or as a permanent structural element, whose lifetime is regulated by an organic matrix. The relevance of ACC in materials science is primarily related to our understanding of CaCO3 crystallization pathways and CaCO3/(bio)polymer nanocomposites. ACC can be synthesized by liquid-liquid phase separation, and it is typically stabilized with macromolecules. We have prepared ACC by milling calcite in a planetary ball mill. Phosphate “impurities” were added in the form of monetite (CaHPO4) to substitute the carbonate anions, thereby stabilizing ACC by substitutional disorder. The phosphate anions do not simply replace the carbonate anions. They undergo shear-driven acid/base and condensation reactions, where stoichiometric (10%) phosphate contents are required for the amorphization to be complete. The phosphate anions generate a strained network that hinders ACC recrystallization kinetically. The amorphization reaction and the structure of BM-ACC were studied by quantitative Fourier transform infrared spectroscopy and solid state P-31, C-13, and H-1 magic angle spinning nuclear magnetic resonance spectroscopy, which are highly sensitive to symmetry changes of the local environment. In the first. and fast.reaction step, the CO32- anions are protonated by the HPO42- groups. The formation of unprecedented hydrogen carbonate (HCO3-) and orthophosphate anions appears to be the driving force of the reaction, because the phosphate group has a higher Coulomb energy and the tetrahedral PO43- unit can fill space more efficiently. In a competing second. and slow.reaction step, pyrophosphate anions are formed in a condensation reaction. No pyrophosphates are formed at higher carbonate contents. High strain leads to such a large energy barrier that any reaction is suppressed. Our findings aid in the understanding of the mechanochemical amorphization of calcium carbonate and emphasize the effect of impurities for the stabilization of the amorphous phases in general. Our approach allowed the synthesis of new amorphous alkaline earth defect variants containing the unique HCO3- anion. Our approach outlines a general strategy to obtain new amorphous solids for a variety of carbonate/phosphate systems that offer promise as biomaterials for bone regeneration.
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Orlecka-Sikora, B., Lasocki, S., Kocot, J., Szepieniec, T., Grasso, J. R., Garcia-Aristizabal, A., et al. (2020). An open data infrastructure for the study of anthropogenic hazards linked to georesource exploitation. Scientific Data, 7(1).
Résumé: Mining, water-reservoir impoundment, underground gas storage, geothermal energy exploitation and hydrocarbon extraction have the potential to cause rock deformation and earthquakes, which may be hazardous for people, infrastructure and the environment. Restricted access to data constitutes a barrier to assessing and mitigating the associated hazards. Thematic Core Service Anthropogenic Hazards (TCS AH) of the European Plate Observing System (EPOS) provides a novel e-research infrastructure. The core of this infrastructure, the IS-EPOS Platform (tcs.ah-epos.eu) connected to international data storage nodes offers open access to large grouped datasets (here termed episodes), comprising geoscientific and associated data from industrial activity along with a large set of embedded applications for their efficient data processing, analysis and visualization. The novel team-working features of the IS-EPOS Platform facilitate collaborative and interdisciplinary scientific research, public understanding of science, citizen science applications, knowledge dissemination, data-informed policy-making and the teaching of anthropogenic hazards related to georesource exploitation. TCS AH is one of 10 thematic core services forming EPOS, a solid earth science European Research Infrastructure Consortium (ERIC) (www.epos-ip.org.).
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Pamato, M. G., Li, Y., Antonangeli, D., Miozzi, F., Morard, G., Wood, I. G., et al. (2020). Equation of State of hcp Fe-C-Si Alloys and the Effect of C Incorporation Mechanism on the Density of hcp Fe Alloys at 300 K. Journal Of Geophysical Research-Solid Earth, 125(12).
Résumé: Si and C are cosmochemically abundant elements soluble in hcp Fe under pressure and temperature and could therefore be present in the Earth's inner core. While recent ab initio calculations suggest that the observed inner core density and velocities could be matched by an Fe-C-Si alloy, the combined effect of these two elements has only recently started to be investigated experimentally. We therefore carried out synchrotron X-ray diffraction measurements of an hcp Fe-C-Si alloy with 4 at% C and 3 at% Si, up to similar to 150 GPa. Density functional theory calculations were also performed to examine different incorporation mechanisms. These calculations suggest interstitial C to be more stable than substitutional C below similar to 350 GPa. In our calculations, we also find that the lowest-energy incorporation mechanism in the investigated pressure range (60-400 GPa) is one where two C atoms occupy one atomic site; however, this is unlikely to be stable at high temperatures. Notably, substitutional C is observed to decrease the volume of the hcp Fe, while interstitial C increases it. This allows us to use experimental and theoretical equations of state to show unambiguously that C in the experimental hcp Fe-C-Si alloys is not substitutional, as is often assumed. This is crucial since assuming an incorrect incorporation mechanism in experiments leads to incorrect density determinations of similar to 4%, undermining attempts to estimate the concentration of C in the inner core. In addition, the agreement between our experiments and calculations supports Si and C as being light elements in the inner core.
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Panduro, E. A. C., Cordonnier, B., Gawel, K., Borve, I., Iyer, J., Carroll, S. A., et al. (2020). Real Time 3D Observations of Portland Cement Carbonation at CO2 Storage Conditions. Environmental Science & Technology, 54(13), 8323–8332.
Résumé: Depleted oil reservoirs are considered a viable solution to the global challenge of CO2 storage. A key concern is whether the wells can be suitably sealed with cement to hinder the escape of CO2. Under reservoir conditions, CO2 is in its supercritical state, and the high pressures and temperatures involved make real-time microscopic observations of cement degradation experimentally challenging. Here, we present an in situ 3D dynamic X-ray micro computed tomography (mu-CT) study of well cement carbonation at realistic reservoir stress, pore-pressure, and temperature conditions. The high-resolution time-lapse 3D images allow monitoring the progress of reaction fronts in Portland cement, including density changes, sample deformation, and mineral precipitation and dissolution. By switching between flow and nonflow conditions of CO2-saturated water through cement, we were able to delineate regimes dominated by calcium carbonate precipitation and dissolution. For the first time, we demonstrate experimentally the impact of the flow history on CO2 leakage risk for cement plugging. In-situ mu-CT experiments combined with geochemical modeling provide unique insight into the interactions between CO2 and cement, potentially helping in assessing the risks of CO(2 )storage in geological reservoirs.
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Papaslioti, E. M., Perez-Lopez, R., Parviainen, A., Phan, V. H., Marchesi, C., Fernandez-Martinez, A., et al. (2020). Effects of redox oscillations on the phosphogypsum waste in an estuarine salt-marsh system. Chemosphere, 242.
Résumé: Salt marshes are natural deposits of heavy metals in estuarine systems, where sulphide precipitation associated with redox changes often results in a natural attenuation of contamination. In the present study, we focus on the effects of variable redox conditions imposed to a highly-polluted phosphogypsum stack that is directly piled over the salt marsh soil in the Tinto River estuary (Huelva, Spain). The behaviour of contaminants is evaluated in the phosphogypsum waste and in the marsh basement, separately, in controlled, experimentally-induced oscillating redox conditions. The results revealed that Fe, and to a lesser extent S, control most precipitation/dissolution processes. Ferric iron precipitates in the form of phosphates and oxyhydroxides, while metal sulphide precipitation is insignificant and appears to be prevented by the abundant formation of Fe phosphates. An antagonistic evolution with changing redox conditions was observed for the remaining contaminants such as Zn, As, Cd and U, which remained mobile in solution during most of experimental run. Therefore, these findings revealed that high concentrations of phosphates inhibit the typical processes of immobilisation of pollutants in salt-marshes which highlights the elevated contaminant potential of phosphogypsum wastes on coastal environments. (C) 2019 Elsevier Ltd. All rights reserved.
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Pedersen, H. A., Leroy, N., Zigone, D., Vallee, M., Ringler, A. T., & Wilson, D. C. (2020). Using Component Ratios to Detect Metadata and Instrument Problems of Seismic Stations: Examples from 18 Yr of GEOSCOPE Data. Seismological Research Letters, 91(1), 272–286.
Résumé: Replacement or deterioration of seismic instruments and the evolution of the installation conditions and sites can alter the seismic signal in very subtle ways; therefore, it is notoriously difficult to monitor the signal quality of permanent seismic stations. We present a simple way to characterize and monitor signal quality, using energy ratios between each pair of the three components, as a complement to existing methods. To calculate stable daily energy ratios over a large frequency range (0.01-5 Hz), we use the daily median energy ratio over all 5 min windows within the day. The method is applied to all GEOSCOPE stations, for continuous BH channel data collected since 2001. We show applications to identify past gain problems (stations ROCAM and CRZF), to provide feedback after field interventions at remote sites (Antarctic station DRV), and to shed light on complex instrument problems (stations ECH and KIP). Our results show that component energy ratios have excellent time resolution and that they are visually simple for identification of problems. They can be used both for ongoing continuous monitoring of the signal quality, or as a tool to identify past problems. The Python code to produce the results in this work and the Python code for daily monitoring used by GEOSCOPE are available (see Data and Resources).
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Peltzer, G., Brown, N. D., Meriaux, A. S., van der Woerd, J., Rhodes, E. J., Finkel, R. C., et al. (2020). Stable Rate of Slip Along the Karakax Section of the Altyn Tagh Fault from Observation of Interglacial and Postglacial Offset Morphology and Surface Dating. Journal Of Geophysical Research-Solid Earth, 125(5).
Résumé: Digital elevation maps obtained using TanDEM-X and Pleiades data combined with newly obtained surface age estimates using cosmogenic radionuclide (CRN) and optically simulated luminescence (OSL) methods are used to quantify the slip rate along the western section of the Altyn Tagh Fault in southern Xinjiang. The reconstruction of the conical shape of massive alluvial fans inferred to be from the Eemian (115 +/- 7 ka) from CRN dating shows consistent left-lateral offsets of 300 +/- 20 m, yielding a slip rate of 2.6 +/- 0.3 mm/year. Successive episodes of incision have left cut terraces inset in wide canyons, 10-25 m below the fans' surface. The incision was followed by the deposition of a broad terrace of early Holocene age, which is reincised by modern stream channels. Near the village of Shanxili, a 200 m wide valley is partially dammed by a shutter ridge displaced by the fault. A fill terrace deposited upstream from the ridge has an OSL age of 8.8 +/- 0.6 ka. The 23 +/- 2 m offset of the riser incising the terrace indicates a minimum postdepositional movement on the fault, yielding a Holocene rate of 2.6 +/- 0.5 mm/year, consistent with the 115-ka average slip rate. Scarp degradation analysis using mass diffusion reveals a nonlinear relationship between fault displacement and degradation coefficient along the progressively exposed fault scarp, a pattern suggesting either seismic clustering or variable diffusion rate since the Eemian. Together with the Gozha Co-Longmu Co fault to the south, the Karakax section of the Altyn Tagh Fault contributes to the eastward movement of the western corner of Tibet.
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Perez-Caceres, I., Poyatos, D. J. M., Vidal, O., Beyssac, O., Nieto, F., Simancas, J. F., et al. (2020). Deciphering the metamorphic evolution of the Pulo do Lobo metasedimentary domain (SW Iberian Variscides). Solid Earth, 11(2), 469–488.
Résumé: The Pulo do Lobo domain is one of the units exposed within the orogenic suture zone between the Ossa-Morena and the South Portuguese zones in the SW Iberian Variscides. This metasedimentary unit has been classically interpreted as a Rheic subduction-related accretionary prism formed during pre-Carboniferous convergence and eventual collision between the South Portuguese Zone (part of Avalonia) and the Ossa-Morena Zone (peri-Gondwanan terrane). Discrete mafic intrusions also occur within the dominant Pulo do Lobo metapelites, related to an intra-orogenic Mississippian transtensional and magmatic event that had a significant thermal input. Three different approaches have been applied to the Devonian-Carboniferous phyllites and slates of the Pulo do Lobo domain in order to study their poorly known low-grade metamorphic evolution. X-ray diffraction (XRD) was used to identify the mineralogy and measure crystallographic parameters (illite “crystallinity” and K-white mica b-cell dimension). Compositional maps of selected samples were obtained from electron probe micro-analysis, which allowed for processing with XMapTools software, and chlorite semiempirical and thermodynamic geothermometry was performed. Thermometry based on Raman spectroscopy of carbonaceous material (RSCM) was used to obtain peak temperatures. The microstructural study shows the existence of two phyllosilicate growth events in the chlorite zone, the main one (M-1) related to the development of a Devonian foliation S-1 and a minor one (M-2) associated with a crenulation cleavage (S-2) developed in middle-upper Carboniferous times. M-1 entered well into epizone (greenschist facies) conditions. M-2 conditions were at lower temperature, reaching the anchizone-epizone boundary. These data accord well with the angular unconformity that separates the Devonian and Carboniferous formations of the Pulo do Lobo domain. The varied results obtained by the different approaches followed, combined with microstructural analysis, provide different snapshots of the metamorphic history. Thus, RSCM temperatures are higher in comparison with the other methods applied, which is interpreted to reflect a faster re-equilibration during the short-lived thermal Mississippian event. Regarding the metamorphic pressure, the data are very homogeneous: very low celadonite content (0 %-10 %) in muscovite (and low values of K-white mica b-cell dimension; 8.995 angstrom mean value), indicating a low pressure-temperature gradient, which is unexpected in a subduction-related accretionary prism. Highlights – A multidisciplinary approach has been applied to study the metamorphism of the Pulo do Lobo metapelites. – Devonian metamorphism entered epizone conditions. – Carboniferous metamorphism reached the anchizone-epizone boundary. – The inferred low-pressure gradient is incompatible with a subduction-related accretionary prism.
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Perrault, M., Gueguen, P., Parra, G., & Sarango, J. (2020). Modification of the data-driven period/height relationship for buildings located in seismic-prone regions such as Quito (Ecuador). Bulletin Of Earthquake Engineering, 18(8), 3545–3562.
Résumé: The fundamental period of structures is a parameter used in structure under design and for evaluating existing structures. Data-driven methods using ambient vibrations have become popular, particularly for the adjustment of empirical relationships applied to building classes. This study presents the results of a survey of ambient vibrations performed in 146 reinforced concrete buildings in the center of Quito (Ecuador). Classical functional forms giving period (T) for height (H) or number of floors (N) are derived and compared with the relationships available in the Ecuadorian seismic design provisions. We highlight variations in the empirical relationships according to soil conditions, but above all according to the date of construction and the historic seismic sequence to which the buildings have been exposed. The cumulative damage effect is finally confirmed by repeating ambient vibration measurements after the 2016 Mw 7.8 Pedernales earthquake located in the subduction zone, about 175 km from Quito. Even with such a long epicentral distance, leading to low macroseismic intensity (I-EMS98 = IV), the seismic ground motion of between 0.017 and 0.081 g recorded in Quito reduced the resonant frequency of the buildings tested by between 2 and 13%. This confirms the effect of cumulative damage in reinforced concrete buildings located in seismic zones, even for weak ground motions, and the variability of empirical T/H relationships associated with damage.
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Perttu, A., Caudron, C., Assink, J. D., Metz, D., Tailpied, D., Perttu, B., et al. (2020). Reconstruction of the 2018 tsunamigenic flank collapse and eruptive activity at Anak Krakatau based on eyewitness reports, seismo-acoustic and satellite observations. Earth And Planetary Science Letters, 541.
Résumé: After several months of eruptive activity, the subaerial cone of Anak Krakatau collapsed on December 22, 2018. The landslide event generated a tsunami that had deadly consequences within the Sunda Strait in Indonesia. Such significant collapse events are common in the geologic record but are a rare phenomenon, in the instrumented record. However, these events can have a potentially large impact on society. We have reconstructed the collapse, along with the activity preceding and following it, by combining information from official reports, remote geophysical observations, and local eyewitness accounts. It appears that the collapse of Anak Krakatau's subaerial cone led to a drastic change in the eruptive style from continuous Strombolian explosions to sustained Surtseyan. Those changes are detectable in the seismo-acoustic measurements, which, when combined with eyewitnesses, allows us to reconstruct the timing and phenomenology of the sequence. Our analysis reveals that intense eruptive activity generated sustained infrasound, unusual but not unique at Anak Krakatau, starting approximately eight hours before the collapse. Within this timeframe, two seismic signals consistent with minor mass movements as well as a momentary quiescence were identified prior to the main collapse. The data presented here indicate that Anak Krakatau failed in one collapse event, producing a tsunami with multiple waves around the volcano, the last one being the largest. Following the collapse, three volcanic plumes could be clearly identified in the satellite data and by eyewitnesses, as well as spectral lines in the seismic data. These lines, observed up to 371 km, suggest a repeating energetic explosive source lasting for seven days. The collapse produced multiple infrasound arrivals observed at regional infrasound stations, but was not recorded on the regional hydroacoustic network. Our analysis of the eruptive sequence demonstrates that a detailed eruption chronology can be reconstructed using remote methods, even in the event of failure or destruction of local monitoring infrastructure. This event also highlights that tsunamigenic flank collapses can occur with little to no warning, and be difficult to interpret in real-time, as a significant amount of non-operational analysis was required after the event, to complete the chronology. (C) 2020 The Author(s). Published by Elsevier B.V.
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Picazo, S., Malvoisin, B., Baumgartner, L., & Bouvier, A. S. (2020). Low Temperature Serpentinite Replacement by Carbonates during Seawater Influx in the Newfoundland Margin. Minerals, 10(2).
Résumé: Serpentinite replacement by carbonates in the seafloor is one of themain carbonation processes in nature providing insights into the mechanisms of CO2 sequestration; however, the onset of this process and the conditions for the reaction to occur are not yet fully understood. Preserved serpentine rim with pseudomorphs of carbonate after serpentine and lobate-shaped carbonate grains are key structural features for replacement of serpentinite by carbonates. Cathodoluminescence microscopy reveals that Ca-rich carbonate precipitation in serpentinite is associated with a sequential assimilation of Mn. Homogeneous delta O-18 values at the μm-scale within grains and host sample indicate low formation temperature (<20 degrees C) from carbonation initiation, with a high fluid to rock ratio. delta C-13 (1-3 +/- 1 parts per thousand) sit within the measured values for hydrothermal systems ( 3-3 parts per thousand), with no systematic correlation with theMn content. delta C-13 values reflect the inorganic carbon dominance and the seawater source of CO2 for carbonate. Thermodynamic modeling of fluid /rock interaction during seawater transport in serpentine predicts Ca-rich carbonate production, at the expense of serpentine, only at temperatures below 50 degrees C during seawater influx. Mg-rich carbonates can also be produced when using a model of fluid discharge, but at significantly higher temperatures (150 degrees C). This has major implications for the setting of carbonation in present-day and in fossil margins.
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Pilz, M., Cotton, F., & Kotha, S. R. (2020). Data-driven and machine learning identification of seismic reference stations in Europe. Geophysical Journal International, 222(2), 861–873.
Résumé: The growing seismic networks and the increasing number of permanent seismic stations can help in improving the physical basis of seismic hazard assessment. For this purpose, the definition of reference site conditions is of great significance. If a reliable estimate of the reference ground motion is known, its modification at any given site can be modelled with respect to that reference site. Since the choice of a well-characterized reference site is not straightforward, mainly due to the high variability in the shallow layers, such choices prove to be affected by large uncertainties. While proxy parameters like the average S-wave velocity over the uppermost 30 m (v(S)(30)) might help in characterizing reference site conditions, such parameters are neither available at all sites nor do they allow concluding that the site is not affected by amplification and attenuation effects. In this study, we identify prospective reference sites across Europe in a harmonized and fully data-driven way. All analysis is based on freely available geological and geophysical data and no on-site measurements or site-specific proxies are required. The study accounts for both the influence of amplification and attenuation in a large frequency range. To address the key conceptual issues, we verify our classification based on machine learning techniques in which the influence of the individual site characterization parameters is investigated. Our study indicates that around 250 sites in Europe over more than 2000 investigated are not affected by local site effects and can de facto be considered as reference sites based on the criteria applied.
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Pineau, M., Le Deit, L., Chauvire, B., Carter, J., Rondeau, B., & Mangold, N. (2020). Toward the geological significance of hydrated silica detected by near infrared spectroscopy on Mars based on terrestrial reference samples. Icarus, 347.
Résumé: Hydrated silica detected on the martian surface, from both orbital and in-situ data, is an indicator of past aqueous conditions. On Earth, several near infrared (NIR) spectral criteria can be used to discriminate silica phases (e.g. opal-A, opal-CT and chalcedony) and their formation processes. We have applied these spectral criteria to Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data in order to investigate the geological origin of hydrated silica on Mars. We used two spectral criteria: (i) the crystallinity spectral criteria on the 1.4-and 1.9 μm absorption bands to distinguish between amorphous (opal-A and hydrated glasses) and more crystalline (opal-CT and chalcedony) varieties of silica, and (ii) the Concavity-Ratio-Criterion (CRC) to differentiate opals of hydrothermal origin from weathering origin. We first adapted the CRC measurements on terrestrial samples to make them comparable to CRISM measurements on Mars: we resampled our terrestrial spectra down to the CRISM resolution, and tested the martian pressure effect on spectral signatures. Then, we selected several areas over nine sites where hydrated silica has been detected on Mars, on the basis of good quality detections. Our results show that two main types of spectra can be distinguished, and these are consistent with two distinct geomorphological contexts proposed by Sun and Milliken (2018): amorphous and/or dehydrated silica-bearing bedrock deposits, and more crystalline and/or hydrated silica-bearing aeolian deposits. The concavity criterion also indicates silica origins that are in agreement with most of the hypothesized geological origins proposed in the literature. Although these results need further strengthening, they are promising for the use of NIR signatures as means of investigating the processes of hydrated silica on Mars.
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Plunian, F., & Alboussiere, T. (2020). Axisymmetric dynamo action is possible with anisotropic conductivity. Physical Review Research, 2(1).
Résumé: A milestone of dynamo theory is Cowling's theorem, known in its modern form as the impossibility for an axisymmetric velocity field to generate an axisymmetric magnetic field by dynamo action. Using anisotropic electrical conductivity, we show that an axisymmetric dynamo is in fact possible with a motion as simple as solid-body rotation. On top of that, the instability analysis can be conducted entirely analytically, leading to an explicit expression of the dynamo threshold, which is the only example in dynamo theory.
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Plunian, F., Teimurazov, A., Stepanov, R., & Verma, M. K. (2020). Inverse cascade of energy in helical turbulence. Journal Of Fluid Mechanics, 895.
Résumé: Using direct numerical simulation of hydrodynamic turbulence with helicity forcing applied at all scales, a near-maximum helical turbulent state is obtained, with an inverse energy cascade at scales larger than the energy forcing scale and a forward helicity cascade at scales smaller than the energy forcing scale. In contrast to previous studies using decimated triads, our simulations contain all possible triads. By computing the shell-to-shell energy fluxes, we show that the inverse energy cascade results from weakly non-local interactions among homochiral triads. Varying the helicity injection range of scales leads to necessary conditions to obtain an inverse energy cascade.
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Poli, P., Boaga, J., Molinari, I., Cascone, V., & Boschi, L. (2020). The 2020 coronavirus lockdown and seismic monitoring of anthropic activities in Northern Italy. Scientific Reports, 10(1).
Résumé: In March/April 2020 the Italian government drastically reduced vehicle traffic and interrupted all non-essential industrial activities over the entire national territory. Italy thus became the first country in the world, with the exception of Hubei, to enact lockdown measures as a consequence of the COVID-19 outbreak and the need to contain it. Italy is also a seismically active area, and as such is monitored by a dense permanent network of seismic stations. We analyse continuous seismic data from many stations in northern and central Italy, and quantify the impact of the lockdown on seismic ambient noise, as a function of time and location. We find that the lockdown reduces ambient noise significantly in the 1-10Hz frequency range; because natural sources of seismic noise are not affected by the lockdown, the seismic signature of anthropic noise can be characterised with unprecedented clarity, by simply comparing the signal recorded before and after the lockdown. Our results correlate well with independent evaluations of the impact of the lockdown (e.g., cell phone displacements), and we submit that ambient-noise seismology is a useful tool to monitor containment measures such as the coronavirus lockdowns.
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Poli, P., Marguin, V., Wang, Q. Y., D'Agostino, N., & Johnson, P. (2020). Seasonal and Coseismic Velocity Variation in the Region of L'Aquila From Single Station Measurements and Implications for Crustal Rheology. Journal Of Geophysical Research-Solid Earth, 125(7).
Résumé: We performed measurements of velocity variations for variable coda waves time lapse using empirical Green's functions reconstructed by autocorrelation of seismic noise recorded during a period of 17 years in the region of L'Aquila, Italy. The time lapse approach permitted us to evaluate the spatial (depth) dependence of velocity variation (dv/v). By quantitatively comparing the 17 years of dv/v time series with independent data (e.g., strain induced by earthquakes and hydrological loading), we unravel a group of physical processes inducing velocity variations in the crust over multiple time and spatial scales. We find that rapid shaking due to three magnitude 6+ earthquakes mainly induced near surface velocity variations. On the other hand, slow strain perturbation (period 5 years, in the preseismic period) associated with hydrological cycles, induced velocity changes primarily in the middle crust. The observed behavior suggests the existence of a large volume of fluid-filled cracks exist deep in the crust. Our study highlights the possibility of using seasonal and multiyear perturbations to probe the physical properties of seismogenic fault volumes and shed new light into the depth-dependent rheology of crustal rocks in the region or L'Aquila.
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Pothon, A., Gueguen, P., Buisine, S., & Bard, P. Y. (2020). Comparing Probabilistic Seismic Hazard Maps with ShakeMap Footprints for Indonesia. Seismological Research Letters, 91(2), 847–858.
Résumé: A number of probabilistic seismic hazard assessment (PSHA) maps have been released for Indonesia over the past few decades. This study proposes a method for testing PSHA maps using U.S. Geological Survey ShakeMap catalog considered as historical seismicity for Indonesia. It consists in counting the number of sites on rock soil for which the independent maximum peak ground acceleration (PGA) of the ShakeMap footprints between May 1968 and May 2018 exceeds the thresholds from the PSHA map studied and in comparing this number with the probability of exceedance given in the PSHA map. Although ShakeMap footprints are not as accurate and complete as continuous recorded ground motion, the spatially distributed ShakeMap covers 7,642,261 grid points, with a resolution of 1 km(2), compensating the lack of instrumental data over this period. This data set is large enough for the statistical analysis of independent PGA values on rock sites only. To obtain the subdata set, we develop a new selection process and a new comparison method, considering the uncertainty of ShakeMap estimates. The method is applied to three PSHA maps (Global Seismic Hazard Assessment Program [GSHAP], Global Assessment Report [GAR], and Standar Nasional Indonesia [SNI2017]) for a selection of sites first located in Indonesia and next only in the western part of the country. The results show that SNI2017 provides the best fit with seismicity over the past 50 yr for both sets of rock sites (whole country and western part only). At the opposite, the GAR and GSHAP seismic hazard maps only fit the seismicity observed for the set of rock sites in western Indonesia. This result indicates that this method can only conclude on the spatial scale of the analysis and cannot be extrapolated to any other spatial resolution.
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Pousse-Beltran, L., Socquet, A., Benedetti, L., Doin, M. P., Rizza, M., & D'Agostino, N. (2020). Localized Afterslip at Geometrical Complexities Revealed by InSAR After the 2016 Central Italy Seismic Sequence. Journal Of Geophysical Research-Solid Earth, 125(11).
Résumé: The Mw 6.5 Norcia earthquake occurred on 30 October 2016, along the Mt Vettore fault (Central Apennines, Italy), it was the largest earthquake of the 2016-2017 seismic sequence that started 2 months earlier with the Mw 6.0 Amatrice earthquake (24 August). To detect potential slow slip during the sequence, we produced Interferometric Synthetic Aperture Radar (InSAR) time series using 12- to 6-day repeat cycles of Sentinel-1A/1B images. Time series indicates that centimeter-scale surface displacements took place during the 10 weeks following the Norcia earthquake. Two areas of subsidence are detected: one in the Castelluccio basin (hanging wall of the Mt Vettore fault) and one in the southern extent of the Norcia earthquake surface rupture, near an inherited thrust. Poroelastic and viscoelastic models are unable to explain these displacements. In the Castelluccio basin, the displacement reaches 13.2 +/- 1.4 mm in the ascending line of sight on 6 January 2017. South of the Norcia earthquake surface rupture (a zone between the Norcia and Amatrice earthquakes), the postseismic surface displacements affect a smaller area but reach 35.5 +/- 1.7 mm in ascending line of sight by January 2017 and follow a logarithmic temporal decay consistent with postseismic afterslip. Our analysis suggests that the structurally complex area located south of the Norcia rupture (30 October) is characterized by a conditionally stable frictional regime. This geometrical and frictional barrier likely halted rupture propagation during the Amatrice (24 August) and Norcia (30 October) earthquakes at shallow depth (<3-4 km).
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Prud'homme, C., Vassallo, R., Crouzet, C., Carcaillet, J., Mugnier, J. L., & Cortes-Aranda, J. (2020). Paired Be-10 sampling of polished bedrock and erratic boulders to improve dating of glacial landforms: an example from the Western Alps. Earth Surface Processes And Landforms, 45(5), 1168–1180.
Résumé: Cosmogenic nuclide dating of glacial landforms may lead to ambiguous results for ice retreat histories. The persistence of significant cosmogenic concentrations inherited from previous exposure may increase the apparent exposure ages for polished bedrocks affected by limited erosion under ice and for erratic boulders transported by glaciers and previously exposed in high-altitude rock walls. In contrast, transient burying by moraines, sediments and snow decreases the apparent exposure age. We propose a new sampling strategy, applied to four sites distributed in the Arc and Arve valleys in the Western Alps, to better constrain the factors that can bias exposure ages associated with glacial processes. We used the terrestrial cosmogenic nuclide Be-10 (TCN) to estimate the exposure time from paired sampling of depth profiles in polished bedrock and on overlying erratic boulders. For a given sampling site, the exposure ages for both the polished bedrock and boulder are expected to be the same. However, in six cases out of seven, boulders had significantly higher Be-10 surface concentrations than those of the associated polished surfaces. In present and past glacial processes, the Be-10 distribution with depth for boulders and bedrocks implies the presence of an inheritance concentration of Be-10. Our study suggests that Be-10 concentrations in erratic boulders and in polished bedrocks provide maximum and minimum exposure ages of the glacial retreat, respectively. (c) 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd
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Reinoza, C. E., Audemard, F. A., Jouanne, F., Pousse-Beltran, L., & Beck, C. (2020). Strain calculations of active tectonic blocks in northeastern Venezuela from GNSS analysis. Journal Of South American Earth Sciences, 102.
Résumé: We study translation, rotation, and strain of active tectonic blocks in Northeastern Venezuela from the Global Navigation Satellite System (GNSS) observations. Since the installation of the geodetic network in 2003, one of the goals was to place at least three observation sites at each tectonic block to study the deformation of each one. Based on this premise, we define at least seven blocks: Bergantin and Caripe blocks south of the El Pilar Fault (EPF), and Cariaco Gulf, Land bridge, Paria, North Peninsula, and Margarita Island blocks north of the EPF. Our preferred block modeling shows angular rotations from 0.02 to 0.29 degrees Ma(-1). It is known that the EPF concentrates the active deformation in this region of the Caribbean-South American plate boundary. However, the existent rotation could accommodate part of the motion. The strain rate tensors (SRT) indicate NW-SE compression and NE-SW extension for the western blocks. To the east, the 4-Land bridge block keeps the NW-SE compression but shows a decrease in the extensional component. The 5-Paria blocks show a complete inversion in the sense of semi-axis. Additionally, we evaluate the possibility of different motions in Margarita block calculating translational vector, rotational velocity, and strain from three GNSS sites at each side thereof. Our results show remarkable similarities for the Macanao Peninsula and Eastern Margarita Island, pointing to both belonging to a single block.
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Ren, C. X., Peltier, A., Ferrazzini, V., Rouet-Leduc, B., Johnson, P. A., & Brenguier, F. (2020). Machine Learning Reveals the Seismic Signature of Eruptive Behavior at Piton de la Fournaise Volcano. Geophysical Research Letters, 47(3).
Résumé: Volcanic tremor is key to our understanding of active magmatic systems, but due to its complexity, there is still a debate concerning its origins and how it can be used to characterize eruptive dynamics. In this study we leverage machine learning techniques using 6 years of continuous seismic data from the Piton de la Fournaise volcano (La Reunion island) to describe specific patterns of seismic signals recorded during eruptions. These results unveil what we interpret as signals associated with various eruptive dynamics of the volcano, including the effusion of a large volume of lava during the August-October 2015 eruption as well as the closing of the eruptive vent during the September-November 2018 eruption. The machine learning workflow we describe can easily be applied to other active volcanoes, potentially leading to an enhanced understanding of the temporal and spatial evolution of volcanic eruptions. Plain Language Summary A good understanding of volcanic activity is key to managing volcanic hazards resulting from eruptive activity. Volcanic tremor is a continuous seismic signal often seen during eruptions associated with the flow of magma through the volcano and is thus an extremely useful tool in characterizing the progression and phases of eruptions. In this study we study this signal at the Piton de la Fournaise volcano, on La Reunion island. Using machine learning algorithms, we investigate characteristics of this signal emitted by the volcano during eruptions to reveal the fundamental frequency at which it occurs, as well as changes in eruptive state that occur during some eruptions in our data set. This workflow may be applied to other volcanos to further our understanding of eruptive dynamics.
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Renard, F., Kandula, N., McBeck, J., & Cordonnier, B. (2020). Creep Burst Coincident With Faulting in Marble Observed in 4-D Synchrotron X-Ray Imaging Triaxial Compression Experiments. Journal Of Geophysical Research-Solid Earth, 125(9).
Résumé: Faults in carbonate rocks show both seismic and aseismic deformation processes, leading to a wide range of slip velocities. We deformed two centimeter-scale cores of Carrara marble at 25 degrees C and imaged the nucleation and growth of faults using dynamic synchrotron X-ray microtomography. The first sample experienced a constant confinement of 30 MPa and no pore fluid. The second sample experienced confinement in the range 35-23 MPa and water as a pore fluid at 10 MPa pore pressure. We increased the axial stress by steps until creep deformation occurred and imaged deformation in 4-D. The samples deformed with a quasi-constant or increasing strain rate when the differential stress was constant, a process called creep. However, for both samples, we also observed transient events that include the acceleration of creep, that is, creep bursts, phenomena similar to slow slip events that occur in continental active faults. During these transient creep events, strain rates increase and correlate in time with strain localization and the slow development of system-spanning fault networks. In both samples, the acceleration of opening and shearing of microfractures accommodated creep bursts. High-resolution time-lapse X-ray microtomography imaging and digital image correlation during triaxial deformation quantify creep in laboratory faults at subgrain spatial resolution. This work demonstrates that transient creep events, that is, creep bursts or slow slip events, correlate with the nucleation and slow growth of faults and not only with slip on preexisting faults. Plain Language Summary Active faults may slip at velocities close to 1 m/s during earthquakes and may also slip at much slower rates, in creep. Sometimes such creep is continuous in time; sometimes it is transient and occurs as creep bursts, also called slow slip events. Using state-of-the-art synchrotron X-ray imaging of core samples of Carrara marble deformed under constant stress conditions and room temperature, we identified such creep bursts. Our 4-D imaging technique allows seeing through the sample and characterizing the microphysical processes that produce creep bursts. Results show that the acceleration of microfractures nucleation, growth, and coalescence in the sample may lead to the formation of system-spanning faults that coincide in time with the macroscopically observed creep burst. These results demonstrate that creep bursts may not only correspond to slow slip events on active preexisting faults but may also indicate the slow development of new active faults.
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Renard, F., McBeck, J., & Cordonnier, B. (2020). Competition between slow slip and damage on and off faults revealed in 4D synchrotron imaging experiments. Tectonophysics, 782.
Résumé: In the continental crust, faults may accommodate deformation through aseismic creep, slow slip events, or seismic slips that produce dynamic damage, or a combination of these endmembers. A variety of parameters controls the occurrence of these mechanical behaviors. In a series of laboratory experiments, we image centimeter-scale faults during sliding under in situ conditions. We perform four experiments of slip on centimeter-scale crystalline rock samples prepared with a saw-cut interface at 45 degrees from the direction to the maximum compressive stress and at stress conditions of 2-3 km depth. We image fault slip and off-fault fracture development using 4D synchrotron X-ray microtomography. Three faults have an initial rough interface, and deformation occurs with increasing differential stress by a combination of slow slip events and off-fault damage, until catastrophic failure and the formation of new faults. Conversely, the pre-cut fault with a smooth initial surface deforms mainly by slow slip, develops numerous striations along its slip plane, and no microfractures are detected in the wall rock. Our experiments reproduce aseismic and seismic faulting behavior, and demonstrate that the roughness of the fault plane is one of the parameters that control the transition between these two behaviors. A fault with a rougher interface may tend to develop more off-fault damage and seismic behavior. For the rough fault experiments, the secondary faulting occurs along a network of faults oriented at high angles from the pre-existing saw-cut plane, a behavior similar to several earthquake sequences that occurred along orthogonal faults.
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Replumaz, A., Jose, M. S., Margirier, A., van der Beek, P., Gautheron, C., Leloup, P. H., et al. (2020). Tectonic Control on Rapid Late Miocene-Quaternary Incision of the Mekong River Knickzone, Southeast Tibetan Plateau. Tectonics, 39(2).
Résumé: The incision history of the Three Rivers (Salween, Mekong, and Yangtze) region in the Southeast Tibetan Plateau has been linked to both tectonic and climatic controls. In this study, we report new apatite (U-Th)/He and fission-track thermochronology data from the >6,000-m-high Kawagebo massif, which forms the edge of the high plateau on the western flank of the steepened knickzone reach of the middle Mekong River valley. Thermal-history modeling of a thermochronological age-elevation profile shows rapid cooling since similar to 1.5 Ma and suggests a mean Quaternary exhumation rate of >1 km/Myr at the valley bottom. The amount of Quaternary exhumation is too high to be caused by fluvial incision alone and requires additional tectonic uplift. Comparing our data from the western flank of the Mekong River valley with published data from the eastern flank shows differential exhumation across the valley in the late Miocene, with the western flank undergoing more exhumation, but relatively uniform exhumation in the Quaternary. We relate rapid exhumation since the late Miocene on the western flank of the Mekong valley and the high topography of the Kawagebo massif to localized tectonic uplift associated with a restraining (left stepping) overstep between the still-active right-lateral Parlung and Zhongdian strike-slip faults. The pattern of river steepness index across the knickzone also indicates that it results from locally focused uplift. Our results demonstrate the importance of detailed thermochronologic studies in this very active region to constrain the complex multiphase tectonic history before invoking any potential climatic forcing of river incision.
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Retailleau, L., Boue, P., Li, L., & Campillo, M. (2020). Ambient seismic noise imaging of the lowermost mantle beneath the North Atlantic Ocean. Geophysical Journal International, 222(2), 1339–1351.
Résumé: Body waves can be extracted from correlation functions computed from seismic records even at teleseismic distances. Here we use P and PcP waves from the secondary microseism frequency band that are propagating between Europe and the Eastern United States to image the core-mantle boundary (CMB) and D '' structure beneath the North Atlantic. This study presents the first 3-D image of the lower mantle obtained from ocean-generated microseism data. Robustness of our results is evaluated by comparing images produced by propagation in both directions. Our observations reveal complex patterns of lateral and vertical variations of P-wave reflectivity with a particularly strong anomaly extending upward in the lower mantle up to 2600 km deep. We compare these results with synthetic data and associate this anomaly to a V-p velocity increase above the CMB. Our image aims at promoting the study of the lower mantle with microseism noise excitations.
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Revil, A., Coperey, A., Heap, M. J., & Carbillet, L. (2020). A geophysical index to map alteration, permeability, and mechanical properties within volcanoes. Application to the soft volcanic rocks from Whakaari/White Island (New Zealand). Journal Of Volcanology And Geothermal Research, 401.
Résumé: The alteration of soft volcanic rocks (i.e., characterized by a low uniaxial compressive strength <35 MPa) can change their permeability and mechanical strength. We built an alteration indicator based on porosity and cation exchange capacity (CEC) to connect the degree of alteration of soft volcanic rocks to their permeability and uniaxial compressive strength. The proposed empirical petrophysical relationships are validated using a dataset of 62 samples from Whakaari/White Island (New Zealand). Since porosity and CEC can be imaged with induced polarization, this geophysical method can be used to map permeability and mechanical properties for near-surface formations at active volcanoes worldwide. (C) 2020 Elsevier B.V. All rights reserved.
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Ritz J., S. B., M. Ferry, C. Larroque, L. Audin, B. Delouis, E. Mathot. (2020). Surface rupture and shallow fault reactivation during the 2019 Mw 4.9 Le Teil earthquake, France. Nature Commun Earth Environ, 1(10).
Résumé: The Rhône River Valley in France, a densely populated area with many industrial facilities including several nuclear power plants, was shaken on November 11th 2019, by the Mw 4.9 Le Teil earthquake. Here, we report field, seismological and interferometric synthetic-aperture radar observations indicating that the earthquake occurred at a very shallow focal depth on a southeast-dipping reverse-fault. We show evidence of surface rupture and up to 15 cm uplift of the hanging wall along a northeast-southwest trending discontinuity with a length of about 5 km. Together, these lines of evidence suggest that the Oligocene La Rouvière fault was reactivated. Based on the absence of geomorphic evidence of cumulative compressional deformation along the fault, we suggest that it had not ruptured for several thousand or even tens of thousands of years. Our observations raise the question of whether displacement from surface rupture represents a hazard in regions with strong tectonic inheritance and very low strain rates.
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Rivera, H. A., Le Roux, J. P., Farias, M., Gutierrez, N. M., Sanchez, A., & Palma-Heldt, S. (2020). Tectonic controls on the Maastrichtian-Danian transgression in the Magallanes-Austral foreland basin (Chile): Implications for the growth of the Southern Patagonian Andes. Sedimentary Geology, 403.
Résumé: The Maastrichtian-Danian transgression was one of the most extensive Atlantic-derived marine incursions in Patagonia. This study examines its stratigraphic record and origin in the Magallanes-Austral Basin, revealing an interplay of sedimentation, tectonism, and base-level changes, which contribute to our understanding of foreland basin dynamics. We present a multidisciplinary approach from a relatively poorly documented sector (51 degrees 38'-53 degrees 50's) of the basin. This approach includes facies and provenance analysis, palynology, sequence stratigraphy, and U-Pb geochronology. These techniques enable us to evaluate the role of climate, tectonics, and eustasy on the transgression, as well as providing insight into the growth of the Southern Patagonian Andes. A first shallowing-upward cyde (late Campanian to late Maastrichtian) is represented by the transition from outer shelf and upper slope deposits (Fuentes and Tres Pasos formations) to shoreface and deltaic environments (Rocallosa and Dorotea formations), favoured by high erosion rates in the fold-thrust belt and eustatic sea-level drop. A subsequent deepening-upward cycle (late Maastrichtian to Paleocene) records the Atlantic transgression, manifested by estuarine deposits in an incised valley (uppermost Dorotea Formation) and deep-water turbidites (Chorrillo Chico Formation and Cabo Nariz beds). Palynological results suggest a temperate palaeoclimate (similar to 6-17 degrees C) during the Maastrichtian-Danian, which agrees with significant cooling of the South Atlantic Ocean at this time. Therefore, relative climatic optima are not a driver of marine ingression. The stratigraphic and tectonic evolution of the succession studied suggests that flexural and dynamic subsidence promoted marine incursion into the Magallanes-Austral Basin. Provenance data indicate sediment input to the basin from the Southern Patagonian Batholith, Rocas Verdes Basin remnants, Tobifera Formation, and metamorphic terranes exposed in the hinterland of the Southern Patagonian Andes during the early Maastrichtian. However, by the Paleocene, sediments derived from the hinterland had been structurally dammed during basinward propagation of the fold-thrust belt. (C) 2020 Elsevier B.V. All rights reserved.
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Rodriguez-Pascua, M. A., Escobar, C. B., Guevara, L. R., Grutzner, C., Audin, L., Walker, R., et al. (2020). Did earthquakes strike Machu Picchu? Journal Of Seismology, 24(4), 883–895.
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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Roman, A., & Arndt, N. (2020). Differentiated Archean oceanic crust: Its thermal structure, mechanical stability and a test of the sagduction hypothesis. Geochimica Et Cosmochimica Acta, 278, 65–77.
Résumé: Many recent studies conclude that plate tectonics started about 3 billion years ago in the mid Archean. The transition from a pre-subduction regime to modern plate tectonics is reported to be marked by changes in trace element ratios or isotopic compositions that monitor the rate of growth of the continental crust, the appearance of eclogitic inclusions in diamonds, or an apparent change in the composition of the upper crust. Behind most of these arguments is the hypothesis that, early in Earth history when the mantle was hotter, subduction was intermittent or impossible. If so, a mechanism other than subduction must have created the granitoids that dominate Archean continental crust. One alternative, commonly referred to as sagduction, proposes that the base of thick oceanic crust founders and partially melts to generate granitic magma. Here we evaluate the sagduction process, starting by discussing two crucial concepts: (1) thick oceanic crust is internally differentiated, with hydrated basalt being restricted to the uppermost layers, (2) the generation of granitic magma requires that water and basalt is present in the lower part of the crust or is taken deep into the mantle. We present the results of numerical modelling that demonstrates that when intrusion is taken into account, the lower portion of the crust is well above dehydration temperatures and therefore essentially dry. We show that any deformation within thick, differentiated crust is restricted to the lowermost layers of dry, infertile mafic-ultramafic cumulates that lack the ingredients essential for the generation of granitic magma. Given the implausibility of the sagduction process, we suggest that subduction was the main mechanism that generated granitoid magmas, in the Archean as today. (C) 2019 Elsevier Ltd. All rights reserved.
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Roumelioti, Z., Hollender, F., & Gueguen, P. (2020). Rainfall-Induced Variation of Seismic Waves Velocity in Soil and Implications for Soil Response: What the ARGONET (Cephalonia, Greece) Vertical Array Data Reveal. Bulletin Of The Seismological Society Of America, 110(2), 441–451.
Résumé: We apply interferometry by deconvolution to compute the shear-wave velocity in shallow sediments (0-83.4 m) based on earthquake records from a vertical accelerometric array (ARGOstoli Network [ARGONET]) on Cephalonia Island, Greece. Analysis of the time variation of measured values reveals a cyclical pattern, which correlates negatively to rainfall and a soil moisture proxy. The pattern includes a sharp reduction in velocity at the beginning of rainy seasons and a gradual rise toward dry periods, the overall variation being around 20%-25% within the shallowest depth interval examined (0-5.6 m) and estimated to reach 40% within the top 2 m. The variation itself and its amplitude are verified by surface-wave dispersion analysis, using ambient vibration data. Synthetic standard spectral ratios suggest that this seasonal effect leaves an imprint on soil response, causing differences in the level of high-frequency ground motion between dry and rainy seasons, and this is verified by earthquake records. Furthermore, the near-surface velocity decrease due to soil saturation can be of the same order of magnitude as the nonlinear coseismic variation, masking the physical process of the nonlinear response of the site due to weak-to-strong-motion shaking. Thus, seasonal variations of seismic-wave velocities in shallow sediments may be important for a number of site-effect related topics, such as high-frequency ground-motion variability, soil anisotropy, kappa measurements, nonlinear site response, and so on.
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Rovezzi, M., Harris, A., Detlefs, B., Bohdan, T., Svyazhin, A., Santambrogio, A., et al. (2020). TEXS: in-vacuum tender X-ray emission spectrometer with 11 Johansson crystal analyzers. Journal Of Synchrotron Radiation, 27, 813–826.
Résumé: The design and first results of a large-solid-angle X-ray emission spectrometer that is optimized for energies between 1.5 keV and 5.5 keV are presented. The spectrometer is based on an array of 11 cylindrically bent Johansson crystal analyzers arranged in a non-dispersive Rowland circle geometry. The smallest achievable energy bandwidth is smaller than the core hole lifetime broadening of the absorption edges in this energy range. Energy scanning is achieved using an innovative design, maintaining the Rowland circle conditions for all crystals with only four motor motions. The entire spectrometer is encased in a high-vacuum chamber that allocates a liquid helium cryostat and provides sufficient space for in situ cells and operando catalysis reactors.
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Roy, S., Vassallo, R., Martinod, J., Ghiglione, M. C., Sue, C., & Allemand, P. (2020). Co-seismic deformation and post-glacial slip rate along the Magallanes-Fagnano fault, Tierra Del Fuego, Argentina. Terra Nova, 32(1), 1–10.
Résumé: Across the extreme south of Patagonia, the Magallanes-Fagnano Fault (MFF) accommodates the left-lateral relative motion between South America and Scotia plates. In this paper, we present an updated view of the geometry of the eastern portion of the MFF outcropping in Tierra del Fuego. We subdivide the MFF in eight segments on the basis of their deformation styles, using field mapping and interpretation of high-resolution imagery. We quantify coseismic ruptures of the strongest recorded 1949, M(w)7.5 earthquake, and determine its eastern termination. We recognize several co-seismic offsets in man-made features showing a sinistral shift up to 6.5 m, greater than previously estimated. Using Be-10 cosmogenic nuclides depth profiles, we date a cumulated offset in post-glacial morphologies and estimate the long-term slip rate of the eastern MFF. We quantify a 6.4 +/- 0.9 mm/a left-lateral fault slip rate, which overlaps geodetic velocity and suggests stable fault behaviour since Pleistocene.
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Salcedo, M., Garambois, S., Le Bouteiller, P., Li, Y. B., Senechal, G., Danquigny, C., et al. (2020). Matrix-free crosshole elliptical-anisotropy tomography: parametrization analysis and ground-penetrating radar applications in carbonates. Near Surface Geophysics, 18(6), 697–712.
Résumé: A novel traveltime tomographic approach is applied to anisotropic media, limited to 2D geometry for the moment. A general anisotropic Eikonal solver based on a discontinuous Galerkin method is combined with an efficient adjoint formulation for multiparameter least-squares inversion. This new approach is tested considering synthetic crosshole ground-penetrating radar data in a configuration inspired by a real experiment acquired in layered carbonate media disturbed by the presence of a deep gallery, which induces a localized high-electromagnetic contrast. This made it possible to define a well-adapted general workflow in this context. We notably show that under the elliptical anisotropic assumption, the parametrization based on vertical and horizontal velocities provides less biased results than those obtained by considering the vertical velocity and the relevant Thomsen parameter epsilon. The initial vertical and horizontal velocity models are identical and built from an isotropic inversion. The presence of the high-contrast gallery generates a weak diffraction pattern, which is taken into account in our tomography approach. It also creates potential artefacts due to the model discretization, which are mitigated by a model regularization term within the definition of the misfit function. This general workflow is then applied to the real experiment dataset. The vertical and horizontal velocity images provide similar structures as those previously obtained by isotropic full waveform inversion, complemented by an image of a rather weak elliptical anisotropy.
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Sancho-Tomas, M., Somogyi, A., Medjoubi, K., Bergamaschi, A., Visscher, P. T., van Driessche, A. E. S., et al. (2020). Geochemical evidence for arsenic cycling in living microbialites of a High Altitude Andean Lake (Laguna Diamante, Argentina). Chemical Geology, 549.
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Schwartz, S., Gautheron, C., Ketcham, R. A., Brunet, F., Corre, M., Agranier, A., et al. (2020). Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry. Earth And Planetary Science Letters, 543.
Résumé: Magnetite is a ubiquitous oxide in ultramafic and mafic rocks, which is present in a large range of geological and tectonic settings. In the case of high-pressure ultramafic rocks, exhumation timing is commonly constrained by geochronometers in nearby lithologies. The development of the magnetite (U-Th-Sm)/He method (MgHe) has opened new perspectives to refine the exhumation history of such rocks. However no thermal history has been deduced using MgHe data so far. Here we applied MgHe dating to magnetite from an HP-LT alpine ophiolite body (Rocher Blanc) from the Schistes lustres units (Western Alps, France) where part the P-T-t history is constrained to further refine the thermal history and demonstrate validity of the method. Textural and geochemical characterizations of the magnetite grains reveal two crystallization environments leading to distinct grain morphologies, euhedral and pseudo-euhedral, with different amounts of mineral inclusions (titanite, chlorite and augite-aegirine). Both magnetite types crystallized during the same retrograde path at T > 250 degrees C, under hydrothermal conditions shown by Si and V oscillatory zoning and low Ti content. MgHe ages derived from euhedral magnetite crystals range from 14.8 +/- 2.1 to 20.9 +/- 3.0 Ma, between zircon and apatite fission track (ZFT) and (AFT) ages deduced from the literature. Pseudo-euhedral grains display older ages interpreted as resulting from the implantation of He from U-rich neighboring minerals such as titanite. For the first time, MgHe data are inverted along with AFT and ZFT data to refine the thermal history of an ophiolite related to their exhumation. The MgHe data suggest that the Rocher Blanc sample has undergone an exhumation in ductile conditions related to subduction dynamics and underplating processes, followed by an exhumation reflecting denudation by erosion under brittle conditions. This exhumation regime change is found to take place at similar to 20 Ma, as opposed to a less constrained similar to 26 Ma cooling as would be inferred from the ZFT and AFT ages alone. Considering published thermochronometric data along the Western Alps, we propose that the exhumation is controlled by the upward indentation of the Apulian mantle producing regional tilting and associated erosion. With the present Schistes lustres ophiolite example, we demonstrate that the MgHe method can be used as a low-temperature thermochronometer (closure temperature in the 200-250 degrees C range) that aids in unraveling the cooling history associated with exhumation of high-pressure ultramafic and mafic rocks at the brittle to ductile transition. (C) 2020 Elsevier B.V. All rights reserved.
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Seibert, C., Feuillet, N., Ratzov, G., Beck, C., & Cattaneo, A. (2020). Seafloor morphology and sediment transfer in the mixed carbonate- siliciclastic environment of the Lesser Antilles forearc along Barbuda to St. Lucia. Marine Geology, 428.
Résumé: The Lesser Antilles arc is a mixed siliciclastic and carbonate active margin made of active volcanic and flat Plio-Quaternary carbonate islands. It was built as a result of a complex tectonic history at the slowly converging boundary between the American plates and the Caribbean plate. The sedimentary processes as a consequence of external forcing (earthquakes, volcanism, hurricanes) were rarely documented in such environment and are poorly understood. We exploited an exceptional dataset of high-resolution marine seafloor data acquired during the last 20 years in the northern part of the Lesser Antilles forearc to document the sediment-transport processes. We achieved a detailed morpho-sedimentary study from multi-beam bathymetry, backscattering, and seismic profiles. Two areas could be characterized: 1) the “Rough Area”, along Barbuda to Guadeloupe carbonated islands, characterized by steep (up to 25 degrees) slopes incised by short canyons, and deep basins controlled by major normal faults; 2) the “Channelized Area”, south of Guadeloupe and bordered by active volcanic islands and carbonate platforms, characterized by gentle slopes incised by long canyons. During sea-level high-stands, the sediment seems exported from the carbonate platform by hurricanes or density cascading but appears to settle at the shelf-edge and canyon heads. During sea-level low-stands, a connection may exist between onshore and offshore systems. However, this sediment supply appears not sufficient to generate canyon formation, likely shaped by regressive processes. Shelf breaks of the carbonate banks, platforms and submarine slopes are affected by sediment failures. Some may be associated to voluminous remobilizations and large mass transport deposits. Large earthquakes are likely the main processes in this area to remobilize sediments toward the deep forearc basins by triggering both slope failures and flushing of the canyon heads.
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Senyukov, S. L., Mikhailov, V. O., Nuzhdina, I. N., Kiseleva, E. A., Droznina, S. Y., Timofeeva, V. A., et al. (2020). A Joint Study of Seismicity and SAR Interferometry Observations for Assessing the Possibility of an Eruption of the Dormant Bolshaya Udina Volcano. Journal Of Volcanology And Seismology, 14(5), 305–317.
Résumé: Seismicity began to be recorded in October 2017 around the dormant Bolshaya Udina Volcano (B. Udina in what follows) situated 10 km southeast of Plosky Tolbachik Volcano. Seismic tomography showed the existence of a long-lived magma chamber south of B. Udina in the area of the Tolud River. The chamber has its top at a depth of about 15 km, and may probably be connected to the Plosky Tolbachik plumbing system (Koulakov et al., 2017). Saltykov et al. (2018) and Koulakov et al. (2019) related the observed resumption of seismic activity to a hypothetical emplacement of magma beneath the Udina volcanoes, pointing out a high likelihood of the resumption of volcanic activity. The present study examines data from permanent seismic stations showing a systematic displacement of the center of seismic energy southward from B. Udina from October 2017 through August 2019. The center characterizes the location of the volume that generates the bulk of seismicity. We used images of the Sentinel-1A satellite (wavelength 5.6 cm) taken from a descending orbit of track 60 during the period from June 7, 2017 through September 23, 2017 (10 images) and during the period from May 21, 2018 to September 30, 2018 (12 images) to determine time series and average velocities of displacement on the slopes of B. Udina. Persistent scatterers could only be identified at the foot of B. Udina. An analysis of displacement time series for the surface of the volcano showed that the character of displacements in 2017 and 2018 on the southwestern and eastern slopes remained nearly the same, while the average rate of displacement on the northwestern slope decreased in 2018. We used three images of the ALOS-2 PALSAR-2 satellite (wavelength 23.5 cm) taken on October 4, 2016, June 13, 2016, and October 2, 2018 from an ascending orbit to construct paired interferograms, which characterize displacements for the time period between images. The displacements on both interferograms did not exceed a few centimeters, except for narrow zones confined to local relief forms. The deformations thus detected were most likely due to surface processes. The deformed volumes related to pressure changes in the magma chamber at a depth of 5 km must have linear dimensions of 10-15 km, while the displacement areas detected in the satellite images are considerably smaller. These results suggested an alternative model that postulates the resumption of seismic activity to accompany the retreat and sinking of magma melt from B. Udina into the chamber in the Tolud R. area as identified by tomographic techniques.
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Sergeant, A., Chmiel, M., Lindner, F., Walter, F., Roux, P., Chaput, J., et al. (2020). On the Green's function emergence from interferometry of seismic wave fields generated in high-melt glaciers: implications for passive imaging and monitoring. Cryosphere, 14(3), 1139–1171.
Résumé: Ambient noise seismology has revolutionized seismic characterization of the Earth's crust from local to global scales. The estimate of Green's function (GF) between two receivers, representing the impulse response of elastic media, can be reconstructed via cross-correlation of the ambient noise seismograms. A homogenized wave field illuminating the propagation medium in all directions is a prerequisite for obtaining an accurate GF. For seismic data recorded on glaciers, this condition imposes strong limitations on GF convergence because of minimal seismic scattering in homogeneous ice and limitations in network coverage. We address this difficulty by investigating three patterns of seismic wave fields: a favorable distribution of icequakes and noise sources recorded on a dense array of 98 sensors on Glacier d'Argentiere (France), a dominant noise source constituted by a moulin within a smaller seismic array on the Greenland Ice Sheet, and crevasse-generated scattering at Gornergletscher (Switzerland). In Glacier d'Argentiere, surface melt routing through englacial channels produces turbulent water flow, creating sustained ambient seismic sources and thus favorable conditions for GF estimates. Analysis of the cross-correlation functions reveals non-equally distributed noise sources outside and within the recording network. The dense sampling of sensors allows for spatial averaging and accurate GF estimates when stacked on lines of receivers. The averaged GFs contain high-frequency ( > 30 Hz) direct and refracted P waves in addition to the fundamental mode of dispersive Rayleigh waves above 1 Hz. From seismic velocity measurements, we invert bed properties and depth profiles and map seismic anisotropy, which is likely introduced by crevassing. In Greenland, we employ an advanced preprocessing scheme which includes matchfield processing and eigenspectral equalization of the cross spectra to remove the moulin source signature and reduce the effect of inhomogeneous wave fields on the GFs. At Gornergletscher, cross-correlations of icequake coda waves show evidence for homogenized incident directions of the scattered wave field. Optimization of coda correlation windows via a Bayesian inversion based on the GF cross coherency and symmetry further promotes the GF estimate convergence. This study presents new processing schemes on suitable array geometries for passive seismic imaging and monitoring of glaciers and ice sheets.
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Seydoux, L., Balestriero, R., Poli, P., de Hoop, M., Campillo, M., & Baraniuk, R. (2020). Clustering earthquake signals and background noises in continuous seismic data with unsupervised deep learning. Nature Communications, 11(1).
Résumé: The continuously growing amount of seismic data collected worldwide is outpacing our abilities for analysis, since to date, such datasets have been analyzed in a human-expert-intensive, supervised fashion. Moreover, analyses that are conducted can be strongly biased by the standard models employed by seismologists. In response to both of these challenges, we develop a new unsupervised machine learning framework for detecting and clustering seismic signals in continuous seismic records. Our approach combines a deep scattering network and a Gaussian mixture model to cluster seismic signal segments and detect novel structures. To illustrate the power of the framework, we analyze seismic data acquired during the June 2017 Nuugaatsiaq, Greenland landslide. We demonstrate the blind detection and recovery of the repeating precursory seismicity that was recorded before the main landslide rupture, which suggests that our approach could lead to more informative forecasting of the seismic activity in seismogenic areas. The authors here tackle the problem that too much seismic data is acquired worldwide to be evaluated in a timely fashion. Seydoux and colleagues develop a machine learning framework that can detect and cluster seismic signals in continuous seismic records.
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Shen, T., Wang, G., Replumaz, A., Husson, L., Webb, A. A. G., Bernet, M., et al. (2020). Miocene Subsidence and Surface Uplift of Southernmost Tibet Induced by Indian Subduction Dynamics. Geochemistry Geophysics Geosystems, 21(10).
Résumé: The Indus-Yarlung suture of southernmost Tibet marks the initial collisional zone, the ongoing India-Asia collision, and yet more than similar to 30 million years after the onset of collision, a thick detrital sedimentary unit was deposited just north of the suture: the Kailas Formation. The mechanism permitting subsidence of the deep intracontinental Kailas basin in a compressional tectonic regime remains uncertain. We present new apatite (16-11 Ma) and zircon (24-19 Ma) fission track (AFT and ZFT) ages from the Gangdese batholith just north of the Kailas basin. ZFT analysis of modern-river sand from the northern Gangdese magmatic arc indicates an exhumation at 27.3 +/- 1.3 Ma. Thermal modeling indicates that the batholith experienced reheating between 28 and 20 Ma, coeval with deposition in the Kailas basin (between 26 and 21 Ma), followed by overall rapid cooling between 20 and 17 Ma. We interpret this thermal history as a phase of regional Oligocene-Miocene sedimentary burial followed by exhumation. By modeling mantle dynamics in the geodynamic framework of the India-Asia collision, we show that transient dynamic topography over the relative southward folding of the Indian slab is consistent with burial and exhumation of the Gangdese magmatic arc during Oligocene-Miocene time. The northward migration of the Indian continent relative to its own stati onary slab created a wave of dynamic topography that caused subsidence in the overriding plate north of the Himalaya, followed by a phase of surface uplift since similar to 27 Ma of the northern Gangdese magmatic arc. During latest Oligocene-early Miocene time, the dynamic deflection center was in the Kailas area, and it progressively relocated southward to its present position at the Ganges basin.
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Shen, T. Y., Wang, G. C., Bernet, M., Replumaz, A., Ai, K. K., Song, B. W., et al. (2020). Long-term exhumation history of the Gangdese magmatic arc: Implications for the evolution of the Kailas Basin, western Tibet. Geological Journal, 55(11), 7239–7250.
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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Sigmundsson, F., Pinel, V., Grapenthin, R., Hooper, A., Halldorsson, S. A., Einarsson, P., et al. (2020). Unexpected large eruptions from buoyant magma bodies within viscoelastic crust. Nature Communications, 11(1).
Résumé: Large volume effusive eruptions with relatively minor observed precursory signals are at odds with widely used models to interpret volcano deformation. Here we propose a new modelling framework that resolves this discrepancy by accounting for magma buoyancy, viscoelastic crustal properties, and sustained magma channels. At low magma accumulation rates, the stability of deep magma bodies is governed by the magma-host rock density contrast and the magma body thickness. During eruptions, inelastic processes including magma mush erosion and thermal effects, can form a sustained channel that supports magma flow, driven by the pressure difference between the magma body and surface vents. At failure onset, it may be difficult to forecast the final eruption volume; pressure in a magma body may drop well below the lithostatic load, create under-pressure and initiate a caldera collapse, despite only modest precursors. Large-volume volcanic eruptions can occur despite only limited precursory activity. Here the authors show that modelling the combined effects of buoyant magma, viscoelastic earth behaviour, and sustained magma channels can explain such behaviour of volcanoes and gives an estimate of pressure evolution in magma bodies.
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Simonnin, P., Sassi, M., Gilbert, B., Charlet, L., & Rosso, K. M. (2020). Phase Transition and Liquid-like Superionic Conduction in Ag2S. Journal Of Physical Chemistry C, 124(18), 10150–10158.
Résumé: Superionic conductivity in certain polymorphs of Ag2S has inspired numerous concepts for materials applications, but the relationship between the structure and the mobility of silver ions remains poorly explored. Here, we report ab initio molecular dynamics simulations for low- (acanthite) and high-temperature (argentite) Ag2S polymorphs that reveal the dynamical processes giving rise to the superionic behavior in the latter. Similarities between their sulfur sublattices enable simulations of silver ion diffusivities and pathways on essentially an equal footing. For the higher temperature polymorph, calculated temperature-dependent mean square displacements and activation energies by the nudged elastic band method show good correspondence with expectations from the experiment. In the superionic state, silver atoms diffuse in a liquid-like behavior with no preferred diffusion pathways, within the relatively stable body-centered cubic sulfur framework. In contrast, conduction in acanthite appears to depend more on the mobilities of electronic charge carriers.
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Soergel, D., Pedersen, H. A., Stehly, L., Margerin, L., Paul, A., Hetenyi, G., et al. (2020). Coda-Q in the 2.5-20 s period band from seismic noise: application to the greater Alpine area. Geophysical Journal International, 220(1), 202–217.
Résumé: Coda-Q is used to estimate the attenuation and scattering properties of the Earth. So far focus has been on earthquake data at frequencies above 1 Hz, as the high noise level in the first and second microseismic peak, and possibly lower scattering coefficient, hinder stable measurements at lower frequencies. In this work, we measure and map coda-Q in the period bands 2.5-5 s, 5-10 s and 10-20 s in the greater Alpine region using noise cross-correlations between station pairs, based on data from permanent seismic stations and from the temporary AlpArray experiment. The observed coda-Q for short interstation distances is independent of azimuth so there is no indication of influence of the directivity of the incoming noise field on our measurements. In the 2.5-5 s and 5-10 s period bands, our measurements are self-consistent, and we observe stable geographic patterns of low and high coda-Q in the period bands 2.5-5 s and 5-10 s. In the period band 10-20 s, the dispersion of our measurements increases and geographic patterns become speculative. The coda-Q maps show that major features are observed with high resolution, with a very good geographical resolution of for example low coda-Q in the Po Plain. There is a sharp contrast between the Po Plain and the Alps and Apennines where coda-Q is high, with the exception a small area in the Swiss Alps which may be contaminated by the low coda-Q of the Po Plain. The coda of the correlations is too short to make independent measurements at different times within the coda, so we cannot distinguish between intrinsic and scattering Q. Measurements on more severely selected data sets and longer time-series result in identical geographical patterns but lower numerical values. Therefore, high coda-Q values may be overestimated, but the geographic distribution between high and low coda-Q areas is respected. Our results demonstrate that noise correlations are a promising tool for extending coda-Q measurements to frequencies lower than those analysed with earthquake data.
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Staicu, L. C., Bajda, T., Drewniak, L., & Charlet, L. (2020). Power Generation: Feedstock for High-Value Sulfate Minerals. Minerals, 10(2).
Résumé: Coal-fired power facilities generate a polymetallic effluent (Flue Gas Desulfurization-FGD) rich in sulfate. FGD effluents may be considered an important secondary resource. This paper investigates the recovery of sulfate as barite (BaSO4), a mineral with high commercial value and a critical raw material. Using equimolar BaCl2, >99% desulfurization of an FGD effluent produced by a coal-fired power plant operating in central Poland was achieved, yielding up to 16.5 kg high purity barite m(-3). The recovered barite was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TGA), scanning electron microscopy analysis (SEM), surface properties (PZC), density, and chemical stability (TCLP), and was compared with a commercial reference material. Barite recovery also led to the reduction in concentration of Al (86%), Cu (52%), K (69%), Mo (62%), Se (40%), Sr (91%), and U (75%) initially present in the FGD effluent. TCLP results indicate the entrapment and the stabilization of -70% Se and -90% Al in the barite structure. Based on this dataset, an in-depth characterization of the recovered barite is presented, and the removal mechanism of the elements is discussed. The study also provides a preliminary cost benefit analysis of the process. To our best knowledge, this is the first work showing barite recovery and metal removal from FGD effluents using a one-step process.
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Stawski, T. M., Besselink, R., Chatzipanagisad, K., Hovelmann, J., Benning, L. G., & Van Driessche, A. E. S. (2020). Nucleation Pathway of Calcium Sulfate Hemihydrate (Bassanite) from Solution: Implications for Calcium Sulfates on Mars. Journal Of Physical Chemistry C, 124(15), 8411–8422.
Résumé: CaSO4 minerals (i .e., gypsum, anhydrite, and bassanite) are widespread in natural and industrial environments. During the last several years, a number of studies have revealed that nucleation in the CaSO4-H2O system is nonclassical, where the formation of crystalline phases involves several steps. Based on these recent insights, we have formulated a tentative general model for calcium sulfate precipitation from solution. This model involves primary species that are formed through the assembly of multiple Ca2+ and SO42- ions into nanoclusters. These nanoclusters assemble into poorly ordered (i.e., amorphous) hydrated aggregates, which in turn undergo ordering into coherent crystalline units. The thermodynamic (meta)stability of any of the three CaSO4 phases is regulated by temperature, pressure, and ionic strength, with gypsum being the stable form at low temperatures and low-to-medium ionic strengths and anhydrite being the stable phase at high temperatures and at lower temperature for high salinities. Bassanite is metastable across the entire phase diagram but readily forms as the primary phase at high ionic strengths across a wide range of temperatures and can persist up to several months. Although the physicochemical conditions leading to bassanite formation in aqueous systems are relatively well established, nanoscale insights into the nucleation mechanisms and pathways are still lacking. To fill this gap and to further improve our general model for calcium sulfate precipitation, we conducted in situ scattering measurements at small-angle X-ray scattering and wide-angle X-ray scattering and complemented these with in situ Raman spectroscopic characterization. Based on these experiments, we show that the process of formation of bassanite from aqueous solutions is very similar to the formation of gypsum: it involves the aggregation of small primary species into larger disordered aggregates, only from which the crystalline phase develops. These data thus confirm our general model of CaSO4 nucleation and provide clues to explain the abundant occurrence of bassanite on the surface of Mars and not on the surface of Earth).
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Su, S., Cebron, D., Nataf, H. C., Cardin, P., Vidal, J., Solazzo, M., et al. (2020). Acoustic spectra of a gas-filled rotating spheroid. European Journal Of Mechanics B-Fluids, 84, 302–310.
Résumé: The acoustic spectrum of a gas-filled resonating cavity can be used to indirectly probe its internal velocity field. This unconventional velocimetry method is particularly interesting for opaque fluid or rapidly rotating flows, which cannot be imaged with standard methods. This requires to (i) identify a large enough number of acoustic modes, (ii) accurately measure their frequencies, and (iii) compare with theoretical synthetic spectra. Relying on a dedicated experiment, an air-filled rotating spheroid of moderate ellipticity, our study addresses these three challenges. To do so, we use a comprehensive theoretical framework, together with finite-element calculations, and consider symmetry arguments. We show that the effects of the Coriolis force can be successfully retrieved through our acoustic measurements, providing the first experimental measurements of the rotational splitting (or Ledoux) coefficients for a large collection of modes. Our results pave the way for the modal acoustic velocimetry to be a robust, versatile, and non-intrusive method for mapping large-scale flows. (C) 2020 Elsevier Masson SAS. All rights reserved.
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Suhardja, S. K., Widiyantoro, S., Metaxian, J. P., Rawlinson, N., Ramdhan, M., & Budi-Santoso, A. (2020). Crustal thickness beneath Mt. Merapi and Mt. Merbabu, Central Java, Indonesia, inferred from receiver function analysis. Physics Of The Earth And Planetary Interiors, 302.
Résumé: In this study, we analysed 2708 receiver functions (RFs) using data recorded by 53 seismographic stations that surround Mt. Merapi and Mt. Merbabu – two volcanos in Central Java – to map the boundary between Earths crust and upper mantle. We observe that a number of RFs from this new dataset have complex signals and do not exhibit typical RF characteristics; in particular, where the converted Ps signal from the Moho discontinuity is the clearest and strongest amplitude arrival following the P onset. This effect may be related to complex shallow velocity structure due to the presence of magmatic rocks and sediments. Further analysis of the RF results using the H-K method suggests that Moho depth varies between 27 and 32 km beneath the array, with no apparent correlation between crustal thickness and surface topography, as one might expect from Airy isostacy. For instance, the Moho is quite shallow beneath Mt. Merapi (up to 27 km depth), despite its elevation of nearly 3 km. This may be a consequence of dynamic support from an active upper mantle coupled with erosion and/or weakening of the lower crust due to the active volcanic plumbing system. To the north of Mt. Merapi, the Moho is deeper (30-31 km depth) below Mt. Merbabu. Vp/Vs ratio estimates from the H-kappa method are relatively high (similar to 1.9) beneath the Mt. Merapi and Kendeng Basin area, which may indicate the presence of a zone of hydrous and active partial melting in the underlying crust. Lower Vp/Vs ratios (similar to 1.7) are found beneath Mt. Merbabu, which may be due to its relative lack of volcanic activity compared to Mt. Merapi.
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Takano, T., Brenguier, F., Campillo, M., Peltier, A., & Nishimura, T. (2020). Noise-based passive ballistic wave seismic monitoring on an active volcano. Geophysical Journal International, 220(1), 501–507.
Résumé: Monitoring temporal changes of volcanic interiors is important to understand magma, fluid pressurization and transport leading to eruptions. Noise-based passive seismic monitoring using coda wave interferometry is a powerful tool to detect and monitor very slight changes in the mechanical properties of volcanic edifices. However, the complexity of coda waves limits our ability to properly image localized changes in seismic properties within volcanic edifices. In this work, we apply a novel passive ballistic wave seismic monitoring approach to examine the active Piton de la Fournaise volcano (La Reunion island). Using noise correlations between two distant dense seismic arrays, we find a 2.4 per cent velocity increase and -0.6 per cent velocity decrease of Rayleigh waves at frequency bands of 0.5-1 and 1-3 Hz, respectively. We also observe a -2.2 per cent velocity decrease of refracted P waves at 550m depth at the 6-12 Hz band. We interpret the polarity differences of seismic velocity changes at different frequency bands and for different wave types as being due to strain change complexity at depth associated with subtle pressurization of the shallow magma reservoir. Our results show that velocity changes measured using ballistic waves provide complementary information to interpret temporal changes of the seismic properties within volcanic edifices.
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Tallon, B., Brunet, T., Leng, J., & Page, J. H. (2020). Energy velocity of multiply scattered waves in strongly scattering media. Physical Review B, 101(5).
Résumé: The important influence of the relative refractive index of scattering inclusions on energy transport of classical waves through disordered media is clearly demonstrated through ultrasonic experiments on monodisperse emulsions. Our ultrasonic techniques measure both the transmitted average wave field and the multiply scattered diffusive intensity, enabling a full characterization of wave transport through the media and the measurement of both the group and energy velocities over a wide range of frequencies. The emulsions were fabricated using microfluidic techniques that permit accurate control of droplet size and concentration, for droplet inclusions with very different acoustic properties relative to the yield stress fluids in which the droplets were immersed. Thus we have been able to investigate emulsions containing either “slow” fluorinated oil droplets (sound speed v(1) less than v(0) of the surrounding fluid) or “fast” liquid metallic droplets (v(1) > v(0)). We find that the energy velocity that describes the transport of energy by the dominant diffusive waves is mainly governed by the sound speed within the scatterers, and can be either much slower or faster than any of the other wave velocities. The possibility that the energy velocity could be faster than any other wave velocity when n(rel) = v(0)/v(1) < 1 was not anticipated in previous work. These observations are successfully explained by theories that are valid for scalar waves in media containing a low concentration of scatterers, and are directly applicable to our dilute “all-fluid” emulsions. The role of droplet resonances on the behavior of the energy velocity is also demonstrated, and the mechanism leading to the large differences in the energy velocity in the two emulsion systems is elucidated through calculations of the energy density inside the droplets relative to the incident energy density.
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Tallon, B., Roux, P., Matte, G., Guillard, J., & Skipetrov, S. E. (2020). Acoustic density estimation of dense fish shoals. Journal Of The Acoustical Society Of America, 148(3), EL234–EL239.
Résumé: Multiple scattering of acoustic waves offers a noninvasive method for density estimation of a dense shoal of fish where traditional techniques such as echo-counting or echo-integration fail. Through acoustic experiments with a multi-beam sonar system in open sea cages, multiple scattering of sound in a fish shoal, and, in particular, the coherent backscattering effect, can be observed and interpreted quantitatively. Furthermore, a volumetric scan of the fish shoal allows isolation of a few individual fish from which target strength estimations are possible. The combination of those two methods allows for fish density estimation in the challenging case of dense shoals.
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Tallon, B., Roux, P., Matte, G., Guillard, J., & Skipetrov, S. E. (2020). Mesoscopic wave physics in fish shoals. Aip Advances, 10(5).
Résumé: Ultrasound scattered by a dense shoal of fish undergoes mesoscopic interference, as is typical of low-temperature electrical transport in metals or light scattering in colloidal suspensions. Through large-scale measurements in open sea, we show a set of striking deviations from classical wave diffusion, making fish shoals good candidates to study mesoscopic wave phenomena. The very good agreement with theories enlightens the role of fish structure in such a strong scattering regime that features slow energy transport and brings acoustic waves close to the Anderson localization transition.
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Tan, Y. J., & Marsan, D. (2020). Connecting a broad spectrum of transient slip on the San Andreas fault. Science Advances, 6(33).
Résumé: Strain accumulated on the deep extension of some faults is episodically released during transient slow-slip events, which can subsequently load the shallow seismogenic region. At the San Andreas fault, the characteristics of slow-slip events are difficult to constrain geodetically due to their small deformation signal. Slow-slip events (SSEs) are often accompanied by coincident tremor bursts composed of many low-frequency earthquakes. Here, we probabilistically estimate the spatiotemporal clustering properties of low-frequency earthquakes detected along the central San Andreas fault. We find that tremor bursts follow a power-law spatial and temporal decay similar to earthquake aftershock sequences. The low-frequency earthquake clusters reveal that the underlying slow-slip events have two modes of rupture velocity. Compared to regular earthquakes, these slow-slip events have smaller stress drop and rupture velocity but follow similar magnitude-frequency, moment-area, and moment-duration scaling. Our results connect a broad spectrum of transient fault slip that spans several orders of magnitude in rupture velocity.
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Tani, L. S. K., Dennouni-Medjati, N., Toubhans, B., & Charlet, L. (2020). Selenium Deficiency-From Soil to Thyroid Cancer. Applied Sciences-Basel, 10(15).
Résumé: Featured Application The paper underlines the link between soil, food and human health, with a particular emphasis on thyroid cancer in case of Se deficiency, in order to provide a scientific basis to Public Health Recommendations. Selenium (Se) is an essential micronutrient present in human diet, entering in the composition of selenoproteins as selenocysteine (Se-Cys) amino acid. At the thyroid level, these proteins play an important role as antioxidant and in hormone metabolism. Selenoproteins are essential for the balance of redox homeostasis and antioxidant defense of mammalian organisms, while the corresponding imbalance is now recognized as the cause of many diseases including cancer. The food chain is the main source of Se in human body. Dietary intake is strongly correlated with Se content in soil and varies according to several factors such as geology and atmospheric input. Both Se deficiency and toxicity have been associated with adverse health effects. This review synthesizes recent data on the transfer of Se from soil to humans, Se U-shaped deficiency and toxicity uptake effects and particularly the impact of Se deficiency on thyroid cancer.
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Tchawe, F. N., Froment, I. B., Campillo, M., & Margerin, L. (2020). On the use of the coda of seismic noise autocorrelations to compute H/V spectral ratios. Geophysical Journal International, 220(3), 1956–1964.
Résumé: The horizontal to vertical spectral ratio (HVSR) of seismic ambient noise has been proven to be a fast and efficient method for characterizing the 1-D resonance frequency of the local subsurface in a practical framework. Over the last decades, theories have been developed in order to extend the exploitation of HVSR beside the frequency of its first peak, notably the diffuse field assumption (DFA) which links the HVSR to the Green's function of the local medium assuming the diffuseness of the seismic ambient noise wavefield. However, the underlying assumption of the seismic ambient noise being a diffuse, equipartitioned field may not be satisfied under certain circumstances. In order to exploit the contribution of scattering in forging diffuse wave fields, we leverage the advantages of coda waves and present a novel procedure for computing the HVSR, using the coda part of ambient noise correlations. We applied this technique to data gathered at the plio-quaternary sedimentary basin of Argostoli, Greece. Results on this data set show the potential of the method to improve the temporal stability of the HVSR measurements compared to the classical computation, and the fit with the theoretical HVSR curve derived from the DFA theory. These results suggest that this procedure could help in extracting physical information from the HVSR and thus could lead to an extended use of these measurements to characterize the mechanical properties of the medium.
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Thery, R., Guillemot, A., Abraham, O., & Larose, E. (2020). Tracking fluids in multiple scattering and highly porous materials: Toward applications in non-destructive testing and seismic monitoring. Ultrasonics, 102.
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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Thomas, P., Chauvire, B., Flower-Donaldson, K., Aldridge, L., Smallwood, A., & Liu, B. (2020). FT-NIR and DSC characterisation of water in opal. Ceramics International, 46(18), 29443–29450.
Résumé: Opal is a hydrous silica (SiO2 center dot nH(2)O) formed through a dissolution-precipitation process. The formation process incorporates water into the structure as bound silanol and molecular water. As the water is distributed in a range of states, multiple methods of characterisation are required to identify each state. This study reports the results of temperature dependent FT-NIR and DSC investigation on natural opal samples of the opal-A (amorphous) and opal-CT (poorly crystalline cristobalite with tridymitic stacking faults) types. Significant differences in the melting behaviour of crystallisable water as well as differences in the spectral characteristics of the non-crystallisable molecular water are observed. These differences are ascribed to the different microstructures of the opal types.
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Torchio, R., Boccato, S., Miozzi, F., Rosa, A. D., Ishimatsu, N., Kantor, I., et al. (2020). Melting Curve and Phase Relations of Fe-Ni Alloys: Implications for the Earth's Core Composition. Geophysical Research Letters, 47(14).
Résumé: Nickel is the second most abundant element in the Earth's core. However, the properties of Fe-Ni alloys are still poorly constrained under planetary cores conditions, in particular concerning the effect of Ni on the melting curve of Fe. Here we show that Ni alloying up to 36 wt% does not affect the melting curve of Fe up to 100 GPa. However, Ni strongly modifies the hexagonal-closed-packed/face-centered-cubic (hcp/fcc) phase boundary, pushing the hcp/fcc/liquid triple point of Fe-20wt%Ni to higher pressures and temperatures. Our results allow constraining the triple point for Fe-10wt%Ni, a composition relevant for the Earth interior, and point out a decrease of the melting temperature at core-mantle boundary by 400 K with respect to pure Fe. A lower amount of light elements than previously predicted is thus required to reduce the crystallization temperature of core materials below that of a peridotitic lower mantle, in better agreement with geochemical observations.
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Toubhans, B., Gazze, S. A., Bissardon, C., Bohic, S., Gourlan, A. T., Gonzalez, D., et al. (2020). Selenium nanoparticles trigger alterations in ovarian cancer cell biomechanics. Nanomedicine-Nanotechnology Biology And Medicine, 29.
Résumé: High dose selenium acts as a cytotoxic agent, with potential applications in cancer treatment. However, clinical trials have failed to show any chemotherapeutic value of selenium at safe and tolerated doses (<90 μg/day). To enable the successful exploitation of selenium for cancer treatment, we evaluated inorganic selenium nanoparticles (SeNP), and found them effective in inhibiting ovarian cancer cell growth. In both SKOV-3 and OVCAR-3 ovarian cancer cell types SeNP treatment resulted in significant cytotoxicity. The two cell types displayed contrasting nanomechanical responses to SeNPs, with decreased surface roughness and membrane stiffness, characteristics of OVCAR-3 cell death. In SKOV-3, cell membrane surface roughness and stiffness increased, both properties associated with decreased metastatic potential. The beneficial effects of SeNPs on ovarian cancer cell death appear cell type dependent, and due to their low in vivo toxicity offer an exciting opportunity for future cancer treatment. (C) 2020 The Authors. Published by Elsevier Inc.
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Toubhans, B., Gourlan, A. T., Telouk, P., Lutchman-Singh, K., Francis, L. W., Conlan, R. S., et al. (2020). Cu isotope ratios are meaningful in ovarian cancer diagnosis. Journal Of Trace Elements In Medicine And Biology, 62.
Résumé: Background: Ovarian cancer diagnosis is currently based on imaging and circulating CA-125 concentrations with well-known limits to sensitivity and specificity. New biomarkers are required to complement CA-125 testing to increase effectiveness. Increases in sensitivity of isotopic separation via multi collector inductively coupled plasma-mass spectrometry have recently allowed highly accurate measurement of copper (Cu) isotopic variations. Studies in breast cancer patients have revealed changes of serum copper isotopic composition demonstrating the potential for development as a cancer biomarker. Evaluating Cu-65/Cu-63 ratios (delta Cu-65) in serum samples from cancer patients has revealed a strong correlation with cancer development. In this study blood samples from forty-four ovarian cancer patients, and 13 ovarian biopsies were investigated. Results: Here we demonstrate that changes in Cu isotopes also occurs in ovarian cancer patients. Copper composition determined by multiple collector inductively coupled plasma mass spectrometry revealed that the copper isotopic ratio delta Cu-65 in the plasma of 44 ovarian cancer patient cohort was significantly lower than in a group of 48 healthy donors, and indicated that serum was enriched for Cu-63. Further analysis revealed that the isotopic composition of tumour biopsies was enriched for Cu-65 compared with adjacent healthy ovarian tissues. Conclusions: We propose that these changes are due to increase lactate and Cu transporter activities in the tumour. These observations demonstrate that, combined with existing strategies, delta Cu-65 could be developed for use in ovarian cancer early detection.
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Traversa, P., Maufroy, E., Hollender, F., Perron, V., Bremaud, V., Shible, H., et al. (2020). RESIF RAP and RLBP Dataset of Earthquake Ground Motion in Mainland France. Seismological Research Letters, 91(4), 2409–2424.
Résumé: This work presents the implementation of a high standards dataset of earthquake ground motions recorded in Metropolitan France between 1996 and 2016. This dataset is intended to serve the scopes of a large seismological community; however, its primary aims are engineering seismology and earthquake engineering applications. The dataset includes records from broadband and accelerometric sensors provided by permanent and temporary seismic networks operated by French research institutions and partners grouped within the Reseau Sismologique et geodesique Francais (RESIF) consortium (see Data and Resources). All the waveforms are first homogenized to acceleration units and underwent a full quality control process including: (1) visual verification and manual phase picking, (2) processing scheme, and (3) consistency check by residual analysis. These make the dataset fully compliant with international standards. Finally, the RESIF dataset includes more than 6500 quality-checked records from 468 earthquakes recorded at 379 stations. Over the 379 stations included in the dataset, 177 are permanent stations (RA and FR networks) and 202 are temporary stations (YP and X7 networks). The dataset is complete down to magnitude M-L 3.5 over the whole French territory and less (about M-L 2.5) in the eastern part. Magnitudes range from M-L 2.4 to 5.6 and from M-w 2.0 to 5.2, whereas distances range from less than 1 to 600 km. The disseminated dataset is constituted of (1) a versioned flatfile containing the metadata and main intensity measures computed on each processed record, (2) time histories, and (3) response spectra for several damping values and Fourier spectra.
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Trevlopoulos, K., Gueguen, P., Helmstetter, A., & Cotton, F. (2020). Earthquake risk in reinforced concrete buildings during aftershock sequences based on period elongation and operational earthquake forecasting. Structural Safety, 84.
Résumé: Rapid post-earthquake damage assessment is critical to short-term earthquake crisis management. Reinforced concrete buildings may accumulate damage during an aftershock sequence, and short-term damage forecasts after the mainshock can aid in decision-making (in particular, on whether to allow immediate occupancy) before further damage actually occurs. This paper presents an operative damage forecasting and building tagging procedure for reinforced concrete buildings during synthetic aftershock sequences near Thessaloniki, Greece, for two hypothetical earthquake scenarios. The synthetic aftershock sequences are simulated, and the time-variant seismic vulnerability is modeled based on fragility curves for the damage state thresholds in terms of period elongation. Period elongation is chosen as a damage proxy because it is available for rapid damage assessment in buildings with permanent monitoring systems or for city-scale post-earthquake surveys. Time-variable damage state probabilities owing to aftershocks are estimated, and a building tagging scheme is proposed based on a traffic-light concept (red-orange-green) to assist in seismic crisis management during aftershock sequences.
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Truche, L., McCollom, T. M., & Martinez, I. (2020). Hydrogen and Abiotic Hydrocarbons: Molecules that Change the World. Elements, 16(1), 13–18.
Résumé: Molecular hydrogen (H-2), methane, and hydrocarbons with an apparent abiotic origin have been observed in a variety of geologic settings, including serpentinized ultramafic rocks, hydrothermal fluids, and deep fractures within ancient cratons. Molecular hydrogen is also observed in vapor plumes emanating from the icy crust of Saturn's moon Enceladus, and methane has been detected in the atmosphere of Mars. Geologic production of these compounds has been the subject of increasing scientific attention due to their use by chemosynthetic biological communities. These compounds are also of interest as possible energy resources. This issue summarizes the geological sources of abiotic H-2 and hydrocarbons on Earth and elsewhere and examines their impact on microbial life and energy resources.
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Ulrich, M., Munoz, M., Boulvais, P., Cathelineau, M., Cluzel, D., Guillot, S., et al. (2020). Serpentinization of New Caledonia peridotites: from depth to (sub-)surface. Contributions To Mineralogy And Petrology, 175(9).
Résumé: Serpentinization processes occur at geological settings notably during oceanic subduction and obduction, where mantle rocks interact with water. Different types of serpentine minerals form according to temperature and pressure conditions, and potentially chemical exchanges. Therefore, the characterization of serpentine minerals, and the possible occurrence of multiple serpentine generations in mantle rocks provide essential constraints on the conditions of fluid-rock interactions in the mantle. The serpentinite sole of the Peridotite Nappe of New Caledonia (Southwest Pacific) is the result of several superimposed serpentinisation events. The latter were discriminated using mineralogical and geochemical approaches and modeling. Lizardite represents more than 80% of the entire serpentine content of the ophiolite. It is crosscut by several veins of other serpentine species in the serpentinite sole. The relative chronology appears as follows: lizardite 1 -> lizardite 2 -> antigorite -> chrysotile -> polygonal serpentine. The transition from primary/magmatic minerals to lizardite 1 is almost isochemical. Then, the development of lizardite 2 yields an enrichment in fluid-mobile elements such as Cs, Rb, Ba, U and light rare-earth elements and an apparent increase of the Fe3+/Fe(T)ratio. The modeling of delta O-18 values (1.9-13.9 parts per thousand) and delta D values (88-106 parts per thousand) of all serpentine species through Monte-Carlo simulations show that New Caledonia serpentines were mainly formed in equilibrium with fluids released by the dehydration of altered oceanic crust (AOC) during subduction between 250 and 350 degrees C. AOC-derived fluids are not the unique source of fluids since a low temperature (100-150 degrees C) meteoric component is also predicted by the models. Thus, serpentine acts as a tape-recorder of fluid-rock interactions into the mantle from depth to (sub-)surface.
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van Baarsel, T., Roux, P., Mars, J. I., & Nicolas, B. (2020). Surface perturbation inverted from angle variations of eigenbeams in an ultrasonic waveguide. Journal Of The Acoustical Society Of America, 148(5), 2841–2850.
Résumé: Ocean acoustic tomography is traditionally performed using the travel-time variations of an acoustic path between a source and a receiver. In the context of shallow-water tomography and multipath propagation, the different acoustic paths can be correctly identified if the source and the receiver are arrays of transducers. Here, a double-beamforming algorithm can be applied to extract a collection of eigenbeams from the raw acoustic dataset. In this study, four observables can be measured for each eigenbeam: the travel-time, the amplitude, and the emitting and receiving angles. In this study, the sensitivity kernel (SK) formulation is used to establish a quantitative relation between a perturbation of the surface of an ultrasonic waveguide and the emitting and receiving angles of each eigenbeam. This theoretical relation is experimentally demonstrated using a forward model experiment designed to measure the SK. The SK formulation is then used in a second experiment to quantitatively and dynamically image the propagation of a surface wave traveling across the surface of the waveguide. The inversion results show that the quality of the joint inversion of the emitting and receiving angles is higher than previous results based on amplitude or travel-time observables.
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Vassallo, R., Mugnier, J. L., Jomard, H., Aranda, J. C., Malik, M. A., Jouanne, F., et al. (2020). Recurrence of large paleo-earthquakes in Kashmir Himalaya seismic gap (Riasi area, India). Journal Of Asian Earth Sciences, 201.
Résumé: In Kashmir Himalaya, the Medlicott-Wadia Thrust is a main active fault responsible for the crustal accretionary prism building during the Late Quaternary. Because of the long seismic silence during the last five centuries, it is a key structure to be studied in order to estimate the regional seismic hazard. In the Riasi area, the analysis of two paleoseismological trenches allowed us identifying and measuring several seismic ruptures over the last similar to 3500 years. We determined that the oldest rupture occurred around 1600-1000 BC, while the youngest occurred after 1470 AD. The latest event is compatible with the great 1555 AD (Mw > 7.5) Kashmir earthquake, whose evidence at the surface had not yet been recognized. Our results show that despite the long-lasting seismic gap, the Medlicott-Wadia Thrust is a main seismogenic structure in the region, able to produce large earthquakes. Their recurrence interval ranges between 500 and 700 years, implying that a main seismic event could occur in the next decades. These seismic ruptures are localized over gently-dipping fault branches associated with decameter-scale scarps. The morphologies observed are due to a significant non-localized component of the deformation in Quaternary sediments.
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Vidal, J., & Cebron, D. (2020). Acoustic and inertial modes in planetary-like rotating ellipsoids. Proceedings Of The Royal Society A-Mathematical Physical And Engineering Sciences, 476(2239).
Résumé: The bounded oscillations of rotating fluid-filled ellipsoids can provide physical insight into the flow dynamics of deformed planetary interiors. The inertial modes, sustained by the Coriolis force, are ubiquitous in rapidly rotating fluids and Vantieghem (2014,Proc. R. Soc. A,470, 20140093.) pioneered a method to compute them in incompressible fluid ellipsoids. Yet, taking density (and pressure) variations into account is required for accurate planetary applications, which has hitherto been largely overlooked in ellipsoidal models. To go beyond the incompressible theory, we present a Galerkin method in rigid coreless ellipsoids, based on a global polynomial description. We apply the method to investigate the normal modes of fully compressible, rotating and diffusionless fluids. We consider an idealized model, which fairly reproduces the density variations in the Earth's liquid core and Jupiter-like gaseous planets. We successfully benchmark the results against standard finite-element computations. Notably, we find that the quasi-geostrophic inertial modes can be significantly modified by compressibility, even in moderately compressible interiors. Finally, we discuss the use of the normal modes to build reduced dynamical models of planetary flows.
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Vidal, J., Su, S., & Cebron, D. (2020). Compressible fluid modes in rigid ellipsoids: towards modal acoustic velocimetry. Journal Of Fluid Mechanics, 885.
Résumé: Motivated by planetary-driven applications and experiments in non-spherical geometries, we study compressible fluid modes in rotating rigid ellipsoids. Such modes are also required for modal acoustic velocimetry (MAV), a promising non-invasive method to track the velocity field components in laboratory experiments. To calculate them, we develop a general spectral method in rigid triaxial ellipsoids. The description is based on an expansion onto global polynomial vector elements, satisfying the non-penetration condition on the boundary. Then, we investigate the diffusionless compressible modes in rotating (and magnetised) rigid ellipsoids. The spectral description is successfully benchmarked against three-dimensional finite-element computations and analytical predictions. A spectral convergence is obtained. Our results have direct implications for MAV in experiments, for instance in the ZoRo experiment (gas-filled rigid spheroid). So far, deformation and rotational effects have been theoretically considered separately, as small perturbations of the solutions in non-rotating spheres. We carefully compare the perturbation approach, in this illustrative geometry, to the polynomial solutions. We show that second-order ellipticity effects are often present, even in weakly deformed ellipsoids. Moreover, high-order effects due to rotation and/or ellipticity should be observed for some acoustic modes in experimental conditions. Thus, perturbation theory should be used with care in MAV. Instead, the spectral polynomial method paves the way for future MAV applications in fluid experiments with rigid ellipsoids.
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Vigneresse, J. L., & Truche, L. (2020). Modeling ore generation in a magmatic context. Ore Geology Reviews, 116.
Résumé: Magmatic ore deposit models are constructed from a set of measurables (e.g., ore grade, fluid composition, structure) from which important parameters (temperature, pressure, chemistry) can be estimated and possible genetic processes can be constrained. Such models include direct, inverse or iterative problems. Direct problems separately consider an Eulerian and a Lagrangian formulation. In the first case, an analytical approach describes the bulk system from an external frame, whereas the Lagrangian approach provides a description from a discrete element attached to the system. Conversely, inverse problems mostly rely on a system of equations or differential equations. Their solution requires a matrix inversion, using statistical criteria to bracket errors. Subsequently, an iterative approach is adopted, commencing with an initial bulk model that is successively refined to fit the observations. The direct problem always results in a unique solution, though the formulation is highly over-determined. Such unique solution highly depends on the input parameters, and multiple solutions vary with the initial imposed conditions. Conversely, the inverse problem is underdetermined by construction. Accordingly, it provides a set of solutions, generally identified and separated by statistical tests, as exemplified by the least squares approximation. Both methods intrinsically ignore feedback loops. Iterative methods are weak in quantifying the results. Based on the insights gained from this review, we developed a new integrative model for porphyry deposits that relies on the magmatic segregation of metals through a fluid sparging process. A formulation under the direct problem basically considers the enrichment factor for groups of metals (e.g., Cu, Mo, Au). A Lagrangian approach using a lattice Boltzmann model examines metal diffusion from the melt toward an immiscible phase, commonly a salty aqueous fluid. Metals first diffuse in the melt, the motion of which slows down when the mush development reduces the porosity, thus tapping the mobile fluid phase. Gas bubbles turn to tubes. They offer more mobility and allow the progression of the fluid phase, leading to metal advection, followed by metal precipitation. The quantitative results are poorly constrained owing to the large uncertainties on the input parameters but the metal enrichment factor fits observations from crustal abundance to ore grade levels. Nevertheless, the results aid in designing an inverse approach linking metal enrichment to metal partitioning, diffusion and viscous melt motion. From this approach, a simple diagram can be deduced using a logarithmic scale to smooth the parametric uncertainties. The diagram serves to illustrate the link between the above parameters and metal enrichment, also explaining differences in ore grade for different metals-magma pairs.
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Vinci, D., Dazas, B., Ferrage, E., Lanson, M., Magnin, V., Findling, N., et al. (2020). Influence of layer charge on hydration properties of synthetic octahedrally-charged Na-saturated trioctahedral swelling phyllosilicates. Applied Clay Science, 184.
Résumé: Smectite hydration impacts dynamical properties of interlayer cations and thus the transfer and fate of H2O, contaminants, and nutriments in surficial environments where this ubiquitous clay mineral is often one of the main mineral components. The influence of key crystal-chemical parameters, such as the amount of charge or the presence of fluorine, rather than hydroxyl groups, in smectite anionic framework, on hydration, organization of interlayer species, and related properties has been described for tetrahedrally substituted trioctahedral smectites (saponites). Despite the ubiquitous character of octahedrally substituted smectites, that make most of the world bentonite deposits, the influence of charge location on smectite hydration properties has not received similar attention. A set of octahedrally substituted trioctahedral smectites (hectorites) with a common structural formula Na(x)Mg(6-x)LixSi(8.0)O(20)(OH)(4) and a layer charge (x) varying from 0.8 to 1.6 was thus synthesized hydrothermally. The distribution of charge-compensating Na+ cations and of associated H2O molecules was determined experimentally from the modeling of X-ray diffraction data obtained along water vapor desorption isotherms. Consistent distributions of charge-compensating cations and of associated H2O molecules were also computed from GCMC simulations as a function of layer charge. Interlayer H2O contents [2.5-5.5 and 8.0-10.0 H2O molecules per O-20(OH)(4) for 1W and 2W hydrates, respectively] are similar in all Na-saturated smectite samples, independent of the location and amount of their layer charge. In contrast to synthetic saponite, for which stability of most hydrated layers was increased by increasing layer charge, the stability of synthetic hectorite hydrates is only marginally affected by layer charge. Consistently, the layer-to-layer distance of Na-saturated hectorite 2W (and 1W) layers is independent of layer charge (15.10-15.65 angstrom and 12.0-12.6 angstrom, respectively). The contrasting hydration behavior of synthetic Na-saturated saponite and hectorite is likely due to different electrostatic attraction between the 2:1 layer and interlayer cation, the charge undersaturation of O atoms at the surface of hectorite 2:1 layer being more diffuse compared to saponite. Combined with previous results on saponites, the present data and sample set provides key constraints to assess the validity of force fields simulating clay-water interactions for an unmatched variety of smectite with contrasting locations and amounts of layer charge deficits.
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Vinci, D., Lanson, B., Lanson, M., Magnin, V., & Findling, N. (2020). Hydration of Na-saturated synthetic stevensite, a peculiar trioctahedral smectite. Clay Minerals, 55(3), 229–237.
Résumé: Smectite interlayer water plays a key role in the mobility of elements and molecules and affects a variety of geological processes. In trioctahedral smectites, in contrast to saponite and hectorite, the layer charge of which originates from isomorphic substitutions, the stevensite layer charge originates from the presence of octahedral vacancies. Despite its common occurrence in lacustrine environments, stevensite hydration has received little attention compared to saponite and hectorite. Early reports mention a specific hydration behaviour, however, with the systematic presence of a low-angle reflection attributed to the regular interstratification of various hydration states. The present study aims to revisit this specific hydration behaviour in more depth. Within this scope, the hydration behaviour of the three smectite varieties above are compared using synthetic trioctahedral smectites of similar layer charge and various compositions of their octahedral sheets. The chemical composition of the octahedral sheet does not appear to influence significantly smectite hydration for saponite and hectorite. Compared to its saponite and hectorite equivalents, H2O content in stevensite is lower by similar to 2.0 mmol H2O per g of dry clay. Consistent with this lower H2O content, Zn-stevensite lacks a stable monohydrated state, with dehydrated layers prevailing from 60% to 0% relative humidity. The presence of the regular interstratification of 0W and 1W layers is responsible for the low-angle reflection commonly observed for stevensite under air-dried conditions. Finally, the stevensite identification method based on X-ray diffraction of heated and ethylene glycol-solvated samples is challenged by the possible influence of the octahedral sheet chemical composition (Zn or Mg in the present study) on hectorite swelling behaviour in synthetic Zn-smectites. The origin of this effect remains undetermined and further work is needed to propose a more general identification method.
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Voisine, E., Rolland, Y., Bernet, M., Carcaillet, J., Duclaux, G., Bascou, J. M., et al. (2020). Antarctic erosion history reconstructed by Terre Adelie moraine geochronology. Antarctic Science, 32(5), 382–395.
Résumé: We report apatite fission-track and Be-10 terrestrial cosmogenic nuclide (TCN) dating of 14 moraine boulders originating from inland Terre Adelie, East Antarctica. These data show cooling of the Proterozoic Terre Adelie craton at < similar to 120 degrees C between 350 and 300 Ma, suggesting > 4 km temperate glacial erosion during the Late Palaeozoic Ice Age, followed by nearly null Mesozoic erosion and low glacial erosion (< 2 km) in the Cenozoic. Based on glacial flux maps, the origin of the boulders may be located similar to 400 km upstream. Preliminary TCN (Be-10) datings of moraine boulders cluster within the last 30 ka. Cosmogenic ages from the Lacroix Nunatak suggest a main deglaciation after the Younger Dryas at c. 10 ka, while those of Cap Prud'homme mostly cluster at 0.6 ka, in agreement with an exhumation of boulders during the Little Ice Age.
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Vu, C. C., Ple, O., Weiss, J., & Amitrano, D. (2020). Revisiting the concept of characteristic compressive strength of concrete. Construction And Building Materials, 263.
Résumé: The characteristic compressive strength is one of the most important material property used in structural design and quality control of concrete. Here we show that the estimation of this characteristic strength following classical standard rules (e.g. EN 1992 or ACI-318) is sample size dependent, i.e. is not a characteristic of the material. From an extensive experimental dataset, an analysis of published strength data, and an interpretation of compressive failure as a critical phase transition from an intact to a failed state, we show that the compressive strength of concrete is characterized by a non-vanishing asymptotic mean strength, sigma(infinity), but a vanishing associated variability towards very large system sizes. Consequently, the asymptotic strength sigma(infinity) can be regarded as the genuine characteristic compressive strength of concrete. Based on this, we propose a new procedure to evaluate this genuine characteristic strength as well as to check the conformity of concrete with strength requirements. (C) 2020 Elsevier Ltd. All rights reserved.
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Vu, C. C., Weiss, J., Ple, O., & Amitrano, D. (2020). Size effects on the mechanical behavior and the compressive failure strength of concrete: an extensive dataset. Data In Brief, 33.
Résumé: This data article provides a series of 492 stress-strain curves and compressive strength values obtained under the uniaxial compression of concrete samples fabricated from three different normal-weight concrete mixtures with four different cylindrical sample sizes ranging from 40 x 80 mm to 160 x 320 mm. These data are related to two research articles: “Revisiting statistical size effects on compressive failure of heterogeneous materials, with a special focus on concrete” (Vu et al., 2018) [1] and “Revisiting the concept of characteristic compressive strength of concrete”(Vu et al., 2020) [2]. In those papers, the strength values were used to (i) analyze and interpret statistical size effects on compressive strength of concrete (in ref. [1]), and (ii) discuss and evaluate the genuine characteristic compressive strength of concrete when size effects on strength are taken into account (in ref. [2]). This dataset could be reused for other statistical analyses on the mechanical behavior of concrete (e.g. elastic and strength properties) and associated possible mixture or size effects. In addition, the characteristic properties of the hardened concrete samples such as the apparent density, the moisture content, the modulus of elasticity as well as the internal microstructures are also provided. (C) 2020 The Authors. Published by Elsevier Inc.
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Wang, Q. Y., & Yao, H. J. (2020). Monitoring of velocity changes based on seismic ambient noise: A brief review and perspective. Earth And Planetary Physics, 4(5), 532–542.
Résumé: Over the past two decades, the development of the ambient noise cross-correlation technology has spawned the exploration of underground structures. In addition, ambient noise-based monitoring has emerged because of the feasibility of reconstructing the continuous Green's functions. Investigating the physical properties of a subsurface medium by tracking changes in seismic wave velocity that do not depend on the occurrence of earthquakes or the continuity of artificial sources dramatically increases the possibility of researching the evolution of crustal deformation. In this article, we outline some state-of-the-art techniques for noise-based monitoring, including moving-window cross-spectral analysis, the stretching method, dynamic time wrapping, wavelet cross-spectrum analysis, and a combination of these measurement methods, with either a Bayesian least-squares inversion or the Bayesian Markov chain Monte Carlo method. We briefly state the principles underlying the different methods and their pros and cons. By elaborating on some typical noise-based monitoring applications, we show how this technique can be widely applied in different scenarios and adapted to multiples scales. We list classical applications, such as following earthquake-related co- and postseismic velocity changes, forecasting volcanic eruptions, and tracking external environmental forcing-generated transient changes. By monitoring cases having different targets at different scales, we point out the applicability of this technology for disaster prediction and early warning of small-scale reservoirs, landslides, and so forth. Finally, we conclude with some possible developments of noise-based monitoring at present and summarize some prospective research directions. To improve the temporal and spatial resolution of passive-source noise monitoring, we propose integrating different methods and seismic sources. Further interdisciplinary collaboration is indispensable for comprehensively interpreting the observed changes.
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Wathelet, M., Chatelain, J. L., Cornou, C., Di Giulio, G., Guillier, B., Ohrnberger, M., et al. (2020). Geopsy: A User-Friendly Open-Source Tool Set for Ambient Vibration Processing. Seismological Research Letters, 91(3), 1878–1889.
Résumé: Ambient vibrations are nowadays considerably used worldwide for numerous types of engineering applications and scientific research. Geopsy and its companion tools are part of that landscape. Since the first release of the program package in 2005, as outcome of the European Union project Site Effects aSsessment from AMbient noisE, Geopsy has become a mature multiplatform open-source package (released under GNU Public License version 3) that has already been recognized as a reference tool for analyzing ambient vibration data in the context of site characterization studies. The community of users has grown from a core group of researchers up to thousands of seismologists and engineers on every career level and on all continents. The versatility of geopsy allows for the processing of all kinds of data needed in site characterization studies, that is, from single station single trace to three-component array recordings. In all of the aforementioned cases, the steps from field acquisition to the production of publication-ready figures are covered and supported by user-friendly graphical user interfaces or corresponding command-line tools for the automation of the complete processing chain. To avoid black-box usage, a number of lower-level tools guarantee maximum flexibility in accessing and controlling processing results at any stage of the analysis.
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Weatherill, G., Kotha, S. R., & Cotton, F. (2020). A regionally-adaptable “scaled backbone” ground motion logic tree for shallow seismicity in Europe: application to the 2020 European seismic hazard model. Bulletin Of Earthquake Engineering, 18(11), 5087–5117.
Résumé: The selection of ground motion models, and the representation of their epistemic uncertainty in the form of a logic tree, is one of the fundamental components of probabilistic seismic hazard and risk analysis. A new ground motion model (GMM) logic tree has been developed for the 2020 European seismic hazard model, which develops upon recently compiled ground motion data sets in Europe. In contrast to previous European seismic hazard models, the new ground model logic tree is built around the scaled backbone concept. Epistemic uncertainties are represented as calibrations to a reference model and aim to characterise the potential distributions of median ground motions resulting from variability in source scaling and attenuation. These scaled backbone logic trees are developed and presented for shallow crustal seismic sources in Europe. Using the new European strong motion flatfile, and capitalising on recent perspectives in ground motion modelling in the scientific literature, a general and transferable procedure is presented for the construction of a backbone model and the regionalisation of epistemic uncertainty. This innovative approach forms a general framework for revising and updating the GMM logic tree at national and European scale as new strong motion data emerge in the future.
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Wu, Z. K., Lanson, B., Feng, X. H., Yin, H., Qin, Z. J., Wang, X. M., et al. (2020). Transformation of Ni-containing birnessite to tectomanganate: Influence and fate of weakly bound Ni(II) species. Geochimica Et Cosmochimica Acta, 271, 96–115.
Résumé: The geochemical behavior of nickel, an essential trace metal element, strongly depends on its interactions with Mn oxides. Interactions between the phyllomanganate birnessite and sorbed or structurally incorporated Ni have been extensively documented together with the fate of Ni along the transformation of these layered species to tunnel Mn oxides (tectomanganates). By contrast, interactions of phyllomanganates with weakly bound Ni species [hydrated Ni, Ni (hydr)oxides], that possibly prevail in natural Ni-rich (>10% NiO) manganates, have received little attention and the influence of these Ni species on the phyllomanganate-to-tectomanganate transformation remains essentially unknown. A set of phyllomanganate precursors with contrasting contents of Ni was thus prepared and subjected to a reflux treatment mimicking the natural phyllomanganate-to-tectomanganate conversion. Layered precursors and reflux products were characterized with a combination of diffractometric, spectroscopic, thermal, and chemical methods. Ni is essentially present as hydrated Ni(II) and Ni(II) (hydr)oxides in Ni-rich layered precursors whereas Ni(II) sorbed at particle edges prevail at low Ni content. No Ni sorbed at layer vacancy sites or structurally incorporated was detected in the initial vacancy-free layered precursors. Consistent with the high content (approximate to 1/3) of JahnTeller distorted Mn(III) octahedra in layered precursors, which is favorable to their conversion to tectomanganates, Ni-free samples fully convert to an a-disordered todorokite, a common tectomanganate with a 3 x 3 tunnel structure. Contrastingly and despite similar high Mn(III) contents in Ni-rich precursors, hydrolysis of interlayer Ni2+ and polymerization of Ni(OH)(2) in phyllomanganate interlayers is kinetically favored during reflux process. Asbolane, a phyllomanganate with an incomplete – island-like – octahedral layer of metal (hydr)oxides, is thus formed rather than todorokite. A nitric acid treatment, aiming at the dissolution of the island-like interlayer Ni(OH)(2) layer, allows an easy and unambiguous differentiation between asbolane and todorokite, the latter being unaffected by the treatment. Both compounds exhibit indeed similar interplanar periodicities and can be confused when using X-ray diffraction, despite contrasting intensity ratios. Migration rate of Mn(III) out of the MnO2 layer relative to the metal hydrolysis and polymerization rate determines the formation of todorokite or asbolane. Here, Ni(OH)(2) polymerization hampers the formation of tectomanganates and likely contributes to the prevalence of phyllomanganates over tectomanganates in natural Ni-rich environments. Most Ni is retained during the reflux process, part of Ni (approximate to 20%) being likely structurally incorporated in the reaction products, thus enhancing the sequestration of Ni in Mn oxides. (C) 2019 Elsevier Ltd. All rights reserved.
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Xie, F., Zhang, Y. X., Larose, E., Duclos, A., Chen, S., Li, X. Y., et al. (2020). Characterizing mechanical change in metals using amplitude-modulated diffuse ultrasound. Structural Health Monitoring-An International Journal, 19(6), 1894–1904.
Résumé: In this article, we present an ultrasonic method based on diffuse ultrasound with successive excitation amplitudes. This method provides amplitude-dependent parameters of diffuse ultrasound using coda wave interferometry, and these parameters can be used to characterize mechanical change in metallic materials. The localized mechanical change caused by an instantaneous 400 degrees C thermal shock in a meter-scale aluminum alloy slab was characterized by measuring the diffuse-wave velocity change and decorrelation coefficient as functions of the excitation amplitude. The potential mechanisms and spatial distribution that cause the observed amplitude-dependent diffuse waveform modification are discussed. Combining the method presented here with complementary approaches will enhance the ability to nondestructively detect early-stage damage in the laboratory or in the field.
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Xie, L. J., Yoneda, A., Xu, F., Higo, Y. J., Wang, C., Tange, Y., et al. (2020). Boron-MgO composite as an X-ray transparent pressure medium in the multi-anvil apparatus (vol 91, 043903, 2020). Review Of Scientific Instruments, 91(6).
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Xu, F., Xie, L. J., Yoneda, A., Guignot, N., King, A., Morard, G., et al. (2020). TiC-MgO composite: an X-ray transparent and machinable heating element in a multi-anvil high pressure apparatus. High Pressure Research, 40(2), 257–266.
Résumé: TiC-MgO composite was developed as a heating element for X-ray study in the multi-anvil high pressure apparatus. We synthesized TiC-MgO blocks (50-70 wt.% of TiC) by compression in a cold isostatic press followed by baking in a gas flow furnace. Heaters of tubular shape were manufactured from the synthesized blocks either by lathe or numerically controlled milling machine. The so-produced heating elements have been proved to generate temperatures up to 2250 K at 10 GPa, condition where classical graphite heaters are not suitable anymore due to graphite-diamond transition. These new heaters have been successfully used for in situ X-ray radiography and diffraction measurements on liquid Fe alloys, exploiting excellent X-ray transparency.
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Yamazaki, T., Van Driessche, A. E. S., & Kimura, Y. (2020). High mobility of lattice molecules and defects during the early stage of protein crystallization. Soft Matter, 16(8), 1955–1960.
Résumé: Protein crystals are expected to be useful not only for their molecular structure analysis but also as functional materials due to their unique properties. Although the generation and the propagation of defects during crystallization play critical roles in the final properties of protein crystals, the dynamics of these processes are poorly understood. By time-resolved liquid-cell transmission electron microscopy, we observed that nanosized crystal defects are surprisingly mobile during the early stages of the crystallization of a lysozyme as a model protein. This highly dynamic behavior of defects reveals that the lattice molecules are mobile throughout the crystal structure. Moreover, the disappearance of the defects indicated that intermolecular bonds can break and reform rapidly with little energetic cost, as reported in theoretical studies. All these findings are in marked contrast to the generally accepted notion that crystal lattices are rigid with very limited mobility of individual lattice molecules.
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Yang, Y., Li, S. Z., Ding, X. D., Sun, J., Weiss, J., & Salje, E. K. H. (2020). Twisting of pre-twinned alpha-Fe nanowires: from mild to wild avalanche dynamics. Acta Materialia, 195, 50–58.
Résumé: We studied the torsion behavior of alpha-Fe nanowires seeded with twin boundaries (TBs) using molecular dynamics simulations. Twisting the wire generates topological defects in the twin walls, namely kinks inside the twin walls for small twist angles, and junctions between kinks for large twist angles. During twisting the kink motion is jerky and uncorrelated at small twist angles. The probability density function (PDF) of jerks strength follows approximately a Gaussian distribution, indicating a mild deformation mode. The kink dynamics transforms from mild to wild at larger twist angles when complex twin patterns with a high density of junctions are generated. The collective motion of kinks now shows avalanche behavior with the energy being power-law distributed. The wildness, which measures the proportion of strain energy relaxed through such avalanches, is correlated with the junction density, and controlled by the external length scale (wire diameter) as well as an internal length scale (twin boundary spacing). Good strain-stress recoverability is achieved when unloading the wire before the formation of complex twin patterns. We correlate the evolution of twin patterns with a statistical analysis of jerk dynamics, which identifies the unique mechanical properties governed by twin boundary motion in nanowires. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Ye, R. C., Kumar, K., de Hoop, M. V., & Campillo, M. (2020). A multi-rate iterative coupling scheme for simulating dynamic ruptures and seismic waves generation in the prestressed earth. Journal Of Computational Physics, 405.
Résumé: We present a novel method to simulate the dynamic evolution of spontaneous ruptures governed by rate- and state-dependent friction laws and the interaction with seismic waves in a prestressed elastically deforming body. We propose a multi-rate iterative coupling scheme based on the variational form of the elastic-gravitational equations, and discretize employing a discontinuous Galerkin method, with nonlinear interior boundary conditions being weakly imposed across the fault surface as numerical fluxes. We introduce necessary interface jump penalty terms as well as an artificial viscous regularization, with the conditions for penalty and viscosity coefficients given based on an energy estimate and a convergence analysis. In the multi-rate scheme, an implicit-explicit Euler scheme in time is invoked, and the time step for the evolution of friction is chosen significantly finer than that for wave propagation and scattering. This is facilitated by the iterative scheme through the underlying decoupling where the linear, elastic wave equation plays the role of a Schur-complement to the friction model. A nonlinearly constrained optimization problem localized to each element on the rupture surface is then formulated and solved using the Gauss-Newton method. We test our algorithm on several benchmark examples and illustrate the generality of our method for realistic rupture simulations. (C) 2019 Elsevier Inc. All rights reserved.
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Ying, C. Y., Lanson, B., Wang, C., Wang, X. M., Yin, H., Yan, Y. P., et al. (2020). Highly enhanced oxidation of arsenite at the surface of birnessite in the presence of pyrophosphate and the underlying reaction mechanisms. Water Research, 187.
Résumé: Manganese(IV) oxides, and more especially birnessite, rank among the most efficient metal oxides for As(III) oxidation and subsequent sorption, and thus for arsenic immobilization. Efficiency is limited how-ever by the precipitation of low valence Mn (hydr)oxides at the birnessite surface that leads to its passivation. The present work investigates experimentally the influence of chelating agents on this oxidative process. Specifically, the influence of sodium pyrophosphate (PP), an efficient Mn(III) chelating agent, on As(III) oxidation by birnessite was investigated using batch experiments and different arsenic concentrations at circum-neutral pH. In the absence of PP, Mn(II/III) species are continuously generated during As(III) oxidation and adsorbed to the mineral surface. Field emission-scanning electron microscopy, synchrotron-based X-ray diffraction and Fourier transform infrared spectroscopy indicate that manganite is formed, passivating birnessite surface and thus hampering the oxidative process. In the presence of PP, generated Mn(II/III) species form soluble complexes, thus inhibiting surface passivation and promoting As(III) conversion to As(V) with PP. Enhancement of As(III) oxidation by Mn oxides strongly depends on the affinity of the chelating agent for Mn(III) and from the induced stability of Mn(III) complexes. Compared to PP, the positive influence of oxalate, for example, on the oxidative process is more limited. The present study thus provides new insights into the possible optimization of arsenic removal from water using Mn oxides, and on the possible environmental control of arsenic contamination by these ubiquitous nontoxic mineral species. (c) 2020 Elsevier Ltd. All rights reserved.
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Ying, H., Feng, X. H., Zhu, M. Q., Lanson, B., Liu, F., & Wang, X. M. (2020). Formation and transformation of schwertmannite through direct Fe(3+)hydrolysis under various geochemical conditions. Environmental Science-Nano, 7(8), 2385–2398.
Résumé: Schwertmannite formation and transformation, key processes that influence the speciation, mobility, and environmental fate of associated trace elements in acid mine drainage (AMD), were primarily studied through Fe(2+)oxidation-hydrolysis. Direct Fe(3+)hydrolysis is another important schwertmannite formation pathway, but the effects of geochemical conditions on the mineralogical properties of schwertmannite formedviasuch a pathway are poorly known. Here, the formation of schwertmannite through direct Fe(3+)hydrolysis enforced by heating or adding OH(-)and subsequent transformation were systematically examined under various geochemical conditions. Pure schwertmannite is obtained through Fe(3+)hydrolysis at 25-60 degrees C for 12 min and subsequent dialysis for 1-15 days, while minor amounts of goethite appear at higher hydrolysis temperatures. A shorter dialysis time and the presence of K(+)or NH(4)(+)both slightly increase schwertmannite crystallinity. During Fe(3+)hydrolysis by adding OH-, sulfate-bearing ferrihydrite initially forms and then quickly transforms into schwertmannite. In contrast, pre-formed ferrihydrite does not transform into schwertmannite under the same solution conditions, despite sulfate adsorption. With decreasing Fe(3+)hydrolysis rate, schwertmannite crystallinity slightly increases and its morphology of “network” structure becomes larger and less dense. As to schwertmannite transformation, high temperature, high pH, and the presence of Fe(2+)favor its transformation to goethite, while a low Fe(3+)hydrolysis rate and a high Cl(-)concentration hinder the transformation. In contrast, the presence of K(+)or high NH(4)(+)concentration favors schwertmannite transformation to jarosite with the former occurring more readily. These new insights into schwertmannite formation and transformation are essential for predicting the environmental fates of associated trace elements in AMD environments.
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Yogeshwar, P., Kupper, M., Tezkan, B., Rath, V., Kiyan, D., Byrdina, S., et al. (2020). Innovative boat-towed transient electromagnetics – Investigation of the Furnas volcanic lake hydrothermal system, Azores. Geophysics, 85(2), E41–E56.
Résumé: Water-covered areas may lead to gaps in surface electromagnetic surveys, causing reduced resolution and, as a consequence, increased uncertainty in derived subsurface models. We have evaluated a boat-towed floating central loop time-domain electromagnetic technique that mitigates this problem. It facilitates obtaining data with a spatial sampling density, which is rarely possible with standard instrumentation on land, and it only requires moderate logistical effort. A unique field study on a shallow volcanic lake demonstrated that this method is feasible with only a minor loss of accuracy when compared to anchored and land soundings. We found that the noise sources arising from the moving instrument and the boat engine can be neglected. The field survey was performed on the Lagoa das Furnas (Sao Miguel, Azores Islands, Portugal), which is located within an active volcanic area and is characterized by fumarolic fields and CO2 degassing. Thus, the associated hydrothermal system is expected to extend below the lake. However, the character, geometry, and extent of this system are unknown because of the lack of boreholes and geophysical studies. In total, 600 soundings, combining towed profiles with anchored and land-based soundings, were acquired with an aim of imaging the hydrothermal system beneath the lake down to 200 m. The results from all three types of measurements compare well and thus led to consistent 1D inversion models. The inversion results delineate a highly conductive, smectite-rich cap layer dipping below the lake away from the main fumarole zone. Near this zone, the extent of the conductor agrees well with an area of intense dispersed CO2 degassing, which appears to be controlled by at least two electrically distinctive fault zones in which the conductor is found at greater depths.
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Yuan, S. Y., Wei, W. W., Wang, D., Shi, P. D., & Wang, S. X. (2020). Goal-Oriented Inversion-Based NMO Correction Using a Convex l(2,1)-Norm. Ieee Geoscience And Remote Sensing Letters, 17(1), 162–166.
Résumé: Normal moveout (NMO) correction is a routine step in seismic data processing, which has an important impact on other seismic processing procedures, seismic inversion, and interpretation. We propose a goal-oriented inversion-based NMO correction method using a convex l(2,1)-norm. The proposed method corrects the superresolution multichannel offsetdependent reflectivity rather than the bandlimited data itself sample by sample, block by block, or wavelet by wavelet. Therefore, the proposed method can essentially reduce the amplitude and even phase distortion introduced by data-based NMO correction methods in the presence of strong wavelet interference. We impose two goal-oriented constraints including both the temporal sparsity and the horizontal continuity of reflectivity, which are approximately represented by a convex l(2,1)-norm, on the geometric moveout relationship from offset-dependent trajectories to zero offsets to build a new objective function for NMO correction. The goal-desired temporal sparsity of reflectivity can induce the superresolution solution; meanwhile, the goal-desired horizontal continuity introduces a reasonable intrinsic structure to further limit the solution space and is particularly suitable to processing interfering reflections. Attributing to these two additional constraints, the new NMO correction method can flatten the interfering events and the intersecting events with favorable offset-dependent amplitude and phase variations even in the presence of noise. Synthetic and real data examples are adopted to verify the performance of our method. The results show that goal-oriented inversion-based NMO correction using the l(2,1)-norm is a potentially effective, stable, and high-quality NMO correction tool, especially for strong wavelet interference and at far offsets.
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Zhang, P., Bian, J. J., Zhang, J. Y., Liu, G., Weiss, J., & Sun, J. (2020). Plate-like precipitate effects on plasticity of Al-Cu alloys at micrometer to sub-micrometer scales. Materials & Design, 188.
Résumé: The continuous miniaturization of modern electromechanical systems calls for a comprehensive understanding of the mechanical properties of metallic materials specific to micrometer and sub-micrometer scales. At these scales, the nature of dislocation-mediated plasticity changes radically: sub-micrometer metallic samples exhibit high yield strengths, however accompanied by detrimental intermittent strain fluctuations endangering structural stability. In this paper, we studied the effects of plate-like theta'-Al2Cu precipitates on the strength and plastic fluctuations of Al-Cu alloys from micro-pillar compression testing. The particularity of our samples is that the plate-like precipitates have diameters commensurate with the external size of the Al-Cu micro-pillars. Our results show that these plate-like precipitates can strengthen the materials through the Orowan mechanism at large sample size. However, the breakdown of the mean-field pinning landscape weakens its suppression effect on plastic intermittency. On the other hand, the plastic intermittency can be inhibited efficiently at small sample size by using the plate-like theta'-Al2Cu precipitates penetrating the entire micro-pillar, in association with the presence of {100}-slip traces along the coherent precipitate/Al matrix interface and enhanced strain isotropy. Besides these experimental observations, we also aim to extract the laws common in different Al alloys, and address the specific plastic mechanisms for Al-Cu micro-crystals. (C) 2020 The Authors. Published by Elsevier Ltd.
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Zhang, P., Salman, O. U., Weiss, J., & Truskinovsky, L. (2020). Variety of scaling behaviors in nanocrystalline plasticity. Physical Review E, 102(2).
Résumé: We address the question of why larger, high-symmetry crystals are mostly weak, ductile, and statistically subcritical, while smaller crystals with the same symmetry are strong, brittle and supercritical. We link it to another question of why intermittent elasto-plastic deformation of submicron crystals features highly unusual size sensitivity of scaling exponents. We use a minimal integer-valued automaton model of crystal plasticity to show that with growing variance of quenched disorder, which can serve in this case as a proxy for increasing size, submicron crystals undergo a crossover from spin-glass marginality to criticality characterizing the second order brittle-to-ductile (BD) transition. We argue that this crossover is behind the nonuniversality of scaling exponents observed in physical and numerical experiments. The nonuniversality emerges only if the quenched disorder is elastically incompatible, and it disappears if the disorder is compatible.
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Zhao, L., Malusa, M. G., Yuan, H. Y., Paul, A., Guillot, S., Lu, Y., et al. (2020). Evidence for a serpentinized plate interface favouring continental subduction. Nature Communications, 11(1).
Résumé: The dynamics of continental subduction is largely controlled by the rheological properties of rocks involved along the subduction channel. Serpentinites have low viscosity at geological strain rates. However, compelling geophysical evidence of a serpentinite channel during continental subduction is still lacking. Here we show that anomalously low shear-wave seismic velocities are found beneath the Western Alps, along the plate interface between the European slab and the overlying Adriatic mantle. We propose that these seismic velocities indicate the stacked remnants of a weak fossilised serpentinite channel, which includes both slivers of abyssal serpentinite formed at the ocean floor and mantle-wedge serpentinite formed by fluid release from the subducting slab. Our results suggest that this serpentinized plate interface may have favoured the subduction of continental crust into the upper mantle and the formation/exhumation of ultra-high pressure metamorphic rocks, providing new constraints to develop the conceptual and quantitative understanding of continental-subduction dynamics. The dynamics of continental subduction is largely controlled by the rheological properties of rocks involved along the subduction channel. Here, the authors reveal a prominent, yet previously undetected, low-velocity body beneath the Western Alps, along the plate interface between the European slab and the overlying Adriatic mantle, which they interpret as a serpentinite layer.
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