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Abbas, M., Jardani, A., Soueid Ahmed, S., Revil, A., Brigaud, L., Begassat, P., et al. (2017). Redox potential distribution of an organic-rich contaminated site obtained by the inversion of self-potential data. Journal Of Hydrology, 554, 111–127.
Résumé: Mapping the redox potential of shallow aquifers impacted by hydrocarbon contaminant plumes is important for the characterization and remediation of such contaminated sites. The redox potential of groundwater is indicative of the biodegradation of hydrocarbons and is important in delineating the shapes of contaminant plumes. The self-potential method was used to reconstruct the redox potential of groundwater associated with an organic-rich contaminant plume in northern France. The self-potential technique is a passive technique consisting in recording the electrical potential distribution at the surface of the Earth. A self-potential map is essentially the sum of two contributions, one associated with groundwater flow referred to as the electrokinetic component, and one associated with redox potential anomalies referred to as the electroredox component (thermoelectric and diffusion potentials are generally negligible). A groundwater flow model was first used to remove the electrokinetic component from the observed self-potential data. Then, a residual self-potential map was obtained. The source current density generating the residual self-potential signals is assumed to be associated with the position of the water table, an interface characterized by a change in both the electrical conductivity and the redox potential. The source current density was obtained through an inverse problem by minimizing a cost function including a data misfit contribution and a regularizer. This inversion algorithm allows the determination of the vertical and horizontal components of the source current density taking into account the electrical conductivity distribution of the saturated and non-saturated zones obtained independently by electrical resistivity tomography. The redox potential distribution was finally determined from the inverted residual source current density. A redox map was successfully built and the estimated redox potential values correlated well with in-situ measurements. (C) 2017 Elsevier B.V. All rights reserved.
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Aben, F. M., Doan, M. - L., Gratier, J. - P., & Renard, F. (2017). Experimental postseismic recovery of fractured rocks assisted by calcite sealing. Geophysical Research Letters, 44(14), 7228–7238.
Résumé: Postseismic recovery within fault damage zones involves slow healing of coseismic fractures leading to permeability reduction and strength increase with time. To better understand this process, experiments were performed by long-term fluid percolation with calcite precipitation through predamaged quartz-monzonite samples subjected to upper crustal conditions of stress and temperature. This resulted in a P wave velocity recovery of 50% of its initial drop after 64 days. In contrast, the permeability remained more or less constant for the duration of the experiment. Microstructures, fluid chemistry, and X-ray microtomography demonstrate that incipient calcite sealing and asperity dissolution are responsible for the P wave velocity recovery. The permeability is unaffected because calcite precipitates outside of the main flow channels. The highly nonparallel evolution of strength recovery and permeability suggests that fluid conduits within fault damage zones can remain open fluid conduits after an earthquake for much longer durations than suggested by the seismic monitoring of fault healing.
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Aben, F. M., Doan, M. - L., Gratier, J. - P., & Renard, F. (2017). High strain rate deformation of porous sandstone and the asymmetry of earthquake damage in shallow fault zones. Earth And Planetary Science Letters, 463, 81–91.
Résumé: In contrast to coseismic pulverization of crystalline rocks, observations of coseismic pulverization in porous sedimentary rocks in fault damage zones are scarce. Also, juxtaposition of stiff crystalline rocks and compliant porous rocks across a fault often yields an asymmetric damage zone geometry, with less damage in the more compliant side. In this study, we argue that such asymmetry near the sub-surface may occur because of a different response of lithology to similar transient loading conditions. Uniaxial unconfined high strain rate loadings with a split Hopkinson pressure bar were performed on dry and water saturated Rothbach sandstone core samples. Bedding anisotropy was taken into account by coring the samples parallel and perpendicular to the bedding. The results show that pervasive pulverization below the grain scale, such as observed in crystalline rock, does not occur in the sandstone samples for the explored strain rate range (60-150s(-1)). Damage is mainly restricted to the scale of the grains, with intragranular deformation occurring only in weaker regions where compaction bands are formed. The presence of water and the bedding anisotropy mitigates the formation of compaction bands and motivates intergranular dilatation. The competition between inter-and intragranular damage during dynamic loading is explained with the geometric parameters of the rock in combination with two classic micromechanical models: the Hertzian contact model and the pore-emanated crack model. In conclusion, the observed microstructures can form in both quasi-static and dynamic loading regimes. Therefore caution is advised when interpreting the mechanism responsible for near-fault damage in sedimentary rock near the surface. Moreover, the results suggest that different responses of lithology to transient loading are responsible for sub-surface damage zone asymmetry. (C) 2017 Elsevier B.V. All rights reserved.
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Aguilar, I., Sabatier, P., Beck, C., Audemard, F., Crouzet, C., Urbani, F., et al. (2017). Calculation of the reservoir age from organic and carbonate fractions of sediments in the Gulf of Cariaco (Caribbean Sea). Quaternary Geochronology, 38, 50–60.
Résumé: A set of 24 AMS C-14 measurements were performed on different sediment fractions from short gravity cores taken from the Gulf of Cariaco (northeastern Venezuela) in order to construct a detailed sedimentary archive for recent centuries. A local reservoir effect was expected because of i) strong upwelling from the neighboring Cariaco Trough and anoxia and ii) the specific geomorphological setting related to active faults with seeps and diapirism. Measurements were thus performed on different components: sediment bulk organic fraction (SBOF), pteropods shells (surface water), bivalve shells (bottom), and plant fragments. Based on comparisons of the different results, we discuss different age corrections and calibrations, which lead us to consider a negligible local reservoir correction (AR) for the bivalve and pteropod shells, which show no reservoir age for carbonate and an absence of water stratification. However, a local 633 +/- 64 yr Delta R appears in the organic fraction of the sediment, and its origin is primary related to the upwelling mechanism. (C) 2017 Elsevier B.V. All rights reserved.
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Airaghi, L., de Sigoyer, J., Lanari, P., Guillot, S., Vidal, O., Monie, P., et al. (2017). Total exhumation across the Beichuan fault in the Longmen Shan (eastern Tibetan plateau, China): Constraints from petrology and thermobarometry. Journal Of Asian Earth Sciences, 140, 108–121.
Résumé: The deep structure and deformation mechanisms of the Longmen Shan thrust belt (Sichuan, China), at the eastern border of the Tibetan plateau, were largely debated after the devastating Mw 7.9 Wenchuan earthquake (2008). Recent geophysical studies and field investigations have been focused on the active motion of the major Beichuan fault, which ruptured during the earthquake. However, the total exhumation across the fault still remains unclear. In the hanging wall of the Beichuan fault, the South China block is exhumed in the Pengguan massif. Close to the Beichuan fault, the rocks of the Pengguan massif underwent greenschist facies metamorphism associated with brittle-ductile deformation. No metamorphism is observed in the footwall of the fault. In this study, we characterize and date the metamorphic history recorded in the hanging wall of the Beichuan fault in order to constrain the depth and timing of exhumation of the rocks of the Pengguan massif along the fault. A high-resolution petrological approach involving chemical analyses and X-ray maps was used to analyze the micrometric metamorphic minerals. The P-T conditions of the greenschist facies metamorphic event were estimated by an inverse multi-equilibrium thermodynamic approach. The results, 280 +/- 30 degrees C and 7 +/- 1 kbar, suggest that the rocks of the Pengguan massif were exhumed from ca. 20 km depth. Our results underline the importance of the thrusting component in the long-term behavior of the Beichuan fault and provide a minimal depth at which the fault is rooted. In situ laser ablation Ar-40/Ar-39 dating of metamorphic white mica revealed that the greenschist overprint occurred at 135-140 Ma. The Pengguan massif was therefore partially thrusted along the Beichuan fault during the Lower Cretaceous, long before the Eocene-Miocene exhumation phase which is well-constrained by low-temperature thermochronology. Our results provide the first independent depth information for the exhumation history of the Pengguan massif and reveal a previously undocumented Lower Cretaceous tectonic event that marks the onset of the thick-skinned deformation in the external domain of the Longmen Shan (East of the Wenchuan Fault).
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Airaghi, L., Lanari, P., de Sigoyer, J., & Guillot, S. (2017). Microstructural vs compositional preservation and pseudomorphic replacement of muscovite in deformed metapelites from the Longmen Shan (Sichuan, China). Lithos, 282, 262–280.
Résumé: Pressure-temperature-deformation (P-T-s) paths for metamorphic rocks that experienced a complex deformation history commonly rely on the link between successive metamorphic assemblages and the different microstructures preserved at the sample scale. However, with changing P-T conditions, metamorphic minerals in a specific microstructure can chemically re-equilibrate. The direct link between deformation phases and mineral compositions for thermobarometry purposes can therefore be distorted. This study focuses on a series of garnet-biotite metapelites from the Longmen Shan (Sichuan, China) that preserve muscovite of different chemistry in distinct microstructures. To quantify the degree of re-equilibration of muscovite, a microstructural study was coupled with high-resolution chemical mapping. The chemical evolution of muscovite was modeled along a P-T loop previously constrained with phase equilibria calculations, semi-empirical and empirical thermobarometry. Results show that metapelites experienced a three-stage metamorphic history: (1) heating and burial up to 11 +/- 2 kbar, 530 +/- 20 degrees C, (2) minor decompression and heating up to 6.5 +/- 1 kbar, 575 +/- 10 degrees C and (3) decompression and cooling down to 4 +/- 1 kbar, 380-450 degrees C. Muscovite partially re-equilibrated by pseudomorphic replacement during the three metamorphic stages, although it is mainly observed in prograde microstructures preceding the pressure peak. The main factors controlling the re-equilibration are the intensity of the deformation and the fluid availability during metamorphism. The P-T conditions of metamorphic assemblages thus reflect pulses of fluids release that enhanced mineral resorption and local replacement. Such micro-chemical behavior is probably relatively common in metapelites and questions the reliability of the P-T predictions based on relict phase chemistry, apparently preserved in microstructures that might have been affected by later re-equilibration. (C) 2017 Elsevier B.V. All rights reserved.
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Akkermans, E., Campillo, M., Deutscher, G., Fink, M., Lagendijk, A., Skipetrov, S., et al. (2017). Roger Maynard 1938-2015. European Physical Journal-Special Topics, 226(7), 1349–1352.
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Ali, S. H., Giurco, D., Arndt, N., Nickless, E., Brown, G., Demetriades, A., et al. (2017). Mineral supply for sustainable development requires resource governance. Nature, 543(7645), 367–372.
Résumé: Successful delivery of the United Nations sustainable development goals and implementation of the Paris Agreement requires technologies that utilize a wide range of minerals in vast quantities. Metal recycling and technological change will contribute to sustaining supply, but mining must continue and grow for the foreseeable future to ensure that such minerals remain available to industry. New links are needed between existing institutional frameworks to oversee responsible sourcing of minerals, trajectories for mineral exploration, environmental practices, and consumer awareness of the effects of consumption. Here we present, through analysis of a comprehensive set of data and demand forecasts, an interdisciplinary perspective on how best to ensure ecologically viable continuity of global mineral supply over the coming decades.
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Amaya, S., Zuluaga, C. A., & Bernet, M. (2017). New fission-track age constraints on the exhumation of the central Santander Massif: Implications for the tectonic evolution of the Northern Andes, Colombia. Lithos, 282, 388–402.
Résumé: The Late Cretaceous to late Neogene exhumation history of the central Santander Massif in the Northern Andes of Colombia is controlled by the geodynamic interactions between the Caribbean, South American and Nazca plates, as well as the Neogene collision and accretion of the Panama arc. Slab-breakoff of the Caribbean plate, with the tip of the slab tear presently being located beneath Bucaramanga, and the east-west oriented Caldas tear are the main structures relating seismic activity and Late Miocene to Pleistocene magmatic/hydrothermal activity and associated gold mineralization in the central Santander Massif. Here we present new apatite (AFT) and zircon fission-track (ZFT) data from 18 samples collected along two profiles in the California-Vetas block (including the Rio Charta), to the south of the Rio Charta fault, and from Bucaramanga to Picacho on the western flank of the central Santander Massif. The fission-track data are used for time temperature history modelling and for estimating long-term average exhumation rates. The California-Vetas block in the central Santander Massif to the north of the Rio Charta fault cooled rapidly at a rate of about 24 degrees C/Myr between 10 and 5 Ma. Fast cooling was not related to post-magmatic cooling or hydrothermal activity, but rather to exhumation, with rates based on apatite fission-track cooling ages on the order of 0.3-0.4 km/Myr. However, long-term average exhumation rates since the Late Cretaceous, based on zircon fission track data, were only on the order of 0.1-0.2 km/Myr. Our data indicate that next to the Rio Charta fault also the Surata fault contributed to the exhumation of the California-Vetas block. The western flank of the central Santander Massif, shows a more complete thermal history along the Bucaramanga-Picacho profile, with the exposure of an exhumed zircon fission-track partial annealing zone. Thermal history modelling of zircon fission-track data of this profile shows that after burial and heating from about 150 Ma on cooling at rates of 7-10 degrees C/Myr started at about 25 Ma. For the lower part of the profile, the early Miocene ZFT ages indicate exhumation at rates of 0.3-0.5 km/Myr along the Bucaramanga fault, but were only about 0.1 km/Myr on the high plateau of the central Santander Massif. (C) 2017 Elsevier B.V. All rights reserved.
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Ameri, G., Hollender, F., Perron, V., & Martin, C. (2017). Site-specific partially nonergodic PSHA for a hard-rock critical site in southern France: adjustment of ground motion prediction equations and sensitivity analysis. Bulletin Of Earthquake Engineering, 15(10), 4089–4111.
Résumé: Modern probabilistic seismic hazard assessment (PSHA) focuses on the separation and different treatment of epistemic and aleatory uncertainties. Recent site-specific PSHA studies have pointed out that, if the site response and its epistemic uncertainties can be appropriately considered by adjustments to median estimates from ground motion prediction equations (GMPEs), the aleatory variability (sigma) of the GMPEs can be replaced by the single-station sigma thus partially relaxing the ergodic assumption employed in the PSHA. The site-specific partially nonergodic approach, correctly applied, provides a more accurate representation of the seismic hazard at a specific site and a more rigorous treatment of uncertainties. This paper presents the strategy followed to apply this relatively recent approach to a critical infrastructure in Southern France located on hard-rock site conditions (Vs30 ae 2000 m/s). The target site conditions are defined in terms of shear-wave velocity (Vs) profiles and high-frequency attenuation (kappa(0)) based on the results of site investigations and on the exploitation of earthquake records at seismic stations in the target site area. The host-to-target Vs-kappa(0) adjustment of median estimates for the selected GMPEs is performed by using the inverse random vibration theory approach (Al Atik et al. in Bull Seismol Soc Am 104:336-346, 2014) considering epistemic uncertainties in target Vs profile and kappa(0). The single-station sigma model is developed based on Rodriguez-Marek et al. (Bull Seismol Soc Am 104:1601-1619, 2013) due to the lack of local data. The results of the site-specific partially nonergodic PSHA are discussed by means of a sensitivity analysis and are compared to the results from standard ergodic PSHA. We found that, for the considered site, the site-specific approach provides a substantial reduction (up to 50%) of the uniform hazard spectra at 10,000-year return period compared to the ergodic approach.
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Amoroso, O., Russo, G., De landro, G., Zollo, A., Garambois, S., Mazzoli, S., et al. (2017). From velocity and attenuation tomography to rock physical modeling: Inferences on fluid-driven earthquake processes at the Irpinia fault system in southern Italy. Geophysical Research Letters, 44(13), 6752–6760.
Résumé: We retrieve 3-D attenuation images of the crustal volume embedding the fault system associated with the destructive M-s 6.9, 1980 Irpinia earthquake by tomographic inversion of t* measurements. A high Q(P) anomaly is found to be correlated with the 1980 fault geometry, while the Q(S) model shows regional-scale variations related to the NE edge of the uplifted pre-Tertiary limestone. An upscaling strategy is used to infer rock properties such as porosity, consolidation, type of fluid mixing, and relative saturation percentage at 8-10 km fault depth. We constrain the porosity and consolidation in the ranges 4-5% and 5-9, respectively, with the possible fluid mixes being both brine-CO2 and CH4-CO2. The consolidation parameter range indicates high pore pressures at the same depths. These results support the evidence for a fracture system, highly saturated in gases and a seismicity triggering mechanism at the fault zone, which is strongly controlled by fluid-induced pore pressure changes.
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Angel, I., Guzman, O., & Carcaillet, J. (2017). Pleistocene Glaciations In The Northern Tropical Andes, South America (Venezuela, Colombia And Ecuador). Cuadernos De Investigacion Geografica, 43(2), 571–590.
Résumé: This article presents an overview of glaciation studies in the northern tropical Andes (Venezuela, Colombia and Ecuador) mostly based on glacial geochronological data. The oldest dated evidences of glaciations are recorded in the Colombian Andes at the Bogota Plain between 3000-3500 m a.s.l., dated between 1-3 Ma. Maximum extent of former glaciers in the northern Andes seems to have occurred prior to the global Last Glacial Maximum (gLGM). In the Venezuelan-Merida Andes, former glaciers mostly reached the lowest recorded elevations during MIS 5-MIS 4, whereas in the Colombian Andes, the maximum extents are recorded prior to 38 ka. In the Ecuadorian Andes the most extensive glacial cover probably occurred during MIS 8. In the northern tropical Andes, studied glacier advances are mainly related to MIS 2 period between the final gLGM to the Oldest Dryas (similar to 18 ka-15 ka). Glacier advances during the Younger Dryas (similar to 12.7 ka-11.7 ka) are not extensively evidenced and mainly restricted to elevations higher than similar to 3500 m a.s.l.
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Archundia, D., Duwig, C., Spadini, L., Uzu, G., Guedron, S., Morel, M. C., et al. (2017). How Uncontrolled Urban Expansion Increases the Contamination of the Titicaca Lake Basin (El Alto, La Paz, Bolivia). Water Air And Soil Pollution, 228(1).
Résumé: Cities in developing countries encounter rapid waves of social transformation and economic development where the environment is mostly a neglected aspect. The Katari watershed encompasses mining areas, El Alto city (one of the fastest growing urban areas in South America and the biggest in the Altiplano) as well as agricultural areas. Its outlet is Cohana Bay, one of the most polluted areas of Lake Titicaca. Here we propose an integrative approach (hydrological, physicochemical, chemical and bacterial data) to understand the pollution problem of this developing area, in which a variety of anthropogenic activities takes place. Both mining and urban areas appear to be sources of metal pollution. Nutrient and bacterial contaminations are mainly related to urban and industrial discharges. These situations have impacts in the basin from the mining area down to Cohana Bay of Lake Titicaca. Pollutant concentration patterns are highly influenced by seasonal hydrology variations. The poor quality of surface waters in the basin represents a risk for human and animal populations, as well as for the quality of aquifers located underneath El Alto city.
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Arias-Ruiz, C., Elliot, M., Bezos, A., Pedoja, K., Husson, L., Cahyarini, S. Y., et al. (2017). Geochemical fingerprints of climate variation and the extreme La Nina 2010-11 as recorded in a Tridacna squamosa shell from Sulawesi, Indonesia. Palaeogeography Palaeoclimatology Palaeoecology, 487, 216–228.
Résumé: We used a Tridacna squamosa (Tridacnidae, Bivalvia) shell that lived between 2006 and 2012 to reconstruct environmental conditions in South East Sulawesi (Indonesia). We focused mainly on estimating the influence of temperature and rainfall on the shell geochemistry, as well as ENSO anomalies. Comparison of the measured and theoretical delta O-18 values show clear seasonal variations and confirms that this species secretes its shell at isotopic equilibrium. The delta O-18 in T. squamosa shows how the increased rainfall associated with monsoon precipitations in this area influences the delta O-18 shell signal during the rainy season, the correlation between shell delta O-18 and SST (r(2) = 0.62) decrease in warm/wet seasons (SST > 28.5 degrees C). Shell Mg/Ca profiles presents better correlation with SST (r(2) = 0.8) than Sr/Ca profiles (r(2) = 0.52). Shell Ba/Ca ratio increases during each dry season when primary productivity is maximum. Secondary Ba/Ca peaks also occur during the certain wet seasons and appear associated with abnormal enhanced runoff. Shell delta C-13 co-varies with primary productivity and salinity, with highest delta C-13 values occurring during the dry seasons. During 2010-11, abnormal values were detected in all geochemical proxies as result of the strong La Nina event. This calibration study demonstrates the ability of T. squamosa shells to accurately reflect present day environmental processes with seasonal resolutions and to define the local signature of hydrological changes associated with ENSO.
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Arndt, N. T., Fontbote, L., Hedenquist, J. W., Kesler, S. E., Thompson, J. F. H., & Wood, D. G. (2017). Future Global Mineral Resources. Geochemical Perspectives, 6(1), 1–171.
Résumé: Some scientists and journalists, and many members of the general public, have been led to believe that the world is rapidly running out of the metals on which our modern society is based. Advocates of the peak metal concept have predicted for many decades that increasing consumption will soon lead to exhaustion of mineral resources. Yet, despite ever-increasing production and consumption, supplies of minerals have continued to meet the needs of industry and society, and lifetimes of reserves remain similar to what they were 30-40 years ago. In this volume, we discuss the reasons for this apparent paradox using our broad experience and expertise on both academic and industrial sides of the minerals sector. Many misconceptions arise from flawed estimates of the size of global mineral resources which stem from a lack of understanding of the critical difference between reserves and resources. Some authors use quoted reserves the amount of metal proven to exist and to be economic for mining at present – when predicting imminent shortages. Resources – the amount that may be accessible in the upper few kilometres of the crust – are far larger. Over the last 150 years, improved technologies, economies of scale and increased efficiency have combined to reduce costs hence allowing lower-grade ore to be mined economically. The net result is that the long-term inflation-adjusted price of most metals has decreased more or less in parallel with increasing production, a second apparent paradox that frequently is not well understood. Using copper as the principal example and other metals as appropriate, we summarise the latest research on ore deposits and the activities of the minerals industry. Following a description of the numerous geological processes that form ore deposits, we outline the scientific methods used by the minerals industry to explore for new deposits. We also discuss how resources are mined and how minerals are processed, as well as recent efforts to reduce related environmental impacts. Economic and societal factors influence supply, and these are as important as the actual presence of a resource. Finally, we discuss the critical roles that geoscientists will play in assuring continued supplies of minerals. These include the development of new concepts and techniques that will assist the discovery, mining, processing, remediation, and management of mineral resources. It is essential that researchers help to educate the general public about the need for continued exploration to find new resources to meet growth in world living standards. We demonstrate that global resources of copper, and probably of most other metals, are much larger than most currently available estimates, especially if increasing efficiencies and higher prices allow lower-grade ores to be mined. These observations indicate that supplies of important mineral commodities will remain adequate for the foreseeable future.
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Aucour, A. - M., Bedell, J. - P., Queyron, M., Thole, R., Lamboux, A., & Sarret, G. (2017). Zn Speciation and Stable Isotope Fractionation in a Contaminated Urban Wetland Soil-Typha latifolia System. Environmental Science & Technology, 51(15), 8350–8358.
Résumé: Wetlands play a key role in the immobilization of metallic contaminants. In this context the mechanisms of Zn sequestration and Zn transfer and storage in Typha latifolia L. colonizing a frequently flooded contaminated soil were studied. A combination of EXAFS spectroscopy, micro X-ray fluorescence (mu XRF) and Zn isotope measurements was applied to soil, plant organs and decaying biomass. Zn was present in the soil as Znlayered double hydroxide, as tetrahedral and octahedral sorbed Zn species, and as ZnS. Octahedral and tetrahedral Zn (attributed to symplastic Zn organic acid and apoplasmic Zn cell wall complexes, respectively) and Zn thiol species were observed in the roots, rhizomes and stems. Iron plaque was present on the rhizomes and roots. Enrichment in light isotopes for Zn sorbed on the plaque relative to the soil (Delta Zn-66(plaque-soil) -0.3 to -0.1%0) suggested the dissolution of ZnS (enriched in light isotopes) in the rhizosphere with subsequent Zn2+ sorption on the root plaque. Furthermore, enrichment in light isotopes of stems relative to leaves (Delta Zn-66(stem-leaves) = -0.2%o) suggested the remobilization of Zn via the phloem, from leaves back to the stems. Overall these data highlight the role of thiols in controlling Zn speciation during its transfer and storage in T. latifolia.
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Baillard, C., Lyon-Caen, H., Bollinger, L., Rietbrock, A., Letort, J., & Adhikari, L. B. (2017). Automatic analysis of the Gorkha earthquake aftershock sequence: evidences of structurally segmented seismicity. Geophysical Journal International, 209(2), 1111–1125.
Résumé: We present the first 3 months of aftershock activity following the 2015 April 25 Gorkha earthquake M-w 7.8 recorded on the Nepalese Seismic network. We deployed an automatic procedure composed of three main stages: (1) coarse determination of the P and S onsets; (2) phase association to declare events and (3) iterative addition and refinement of onsets using the Kurtosis characteristic function. In total 9188 events could be located in the Kathmandu region with the majority having small location errors (<4.5, 9 and 10 km in the X-, Y- and Z-directions, respectively). Additionally, we propose a new attenuation law to estimate local magnitudes in the region. This new seismic catalogue reveals a detailed insight into the Gorkha aftershock sequence and its relation to the main shock rupture models and tectonic structures in the region. Most aftershocks fall within the Main Himalayan Thrust (MHT) shear zone or in its hangingwall. Significant temporal and lateral variations of aftershocks location are observed among them: (1) three distinct stages, highlighting subsequent jump-offs at the easternmost termination, (2) the existence of a seismic gap north of Kathmandu which matches with a low slip zone in the rupture area of the main shock, (3) the confinement of seismic activity in the trace of the May 12 M-w 7.3 earthquake within the MHT and its hangingwall through a 30 x 30 km(2) region and (4) a shallow westward-dipping structure east of the Kathmandu klippe. These new observations with the inferred tectonic structures at depth suggest a tectonic control of part of the aftershock activity by the lateral breaks along the MHT and by the geometry of the duplex above the thrust.
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Bajard, M., Poulenard, J., Sabatier, P., Develle, A. - L., Giguet-Covex, C., Jacob, J., et al. (2017). Progressive and regressive soil evolution phases in the Anthropocene. Catena, 150, 39–52.
Résumé: Soils have a substantial role in the environment because they provide several ecosystem services such as food supply or carbon storage. Agricultural practices can modify soil properties and soil evolution processes, hence threatening these services. These modifications are poorly studied, and the resilience/adaptation times of soils to disruptions are unknown. Here, we study the evolution of pedogenetic processes and soil evolution phases (progressive or regressive) in response to human-induced erosion from a 4000-year lake sediment sequence (Lake La Thuile, French Alps). Erosion in this small lake catchment in the montane area is quantified from the terrigenous sediments that were trapped in the lake and compared to the soil formation rate. To access this quantification, soil processes evolution are deciphered from soil and sediment geochemistry comparison. Over the last 4000 years, first impacts on soils are recorded at approximately 1600 yr cal. BP, with the erosion of surface horizons exceeding 10 t.km(-2).yr(-1). Increasingly deep horizons were eroded with erosion accentuation during the Higher Middle Ages (1400-850 yr cal. BP), reaching 1000 t.km(-2).yr(-1), and leading to the remobilization of carbonated and poorly weathered material, hence rejuvenating soil development. Erosion exceeded the soil formation rate and constituted a regression in the development of soils. The tolerable erosion limit is thus defined for erosion from 25 to 30 t.km(-2).yr(-1). Beyond this limit, the sustainability of the agroecosystem is limited and ecosystem services decrease. Afterwards, pedogenesis evolved again from progressive (700-300 yr cal. BP) to regressive (300 yr cal. BP-today) phases. Erosion was less important during the last 700 years than during the Middle Ages but with the same weathering stages, indicating that soils were deeply affected during the Middle-Age and have yet not recovered. Our results highlight the importance of the human factor in the pedogenesis over last millennia and suggest that the studied agro-ecosystem entered the Anthropocene 1400 years ago. (C) 2016 Elsevier B.V. All rights reserved.
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Bardelli, F., Veronesi, G., Capella, S., Bellis, D., Charlet, L., Cedola, A., et al. (2017). New insights on the biomineralisation process developing in human lungs around inhaled asbestos fibres. Scientific Reports, 7.
Résumé: Once penetrated into the lungs of exposed people, asbestos induces an in vivo biomineralisation process that leads to the formation of a ferruginous coating embedding the fibres. The ensemble of the fibre and the coating is referred to as asbestos body and is believed to be responsible for the high toxicological outcome of asbestos. Lung tissue of two individuals subjected to prolonged occupational exposure to crocidolite asbestos was investigated using synchrotron radiation micro-probe tools. The distribution of K and of elements heavier than Fe (Zn, Cu, As, and Ba) in the asbestos bodies was observed for the first time. Elemental quantification, also reported for the first time, confirmed that the coating is highly enriched in Fe (similar to 20% w/w), and x-ray absorption spectroscopy indicated that Fe is in the 3+ oxidation state and that it is present in the form of ferritin or hemosiderin. Comparison of the results obtained studying the asbestos bodies upon removing the biological tissue by chemical digestion and those embedded in histological sections, allowed unambiguously distinguishing the composition of the asbestos bodies, and understanding to what extent the digestion procedure altered their chemical composition. A speculative model is proposed to explain the observed distribution of Fe.
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Barnoud, A., Bouligand, C., Coutant, O., & Carlut, J. (2017). Magnetic structure of Basse-Terre volcanic island (Guadeloupe, Lesser Antilles) inferred from 3D inversion of aeromagnetic data. Journal Of Volcanology And Geothermal Research, 348, 1–11.
Résumé: We interpret aeromagnetic data to constrain the magnetic structure of the island of Basse-Terre, Guadeloupe, Lesser Antilles. Aeromagnetic data are inverted in the spatial domain with a Bayesian formulation to retrieve the 3D distribution of rock magnetization intensity and polarity. The inversion is regularized using a correlation length and standard deviation for magnetization chosen to be consistent with results from paleomagnetic measurements on lava flow samples from Basse-Terre. The resulting 3D model of magnetization is consistent at the surface with observed polarities and at depth with a 2D model obtained from a Parker and Huestis (1974) inversion in the Fourier domain. The inferred magnetic structure is compared with the available geological information deduced from published geological, geomorphological and geochronological studies. in the southern part of the island, very low magnetization is observed around the Soufriere lava dome, last activity of the Grande-Decouverte-Carmichael-Soufriere composite volcano, in relation with a high level of hydrothermal alteration. High-magnetizations in the South-East might reflect the presence of massive lava flows and lava domes from the Madeleine vents and Monts Caralbes. Medium magnetizations in the South-West coincide with the location of debris avalanche deposits associated with the collapse of the former Carmichael volcano and might reflect less massive lava structure at depth. Using the volume of normal polarity in the South part of Basse-Terre recovered in our 3D model of rock magnetization, we estimate an average construction rate of similar to 9.4 x 10(-4) km(3)/yr during the Brunhes chron which provides new insights on the volcanic activity of La Soufriere volcano. (C) 2017 Elsevier B.V. All rights reserved.
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Barre, G., Truche, L., Bazarkina, E. F., Michels, R., & Dubessy, J. (2017). First evidence of the trisulfur radical ion S-3(-) and other sulfur polymers in natural fluid inclusions. Chemical Geology, 462, 1–14.
Résumé: Sulfur plays a key role in numerous processes occurring in the Earth's crust. However, its speciation in deep and hot geological fluids remains poorly constrained. Here, we used quantitative in-situ Raman spectroscopy on natural fluid inclusions from deep sedimentary environments where thermochemical sulfate reduction (TSR) occurred to determine the sulfur speciation at temperatures representative of their entrapment conditions (100-300 degrees C). Results unambiguously demonstrate the presence of the trisulfur ion S-3(-) and other polymeric S species (Sn2- +/- S-n(0)) at temperature (T) > 100 degrees C, whereas only sulfide and sulfate were detected at 25 degrees C. From 200 to 300 C, sulfate and sulfide, the two dominant S species, Contribute to 41 9% and 59 9% of the mean total dissolved S concentration aStot] = 0.25 mol/kgH(2)O = 0.8 wt%), respectively. The S3 concentration accounts for 0.2 to 3% of Stot in this T range, with a maximum recorded concentration of 2.9 x 10 2 mol/kgH(2)O (2780 ppm) at 300 degrees C. This observation implies that the TSR process occurs under physico-chemical conditions that enhanced the stability of S-3 and other polymeric S species. This conclusion has important consequences for the genesis of base metal sulfide deposits and sour gas fields where reduced sulfur originates from TSR.
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Barrois, O., Gillet, N., & Aubert, J. (2017). Contributions to the geomagnetic secular variation from a reanalysis of core surface dynamics. Geophysical Journal International, 211(1), 50–68.
Résumé: We invert for motions at the surface of Earth's core under spatial and temporal constraints that depart from the mathematical smoothings usually employed to ensure spectral convergence of the flow solutions. Our spatial constraints are derived from geodynamo simulations. The model is advected in time using stochastic differential equations coherent with the occurrence of geomagnetic jerks. Together with a Kalman filter, these spatial and temporal constraints enable the estimation of core flows as a function of length and time-scales. From synthetic experiments, we find it crucial to account for subgrid errors to obtain an unbiased reconstruction. This is achieved through an augmented state approach. We show that a significant contribution from diffusion to the geomagnetic secular variation should be considered even on short periods, because diffusion is dynamically related to the rapidly changing flow below the core surface. Our method, applied to geophysical observations over the period 1950-2015, gives access to reasonable solutions in terms of misfit to the data. We highlight an important signature of diffusion in the Eastern equatorial area, where the eccentric westward gyre reaches low latitudes, in relation with important up/downwellings. Our results also confirm that the dipole decay, observed over the past decades, is primarily driven by advection processes. Our method allows us to provide probability densities for forecasts of the core flow and the secular variation.
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Bato, M. G., Pinel, V., & Yan, Y. (2017). Assimilation of Deformation Data for Eruption Forecasting: Potentiality Assessment Based on Synthetic Cases. Frontiers In Earth Science, 5.
Résumé: In monitoring active volcanoes, the magma overpressure is one of the key parameters used in forecasting volcanic eruptions. This parameter can be inferred from the ground displacements measured on the Earth's surface by applying inversion techniques. However, in most studies, the huge amount of information about the behavior of the volcano contained in the temporal evolution of the deformation signal is not fully exploited by inversion. Our work focuses on developing a strategy in order to better forecast the magma overpressure using data assimilation. We take advantage of the increasing amount of geodetic data [i.e., Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS)] recorded on volcanoes nowadays together with the wide-range availability of dynamical models that can provide better understanding about the volcano plumbing system. Here, we particularly built our strategy on the basis of the Ensemble Kalman Filter (EnKF). We forecast the temporal behaviors of the magma overpressures and surface deformations by adopting a simple and generic two-magma chamber model and by using synthetic GNSS and/or InSAR data. We prove the ability of EnKF to both estimate the magma pressure evolution and constrain the characteristics of the deep volcanic system (i.e., reservoir size as well as basal magma inflow). High temporal frequency of observation is required to ensure the success of EnKF and the quality of assimilation is also improved by increasing the spatial density of observations in the near-field. We thus show that better results are obtained by combining a few GNSS temporal series of high temporal resolution with InSAR images characterized by a good spatial coverage. We also show that EnKF provides similar results to sophisticated Bayesian-based inversion while using the same dynamical model with the advantage of EnKF to potentially account for the temporal evolution of the uncertain model parameters. Our results show that EnKF works well with the synthetic cases and there is a great potential in using the method for real-time monitoring of volcanic unrest.
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Beauval, C., Mariniere, J., Laurendeau, A., Singaucho, J. - C., Viracucha, C., Vallee, M., et al. (2017). Comparison of Observed Ground-Motion Attenuation for the 16 April 2016 M-w 7.8 Ecuador Megathrust Earthquake and Its Two Largest Aftershocks with Existing Ground-Motion Prediction Equations. Seismological Research Letters, 88(2), 287–299.
Résumé: A megathrust subduction earthquake (M-w 7.8) struck the coast of Ecuador on 16 April 2016 at 23:58 UTC. This earthquake is one of the best-recorded megathrust events to date. Besides the mainshock, two large aftershocks have been recorded on 18 May 2016 at 7:57 (M-w 6.7) and 16:46 (M-w 6.9). These data make a significant contribution for understanding the attenuation of ground motions in Ecuador. Peak ground accelerations and spectral accelerations are compared with four ground-motion prediction equations (GMPEs) developed for interface earthquakes, the global Abrahamson et al. (2016) model, the Japanese equations by Zhao, Zhang, et al. (2006) and Ghofrani and Atkinson (2014), and one Chilean equation (Montalva et al., 2017). The four tested GMPEs are providing rather close predictions for the mainshock at distances up to 200 km. However, our results show that high-frequency attenuation is greater for back-arc sites, thus Zhao, Zhang, et al. (2006) and Montalva et al. (2017), who are not taking into account this difference, are not considered further. Residual analyses show that Ghofrani and Atkinson (2014) and Abrahamson et al. (2016) are well predicting the attenuation of ground motions for the mainshock. Comparisons of aftershock observations with the predictions from Abrahamson et al. (2016) indicate that the GMPE provide reasonable fit to the attenuation rates observed. The event terms of the M-w 6.7 and 6.9 events are positive but within the expected scatter from worldwide similar earthquakes. The intraevent standard deviations are higher than the intraevent variability of the model, which is partly related to the poorly constrained V-S30 proxies. The Pedernales earthquake produced a large sequence of aftershocks, with at least nine events with magnitude higher or equal to 6.0. Important cities are located at short distances (20-30 km), and magnitudes down to 6.0 must be included in seismic-hazard studies. The next step will be to constitute a strong-motion interface database and test the GMPEs with more quantitative methods.
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Beckers, A., Beck, C., Hubert-Ferrari, A., Reyss, J. - L., Mortier, C., Albini, P., et al. (2017). Sedimentary impacts of recent moderate earthquakes from the shelves to the basin floor in the western Gulf of Corinth. Marine Geology, 384, 81–102.
Résumé: In seismically active areas, long term records of large earthquakes are indispensable to constrain reccurence patterns of large earthquakes. In the western Corinth Rift, one of the most active areas in Europe in terms of seismicity, data about ancient earthquakes are still insufficient, despite historical records covering the last two millenia and several studies in onshore paleoseimology. In this paper, we test the use of offshore sediments from the Gulf of Corinth to identify sediment failures and tsunamis that have been triggered by historical earthquakes. Two shelves (40-100 m deep), one sub-basin (180 m) and the basin floor (330 m) have been sampled by short gravity cores. The cores were analyzed in order to identify and characterize event deposits. The age control has been provided by Cs-137 and Pb-210 activity measurements showing that the cores represent 2 to 4 centuries of sedimentation. In each site, sandy event deposits are interbeded in the muddy, hemipelagic sedimentation. The age of event deposits has been compared to the record of historical earthquakes using new and published macroseismic data. This comparison shows temporal coincidence of some event deposits and documented earthquakes with a macroseismic intensity >= VII in the area, e.g. in 1861 CE, 1888 CE and 1909 CE. In nearshore, shallow-water settings, the record of event deposits does not exactly fit with the historical record of large earthquakes because too few event deposits are present. This may be due to the absence of sediment failures or to a lower preservation of the deposits in such settings. In the deepest site, in the basin floor, the correspondence is better: a sandy turbidite probably corresponds to each large earthquake since 1850 CE, except one aseismic sediment density flow that occurred at the end of the 20th century. Surprisingly, the Ms = 6.2, June 15,1995 Aigion earthquake is only possibly recorded in one nearshore site on the Aigion Shelf, in the form of a tsunami back-wash flow deposit. This study showed that moderate earthquakes (M 5.8-6.5) can significantly impact marine sediments. Regarding the evaluation of seismic hazard in the area, the basin floor is proposed as a promising site for long term paleoseismology in the Gulf of Corinth, while shallower settings need to be considered more carefully. (C) 2016 Published by Elsevier B.V.
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Benavente, C., Zerathe, S., Audin, L., Hall, S. R., Robert, X., Delgado, F., et al. (2017). Active transpressional tectonics in the Andean forearc of southern Peru quantified by Be-10 surface exposure dating of an active fault scarp. Tectonics, 36(9), 1662–1678.
Résumé: Our understanding of the style and rate of Quaternary tectonic deformation in the forearc of the Central Andes is hampered by a lack of field observations and constraints on neotectonic structures. Here we present a detailed analysis of the Purgatorio fault, a recently recognized active fault located in the forearc of southern Peru. Based on field and remote sensing analysis (Pleiades DEM), we define the Purgatorio fault as a subvertical structure trending NW-SE to W-E along its 60km length, connecting, on its eastern end, to the crustal Incapuquio Fault System. The Purgatorio fault accommodates right-lateral transpressional deformation, as shown by the numerous lateral and vertical plurimetric offsets recorded along strike. In particular, scarp with a 5m cumulative throw is preserved and displays cobbles that are cut and covered by slickensides. Cosmogenic radionuclide exposure dating (Be-10) of quartzite cobbles along the vertical fault scarp yields young exposure ages that can be bracketed between 0 to 6ka, depending on the inheritance model that is applied. Our preferred scenario, which takes in account our geomorphic observations, implies at least two distinct rupture events, each associated with similar to 3 and similar to 2m of vertical offset. These two events plausibly occurred during the last thousand years. Nevertheless, an interpretation invoking more tectonic events along the fault cannot be ruled out. This work affirms crustal deformation along active faults in the Andean forearc of southern Peru during the last thousand years.
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Bensalem, R., Chatelain, J. - L., Machane, D., Oubaiche, E. H., Bouchelouh, A., Benkaci, N., et al. (2017). Mediterranean Sea and anthropogenic influences on ambient vibration amplitudes in the low-frequency and high-frequency domains in the Algiers region. Arabian Journal Of Geosciences, 10(13).
Résumé: Ambient vibrations have been continuously recorded at Dar El Beida, about 20 km from Algiers (Algeria). This data set allows determining that, in the low-frequency domain (<1 Hz), ambient vibration sources are mainly linked to Mediterranean Sea effects, while in the high-frequency domain, they are closely related to anthropogenic activity. Climatic conditions have an influence on the ambient vibration spectral amplitudes in the low-frequency domain, which is not the case in the high-frequency domain. The limit between the low-frequency and high-frequency domain, based on natural versus anthropogenic activity, is not clear cut and lies between 1.25 and 1.50 Hz. Variations of H/V peak amplitudes in the low-frequency domain are clearly linked to the climatic conditions. In the high-frequency domain, H/V peaks are not related to climatic conditions and cannot be clearly related to anthropogenic source changes.
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Bergantz, G. W., Schleicher, J. M., & Burgisser, A. (2017). On the kinematics and dynamics of crystal-rich systems. J. Geophys. Res.-Solid Earth, 122(8), 6131–6159.
Résumé: Partially molten rocks, often called a mush, are examples of a hydrogranular mixture where the dynamics are controlled by both fluid and crystal-crystal interactions. An obstacle to progress in understanding high-temperature hydrogranular systems has been the lack of adequate levels of description of microphysical processes. Here we rationalize the hydrogranular kinematic and dynamic states by applying the concept of particle (crystal) force chains. We exemplify this with discrete-element computational fluid dynamic simulations of the intrusion of a basaltic melt into an olivine-basalt mush, where crystal-scale force chains, crystal transport, and melt mixing are resolved. To describe the microscale kinematics of the system, we introduce the coordination number and the fabric tensors of particle contacts and forces. We quantify the changing contact and force fabric anisotropy, coaxiality, and the connectedness of the mush, under dynamic conditions. To describe the dynamics, particle and fluid characteristic response times are derived. These are used to define local and bulk Stokes numbers, and viscous and inertia numbers, which quantify the multiphase coupling under crystal-rich conditions. We employ the Sommerfeld number, which describes the importance of crystal-melt lubrication, with a viscous number to illustrate the dynamic regimes of crystal-rich magmas. We show that the notion of mechanical “lock up” is not uniquely identified with a particular crystal volume fraction and that distinct mechanical behaviors can emerge simultaneously within a crystal-rich system. We also posit that this framework describes magmatic fabrics and processes which “unlock” a crystal mush prior to eruption or mixing.
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Berge-Thierry, C., Svay, A., Laurendeau, A., Chartier, T., Perron, V., Guyonnet-Benaize, C., et al. (2017). Toward an integrated seismic risk assessment for nuclear safety improving current French methodologies through the SINAPS@ research project. Nuclear Engineering And Design, 323, 185–201.
Résumé: The Tohoku earthquake and associated tsunami in March 2011 caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant, where level 7 (International Atomic Energy Agency (IAEA) INES scale) meltdown at three reactors occurred. The underestimation of the seismic and tsunami hazards has been recognized and the seismic margins assessment of the nuclear plants remains a priority for the whole nuclear community. In this framework a five-year research project called SINAPS@(Earthquake and Nuclear Installations: Ensuring and Sustaining Safety) is currently on-going in France. A reliable estimate of seismic margins is possible only if all uncertainties, epistemic and aleatory, are effectively identified, quantified and integrated in the seismic risk analysis. SINAPS@brings together a multidisciplinary community of researchers and engineers from the academic and the nuclear world. SINAPS@ aims at exploring the uncertainties associated to databases, physical processes and methods used at each stage of seismic hazard, site effects, soil and structure interaction, structural and nuclear components vulnerability assessments, in a safety approach: the main objective is ultimately to identify the sources of potential seismic margins resulting from assumptions or when selecting the seismic design level or the design strategy. The whole project is built around an “integrating” work package enabling to test state-of-the-art practices and to challenge new methodologies for seismic risk assessment: the real case of Kashiwazaki-Kariwa Japanese nuclear plant, shocked by the severe earthquake in 2007 provided a rich dataset which will be used to compare with the predictions. The present paper proposes for each step of the seismic risk analysis a review of the state of practice in France in the nuclear field and then precise the objectives and research strategy of SINAPS@ to overcome identified limitations or weaknesses. Scientific issues are illustrated through preliminary results of the project. (C) 2016 Elsevier B.V. All rights reserved.
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Bergemann, C., Gnos, E., Berger, A., Whitehouse, M., Mullis, J., Wehrens, P., et al. (2017). Th-Pb ion probe dating of zoned hydrothermal monazite and its implications for repeated shear zone activity: An example from the Central Alps, Switzerland. Tectonics, 36(4), 671–689.
Résumé: Th-Pb age dating of zoned hydrothermal monazite from alpine-type fissures/clefts is a powerful tool for constraining polyphase deformation at temperatures below 350 degrees C and presents an alternative to K/Ar and Ar-40/Ar-39 dating techniques for dating brittle tectonics. This study considers the relationship between cleft orientations in ductile shear zones and cleft mineral crystallization during subsequent brittle overprinting. In the Grimsel area, located in the Aar Massif of the Central Alps, horizontal clefts formed during a primary thrust dominated deformation, while younger and vertically oriented clefts developed during secondary strike-slip movements. The change is due to a switch in orientation between the principal stress axes sigma(2) and sigma(3). The transition is associated with monazite crystallization and chloritization of biotite at around 11.5 Ma. Quartz fluid inclusion data allow a link between deformation stages and temperatures to be established and indicate that primary monazite crystallization occurred in both cleft systems at 300-350 degrees C. While cleft monazite crystallization ceases at similar to 11 Ma in inactive shear zones, monazite growth, and/or dissolution-reprecipitation continues under brittle deformation conditions in vertical clefts during later deformation until similar to 7 Ma. This younger shear zone activity occurs in association with dextral strike-slip movement of the Rhone-Simplon fault system. With the exception of varying Th/U values correlated with the degree of oxidation, there is only limited compositional variation in the studied cleft monazites.
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Bermudez, M. A., Hoorn, C., Bernet, M., Carrillo, E., van der Beek, P. A., Garver, J. I., et al. (2017). The detrital record of late-Miocene to Pliocene surface uplift and exhumation of the Venezuelan Andes in the Maracaibo and Barinas foreland basins. Basin Research, 29(Feb), 370–395.
Résumé: A multidisciplinary approach, combining sediment petrographic, palynological and thermochronological techniques, has been used to study the Miocene-Pliocene sedimentary record of the evolution of the Venezuelan Andes. Samples from the Maracaibo (pro-wedge) and Barinas (retro-wedge) foreland basins, proximal to this doubly vergent mountain belt, indicate that fluvial and alluvial-fan sediments of similar composition were shed to both sides of the Venezuelan Andes. Granitic and gneissic detritus was derived from the core of the mountain belt, whereas sedimentary cover rocks and uplifted foreland basin sediments were recycled from its flanks. Palynological evidence from the Maracaibo and Barinas basins constrains depositional ages of the studied sections from late Miocene to Pliocene. The pollen assemblages from the Maracaibo Basin are indicative of mountain vegetation, implying surface elevations of up to 3500-4000m in the Venezuelan Andes at this time. Detrital apatite fission-track (AFT) data were obtained from both stratigraphic sections. In samples from the Maracaibo basin, the youngest AFT grain-age population has relatively static minimum ages of 5 +/- 2Ma, whereas for the Barinas basin samples AFT minimum ages are 7 +/- 2Ma. With exception of two samples collected from the Eocene Paguey Formation and from the very base of the Miocene Parangula Formation, no evidence for resetting and track annealing in apatite due to burial heating in the basins was found. This is supported by rock-eval analyses on organic matter and thermal modelling results. Therefore, for all other samples the detrital AFT ages reflect source area cooling and impose minimum age constraints on sediment deposition. The main phase of surface uplift, topography and relief generation, and erosional exhumation in the Venezuelan Andes occurred during the late Miocene to Pliocene. The Neogene evolution of the Venezuelan Andes bears certain similarities with the evolution of the Eastern Cordillera in Colombia, although they are not driven by exactly the same underlying geodynamic processes. The progressive development of the two mountain belts is seen in the context of collision of the Panama arc with northwestern South America and the closure of the Panama seaway in Miocene times, as well as contemporaneous movement of the Caribbean plate to the east and clock-wise rotation of the Maracaibo block.
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Beucher, R., Sue, C., & Tricart, P. (2017). Orogen-parallel brittle extension as a major tectonic imprint in the Neogene evolution of the south-western Alpine arc. International Journal Of Earth Sciences, 106(8), 2973–2990.
Résumé: We present a new analysis of the late Alpine brittle deformation in the southern branch of the western Alpine arc, focusing on the stack of internal metamorphic nappes east of the Argentera external crystalline massif. The regional-scale fault network is dominated by a NW-SE-striking right-lateral fault system that follows the general curvature of the arc and controls the overall morphology of the area. A second fault set strikes N-S and is mainly represented by normal faults which accommodate orogen-parallel extension. Structural analysis and paleostress tensors derived from inversion of fault-slip data reveal a complex pattern of deformation involving extensional and strike-slip deformation events. The orogen-parallel extension previously described in the internal zones at the east of the Pelvoux massif is confirmed further south, and we show that it is combined with right-lateral strike-slip deformation that increases in intensity towards the south-west. The stability of the minimum stress axis (sigma 3) direction suggests that extensional and transcurrent regimes are contemporaneous and highlights regional interferences between inner brittle extension, parallel to the strike of the belt, and the strike-slip strain field driven by the counterclockwise rotation of the Apulia-Adria plate. The curved geometry of the belt constrains the direction of extension and the coupling relationship between the internal and external Alpine zones. We propose that the Neogene tectonic history is a result of the unique curved tectonic architecture of the south-western Alps with respect to the rotation of the Apulia-Adria indenting plate. The southern tip of the western Alpine arc represents a transitional zone between extension in the inner chain and strike-slip/compression in the outer parts.
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Bievre, G., Lacroix, P., Oxarango, L., Goutaland, D., Monnot, G., & Fargier, Y. (2017). Integration of geotechnical and geophysical techniques for the characterization of a small earth-filled canal dyke and the localization of water leakage. Journal Of Applied Geophysics, 139, 1–15.
Résumé: This paper investigates the combined use of extensive geotechnical, hydrogeological and geophysical techniques to assess a small earth dyke with a permanent hydraulic head, namely a canal embankment. The experimental site was chosen because of known issues regarding internal erosion and piping phenomena. Two leakages were visually located following the emptying of the canal prior to remediation works. The results showed a good agreement between the geophysical imaging techniques (Electrical Resistivity Tomography, P- and SH-waves Tomography) and the geotechnical data to detect the depth to the bedrock and its lateral variations. It appeared that surface waves might not be fully adapted for dyke investigation because of the particular geometry of the studied dyke, non-respectful of the 10 assumption, and which induced depth and velocity discrepancies retrieved from Rayleigh and Love waves inversion. The use of these classical prospecting techniques however did not allow to directly locate the two leakages within the studied earth dyke. The analysis of ambient vibration time series with a modified beam-forming algorithm allowed to localize the most energetic water flow prior to remediation works. It was not possible to detect the leakage after remediation works, suggesting that they efficiently contributed to significantly reduce the water flow. The second leakage was not detected probably because of a non-turbulent water flow, generating few energetic vibrations. (C) 2017 Elsevier B.V. All rights reserved.
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Billerot, A., Duchene, S., Vanderhaeghe, O., & de Sigoyer, J. (2017). Gneiss domes of the Danba Metamorphic Complex, Songpan Ganze, eastern Tibet. Journal Of Asian Earth Sciences, 140, 48–74.
Résumé: In this paper we address the formation and exhumation of the Danba Metamorphic Complex (DMC) that represents the deepest structural level of the Songpan Ganze terrane situated along the eastern margin of the Tibetan plateau. The DMC comprises a variety of gneiss domes and offers a unique opportunity to decipher their development during orogenic evolution. For that purpose, PTtD paths of metamorphic rocks sampled at different structural levels have been reconstructed. The DMC is composed of Triassic metaturbidites of the Xikang group, Paleozoic metasedimentary cover and basement of the Yangtze craton. The DMC is structurally marked by transposition of the upright S-1 foliation of the Triassic metaturbidites into a NW-SE trending S-2 composite foliation dipping to the NE. Transposition is associated with a localized top-to-the-northeast shear zone along the northeastern edge of the DMC and with pervasive top-to-the-southwest shearing from the core to the border of the complex. These structures are consistent with extrusion of the core of the DMC relative to the lower grade Triassic metaturbidites. The position of the biotite isograd overlapping the structural boundary of the DMC suggests that the Triassic metaturbidites have been affected by an increase in temperature as a result of extrusion. Within the DMC, the position of the metamorphic index minerals relative to the composite S-2 foliation reveals that biotite, garnet, staurolite and kyanite grew before the transposition into S-2, in contrast with sillimanite which crystallizes in the hinge of F-2 folds and along the axial planar S-2 schistosity. The sillimanite isograd delineates regional-scale overturned F-2 folds and cross-cuts the staurolite and kyanite isograds consistent with an increase in temperature during Dy. The melt-in isograd characterizes the deepest structural level of the DMC. PT conditions for these metamorphic rocks, determined using pseudosections and conventional thermometry, indicate a temperature increase from 400 degrees C to more than 600 degrees C from the edge to the core of the DMC for a relatively homogeneous pressure ranging from 5 to 6.5 kbar suggesting that isograds and isotherms represent the syn-D-2 thermal structure of the orogenic crust. Migmatites exposed in the deepest structural level of the DMC yield a pressure significantly lower than the surrounding metamorphic rock suggesting that they crystallized after D-2 and after some exhumation of their hosts. Three different types of gneiss domes are distinguished on the basis of their position relative to the isograds, their structural characteristics, and their position relative to the margin of the Yangtze craton. Close to the craton and at the highest structural level, the Gezong dome represents a basement-rooted tectonic slice, in an intermediate position, the Gongcai dome corresponds to a basement-cored nappe, and further away and at the deepest structural level, the Bawang, Cunuchan and Qingaling domes are migmatitecored domes. The presence at the current-day surface of this variety of gneiss domes reflects the difference in burial of the margin during the Mesozoic Indosinian orogeny. (C) 2017 Elsevier Ltd. All rights reserved.
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Billi, A., Berardi, G., Gratier, J. - P., Rossetti, F., Vignaroli, G., Baykara, M. O., et al. (2017). First records of syn-diagenetic non-tectonic folding in quaternary thermogene travertines caused by hydrothermal incremental veining. Tectonophysics, 700, 60–79.
Résumé: This study is the first documentation of syn-diagenetic non-tectonic contractional deformations observed in two Pleistocene thermogene travertine deposits from the late Miocene-Pleistocene Tuscan extensional-hydrothermal province (Italy). The deposits consist of primary porous beds hosting secondary bed-parallel carbonate veins. The porous beds are generally flat-lying, particularly in the upper section of the deposits, whereas the veined beds frequently form undulated structures. These structures are up to a few meters in wavelength, are mostly confined within the lower-middle section of the deposits, and are here mostly interpreted as folds. Field observations, UTh geochronology, and stable isotope analyses are used to characterize the origin of veins and folds. Radiometrically-determined age inversions, structure overprinting relationships, downward growth of vein crystals, deformation of primary sedimentary structures, and downward increasing frequency of veins and folds show that the undulated travertine beds can be mainly interpreted as the product of syn-diagenetic hydrothermal rejuvenation causing non-tectonic veining and folding. The non-tectonic hypothesis is also supported by the absence of contractional deformation in the travertine-hosting sediments. The folds were generated by complex mechanisms including bending and buckling caused by laterally-confined volume expansion during syn-diagenetic circulation of mineralizing fluids and related incremental veining. Modeling some folds with the Biot-Ramberg's buckling equation shows a vein-to-host travertine viscosity ratio between 1.5 and 4, confirming the syn-diagenetic origin of folds. Veining and folding changed some original properties of travertines including rheology, fabric, porosity, and chronological sequence. The identification of these structures and related changes of rock properties (e.g., age rejuvenation) is relevant for the proper interpretation of thermogene travertines as recorders of many geological processes including paleoclimate oscillations, earthquake occurrences, hydrothermal circulations, and uplift or incision rates. Synthesizing, the studied thermogene travertines appear more like sedimentary-hydrothermal-hybrid zoned deposits rather than pure sedimentary systems uniquely responding to the superposition law. (C) 2017 Elsevier B.V. All rights reserved.
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Billi, A., Berardi, G., Gratier, J. - P., Rossetti, F., Vignaroli, G., Baykara, M. O., et al. (2017). Reply to the comment on “First records of syn-diagenetic non-tectonic folding in Quaternary thermogene travertines caused by hydrothermal incremental veining” by Billi et alii. Tectonophysics, 721, 501–512.
Résumé: In our previous paper (Billi et at, 2017), using field geological observations, U-Th dating, and stable isotope analyses, we studied two deposits of Pleistocene thermogene travertines from Tuscany in central Italy. We concluded our study (1) warning that the common stratigraphic concept of travertine being a sedimentary succession with age younging from bottom to top is not always correct, (2) demonstrating that CaCO3 mineralization and veins can develop within the travertines after their formation with this syn-diagenetic process being able to modify the continuous bottom-up age evolution, and (3) showing that this post-depositional mineralization-veining process can not only modify the temporal succession but also deform and change the initial depositional travertine structure and its petrophysical properties. These conclusions could potentially make the interpretation of a travertine series more difficult than commonly thought. Alcicek et alii questioned our conclusions claiming that the travertine structures that we observed in Tuscany and interpreted as post-depositional features should have been interpreted, in analogy to similar structures from travertines elsewhere, as primary structures. Although we recognize, as already thoroughly stated in Billi et al. (2017), that the travertine depositional/post-de-positional processes generally require further studies, we reaffirm the validity of our original interpretation at least for the structures analyzed in our previous paper. We, therefore, counter all criticisms by Alcicek et alii and conclude by indicating the way forward to further explore the depositional and post-depositional processes of thermogene travertines.
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Bodin, X., Krysiecki, J. - M., Schoeneich, P., Le Roux, O., Lorier, L., Echelard, T., et al. (2017). The 2006 Collapse of the Berard Rock Glacier (Southern French Alps). Permafrost And Periglacial Processes, 28(1), 209–223.
Résumé: In the Mediterranean French Alps, the Berard rock glacier suddenly collapsed during the summer of 2006; this was a rarely documented event in the world, exceptional for the amount of disturbed material (estimated at 250 000-500 000 m(3)). Located near the lower limit of permafrost, the Berard rock glacier collapse might exemplify the possible consequences of the degradation of ice-rich mountain permafrost. The causes of the collapse may include long-term atmospheric warming, recent air temperature anomalies, niveo-meteorological conditions prior to the collapse, geological settings and topographical context. Geomorphological interpretations and analysis of climatic data-sets allow us to specify the different stages of the collapse and discuss the respective roles of the geological and hydro-climatic factors and unfrozen water in the ground which could have led to the collapse. Geophysical measurements and ice observations in the scarp reveal that the internal structure of the intact part of the rock glacier is composed of both ice-cemented and massive-ice layers. The rock glacier also contains a high proportion of fine material (essentially silt and clay), which could have played an important role in the collapse. Geodetic measurements repeated since 2007 show that, with the exception of the upper part, the whole rock glacier was still experiencing destabilisation in 2010, with very high deformation rates exceeding 30 m in 3 years. The continuous monitoring of surface displacement carried out during the summer of 2007 has not shown any clear meteorological control on the post-collapse rock glacier dynamics. Copyright (c) 2016 John Wiley & Sons, Ltd.
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Bonilla, L. F., Gueguen, P., Lopez-Caballero, F., Mercerat, E. D., & Gelis, C. (2017). Prediction of non-linear site response using downhole array data and numerical modeling: The Belleplaine (Guadeloupe) case study. Physics And Chemistry Of The Earth, 98, 107–118.
Résumé: In this study, we analyze the acceleration time histories data at the Belleplaine (Guadeloupe, French West Indies) vertical array, recorded between 2008 and 2014, to evaluate the seismic response of sediments. First, we apply seismic interferometry by deconvolution method to compute the in-situ shear wave velocity between the sensor at the surface and the two shallow sensors located at GL-15m and GL-39m depth. The efficiency of this method is discussed by studying the variability of the velocity profile obtained and comparing with the in-situ geophysical survey of the site. Computed strains between sensors remain very weak, lower than 10(-5), meaning that nonlinearities are not expected for these events. Moreover, the small dispersion of shear wave velocities values deduced from seismic interferometry may be related to the elastic behavior of the soil column. Furthermore, the transfer functions between each sensor combination are inverted to obtain a new velocity profile compatible with the geological knowledge of the site. The lag times calculated by seismic interferometry are then used to constrain random perturbations of the inverted velocity profile, allowing to study the variability of the 1D soil response. Since recorded motion has a PGA less than 10 cm/s(2) in the dataset, we numerically predict the nonlinear response of the site using strong motion from a worldwide dataset. Furthermore, we study the ratio between the PGV and the medium shear velocity as a proxy showing the development of shear deformation during strong motion. Finally, using strong motion events from a worldwide dataset, we numerically predict the nonlinear response of the site based on shear wave velocity variation and the strain proxy computed by the particle velocity versus shear wave velocity ratio. We conclude that seismic interferometry by deconvolution is a robust and accurate solution to help extracting the shear wave velocity profile and to monitor the soil nonlinear response. This technique can be used when strong earthquakes will be recorded at this experimental site in order to track and assess nonlinear effects in the soil column. (C) 2017 Elsevier Ltd. All rights reserved.
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Bottelin, P., Baillet, L., Larose, E., Jongmans, D., Hantz, D., Brenguier, O., et al. (2017). Monitoring rock reinforcement works with ambient vibrations: La Bourne case study (Vercors, France). Engineering Geology, 226, 136–145.
Résumé: This study uses ambient vibrations to monitor rock bolting works, the efficacy of which is usually difficult to estimate. The test site is a 760 m(3) unstable limestone column located in the Bourne valley (Vercors, France). The rock column's resonance frequencies (fx) were identified, corrected for reversible thermal effects and monitored over time. We observed clear increases in fx up to similar to 17% resulting from the additional stiffness provided by the steel rock bolts. Numerical modeling helped to confirm that the rebar elements were grouted on both sides of the fracture. The major column's resonance features, such as the resonance frequencies and mode shapes, were successfully simulated, including their evolution with bolting. The amount of fx increase depends on the mode considered, likely controlled by bolt location in comparison with the modal shape. This study confirms the potential of ambient vibrations to provide global in-depth information on the stability evolution of rock compartments, with versatile applications for monitoring potential rockfalls or reinforcement works.
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Bottero, J. Y., Rose, J., de Garidel, C., Masion, A., Deutsch, T., Brochard, G., et al. (2017). SERENADE: safer and ecodesign research and education applied to nanomaterial development, the new generation of materials safer by design. Environmental Science-Nano, 4(3), 526–538.
Résumé: SERENADE is a French project which aims to develop and apply the “safer by design” process to create safer nano-products. It achieves this goal by combining knowledge and scientific approaches from a range of disciplines towards this common goal. This tutorial review presents the conceptual approach to “Safer by Design” and provides several examples of case studies primarily for TiO2 (anatase) present in paints and cements to demonstrate how the approach can inform design decisions. Particular attention is paid to chronic low dose exposure scenarios.
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Bourdelle, F., Mosser-Ruck, R., Truche, L., Lorgeoux, C., Pignatelli, I., & Michau, N. (2017). A new view on iron-claystone interactions under hydrothermal conditions (90 degrees C) by monitoring in situ pH evolution and H-2 generation. Chemical Geology, 466, 600–607.
Résumé: Many countries are considering the geological disposal of high-level radioactive waste combining natural clayey and engineered barriers (e.g. steel canister, bentonite, clay host rock, concrete). This configuration can lead to metallic iron-claystone interactions. Although a lot of experimental data on iron/clay interactions already exists, none of it allows the understanding and quantifying of the close interactions between the mineralogical transformations and the iron corrosion process. To fill this gap, a parametric kinetic investigation of iron/claystone interactions at 90 degrees C in a water saturated-anoxic medium was carried out. A new approach is adopted to monitor a series of original experiments with various Fe-0/claystone mass ratios. The continuous in situ monitoring of H-2 production and of pH time-evolution allows to precisely follow the reaction rate and the chemical changes induced by the mineralogical transformations. In addition, gas composition and solid run products were characterized. We highlight that the Callovo-Oxfordian claystone of the Paris Basin (France) investigated here, in contact with metallic iron, drives the iron corrosion process, by controlling some medium parameters (like pH) and by acting as a Fe-consumer incorporating the released iron into neoformed Fe-rich clays minerals.
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Burgisser, A., Chevalier, L., Gardner, J. E., & Castro, J. M. (2017). The percolation threshold and permeability evolution of ascending magmas. Earth And Planetary Science Letters, 470, 37–47.
Résumé: The development of gas permeability in magmas is a complex phenomenon that directly influences the style of a volcanic eruption. The emergence of permeability is linked to the concept of percolation threshold, which is the point beyond which gas bubbles are connected in a continuous network that allows gas escape. Measurements of the percolation threshold, however, range from similar to 30 to 78 vol%. No known combination of parameters can explain such a wide range of threshold values, which affects our understanding of the relationship between percolation and permeability. We present permeability calculations on bubble-bearing rhyolitic melts that underwent experimental decompression. Samples were analyzed by X-ray microtomography to image the bubble networks in 3D. We develop a percolation threshold for magmas that depends on the bubble network characteristics of this sample set. This relationship recovers the behavior of a wide range of volcanic samples by separating permeable samples from impermeable ones with a success rate of 88%. We use this percolation threshold to propose simplified permeability relationships that rely on parameters widely used in numerical modeling of magma flow. These relationships are valid within one order of magnitude for the viscous permeability coefficient and within two orders of magnitude for the inertial coefficient. They recover the ranges of values previously covered by isolated relationships, reassembling them within a single framework. We test the implications of such unification on eruptive dynamics with a 1D, two-phase conduit flow model. This test shows that varying the percolation threshold has little influence on vertical gas loss and ascent dynamics. (C) 2017 Elsevier B.V. All rights reserved.
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Byrdina, S., Friedel, S., Vandemeulebrouck, J., Budi-Santoso, A., Suhari, Suryanto, W., et al. (2017). Geophysical image of the hydrothermal system of Merapi volcano. Journal Of Volcanology And Geothermal Research, 329, 30–40.
Résumé: We present an image of the hydrothermal system of Merapi volcano based on results from electrical resistivity tomography (ERT), self-potential, and CO2 flux mappings. The ERT models identify two distinct low-resistivity bodies interpreted as two parts of a probably interconnected hydrothermal system: at the base of the south flank and in the summit area. In the summit area, a sharp resistivity contrast at ancient crater rim Pasar-Bubar separates a conductive hydrothermal system (20-50 ohm m) from the resistive andesite lava flows and pyroclastic deposits (2000-50,000.0 m). The existence of preferential fluid circulation along this ancient crater rim is also evidenced by self-potential data. The significative diffuse CO2 degassing (with a median value of 400 g m(-2) d(-1)) is observed in a narrow vicinity of the active crater rim and close to the ancient rim of Pasar-Bubar. The total CO2 degassing across the accessible summital area with a surface of 1.4.10(5) m(2) is around 20 t d(-1). Before the 2010 eruption, Toutain et al. (2009) estimated a higher value of the total diffuse degassing from the summit area (about 200-230 t d(-1)). This drop in the diffuse degassing from the summit area can be related to the decrease in the magmatic activity, to the change of the summit morphology, to the approximations used by Toutain et al. (2009), or, more likely, to a.combination of these factors. On the south flank of Merapi, the resistivity model shows spectacular stratification. While surficial recent andesite lava flows are characterized by resistivity exceeding 100,000 ohm m, resistivity as low as 10 ohm m has been encountered at a depth of 200 m at the base of the south flank and was interpreted as a presence of the hydrothermal system. No evidence of the hydrothermal system is found on the basis of the north flank at the same depth. This asymmetry might be caused by the asymmetry of the heat supply source of Merapi whose activity is moving south or/and to the asymmetry in topography caused by the presence of Merbabu volcano in the north. On the basis of our results we suggest that stratified pyroclastic deposits on the south flank of Merapi screen and separate the flow of hydrothermal fluids with the gaseous part rising through the crater rims, while the liquid part is flowing downwards to the base of the edifice. (C) 2016 Elsevier B.V. All rights reserved.
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Byrdina, S., Revil, A., Gunawan, H., Saing, U. B., & Grandis, H. (2017). Hydrothermal System of the Papandayan Volcano from Temperature, Self-Potential (SP) and Geochemical Measurements (Vol. 1861).
Résumé: Papandayan volcano in West Java Indonesia is characterized by intense hydrothermal activities manifested by numerous fumaroles at three craters or kawah i.e. Mas Manuk and Baru. The latter was created after November 2002 phreatic eruption. Since 2011 numerous volcano-tectonic B events are encountered and the volcano was set on alert status on several occasions. The purpose of the present study is to delineate the structure of the summital hydrothermal system from Self-Potential (SP) soil temperature and gas concentrations in the soil (CO2 SO2 and H2S) data. This combination of geophysical and geochemical methods allows identification of the weak permeable zones serving as preferential pathways for hydrothermal circulation and potential candidates to future landslides or flank collapses. This study is an on-going collaborative research project and we plan to conduct electrical resistivity tomography (ERT) and also Induced-Polarization (IP) surveys. Additional data would allow the 3D imaging of the studied area. The IP parameters will be used to characterise and to quantify the degree of alteration of the volcanic rocks as has been shown very recently in the laboratory studies. There are also rocks and soil samples that will undergo laboratory analyses at ISTerre for IP and complex resistivity parameters at the sample scale that will help to interpret the survey results.
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Byrdina, S., Revil, A., Gunawan, H., Saing, U. B., & Grandis, H. (2017). Hydrothermal System of the Papandayan Volcano from Temperature, Self-Potential (SP) and Geochemical Measurements (Vol. 1861). Amer Inst Physics.
Résumé: Papandayan volcano in West Java Indonesia is characterized by intense hydrothermal activities manifested by numerous fumaroles at three craters or kawah i.e. Mas Manuk and Baru. The latter was created after November 2002 phreatic eruption. Since 2011 numerous volcano-tectonic B events are encountered and the volcano was set on alert status on several occasions. The purpose of the present study is to delineate the structure of the summital hydrothermal system from Self-Potential (SP) soil temperature and gas concentrations in the soil (CO2 SO2 and H2S) data. This combination of geophysical and geochemical methods allows identification of the weak permeable zones serving as preferential pathways for hydrothermal circulation and potential candidates to future landslides or flank collapses. This study is an on-going collaborative research project and we plan to conduct electrical resistivity tomography (ERT) and also Induced-Polarization (IP) surveys. Additional data would allow the 3D imaging of the studied area. The IP parameters will be used to characterise and to quantify the degree of alteration of the volcanic rocks as has been shown very recently in the laboratory studies. There are also rocks and soil samples that will undergo laboratory analyses at ISTerre for IP and complex resistivity parameters at the sample scale that will help to interpret the survey results.
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Carrero, S., Fernandez-Martinez, A., Perez-Lopez, R., Lee, D., Aquilanti, G., Poulain, A., et al. (2017). The nanocrystalline structure of basaluminite, an aluminum hydroxide sulfate from acid mine drainage. American Mineralogist, 102(12), 2381–2389.
Résumé: Basaluminite is a poorly crystalline aluminum hydroxysulfate that precipitates in waters affected by acid mine drainage (AMD) and in acid sulfate soils (ASS). Its ability to sequester potentially toxic elements, such as Cu and As, makes it an important component of these systems, with strong environmental implications. Although it was initially described as a mineral, basaluminite is now considered a nanoscale variety of felsobanyaite, a rare mineral. In the present study, chemical analyses of natural and synthetic basaluminites are combined with data from advanced nanoscale characterization techniques such as high-energy X-ray diffraction (HEXD) and their corresponding pair distribution function (PDF) analyses, extended X-ray absorption fine structure (EXAFS), and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. X-ray scattering data are analyzed with reverse Monte Carlo (RMC) modeling to obtain an atomistic representation of the disorder presents in this nanomineral. Sulfur K-edge EXAFS results show that sulfate is coordinated to the aluminum-octahedral framework of basaluminite mainly through outer-sphere ligands, though the existence of inner-sphere ligands seems to be significant in synthetic samples. PDF analyses show that both synthetic and natural basaluminites have identical short-range order, with similar to 1.2 nm coherent domain size, and share structural characteristics with felsobanyaite. Interestingly, Al-27 ssNMR reveals the presence of, respectively, similar to 1 and 5% of tetrahedral and pentahedral coordinations. RMC models of basaluminite highlight the presence of structural point defects. The understanding of this nanocrystalline character has important implications in terms of the reactivity of this nanomineral in AMD and ASS. The lack of correlation between the spatial and temporal occurrence of basaluminite and felsobanyaite suggests that the similarities between both mineral structures could be fortuitous, and highlights the need for a re-evaluation of the status of basaluminite as a nanomineral.
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Carrero, S., Fernandez-Martinez, A., Perez-Lopez, R., & Miguel Nieto, J. (2017). Basaluminite structure and its environmental implications (Vol. 17).
Résumé: Basaluminite is a nanocrystalline aluminum oxyhydrosulfate of important environmental implications. It is present in areas affected by acid mine drainage and acid sulfate soils, where potential toxic elements present in solution, such as Cu and As, can be retained by co-precipitation or adsorption onto it. Basaluminite has been described as a nanomineral variety of felsobanyaite. In the present study, high-energy X-ray diffraction (HEXD) and extended X-ray adsorption fine structure (EXAFS) experiments were performed to determine the local order of basaluminite nanoparticles. Pair distribution function (PDF) analyses showed that both synthetic and natural basaluminite have identical short-range order, with 1 nm coherent domain size. PDFs also show strong similarities between the local order of basaluminite and felsobanyaite. On the other hand, S K-edge EXAFS showed different structural coordination between natural and synthetic basaluminite, where sulfate in the natural phase were coordinated in outer-sphere positions whereas inner-sphere sulfate was observed in the synthetic samples. Preliminary results indicated that basaluminite is a highly defective felsobanyaite mineral nanoparticle. This nanocrystalline character has therefore important implication in terms of stability in natural condition and contaminant mobility in stream affected by acid sulfate water. (C) 2017 The Authors. Published by Elsevier
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Carrero, S., Fernandez-Martinez, A., Perez-Lopez, R., Poulain, A., Salas-Colera, E., & Miguel Nieto, J. (2017). Arsenate and Selenate Scavenging by Basaluminite: Insights into the Reactivity of Aluminum Phases in Acid Mine Drainage. Environmental Science & Technology, 51(1), 28–37.
Résumé: Basaluminite precipitation may play an important role in the behavior of trace elements in water and sediments affected by acid mine drainage and acid sulfate soils. In this study, the affinity of basaluminite and schwertmannite for arsenate and selenate is compared, and the coordination geometries of these oxyanions in both structures are reported. Batch isotherm experiments were conducted to examine the sorption capacity of synthetic schwertmannite and basaluminite and the potential competitive effect of sulfate. In addition, synchrotron-based techniques such as differential pair distribution function (d-PDF) analysis and extended X-ray absorption fine structure (EXAFS) were used to determine the local structure of As(V) and Se(VI) complexes. The results show that oxyanion exchange with structural sulfate was the main mechanism for removal of selenate, whereas arsenate was removed by a combination of surface complexes and oxyanion exchange. The arsenate adsorption capacity of basaluminite was 2 times higher than that of schwertmannite and 3 times higher than that of selenate in both phases. The sulfate:arsenate and sulfate:selenate exchange ratios were 1:2 and 1:1, respectively. High sulfate concentrations in the solutions did not show a competitive effect on arsenate sorption capacity but had a strong impact on selenate uptake, suggesting some kind of specific interaction for arsenate. Both d-PDF and EXAFS results indicated that the bidentate binuclear inner sphere was the most probable type of ligand for arsenate on both phases and for selenate on schwertmannite, whereas selenate forms outer sphere. complexes in the aluminum octahedral interlayer of basaluminite. Overall, these results show a strong affinity of poorly crystalline aluminum phases such as basaluminite for As(V) and Se(VI) oxyanions, with adsorption capacities on the same order of Magnitude as those of iron oxides. The results obtained in this study are relevant to the understanding of trace element behavior in environments affected by acid water, potentially opening new research lines focused on remediation by natural attenuation processes or engineered water treatment systems.
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Castillo-Michel, H. A., Larue, C., Pradas del Real, A. E., Cotte, M., & Sarret, G. (2017). Practical review on the use of synchrotron based micro- and nano- X-ray fluorescence mapping and X-ray absorption spectroscopy to investigate the interactions between plants and engineered nanomaterials. Plant Physiology And Biochemistry, 110, 13–32.
Résumé: The increased use of engineered nanomaterials (ENMs) in commercial products and the continuous development of novel applications, is leading to increased intentional and unintentional release of ENMs into the environment with potential negative impacts. Particularly, the partition of nanoparticles (NPs) to waste water treatment plant (WWTP) sludge represents a potential threat to agricultural ecosystems where these biosolids are being applied as fertilizers. Moreover, several applications of ENMs in agriculture and soil remediation are suggested. Therefore, detailed risk assessment should be done to evaluate possible secondary negative impacts. The impact of ENMS on plants as central component of ecosystems and worldwide food supply is of primary relevance. Understanding the fate and physical and chemical modifications of NPs in plants and their possible transfer into food chains requires specialized analytical techniques. Due to the importance of both chemical and physical factors to consider for a better understanding of ENMs behavior in complex matrices, these materials can be considered a new type of analyte. An ideal technique should require minimal sample preparation, be non-destructive, and offer the best balance between sensitivity, chemical specificity, and spatial resolution. Synchrotron radiation (SR) techniques are particularly adapted to investigate localization and speciation of ENMs in plants. SR X-ray fluorescence mapping (SR-XFM) offers multi-elemental detection with lateral resolution down to the tens of nm, in combination with spatially resolved X-ray absorption spectroscopy (XAS) speciation. This review will focus on important methodological aspects regarding sample preparation, data acquisition and data analysis of SR-XFM/XAS to investigate interactions between plants and ENMs. (C) 2016 Elsevier Masson SAS. All rights reserved.
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Causse, M., Cultrera, G., Moreau, L., Herrero, A., Schiappapietra, E., & Courboulex, F. (2017). Bayesian rupture imaging in a complex medium: The 29 May 2012 Emilia, Northern Italy, earthquake. Geophysical Research Letters, 44(15), 7783–7792.
Résumé: We develop a new approach to image earthquake rupture from strong motion data. We use a large data set of aftershock waveforms, interpolated over the seismic fault to obtain Green's function approximations. Next we deploy a Bayesian inversion method to characterize the slip distribution, the rupture velocity, the slip duration, and their uncertainties induced by errors in the Green's functions. The method is applied to the 29 May 2012 M-w 6 Emilia earthquake, which ruptured a fault buried below the Po Plain sediments (Northern Italy). Despite the particularly complex wave propagation, the near-field strong motion observations are well reproduced with 15 rupture parameters. The rupture and slip velocities were notably slow (similar to 0.5 V-s and <0.5 m/s, respectively), implying that the fault was difficult to break. This method opens some perspectives for earthquake rupture studies in areas where numerical simulations suffer from imprecise knowledge of the velocity structure.
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Cebron, D., Viroulet, S., Vidal, J., Masson, J. - P., & Viroulet, P. (2017). Experimental and theoretical study of magnetohydrodynamic ship models. Plos One, 12(6).
Résumé: Magnetohydrodynamic (MHD) ships represent a clear demonstration of the Lorentz force in fluids, which explains the number of students practicals or exercises described on the web. However, the related literature is rather specific and no complete comparison between theory and typical small scale experiments is currently available. This work provides, in a self-consistent framework, a detailed presentation of the relevant theoretical equations for small MHD ships and experimental measurements for future benchmarks. Theoretical results of the literature are adapted to these simple battery/magnets powered ships moving on salt water. Comparison between theory and experiments are performed to validate each theoretical step such as the Tafel and the Kohlrausch laws, or the predicted ship speed. A successful agreement is obtained without any adjustable parameter. Finally, based on these results, an optimal design is then deduced from the theory. Therefore this work provides a solid theoretical and experimental ground for small scale MHD ships, by presenting in detail several approximations and how they affect the boat efficiency. Moreover, the theory is general enough to be adapted to other contexts, such as large scale ships or industrial flow measurement techniques.
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Cerepi, A., Cherubini, A., Garcia, B., Deschamps, H., & Revil, A. (2017). Streaming potential coupling coefficient in unsaturated carbonate rocks. Geophysical Journal International, 210(1), 291–302.
Résumé: The seismoelectric and self-potential methods are showing promises to characterize both the vadose zone of the Earth, hydrocarbon reservoirs and CO2 sequestration. That said, the dependence of a key parameter, the streaming coupling coefficient, with the saturation remains highly debated. We explore here the relationship between the streaming potential coupling coefficient, the electrical resistivity, the capillary pressure curves and the permeability in two saturated and partially saturated carbonate rocks characterized by distinct textures. We investigate a limestone from the Paris basin (the Brauvilliers limestone) and a dolostone from the Aquitain basin (sample labeled LS2), both in France. The two core samples are characterized in terms of their porosity and intrinsic formation factor. A new core flooding system is used to measure simultaneously and, for the first time, both the relative permeability, the resistivity index and the streaming potential coupling coefficient in steady-state two-phase flow conditions as a function of the saturation with CO2 or N-2. The results are compared with a recently developed theoretical model, which can accommodate either the Brooks and Corey model or the van Genuchten model for the capillary pressure curves. This model is predicting a set of relationships between the streaming potential coupling coefficient, the relative permeability and the second Archie's exponent. We found a good agreement between the model based on the van Genuchten approach and experimental data, but still we could not fit all the curves with the same value of the pore size index. or van Genuchten exponent mv especially for the relative permeability.
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Chabane, S., Machane, D., Tebbouche, M. Y., Khaldaoui, F., Oubaiche, E. - H., Bensalem, R., et al. (2017). Ambient seismic vibration analysis and ground characterization in the vicinity of Algiers seismic zone. Arabian Journal Of Geosciences, 10(3).
Résumé: The Dar El Beida area, situated in the Mitidja basin, in the north central Tellian Atlas is characterized by its Plio-Quaternary sediments. The site effect analysis in this zone surrounding Algiers city is very important. The soil is constituted from recent soft sediments capable of amplifying seismic motion. Indeed, the analysis thanks to the ratio H/V ambient vibration method confirms these assumptions. An electric resistivity tomography strengthened the results obtained from ambient vibration for site characterization. This demonstrates once again the more or less homogeneous character of formations in this area. However, strongly amplifying its sediments largely explains the seismic acceleration of 0.52 g recorded following the 2003 Boumerdes earthquake.
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Chamel, G., Gourlan, A. T., Telouk, P., Sayag, D., Milliard, V., Loiseau, C., et al. (2017). Retrospective evaluation of blood copper stable isotopes ratio Cu-65/Cu-63 as a biomarker of cancer in dogs. Veterinary And Comparative Oncology, 15(4), 1323–1332.
Résumé: Previous studies in humans with breast, colorectal or liver cancer showed that neoplasia was associated with a modification of the blood ratio between Cu-65 and Cu-63 (partial derivative Cu). The aim of the present study was to compare the blood partial derivative Cu of dogs with cancer to healthy controls or dogs with non-oncologic disease. One hundred and seventeen dogs were included in the study (35 dogs with cancer, 33 dogs with non-neoplastic disease, and 49 healthy controls). The partial derivative Cu of dogs with cancer was significantly lower than the ratio of healthy controls (P < 0.0001) but not significantly different from dogs with non-oncologic disease. Six dogs with lymphoma were also evaluated after they achieved clinical remission and five out of six had an increase of partial derivative Cu. Further studies are warranted but these results suggest that partial derivative Cu could help in the diagnosis of cancer in a controlled clinical context, and may be a potential biomarker for the follow-up of cancer.
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Champenois, J., Baize, S., Vallee, M., Jomard, H., Alvarado, A., Espin, P., et al. (2017). Evidences of Surface Rupture Associated With a Low-Magnitude (M(w)5.0) Shallow Earthquake in the Ecuadorian Andes. Journal Of Geophysical Research-Solid Earth, 122(10), 8446–8458.
Résumé: This study analyzes surface displacements generated by a low-magnitude crustal earthquake in the Ecuadorian Andes by combining analysis of synthetic aperture radar (SAR) interferometry, geological field investigations, and seismological data. In March 2010, a significant surface faulting event occurred in the Pisayambo area (Eastern Cordillera), along the major dextral fault zone bounding the North Andean Sliver and the South America Plate. Interferograms were inverted to determine fault plane geometry and slip displacement distribution. The event affected a 9km long previously unknown fault, referred as the Laguna Pisayambo Fault, with purely dextral movement reaching 45cm and concentrated in the top 3km of the crust. Geological investigations confirm both the fault mechanism and the amplitude of displacements. While these large displacements would be related to an event with a magnitude of 5.44 if using a standard crustal rigidity, we show that they can be convincingly associated with an M(w)5.0 earthquake, that occurred on 26 March 2010. Reconciling the apparent differences in magnitude requires the existence of a low-rigidity medium at shallow depths and/or postseismic activity of the fault. However, considering only the latter hypothesis would imply an unusually active postseismic process, in which 400-500% of the coseismic moment is released in the 6days following the earthquake. Our observations highlight that the scaling laws relating surface observations to earthquake magnitude, classically used for seismic hazard assessment, should be carefully used. This study also illustrates how systematic InSAR analysis, even in places where no clues of ground deformation are present, can reveal tectonic processes.
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Charlet, L., Alt-Epping, P., Wersin, P., & Gilbert, B. (2017). Diffusive transport and reaction in clay rocks: A storage (nuclear waste, CO2, H-2), energy (shale gas) and water quality issue. Advances In Water Resources, 106, 39–59.
Résumé: Clay rocks are low permeability sedimentary formations that provide records of Earth history, influence the quality of water resources, and that are increasingly used for the extraction or storage of energy resources and the sequestration of waste materials. Informed use of clay rock formations to achieve low carbon or carbon-free energy goals requires the ability to predict the rates of diffusive transport processes for chemically diverse dissolved and gaseous species over periods up to thousands of years. We survey the composition, properties and uses of clay rock and summarize fundamental science challenges in developing confident conceptual and quantitative gas and solute transport models. (C) 2017 Published by Elsevier Ltd.
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Charlet, L., Blancho, F., Bonnet, T., Garambois, S., Boivin, P., Ferber, T., et al. (2017). Industrial mercury pollution in a mountain valley: a combined geophysical and geochemical study (Vol. 17).
Résumé: Many alpine valleys have inherited strong industrial remnants. Chemical and metallurgical companies were set up in these narrow glacial valleys at the beginning of the industrial era to benefit from cheap labor and hydroelectricity. Regulations concerning solid and liquid waste handling did not exist, and contaminated sediments were often used as soil amendment to improve soil texture, spreading the contamination, which local Authorities have now to deal with. In the present study we report on mercury contamination in the narrow alpine valley known as canton of Valais valley. Waste materials and contaminated sediments were deposited in the valley for many years. An electromagnetic conductivity survey allowed a definitive mapping of the extent of such practices because an EM conductivity contrast was clearly detectable between the added silty-clay material and the natural silty-sand soil. High EM conductivity correlates quite well with high Hg surface soil content. Cores drilled at hotspots and along the canal were analyzed for total mercury, methyl mercury, and core sedimentary features recorded. While up to 70 cm thick, dredged, Hg-contaminated material was found to lay above the original sandy soil in housing areas, the mercury contamination extends down to 1.5 m depth, i.e. down to the water table, probably caused by the high sediment material organic content (OC), and OC-Hg enhanced transport. Methylation reductive conditions were observed, together with high MeHg relative abundance ([ MeHg]/ [HgT] > 0.1%), in two environments, namely the zone of fluctuating water table and the canal water/sediment interface. Groundwater quality was not impacted, because of large groundwater fluxes observed in these glacial alpine valleys. (C) 2017 The authors. Published by Elsevier B.V.
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Chen, Y., Remy, D., Froger, J. - L., Peltier, A., Villeneuve, N., Darrozes, J., et al. (2017). Long-term ground displacement observations using InSAR and GNSS at Piton de la Fournaise volcano between 2009 and 2014. Remote Sensing Of Environment, 194, 230–247.
Résumé: Monitoring ground surface displacement of volcanoes over a long period of time helps improve understanding of the volcano structure, dynamics and mechanisms. In this paper, we investigate the spatio-temporal behavior of the long-term displacement field at Piton de la Fournaise volcano (12 Reunion Island) by means of X-band InSAR and GNSS time series analysis from 2009 to 2014. We propose a new correction approach based on principal component analysis to mitigate the long-wavelength artifact in the interferograms over the study area. Our results show that most of the volcanic edifice including the Central Cone, the Eastern Flank and recent lava flow fields was affected by varying degrees of ground motion. More importantly, a widespread sector (similar to 20 km(2)) affected by time-dependent downward and eastward motion was observed on the Eastern Flank of Piton de la Fournaise. The combined analysis of InSAR and GNSS time series and previous studies allows us to confirm that this large mobile sector on the Eastern Flank underwent deformation for at least 7 years following the end of the large March-April 2007 eruption, including a stage of transient strain from the end of eruption to February 2011, followed by a stage of steady-state strain until late 2014. Several possible origins, including a pre-existing structural discontinuity, summit stress associated with magmatism, and activated fault movement are explored to explain the observed widespread long-term seaward motion that is considered to be direct evidence of potential flank instability. (C) 2017 Elsevier Inc. All rights reserved.
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Chevalier, L., Collombet, M., & Pinel, V. (2017). Temporal evolution of magma flow and degassing conditions during dome growth, insights from 2D numerical modeling. Journal Of Volcanology And Geothermal Research, 333, 116–133.
Résumé: Understanding magma degassing evolution during an eruption is essential to improving forecasting of effusive/explosive regime transitions at andesitic volcanoes. Lava domes frequently form during effusive phases, inducing a pressure increase both within the conduit and within the surrounding rocks. To quantify the influence of dome height on magma flow and degassing, we couple magma and gas flow in a 2D numerical model. The deformation induced by magma flow evolution is also quantified. From realistic initial magma flow conditions in effusive regime (Collombet, 2009), we apply increasing pressure at the conduit top as the dome grows. Since volatile solubility increases with pressure, dome growth is then associated with an increase in magma dissolved water content at a given depth, which corresponds with a decrease in magma porosity and permeability. Magma flow evolution is associated with ground deflation of a few rad in the near field. However this signal is not detectable as it is hidden by dome subsidence (a few mrad). A Darcy flow model is used to study the impact of pressure and permeability conditions on gas flow in the conduit and surrounding rock. We show that dome permeability has almost no influence on magma degassing. However, increasing pressure in the surrounding rock, due to dome loading, as well as decreasing magma permeability in the conduit limit permeable gas loss at the conduit walls, thus causing gas pressurization in the upper conduit by a few tens of MPa. Decreasing magma permeability and increasing gas pressure increase the likelihood of magma explosivity and hazard in the case of a rapid decompression due to dome collapse. (C) 2017 Elsevier B.V. All rights reserved.
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Chevalier, L., Collombet, M., & Pinel, V. (2017). Temporal evolution of magma flow and degassing conditions during dome growth, insights from 2D numerical modeling (vol 333, pg 116, 2017). Journal Of Volcanology And Geothermal Research, 341, 371–373.
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Chi Cong Vu Jérôme Weiss, O. P., David Amitrano. (2017). Statistical size effects on compressive strength and mechanical behavior of concrete. Key Engineering Materials, 754, 317–320.
Résumé: The size effect on strength of concrete has been studied for a long time from various approaches. In particular, the weakest-link theory remains nowadays the basic tool to interpret statistical size effects, i.e. how the probability of failure under a given stress depends on external size. The main shortcoming of Weibull’s theory is that the activation of fracture from the weakest flaw is assumed to set the final strength, i.e. possible interactions between microcracks and defects during progressive damage are implicitly neglected. The objective of this study is to determine experimentally the influence of “external” (sample) size and “internal” (microstructural) size on compressive strength of concrete. For this purpose, more than 250 uniaxial compression tests were conducted on concrete specimens with two different cylindrical sizes (110×220 mm and 160×320 mm) and prepared from three different compositions (mean aggregate size and proportion). The relationships between compressive strength, dissipated energy up to failure in one hand, and microstructural as well as specimen sizes on the other hand, were analyzed statistically. This demonstrated the failure of the weakest-link approach to describe size effects on compressive strength of concrete.
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Chiarantini, L., Rimondi, V., Bardelli, F., Benvenuti, M., Cosio, C., Costagliola, P., et al. (2017). Mercury speciation in Pinus nigra barks from Monte Amiata (Italy): An X-ray absorption spectroscopy study. Environmental Pollution, 227, 83–88.
Résumé: This study determined, by means of X-ray absorption near-edge structure (XANES) spectroscopy, the speciation of mercury (Hg) in black pine (Pinus nigra) barks from Monte Amiata, that were previously shown to contain exceptionally high (up to some mg kg(-1)) Hg contents because of the proximity to the former Hg mines and roasting plants. Linear fit combination (LCF) analysis of the experimental spectra compared to a large set of reference compounds showed that all spectra can be fitted by only four species: beta-HgS (metacinnabar), Hg-cysteine, Hg bound to tannic acid, and Hg-0. The first two are more widespread, whereas the last two occur in one sample only; the contribution of organic species is higher in deeper layers of barks than in the outermost ones. We interpret these results to suggest that, during interaction of barks with airborne Hg, the metal is initially mechanically captured at the bark surface as particulate, or physically adsorbed as gaseous species, but eventually a stable chemical bond is established with organic ligands of the substrate. As a consequence, we suggest that deep bark Hg may be a good proxy for long term time-integrated exposure, while surface bark Hg is more important for recording short term events neat Hg point sources. (C) 2017 Elsevier Ltd. All rights reserved.
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Chiodini, G., Giudicepietro, F., Vandemeulebrouck, J., Aiuppa, A., Caliro, S., De Cesare, W., et al. (2017). Fumarolic tremor and geochemical signals during a volcanic unrest. Geology, 45(12), 1131–1134.
Résumé: Fumaroles are known to generate seismic and infrasonic tremor, but this fumarolic tremor has so far received little attention. Seismic records taken near the Pisciarelli fumarole, a vigorously degassing vent of the restless Campi Flegrei volcano in Italy, reveal a fumarole-sourced tremor whose amplitude has recently intensified. We use independent geochemical evidence to interpret this fumarolic tremor for the first time quantitatively. We find that the temporal increase in fumarolic tremor RSAM (real-time seismic-amplitude measurement) quantitatively correlates with increases in independent proxies of fumarole activity, including the CO2 concentrations in the fumarole's atmospheric plume, the fumarole composition (CO/CO2 and H-2/H2O ratios), and temperature (T) and pressure (P) conditions of the source hydrothermal system. This association between RSAM and geochemical data suggests that the current escalation in fumarolic tremor is driven by increased gas transport and venting from a hydrothermal system that evolves toward higher T-P conditions. More widely, our results suggest that monitoring the tremor generated by fumaroles can pave the way to real-time tracking and interpreting the evolution of an ongoing hydrothermal-magmatic unrest, thus complementing information from periodic gas surveys. Our novel method of fumarole monitoring, based on well-established seismic techniques, is potentially suitable for capturing signals of unrest at any active volcano, including those in remote regions.
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Chiodini, G., Selva, J., Del Pezzo, E., Marsan, D., De Siena, L., D'Auria, L., et al. (2017). Clues on the origin of post-2000 earthquakes at Campi Flegrei caldera (Italy). Scientific Reports, 7, 4472.
Résumé: The inter-arrival times of the post 2000 seismicity at Campi Flegrei caldera are statistically distributed into different populations. The low inter-arrival times population represents swarm events, while the high inter-arrival times population marks background seismicity. Here, we show that the background seismicity is increasing at the same rate of (1) the ground uplift and (2) the concentration of the fumarolic gas specie more sensitive to temperature. The seismic temporal increase is strongly correlated with the results of recent simulations, modelling injection of magmatic fluids in the Campi Flegrei hydrothermal system. These concurrent variations point to a unique process of temperature-pressure increase of the hydrothermal system controlling geophysical and geochemical signals at the caldera. Our results thus show that the occurrence of background seismicity is an excellent parameter to monitor the current unrest of the caldera.
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Colombero, C., Baillet, L., Comina, C., Jongmans, D., & Vinciguerra, S. (2017). Characterization of the 3-D fracture setting of an unstable rock mass: From surface and seismic investigations to numerical modeling. Journal Of Geophysical Research-Solid Earth, 122(8), 6346–6366.
Résumé: The characterization of the fracturing state of a potentially unstable rock cliff is a crucial requirement for stability assessments and mitigation purposes. Classical measurements of fracture location and orientation can however be limited by inaccessible rock exposures. The steep topography and high-rise morphology of these cliffs, together with the widespread presence of fractures, can additionally condition the success of geophysical prospecting on these sites. In order to mitigate these limitations, an innovative approach combining noncontact geomechanical measurements, active and passive seismic surveys, and 3-D numerical modeling is proposed in this work to characterize the 3-D fracture setting of an unstable rock mass, located in NW Italian Alps (Madonna del Sasso, VB). The 3-D fracture geometry was achieved through a combination of field observations and noncontact geomechanical measurements on oriented pictures of the cliff, resulting from a previous laser-scanning and photogrammetric survey. The estimation of fracture persistence within the rock mass was obtained from surface active seismic surveys. Ambient seismic noise and earthquakes recordings were used to assess the fracture control on the site response. Processing of both data sets highlighted the resonance properties of the unstable rock volume decoupling from the stable massif. A finite element 3-D model of the site, including all the retrieved fracture information, enabled both validation and interpretation of the field measurements. The integration of these different methodologies, applied for the first time to a complex 3-D prone-to-fall mass, provided consistent information on the internal fracturing conditions, supplying key parameters for future monitoring purposes and mitigation strategies.
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Colombi, A., Ageeva, V., Smith, R. J., Clare, A., Patel, R., Clark, M., et al. (2017). Enhanced sensing and conversion of ultrasonic Rayleigh waves by elastic metasurfaces. Scientific Reports, 7.
Résumé: Recent years have heralded the introduction of metasurfaces that advantageously combine the vision of sub-wavelength wave manipulation, with the design, fabrication and size advantages associated with surface excitation. An important topic within metasurfaces is the tailored rainbow trapping and selective spatial frequency separation of electromagnetic and acoustic waves using graded metasurfaces. This frequency dependent trapping and spatial frequency segregation has implications for energy concentrators and associated energy harvesting, sensing and wave filtering techniques. Different demonstrations of acoustic and electromagnetic rainbow devices have been performed, however not for deep elastic substrates that support both shear and compressional waves, together with surface Rayleigh waves; these allow not only for Rayleigh wave rainbow effects to exist but also for mode conversion from surface into shear waves. Here we demonstrate experimentally not only elastic Rayleigh wave rainbow trapping, by taking advantage of a stop-band for surface waves, but also selective mode conversion of surface Rayleigh waves to shear waves. These experiments performed at ultrasonic frequencies, in the range of 400-600 kHz, are complemented by time domain numerical simulations. The metasurfaces we design are not limited to guided ultrasonic waves and are a general phenomenon in elastic waves that can be translated across scales.
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Colquitt, D. J., Colombi, A., Craster, R. V., Roux, P., & Guenneau, S. R. L. (2017). Seismic metasurfaces: Sub-wavelength resonators and Rayleigh wave interaction. Journal Of The Mechanics And Physics Of Solids, 99, 379–393.
Résumé: We consider the canonical problem of an array of rods, which act as resonators, placed on an elastic substrate; the substrate being either a thin elastic plate or an elastic half-space. In both cases the flexural plate, or Rayleigh surface, waves in the substrate interact with the resonators to create interesting effects such as effective band-gaps for surface waves or filters that transform surface waves into bulk waves; these effects have parallels in the field of optics where such sub wavelength resonators create metamaterials in the bulk and metasurfaces at the free surfaces. Here we carefully analyse this canonical problem by extracting the dispersion relations analytically thereby examining the influence of both the flexural and compressional resonances on the propagating wave. For an array of resonators atop an elastic half-space we augment the analysis with numerical simulations. Amongst other effects, we demonstrate the striking effect of a dispersion curve which corresponds to a mode that transitions from Rayleigh wave-like to shear wave -like behaviour and the resultant change in the fields from surface to bulk waves.
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Condie, K. C., Arndt, N., Davaille, A., & Puetz, S. J. (2017). Zircon age peaks: Production or preservation of continental crust? Geosphere, 13(2), 227–234.
Résumé: Zircon age peaks are commonly interpreted either as crustal production peaks or as selective preservation peaks of subduction-produced crust selectively preserved during continent-continent collision. We contribute to this ongoing debate, using the Nd isotopic compositions of felsic igneous rocks and their distribution during the accretionary and collisional phases of orogens. The proportion of juvenile input into the continental crust is estimated with a mixing model using arc-like mantle and reworked continental crust end members. Orogen length and duration proxies for juvenile crustal volume show that the amount of juvenile crust produced and preserved at zircon age peaks during the accretionary phase of orogens is >= 3 times that preserved during the collisional phase of orogens. The fact that most juvenile crust is both produced and preserved during the accretionary phase of orogens does not require craton collisions for its preservation, thus favoring the interpretation of zircon age peaks as crustal production peaks. Most juvenile continental crust older than 600 Ma is produced and preserved before final supercontinent assembly and does not require supercontinent assembly for its preservation. Episodic destabilization of a compositionally heterogeneous layer at the base of the mantle may produce mantle plume events leading to enhanced subduction and crustal production. Our Nd isotope model for cumulative continental growth based on juvenile crust proxies for the past 2.5 b.y. suggests a step-like growth curve with rapid growth in accretionary orogens at the times of zircon age peaks.
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Cordier, C., Sauzeat, L., Arndt, N. T., Boullier, A. - M., Batanova, V., & Barou, F. (2017). Quantitative Modelling of the Apparent Decoupling of Mg# and Ni in Kimberlitic Olivine Margins: a Reply to the Comment on Cordier et al. (2015) by A. Moore. Journal Of Petrology, 58(2), 391–393.
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Cortes-Aranda, J., Mugnier, J. - L., Jouanne, F., Vassallo, R., Carcaillet, J., & Awan, A. A. (2017). Holocene shortening rates and seismic hazard assessment for the frontal Potwar Plateau, NW Himalaya of Pakistan: Insights from Be-10 concentrations on fluvial terraces of the Mahesian Anticline. Quaternary International, 462, 75–89.
Résumé: We present the results of a structural neotectonic survey undertaken on the Mahesian Anticline in the frontal Himalaya of Pakistan. This anticline resulted from the folding of Precambrian to Tertiary layers that was controlled by a thrust and a backthrust, interacting in a complex way. Four generations of fluvial terraces formed by the Jhelum River and two tributaries have been distinguished on the SE flank of the anticline. Two of these terraces, T2 and T3, have been left hanging by fold development and have been dated by cosmogenic Be-10 to 6.5 +/- 0.2 ka and 3.3 +/- 0.7 ka, respectively. From such ages an uplift rate of similar to 10 mm/y was determined for the Holocene. That uplift is induced by a shortening rate of similar to 10 mm/y. We highlight that the Mahesian Anticline and Frontal Salt Range Thrust, together with the Kalabagh western lateral ramp and the Jhelum eastern lateral ramp, delineate the active tectonic boundary of the Potwar Plateau. This thrust sheet moves above the salt level without out-of-sequence deformation. Moreover, the small but significant difference between the long-term deformation rates (8.4 mm/y) and the geodetic velocities (2-5 mm/y) detected for the Central Potwar Plateau seems to be linked to episodic spurts of accelerated creeping of the thick salt level, triggered by earthquakes located to the north on the deep (>15 km) part of the MHT. In addition, the large difference between the long-term deformation rates and the geodetic velocities (less than 2 mm/y) reported for the eastern Potwar Plateau seems to be linked to the accumulation of a slip deficit around asperities formed where the salt is missing. This deficit may be recovered during earthquakes potentially as great as Mw 7. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.
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Cossa, D., de Madron, X. D., Schafer, J., Lanceleur, L., Guedron, S., Buscail, R., et al. (2017). The open sea as the main source of methylmercury in the water column of the Gulf of Lions (Northwestern Mediterranean margin). Geochimica Et Cosmochimica Acta, 199, 222–237.
Résumé: Despite the ecologic and economical importance of coastal areas, the neurotoxic bioaccumulable monomethylmercury (MMHg) fluxes within the ocean margins and exchanges with the open sea remain unassessed. The aim of this paper is to address the questions of the abundance, distribution, production and exchanges of methylated mercury species (MeHgT), including MMHg and dimethylmercury (DMHg), in the waters, atmosphere and sediments of the Northwestern Mediterranean margin including the Rhone River delta, the continental shelf and its slope (Gulf of Lions) and the adjacent open sea (North Gyre). Concentrations of MeHgT ranged from <0.02 to 0.48 pmol L-1 with highest values associated with the oxygen-deficient zone of the open sea. The methylated mercury to total mercury proportion (MeHgT/HgT) increased from 2% to 4% in the Rhone River to up to 30% (averaging 18%) in the North Gyre waters, whereas, within the shelf waters, MeHgT/HgT proportions were the lowest (1-3%). We calculate that the open sea is the major source of MeHgT for the shelf waters, with an annual flux estimated at 0.68 +/- 0.12 kmol a(-1) (i.e., equivalent to 12% of the HgT flux). This MeHgT influx is more than 80 times the direct atmospheric deposition or the in situ net production, more than 40 times the estimated “maximum potential” annual efflux from shelf sediment, and more than 7 times that of the continental sources. In the open sea, ratios of MMHg/DMHg in waters were always <1 and minimum in the oxygen deficient zones of the water column, where MeHg concentrations are maximum. This observation supports the idea that MMHg could be a degradation product of DMHg produced from inorganic divalent Hg. (C) 2016 Elsevier Ltd. All rights reserved.
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Cotte, M., Pouyet, E., Salome, M., Rivard, C., De Nolf, W., Castillo-Michel, H., et al. (2017). The ID21 X-ray and infrared microscopy beamline at the ESRF: status and recent applications to artistic materials. Journal Of Analytical Atomic Spectrometry, 32(3), 477–493.
Résumé: The ID21 beamline (European Synchrotron Radiation facility, France) is a multi micro-analytical platform combining X-ray and infrared micro-probes, for characterization of elements, species, molecular groups and crystalline structures in complex materials. Applications are mainly in the fields of cultural heritage, life science, environmental and earth sciences, materials sciences. Here, we first present the status of instruments: (i) the scanning micro-spectroscopy end-station, operating from 2.0 to 9.2 keV, under vacuum and offering cryo conditions, for the acquisition of 2D micro X-ray fluorescence (mu XRF) maps, single point micro X-ray Absorption Near Edge Structure (mu XANES) spectra and speciation maps with sub-micrometric resolution; (ii) the XANES full-field end-station, operating in the same vacuum and energy conditions, for the acquisition of hyper-spectral radiographs of thin concentrated samples, resulting in speciation maps with micrometric resolution and millimetric field of view; (iii) the scanning micro-X-ray diffraction (mu XRD)/mu XRF end-station, operating at 8.5 keV, in air, for the acquisition of 2D crystalline phase maps, with micrometric resolution; and (iv) the scanning infrared microscope, operating in the mid-infrared range for the acquisition of molecular maps and some structural maps with micrometric resolution. Recent hardware and software developments are presented, as well as new protocols for improved sample preparation of thin sections. Secondly, a review of recent applications for the study of cultural heritage is presented, illustrated by various examples: determination of the origin of the color in blue Chinese porcelains and in brown Sevres porcelains; detection of lead in ink on Herculaneum papyri; identification and degradation of modeling materials used by Auguste Rodin and of chrome yellow pigments used by Vincent van Gogh. Cryo capabilities are illustrated by the analysis of plants exposed to chromate solutions. These examples show the variety of materials analyzed, of questions tackled, and particularly the multiple advantages of the ID21 analytical platform for the analysis of ancient and artistic materials.
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Crouzet, C., Brunet, F., Montes-Hernandez, G., Recham, N., Findling, N., Ferrasse, J. - H., et al. (2017). Hydrothermal Valorization of Steel Slags-Part I: Coupled H-2 Production and CO2 Mineral Sequestration. Frontiers In Energy Research, 5.
Résumé: A new process route for the valorization of BOF steel slags combining H-2 production and CO2 mineral sequestration is investigated at 300 degrees C (HT) under hydrothermal conditions. A BOF steel slag stored several weeks outdoor on the production site was used as starting material. To serve as a reference, room temperature (RT) carbonation of the same BOF steel slag has been monitored with in situ Raman spectroscopy and by measuring pH and PCO2 on a time-resolved basis. CO2 uptake under RT and HT are, respectively, 243 and 327 kg CO2/t of fresh steel slag, which add up with the 63 kg of atmospheric CO2 per ton already uptaken by the starting steel slag on the storage site. The CO2 gained by the sample at HT is bounded to the carbonation of brownmillerite. H-2 yield decreased by about 30% in comparison to the same experiment performed without added CO2, due to sequestration of ferrous iron in a Mg-rich siderite phase. Ferric iron, initially present in brownmillerite, is partitioned between an Fe-rich clay mineral of saponite type and metastable hematite. Saponite is likely stabilized by the presence of Al, whereas hematite may represent a metastable product of brownmillerite carbonation. Mg-rich wOstite is involved in at least two competing reactions, i.e., oxidation into magnetite and carbonation into siderite. Results of both water-slag and water-CO2-slag experiments after 72 h are consistent with a kinetics enhancement of the former reaction when a CO2 partial pressure imposes a pH between 5 and 6. Three possible valorization routes, (1) RT carbonation prior to hydrothermal oxidation, (2) RT carbonation after hydrothermal treatment, and (3) combined HT carbonation and oxidation are discussed in light of the present results and literature data.
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Crouzet, C., Brunet, F., Recham, N., Auzende, A. - L., Findling, N., Magnin, V., et al. (2017). Hydrothermal Steel Slag Valorization-Part II: Hydrogen and Nano-Magnetite Production. Frontiers In Earth Science, 5.
Résumé: The effect of acidic conditions (in a pH range of 3 to 6) and temperature on the kinetics of the hydrothermal oxidation of ferrous iron contained in BOF steel slag has been tested in the 150-350 degrees C range for acid acetic concentrations from 0 to 4M. Reaction progress was monitored with the amount of produced H-2. Higher temperature and lower pH are found to enhance the hydrothermal oxidation kinetics of the slag. These two parameters are believed to increase iron dissolution rate which has already been identified as the rate limiting step of the hydrothermal oxidation of pure FeO. An activation energy of 28 +/- 4 kJ/mole is found for the hydrothermal oxidation of the steel slag which compares very well with that of pure FeO under similar conditions. In the case of the slag run in water at 300 degrees C for 70.5 h, magnetite product has been separated magnetically and characterized. Particles were found to fall in three size ranges: 10-30 nm, 100-300 nm, and 1-10 μm. The smallest fraction (10-30 nm) is comparable to the 10-20 nm size range that is achieved when nanomagnetite are synthesized by co-precipitation methods. Obviously, the production of nanomagnetite enhances the economic interest of the hydrothermal processing of steel slags, which has already proven its capacity to produce high-purity H-2.
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Crouzet, C., Brunet, F., Recham, N., Findling, N., Lanson, M., Guyot, F., et al. (2017). Hydrogen production by hydrothermal oxidation of FeO under acidic conditions. International Journal Of Hydrogen Energy, 42(2), 795–806.
Résumé: The production of H-2 by oxidation of FeO, taken here as model compound for steel slags, has been investigated both in pure water and under acidic aqueous conditions in the 373 -573 K temperature range. Whereas after 65 h, H-2 yield was negligible in pure water at 423 K, the reaction 3 FeO(s) + H2O(l) -> Fe3O4(sc) + H-2(aq) reached near completion at the same temperature within 10 h in a solution containing 0.05 mol/l acetic acid. Increasing acetic acid concentration by one order of magnitude did not yield significantly more H-2. At identical initial pH, acetic acid was found to be more efficient than oxalic acid and hydrochloric acid at enhancing H-2 production. Acidic conditions increased FeO dissolution kinetics and, consequently, improved H-2 yield. The specific efficiency of acetic acid resides in its thermal stability as well as in the potential of ligand-promoted Fe(II) dissolution. We show that the positive kinetics effect of mild acetic acid solutions over H-2 yield evidenced on FeO does not apply directly to steel slags which buffer the pH to high values due to the presence of large amounts of CaO. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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Cumella, S. P., Woodruff, W. F., & Revil, A. (2017). Piceance Basin Mesaverde anomalous self-potential response: Identification of capillary seals in a basin-centered gas accumulation. AAPG Bull., 101(1), 19–37.
Résumé: Wells in the Piceance Basin show anomalous large-magnitude (up to 200 mV), large-interval (>2000 ft [610 m]) self-potential (SP) log responses in the Mesaverde gas-producing interval that can be best explained by electrokinetic potential resulting from water flow toward producing Mesaverde wells. Water flow is compartmentalized by capillary seals that are formed when gas generated from coals saturates adjacent thinly bedded sandstones and shales. Capillary seals can be identified by shifts in the SP baseline. The first wells drilled in an area with no previous Mesaverde production have very little SP response, as is expected in tight sandstones with single-to double-digit microdarcy permeability. After Mesaverde production is established in a new area, the SP log begins to show stepwise changes to more negative values beginning in the upper Mesaverde and becoming increasingly more negative with increased depth. The magnitude of the change to more negative values increases with time in an area of active Mesaverde production; some of the more recent SP logs have negative deflections of over 200 mV. This type of SP anomaly has not been reported before, and these anomalies can be used to identify large-scale water movement within a reservoir.
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Dansereau, V., Weiss, J., Saramito, P., Lattes, P., & Coche, E. (2017). Ice bridges and ridges in the Maxwell-EB sea ice rheology. Cryosphere, 11(5), 2033–2058.
Résumé: This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB), is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a Mohr-Coulomb damage criterion that allows for pure (uniaxial and biaxial) tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.
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Daout, S., Doin, M. - P., Peltzer, G., Socquet, A., & Lasserre, C. (2017). Large-scale InSAR monitoring of permafrost freeze-thaw cycles on the Tibetan Plateau. Geophysical Research Letters, 44(2), 901–909.
Résumé: Multitemporal interferometric synthetic aperture radar (InSAR) observations are used to characterize spatial variations of the permafrost active layer and its temporal evolution in Northwestern Tibet. We develop a method to enhance InSAR performances for such difficult terrain conditions and construct an 8year timeline of the surface deformation over a 60,000 km(2) area. The ground movement induced by the active layer's response to climate forcing is limited to Cenozoic sedimentary basins and is spatially variable in both its seasonal amplitude (2.5-12mm) and multiannual trend (-2 to 3mm/yr). A degree-day integrated model adjusted to the data indicates that subsidence occurs when the surface temperature exceeds zero (May to October) over areas where seasonal movements are large (>8mm). The period of subsidence is delayed by 1-2months over areas where smaller seasonal movements are observed, suggesting an unsaturated soil where water occurs in the deeper part of the active layer.
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Daval, D., Bernard, S., Remusat, L., Wild, B., Guyot, F., Micha, J. S., et al. (2017). Dynamics of altered surface layer formation on dissolving silicates. Geochimica Et Cosmochimica Acta, 209, 51–69.
Résumé: The extrapolation of mineral dissolution kinetics experiments to geological timescales has frequently been challenged by the observation that mineral dissolution rates decrease with time. In the present study, we report a detailed investigation of the early stages of wollastonite dissolution kinetics, linking time-resolved measurements of wollastonite dissolution rate as a function of crystallographic orientation to the evolution of physicochemical properties (i. e., diffusivity, density, and thickness) of amorphous silica-rich layers (ASSLs) that developed on each surface. Batch dissolution experiments conducted at room temperature and at far-from-equilibrium conditions revealed that the initial (i. e., ASSL-free) dissolution rate of wollastonite (R(hkl)) based on Ca release observe the following trend: R-(010) approximate to R-(100) > R-(101) > R-(001). A gradual decrease of the dissolution rate of some faces by up to one oR(er of magnitude resulted in a modification of this trend after two days: R-(010) >> R-(100) >> R-(101) approximate to R-(001). In parallel, the diffusivity of ASSLs developed on each face was estimated based on the measurement of the concentration profile of a conservative tracer (methylene blue) across the ASSL using nanoSIMS. The apparent diffusion coefficients of methylene blue as a function of the crystallographic orientation (D(hkl) app) observe the following trend: R-(010) app P D-app((100)) >= D-app((101)) >= D-app((001)) , and decreases as a function of time for the (100) and (101) faces. Finally, the density of ASSL was estimated based on the modeling of X-ray reflectivity patterns acquired as a function of time. The density of ASSLs developed on the (010) faces remains low and constant, whereas it increases for the ASSLs developed on the (001) faces. On the whole, our results suggest that the impact of the formation of ASSLs on the wollastonite dissolution rate is anisotropic: while some crystal faces are weakly affected by the formation of non-passivating ASSLs (e. g., the (010) face), the dissolution of other faces is hampered by passivating ASSLs within a few hours. The observed passivation is suggested to originate from the progressive densification of the ASSL, which limits the transport of reactive species from and to the dissolving wollastonite surface, as evidenced by the estimated diffusivity of the ASSLs. Because the apparent face-specific diffusivity of the ASSLs is correlated with the face-specific initial (i. e., ASSL-free) dissolution rate of wollastonite, we propose that the extent of ASSL densification (and the resulting impact on ion transport) is (at least partly) controlled by the absolute mineral dissolution rate. Overall, this study argues that the formation and microstructural evolution of ASSLs are likely candidates for mineral ageing, highlighting the need for determining the parameters controlling the spontaneous changes of ASSL diffusivity as a function of the reaction progress. (C) 2017 Elsevier Ltd. All rights reserved.
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De Landro, G., Serlenga, V., Russo, G., Amoroso, O., Festa, G., Bruno, P. P., et al. (2017). 3D ultra-high resolution seismic imaging of shallow Solfatara crater in Campi Flegrei (Italy): New insights on deep hydrothermal fluid circulation processes. Scientific Reports, 7.
Résumé: Seismic tomography can be used to image the spatial variation of rock properties within complex geological media such as volcanoes. Solfatara is a volcano located within the Campi Flegrei, a still active caldera, so it is of major importance to characterize its level of activity and potential danger. In this light, a 3D tomographic high-resolution P-wave velocity image of the shallow central part of Solfatara crater is obtained using first arrival times and a multiscale approach. The retrieved images, integrated with the resistivity section and temperature and the CO2 flux measurements, define the following characteristics: 1. A depth-dependent P-wave velocity layer down to 14 m, with V-p < 700 m/s typical of poorly-consolidated tephra and affected by CO2 degassing; 2. An intermediate layer, deepening towards the mineralized liquid-saturated area (Fangaia), interpreted as permeable deposits saturated with condensed water; 3. A deep, confined high velocity anomaly associated with a CO2 reservoir. These features are expression of an area located between the Fangaia, water saturated and replenished from deep aquifers, and the main fumaroles, superficial relief of the deep rising CO2 flux. Therefore, the changes in the outgassing rate greatly affect the shallow hydrothermal system, which can be used as a “mirror” of fluid migration processes occurring at depth.
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Deal, E., Favre, A. - C., & Braun, J. (2017). Rainfall variability in the Himalayan orogen and its relevance to erosion processes. Water Resources Research, 53(5), 4004–4021.
Résumé: Rainfall is an important driver of erosion processes. The mean rainfall rate is often used to account for the erosive impact of a particular climate. However, for some erosion processes, erosion rate is a nonlinear function of rainfall, e.g., due to a threshold for erosion. When this is the case, it is important to take into account the full distribution of rainfall, instead of just the mean. In light of this, we have characterized the variability of daily rainfall over the Himalayan orogen using high spatial and temporal resolution rainfall data sets. We find significant variations in rainfall variability over the Himalayan orogen, with increasing rainfall variability to the west and north of the orogen. By taking into account variability of rainfall in addition to mean rainfall rate, we find a pattern of rainfall that, from a geomorphological perspective, is significantly different from mean rainfall rate alone. Using these findings, we argue that short-term rainfall variability may help explain observed short and long-term erosion rates in the Himalayan orogen. Plain Language Summary An important topic in earth science is understanding how climate and tectonic forces interact to shape the surface of the Earth. One of the main influences that climate has on the Earth's surface is to cause erosion by delivering water to landscapes as rain and snow. Wetter climates should, in general, cause more erosion than drier climates, which is why the mean annual rainfall has traditionally been used as a measure of the erosive strength of climate. However, field evidence seems to suggest that the effect of climate is more sophisticated than can be captured with the mean annual rainfall. There is a considerable body of theory demonstrating that the intensity of rainfall, or storminess, is an equally important aspect of how climate causes erosion. In light of this, we have characterized the storminess in the Himalayan mountain range, a place with high erosion rates driven by rainfall. We show that there is large variation in storminess from place to place in the Himalayas, and that this can help explain observed rates of erosion, which do not match mean annual rainfall rates.
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Debure, M., Montes-Hernandez, G., Lerouge, C., Made, B., & Tournassat, C. (2017). Effect of trace elements on carbonate thermodynamic constants (Vol. 17).
Résumé: This study is a preliminary work on the description and the modeling of mechanisms potentially causing discrepancies between experimental data and thermodynamic calculation performed on carbonate equilibrium at high temperature. A better understanding of dolomite dissolution/precipitation processes that occur during its equilibration is important for investigations of high-level radioactive waste disposal or Carbon and Capture Storage (CCS). The first results demonstrated the fast dolomite equilibration in solution (within 12 days) and the good agreement between experimental and thermodynamic calculations at 25 degrees C for dolomite and calcite-dolomite systems whereas discrepancies are observed at higher temperature (80 degrees C). As shown from cathodoluminescence photomicrographs, one of the expected mechanisms causing those differences is the incorporation of trace elements such as Mg, Mn or Ba found in natural systems. (C) 2017 The Authors. Published by Elsevier B.V.
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Deffontaines, B., Chang, K. J., Champenois, J., Fruneau, B., Pathier, E., Hu, J. C., et al. (2017). Active interseismic shallow deformation of the Pingting terraces (Longitudinal Valley – Eastern Taiwan) from UAV high-resolution topographic data combined with InSAR time series. Geomatics Natural Hazards & Risk, 8(1), 120–136.
Résumé: We focus herein on the location, characterization and the quantification of the most active structural feature of Taiwan: the Longitudinal Valley Fault that corresponds to the suture in between the Philippine and Eurasian Plates. In order to determine and monitor its present inter-seismic deformation, we focus on the Pingting Terraces area, situated in the South Longitudinal Valley (Eastern Taiwan). We first determine the structural geometry issued from both photo-interpretation deduced from new unmanned aerial vehicle (UAV) high-resolution Digital Terrain Model data that we acquired (34.78 km(2) with 7.73 cm ground sampling distance), combined with geological field work. In order to characterize and quantify the present deformational patterns over the Pingting terraces, we used an InSAR time series Interferometry algorithm (MT-InSAR) applied to nine L-band SAR images from ALOS satellite acquired over the period 2007-2010. The unprecedented density of measurements (about 120 points per km(2) for a total of 6,400 points) gives a continuous overview of the inter-seismic shallow deformation. The structural geometry combined with the mean velocity map (MT-InSAR) reveals two clear active faults situated above the scarps of the Pingting terraces and responsible for up to 7 and 20 mm/yr velocity offsetalong the radar line of sight. A temporal analysis of the deformation is performed with one measurement at each SAR acquisition date, giving major improvements in the characterization and quantification of the Longitudinal Valley active Fault trace.
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Del Gaudio, S., Hok, S., Festa, G., Causse, M., & Lancieri, M. (2017). Near-Fault Broadband Ground Motion Simulations Using Empirical Green's Functions: Application to the Upper Rhine Graben (France-Germany) Case Study. Pure And Applied Geophysics, 174(9), 3479–3501.
Résumé: Seismic hazard estimation relies classically on data-based ground motion prediction equations (GMPEs) giving the expected motion level as a function of several parameters characterizing the source and the sites of interest. However, records of moderate to large earthquakes at short distances from the faults are still rare. For this reason, it is difficult to obtain a reliable ground motion prediction for such a class of events and distances where also the largest amount of damage is usually observed. A possible strategy to fill this lack of information is to generate synthetic accelerograms based on an accurate modeling of both extended fault rupture and wave propagation process. The development of such modeling strategies is essential for estimating seismic hazard close to faults in moderate seismic activity zones, where data are even scarcer. For that reason, we selected a target site in Upper Rhine Graben (URG), at the French-German border. URG is a region where faults producing micro-seismic activity are very close to the sites of interest (e.g., critical infrastructures like supply lines, nuclear power plants, etc.) needing a careful investigation of seismic hazard. In this work, we demonstrate the feasibility of performing near-fault broadband ground motion numerical simulations in a moderate seismic activity region such as URG and discuss some of the challenges related to such an application. The modeling strategy is to couple the multi-empirical Green's function technique (multi-EGFt) with a k (-2) kinematic source model. One of the advantages of the multi-EGFt is that it does not require a detailed knowledge of the propagation medium since the records of small events are used as the medium transfer function, if, at the target site, records of small earthquakes located on the target fault are available. The selection of suitable events to be used as multi-EGF is detailed and discussed in our specific situation where less number of events are available. We then showed the impact that each source parameter characterizing the k(-2) model has on ground motion amplitude. Finally we performed ground motion simulations showing results for different probable earthquake scenarios in the URG. Dependency of ground motions and of their variability are analyzed at different frequencies in respect of rupture velocity, roughness degree of slip distribution (stress drop), and hypocenter location. In near-source conditions, ground motion variability is shown to be mostly governed by the uncertainty on source parameters. In our specific configuration (magnitude, distance), the directivity effect is only observed in a limited frequency range. Rather, broadband ground motions are shown to be sensitive to both average rupture velocity and its possible variability, and to slip roughness. Ending up with a comparison of simulation results and GMPEs, we conclude that source parameters and their variability should be set up carefully to obtain reliable broadband ground motion estimations. In particular, our study shows that slip roughness should be set up in respect of the target stress drop. This entails the need for a better understanding of the physics of earthquake source and its incorporation in the ground motion modeling.
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del Real, A. E. P., Silvan, J. M., de Pascual-Teresa, S., Guerrero, A., Garcia-Gonzalo, P., Lobo, M. C., et al. (2017). Role of the polycarboxylic compounds in the response of Silene vulgaris to chromium. Environmental Science And Pollution Research, 24(6), 5746–5756.
Résumé: This work aims to investigate the nature and the specific mechanisms by which polycarboxylic compounds participate in the tolerance of Silene vulgaris to Cr with special attention given to the rhizosphere system. This knowledge is important to use this species in the implementation of phytoremediation technologies in Cr-polluted soils. According to the results, chromium is chelated and mobilized by the citric and malic acids in plant tissues, while oxalic acid might participate in the reduction and chelation of Cr in the rhizosphere. At the applied doses, the response of both exudation rate and root exudate composition (total polyphenols and quercitin) seems to involve a rearrangement in the lignification of the plant cell wall to immobilize Cr. Quercetin-3-dirhamnosyl-galactoside and apiin (apigenin-7-O-apiosyl-glucoside) have been identified as the major polyphenols in the root exudates of S. vulgaris. The increments found in the apiin concentration in root exudates seem to be related to the protection against Cr toxicity by chelation of Cr or by free radical scavenging. Though earlier response is detected in plant tissues, results from this work together with previous studies in S. vulgaris indicate that exudation might be a regulated mechanism of protection under Cr exposition in S. vulgaris that may involve mainly Cr reduction and chelation.
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Deng, Y., Shi, X., Xu, H., Sun, Y., Wu, J., & Revil, A. (2017). Quantitative assessment of electrical resistivity tomography for monitoring DNAPLs migration – Comparison with high-resolution light transmission visualization in laboratory sandbox. Journal Of Hydrology, 544, 254–266.
Résumé: Real-time monitoring of dense non-aqueous phase liquids (DNAPLs) migration and distribution is essential for the decision of an effective remediation strategy. Light transmission visualization (LTV) has shown its accuracy and efficiency for measuring DNAPLs saturation and water content in the laboratory, but it cannot be implemented in three dimensional sandbox or field-scale sites. Recently developed electrical resistivity tomography (ERT) has been applied in monitoring the migration and distribution of DNAPLs in bench- and field-scale studies. However, the evaluation of the ability of ERT for monitoring DNAPLs migration by a direct comparison of ERT with high-resolution techniques such as LTV within an experimental system is still lacking. Two sandbox experiments with different permeability conditions are conducted to quantitatively assess the capability of ERT for monitoring the DNAPLs migration. During the injections, LTV method is used to visualize the DNAPLs migration and provide high-resolution saturation data while ERT method is applied to capture the change of resistivity. The results from the comparison between LTV and ERT methods show that ERT is successful in detecting the accumulation and flow bypassing phenomenon around the low-permeability lenses, as well as the penetration through the high permeability lenses. There is a fair correlation between the resistivity and saturation with overall correlation coefficients above 0.6, except at last stage. However, using classical regularization techniques (based on smoothness), the area of DNAPLs plume determined by ERT is commonly overestimated. Compared to the plume around the low-permeability lenses, the plume around the high-permeability lenses estimated by ERT is more extensive due to larger resistivity contrasts. In addition, ERT measurements indicate that the resistivity increase caused by the low-saturation DNAPLs is not apparent enough, which is likely to be covered up under the changing hydrogeochemical environments in field investigations. (C) 2016 Elsevier B.V. All rights reserved.
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Derras, B., Bard, P. - Y., & Cotton, F. (2017). V-S30, slope, H-800 and f(0): performance of various site-condition proxies in reducing ground-motion aleatory variability and predicting nonlinear site response. Earth Planets And Space, 69.
Résumé: The aim of this paper is to investigate the ability of various site-condition proxies (SCPs) to reduce ground-motion aleatory variability and evaluate how SCPs capture nonlinearity site effects. The SCPs used here are time-averaged shear-wave velocity in the top 30 m (V-S30), the topographical slope (slope), the fundamental resonance frequency (f(0)) and the depth beyond which V-s exceeds 800 m/s (H800). We considered first the performance of each SCP taken alone and then the combined performance of the 6 SCP pairs [V-S30-f(0)], [V-S30-H-800], [f(0)-slope], [H-800-slope], [V-S30-slope] and [f(0)-H-800]. This analysis is performed using a neural network approach including a random effect applied on a KiK-net subset for derivation of ground-motion prediction equations setting the relationship between various ground-motion parameters such as peak ground acceleration, peak ground velocity and pseudo-spectral acceleration PSA (T), and Mw, RJB, focal depth and SCPs. While the choice of SCP is found to have almost no impact on the median groundmotion prediction, it does impact the level of aleatory uncertainty. VS30 is found to perform the best of single proxies at short periods (T < 0.6 s), while f(0) and H-800 perform better at longer periods; considering SCP pairs leads to significant improvements, with particular emphasis on [V-S30-H-800] and [f(0)-slope] pairs. The results also indicate significant nonlinearity on the site terms for soft sites and that the most relevant loading parameter for characterising nonlinear site response is the “stiff” spectral ordinate at the considered period.
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Deschanel, S., Ben Rhouma, W., & Weiss, J. (2017). Acoustic emission multiplets as early warnings of fatigue failure in metallic materials. Scientific Reports, 7, Deschanel.
Résumé: Fatigue, i.e. the failure of mechanical structures under cycling loading, remains a considerable technological challenge as it occurs unexpectedly when the structure is operating apparently in a safe and steady state regime, without external signs of mechanical deterioration. Here we report for the first time, in different metallic materials, the detection of acoustic emissions specific of fatigue crack growth. These so-called acoustic multiplets are characterized by nearly identical waveforms, signature of a unique source, are repeatedly triggered over many successive loading cycles at the same stress level, and originate from a single location. They mark the slow, incremental propagation of a fatigue crack at each cycle, or the rubbing along its faces. Being specific to fatigue cracking, they can be used as early warnings of crack propagation, which will ultimately lead to structural failure. Their detection and characterization thus open the way towards a new, reliable monitoring of the onset of fatigue cracking during mechanical tests or within structures in service.
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Di Bartolomeo, M., Lacerra, G., Baillet, L., Chatelet, E., & Massi, F. (2017). Parametrical experimental and numerical analysis on friction-induced vibrations by a simple frictional system. Tribology International, 112, 47–57.
Résumé: This paper presents an experimental and numerical analysis on friction-induced vibrations arising from the frictional contact between two bodies in relative motion. The sliding contact has been reproduced within a mechanical system characterized by a simple dynamics, in order to better distinguish between the dynamic response of the system and the broadband excitation coming from the contact. The effects of some parameters, mainly relative velocity, roughness and normal load, on the magnitude and frequency content of the induced vibrations are investigated, also by comparing results from experimental measurements and simulations. A distinction between weak and strong coupling is recovered by the experimental results. Finally, accounting for the contribution of the roughness to the contact-induced vibrations, a conceptually innovative method to implement the effect of the roughness in the numerical simulation is proposed.
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Di Rosa, M., De Giorgi, A., Marroni, M., & Vidal, O. (2017). Syn-convergence exhumation of continental crust: evidence from structural and metamorphic analysis of the Monte Cecu area, Alpine Corsica (Northern Corsica, France). Geological Journal, 52(6), 919–937.
Résumé: In the Corsica Island, a stack of metamorphic continental units derived from the European continental margin is thrust over a pre-Alpine basement during the convergence-related processes in the Late Eocene-Early Miocene time span. The Piedigriggio-Prato Unit is representative of these units. Its tectono-metamorphic history has been reconstructed by an integrated approach, ranging from map- to meso- and microscopic scale analyses. This unit is characterized by a polyphase deformation history that consists of three deformation phases developed under retrograde metamorphism ranging from blueschist to sub-greenschist facies metamorphic conditions. At the map-scale, the Piedigriggio-Prato Unit is characterized by km-size isoclinal folds deformed by open to closed recumbent folds producing Type 3 fold interference pattern. The features of the deformations and the P-T conditions suggest that the first two phases were acquired during the ductile extrusion of the Piedigriggio-Prato Unit. Before the Early Miocene, the gravitational collapse of over-thickened continental crust produced vertical shortening and the consequently recumbent F3 folds. The exhumation history of the Piedigriggio-Prato Unit can be viewed as representative for the exhumation of a continental crust fragment during the transition from the continental subduction to the continental collision. Copyright (c) 2016 John Wiley & Sons, Ltd.
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Domingos, J., Jault, D., Pais, M. A., & Mandea, M. (2017). The South Atlantic Anomaly throughout the solar cycle. Earth And Planetary Science Letters, 473, 154–163.
Résumé: The Sun-Earth's interaction is characterized by a highly dynamic electromagnetic environment, in which the magnetic field produced in the Earth's core plays an important role. One of the striking characteristics of the present geomagnetic field is denoted the South Atlantic Anomaly (SAA) where the total field intensity is unusually low and the flux of charged particles, trapped in the inner Van Allen radiation belts, is maximum. Here, we use, on one hand, a recent geomagnetic field model, CHAOS-6, and on the other hand, data provided by different platforms (satellites orbiting the Earth – POES NOAA for 1998-2014 and CALIPSO for 2006-2014). Evolution of the SAA particle flux can be seen as the result of two main effects, the secular variation of the Earth's core magnetic field and the modulation of the density of the inner radiation belts during the solar cycle, as a function of the L value that characterises the drift shell, where charged particles are trapped. To study the evolution of the particle flux anomaly, we rely on a Principal Component Analysis (PCA) of either POES particle flux or CALIOP dark noise. Analysed data are distributed on a geographical grid at satellite altitude, based on a L-shell reference frame constructed from the moving eccentric dipole. Changes in the main magnetic field are responsible for the observed westward drift. Three PCA modes account for the time evolution related to solar effects. Both the first and second modes have a good correlation with the thermospheric density, which varies in response to the solar cycle. The first mode represents the total intensity variation of the particle flux in the SAA, and the second the movement of the anomaly between different L-shells. The proposed analysis allows us to well recover the westward drift rate, as well as the latitudinal and longitudinal solar cycle oscillations, although the analysed data do not cover a complete (Hale) magnetic solar cycle (around 22 yr). Moreover, the developments made here would enable us to forecast the impact of the South Atlantic Anomaly on space weather. A model of the evolution of the eccentric dipole field (magnitude, offset and tilt) would suffice, together with a model for the solar cycle evolution. (C) 2017 Elsevier B.V. All rights reserved.
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Doubre, E., Deprez, A., Masson, F., Socquet, A., Lewi, E., Grandin, R., et al. (2017). Current deformation in Central Afar and triple junction kinematics deduced from GPS and InSAR measurements. Geophysical Journal International, 208(2), 936–953.
Résumé: Kinematics of divergent boundaries and Rift-Rift-Rift junctions are classically studied using long-term geodetic observations. Since significant magma-related displacements are expected, short-term deformation provides important constraints on the crustal mechanisms involved both in active rifting and in transfer of extensional deformation between spreading axes. Using InSAR and GPS data, we analyse the surface deformation in the whole Central Afar region in detail, focusing on both the extensional deformation across the Quaternary magmato-tectonic rift segments, and on the zones of deformation transfer between active segments and spreading axes. The largest deformation occurs across the two recently activated Asal-Ghoubbet (AG) and Manda Hararo-Dabbahu (MH-D) magmato-tectonic segments with very high strain rates, whereas the other Quaternary active segments do not concentrate any large strain, suggesting that these rifts are either sealed during interdyking periods or not mature enough to remain a plate boundary. Outside of these segments, the GPS horizontal velocity field shows a regular gradient following a clockwise rotation of the displacements from the Southeast to the East of Afar, with respect to Nubia. Very few shallow creeping structures can be identified as well in the InSAR data. However, using these data together with the strain rate tensor and the rotations rates deduced from GPS baselines, the present-day strain field over Central Afar is consistent with the main tectonic structures, and therefore with the long-term deformation. We investigate the current kinematics of the triple junction included in our GPS data set by building simple block models. The deformation in Central Afar can be described by adding a central microblock evolving separately from the three surrounding plates. In this model, the northern block boundary corresponds to a deep EW-trending trans-tensional dislocation, locked from the surface to 10-13 km and joining at depth the active spreading axes of the Red Sea and the Aden Ridge, from AG to MH-D rift segments. Over the long-term, this plate configuration could explain the presence of the en-echelon magmatic basins and subrifts. However, the transient behaviour of the spreading axes implies that the deformation in Central Afar evolves depending on the availability of magma supply within the well-established segments.
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Dumont, S., Klinger, Y., Socquet, A., Doubre, C., & Jacques, E. (2017). Magma influence on propagation of normal faults: Evidence from cumulative slip profiles along Dabbahu-Manda-Hararo rift segment (Afar, Ethiopia). Journal Of Structural Geology, 95, 48–59.
Résumé: Measuring displacement-length profiles along normal faults provides crucial information on fault growth processes. Here, based on satellite imagery and topography we analyze 357 normal faults distributed along the active rift of Dabbahu-Manda-Hararo (DMH), Afar, which offers a unique opportunity to investigate the influence of magmatism on fault growth processes. Our measurements reveal a large variety of slip profiles that are not consistent with elastic deformation. Their analysis contributes towards a better understanding of the lateral propagation of faults, especially when nucleation points and existence of barriers are included. Using the fault growth model of Manighetti et al. (2001), we determine the preferred direction of lateral propagation for each fault. Our results suggest that lateral propagation of faults is easier away from areas where magma has been stored for long time at crustal depth, and has thus modified the thermo-mechanical properties of the host-rock. However, these areas correspond also to areas where the initiation of fault growth appears as easiest along the rift. In combining these results with the analysis of rift width and the position of magma reservoirs along DMH rift, we show that fault growth keeps track of the magma presence and/or movement in the crust. (C) 2016 Elsevier Ltd. All rights reserved.
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Dunkel, K. G., Austrheim, H., Renard, F., Cordonnier, B., & Jamtveit, B. (2017). Localized slip controlled by dehydration embrittlement of partly serpentinized dunites, Leka Ophiolite Complex, Norway. Earth And Planetary Science Letters, 463, 277–285.
Résumé: Dehydration of partly or completely serpentinized ultramafic rocks can increase the pore fluid pressure and induce brittle failure, a process referred to as dehydration embrittlement. However the extents of strain localization and unstable frictional sliding during deserpentinization are still under debate. In the layered ultramafic sections of the Leka Ophiolite Complex in the Central Norwegian Caledonides, prograde metamorphism of serpentinite veins led to local fluid production and to the growth of Mg-rich and coarse- grained olivine with abundant magnetite inclusions and delta O-18 values 1.0- 1.5 % below the host rock. Embrittlement associated with the dehydration caused faulting along highly localized (<10 μm-wide) slip planes near the centers of the original serpentinite veins and pulverization of wall rock olivine. These features along with an earthquake-like size distribution of fault offsets suggest unstable frictional sliding rather than slower creep. Structural heterogeneities in the form of serpentinite veins clearly have first-order controls on strain localization and frictional sliding during dehydration. As most of the oceanic lithosphere is incompletely serpentinized, heterogeneities represented by a non-uniform distribution of serpentinite are common and may increase the likelihood that dehydration embrittlement triggers earthquakes.(C) 2017 Elsevier B. V. All rights reserved.
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Economos, R., Boehnke, P., & Burgisser, A. (2017). Sulfur isotopic zoning in apatite crystals: A new record of dynamic sulfur behavior in magmas. Geochimica Et Cosmochimica Acta, 215, 387–403.
Résumé: The mobility and geochemical behavior of sulfur in magmas is complex due to its multi-phase (solid, immiscible liquid, gaseous, dissolved ions) and multi-valent (from S-2 to S6+) nature. Sulfur behavior is closely linked with the evolution of oxygen fugacity (fO(2)) in magmas; the record of fO(2) evolution is often enigmatic to extract from rock records, particularly for intrusive systems. We apply a novel method of measuring S isotopic ratios in zoned apatite crystals that we interpret as a record of open-system magmatic processes. We interrogate the S concentration and isotopic variations preserved in multiple apatite crystals from single hand specimens from the Cadiz Valley Batholith, CA via electron microprobe and ion microprobe. Isotopic variations in single apatite crystals ranged from 0 to 3.8% delta S-34 and total variation within a single hand sample was 6.1% delta S-34. High S concentration cores yielded high isotopic ratios while low S concentration rims yielded low isotopic ratios. We discuss a range of possible natural scenarios and favor an explanation of a combination of magma mixing and opensystem, ascent-driven degassing under moderately reduced conditions: fO(2) at or below NNO+1, although the synchronous crystallization of apatite and anhydrite is also a viable scenario. Our conclusions have implications for the coupled S and fO(2) evolution of granitic plutons and suggest that in-situ apatite S isotopic measurements could be a powerful new tool for evaluating redox and S systematics in magmatic systems. (C) 2017 Elsevier Ltd. All rights reserved.
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El Goresy, A., Lin, Y., Miyahara, M., Gannoun, A., Boyet, M., Ohtani, E., et al. (2017). Origin of EL3 chondrites: Evidence for variable C/O ratios during their course of formationA state of the art scrutiny. Meteoritics & Planetary Science, 52(5), 781–806.
Résumé: Mineral inventories of enstatite chondrites; (EH and EL) are strictly dictated by combined parameters mainly very low dual oxygen (fO(2)) and sulfur (fS(2)) fugacities. They are best preserved in the Almahata Sitta MS-17, MS-177 fragments, and the ALHA 77295 and MAC 88136 Antarctic meteorites. These conditions induce a stark change of the geochemical behavior of nominally lithophile elements to chalcophile or even siderophile and changes in the elemental partitioning thus leading to formation of unusual mineral assemblages with high abundance of exotic sulfide species and enrichment in the metallic alloys, for example, silicides and phosphides. Origin and mode of formation of these exotic chondrites, and their parental source regions could be best scrutinized by multitask research experiments of the most primitive members covering mineralogical, petrological, cosmochemical, and indispensably short-lived isotopic chronology. The magnitude of temperature and pressure prevailed during their formation in their source regions could eventually be reasonably estimated: pre- and postaccretionary could eventually be deduced. The dual low fugacities are regulated by the carbon to oxygen ratios estimated to be >0.83 and <1.03. These parameters not only induce unusual geochemical behavior of the elements inverting many nominally lithophile elements to chalcophile or even siderophile or anthracophile. Structure and mineral inventories in EL3 and EH3 chondrites are fundamentally different. Yet EH3 and EL3 members store crucial information relevant to eventual source regions and importantly possible variation in C/O ratio in the course of their evolution. EL3 and EH3 chondrites contain trichotomous lithologies (1) chondrules and their fragments, (2) polygonal enstatite-dominated objects, and (3) multiphase metal-rich nodules. Mineralogical and cosmochemical inventories of lithologies in the same EL3 indicate not only similarities (REE inventory and anomalies in oldhamite) but also distinct differences (sinoite-enstatite-graphite relationship). Oldhamite in chondrules and polygonal fragments in EL3 depict negative Eu anomaly attesting a common cosmochemical source. Metal-dominated nodules in both EL3 and EH3 are conglomerates of metal clasts and sulfide fragments in EH3 and concentrically zoned C-bearing metal micropebbles (25m 50m) in EL3 thus manifesting a frozen in unique primordial accretionary metal texture and composition. Sinoite-enstatite-diopside-graphite textures reveal a nucleation and growth strongly suggestive of fluctuating C/O ratio during their nucleation and growth in the source regions. Mineral inventories, sulfide phase relations, sinoite-enstatite-graphite intergrowth, carbon and nitrogen isotopic compositions of graphite, spatial nitrogen abundance in graphite in metal nodules, and last but not least I-129/Xe-129 and Mn-53/Cr-53 systematics negate any previously suggested melting episode, pre-accretionary or dynamic, in parental asteroids.
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Fayjaloun, R., Causse, M., Voisin, C., Cornou, C., & Cotton, F. (2017). Spatial Variability of the Directivity Pulse Periods Observed during an Earthquake. Bulletin Of The Seismological Society Of America, 107(1), 308–318.
Résumé: The ground velocity pulses generated by rupture directivity effects in the near-fault region can cause a large amount of damage to structures. Proper estimation of the period of such velocity pulses is of particular importance in characterizing near-fault seismic hazard and mitigating potential damage. We propose a simple equation to determine the pulse period as a function of the site location with respect to the fault rupture (defined by the hypocentral distance hypD, the closest distance to the rupture area clsD, and the length of the rupture area that breaks toward the site D) and some basic rupture properties (average rupture speed and average rise time). Our equation is first validated from a dataset of synthetic velocity time histories, deploying simulations of various strike-slip extended ruptures in a homogeneous medium. The analysis of the synthetic dataset confirms that the pulse period does not depend on the whole rupture area, but only on the parameter D. It also reveals that the pulse period is not sensitive to the level of slip heterogeneity on the fault plane. Our model is tested next on a real dataset build from the Next Generation Attenuation-West2 Project database, compiling 110 observations of velocity pulse periods from 10 strike-slip events and 6 non-strike-slip events. The standard deviation of the natural logarithm residuals between observations and predictions is similar to 0.5. Furthermore, the correlation coefficient between observations and predictions equals similar to 0.8, indicating that despite its simplicity, our model explains fairly well the spatial variability of the pulse periods.
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Fichtner, A., Stehly, L., Ermert, L., & Boehm, C. (2017). Generalized interferometry – I: theory for interstation correlations. Geophysical Journal International, 208(2), 603–638.
Résumé: We develop a general theory for interferometry by correlation that (i) properly accounts for heterogeneously distributed sources of continuous or transient nature, (ii) fully incorporates any type of linear and nonlinear processing, such as one-bit normalization, spectral whitening and phase-weighted stacking, (iii) operates for any type of medium, including 3-D elastic, heterogeneous and attenuating media, (iv) enables the exploitation of complete correlation waveforms, including seemingly unphysical arrivals, and (v) unifies the earthquake-based two-station method and ambient noise correlations. Our central theme is not to equate interferometry with Green function retrieval, and to extract information directly from processed interstation correlations, regardless of their relation to the Green function. We demonstrate that processing transforms the actual wavefield sources and actual wave propagation physics into effective sources and effective wave propagation. This transformation is uniquely determined by the processing applied to the observed data, and can be easily computed. The effective forward model, that links effective sources and propagation to synthetic interstation correlations, may not be perfect. A forward modelling error, induced by processing, describes the extent to which processed correlations can actually be interpreted as proper correlations, that is, as resulting from some effective source and some effective wave propagation. The magnitude of the forward modelling error is controlled by the processing scheme and the temporal variability of the sources. Applying adjoint techniques to the effective forward model, we derive finite-frequency Frechet kernels for the sources of the wavefield and Earth structure, that should be inverted jointly. The structure kernels depend on the sources of the wavefield and the processing scheme applied to the raw data. Therefore, both must be taken into account correctly in order to make accurate inferences on Earth structure. Not making any restrictive assumptions on the nature of the wavefield sources, our theory can be applied to earthquake and ambient noise data, either separately or combined. This allows us (i) to locate earthquakes using interstation correlations and without knowledge of the origin time, (ii) to unify the earthquake-based two-station method and noise correlations without the need to exclude either of the two data types, and (iii) to eliminate the requirement to remove earthquake signals from noise recordings prior to the computation of correlation functions. In addition to the basic theory for acoustic wavefields, we present numerical examples for 2-D media, an extension to the most general viscoelastic case, and a method for the design of optimal processing schemes that eliminate the forward modelling error completely. This work is intended to provide a comprehensive theoretical foundation of full-waveform interferometry by correlation, and to suggest improvements to current passive monitoring methods.
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Fondriest, M., Doan, M. - L., Aben, F., Fusseis, F., Mitchell, T. M., Voorn, M., et al. (2017). Static versus dynamic fracturing in shallow carbonate fault zones. Earth And Planetary Science Letters, 461, 8–19.
Résumé: Moderate to large earthquakes often nucleate within and propagate through carbonates in the shallow crust. The occurrence of thick belts of low-strain fault-related breccias is relatively common within carbonate damage zones and was generally interpreted in relation to the quasi-static growth of faults. Here we report the occurrence of hundreds of meters thick belts of intensely fragmented dolostones along a major transpressive fault zone in the Italian Southern Alps. These fault rocks have been shattered in-situ with negligible shear strain accumulation. The conditions of in-situ shattering were investigated by deforming the host dolostones in uniaxial compression both under quasi-static (strain rate similar to 10(-5) s(-1)) and dynamic (strain rate >50 s(-1)) loading. Dolostones deformed up to failure under low-strain rate were affected by single to multiple discrete extensional fractures sub-parallel to the loading direction. Dolostones deformed under high-strain rate were shattered above a strain rate threshold of similar to 120 s(-1) and peak stresses on average larger than the uniaxial compressive strength of the rock, whereas they were split in few fragments or remained macroscopically intact at lower strain rates. Fracture networks were investigated in three dimensions showing that low- and high-strain rate damage patterns (fracture intensity, aperture, orientation) were significantly different, with the latter being similar to that of natural in-situ shattered dolostones (i.e., comparable fragment size distributions). In-situ shattered dolostones were thus interpreted as the result of high energy dynamic fragmentation (dissipated strain energies >1.8 MJ/m(3)) similarly to pulverized rocks in crystalline lithologies. Given their seismic origin, the presence of in-situ shattered dolostones can be used in earthquake hazard studies as evidence of the propagation of seismic ruptures at shallow depths. (C) 2016 Elsevier B.V. All rights reserved.
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Fouinat, L., Sabatier, P., Poulenard, J., Etienne, D., Crouzet, C., Develle, A. - L., et al. (2017). One thousand seven hundred years of interaction between glacial activity and flood frequency in proglacial Lake Muzelle (western French Alps). Quaternary Research, 87(3), 407–422.
Résumé: Local glacial fluctuations and flood occurrences were investigated in the sediment sequence of proglacial Lake Muzelle. Based on geochemical analysis and organic matter content established using loss on ignition and reflectance spectroscopy, we identified six periods of increased glacial activity over the last 1700 yr. Each is in accordance with records from reference glaciers in the Alps. A total of 255 graded layers were identified and interpreted as flood deposits. Most of these occurred during glacial advances such as the Little Ice Age period and exhibit thicker deposits characterized by an increase in the fine grain-size fraction. Fine sediment produced by glacial activity is transported to the proglacial lake during heavy rainfall events. The excess of glacial flour during these periods seems to increase the watershed's tendency to produce flood deposits in the lake sediment, suggesting a strong influence of the glacier on flood reconstruction records. Thus, both flood frequency and intensity, which is estimated based on layer thickness as a proxy, cannot be used in reconstruction of past extreme events because of their variability. There is a need to take into account changes in sediment supply in proglacial areas that could preclude satisfactory interpretation of floods in terms of past climate variability.
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Frank, W. B., Poli, P., & Perfettini, H. (2017). Mapping the rheology of the Central Chile subduction zone with aftershocks. Geophysical Research Letters, 44(11), 5374–5382.
Résumé: The postseismic deformation following a large (M-w>7) earthquake is expressed both seismically and aseismically. Recent studies have appealed to a model that suggests that the aseismic slip on the plate interface following the mainshock can be the driving factor in aftershock sequences, reproducing both the geodetic (afterslip) and seismic (aftershocks) observables of postseismic deformation. Exploiting this model, we demonstrate how a dense catalog of aftershocks following the 2015 M(w)8.3 Illapel earthquake in Central Chile can constrain the frictional and rheological properties of the creeping regions of the subduction interface. We first expand the aftershock catalog via a 19month continuous matched-filter search and highlight the log-time expansion of seismicity following the mainshock, suggestive of afterslip as the main driver of aftershock activity. We then show how the time history of aftershocks can constrain the temporal evolution of afterslip. Finally, we use our dense aftershock catalog to estimate the rate and state rheological parameter (a – b)sigma as a function of depth and demonstrate that this low value is compatible either with a nearly velocity-neutral friction (a approximate to b) in the regions of the megathrust that host afterslip, or an elevated pore fluid pressure (low effective normal stress sigma) along the plate interface. Our results present the first snapshot of rheology in depth together with the evolution of the tectonic stressing rate along a plate boundary. The framework described here can be generalized to any tectonic context and provides a novel way to constrain the frictional properties and loading conditions of active faults. Plain Language Summary The slow postseismic deformation, or afterslip, that lasts several years following a major earthquake can be as strong as the earthquake itself and is therefore a key component in understanding the seismic hazard along tectonic plate boundaries. Afterslip is typically studied with GPS that measures the deformation at the surface, but with a low spatial precision. It is therefore difficult, if not impossible, to tease out the finer details of how the plate interface responds to a large earthquake and to identify which parts of the plate interface could rupture next. Here we develop a new framework to study what happens after a major earthquake using the precise evolution in time and space of aftershocks. We leverage the high-resolution aftershock distribution to determine how the friction of the plate boundary varies in depth, which allows us to better understand which parts of the plate interface are susceptible to afterslip. Our methods described here can be generalized to any tectonic plate boundary and provide a novel way to constrain how active faults are influenced by major earthquakes.
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Frery, E., Gratier, J. - P., Ellouz-Zimmerman, N., Deschamps, P., Blamart, D., Hamelin, B., et al. (2017). Geochemical transect through a travertine mount: A detailed record of CO2-enriched fluid leakage from Late Pleistocene to present-day – Little Grand Wash fault (Utah, USA). Quaternary International, 437, 98–106.
Résumé: Active and fossil endogenic travertine mounts scattered along the Little Grand Wash fault are studied as records of Quaternary CO2-enriched fluid leakage. This study focusses on a particular area where a fossil mount formed in a near-surface setting by successive circulation/sealing episodes from Late Pleistocene to Mid-Holocene and where a modern surface travertine is still being formed by a CO2-enriched fluid source. The fossil mount is composed of horizontal and vertical veins whereby the vertical veins recorded numerous cycles of circulation/sealing/dissolution events and were used as conduits for the CO2-enriched fluid circulation from the depth to the surface or along sub-horizontal fractures where successive precipitation events are recorded. The modern travertine is being built at the surface by successive eruption of Crystal Geyser, an anthropic geyser active since the 1930's. delta C-13 and delta O-18 signatures and U/Th datings, ranging from 11.5 ky till present-day allows calibrating in detail the CO2-enriched fluid leakage along a single fault segment and in a post glacial context, as last glaciations in the study area took place 15 ky ago. The dataset shows a high decrease of the oxygen stable isotope values till about 6 ky, then the variations reflect a constant range until present-day. This tends to restrain the period of local increase of the meteoric water input in the aquifer that is sourcing the CO2-enriched water. The fossil travertine represents a 7 ky-long record of CO2 leakage above a natural reservoir, from Late Pleistocene to Mid-Holocene. The flux of CO2 leakage through time and the total escaping volume have been computed and appears to be low in comparison with an anthropogenic leak provoked, for instance, by a non-sealed well. (C) 2016 Elsevier Ltd and INQUA. All rights reserved.
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Garcia-Gonzalo, P., del Real, A. E. P., Pirredda, M., Gismera, M. J., Lobo, M. C., & Perez-Sanz, A. (2017). Phytoavailability of Cr in Silene vulgaris: The role of soil, plant genotype and bacterial rhizobiome. Ecotoxicology And Environmental Safety, 144, 283–290.
Résumé: Understanding the metal behavior at the soil-root interface is of utmost significance for a successful implementation of phytoremediation. In this study, we investigated the differences in chromium (Cr) uptake, chemical changes in soil solution and the shifts in rhizosphere bacterial communities of two genotypes of Silene vulgaris (SV21, SV38) with different tolerance to Cr. A greenhouse experiment was performed in two soils that differed on pH and organic matter (OM) content. An industrial sludge with high content in Cr was used as pollution source. The soil solution in the rhizosphere was sample by Rhizon Soil Moisture Samplers. The total concentration of Cr reached the highest values in soil solution samplers from calcareous soils with poor contents in OM. Plants grown in this soil also increased the Cr uptake in roots of both genotypes, but the concentration was higher in genotype SV-38 than in SV21. The clustering analysis of denaturing gradient gel electrophoresis (DGGE) of 16S rRNA fragments revealed major differences in bacterial community structure related to Cr pollution, followed by soil type and finally, plant genotype. Diversity indices based on DGGE profiles were the highest in alkaline soil, and between genotypes, values were significantly greater in SV38. Canonical conespondence analysis (CCA) showed that changes in bacterial community structure of rhizosphere were highly correlated with total Cr concentration and soil solution pH. The isolation and identification of S. vulgaris bacterial rhizosphere revealed a different composition according to soil type and plant genotype. Results suggested the potential role of Pseudomonas fluorescens on Cr mobilization and therefore, on enhanced metal bioavailability and may provide a starting point for further studies aimed at the combined use of tolerant plants and selected metal mobilizing rhizobacteria, in the microbial-assisted phytoremediation of Cr-polluted soils.
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Garcia-Gonzalo, P., Pradas del Real, A. E., Lobo, M. C., & Perez-Sanz, A. (2017). Different genotypes of Silene vulgaris (Moench) Garcke grown on chromium-contaminated soils influence root organic acid composition and rhizosphere bacterial communities. Environmental Science And Pollution Research, 24(33), 25713–25724.
Résumé: Plant-microbe interactions are considered to be important processes determining the efficiency of phytoremediation of heavy metal-contaminated soils. However, relatively little is known about how these interactions are influenced by chromium (Cr) contamination. The effect of Cr stress on metal uptake, root organic acid composition, and rhizosphere bacterial communities was studied using two genotypes of the metallophyte Silene vulgaris, which have shown different tolerance to Cr(VI). The results indicated that root biomass and shoot biomass were not significantly influenced by Cr treatment, but metal uptake in shoots and roots was significantly impacted by the genotype. Principal component analyses (PCA) showed that variation in organic acids oxalic, citric, malic, formic, lactic, acetic, and succinic differed between genotypes. Changes in root organic acid contents in response to Cr revealed a significant increase of oxalic acid in genotype SV-21. The denaturing gradient gel electrophoresis (DGGE) cluster analysis showed that the community structure (determined by PCR-DGGE) was affected by plant genotype and, to a lesser extent, by Cr contamination, the first being the most influential factor shaping the rhizosphere microbiome. Under Cr pollution, a shift in the relative abundance of specific taxa was found and dominant phylotypes were identified as Variovorax in SV-21 and Chitinophaga niastensis, Pontibacter sp., and Ramlibacter sp. in SV-38. These results provided the basis for further studies aimed at the combined use of plants and soil microorganisms in the remediation of Cr-polluted soils.
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Garcon, M., Carlson, R. W., Shirey, S. B., Arndt, N. T., Horan, M. F., & Mock, T. D. (2017). Erosion of Archean continents: The Sm-Nd and Lu-Hf isotopic record of Barberton sedimentary rocks. Geochimica Et Cosmochimica Acta, 206, 216–235.
Résumé: Knowing the composition, nature and amount of crust at the surface of the early Earth is crucial to understanding the early geodynamics of our planet. Yet our knowledge of the Hadean-Archean crust is far from complete, limited by the poor preservation of Archean terranes, and the fact that less attention has been paid to the sedimentary record that tracks erosion of these ancient remnants. To address this problem and get a more comprehensive view of what an Archean continent may have looked like, we investigated the trace element and Sm-Nd, Lu-Hf isotopic records of Archean metasedimentary rocks from South Africa. We focused our study on sandstone and mudstone from drill core in the Fig Tree Group (3.23-3.26 Ga) of the Barberton granite-greenstone belt, but also analyzed the 3.4 Ga Buck Reef cherts and still older (3.5-3.6 Ga) meta-igneous rocks from the Ancient Gneiss Complex, Swaziland. Based on principal component analysis of major and trace element data, the Fig Tree metasedimentary rocks can be classified into three groups: crustal detritus-rich sediments,Si-rich sediments and Ca-, Fe-rich sediments. The detritus-rich sediments have preserved the Sm-Nd and Lu-Hf isotopic signatures of their continental sources, and hence can be used to constrain the composition of crust eroded in the Barberton area in the Paleoarchean period. Based on Sm/Nd ratios, we estimate that this crust was more mafic than today, with an average SiO2 content of 60.5 +/- 2 wt.%. This composition is further supported by isotopic mixing calculations suggesting that the sedimentary source area contained equal proportions of mafic-ultramafic and felsic rocks. This implies that the Archean crust exposed to weathering was more mafic than today but does not exclude a more felsic composition at depth. Neodymium and Hf crustal residence ages show that the eroded crust was, on average, similar to 300-400 Ma older than the deposition age of the sediments, which highlights the importance of intracrustal reworking of older crust at similar to 3.2 Ga in the Barberton area. The Si-rich sediments have slightly positive epsilon(Nd) ((t=3.23Ga)) but extremely radiogenic epsilon(Hf) ((t=3.23Ga)), up to +11. Based on analyses of 3.4 Ga Buck Reef cherts, we suggest that the radiogenic Hf isotopic signature of the Si-rich sediments can be accounted for by the old chert clasts or detrital silicified rock fragments present in the rocks. The latter have extremely high Lu/Hf ratios such that their eHf values would increase dramatically, by about +100 epsilon units every 100 Ma. In the Ca-, Fe-rich sediments, one sample contains carbonate that preserves the typical rare-earth element features of seawater precipitates. The initial Nd isotopic composition of this sample (epsilon(Nd) ((t=3.23Ga))=+1.7) is within the range of previous estimates for Archean anoxic seawater. (C) 2017 Elsevier Ltd. All rights reserved.
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Garnier, V., Payan, C., Lott, M., Ranaivomanana, N., Balayssac, J. P., Verdier, J., et al. (2017). Non-destructive Evaluation of Containment Walls in Nuclear Power Plants (Vol. 1806).
Résumé: Two functions are regularly tested on containment walls in order to anticipate a possible accident. The first is mechanical to resist a possible internal over-pressure and the second is to prevent leakage. The AAPR reference accident is the rupture of a pipe in the primary circuit of a nuclear plant. In this case, the pressure and temperature can reach 5 bar and 180 C in 20 seconds. The national project Non-destructive testing of the containment structures of nuclear plants' aims at studying the non-destructive techniques capable to evaluate the concrete properties and its damaging and cracks. This 4-year-project is segmented into two parts. The first consists in developing and selecting the most relevant NDEs in the laboratory to reach these goals. These evaluations are developed in conditions representing the real conditions of the stresses generated during ten-yearly visits of the plants or those related to an accident. The second part consists in applying the selected techniques to two containment structures under pressure. The first structure is proposed by ONERA and the second is a mockup of a containment wall on a 1/3 scale made by EDF within the VeRCoRs project. Communication is focused on the part of the project that concerns the damage and crack process characterization by means of NDT. The tests are done in 3 or 4 points bending in order to study the cracks' generation, their propagation, as well as their opening and closing. The main ultrasonic techniques developed concern linear or non-linear acoustic: acoustic emission [1], Locadiff [2], energy diffusion, surface wave's velocity and attenuation, DAET [3]. The recorded data contribute to providing the mapping of the investigated parameters, either in volume, in surface or globally. Digital image correlation is an important additional asset to validate the coherence of the data. The spatial normalization of the data in the specimen space allows proposing algorithms on the combination of the experimental data. The tests results are presented and they show the capacity and the limits of the evaluation of the volume, surface or global data. A data fusion procedure is associated with these results.
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Gaschnig, R. M., Reinhard, C. T., Planavsky, N. J., Wang, X., Asael, D., & Chauvel, C. (2017). The Molybdenum Isotope System as a Tracer of Slab Input in Subduction Zones: An Example From Martinique, Lesser Antilles Arc. Geochemistry Geophysics Geosystems, 18(12), 4674–4689.
Résumé: Molybdenum isotopes are fractionated by Earth-surface processes and may provide a tracer for the recycling of crustal material into the mantle. Here, we examined the Mo isotope composition of arc lavas from Martinique in the Lesser Antilles arc, along with Cretaceous and Cenozoic Deep Sea Drilling Project sediments representing potential sedimentary inputs into the subduction zone. Mo stable isotope composition (defined as delta(98) Mo in %o deviation from the NIST 3134 standard) in lavas older than similar to 7 million years (Ma) exhibits a narrow range similar to and slightly higher than MORB, whereas those younger than similar to 7 Ma show a much greater range and extend to unusually low delta Mo-98 values. Sediments from DSDP Leg 78A, Site 543 have uniformly low d delta Mo-98 values whereas Leg 14, Site 144 contains both sediments with isotopically light Mo and Mo-enriched black shales with isotopically heavy Mo. When coupled with published radiogenic isotope data, Mo isotope systematics of the lavas can be explained through binary mixing between a MORB-like end-member and different sedimentary compositions identified in the DSDP cores. The lavas older than similar to 7 Ma were influenced by incorporation of isotopically heavy black shales into the mantle wedge. The younger lavas are the product of mixing isotopically light sedimentary material into the mantle wedge. The change in Mo isotope composition of the lavas at similar to 7 Ma is interpreted to reflect the removal of the Cretaceous black shale component due to the arrival of younger ocean crust where the age-equivalent Cretaceous sediments were deposited in shallower oxic waters. Isotopic fractionation of Mo during its removal from the slab is not required to explain the observed systematics in this system.
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Gavilan, L., Remusat, L., Roskosz, M., Popescu, H., Jaouen, N., Sandt, C., et al. (2017). X-Ray-induced Deuterium Enrichment of N-rich Organics in Protoplanetary Disks: An Experimental Investigation Using Synchrotron Light. Astrophysical Journal, 840(1).
Résumé: The deuterium enrichment of organics in the interstellar medium, protoplanetary disks, and meteorites has been proposed to be the result of ionizing radiation. The goal of this study is to simulate and quantify the effects of soft X-rays (0.1-2 keV), an important component of stellar radiation fields illuminating protoplanetary disks, on the refractory organics present in the disks. We prepared tholins, nitrogen-rich organic analogs to solids found in several astrophysical environments, e.g., Titan's atmosphere, cometary surfaces, and protoplanetary disks, via plasma deposition. Controlled irradiation experiments with soft X-rays at 0.5 and 1.3 keV were performed at the SEXTANTS beamline of the SOLEIL synchrotron, and were immediately followed by ex-situ infrared, Raman, and isotopic diagnostics. Infrared spectroscopy revealed the preferential loss of singly bonded groups (N-H, C-H, and R-N equivalent to C) and the formation of sp(3) carbon defects with signatures at similar to 1250-1300 cm(-1). Raman analysis revealed that, while the length of polyaromatic units is only slightly modified, the introduction of defects leads to structural amorphization. Finally, tholins were measured via secondary ion mass spectrometry to quantify the D, H, and C elemental abundances in the irradiated versus non-irradiated areas. Isotopic analysis revealed that significant D-enrichment is induced by X-ray irradiation. Our results are compared to previous experimental studies involving the thermal degradation and electron irradiation of organics. The penetration depth of soft X-rays in μm-sized tholins leads to volume rather than surface modifications: lower-energy X-rays (0.5 keV) induce a larger D-enrichment than 1.3 keV X-rays, reaching a plateau for doses larger than 5 x 10(27) eV cm(-3). Synchrotron fluences fall within the expected soft X-ray fluences in protoplanetary disks, and thus provide evidence of a new non-thermal pathway to deuterium fractionation of organic matter.
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Gemignani, L., Sun, X., Braun, J., van Gerve, T. D., & Wijbrans, J. R. (2017). A new detrital mica Ar-40/Ar-39 dating approach for provenance and exhumation of the Eastern Alps. Tectonics, 36(8), 1521–1537.
Résumé: Detrital thermochronology can be used as a tool to quantitatively constrain exhumation rates and its spatial variability from active mountain belts. Commonly used methods for this purpose assume a steady state relationship between tectonic uplift and erosion. However, this assumption does not account for the transitory response of a dynamic orogenic system to changes in the boundary conditions. We propose a different approach that uses the observed detrital age distributions as markers of the past exhumation and of the present-day erosion and mixing occurring in a river system. In this paper, we present new Ar-40/Ar-39 biotite and white mica age distributions for 19 modern river sands from the Eastern Alps north of the Periadriatic line. The results present three main clusters of ages at similar to 0.5-50, similar to 60-120, and similar to 250-350 Ma that record the main orogenic phases in this sector of the Alps. We have applied two numerical methods to the cooling ages to (a) linearly compute the spatial variability of the relative present-day erosion of a set of four detrital mineral samples from drainage basins along the Inn River and (b) quantify the rates of the cooling and erosion in the Tauern Window during Paleocene-Miocene time of the Alpine orogeny. Our results suggest a 0.34-0.84 mm/yr range of exhumation rates for the Tauern Window since the Miocene. Our estimates of exhumation rates of the western Tauern Window are higher than those for the eastern Tauern Window, which is consistent with the previous studies.
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Gillet, N., Jault, D., & Canet, E. (2017). Excitation of travelling torsional normal modes in an Earth's core model. Geophysical Journal International, 210(3), 1503–1516.
Résumé: The proximity between the 6 yr recurrence time of the torsional Alfv en waves that have been inferred in the Earth's outer core over 1940-2010 and their 4 yr traveltime across the fluid core is nicely explained if these travelling waves are to be considered as normal modes. We discuss to what extent the emergence of free torsional modes from a stochastic forcing in the fluid core is compatible with some dissipation, specifically with an electromagnetic torque strong enough to account for the observed length of day variations of 6 yr period. In a spherical cavity enclosed by an insulating mantle, torsional normal modes consist of standing waves. In the presence of a conducting mantle, they transform into outward travelling waves very similar to the torsional waves that have been detected in the Earth's outer core. With such a resonant response a periodic forcing is not required to explain the regular recurrence of torsional waves; neither is the search for a source of motions in the vicinity of the cylindrical surface tangent to the inner core, where travelling waves seem to emerge. We discuss these results in the light of the reflection properties of torsional waves at the equator. We are able to reproduce the properties found for geophysical time-series of geostrophic flows (detection of a normal mode, almost total absorption at the equator) if the conductance of the lowermost mantle is 3 x 10(7) to 10(8) S.
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Goitom, B., Werner, M. J., Goda, K., Kendall, J. - M., Hammond, J. O. S., Ogubazghi, G., et al. (2017). Probabilistic Seismic-Hazard Assessment for Eritrea. Bulletin Of The Seismological Society Of America, 107(3), 1478–1494.
Résumé: To date little is known about seismic hazard in Eritrea, despite its location in a volcanically and tectonically active region, and the gathering pace of major infrastructure projects. In response, we report the findings of a comprehensive probabilistic seismic-hazard assessment for Eritrea and adjacent areas. Seismic source and groundmotion models are constructed separately; we use an adaptive spatiotemporal smoothing method to map expected patterns of seismicity. To construct a consistent earthquake catalog from different data sets, we use orthogonal regression to convert and unify different magnitude scales. A sensitivity analysis of the different input parameters helps constrain them and disaggregation of site-specific hazard estimates yields insights into the relative contribution from seismic sources of different magnitudes and distances. The results highlight seismic hazard in proximity to the Red Sea, Gulf of Aden, Afar depression, and along the boundaries of the Danakil microplate. We estimate a 10% chance over 50 years of observing pseudospectral accelerations (PSAs) at 0.2 s exceeding 0:16g in the port city of Massawa (population similar to 32,000) and the town of Bada (population similar to 4000). For the capital, Asmara (population similar to 520,000), we calculate a PSA of 0: 11g at 0.2 s. Compared with previous studies, our results provide greater spatial resolution, use more recent ground-motion models, and benefit from a smoothed seismicity method. Our aims are to stimulate further studies and contribute to the safe development of the region in light of its exposure to seismic hazards.
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Golowin, R., Portnyagin, M., Hoernle, K., Sobolev, A., Kuzmin, D., & Werner, R. (2017). The role and conditions of second-stage mantle melting in the generation of low-Ti tholeiites and boninites: the case of the Manihiki Plateau and the Troodos ophiolite. Contributions To Mineralogy And Petrology, 172(11-12).
Résumé: High-Mg, low-Ti volcanic rocks from the Manihiki Plateau in the Western Pacific share many geochemical characteristics with subduction-related boninites such as high-Ca boninites from the Troodos ophiolite on Cyprus, which are believed to originate by hydrous re-melting of previously depleted mantle. In this paper we compare the Manihiki rocks and Troodos boninites using a new dataset on the major and trace element composition of whole rocks and glasses from these locations, and new high-precision, electron microprobe analyses of olivine and Cr-spinel in these rocks. Our results show that both low-Ti Manihiki rocks and Troodos boninites could originate by re-melting of a previously depleted lherzolite mantle source (20-25% of total melting with 8-10% melting during the first stage), as indicated by strong depletion of magmas in more to less incompatible elements (Sm/Yb < 0.8, Zr/Y < 2, Ti/V < 12) and high-Cr-spinel compositions (Cr# > 0.5). In comparison with Troodos boninites, the low-Ti Manihiki magmas had distinctively lower -H2O contents (< 0.2 vs. > 2 wt% in boninites), similar to 100 degrees C higher liquidus temperatures at a given olivine Fo-number, lower fO(2) (Delta QFM < + 0.2 vs. Delta QFM > + 0.2) and originated from deeper and hotter mantle (1.4-1.7 GPa, similar to 1440 degrees C vs. 0.8-1.0 GPa, similar to 1300 degrees C for Troodos boninites). The data provide new evidence that re-melting of residual upper mantle is not only restricted to subduction zones, where it occurs under hydrous conditions, but can also take place due to interaction of previously depleted upper mantle with mantle plumes from the deep and hotter Earth interior.
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Got, J. - L., Carrier, A., Marsan, D., Jouanne, F., Vogfjord, K., & Villemin, T. (2017). An analysis of the nonlinear magma-edifice coupling at Grimsvotn volcano (Iceland). Journal Of Geophysical Research-Solid Earth, 122(2), 826–843.
Résumé: Continuous monitoring of seismicity and surface displacement of active volcanoes can reveal important features of the eruptive cycle. Here high-quality GPS and earthquake data recorded at Grimsvotn volcano by the Icelandic Meteorological Office during the 2004-2011 intereruptive period are analyzed. These showed a characteristic pattern, with an initial similar to 2 year long exponential decay followed by similar to 3 year long constant surface displacement inflation rate. We model it by using a one magma reservoir model in an elastic damaging edifice, with incompressible magma and constant pressure at the base of the magma conduit. Seismicity rate and damage were first modeled, and simple analytical expressions were derived for the magma reservoir overpressure and surface displacement as functions of time. Very good fits of the seismicity and surface displacement data were obtained by fitting only three phenomenological parameters. Characteristic time and power strain show maxima from which reference times were inferred that split the intereruptive period into five periods. After the pressurization periods, damage occurring in the third period induced weakly nonlinear variations in magma overpressure and flow, and surface displacement. During the fourth period, the damage dominated and variations became more strongly nonlinear, the reservoir overpressure decreased, and magma flow increased. This process lasted until the power strain reached its second maximum, where instability was generalized. This maximum is a physical limit, the occurrence of which shortly precedes rupture and, eventually, eruption. This analysis allows characterization of the state of the volcanic edifice during the intereruptive period and supports medium-term prediction of rupture and eruption.
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Gourbet, L., Leloup, P. H., Paquette, J. - L., Sorrel, P., Maheo, G., Wang, G. C., et al. (2017). Reappraisal of the Jianchuan Cenozoic basin stratigraphy and its implications on the SE Tibetan plateau evolution. Tectonophysics, 700, 162–179.
Résumé: We present a new stratigraphy of the Jianchuan basin, one of the largest Cenozoic sedimentary basins in southeastern Tibet. This basin was regarded as recording sedimentation from the Eocene up to the Pliocene, and as such has been the focus of several studies aiming at constraining the environmental, tectonic and topographic evolution of the area. Within the Shuanghe andJianchuan formations thirteen new zircon U/Pb ages and one biotite Ar-40/Ar-39 age of interbedded and cross-cutting ultrapotassic magmatic rocks show that a brief magmatic event occurred from similar to 35.7 to similar to 34.5 Ma (352 +/- 0.4 Ma on average). The uppermost formation (Jianchuan Fm), supposedly Pliocene in age, is related to this magmatic event and is 35.4 +/- 0.8 Ma old. All sedimentary formations are thus Eocene in age, with neither Oligocene nor Miocene sediments. The coal-bearing Shuanghe Formation yields a fossil of a large amynodontid typical of the Upper Eocene Ergilian interval (37.2 to 33.9 Ma). Sedimentation of the Shuanghe Formation took place in a short time interval at similar to 35.9 +/- 0.9 Ma, after a large-scale drainage reorganization that induced the abandonment of a large braided-river system. This reorganization was possibly linked with the initiation of the left-lateral Ailao-Shan Red River fault and/or to widespread magmatism in the Jianchuan basin. Previous high paleoaltitude estimates for the Jianchuan basin are thoroughly re-evaluated and yield a value of 1200 1200 m.a.s.l. for the Upper Eocene. (C) 2017 Elsevier B.V. All rights reserved.
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Grangeon, S., Fernandez-Martinez, A., Baronnet, A., Marty, N., Poulain, A., Elkaim, E., et al. (2017). Quantitative X-ray pair distribution function analysis of nanocrystalline calcium silicate hydrates: a contribution to the understanding of cement chemistry. Journal Of Applied Crystallography, 50, 14–21.
Résumé: The structural evolution of nanocrystalline calcium silicate hydrate (C-S-H) as a function of its calcium to silicon (Ca/Si) ratio has been probed using qualitative and quantitative X-ray atomic pair distribution function analysis of synchrotron X-ray scattering data. Whatever the Ca/Si ratio, the C-S-H structure is similar to that of tobermorite. When the Ca/Si ratio increases from similar to 0.6 to similar to 1.2, Si wollastonite-like chains progressively depolymerize through preferential omission of Si bridging tetrahedra. When the Ca/Si ratio approaches similar to 1.5, nanosheets of portlandite are detected in samples aged for 1 d, while microcrystalline portlandite is detected in samples aged for 1 year. High-resolution transmission electron microscopy imaging shows that the tobermorite-like structure is maintained to Ca/Si > 3.
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Grangeon, S., Fernandez-Martinez, A., Claret, F., Marty, N., Tournassat, C., Warmont, F., et al. (2017). In-situ determination of the kinetics and mechanisms of nickel adsorption by nanocrystalline vernadite. Chemical Geology, 459, 24–31.
Résumé: In-situ kinetics and mechanisms of Ni2+ uptake by synthetic vernadite were determined at pH 5.8 and I = 0.1 M NaCl using wet chemistry, atomic-resolution scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) and synchrotron high-energy X-ray scattering (HEXS) in both the Bragg-rod and pair distribution function formalisms. The structural formula of the initial solids was (Mn0.053+Na0.23+)-Mn-Tc(H2O)(0.69)H+ (0.06) [(Mn4+ (0.86)Mn(0.04)(3+)vac(0.1))O-2), where species under brackets form the layer having “vac” layer vacancies, and where other species are present in the interlayer, with TC standing for “triple corner sharing” configuration. According to HEXS and STEM-EELS, adsorbed Ni2+ adopted mainly a TC configuration, and had a Debye-Waller factor about four times higher than layer Mn. Steady-state was reached after similar to 2.2 h of contact time, and the final structural formula of the solid was (Ni0.122+Mn3+)-Ni-Tc-Mn-Tc Na-0.05(+) 0.12H2O0.36H0.01+(Mn(0.87)(4+)vac(0.13))O-2]. Atomic-scale imaging of the solids also evinced the presence of minor Ni adsorbed at the crystal edge. The retention coefficient R-D = 10(3.76 +/-) (0.06) L kg(-1), computed from PDF data modelling and solution chemistry results, was in agreement with those available in the literature.
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Grangeon, S., Warmont, F., Tournassat, C., Lanson, B., Lanson, M., Elkaim, E., et al. (2017). Nucleation and growth of feitknechtite from nanocrystalline vernadite precursor. Eur. J. Mineral., 29(4), 767–776.
Résumé: Vernadite is a nanocrystalline manganese oxide, which controls the fate of many trace elements in soils and sediments through sorption and oxidative-degradation mechanisms. This exceptional reactivity directly results from its crystal structure, which may however evolve upon contact with redox-sensitive species. Understanding these changes is a prerequisite to predict and model the geochemical cycle of trace elements in the environment. Here, the structural and morphological modifications affecting synthetic nanocrystalline vernadite (delta-MnO2) upon contact with increasing concentrations of Mn2+ were investigated using wet chemistry, synchrotron X-ray diffraction and transmission electron microscopy. Fresh delta-MnO2 crystals had an Mn oxidation state of 3.94 +/- 0.05 and a similar to 10 angstrom layer-to-layer distance. Crystal size was similar to 10 nm in the layer plane, and similar to 1 nm perpendicular to that. Upon contact with aqueous Mn2+ under anoxic conditions, delta-MnO2 crystals underwent several morphological and mineral evolutions, starting with the stacking, perpendicular to the layer plane, of delta-MnO2 crystals to form crystals similar to 10 nm x 2 nm which were then subjected to oriented aggregation both along and perpendicular to the layer plane to form lath-like crystals with dimensions of similar to 100 nm x 20 nm. Finally, these laths stacked perpendicular to the layer plane to form synthetic feitknechtite (beta-MnOOH) crystals with sizes up to similar to 100 nm x 500 nm when the Mn2+ loading reached 31.9 mmol g(-1). Structural transformation from delta-MnO2 to synthetic feitknechtite was detected at Mn2+ loading equal to or higher than 3.27 mmol g(-1). These mechanisms are likely to influence the geochemical fate of trace elements in natural settings where Mn2+ is abundant. Firstly, the systematic increase in crystal size with increasing Mn2+ loading may impact the sorption capacity of vernadite and feitknechtite by reducing the density of reactive edge sites. Secondly, the fate of trace elements initially sorbed at the vernadite surface is unclear, as they could either be released in solution or incorporated into the feitknechtite lattice.
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Greber, N. D., Dauphas, N., Puchtel, I. S., Hofmann, B. A., & Arndt, N. T. (2017). Titanium stable isotopic variations in chondrites, achondrites and lunar rocks. Geochimica Et Cosmochimica Acta, 213, 534–552.
Résumé: Titanium isotopes are potential tracers of processes of evaporation/condensation in the solar nebula and magmatic differentiation in planetary bodies. To gain new insights into the processes that control Ti isotopic variations in planetary materials, 25 komatiites, 15 chondrites, 11 HED-clan meteorites, 5 angrites, 6 aubrites, a martian shergottite, and a KREEP-rich impact melt breccia have been analyzed for their mass-dependent Ti isotopic compositions, presented using the delta Ti-49 notation (deviation in permil of the Ti-49/(47) Ti ratio relative to the OL-Ti standard). No significant variation in delta Ti-49 is found among ordinary, enstatite, and carbonaceous chondrites, and the average chondritic delta Ti-49 value of +0.004 +/- 0.010% is in excellent agreement with the published estimate for the bulk silicate Earth, the Moon, Mars, and the HED and angrite parent-bodies. The average delta Ti-49 value of komatiites of -0.001 +/- 0.019% is also identical to that of the bulk silicate Earth and chondrites. OL-Ti has a Ti isotopic composition that is indistinguishable from chondrites and is therefore a suitable material for reporting delta Ti-49 values. Previously published isotope data on another highly refractory element, Ca, show measurable variations among chondrites. The decoupling between Ca and Ti isotope systematics most likely occurred during condensation in the solar nebula. Aubrites exhibit significant variations in delta Ti-49 , from -0.07 to +0.24%. This is likely due to the uniquely reducing conditions under which the aubrite parent-body differentiated, allowing chalcophile Ti3+ and lithophile Ti4+ to co-exist. Consequently, the observed negative correlation between delta Ti-49 values and MgO concentrations among aubrites is interpreted to be the result of isotope fractionation driven by the different oxidation states of Ti in this environment, such that isotopically heavy Ti4+ was concentrated in the residual liquid during magmatic differentiation. Finally, KREEPy impact melt breccia SaU 169 exhibits a heavy delta Ti-49 value of +0.330 +/- 0.034% which is interpreted to result from Ti isotopic fractionation during ilmenite precipitation in the late stages of lunar magma ocean crystallization. A Rayleigh distillation calculation predicts that a delta Ti-49 value of +0.330% is achieved after removal of 94% of Ti in ilmenite. (C) 2017 Elsevier Ltd. All rights reserved.
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Greber, N. D., Dauphas, N., Puchtel, I. S., Hofmann, B. A., & Arndt, N. T. (2017). Titanium stable isotopic variations in chondrites, achondrites and lunar rocks. Geochimica Et Cosmochimica Acta, 213, 534–552.
Résumé: Titanium isotopes are potential tracers of processes of evaporation/condensation in the solar nebula and magmatic differentiation in planetary bodies. To gain new insights into the processes that control Ti isotopic variations in planetary materials, 25 komatiites, 15 chondrites, 11 HED-clan meteorites, 5 angrites, 6 aubrites, a martian shergottite, and a KREEP-rich impact melt breccia have been analyzed for their mass-dependent Ti isotopic compositions, presented using the delta Ti-49 notation (deviation in permil of the Ti-49/(47) Ti ratio relative to the OL-Ti standard). No significant variation in delta Ti-49 is found among ordinary, enstatite, and carbonaceous chondrites, and the average chondritic delta Ti-49 value of +0.004 +/- 0.010% is in excellent agreement with the published estimate for the bulk silicate Earth, the Moon, Mars, and the HED and angrite parent-bodies. The average delta Ti-49 value of komatiites of -0.001 +/- 0.019% is also identical to that of the bulk silicate Earth and chondrites. OL-Ti has a Ti isotopic composition that is indistinguishable from chondrites and is therefore a suitable material for reporting delta Ti-49 values. Previously published isotope data on another highly refractory element, Ca, show measurable variations among chondrites. The decoupling between Ca and Ti isotope systematics most likely occurred during condensation in the solar nebula. Aubrites exhibit significant variations in delta Ti-49 , from -0.07 to +0.24%. This is likely due to the uniquely reducing conditions under which the aubrite parent-body differentiated, allowing chalcophile Ti3+ and lithophile Ti4+ to co-exist. Consequently, the observed negative correlation between delta Ti-49 values and MgO concentrations among aubrites is interpreted to be the result of isotope fractionation driven by the different oxidation states of Ti in this environment, such that isotopically heavy Ti4+ was concentrated in the residual liquid during magmatic differentiation. Finally, KREEPy impact melt breccia SaU 169 exhibits a heavy delta Ti-49 value of +0.330 +/- 0.034% which is interpreted to result from Ti isotopic fractionation during ilmenite precipitation in the late stages of lunar magma ocean crystallization. A Rayleigh distillation calculation predicts that a delta Ti-49 value of +0.330% is achieved after removal of 94% of Ti in ilmenite. (C) 2017 Elsevier Ltd. All rights reserved.
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Gresse, M., Vandemeulebrouck, J., Byrdina, S., Chiodini, G., Revil, A., Johnson, T. C., et al. (2017). Three-Dimensional Electrical Resistivity Tomography of the Solfatara Crater (Italy): Implication for the Multiphase Flow Structure of the Shallow Hydrothermal System. Journal Of Geophysical Research-Solid Earth, 122(11), 8749–8768.
Résumé: The Solfatara volcano is the main degassing area of the Campi Flegrei caldera, characterized by 60years of unrest. Assessing such renewal activity is a challenging task because hydrothermal interactions with magmatic gases remain poorly understood. In this study, we decipher the complex structure of the shallow Solfatara hydrothermal system by performing the first 3-D, high-resolution, electrical resistivity tomography of the volcano. The 3-D resistivity model was obtained from the inversion of 43,432 resistance measurements performed on an area of 0.68km(2). The proposed interpretation of the multiphase hydrothermal structures is based on the resistivity model, a high-resolution infrared surface temperature image, and 1,136 soil CO2 flux measurements. In addition, we realized 27 soil cation exchange capacity and pH measurements demonstrating a negligible contribution of surface conductivity to the shallow bulk electrical conductivity. Hence, we show that the resistivity changes are mainly controlled by fluid content and temperature. The high-resolution tomograms identify for the first time the structure of the gas-dominated reservoir at 60m depth that feeds the Bocca Grande fumarole through a 10m thick channel. In addition, the resistivity model reveals a channel-like conductive structure where the liquid produced by steam condensation around the main fumaroles flows down to the Fangaia area within a buried fault. The model delineates the emplacement of the main geological structures: Mount Olibano, Solfatara cryptodome, and tephra deposits. It also reveals the anatomy of the hydrothermal system, especially two liquid-dominated plumes, the Fangaia mud pool and the Pisciarelli fumarole, respectively.
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Gualandi, A., Perfettini, H., Radiguet, M., Cotte, N., & Kostoglodov, V. (2017). GPS deformation related to the M-w 7.3, 2014, Papanoa earthquake (Mexico) reveals the aseismic behavior of the Guerrero seismic gap. Geophysical Research Letters, 44(12), 6039–6047.
Résumé: We present the study of 21 continuous GPS (cGPS) stations in Mexico during the time interval that goes from 1 October 2013 to 31 December 2014. The area under investigation produced a slow slip event (SSE) that started in February 2014 and lasted at least until December 2014. Superimposed on this transient signal, the M(w)7.3 Papanoa earthquake struck the region on 18 April 2014 and affected multiple stations. Thanks to an independent component analysis (ICA) technique we are able to separate the postseismic deformation associated with this earthquake from the deformation related to the ongoing SSE. We infer the slip distributions associated with the three tectonically related processes: the coseismic and postseismic slip and the SSE. The inferred postseismic slip distribution reduces the amount of slip related to the SSE in the updip portion of the slab. The moment released by the postseismic processes (afterslip and aftershocks) is estimated to be [8.06 +/- 0.24] x 10(19)Nm, equivalent to [71 +/- 4]% of the moment associated with the main shock. More than 88% of the postseismic moment is released aseismically and the afterslip spatially correlates with the Guerrero seismic gap, suggesting that the region is controlled by stable sliding behavior and rate-strengthening frictional properties.
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Guedron, S., Point, D., Acha, D., Bouchet, S., Baya, P. A., Tessier, E., et al. (2017). Mercury contamination level and speciation inventory in Lakes Titicaca & Uru-Uru (Bolivia): Current status and future trends. Environmental Pollution, 231, 262–270.
Résumé: Aquatic ecosystems of the Bolivian Altiplano (similar to 3800 m a.s.l.) are characterized by extreme hydro-climatic constrains (e.g., high UV-radiations and low oxygen) and are under the pressure of increasing anthropogenic activities, unregulated mining, agricultural and urban development. We report here a complete inventory of mercury (Hg) levels and speciation in the water column, atmosphere, sediment and key sentinel organisms (i.e., plankton, fish and birds) of two endorheic Lakes of the same watershed differing with respect to their size, eutrophication and contamination levels. Total Hg (THg) and mono-methylmercury (MMHg) concentrations in filtered water and sediment of Lake Titicaca are in the lowest range of reported levels in other large lakes worldwide. Downstream, Hg levels are 3-10 times higher in the shallow eutrophic Lake Uru-Uru than in Lake Titicaca due to high Hg inputs from the surrounding mining region. High percentages of MMHg were found in the filtered and unfiltered water rising up from <1 to similar to 50% THg from the oligoihetero-trophic Lake Titicaca to the eutrophic Lake Uru-Uru. Such high % MMHg is explained by a high in situ MMHg production in relation to the sulfate rich substrate, the low oxygen levels of the water column, and the stabilization of MMHg due to abundant ligands present in these alkaline waters. Differences in MMHg concentrations in water and sediments compartments between Lake Titicaca and Uru-Uru were found to mirror the offset in MMHg levels that also exist in their respective food webs. This suggests that in situ MMHg baseline production is likely the main factor controlling MMHg levels in fish species consumed by the local population. Finally, the increase of anthropogenic pressure in Lake Titicaca may probably enhance eutrophication processes which favor MMHg production and thus accumulation in water and biota. (C) 2017 Elsevier Ltd. All rights reserved.
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Gueguen, P., Langlais, M., Garambois, S., Voisin, C., & Douste-Bacque, I. (2017). How sensitive are site effects and building response to extreme cold temperature? The case of the Grenoble's (France) City Hall building. Bulletin Of Earthquake Engineering, 15(3), 889–906.
Résumé: In this paper, a simple analysis is done to explain the observed increase of resonance frequency of City-Hall building in Grenoble (France), a 12-story reinforced concrete building. This period corresponds also to the observed variation of the resonance frequency of the Grenoble's sedimentary basin. The postulated hypothesis is that the frequency increase reflects the stiffness increase of the soil-structure system related to the cold period that hit Western Europe in 2012. To explore this hypothesis we have processed continuous recording during the early 2012 recorded at the roof level and at a close free-field accelerometric station. The variation of site effect is monitored by the horizontal-to-vertical spectral ratio of seismic noise, and the variation of apparent and system frequencies of the building by the random decrement technique. Apparent frequency is computed by deconvolution method between roof and basement. The maximum freezing penetration is 0.75 m and the horizontal relative motion stiffness of the foundation is strongly sensitive to the modification of the upper soil layer. The results suggest a variation (< 1 %) larger than twice the standard deviation of the natural wandering of resonance frequency observed at City-Hall building for normal weather conditions, and question on the development of realistic models developed for the detection of damage and for the physical interpretation of such frequency variations observed in actual buildings.
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Guervilly, C., & Cardin, P. (2017). Multiple zonal jets and convective heat transport barriers in a quasi-geostrophic model of planetary cores. Geophysical Journal International, 211(1), 455–471.
Résumé: We study rapidly rotating Boussinesq convection driven by internal heating in a full sphere. We use a numerical model based on the quasi-geostrophic approximation for the velocity field, whereas the temperature field is 3-D. This approximation allows us to perform simulations for Ekman numbers down to 10(-8), Prandtl numbers relevant for liquid metals (similar to 10(-1)) and Reynolds numbers up to 3 x 10(4). Persistent zonal flows composed of multiple jets form as a result of the mixing of potential vorticity. For the largest Rayleigh numbers computed, the zonal velocity is larger than the convective velocity despite the presence of boundary friction. The convective structures and the zonal jets widen when the thermal forcing increases. Prograde and retrograde zonal jets are dynamically different: in the prograde jets (which correspond to weak potential vorticity gradients) the convection transports heat efficiently and the mean temperature tends to be homogenized; by contrast, in the cores of the retrograde jets (which correspond to steep gradients of potential vorticity) the dynamics is dominated by the propagation of Rossby waves, resulting in the formation of steep mean temperature gradients and the dominance of conduction in the heat transfer process. Consequently, in quasi-geostrophic systems, the width of the retrograde zonal jets controls the efficiency of the heat transfer.
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Guettiche, A., Gueguen, P., & Mimoune, M. (2017). Economic and Human Loss Empirical Models for Earthquakes in the Mediterranean Region, with Particular Focus on Algeria. International Journal Of Disaster Risk Science, 8(4), 415–434.
Résumé: In this study, loss estimation models were developed for reasonably accurate assessment of economic and human losses from seismic events in the Mediterranean region, based on damage assessment at an urban scale. Data were compiled from existing worldwide databases, and completed with earthquake information from regional studies. Economic data were converted to a single common currency unit (2015 USD value) and the wealth of the areas affected by 65 earthquakes of the region from 1900 to 2015 was assessed. Reduced-form models were used to determine economic and human losses, with earthquake magnitude and intensity as hazard-related variables, and gross domestic product of the affected area and the affected population as exposure-related variables. Damage to buildings was also used as a hazard-related variable to predict economic and human losses. Finally, site-specific regression models were proposed for economic and human losses due to earthquakes in the Mediterranean region, and more specifically, in Algeria. We show that by introducing the damage variable into the models, prediction error can be reduced, and that accuracy of loss model estimation is site dependent and requires regional data on earthquake losses to improve. A case study for Constantine, Algeria shows the improvements needed for increased accuracy.
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Guettiche, A., Gueguen, P., & Mimoune, M. (2017). Seismic vulnerability assessment using association rule learning: application to the city of Constantine, Algeria. Natural Hazards, 86(3), 1223–1245.
Résumé: We performed a seismic vulnerability assessment of the city of Constantine (Algeria) using the Risk-UE and datamining-based methods [association rule learning (ARL)]. The ARL method consists in establishing relationships between building attributes (number of stories or building age) and the vulnerability classes of the European Macroseismic Scale, EMS98. This approach avoids the costly process of drawing up an inventory of building characteristics in the field, which often discourages the assessment of seismic risk initiatives in weak to moderate seismic-prone regions. We showed that the accuracy of the assessment is independent of the subset used for the learning phase leading to development of the Constantine vulnerability proxy. Considering only two attributes, the vulnerability assignment is equal to about 75%, reaching 99% if material is added to the attributes considered. Comparison of Risk-UE and ARL results revealed a reliable assessment of vulnerability, the differences having only a slight impact on the probability of exceeding the damage level computed by EMS98 or Risk-UE in Constantine. The results of this study suggest that the ARL-based vulnerability proxy is efficient and could be applied to the rest of Algeria.
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Guettiche, A., Gueguen, P., & Mimoune, M. (2017). Seismic vulnerability assessment using association rule learning: application to the city of Constantine, Algeria. Natural Hazards, 86(3), 1223–1245.
Résumé: We performed a seismic vulnerability assessment of the city of Constantine (Algeria) using the Risk-UE and datamining-based methods [association rule learning (ARL)]. The ARL method consists in establishing relationships between building attributes (number of stories or building age) and the vulnerability classes of the European Macroseismic Scale, EMS98. This approach avoids the costly process of drawing up an inventory of building characteristics in the field, which often discourages the assessment of seismic risk initiatives in weak to moderate seismic-prone regions. We showed that the accuracy of the assessment is independent of the subset used for the learning phase leading to development of the Constantine vulnerability proxy. Considering only two attributes, the vulnerability assignment is equal to about 75%, reaching 99% if material is added to the attributes considered. Comparison of Risk-UE and ARL results revealed a reliable assessment of vulnerability, the differences having only a slight impact on the probability of exceeding the damage level computed by EMS98 or Risk-UE in Constantine. The results of this study suggest that the ARL-based vulnerability proxy is efficient and could be applied to the rest of Algeria.
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He, J., Ma, B., Kang, M., Wang, C., Nie, Z., & Liu, C. (2017). Migration of Se-75(IV) in crushed Beishan granite: Effects of the iron content. Journal Of Hazardous Materials, 324, 564–572.
Résumé: The diffusion of selenite (labeled with Se-75) in compacted Beishan granite (BsG) was investigated using the in-diffusion capillary method at pH values from similar to 2.0 to similar to 11.0 under oxic and anoxic conditions. The results indicate that the apparent diffusion coefficient (D-a) values of selenite in BsG always reached the minimum at approximately pH 5. Unexpectedly, the D-a values under oxic conditions are nearly one order of magnitude lower than those under the anoxic conditions. Further characterization reveals the existence of redox-sensitive Fe(II)-containing components, which can be responsible for the great difference in D-a values. Fe(2p) X-ray photoelectron spectroscopy (XPS) results show that more Fe(III)oxyhydroxide coating is formed on the granite's surface under aerobic conditions than is formed under anaerobic conditions. Correspondingly, Se(3d) spectra indicate that more selenium is sorbed under oxic conditions, and the sorbed amount always reached the maximum at pH values from similar to 4 to similar to 5. A linear combination fit of X-ray absorption near edge structure (XANES) spectroscopy data revealed that Se(0) was formed under anoxic condition and that selenite preferred to form inner-sphere complexes with Fe(III)-oxyhydroxide. Overall, this study indicates that natural Fe-bearing minerals can greatly attenuate selenite diffusion and the retardation would be enhanced under aerobic conditions. (C) 2016 Elsevier B.V. All rights reserved.
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Heenan, J. W., Ntarlagiannis, D., Slater, L. D., Beaver, C. L., Rossbach, S., Revil, A., et al. (2017). Field-scale observations of a transient geobattery resulting from natural attenuation of a crude oil spill. Journal Of Geophysical Research-Biogeosciences, 122(4), 918–929.
Résumé: We present evidence of a geobattery associated with microbial degradation of a mature crude oil spill. Self-potential measurements were collected using a vertical array of nonpolarizing electrodes, starting at the land surface and passing through the smear zone where seasonal water table fluctuations have resulted in the coating of hydrocarbons on the aquifer solids. These passive electrical potential measurements exhibit a dipolar pattern associated with a current source. The anodic and cathodic reactions of this natural battery occur below and above the smear zone, respectively. The smear zone is characterized by high magnetic susceptibility values associated with the precipitation of semiconductive magnetic iron phase minerals as a by-product of biodegradation, facilitating electron transfer between the anode and the cathode. This geobattery response appears to have a transient nature, changing on a monthly scale, probably resulting from chemical and physical changes in subsurface conditions such as water table fluctuations.
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Hermann, A., Sauzeat, L., Guillou, H., Maury, R. C., Chauvel, C., Liorzou, C., et al. (2017). Combined geochemical and geochronological analyses of stone artefacts provide unambiguous evidence of intra- and inter-island interactions in Polynesia. Journal Of Archaeological Science-Reports, 13, 75–87.
Résumé: Stone tool geochemistry provides hard evidence for post-settlement voyaging and inter-island contacts in East Polynesia. This offers promising information on inter-community exchange networks that are not documented by ethnographic accounts. Drawing on “geochemical fingerprints”, provenance studies have slowly integrated geological data in order to better constrain the origin of archaeological material. However, the occurrence of overlapping geochemical signatures within Polynesian islands can cause difficulties when attempting to differentiate sources. Identifying clear geochemical characteristics for each island is therefore critical for a comprehensive understanding of the interaction patterns in East Polynesian societies. In this paper, we combine major and trace element data with isotopes as well as Ar-40-Ar-39 ages to constrain the local procurement networks that were occurring on the island of Tupua'i (Austral-Cook chain). We also demonstrate that some Tupua'i archaeological material originated from Eiao Island (Marquesas chain) circa 2000 km north. This represents the first hard evidence for inter-island connections between the Austral and the Marquesas Archipelagos. (C) 2017 Elsevier Ltd. All rights reserved.
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Hewins, R. H., Zanda, B., Humayun, M., Nemchin, A., Lorand, J. P., Pont, S., et al. (2017). Regolith breccia Northwest Africa 7533: Mineralogy and petrology with implications for early Mars. Meteorit. Planet. Sci., 52(1), 89–124.
Résumé: Northwest Africa 7533, a polymict Martian breccia, consists of fine-grained clast-laden melt particles and microcrystalline matrix. While both melt and matrix contain medium-grained noritic-monzonitic material and crystal clasts, the matrix also contains lithic clasts with zoned pigeonite and augite plus two feldspars, microbasaltic clasts, vitrophyric and microcrystalline spherules, and shards. The clast-laden melt rocks contain clump-like aggregates of orthopyroxene surrounded by aureoles of plagioclase. Some shards of vesicular melt rocks resemble the pyroxene-plagioclase clump-aureole structures. Submicron size matrix grains show some triple junctions, but most are irregular with high intergranular porosity. The noritic-monzonitic rocks contain exsolved pyroxenes and perthitic intergrowths, and cooled more slowly than rocks with zoned-pyroxene or fine grain size. Noritic material contains orthopyroxene or inverted pigeonite, augite, calcic to intermediate plagioclase, and chromite to Cr-bearing magnetite; monzonitic clasts contain augite, sodic plagioclase, K feldspar, Ti-bearing magnetite, ilmenite, chlorapatite, and zircon. These feldspathic rocks show similarities to some rocks at Gale Crater like Black Trout, Mara, and Jake M. The most magnesian orthopyroxene clasts are close to ALH 84001 orthopyroxene in composition. All these materials are enriched in siderophile elements, indicating impact melting and incorporation of a projectile component, except for Ni-poor pyroxene clasts which are from pristine rocks. Clast-laden melt rocks, spherules, shards, and siderophile element contents indicate formation of NWA 7533 as a regolith breccia. The zircons, mainly derived from monzonitic (melt) rocks, crystallized at 4.43 +/- 0.03Ga (Humayun etal. ) and a Sm-147-Nd-143 isochron for NWA 7034 yielding 4.42 +/- 0.07Ga (Nyquist etal. ) defines the crystallization age of all its igneous portions. The zircon from the monzonitic rocks has a higher O-17 than other Martian meteorites explained in part by assimilation of regolith materials enriched during surface alteration (Nemchin etal. ). This record of protolith interaction with atmosphere-hydrosphere during regolith formation before melting demonstrates a thin atmosphere, a wet early surface environment on Mars, and an evolved crust likely to have contaminated younger extrusive rocks. The latest events recorded when the breccia was on Mars are resetting of apatite, much feldspar and some zircons at 1.35-1.4Ga (Bellucci etal. ), and formation of Ni-bearing pyrite veins during or shortly after this disturbance (Lorand etal. ).
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Hollingsworth, J., Ye, L., & Avouac, J. - P. (2017). Dynamically triggered slip on a splay fault in the M-w 7.8, 2016 Kaikoura (New Zealand) earthquake. Geophysical Research Letters, 44(8), 3517–3525.
Résumé: We investigate the Mw 7.8, 2016 Kaikoura (New Zealand) earthquake by using optical satellite imagery and seismology to reveal the main features of the rupture process. Correlation of Landsat8 images reveals a 30-40 km surface rupture on the Kekerengu Fault and Jordan Thrust, with up to 12 m of right-lateral slip. A previously unrecognized conjugate strike-slip fault, the Papatea Fault, also slipped coseismically (3-4 m). The global centroid moment tensor (gCMT) centroid indicates both thrust and right-lateral slip and is located similar to 100 km NE of the main shock epicenter. The significant non-double-couple component of the gCMT (25%) suggests that the main shock is not well represented by a single planar fault. Back projection of teleseismic P waves reveals two main bursts of seismic radiation: (1) at 10-20 s, near the main shock epicenter, and (2) at similar to 70 s, close to the observed surface ruptures. We determine a finite source kinematic model of the rupture from the inversion of seismic waveforms. We use two faults in our model, defined to match the observed slip on the Kekerengu Fault, and a deeper offshore fault with a lower dip angle to satisfy the long period seismological observations. We compute the equivalent moment tensor from our finite source model and find it to be remarkably consistent with the gCMT solution. Although little is known about the geometry of these faults at depth, if the Kekerengu Fault splays from the deeper thrust, then it provides a rare example where the contribution of slip on a splay fault can be clearly isolated in the seismological waveforms. Plain Language Summary Through a combined analysis of satellite images and seismic waves, we investigate the recent Mw 7.8 earthquake near Kaikoura, New Zealand. We observe major surface ruptures, with up to 12m strike-slip displacement, located far from onset of earthquake slip. Properties of the seismic waves indicate that the earthquake slipped on a dipping thrust fault at depth and propagated to the northeast for 120 s. Halfway through the rupture, the earthquake triggered simultaneous slip on a neighboring fault, which possibly splays from the main thrust, and which was responsible for the observed surface offsets. Splay faults are commonly observed at converging plate boundaries globally and are suspected to pose a seismic and tsunamic hazard. This is the first time where simultaneous slip on a possible megathrust and associated splay fault has been directly observed in the seismic data.
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Hoummady, E., Golfier, F., Cathelineau, M., Truche, L., Durupt, N., Blanvillain, J. - J., et al. (2017). A multi-analytical approach to the study of uranium-ore agglomerate structure and porosity during heap leaching. Hydrometallurgy, 171, 33–43.
Résumé: Agglomeration is commonly used for processing clay-rich ores in order to prevent undesirable effects, especially the risks of plugging or preferential channelling within the heap leaching piles. As the mechanical and chemical stability of the agglomerates is of crucial importance for the behaviour of the pile, a detailed characterization of the structure and porosity of agglomerates seems necessary. In the present study, uranium-bearing clay rich ore was agglomerated and agglomerates were studied before as well as after 10 days of leaching. A multi-analytical approach (by X-ray tomography, SEM, XRD and MIP analyses) was used for the study of the mineralogy, porosity distribution and textures of the agglomerates. X-ray tomography and SEM images showed that agglomerates were the result of coalescence and layering of micro-agglomerates where each one in turn was composed of a nucleus embedded within phyllosilicates and an aluminous silicate matrix. MIP analyses highlighted that unleashed agglomerates had a low connected porosity (between 3 and 7%). During the 24 first hours of process, the connected porosity increased by a factor 2 because of the leaching of the aluminous silicate matrix and about 60% of the uranium was recovered. During the next 9 days, the formation of a secondary aluminous silicate matrix derived from the dissolution of illites resulted in the plugging of mesopores and therefore led to a decrease of porosity and uranium extraction extent.
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Isgett, S. J., Houghton, B. F., Fagents, S. A., Biass, S., Burgisser, A., & Arbaret, L. (2017). Eruptive and shallow conduit dynamics during Vulcanian explosions: insights from the Episode IV block field of the 1912 eruption of Novarupta, Alaska. Bulletin Of Volcanology, 79(8).
Résumé: The study of similar to 1300 juvenile and lithic blocks from a Vulcanian phase of the 1912 eruption of Novarupta provides new insight into the state of the magma as an eruption passes from sustained Plinian to dome growth. Blocks that were predominantly ballistically ejected were measured and sampled within an similar to 2-3-km radius from vent and supply a picture of a dynamic and complex shallow conduit prior to magma fragmentation in repeated small explosions. Extreme conduit heterogeneity is expressed in the diverse range of dacitic block types, including pumiceous, dense, banded, and variably welded breccia clasts, all with varied degrees of surface breadcrusting. We present new maps of block lithology and size, making Episode IV the most thoroughly mapped Vulcanian deposit to date. Sectorial regions rich in specific lithologies together with the block size data suggest multiple, small explosions. Modeling of block trajectories to reproduce the field data indicates that ejection velocities range from 50 to 124 m/s with a median of similar to 70 m/s. We propose that individual explosions originated from a heterogeneous shallow conduit characterized both by the juxtaposition of magma domains of contrasting texture and vesiculation state and by the intimate local mingling of different textures on short vertical and horizontal length scales at the contacts between these domains. In our model, each explosion disrupted the conduit to only shallow depths and tapped diverse, localized pockets within the conduit. This contrasts with existing models for repetitive Vulcanian explosions, and suggests that the dynamics of Episode IV were more complex than a simple progressive top-down evacuation of a horizontally stratified conduit.
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Jaillard, E., Bouillin, J. - P., Ouali, J., Dumont, T., Latil, J. - L., & Chihaoui, A. (2017). Albian salt-tectonics in Central Tunisia: Evidences for an Atlantic-type passive margin. Journal Of African Earth Sciences, 135, 220–234.
Résumé: Tunisia is part of the south-Tethyan margin, which comprises Triassic evaporites and a thick series of Jurassic and Cretaceous, mainly marine deposits, related to the Tethyan rifting evolution. A survey of various Cretaceous outcrops of central Tunisia (Kasserine-El Kef area), combined with literature descriptions, shows that the style of Albian deformation changes from the proximal (South) to the distal part (North) of the margin. The southern part is dominated by tilted blocks and growth faults, which evolve to the north to turtle-back and roll-over structures. Farther North, deformation is dominated by the extrusion of diapirs and salt walls. Such a distribution of deformation strongly suggests that the whole sedimentary cover glided northward on the Triassic evaporites during Albian times, as described for the Atlantic passive margin or for the Gulf of Mexico. Subsequently, these halokinetic structures have been folded during Alpine compressional tectonics. (C) 2017 Elsevier Ltd. All rights reserved.
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Jara, J., Socquet, A., Marsan, D., & Bouchon, M. (2017). Long-Term Interactions Between Intermediate Depth and Shallow Seismicity in North Chile Subduction Zone. Geophysical Research Letters, 44(18), 9283–9292.
Résumé: We document interactions between intermediate depth and interplate seismicity in the North Chile subduction zone, over a 25 year period (1990-2015). We show that the 2005 M-w 7.8 Tarapaca slab-pull earthquake was followed by 9 years of enhanced deep and shallow seismicity, together with the decrease of eastward average GPS velocities and associated interplate coupling, eventually leading to the 2014 M-w 8.1 Iquique megathrust earthquake. In contrast, megathrust ruptures (e.g., M-w 8.0 Antofagasta in 1995, or M-w 8.1 Iquique in 2014) initiate several years of silent background seismicity in the studied area, both at shallow and intermediate depths. The plunge of a rigid slab into a viscous asthenospheric mantle could explain the observed synchronization between deep and shallow seismicity and their long-term interactions.
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Ji, Y., Sarret, G., Schulin, R., & Tandy, S. (2017). Fate and chemical speciation of antimony (Sb) during uptake, translocation and storage by rye grass using XANES spectroscopy. Environmental Pollution, 231, 1322–1329.
Résumé: Antimony (Sb) is a contaminant of increased prevalence in the environment, but there is little knowledge about the mechanisms of its uptake and translocation within plants. Here, we applied for the synchrotron based X-ray absorption near-edge structure (XANES) spectroscopy to analyze the speciation of Sb in roots and shoots of rye grass (Lolium perenne L Calibra). Seedlings were grown in nutrient solutions to which either antimonite (Sb(III)), antimonate (Sb(V)) or trimethyl-Sb(V) (TMSb) were added. While exposure to Sb(III) led to around 100 times higher Sb accumulation in the roots than the other two treatments, there was no difference in total Sb in the shoots. Antimony taken up in the Sb(III) treatment was mainly found as Sb-thiol complexes (roots: >76% and shoots: 60%), suggesting detoxification reactions with compounds such as glutathione and phytochelatins. No reduction of accumulated Sb(V) was found in the roots, but half of the translocated Sb was reduced to Sb(III) in the Sb(V) treatment Antimony accumulated in the TMSb treatment remained in the methylated form in the roots. By synchrotron based XANES spectroscopy, we were able to distinguish the major Sb compounds in plant tissue under different Sb treatments. The results help to understand the translocation and transformation of different Sb species in plants after uptake and provide information for risk assessment of plant growth in Sb contaminated soils. (C) 2017 Elsevier Ltd. All rights reserved.
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Jiang, L., Hong, Y., Roux, P., Wu, J., & Shu, H. (2017). Active wideband higher-order raypath separation in multipath environment. Journal Of The Acoustical Society Of America, 141(1), EL38–EL44.
Résumé: Multiple raypaths propagation is caused by reflection and refraction at the surface and the bottom of the water column. In this study, an active wideband higher-order separation is proposed, which enables the separation of raypaths interrupted by colored noise (as traditionally found in ocean environments) in the angle-vs-time domain. A comparative study shows that the proposed algorithm achieves a more accurate separation than other algorithms. Moreover, with the proposed approach, it is not necessary to assume that the number of sensors is larger than that of the sources. Furthermore, numerical results validate the noise suppression property of the proposed method. (C) 2017 Acoustical Society of America
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Jolivet, M., Arzhannikova, A., Frolov, A., Arzhannikov, S., Kulagina, N., Akulova, V., et al. (2017). Late Jurassic – Early Cretaceous paleoenvironmental evolution of the Transbaikal basins (SE Siberia): implications for the Mongol-Okhotsk orogeny. Bulletin De La Societe Geologique De France, 188(1-2).
Résumé: The Late Jurassic-Early Cretaceous tectonic evolution of SE Siberia was marked by the closure of the Mongol- Okhotsk ocean. While this geodynamic event led to compressive deformation and denudation in a wide area encompassing the North-Altay, Sayan and Baikal Patom ranges, it was contemporaneous to widespread extension from the Transbaikal region situated immediately north of the suture zone to the Pacific plate, affecting eastern Mongolia and northeastern China. In this study we review the paleontological and sedimentological data available in the Russian literature and provide new macro-floral and palynological data from the Mesozoic sediments of three Transbaikal basins. These data are used to describe the paleoenvironmental and paleoclimatic evolution of the Transbaikal area in order to assess the topographic evolution of the region in relation with the closure of the Mongol-Okhotsk ocean. We establish that the Transbaikal basins evolved in a continuously extensional tectonic setting from at least the Early-Middle Jurassic to the Early Cretaceous. The associated sedimentary environments are characterized by retrogradation from alluvial fan -braided river dominated systems prevailing during the Early to Middle Jurassic initial opening of the basins to meandering river-lacustrine systems that developed during the Late Jurassic-Early Cretaceous interval. No evidence of high relief topography was found and we conclude that, while compression and denudation occurred in the North Altai, Sayan and Patom ranges, in the Transbaikal region, the docking of the Mongolia-North China continent to Siberia was a “ soft collision” event, possibly involving a major strike-slip displacement that did not lead to an orogenic event implying strong compressive deformation, crustal thickening and topography building.
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Jomelli, V., Mokadem, F., Schimmelpfennig, I., Chapron, E., Rinterknecht, V., Favier, V., et al. (2017). Sub-Antarctic glacier extensions in the Kerguelen region (49 degrees S, Indian Ocean) over the past 24,000 years constrained by Cl-36 moraine dating. Quaternary Science Reviews, 162, 128–144.
Résumé: Similar to many other regions in the world, glaciers in the southern sub-polar regions are currently retreating. In the Kerguelen Islands (49 degrees S, 69 degrees E), the mass balance of the Cook Ice Cap (CIC), the largest ice cap in this region, experienced dramatic shrinking between 1960 and 2013 with retreat rates among the highest in the world. This observation needs to be evaluated in a long-term context. However, data on the past glacier extents are sparse in the sub-Antarctic regions. To investigate the deglaciation pattern since the Last Glacial Maximum (LGM) period, we present the first 13 cosmogenic Cl-36 surface exposure ages from four sites in the Kerguelen Islands. The Cl-36 ages from erratic and moraine boulders span from 24.4 +/- 2.7 ka to 03 +/- 0.1 ka. We combined these ages with existing glacio-marine radiocarbon ages and bathymetric data to document the temporal and spatial changes of the island's glacial history. Ice began to retreat on the main island before 24.4 +/- 2.7 ka until around the time of the Antarctic Cold Reversal (ACR) period (-14.5-12.9 ka), during which the Bontemps moraine was formed by the advance of a CIC outlet glacier. Deglaciation continued during the Holocene probably until 3 ka with evidence of minor advances during the last millennium. This chronology is in pace with major changes in delta O-18 in a recent West Antarctica ice core record, showing that Kerguelen Islands glaciers are particularly sensitive and relevant to document climate change in the southern polar regions. (C) 2017 Elsevier Ltd. All rights reserved.
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Jouanne, F., Mugnier, J. L., Sapkota, S. N., Bascou, P., & Pecher, A. (2017). Estimation of coupling along the Main Himalayan Thrust in the central Himalaya. Journal Of Asian Earth Sciences, 133, 62–71.
Résumé: We analyze episodic (1995-2010) and permanent GNSS data quantifying interseismic velocities in the Himalaya of Nepal so as to constrain spatial variations in coupling along the Main Himalayan Thrust. To estimate this coupling, we model the MHT with the help of cross sections allowing us to constrain its changes in geometry from far-western Nepal to central and eastern Nepal. We determine that the upper flat of the MHT is nearly totally locked, the crustal ramp is partially locked, and that free slip is localized only along the lower flat north of the Himalaya. This location of increased coupling probably corresponds to the brittle/ductile change in rheology along the MHT and explains the location of very large (greater than the Gorkha 2015 event) earthquake epicenters north of the crustal ramp. Including the simulation of the Western Nepal Fault System in the continuation of the Karakorum fault does not improve simulation of the interseismic velocity field. The 25 April Gorkha earthquake nucleated in a highly coupled part of the upper flat of the MHT and propagated eastward along a less coupled part of the MHT. (C) 2016 Elsevier Ltd. All rights reserved.
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Jourdon, A., Petit, C., Rolland, Y., Loury, C., Bellahsen, N., Guillot, S., et al. (2017). New structural data on Late Paleozoic tectonics in the Kyrgyz Tien Shan (Central Asian Orogenic Belt). Gondwana Research, 46, 57–78.
Résumé: The tectonic evolution of the Central Asian Orogenic Belt (CAOB) is characterized by the successive accretion of lithospheric blocks, leading to different interpretations about the polarity of subductions during the Paleozoic, the number of microplates and oceanic basins and the timing of tectonic events. This is especially the case in the Tien Shan area. In this paper, we propose new structural maps and cross-sections of Middle and South Kyrgyz Tien Shan (MTS and STS respectively). These cross-sections highlight an overall dextral strike-slip shear zone in the MTS at the crustal scale and a North verging structure in the STS. These structures are Carboniferous in age and sealed by a late Carboniferous conglomerate, later overlain by Mesozoic and Cenozoic deposits. The STS exhibits two deformation phases: (1) a top-to-the-South normal shearing that can be related to subduction or exhumation dynamics and (2) a top to the North nappe stacking that we link to the late Paleozoic collisional events between the MTS and the Tarim block. We propose a new interpretation of the tectonic evolution of the Kyrgyz Tien Shan during the Late Paleozoic collision. This model involves a partitioned collisional deformation in Late Carboniferous times, with an orthogonal collision to the south, between the Tarim and MTS, and a strike-slip regime to the north along a dextral E-W zone located between the MTS and the North Tien-Shan/Kazakh platform, the so-called Nikolaev Line. The docking of the large Tarim Craton against the CAOB corresponds to a collision phase, which ended the long-lived Paleozoic subduction history in the CAOB and was followed in the TS region by intense strike-slip deformation during the Permian. (C) 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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Kaduri, M., Gratier, J. - P., Renard, F., Cakir, Z., & Lasserre, C. (2017). The implications of fault zone transformation on aseismic creep: Example of the North Anatolian Fault, Turkey. Journal Of Geophysical Research-Solid Earth, 122(6), 4208–4236.
Résumé: Aseismic creep is observed at surface along several segments of the North Anatolian right-lateral active fault in Turkey, a major plate boundary between Eurasia and Anatolia. Identifying the mechanisms that control creep and their temporal and spatial change represents a major challenge for predicting the mechanical evolution of active faults, the interplay between creep and earthquakes, and the link between short-term observations from geodesy and the long-term fault zone evolution. We combine geological observations, laboratory analyses, and imaging techniques, shedding new light on the mechanism of fault creep along the North Anatolian Fault (NAF) and its time-dependent change. A clear correlation is shown between shallow creep and near-surface fault gouge composition: locked segments of the NAF are mostly composed of massive limestones without clay gouges, whereas creeping segments comprise clay gouges that contain low-friction minerals. Such fault gouges appear to result from a progressive change of initial volcanic host rocks during their deformation. Anastomosing cleavage develops during the first stage of displacement, leading to layering, oblique at first and then subparallel to the fault, which accommodates part of the aseismic creep by pressure solution. Soluble minerals are dissolved, leading to passive concentration of phyllosilicates in the gouges where alteration transformations by fluid flow produce low friction minerals. At the same time damage zones are fractured and fractures are sealed by carbonates. As a result, these mineralogical and structural transformations weaken the gouge and strengthen the damage zone leading to the change from diffuse to localized seismic-aseismic zones.
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Kamenetsky, V. S., Maas, R., Kamenetsky, M. B., Yaxley, G. M., Ehrig, K., Zellmer, G. F., et al. (2017). Multiple mantle sources of continental magmatism: Insights from “high-Ti” picrites of Karoo and other large igneous provinces. Chemical Geology, 455, 22–31.
Résumé: Magmas forming large igneous provinces (LIP) on continents are generated by extensive melting in the deep crust and underlying mantle and associated with break-up of ancient supercontinents, followed by formation of a new basaltic crust in the mid-oceanic rifts. A lack of the unifying model in understanding the sources of LIP magmatism is justified by lithological and geochemical complexity of erupted magmas on local (e.g. a cross-section) and regional (a single and different LIP) scales. Moreover, the majority of LIP rocks do not fit general criteria for recognizing primary/primitive melts (i.e. <8 wt% MgO and absence of high-Fo olivine phenocrysts). This study presents the mineralogical (olivine, Cr-spinel, orthopyroxene), geochemical (trace elements and SrNd-Hf-Pb isotopes) and olivine-hosted melt inclusion compositional characteristics of a single primitive (16 wt%MgO), high-Ti (2.5 wt% TiO2) picrite with high-Mg olivine (up to 91 mol%Fo) from the Letaba Formation in the similar to 180 Ma Karoo LIP (south Africa). The olivine compositions (unusually high delta O-18 (6.17%circle), high NiO (0.360.56 wt) and low MnO and CaO (0.12-0.20 and 0.12-0.22 wt%, respectively)) are used to argue for a non-peridotitic mantle source. This is supported by the enrichment of the rock and melts in most incompatible trace elements and depletion in heavy rare earth elements (e.g. high Gd/Yb) that reflects residual garnet in the source of melting. The radiogenic isotopes resemble those of the model enriched mantle (EM-1) and further argue for a long-term enrichment of the source in incompatible trace elements. The enriched high-Ti compositions, strongly fractionated incompatible trace elements, presence of primitive olivine and high-Cr spinel in the Letaba picrites are closely matched by olivine-phyric rocks from the similar to 260 Ma Emeishan (Yongsheng area, SW China) and similar to 250 Ma Siberian (Maimecha-Kotuy region, N Siberia) LIPs. However, many other compositional parameters (e.g. trace element and delta O-18 compositions of olivine phenocrysts, Fe2+/ Fe3+ in Cr-spinel, Sr-Nd-Hf isotope ratios) only partially overlap or even diverge. We thus imply that parental melts of enriched picritic rocks with forsteritic olivine from three major continental igneous provinces – Karoo, Emeishan and Siberia cannot be assigned to a common mantle source and similar melting conditions. The Karoo picrites also exhibit some mineralogical and geochemical similarities with rocks and glasses in the south Atlantic Ridge and adjacent fracture zones. The geodynamic reconstructions of the continental plate motions since break-up of the Gondwanaland in the Jurassic support the current position of the source of the Karoo magmatism in the southernmost Atlantic. Co-occurrence of modern and recent anomalous rocks with normal mid-ocean ridge basalts in this region can be related to blocks/rafts of the ancient lithosphere, stranded in the ambient upper mantle and occasionally sampled by rifting-related decompressional melting. (C) 2016 Elsevier B.V. All rights reserved.
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Kaplan, E. J., Schaeffer, N., Vidal, J., & Cardin, P. (2017). Subcritical Thermal Convection of Liquid Metals in a Rapidly Rotating Sphere. Physical Review Letters, 119(9).
Résumé: Planetary cores consist of liquid metals (low Prandtl number Pr) that convect as the core cools. Here, we study nonlinear convection in a rotating (low Ekman number Ek) planetary core using a fully 3D direct numerical simulation. Near the critical thermal forcing (Rayleigh number Ra), convection onsets as thermal Rossby waves, but as Ra increases, this state is superseded by one dominated by advection. At moderate rotation, these states (here called the weak branch and strong branch, respectively) are smoothly connected. As the planetary core rotates faster, the smooth transition is replaced by hysteresis cycles and subcriticality until the weak branch disappears entirely and the strong branch onsets in a turbulent state at Ek < 10(-6). Here, the strong branch persists even as the thermal forcing drops well below the linear onset of convection (Ra = 0.7Ra(crit) in this study). We highlight the importance of the Reynolds stress, which is required for convection to subsist below the linear onset. In addition, the Peclet number is consistently above 10 in the strong branch. We further note the presence of a strong zonal flow that is nonetheless unimportant to the convective state. Our study suggests that, in the asymptotic regime of rapid rotation relevant for planetary interiors, thermal convection of liquid metals in a sphere onsets through a subcritical bifurcation.
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Karimi, K., Ferrero, E. E., & Barrat, J. - L. (2017). Inertia and universality of avalanche statistics: The case of slowly deformed amorphous solids. Physical Review E, 95(1).
Résumé: By means of a finite elements technique we solve numerically the dynamics of an amorphous solid under deformation in the quasistatic driving limit. We study the noise statistics of the stress-strain signal in the steady-state plastic flow, focusing on systems with low internal dissipation. We analyze the distributions of avalanche sizes and durations and the density of shear transformations when varying the damping strength. In contrast to avalanches in the overdamped case, dominated by the yielding point universal exponents, inertial avalanches are controlled by a nonuniversal damping-dependent feedback mechanism, eventually turning negligible the role of correlations. Still, some general properties of avalanches persist and new scaling relations can be proposed.
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Kasprzyk, C., Kaplan, E., Seilmayer, M., & Stefani, F. (2017). Transitions In A Magnetized Quasi-Laminar Spherical Couette Flow. Magnetohydrodynamics, 53(2), 393–401.
Résumé: First results of a new spherical Couette experiment are presented. The liquid metal flow in a spherical shell is exposed to a homogeneous axial magnetic field. For a Reynolds number Re = 1000, we study the effect of increasing Hartmann number Ha. The resulting flow structures are inspected by ultrasound Doppler velocimetry. With a weak applied magnetic field, we observe an equatorially antisymmetric jet instability with the azimuthal wave number m = 3. As the magnetic field strength increases, this instability vanishes. When the field is increased further, an equatorially symmetric return flow instability arises. Our observations are shown to be in good agreement with linear stability analysis and non-linear flow simulations.
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Kouketsu, Y., Hattori, K., & Guillot, S. (2017). Protolith of the Stak eclogite in the northwestern Himalaya. Italian Journal Of Geosciences, 136(1), 64–72.
Résumé: This paper reports the major, minor and trace element abundances and Nd isotope compositions of bulk rock samples of eclogites from the Stak Valley in northwestern Himalaya and discusses their protolith. Major element compositions confirm the basaltic nature of the protolith. Trace element abundances normalized to the primitive mantle show almost flat patterns at ten times the primitive mantle values with slightly high concentrations of Th and light rare earth elements. These patterns are similar to those of enriched MORBs. Neodymium isotope compositions are chondritic and the values of eNd lie between those of MORB and old Indian continental crust. Immobile trace element contents of Stak eclogites are similar to those of the Permian Panjal Traps and significantly different from those of the Deccan Traps erupted at 73-66 Ma in the northwestern Indian plate, suggesting that the Panjal Traps is the protolith of the Stak eclogites. The protoliths of ultra-high pressure eclogites in the Kaghan and Tso Moran massifs in northwestern Himalaya are also interpreted to be the Panjal Traps. The results of this study suggest that a large Permian igneous province developed at the northwestern margin of the Indian plate before the collision with the Eurasian continent.
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Krasheninnikov, S. P., Sobolev, A. V., Batanova, V. G., Kargaltsev, A. A., & Borisov, A. A. (2017). Experimental testing of olivine-melt equilibrium models at high temperatures. Doklady Earth Sciences, 475(2), 919–922.
Résumé: Data are presented on the equilibrium compositions of olivine and melts in the products of 101 experiments performed at 1300-1600A degrees C, atmospheric pressure, and controlled oxygen fugacity by means of new equipment at the Vernadsky Institute. It was shown that the available models of the olivine-melt equilibrium describe with insufficient adequacy the natural systems at temperatures over 1400A degrees C. The most adequate is the model by Ford et al. (1983). However, this model overestimates systematically the equilibrium temperature with underestimating by 20-40A degrees C at 1450-1600A degrees C. These data point to the need for developing a new, improved quantitative model of the olivine-melt equilibrium for high-temperature magnesian melts, as well as to the possibility of these studies on the basis of the equipment presented.
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Kristek, J., Moczo, P., Chaljub, E., & Kristekova, M. (2017). An orthorhombic representation of a heterogeneous medium for the finite-difference modelling of seismic wave propagation. Geophysical Journal International, 208(2), 1250–1264.
Résumé: The possibility of applying one explicit finite-difference (FD) scheme to all interior grid points (points not lying on a grid border) no matter what their positions are with respect to the material interface is one of the key factors of the computational efficiency of the FD modelling. Smooth or discontinuous heterogeneity of the medium is accounted for only by values of the effective grid moduli and densities. Accuracy of modelling thus very much depends on how these effective grid parameters are evaluated. We present an orthorhombic representation of a heterogeneous medium for the FD modelling. We numerically demonstrate its superior accuracy. Compared to the harmonic-averaging representation the orthorhombic representation is more accurate mainly in the case of strong surface waves that are especially important in local surface sedimentary basins. The orthorhombic representation is applicable to modelling seismic wave propagation and earthquake motion in isotropic models with material interfaces and smooth heterogeneities using velocity-stress, displacement-stress and displacement FD schemes on staggered, partly staggered, Lebedev and collocated grids.
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Lafay, R., Baumgartner, L. P., Stephane, S., Suzanne, P., German, M. - H., & Torsten, V. (2017). Petrologic and stable isotopic studies of a fossil hydrothermal system in ultramafic environment (Chenaillet ophicalcites, Western Alps, France): Processes of carbonate cementation. Lithos, 294, 319–338.
Résumé: The Late Jurassic Chenaillet ophiolitic complex (Western Alps) represents parts of an oceanic core-complex of the Liguria-Piemonte domain. A model for the origin and evolution of the Chenaillet ophicalcites based on textural and isotopic characterization is presented. The Chenaillet ophicalcites correspond to brecciated serpentinized peridotites that record seafloor shallow serpentinization at a minimum temperatures of 150 degrees C followed by authigenic carbonation. Carbonation starts with a network of micrometric to millimetric pre- or syn-clast formation calcite veins accompanied by a pervasive carbonation of residual olivine and serpentine inside the serpentinite mesh core. A matrix of small calcite (<50 μm, 12 μm in average) cemented clasts after their individualization. Texture of the breccia, grain size distribution within the matrix, and chrysotile clusters support rapid cementation from a strongly oversaturated fluid due most likely to hydrothermal fluid cooling and decompression. Later fluids infiltrated by multiple crack formation and some dolomite locally formed along serpentinitecalcite interfaces. Carbonates have delta C-13 (VPDB) values that range between-5%0 and + 0.4%0. The lower values were obtained for calcite within the serpentinite clasts. The delta O-18 (VSMOW) values have a range between +11% and +16% in carbonated clasts. The delta O-18 values in the matrix are fairly homogeneous with an average at +12%0 and the late calcite veins have values between + 12.5 and +15.5%. These values suggest a relatively high temperature of formation for all the carbonates. Carbonates within clast are mainly characterized by a formation temperature in the range of 110 degrees C to 180 degrees C assuming a delta O-18 value of seawater of 0%0, the matrix forms at a temperature of ca. 165 degrees C. Late veins are characterized by a formation temperature ranging between 120 and 155 degrees C. We propose a model where serpentinization is followed by discrete carbonation then brecciation and cementation as a consequence of continuous hydrothermal fluid circulation in the serpentinite basement. This is comparable to observations made in the stockwork of present-day long-lived oceanic hydrothermal systems. (C) 2017 Elsevier B.V. All rights reserved.
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Latifa, A., Lhoussaine, B., Etienne, J., Moussa, M., Yassine, A. B., Ahmed, E., et al. (2017). Impact of rock-water interactions and recharge on water resources quality of the Agadir-Essaouira basin, southwestern Morocco. Arab. J. Geosci., 10(7), 16 pp.
Résumé: The Agadir-Essaouira area in the occidental High Atlas Mountains of Morocco is characterized by a semi-arid climate. The scarcity and quality of water resources, exacerbated by long drought periods, constitute a major problem for a sustainable development of this region. Groundwater resources of carbonate units within Jurassic and Cretaceous aquifers are requested for drinking and irrigation purposes. In this study, we collected 84 samples from wells, boreholes, springs, and rivers. Hydrochemical and isotopic data were used to examine the mineralization and origin of water, which control groundwater quality. The chemical composition of water seems to be controlled by water-rock interactions, such as dissolution of carbonates (calcite and dolomite), weathering of gypsum, as well as ion exchange processes, which explain the observed variability. Stable isotopes results show that groundwater from the mainly marly Cretaceous aquifer are submitted to an evaporation effect, while samples from the chiefly calcareous Jurassic aquifer indicate a meteoric origin, due to a rapid infiltration of recharge runoff through the karstic outcrops. The low values of delta O-18 and delta H-2 suggest a local recharge from areas with elevations ranging from 400 to 1200 m for the Cretaceous aquifer and from 800 to 1500 m for the Jurassic units.
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Laurendeau, A., Courboulex, F., Bonilla, L. F., Alvarado, A., Alfonso Naya, V., Gueguen, P., et al. (2017). Low-Frequency Seismic Amplification in the Quito Basin (Ecuador) Revealed by Accelerometric Recordings of the RENAC Network. Bulletin Of The Seismological Society Of America, 107(6), 2917–2926.
Résumé: Quito, the capital city of Ecuador, with a population close to three million inhabitants, is located in an earthquake-prone region that has been struck by important events in the past. The city is built on the hanging wall of an active reverse fault, constituting a piggy-back basin filled with volcanic and fluvial origin deposits. To date, the Quito basin deep structure remains unknown as well as its effect on amplification of seismic waves. Since 2009, a permanent accelerometric network has been deployed in the city (Red Nacional de Acelerografos de Quito at present 18 stations) and operates in continuous recording mode. We select the 179 best-recorded earthquakes and estimate the horizontal-to-vertical and the standard spectral ratios to highlight site effects in the basin. We find that the southern part of the basin presents a strong site amplification at low frequencies (peak around 0.35 Hz with an amplitude larger than 3) that is not present in the northern part. The recordings of the 16 April 2016 M-w 7.8 Pedernales earthquake that occurred on the subduction interface 150 km away from Quito confirm this low-frequency amplification in the southern part of the city, by observing larger amplitudes and longer durations of the signals. Higher frequencies (around 4 Hz) are also amplified at given sites, but they are spatially more variable.
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Le Beon, M., Huang, M. - H., Suppe, J., Huang, S. - T., Pathier, E., Huang, W. - J., et al. (2017). Shallow geological structures triggered during the M-w 6.4 Meinong earthquake, southwestern Taiwan. Terrestrial Atmospheric And Oceanic Sciences, 28(5), 663–681.
Résumé: The Meinong earthquake generated up to similar to 10 cm surface displacement located 10 – 35 km west of the epicenter and monitored by InSAR and GPS. In addition to coseismic deformation related to the deep earthquake source, InSAR revealed three sharp surface displacement gradients. One of them is extensional and is inconsistent with the westward interseismic shortening of similar to 45 mm yr(-1) in this region. The gradient sharpness suggests slip triggering on shallow structures, some of which were not well documented before. To characterize these shallow structures, we investigated potential surface ruptures in the field. Sets of similar to NS tension cracks distributed over 25 – 300 m width, with cumulative extension in the same order as InSAR observations, were found along 5.5 km distance along the extensional gradient and are interpreted as surface rupture. We build two E-W regional balanced cross-sections, based on surface geology, subsurface data, and coseismic and interseismic geodetic data. From the Coastal Plain to the east edge of the coseismic deformation area, we propose a series of three active west-dipping backthrusts: the Houchiali fault, the Napalin-Pitou back-thrust, and the Lungchuan backthrust. They all root on the 3.5 – 4.0 km deep Tainan detachment located near the base of the 3-km-thick Gutingkeng mudstone. Further east, the detachment would ramp down to similar to 7 km depth. Coseismic surface deformation measurements suggest that, in addition to the deeper (15 – 0 km) main rupture plane, mostly the ramp, the Lungchuan backthrust, and the Tainan detachment were activated during or right after the earthquake. Local extension is considered as transient deformation at the west edge of the shallow main slip zone.
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Le Breton, M., Baillet, L., Larose, E., Rey, E., Benech, P., Jongmans, D., et al. (2017). Outdoor meteorological effects on UHF RFID phase shift: experimental simulations.
Résumé: The present study investigates meteorological factors that affect the phase of RFID passive tags at 868 MHz, in outdoor conditions. The study identifies the effect of the water on the antennas, the temperature of the cables and tags, the moisture of the tag support, and the atmospheric conditions. These effects could lead to over 8 radians phase drift, over a year in a typical environment. That leads to a possible yearly error of 20 centimeters in a typical outdoor ranging application. The article proposes techniques to correct those effects, in order to increase the accuracy of phase-based outdoor monitoring applications.
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Le Roy, M., Deline, P., Carcaillet, J., Schimmelpfennig, I., & Ermini, M. (2017). Be-10 exposure dating of the timing of Neoglacial glacier advances in the Ecrins-Pelvoux massif, southern French Alps. Quaternary Science Reviews, 178, 118–138.
Résumé: Alpine glacier variations are known to be reliable proxies of Holocene climate. Here, we present a terrestrial cosmogenic nuclide (TCN)-based glacier chronology relying on 24 new Be-10 exposure ages, which constrain maximum Neoglacial positions of four small to mid-sized glaciers (Rateau, Lautaret, Bonnepierre and Etages) in the Ecrins-Pelvoux massif, southern French Alps. Glacier advances, marked by (mainly lateral) moraine ridges that are located slightly outboard of the Little Ice Age (LIA, c. 1250-1860 AD) maximum positions, were dated to 4.25 +/- 0.44 ka, 3.66 +/- 0.09 ka, 2.09 +/- 0.10 ka, c. 1.31 +/- 0.17 ka and to 0.92 +/- 0.02 ka. The '4.2 ka advance, albeit constrained by rather scattered dates, is to our knowledge exposure-dated here for the first time in the Alps. It is considered as one of the first major Neoglacial advance in the western Alps, in agreement with other regional paleoclimatological proxies. We further review Alpine and Northern Hemisphere mid-to-high latitude evidence for climate change and glacier activity concomitant with the '4.2 ka event. The '2.1 ka advance was not extensively dated in the Alps and is thought to represent a prominent advance in early Roman times. Other Neoglacial advances dated here match the timing of previously described Alpine Neoglacial events. Our results also suggest that a Neoglacial maximum occurred at Etages Glacier 0.9 ka ago, i.e. during the Medieval Climate Anomaly (MCA, c. 850-1250 AD). At Rateau Glacier, discordant results are thought to reflect exhumation and snow cover of the shortest moraine boulders. Overall, this study highlights the need to combine several sites to develop robust Neoglacial glacier chronologies in order to take into account the variability in moraine deposition pattern and landform obliteration and conservation. (C) 2017 Elsevier Ltd. All rights reserved.
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Lecocq, T., Longuevergne, L., Pedersen, H. A., Brenguier, F., & Stammler, K. (2017). Monitoring ground water storage at mesoscale using seismic noise: 30 years of continuous observation and thermo-elastic and hydrological modeling. Scientific Reports, 7.
Résumé: Groundwater is a vital freshwater resource for both humans and ecosystems. Achieving sustainable management requires a detailed knowledge of the aquifer structure and of its behavior in response to climatic and anthropogenic forcing. Traditional monitoring is carried out using piezometer networks, and recently complemented with new geophysical or satellite-based observations. These techniques survey either local (small-scale) water systems or regional areas (large scale) but, to date, adequate observation tools are lacking at the water management scale (i.e. several tens of kms), which is generally explored by modeling. Using 30 years of continuous recording by four seismic stations of the Grafenberg Array (Germany), we demonstrate that long-term observations of velocity variations (approximately 0.01%) of surface waves can be extracted from such recordings of ocean-generated seismic noise. These small variations can be explained by changes to mechanical properties of the complex aquifer system in the top few hundred meters of the crust. The velocity changes can be interpreted as effects of temperature diffusion and water storage changes. Seismic noise recordings may become a new and valuable tool to monitor heterogeneous groundwater systems at mesoscale, in addition to existing observation methods.
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Lehmann, S. G., Bourgoin-Voillard, S., Seve, M., & Rachidi, W. (2017). Tubulin Beta-3 Chain as a New Candidate Protein Biomarker of Human Skin Aging: A Preliminary Study. Oxidative Medicine And Cellular Longevity, .
Résumé: Skin aging is a complex process, and a lot of efforts have been made to identify new and specific targets that could help to diagnose, prevent, and treat skin aging. Several studies concerning skin aging have analyzed the changes in gene expression, and very few investigations have been performed at the protein level. Moreover, none of these proteomic studies has used a global quantitative labeled proteomic offgel approach that allows a more accurate description of aging phenotype. We applied such an approach on human primary keratinocytes obtained from sun-nonexposed skin biopsies of young and elderly women. A total of 517 unique proteins were identified, and 58 proteins were significantly differentially expressed with 40 that were downregulated and 18 upregulated with aging. Gene ontology and pathway analysis performed on these 58 putative biomarkers of skin aging evidenced that these dysregulated proteins were mostly involved in metabolism and cellular processes such as cell cycle and signaling pathways. Change of expression of tubulin beta-3 chain was confirmed by western blot on samples originated from several donors. Thus, this study suggested the tubulin beta-3 chain has a promising biomarker in skin aging.
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Lehmann, S. G., Bourgoin-Voillard, S., Seve, M., & Rachidi, W. (2017). Tubulin Beta-3 Chain as a New Candidate Protein Biomarker of Human Skin Aging: A Preliminary Study. Oxidative medicine and cellular longevity, 2017, 5140360.
Résumé: Skin aging is a complex process, and a lot of efforts have been made to identify new and specific targets that could help to diagnose, prevent, and treat skin aging. Several studies concerning skin aging have analyzed the changes in gene expression, and very few investigations have been performed at the protein level. Moreover, none of these proteomic studies has used a global quantitative labeled proteomic offgel approach that allows a more accurate description of aging phenotype. We applied such an approach on human primary keratinocytes obtained from sun-nonexposed skin biopsies of young and elderly women. A total of 517 unique proteins were identified, and 58 proteins were significantly differentially expressed with 40 that were downregulated and 18 upregulated with aging. Gene ontology and pathway analysis performed on these 58 putative biomarkers of skin aging evidenced that these dysregulated proteins were mostly involved in metabolism and cellular processes such as cell cycle and signaling pathways. Change of expression of tubulin beta-3 chain was confirmed by western blot on samples originated from several donors. Thus, this study suggested the tubulin beta-3 chain has a promising biomarker in skin aging.
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Lemasquerier, D., Grannan, A. M., Vidal, J., Cebron, D., Favier, B., Le Bars, M., et al. (2017). Libration-driven flows in ellipsoidal shells. Journal Of Geophysical Research-Planets, 122(9), 1926–1950.
Résumé: Planets and satellites can undergo physical librations, which consist of forced periodic variations in their rotation rate induced by gravitational interactions with nearby bodies. This mechanical forcing may drive turbulence in interior fluid layers such as subsurface oceans and metallic liquid cores through a libration-driven elliptical instability (LDEI) that refers to the resonance of two inertial modes with the libration-induced base flow. LDEI has been studied in the case of a full ellipsoid. Here we address for the first time the question of the persistence of LDEI in the more geophysically relevant ellipsoidal shell geometries. In the experimental setup, an ellipsoidal container with spherical inner cores of different sizes is filled with water. Direct side view flow visualizations are made in the librating frame using Kalliroscope particles. A Fourier analysis of the light intensity fluctuations extracted from recorded movies shows that the presence of an inner core leads to spatial heterogeneities but does not prevent LDEI. Particle image velocimetry and direct numerical simulations are performed on selected cases to confirm our results. Additionally, our survey at a fixed forcing frequency and variable rotation period (i.e., variable Ekman number, E) shows that the libration amplitude at the instability threshold varies as similar to E-0.65. This scaling is explained by a competition between surface and bulk dissipation. When extrapolating to planetary interior conditions, this leads to the E-1/2 scaling commonly considered. We argue that Enceladus' subsurface ocean and the core of the exoplanet 55 CnC e should both be unstable to LDEI. Plain Language Summary Because of their gravitational interactions with other bodies, planets and moons are subjected to mechanical forcings that perturb their spin rate. The motivation of this study is to determine whether one of these forcings, called libration, can drive global-scale flows in interior fluid layers, like the subsurface ocean of Europa or the liquid inner core of Io. Turbulent flows in these layers are of interest because they can be linked to the generation of magnetic fields, planetary heat fluxes, and energy dissipation rates. Furthermore, since it has been proposed that life may be harbored within these subsurface oceans, their internal structure and dynamics are of broad interest to the planetary science community and beyond. To model libration experimentally, containers of a given geometry are filled with water and are made to librate. Previous studies have shown that the flow can become unstable for precise oscillation frequencies. By combining laboratory experiments, numerical simulations, and a theoretical analysis, we show for the first time that this instability persists in an ellipsoidal shell geometry, i.e., an ellipsoid inside of which is suspended a spherical inner core. This result is of primary importance since most liquid cores and subsurface oceans are expected to have this geometry. Furthermore, our results show that the generated turbulence can be latitudinally inhomogeneous. By performing a survey, we extrapolate our results to planetary interior conditions and show that libration is capable of driving turbulence in planetary cores (e.g., the exoplanet 55 CnC e) and subsurface oceans (e.g., Enceladus).
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Lemelle, L., Simionovici, A., Schoonjans, T., Tucoulou, R., Enrico, E., Salome, M., et al. (2017). Analytical requirements for quantitative X-ray fluorescence nano-imaging of metal traces in solid samples. Trac-Trends In Analytical Chemistry, 91, 104–111.
Résumé: Quantitative nano-imaging of metal traces in a solid is a recent capability arising from the construction of hard X-ray nanoprobes dedicated to X-ray Fluorescence (XRF) imaging on upgraded third generation synchrotrons. Micrometer sample preparation valid for trace analysis is a fundamental part of the required developments to capitalize on the reduced Minimum Detection Limits. Practical guidelines lead us to propose a customized use of Focused Ion Beams (FIB) backed by state of the art Monte Carlo XRF modeling to initiate preparations of new samples and certified standards. The usefulness of these developments is illustrated by the first detection of Ni traces (4.57E+07 +/- 3.2E+06 (7.1%) at μm(-3)) in a 3.35 Ga old microstructure of putative microbial origin from Barberton (South Africa). A list of feasibility checks provides a way of getting below 5 ppm MDLs for acquisition-times of 10 s with an analytical precision better than 10%. (C) 2017 Elsevier B.V. All rights reserved.
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Lengline, O., Frank, W. B., Marsan, D., & Ampuero, J. - P. (2017). Imbricated slip rate processes during slow slip transients imaged by low-frequency earthquakes. Earth And Planetary Science Letters, 476, 122–131.
Résumé: Low Frequency Earthquakes (LFEs) often occur in conjunction with transient strain episodes, or Slow Slip Events (SSEs), in subduction zones. Their focal mechanism and location consistent with shear failure on the plate interface argue for a model where LFEs are discrete dynamic ruptures in an otherwise slowly slipping interface. SSEs are mostly observed by surface geodetic instruments with limited resolution and it is likely that only the largest ones are detected. The time synchronization of LFEs and SSEs suggests that we could use the recorded LFEs to constrain the evolution of SSEs, and notably of the geodetically-undetected small ones. However, inferring slow slip rate from the temporal evolution of LFE activity is complicated by the strong temporal clustering of LFEs. Here we apply dedicated statistical tools to retrieve the temporal evolution of SSE slip rates from the time history of LFE occurrences in two subduction zones, Mexico and Cascadia, and in the deep portion of the San Andreas fault at Parkfield. We find temporal characteristics of LFEs that are similar across these three different regions. The longer term episodic slip transients present in these datasets show a slip rate decay with time after the passage of the SSE front possibly as t(-1/4). They are composed of multiple short term transients with steeper slip rate decay as t(-alpha) with alpha between 1.4 and 2. We also find that the maximum slip rate of SSEs has a continuous distribution. Our results indicate that creeping faults host intermittent deformation at various scales resulting from the imbricated occurrence of numerous slow slip events of various amplitudes. (C) 2017 Elsevier B.V. All rights reserved.
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Leonard, D. N., & Hellmann, R. (2017). Exploring dynamic surface processes during silicate mineral (wollastonite) dissolution with liquid cell TEM. Journal Of Microscopy, 265(3), 358–371.
Résumé: Most liquid cell transmission electron microscopy (LC TEM) studies focus on nanoparticles or nanowires, in large part because the preparation and study of materials in this size range is straightforward. By contrast, this is not true for samples in the micrometre size range, in large part because of the difficulties associated with sample preparation starting from a 'bulk' material. There are also many advantages inherent to the study of micrometre-sized samples compared to their nanometre-sized counterparts. Here, we present a liquid cell transmission electron study that employed an innovative sample preparation technique using focused ion beam (FIB) milling to fabricate micrometre-sized electron transparent lamellae that were then welded to the liquid cell substrate. This technique, for which we have described in detail all of the fabrication steps, allows for samples having dimensions of several square micrometres to be observed by TEM in situ in a liquid. We applied this technique to test whether we could observe and measure in situ dissolution of a crystalline material called wollastonite, a calcium silicate mineral. More specifically, this study was used to observe and record surface dynamics associated with step and terrace edge movement, which are ultimately linked to the overall rate of dissolution. The wollastonite lamella underwent chemical reactions in pure deionized water at ambient temperature in a liquid cell with a 5-mu m-spacer thickness. The movement of surface steps and terraces was measured periodically over a period of almost 5 h. Quite unexpectedly, the one-dimensional rates of retreat of these surface features were not constant, but changed over time. In addition, there were noticeable quantitative differences in retreat rates as a function crystallographic orientation, indicating that surface retreat is anisotropic. Several bulk rates of dissolution were also determined (1.6-4.2 10(-7) mol m(-2) s(-1) ) using the rates of retreat of representative terraces and steps, and were found to be within one order of magnitude of dissolution rates in the literature based on aqueous chemistry data.
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Leroy, P., Li, S., Jougnot, D., Revil, A., & Wu, Y. (2017). Modelling the evolution of complex conductivity during calcite precipitation on glass beads. Geophysical Journal International, 209(1), 123–140.
Résumé: When pH and alkalinity increase, calcite frequently precipitates and hence modifies the petro-physical properties of porous media. The complex conductivity method can be used to directly monitor calcite precipitation in porous media because it is sensitive to the evolution of the mineralogy, pore structure and its connectivity. We have developed a mechanistic grain polarization model considering the electrochemical polarization of the Stern and diffuse layers surrounding calcite particles. Our complex conductivity model depends on the surface charge density of the Stern layer and on the electrical potential at the onset of the diffuse layer, which are computed using a basic Stern model of the calcite/water interface. The complex conductivity measurements of Wu et al. on a column packed with glass beads where calcite precipitation occurs are reproduced by our surface complexation and complex conductivity models. The evolution of the size and shape of calcite particles during the calcite precipitation experiment is estimated by our complex conductivity model. At the early stage of the calcite precipitation experiment, modelled particles sizes increase and calcite particles flatten with time because calcite crystals nucleate at the surface of glass beads and grow into larger calcite grains. At the later stage of the calcite precipitation experiment, modelled sizes and cementation exponents of calcite particles decrease with time because large calcite grains aggregate over multiple glass beads and only small calcite crystals polarize.
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Linga, G., Mathiesen, J., & Renard, F. (2017). Self-similar distributions of fluid velocity and stress heterogeneity in a dissolving porous limestone. Journal Of Geophysical Research-Solid Earth, 122(3), 1726–1743.
Résumé: In a porous rock, the spatial distribution of the pore space induces a strong heterogeneity in fluid flow rates and in the stress distribution in the rock mass. If the rock microstructure evolves through time, for example, by dissolution, fluid flow and stress will evolve accordingly. Here we consider a core sample of porous limestone that has undergone several steps of dissolution. Based on 3-D X-ray tomography scans, we calculate numerically the coupled system of fluid flow in the pore space and stress in the solid. We determine how the flow field affects the stress distribution both at the pore wall surface and in the bulk of the solid matrix. We show that during dissolution, the heterogeneous stress evolves in a self-similar manner as the porosity is increased. Conversely, the fluid velocity shows a stretched exponential distribution. The scalings of these common master distributions offer a unified description of the porosity evolution, pore flow, and the heterogeneity in stress for a rock with evolving microstructure. Moreover, the probability density functions of stress invariants (mechanical pressure or von Mises stress) display heavy tails toward large stresses. If these results can be extended to other kinds of rocks, they provide an additional explanation of the sensitivity to failure of porous rocks under slight changes of stress.
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Liu, W., Chen, R., Cai, H., Luo, W., & Revil, A. (2017). Correlation analysis for spread-spectrum induced-polarization signal processing in electromagnetically noisy environments. Geophysics, 82(5), E243–E256.
Résumé: In induced-polarization (IP) surveys, the raw data are usually distorted significantly by the presence of electromagnetic (EM) interferences, including cultural noise. Several methods have been proposed to improve the signal-to-noise ratio of these data. However, signal processing in an electromagnetically noisy environment is still a challenging problem. We have determined a new and simple technique based on the analysis of the correlation between the measured potential and the injected primary current signals. This processing is applied to the data acquired using a new frequency-domain IP method called the spread-spectrum induced-polarization (SSIP) approach. In this approach, we use a pseudorandom m-sequence (also called the maximum length sequence) for the injected primary current. One of the advantages of this sequence is to be essentially spectrally flat in a given frequency range. Therefore, complex resistivity can be determined simultaneously at various frequencies. A new SSIP data set is acquired in the vicinity of Baiyin mine, Gansu Province, China. The correlation between potential difference and transmitting current signals for each period can be used to assess data quality. Only when the correlation coefficient between the two signals is greater than 0.5 can the SSIP data be used for subsequent processing and tomography. We determine what threshold value should be used for the correlation coefficient to extract high-quality apparent complex resistivity data and eliminate EM-contaminated data. We then compare the pseudosections with and without using the correlation analysis. When the correlation analysis is used, the noisy data are filtered out, and the target anomaly obtained through tomography is clearly enhanced. The inversion results of the apparent complex resistivity (amplitude and phase) for the survey area are consistent with some independent geologic and drilling information regarding the position of the ore body demonstrating the effectiveness of the approach.
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Lupker, M., Lave, J., France-Lanord, C., Christl, M., Bourles, D., Carcaillet, J., et al. (2017). Be-10 systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis. Earth Surface Dynamics, 5(3), 429–449.
Résumé: The Tsangpo-Brahmaputra River drains the eastern part of the Himalayan range and flows from the Tibetan Plateau through the eastern Himalayan syntaxis downstream to the Indo-Gangetic floodplain and the Bay of Bengal. As such, it is a unique natural laboratory to study how denudation and sediment production processes are transferred to river detrital signals. In this study, we present a new Be-10 data set to constrain denudation rates across the catchment and to quantify the impact of rapid erosion within the syntaxis region on cosmogenic nuclide budgets and signals. The measured Be-10 denudation rates span around 2 orders of magnitude across individual catchments (ranging from 0.03 to > 4 mm yr(-1)) and sharply increase as the Tsangpo-Brahmaputra flows across the eastern Himalaya. The increase in denudation rates, however, occurs similar to 150 km downstream of the Namche Barwa-Gyala Peri massif (NBGPm), an area which has been previously characterized by extremely high erosion and exhumation rates. We suggest that this downstream lag is mainly due to the physical abrasion of coarse-grained, low Be-10 concentration, landslide material produced within the syntaxis that dilutes the upstream high-concentration Be-10 flux from the Tibetan Plateau only after abrasion has transferred sediment to the studied sand fraction. A simple abrasion model produces typical lag distances of 50 to 150 km compatible with our observations. Abrasion effects reduce the spatial resolution over which denudation can be constrained in the eastern Himalayan syntaxis. In addition, we also highlight that denudation rate estimates are dependent on the sediment connectivity, storage, and quartz content of the upstream Tibetan Plateau part of the catchment, which tends to lead to an overestimation of downstream denudation rates. While no direct Be-10 denudation measurements were made in the syntaxis, the dilution of the upstream Be-10 signal, measured in Tsangpo-Brahmaputra sediments, provides constraints on the denudation rates in that region. These denudation estimates range from ca. 2 to 5 mm yr(-1) for the entire syntaxis and ca. 4 to 28 mm yr(-1) for the NBGPm, which is significantly higher than other large catchments. Overall, Be-10 concentrations measured at the outlet of the Tsangpo-Brahmaputra in Bangladesh suggest a sediment flux between 780 and 1430 Mt yr(-1) equivalent to a denudation rate between 0.7 and 1.2 mm yr(-1) for the entire catchment.
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Lyu, C., Pedersen, H. A., Paul, A., Zhao, L., & Solarino, S. (2017). Shear wave velocities in the upper mantle of the Western Alps: new constraints using array analysis of seismic surface waves. Geophysical Journal International, 210(1), 321–331.
Résumé: It remains challenging to obtain absolute shear wave velocities of heterogeneities of small lateral extension in the uppermost mantle. This study presents a cross-section of Vs across the strongly heterogeneous 3-D structure of the western European Alps, based on array analysis of data from 92 broad-band seismic stations from the CIFALPS experiment and from permanent networks in France and Italy. Half of the stations were located along a dense sublinear array. Using a combination of these stations and off-profile stations, fundamental-mode Rayleigh wave dispersion curves were calculated using a combined frequency-time beamforming approach. We calculated dispersion curves for seven arrays of approximately 100 km aperture and 14 arrays of approximately 50 km aperture, the latter with the aim of obtaining a 2-D vertical cross-section of Vs beneath the western Alps. The dispersion curves were inverted for Vs(z), with crustal interfaces imposed from a previous receiver function study. The array approach proved feasible, as Vs(z) from independent arrays vary smoothly across the profile length. Results from the seven large arrays show that the shear velocity of the upper mantle beneath the European plate is overall low compared to AK135 with the lowest velocities in the internal part of the western Alps, and higher velocities east of the Alps beneath the Po plain. The 2-D Vs model is coherent with (i) a similar to 100 km thick eastward-dipping European lithosphere west of the Alps, (ii) very high velocities beneath the Po plain, coherent with the presence of the Alpine (European) slab and (iii) a narrow low-velocity anomaly beneath the core of the western Alps (from the Brianc, onnais to the Dora Maira massif), and approximately colocated with a similar anomaly observed in a recent teleseismic P-wave tomography. This intriguing anomaly is also supported by traveltime variations of subvertically propagating body waves from two teleseismic events that are approximately located on the profile great circle.
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Ma, B., Fernandez-Martinez, A., Grangeon, S., Toumassat, C., Findling, N., Claret, F., et al. (2017). Evidence of Multiple Sorption Modes in Layered Double Hydroxides Using Mo As Structural Probe. Environmental Science & Technology, 51(10), 5531–5540.
Résumé: Layered double hydroxides (LDHs) have been considered as effective phases for the remediation of aquatic environments, to remove anionic contaminants mainly through anion exchange mechanisms. Here, a combination of batch isotherm experiments and X-ray techniques was used to examine molybdate (MoO42-) sorption mechanisms on CaAl LDHs with increasing loadings of molybdate. Advanced modeling of aqueous data shows that the sorption isotherm can be interpreted by three retention mechanisms, including two types of edge sites complexes, interlayer anion exchange, and CaMoO4 precipitation. Meanwhile, Mo geometry evolves from tetrahedral to octahedral on the edge, and back to tetrahedral coordination at higher Mo loadings, indicated by Mo Kedge X-ray absorption spectra. Moreover, an anion exchange process on both CaAl LDHs was followed by in situ time-resolved synchrotron-based X-ray diffraction, remarkably agreeing with the sorption isotherm. This detailed molecular view shows that different uptake mechanisms edge sorption, interfacial dissolution-reprecipitation are at play and control anion uptake under environmentally relevant conditions, which is contrast to the classical view of anion exchange as the primary retention mechanism. This work puts all these mechanisms in perspective, offering a new insight into the complex interplay of anion uptake mechanisms by LDH phases, by using changes in Mo geometry as powerful molecular-scale probe.
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Mahaney, W. C., Allen, C. C. R., Pentlavalli, P., Kulakova, A., Young, J. M., Dirszowsky, R. W., et al. (2017). Biostratigraphic Evidence Relating to the Age-Old Question of Hannibal's Invasion of Italy, I: History and Geological Reconstruction. Archaeometry, 59(1), 164–178.
Résumé: Controversy over the alpine route that Hannibal of Carthage followed from the Rhone Basin into Italia has raged amongst classicists and ancient historians for over two millennia. The motivation for identifying the route taken by the Punic Army through the Alps lies in its potential for identifying sites of historical archaeological significance and for the resolution of one of history's most enduring quandaries. Here, we present stratigraphic, geochemical and microbiological evidence recovered from an alluvial floodplain mire located below the Col de la Traversette (similar to 3000 m aslabove sea level) on the French/Italian border that potentially identifies the invasion route as the one originally proposed by Sir Gavin de Beer (de Beer ). The dated layer is termed the MAD bed (mass animal deposition) based on disrupted bedding, greatly increased organic carbon and key/specialized biological components/compounds, the latter reported in Part II of this paper. We propose that the highly abnormal churned up (bioturbated) bed was contaminated by the passage of Hannibal's animals, possibly thousands, feeding and watering at the site, during the early stage of Hannibal's invasion of Italia (218 bc).
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Mahaney, W. C., Allen, C. C. R., Pentlavalli, P., Kulakova, A., Young, J. M., Dirszowsky, R. W., et al. (2017). Biostratigraphic Evidence Relating to the Age-Old Question of Hannibal's Invasion of Italy, II: Chemical Biomarkers and Microbial Signatures. Archaeometry, 59(1), 179–190.
Résumé: As discussed in Part I, a large accumulation of mammalian faeces at the mire site in the upper Guil Valley near Mt. Viso, dated to 2168cal C-14 yr., provides the first evidence of the passage of substantial but indeterminate numbers of mammals within the time frame of the Punic invasion of Italia. Specialized organic biomarkers bound up in a highly convoluted and bioturbated bed constitute an unusual anomaly in a histosol comprised of fibric and hemist horizons that are usually expected to display horizontal bedding. The presence of deoxycholic acid and ethylcoprostanol derived from faecal matter, coupled with high relative numbers of Clostridia 16S rRNA genes, suggests a substantial accumulation of mammalian faeces at the site over 2000years ago. The results reported here constitute the first chemical and biological evidence of the passage of large numbers of mammals, possibly indicating the route of the Hannibalic army at this time. Combined with the geological analysis reported in Part I, these data provide a background supporting the need for further historical archaeological exploration in this area.
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Mahaney, W. C., Somelar, P., Pulleyblank, C., Tricart, P., West, A., Young, J. M., et al. (2017). Notes On Magnetic Susceptibility In The Guil Valley Alluvial Mire Correlated With The Punic Invasion Of Italia In 218 Bc. Mediterranean Archaeology & Archaeometry, 17(1), 23–35.
Résumé: The enigma of Hannibal's route across the Alps in 218 BC is one of the most enduring questions of antiquity. Many authorities, some of whom have never ventured into the mountains, have argued for various preferred crossings of the Alps. Earlier efforts to identify the route focused on the two-tier rockfall and regrouping area on the lee side of the Range, originally described by Polybius in his The Rise of the Roman Empire, by Livy in The War with Hannibal, and later by Sir Gavin de Beer who searched out the topography and stream dynamics in the area of several projected crossing routes. Recently, attention shifted to the alluvial mire in the upper Guil River after cores and sections (sites G5 and G5A, Mahaney et al., 2016a) revealed the presence of churned-up or bioturbated beds, called the Mass Animal Deposition (MAD) layer. At approximately 45 +/- 15 cm depth, the top of the MAD layer contains abundant bacteria belonging to the class Clostridia that are found in the mammalian gut and fecal deposits, all dated by AMS C-14 to 2168 cal yr BP (i.e., 218 BC with a 95% confidence interval). Samples for magnetic susceptibility collected from three additional sections (G5B, G5C and G5D) carrying the churned-up beds reveal heightened magnetic intensity within these bioturbated sediments that is suggestive of high magnetite content, one form of iron that often was used to cast weapons in ancient times. Magnetic susceptibility levels are highest within the churned-up beds with minor exceptions in two of the three sections analyzed, possibly indicating the presence of weathered tools, implements or weapons lost or discarded. The available data is sufficient to suggest that a GPR survey of the entire mire might well lead to recovery of the first artifacts from the invasion that would shed enormous light on the culture of ancient Carthage.
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Maineult, A., Revil, A., Camerlynck, C., Florsch, N., & Titov, K. (2017). Upscaling of spectral induced polarization response using random tube networks. Geophysical Journal International, 209(2), 948–960.
Résumé: In order to upscale the induced polarization (IP) response of porous media, from the pore scale to the sample scale, we implement a procedure to compute the macroscopic complex resistivity response of random tube networks. A network is made of a 2-D square-meshed grid of connected tubes, which obey to a given tube radius distribution. In a simplified approach, the electrical impedance of each tube follows a local Pelton resistivity model, with identical resistivity, chargeability and Cole-Cole exponent values for all the tubes-only the time constant varies, as it depends on the radius of each tube and on a diffusion coefficient also identical for all the tubes. By solving the conservation law for the electrical charge, the macroscopic IP response of the network is obtained. We fit successfully the macroscopic complex resistivity also by a Pelton resistivity model. Simulations on uncorrelated and correlated networks, for which the tube radius distribution is so that the decimal logarithm of the radius is normally distributed, evidence that the local and macroscopic model parameters are the same, except the Cole-Cole exponent: its macroscopic value diminishes with increasing heterogeneity (i.e. with increasing standard deviation of the radius distribution), compared to its local value. The methodology is also applied to six siliciclastic rock samples, for which the pore radius distributions from mercury porosimetry are available. These samples exhibit the same behaviour as synthetic media, that is, the macroscopic Cole-Cole exponent is always lower than the local one. As a conclusion, the pore network method seems to be a promising tool for studying the upscaling of the IP response of porous media.
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Malusa, M. G., Zhao, L., Eva, E., Solarino, S., Paul, A., Guillot, S., et al. (2017). Earthquakes in the western Alpine mantle wedge. Gondwana Research, 44, 89–95.
Résumé: The assessment of seismic activity in the shallow continental mantle has long been hindered by the low resolution of both seismic imaging and earthquake locations in young collision zones. Here, we combine the most recent and high-resolution image of the lithospheric structure of the Western Alps with a high quality dataset of anomalously deep earthquakes recorded in the same area in the past 25 yrs. We show that these earthquakes are aligned on an active lithospheric strike-slip fault, and we provide evidence that this fault is located in the mantle wedge beneath the Adriatic Moho. Our results: (i) provide direct evidence that deep material can be seismogenic or not depending on the lithology; (ii) confirm the role of serpentinization in favoring the aseismic creep of mantle rocks; and (iii) demonstrate that the upper mantle can be stiff and seismogenic not only in cold cratons, but also in young orogenic belts. (C) 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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Malvoisin, B., Chopin, C., Baronnet, A., Brunet, F., Bezacier, L., & Guillot, S. (2017). Fe-Ni-rich Silicate Aggregates Formed after Sulfides in High-pressure Serpentinites. Journal Of Petrology, 58(5), 963–978.
Résumé: High-pressure serpentinites from Alpine Corsica, the Piedmont Zone (Western Alps), the Tso Morari dome (Himalaya), the Dominican Republic and Cuba (Greater Antilles) contain reddish (Ni,Fe)-rich silicate aggregates, a few hundred micrometers in size, which have not been reported so far from lower-pressure serpentinites, nor found there through systematic screening. The high atomic (Ni + Fe)/Si ratio (5 +/- 4) of these aggregates, as well as their occurrence as coronas around (Ni,Fe)-sulfides, indicates their formation at the expense of sulfides and serpentine. The high (Ni + Fe)/Si ratio may suggest the presence of an Fe or Ni analogue of the rare serpentine-related minerals balangeroite or cronstedtite. However, compositional variations within and between aggregates, synchrotron X-ray diffraction data acquired on single aggregates, and transmission electron microscopy reveal that these aggregates are not a single phase but rather a mixture at the hundreds of nanometer scale of oxyhydroxides, mainly goethite (FeOOH) + (Ni,Fe)-rich serpentine +/- chlorite +/- reevesite [Ni6Fe2(OH)(16)(CO3)center dot 4H(2)O] +/- magnetite. In addition to microtexture and mineralogy, strong chemical variations at the border of the aggregates and along micro-veins suggest formation through a low-temperature alteration process. However, the occurrence of such pseudomorphic aggregates only in high-pressure serpentinites suggests that they were formed at the expense of a high-pressure silicate precursor of high M2+/Si ratio, still to be identified but which could be a main nickel carrier at depth in subduction zones.
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Margirier, A., Audin, L., Robert, X., Pecher, A., & Schwartz, S. (2017). Stress field evolution above the Peruvian flat-slab (Cordillera Blanca, northern Peru). Journal Of South American Earth Sciences, 77, 58–69.
Résumé: In subduction settings, the tectonic regime of the overriding plate is closely related to the geometry of the subducting plate. Flat-slab segments are supposed to increase coupling at the plate interface in the Andes, resulting in an increase and eastward migration of the shortening in the overriding plate. Above the Peruvian flat-slab, a 200 km-long normal fault trend parallel to the range and delimits the western flank of the Cordillera Blanca. In a context of flat subduction, expected to produce shortening, the presence of the Cordillera Blanca normal fault (CBNF) is surprising. We performed a systematic inversion of striated fault planes in the Cordillera Blanca region to better characterize the stress field above the Peruvian flat-slab. It evidences the succession of different tectonic regimes. NE-SW extension is predominant in most of the sites indicating a regional extension. We suggest that the Peruvian flat-slab trigger extension in the Western Cordillera while the shortening migrated eastward. Finally, we propose that flat-slab segments do not increase the coupling at the trench neither the shortening in the overriding plate but only favor shortening migration backward. However, the stress field of the overriding plate arises from the evolution of plate interface properties through time due to bathymetric anomaly migration. (C) 2017 Elsevier Ltd. All rights reserved.
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Mariet, A. - L., Sarret, G., Begeot, C., Walter-Simonnet, A. - V., & Gimbert, F. (2017). Lead Highly Available in Soils Centuries after Metallurgical Activities. Journal Of Environmental Quality, 46(6), 1236–1242.
Résumé: Lead (Pb)-contaminated sites that resulted from past mining and smelting activities still pose toxicological and ecotoxicological issues worldwide. A large body of research has been dedicated to evaluating the contamination and proposing mitigation strategies for recently contaminated sites (from the 19th century until the present). The possible impact of older contaminations has been much less investigated. The present study focuses on soils affected by Pb-silver mining and smelting activities during the 15th to 18th centuries. A combination of sequential extractions and X-ray absorption spectroscopy was used to determine the Pb fractionation and speciation in these soils. Despite the long passage of time, Pb was still highly available (1 and 6% of Pb present in the exchangeable fraction and 46 to 71% in the reducible fraction) and mostly present as Pb sorbed on iron (oxyhydr) oxides. Galena (lead sulfide, PbS) was observed in a soil sample from a kitchen garden, suggesting the recent use of smelter slags as soil amendments. This study shows that Pb is still highly available on this site after almost five centuries, probably because of the acidic character of the soil and the soil composition.
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Marsan, D., & Helmstetter, A. (2017). How variable is the number of triggered aftershocks? Journal Of Geophysical Research-Solid Earth, 122(7), 5544–5560.
Résumé: Aftershock activity depends at first order on the main shock magnitude but also shows important fluctuations between shocks of equal magnitude. We here investigate these fluctuations, by quantifying them and by relating them to the main shock stress drop and other variables, for southern California earthquakes. A method is proposed in order to only count directly triggered aftershocks, rather than secondary aftershocks (i.e., triggered by previous aftershocks), and to only quantify fluctuations going beyond the natural Poisson variability. Testing of the method subjected to various model errors allows to quantify its robustness. It is found that these fluctuations follow a distribution that is well fitted by a lognormal distribution, with a coefficient of variation of about 1.0 to 1.1. A simple model is proposed to relate this observed dependence to main shock stress drop variability.
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Marsan, D., Bouchon, M., Gardonio, B., Perfettini, H., Socquet, A., & Enescu, B. (2017). Change in seismicity along the Japan trench, 1990-2011, and its relationship with seismic coupling. Journal Of Geophysical Research-Solid Earth, 122(6), 4645–4659.
Résumé: We investigate the temporal evolution of the background seismicity rate related to the subduction of the Pacific plate in northeast Japan, at latitudes 34 degrees to 42 degrees, for the 1 January 1990 to 9 March 2011 period. Two declustering methods are used to identify robust features. We find that the dominant behavior is a lowering down of activity, especially in the northern half of our studied area, where changes appear related to the cycle of M7.5+ earthquakes, in particular the 1968 Tokachi and the 1994 Sanriku earthquakes. Acceleration of background seismicity is observed offshore the Kanto region and could mark a long-term decoupling of the Pacific and the Philippine Sea plates over a 100km long segment along the Sagimi Trough, which cannot be simply explained by the earthquake cycle model. Our analysis further suggests that changes in background seismicity are plausibly related to changes in seismic coupling and thus further strengthens the recent observation that seismic coupling does vary at the timescales of tens of years, for the Japanese subduction zone.
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Martinez-Casado, F. J., Ramos-Riesco, M., Rodriguez-Cheda, J. A., Redondo-Yelamos, M. I., Garrido, L., Fernandez-Martinez, A., et al. (2017). Lead(II) soaps: crystal structures, polymorphism, and solid and liquid mesophases. Physical Chemistry Chemical Physics, 19(26), 17009–17018.
Résumé: The long-chain members of the lead(II) alkanoate series or soaps, from octanoate to octadecanoate, have been thoroughly characterized by means of XRD, PDF analysis, DSC, FTIR, ssNMR and other techniques, in all their phases and mesophases. The crystal structures at room temperature of all of the members of the series are now solved, showing the existence of two polymorphic forms in the room temperature crystal phase, different to short and long-chain members. Only nonanoate and decanoate present both forms, and this polymorphism is proven to be monotropic. At higher temperature, these compounds present a solid mesophase, defined as rotator, a liquid crystal phase and a liquid phase, all of which have a similar local arrangement. Since some lead(II) soaps appear as degradation compounds in oil paintings, the solved crystal structures of lead(II) soaps can now be used as fingerprints for their detection using X-ray diffraction. Pair distribution function analysis on these compounds is very similar in the same phases and mesophases for the different members, showing the same short range order. This observation suggests that this technique could also be used in the detection of these compounds in disordered phases or in the initial stages of formation in paintings.
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Matonti, C., Guglielmi, Y., Viseur, S., Garambois, S., & Marie, L. (2017). P-wave velocity anisotropy related to sealed fractures reactivation tracing the structural diagenesis in carbonates. Tectonophysics, 705, 80–92.
Résumé: Fracture properties are important in carbonate reservoir characterization, as they are responsible for a large part of the fluid transfer properties at all scales. It is especially true in tight rocks where the matrix transfer properties only slightly contribute to the fluid flow. Open fractures are known to strongly affect seismic velocities, amplitudes and anisotropy. Here, we explore the impact of fracture evolution on the geophysical signature and directional V-p anisotropy of fractured carbonates through diagenesis. For that purpose, we studied a meter-scale, parallelepiped quarry block of limestone using a detailed structural and diagenetic characterization, and numerous V-p measurements. The block is affected by two en-echelon fracture clusters, both being formed in opening mode (mode 1) and cemented, but only one being reactivated in shear. We compared the diagenetic evolution of the fractures, which are almost all 100% filled with successive calcite cements, with the P-wave velocities measured across this meter-scale block of carbonate, which recorded the tectonic and diagenetic changes of a South Provence sedimentary basin. We found that a directional V-p anisotropy magnitude as high as 8-16% correlates with the reactivated fractures' cluster dip angle, which is explained by the complex filling sequence and softer material present inside the fractures that have been reactivated during the basin's tectonic inversion. We show that although a late karstification phase preferentially affected these reactivated fractures, it only amplified the pre-existing anisotropy due to tectonic shear. We conclude that V-p anisotropy measurements may help to identify the fracture sealing/opening processes associated with polyphased tectonic history, the anisotropy being independent of the current stress state. This case shows that velocity anisotropies induced by fractures resulted here from a cause that is different from how these features have often been interpreted: selective reactivation of sealed fractures clusters rather than direction of currently open ones. (C) 2017 Elsevier B.V. All rights reserved.
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Maufroy, E., Chaljub, E., Theodoulidis, N. P., Roumelioti, Z., Hollender, F., Bard, P. - Y., et al. (2017). Source-Related Variability of Site Response in the Mygdonian Basin (Greece) from Accelerometric Recordings and 3D Numerical Simulations. Bulletin Of The Seismological Society Of America, 107(2), 787–808.
Résumé: We compare different methods to estimate frequency-domain amplification and duration lengthening of earthquake ground motion in the Mygdonian basin (Greece). Amplification is measured by standard spectral ratios (SSRs) of horizontal component or by single-station earthquake horizontal-to-vertical ratios (EHVRs). Duration lengthening is measured either by the group delay method (Beauval et al., 2003) and labeled GDDL, or based on the significant duration (Trifunac and Brady, 1975) and labeled TBDL. The methods are applied both to high-quality recordings of the European experimental site EUROSEISTEST array and to a large set of 3D synthetics computed in a new basin model for 1260 sources regularly distributed in depth, distance, and azimuth from the center of the array. The analysis of the recordings in the center of the basin shows an anticorrelation between amplification and duration lengthening, that is, maxima (resp. minima) of GDDL correspond to minima (resp. maxima) of SSR. The maxima of GDDL are also found to coincide with those of SSR variability. This is confirmed by the analysis of the synthetics, which also reveals a pronounced north-south asymmetry of both amplification and duration lengthening caused by nonisotropic excitation of surface waves at the basin edges. We find that all estimates of site response depend on source location and that EHVR is also strongly sensitive to energy partitioning in the analyzed wavefield. We quantify the source-related variability of each estimate, discuss the biases in site response estimation using incomplete source catalogs, and investigate whether the azimuthal dependence of site response can be identified in the recordings.
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Mercier, J., Braun, J., & van der Beek, P. (2017). Do along-strike tectonic variations in the Nepal Himalaya reflect different stages in the accretion cycle? Insights from numerical modeling. Earth And Planetary Science Letters, 472, 299–308.
Résumé: Whereas the large-scale morphology and dynamics of orogenic wedges are well explained by critical taper theory, many questions remain unanswered regarding the details of how deformation is accommodated internally. Here, we investigate the dynamics of a collisional orogenic wedge bounded by an over-thickened continental plateau, using two-dimensional thermo-mechanical numerical models. These models, applied to the Himalayan orogen and compared with reference cross-sections, lead us to propose a new hypothesis to explain along-strike variations in tectonic style, topography and exhumation patterns observed along the Himalayan range by a combination of two mechanisms. First, numerical models produce a cycle of crustal ramp formation and advection toward the rear of the wedge. The asynchronous evolution of this cycle along different segments of the range may account for the well-documented lateral variations in the geometry of the Main Himalayan Thrust (MHT) and for the existence of a well-defined topographic transition in some segments of the range. Second, the models suggest that the formation of duplexes leading to the isolation of klippen along the range front may be controlled by rheological contrasts between the Tibetan plateau and/or the Greater Himalayan Sequence and the colliding Indian plate. (C) 2017 Elsevier B.V. All rights reserved.
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Mercier, J., Braun, J., & van der Beek, P. (2017). Do along-strike tectonic variations in the Nepal Himalaya reflect different stages in the accretion cycle? Insights from numerical modeling. Earth And Planetary Science Letters, 472, 299–308.
Résumé: Whereas the large-scale morphology and dynamics of orogenic wedges are well explained by critical taper theory, many questions remain unanswered regarding the details of how deformation is accommodated internally. Here, we investigate the dynamics of a collisional orogenic wedge bounded by an over-thickened continental plateau, using two-dimensional thermo-mechanical numerical models. These models, applied to the Himalayan orogen and compared with reference cross-sections, lead us to propose a new hypothesis to explain along-strike variations in tectonic style, topography and exhumation patterns observed along the Himalayan range by a combination of two mechanisms. First, numerical models produce a cycle of crustal ramp formation and advection toward the rear of the wedge. The asynchronous evolution of this cycle along different segments of the range may account for the well-documented lateral variations in the geometry of the Main Himalayan Thrust (MHT) and for the existence of a well-defined topographic transition in some segments of the range. Second, the models suggest that the formation of duplexes leading to the isolation of klippen along the range front may be controlled by rheological contrasts between the Tibetan plateau and/or the Greater Himalayan Sequence and the colliding Indian plate. (C) 2017 Elsevier B.V. All rights reserved.
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Merkulova, M. V., Munoz, M., Brunet, F., Vidal, O., Hattori, K., Vantelon, D., et al. (2017). Experimental insight into redox transfer by iron- and sulfur-bearing serpentinite dehydration in subduction zones. Earth And Planetary Science Letters, 479, 133–143.
Résumé: Dehydration of antigorite in subduction zones releases a large amount of aqueous fluid and volatile elements, which can potentially oxidize the mantle wedge. The redox capacity of three synthetic serpentinites with variable Fe-total, Fe3+ and S- contents is investigated using XANES spectroscopy at both, Fe and S K-edges. Experiments are performed between 450 and 900 degrees C, at 2 GPa and fO(2) similar to QFM-2; conditions similar to those encountered in subduction zones. Redox reactions in the synthetic serpentinites, which involve Fe and S can be summarized as follows: 1) the reduction of (S-)-pyrite into (S2-)-pyrrhotite (similar to 450 degrees C), with similar to 4.4 mg/g of the sulfur degassed most likely as H2S, 2) the consumption of magnetite that reacts with antigorite to form Fe-rich olivine (<500 degrees C), 3) the reduction of (Fe3+)-antigorite into (Fe2+)-antigorite (similar to 580 degrees C), occurring about 100 degrees C below the temperature of antigorite breakdown, 4) the main (Fe2+)-antigorite breakdown that forms olivine and enstatite (similar to 675 degrees C), and 5) the decomposition of minor amounts of (Fe2+/3+)-clinochlore (similar to 800 degrees C). The bulk Fe3+/Fe-total ratio is found to decrease with run temperature from 0.82-0.97 depending on the hydrous starting material, down to 0.1-0.2 in the high-temperature anhydrous assemblages. The evolution of mineral modes and Fe3+/Fetotal with temperature in our synthetic samples shows similar trends to what has been reported in serpentinite rocks collected, for example, along a metamorphic transect in the western Alps. We show that a large amount of O-2-equivalent – up to 10 mol/kg of rock – can be generated at temperature around 450 degrees C due to the presence of oxides and sulfides such as magnetite and pyrite. Owing to the poor capacity of aqueous fluid to transfer redox conditions, we surmise that this O-2-equivalent is “consumed” at the scale of the lithospheric-mantle top which is partially serpentinized and therefore bear strong redox gradients. (C) 2017 Elsevier B.V. All rights reserved.
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Metivier, L., Brossier, R., Operto, S., & Virieux, J. (2017). Full Waveform Inversion and the Truncated Newton Method. Siam Review, 59(1), 153–195.
Résumé: Full waveform inversion (FWI) is a powerful method for reconstructing subsurface parameters from local measurements of the seismic wavefield. This method consists in minimizing the distance between predicted and recorded data. The predicted data are computed as the solution of a wave-propagation problem. Conventional numerical methods for the solution of FWI problems are gradient-based methods, such as the preconditioned steepest descent, the nonlinear conjugate gradient, or more recently the l-BFGS quasi-Newton algorithm. In this study, we investigate the desirability of applying a truncated Newton method to FWI. The inverse Hessian operator plays a crucial role in the parameter reconstruction, as it should help to mitigate finite-frequency effects and to better remove artifacts arising from multiscattered waves. For multiparameter reconstruction, the inverse Hessian operator also offers the possibility of better removing trade-offs due to coupling effects between parameter classes. The truncated Newton method allows us to better account for this operator. This method is based on the computation of the Newton descent direction by solving the corresponding linear system through the conjugate gradient method. The large-scale nature of FWI problems requires us, however, to carefully implement this method to avoid prohibitive computational costs. First, this requires working in a matrix-free formalism and the capability of efficiently computing Hessian-vector products. For this purpose, we propose general second-order adjoint state formulas. Second, special attention must be paid to defining the stopping criterion for the inner linear iterations associated with the computation of the Newton descent direction. We propose several possibilities and establish a theoretical link between the Steihaug-Toint method, based on trust regions, and the Eisenstat and Walker stopping criterion, designed for a method globalized by linesearch. We investigate the application of the truncated Newton method to two case studies. The first is a standard case study in seismic imaging based on the Marmousi model. The second is inspired by a near-surface imaging problem for the reconstruction of high-velocity structures. In the latter case, we demonstrate that the presence of large amplitude multiscattered waves prevents standard methods from converging, while the truncated Newton method provides more reliable results.
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Migdisova, N. A., Sobolev, A. V., Sushchevskaya, N. M., Dubinin, E. P., & Kuz'min, D. V. (2017). Mantle heterogeneity at the Bouvet triple junction based on the composition of olivine phenocrysts. Russian Geology And Geophysics, 58(11), 1289–1304.
Résumé: Tholeiitic melts from the Bouvet triple junction (BTJ) of rift zones in the South Atlantic are moderately enriched rocks with specific lithophile-element patterns. The high (Gd/Yb)(n) values (up to 2.5) in some tholeiite compositions suggest the presence of garnet in the mantle source of primary BTJ melts. The high Ni and low Mn contents of the most magnesian olivines determined by high-precision probe microanalysis suggest the presence of pyroxenite, along with typical peridotite, in the melting source. The unusually wide within-sample variation in the proportions of pyroxenitic component in the source region (XPx Mn/Fe = 0-90%) indicates different degrees of mantle heterogeneity beneath the spreading zone. Based on geochemical data, this component is a silica-oversaturated eclogite, reacting with peridotite to form olivine-free pyroxenite in the melting source. This component is probably represented either by subducted and recycled oceanic crust or by fragments of the ancient continental lithosphere buried into the mantle after the Gondwana breakup. The observed global and local mantle heterogeneities might have been developed during the complex geodynamic evolution of the Southern Ocean, whose opening was affected by the activity of the Mesozoic Karoo-Maud-Ferrar plume and multiple jumps of the spreading axes, which led to the involvement of fragments of the early oceanic lithosphere in the melting process. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.
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Molinari, A., & Perfettini, H. (2017). A micromechanical model of rate and state friction: 2. Effect of shear and normal stress changes. Journal Of Geophysical Research-Solid Earth, 122(4), 2638–2652.
Résumé: In this paper we analyze the influence of shear and normal stress changes on frictional properties. This problem is fundamental as, for instance, sudden stress changes are naturally induced on active faults by nearby earthquakes. As any stress changes can be seen as resulting from a succession of infinitesimal stress steps, the role of sudden stress changes is crucial to our understanding of fault dynamics. Laboratory experiments carried out by Linker and Dieterich (1992) and Nagata et al. (2012), considering steps in normal and shear stress, respectively, show an instantaneous response of the state variable (a proxy for the evolution of contact surface in our model) to a sudden stress change. We interpret this response as being due to an (instantaneous) elastic response of the plastic and elastic contacts. We assume that the anelastic response of the plastic contacts is frozen during sudden stress changes. The contacts, which were driven by plasticity before the stress change, are elastically accommodated during the sudden variation of the load. On the contrary, when the loading is slowly varying, elastic deformation of plastic contacts can be neglected. Our model is able to explain the evolution law for the state variable reported by Linker and Dieterich (1992). Plain Language Summary In this paper we analyze the influence of shear and normal stress changes on frictional properties. This problem is fundamental as, for instance, sudden stress changes are naturally induced on active faults by nearby earthquakes. Our model is able to retrieve the Linker and Dieterich evolution law, which is a reference one that describes the evolution of friction under variable normal stress. Our model assumption is that the plastic contacts that accommodate friction on a fault have an instantaneous elastic response to sudden changes in shear and normal stress. This allows the extrapolation of our frictional model to fault scale.
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Montanaro, C., Mayer, K., Isaia, R., Gresse, M., Scheu, B., Yilmaz, T. I., et al. (2017). Hydrothermal activity and subsoil complexity: implication for degassing processes at Solfatara crater, Campi Flegrei caldera. Bulletin Of Volcanology, 79(12).
Résumé: The Solfatara area and its fumaroles are the main surface expression of the vigorous hydrothermal activity within the active Campi Flegrei caldera system. At depth, a range of volcanic and structural processes dictate the actual state of the hydrothermal system below the crater. The presence of a large variety of volcanic products at shallow depth (including pyroclastic fallout ash beds, pyroclastic density current deposits, breccias, and lavas), and the existence of a maar-related fault system appears to exert major controls on the degassing and alteration behavior. Adding further to the complexity of this environment, variations in permeability and porosity, due to subsoil lithology and alteration effects, may further influence fluid flow towards the surface. Here, we report results from a field campaign conducted in July 2015 that was designed to characterize the in situ physical (temperature, humidity) and mechanical (permeability, strength, stiffness) properties of the Solfatara crater subsoil. The survey also included a mapping of the surficial hydrothermal features and their distributions. Finally, laboratory measurements (porosity, granulometry) of selected samples were performed. Our results enable the discrimination of four main subsoils around the crater: (1) the Fangaia domain located in a topographic low in the southwestern sector, (2) the silica flat domain on the western altered side, (3) the new crust domain in the central area, and (4) the crusted hummocks domain that dominates the north, east, and south parts. These domains are surrounded by encrusted areas, reworked material, and vegetated soil. The distribution of these heterogeneous subsoils suggests that their formation is mostly related to (i) the presence of the Fangaia domain within the crater and (ii) a system of ring faults bordering it. The subsoils show an alternation between very high and very low permeabilities, a fact which seems to affect both the temperature distribution and surficial degassing. A large range of surface temperatures (from 25 up to 95 degrees C) has been measured across these surfaces, with the hottest spot corresponding to the mud pools, the area of new crust formation, and the crusted hummocks. In the subsoil, the distribution of temperature is more complex and controlled by the presence of coarser, and more permeable, sandy/pebbly levels. These act as preferential pathways for hot hydrothermal fluid circulation. In contrast, low permeability, fine-grained levels act as thermal insulators that remain relatively cold and hinder fluid escape to the surface. Hot gases reach the surface predominantly along (vertical) fractures. When this occurs, mound-like structures can be formed by a cracking and healing process associated with significant degassing. It is anticipated that the results presented here may contribute to an improved understanding of the hazard potential associated with the ongoing hydrothermal activity within the Solfatara crater. At this site the permeability of the near-surface environment and its changes in space and time can affect the spatial and temporal distribution of gas and heat emission. Particularly, in areas where reduction in permeability occurs, it can produce pore pressure augmentation that may result in explosive events.
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Morard, G., Andrault, D., Antonangeli, D., Nakajima, Y., Auzende, A. L., Boulard, E., et al. (2017). Fe-FeO and Fe-Fe3C melting relations at Earth's core-mantle boundary conditions: Implications for a volatile-rich or oxygen-rich core. Earth And Planetary Science Letters, 473, 94–103.
Résumé: Eutectic melting temperatures in the Fe-FeO and Fe-Fe3C systems have been determined up to 150 GPa. Melting criteria include observation of a diffuse scattering signal by in situ X-Ray diffraction, and textural characterisation of recovered samples. In addition, compositions of eutectic liquids have been established by combining in situ Rietveld analyses with ex situ chemical analyses. Gathering these new results together with previous reports on Fe-S and Fe-Si systems allow us to discuss the specific effect of each light element (Si, S, O, C) on the melting properties of the outer core. Crystallization temperatures of Si-rich core compositional models are too high to be compatible with the absence of extensive mantle melting at the core-mantle boundary (CMB) and significant amounts of volatile elements such as S and/or C (>5 at%, corresponding to >2 wt%), or a large amount of O(>15 at% corresponding to similar to 5 wt%) are required to reduce the crystallisation temperature of the core material below that of a peridotitic lower mantle. (C) 2017 Elsevier B.V. All rights reserved.
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Morard, G., Nakajima, Y., Andrault, D., Antonangeli, D., Auzende, A. L., Boulard, E., et al. (2017). Structure and Density of Fe-C Liquid Alloys Under High Pressure. Journal Of Geophysical Research-Solid Earth, 122(10), 7813–7823.
Résumé: The density and structure of liquid Fe-C alloys have been measured up to 58GPa and 3,200K by in situ X-ray diffraction using a Paris-Edinburgh press and laser-heated diamond anvil cell. Study of the pressure evolution of the local structure inferred by X-ray diffraction measurements is important to understand the compression mechanism of the liquid. Obtained data show that the degree of compression is greater for the first coordination sphere than the second and third coordination spheres. The extrapolation of the measured density suggests that carbon cannot be the only light element alloyed to iron in the Earth's core, as 8-16 at % C (1.8-3.7 wt % C) would be necessary to explain the density deficit of the outer core relative to pure Fe. This concentration is too high to account for outer core velocity. The presence of other light elements (e.g., O, Si, S, and H) is thus required.
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Moreau, L., Lachaud, C., Thery, R., Predoi, M. V., Marsan, D., Larose, E., et al. (2017). Monitoring ice thickness and elastic properties from the measurement of leaky guided waves: A laboratory experiment. Journal Of The Acoustical Society Of America, 142(5), 2873–2880.
Résumé: The decline of Arctic sea ice extent is one of the most spectacular signatures of global warming, and studies converge to show that this decline has been accelerating over the last four decades, with a rate that is not reproduced by climate models. To improve these models, relying on comprehensive and accurate field data is essential. While sea ice extent and concentration are accurately monitored from microwave imagery, an accurate measure of its thickness is still lacking. Moreover, measuring observables related to the mechanical behavior of the ice (such as Young's modulus, Poisson's ratio, etc.) could provide better insights in the understanding of sea ice decline, by completing current knowledge so far acquired mostly from radar and sonar data. This paper aims at demonstrating on the laboratory scale that these can all be estimated simultaneously by measuring seismic waves guided in the ice layer. The experiment consisted of leaving a water tank in a cold room in order to grow an ice layer at its surface. While its thickness was increasing, ultrasonic guided waves were generated with a piezoelectric source, and measurements were subsequently inverted to infer the thickness and mechanical properties of the ice with very good accuracy. (C) 2017 Acoustical Society of America.
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Moreau, L., Stehly, L., Boue, P., Lu, Y., Larose, E., & Campillo, M. (2017). Improving ambient noise correlation functions with an SVD-based Wiener filter. Geophysical Journal International, 211(1), 418–426.
Résumé: This paper introduces a technique for improving seismic noise correlation functions (NCF) via a singular value decomposition (SVD) of a list of NCF and the Wiener filter. SVD is commonly used for denoising signals by keeping singular values associated with signal while rejecting others. However, singular vectors associated with signal may contain non-coherent information, so the reconstructed matrix generally still contains random perturbations. The Wiener filter is a different approach where signals statistics are used to remove incoherent signal parts. We suggest to combine both these approaches by applying the Wiener filter to the singular vectors, in order to maximize coherency directly in the signal subspace prior to reconstructing the NCF matrix. This denoising method significantly enhances signal-to-noise ratio in NCF. Benefits are demonstrated to be both in the convergence towards the Green's function for tomography purposes, and in the time-resolution improvement for monitoring applications.
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Mouchene, M., van der Beek, P., Carretier, S., & Mouthereau, F. (2017). Autogenic versus allogenic controls on the evolution of a coupled fluvial megafan-mountainous catchment system: numerical modelling and comparison with the Lannemezan megafan system (northern Pyrenees, France). Earth Surface Dynamics, 5(1), 125–143.
Résumé: Alluvial megafans are sensitive recorders of landscape evolution, controlled by both autogenic processes and allogenic forcing, and they are influenced by the coupled dynamics of the fan with its mountainous catchment. The Lannemezan megafan in the northern Pyrenean foreland was abandoned by its mountainous feeder stream during the Quaternary and subsequently incised, leaving a flight of alluvial terraces along the stream network. We use numerical models to explore the relative roles of autogenic processes and external forcing in the building, abandonment and incision of a foreland megafan, and we compare the results with the inferred evolution of the Lannemezan megafan. Autogenic processes are sufficient to explain the building of a megafan and the long-term entrenchment of its feeding river on time and space scales that match the Lannemezan setting. Climate, through temporal variations in precipitation rate, may have played a role in the episodic pattern of incision on a shorter timescale. In contrast, base-level changes, tectonic activity in the mountain range or tilting of the foreland through flexural isostatic rebound do not appear to have played a role in the abandonment of the megafan.
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Mouchene, M., van der Beek, P., Mouthereau, F., & Carcaillet, J. (2017). Controls on Quaternary incision of the Northern Pyrenean foreland: Chronological and geomorphological constraints from the Lannemezan megafan, SW France. Geomorphology, 281, 78–93.
Résumé: Alluvial fans and megafans hold a key position in the sediment routing system and are particularly sensitive to changes in geodynamic and climatic forcing, as well as autogenic fluvial processes. The Lannemezan megafan in the Northern Pyrenean foreland (SW France) was built during Miocene to Pliocene times and subsequently abandoned as the stream network deeply entrenched the foreland. We report new cosmogenic nuclide (Be-10, Al-26) exposure dates for the abandoned fan surface and a series of alluvial terraces along the Neste and Garonne rivers. Our results show that abandonment of the fan occurred at or before similar to 300 ka, and we suggest that this abandonment is the result of the autogenic dynamics of the river system leading to the capture of the feeding Neste River by the Garonne. However, the incision episodes that produced the terrace levels are concomitant to major climatic shifts. Detailed analysis of stream network morphometry does not reveal knickpoints or patterns in the steepness index and chi-values that could be linked to either active tectonic features, base-level change or network reorganization. We therefore suggest that fan abandonment and long-term incision occurred through autogenic processes and that climate shifts may have modulated the incision, allowing for the formation and persistence of alluvial terraces. (C) 2017 Elsevier B.V. All rights reserved.
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Mugnier, J. - L., Jouanne, F., Bhattarai, R., Cortes-Aranda, J., Gajurel, A., Leturmy, P., et al. (2017). Segmentation of the Himalayan megathrust around the Gorkha earthquake (25 April 2015) in Nepal. Journal Of Asian Earth Sciences, 141, 236–252.
Résumé: We put the 25 April 2015 earthquake of Nepal (Mw 7.9) into its structural geological context in order to specify the role of the segmentation of the Himalayan megathrust. The rupture is mainly located NW of Kathmandu, at a depth of 13-15 km on a flat portion of the Main Himalayan Thrust (MHT) that dips towards the N-NE by 7-10 degrees. The northern bound of the main rupture corresponds to the transition towards a steeper crustal ramp. This ramp, which is partly coupled during the interseismic period, is only locally affected by the earthquake. The southern bound of the rupture was near the leading edge of the Lesser Himalaya antiformal duplex and near the frontal footwall ramp of the upper Nawakot duplex. The rupture has been affected by transversal structures: on the western side, the Judi lineament separates the main rupture zone from the nucleation area; on the eastern side, the Gaurishankar lineament separates the 25 April 2015 rupture from the 12 May 2015 (Mw 7.2) rupture. The origin of these lineaments is very complex: they are probably linked to pre-Himalayan faults that extend into the Indian shield beneath the MHT. These inheritedtaults induce transverse warping of the upper lithosphere beneath the MHT, control the location of lateral ramps of the thrust system and concentrate the hanging wall deformation at the lateral edge of the ruptures. The MHT is therefore segmented by stable barriers that define at least five patches in Central Nepal. These barriers influence the extent of the earthquake ruptures. For the last two centuries: the 1833 (Mw 7.6) earthquake was rather similar in extent to the 2015 event but its rupture propagated south-westwards from an epicentre located NE of Kathmandu; the patch south of Kathmandu was probably affected by at least three earthquakes of Mw 7 that followed the 1833 event a few days later or 33 years (1866 event, Mw 7.2) later; the 1934 earthquake (Mw 8.4) had an epicentre similar to 170 km east of Kathmandu, may have propagated as far as Kathmandu and jumped the Gaurishankar lineament. This combined structural approach and earthquake study allows us to propose that the MHT in the central/eastern Himalaya is segmented by stable barriers that define barrier-type earthquake families. However for each individual earthquake within a family, the rupture histories could be different. Furthermore, the greatest earthquakes could have broken the barriers and affected the patches of several families. The concept of a regular recurrence of characteristic earthquakes is therefore misleading to describe the succession of Himalayan earthquakes. (C) 2017 Elsevier Ltd. All rights reserved.
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Mugnier, J. - L., Vignon, V., Jayangondaperumal, R., Vassallo, R., Malik, M. A., Replumaz, A., et al. (2017). A complex thrust sequence in western Himalaya: The active Medlicott Wadia Thrust. Quaternary International, 462, 109–123.
Résumé: The recent activity of the Medlicott-Wadia Thrust (MWT) is investigated by geomorphic and tectonic studies in the Riasi zone, south of the Pir Panjal range (India, Jammu-Kasmir state of western Himalaya). In the Riasi area, the MWT forms a splay of five faults that dip northward. The recent activity of the splay is quantified using a set of deformed Quaternary alluvial units. The central branch of the thrust splay moved Precambrian limestones above Quaternary sediments and is sealed by 36 +/- 3 ka (youngest OSL age) deposits. The other branches offset the top of a 15 +/- 1 ka (youngest OSL age) alluvial fan by 180 to 120 m; the two southernmost branches form 17-34 m high non-cylindrical scarps and the two northernmost branches also offset the fan by similar to 8 m and similar to 54 m, respectively. A balanced cross-section parallel to the N210 degrees E thrust motion suggests that the sequence of activity is complex: an in-sequence propagation is found for the three southern Tea, Scorpion and Rain faults and an out-of-sequence reactivation for the northern Pillar fault. Furthermore, several thrusts simultaneously activated for intervals of a few thousand years, whereas others are episodically inactive. Nearly 10 mm/yr of India-Eurasia convergence is regularly absorbed by the MWT, a value greater than the one estimated for the western segment of the MWT affected by the 2005 Kashmir earthquake, where the thrust tectonics interacts with the complex kinematics of the syntax. This work indicates that the MWT is very active and might be related to thick-skinned tectonics in the western Himalaya. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.
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Myagkiy, A., Truche, L., Cathelineau, M., & Golfier, F. (2017). Revealing the conditions of Ni mineralization in the laterite profiles of New Caledonia: Insights from reactive geochemical transport modelling. Chemical Geology, 466, 274–284.
Résumé: New Caledonia is one of the world's largest nickel laterite deposits that form from intense chemical and mechanical weathering of a peridotite bedrock. As a result of such a weathering process a subsequent downward migration of Si, Mg and Ni takes place, which eventually leads to redistribution of the elements in depth and over time depending on their mobility. Being released from ultramafic parent rock to groundwater, the mobility of nickel is to a great extent controlled by sorption, substitution and dissolution/precipitation processes. Therefore, the final profile of nickel enrichment is the result of the superposition of these possible fates of nickel. The way how Ni is redistributed in between them represents and defines its mineralization in laterite. Knowledge of these processes along with factors, controlling them appears to be a key to detailed understanding of laterite formation. In this study a numerical model, which solves the reaction-transport differential equations, is used to simulate the formation of laterite profile from ultramafic bedrock with particular emphasis on modelled Ni enrichment curve, its comparison with in situ observations, and detailed understanding of trace elements mobility. Since nickel deposits in New Caledonia is characterized by oxide and hydrous Mg silicate ores, three different concurrent fates of Ni deposition in a profile were taken into account in the modelling: i) Ni in a goethite crystal lattice, ii) Ni sorbed on weak and strong goethite sorption sites, and iii) Ni precipitated with silicates (garnierite). Simulations were performed using PHREEQC associated with llnl. dat thermodynamic database that has been edited in order to account garnierite minerals used in the calculations. The work outline is represented by: i) long term (10 Ma) simulation of nickel laterite formation and evolution, ii) analysis of mobility of the elements and understanding its controlling factors, iii) comparison of modelled and in situ Ni enrichment profile and analysis of nickel distribution in between different retention processes, iv) modelling and in depth understanding of these retention processes. The modelling reveals that the vertical progression of the pH front controls thickening of iron-rich zone, explains the vertical mobility of the elements and governs the Ni enrichment. Adsorption itself plays an important role in lateritization process retarding Ni mobility, but i) becomes significant in a narrow range of pH (slightly alkaline) due to competition of Mg and Ni for sorption sites and ii) does not explain such a high nickel content in limonite nowadays, suggesting that Ni is held in goethite mostly by stronger ties i.e. substituted for Fe in the crystal lattice of iron oxide. 1-D modelling appears to be a powerful tool in understanding the general behavior of trace elements upon the formation of laterite and at the same time reveals that locally Ni mineralizations should be explained by more complex processes, such as lateral transfers, convective flows and preferential pathways.
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Nazarova, D. P., Portnyagin, M. V., Krasheninnikov, S. P., Mironov, N. L., & Sobolev, A. V. (2017). Initial H2O Content and Conditions of Parent Magma Origin for Gorely Volcano (Southern Kamchatka) Estimated by Trace Element Thermobarometry. Doklady Earth Sciences, 472(1), 100–103.
Résumé: The formation conditions of the parental magmas of Gorely volcano, which is located behind a volcanic front in Southern Kamchatka, have been evaluated using the modern methods of micro-element thermobarometry. These magmas contained 1.7 +/- 0.8 (2 sigma) wt % of H2O, the majority (82%) of which has been lost from inclusions. They crystallized at 1121 +/- 17 degrees C and an oxygen fugacity of Delta QFM 1.2 +/- 0.2, and could have been produced by about 11% melting of an enriched MORB source (E -DMM) at a temperature of about 1270 degrees C, and a pressure of about 1.5 GPa. A distinctive feature of Gorely volcano, compared with frontal volcanoes of Kamchatka, is the unusually high temperature (925 +/- 20 degrees C) of formation of the subduction component corresponding to the region of existence of water-bearing melts.
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Niu, Q., Revil, A., Li, Z., & Wang, Y. - H. (2017). Relationship between electrical conductivity anisotropy and fabric anisotropy in granular materials during drained triaxial compressive tests: a numerical approach. Geophysical Journal International, 210(1), 1–17.
Résumé: The anisotropy of granular media and its evolution during shearing are important aspects required in developing physics-based constitutive models in Earth sciences. The development of relationships between geoelectrical properties and the deformation of porous media has applications to the monitoring of faulting and landslides. However, such relationships are still poorly understood. In this study, we first investigate the definition of the electrical conductivity anisotropy tensor of granular materials in presence of surface conductivity of the grains. Fabric anisotropy is related to the components of the fabric tensor. We define an electrical anisotropy factor based on the Archie's exponent second-order symmetric tensormof granular materials. We use numerical simulations to confirm a relationship between the evolution of electrical and fabric anisotropy factors during shearing. To realize the simulations, we build a virtual laboratory in which we can easily perform synthetic experiments. We first simulate drained compressive triaxial tests of loose and dense granular materials (porosity 0.45 and 0.38, respectively) using the discrete element method. Then, the electrical conductivity tensor of a set of deformed synthetic samples is computed using the finite-difference method. The numerical results showthat shear strains are responsible for a measurable anisotropy in the bulk conductivity of granular media. The observed electrical anisotropy response, during shearing, is distinct for dense and loose synthetic samples. Electrical and fabric anisotropy factors exhibit however a unique linear correlation, regardless of the shear strain and the initial state (porosity) of the synthetic samples. The practical implication of this finding confirms the usefulness of the electrical conductivity method in studying the fabric tensor of granular media. This result opens the door in using time-lapse electrical resistivity to study non-intrusively the evolution of anisotropy of soils and granular rocks during deformation, for instance during landslides, and to use the evolution of the conductivity tensor to monitor mechanical properties.
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Nooghabi, A. H., Boschi, L., Roux, P., & de Rosny, J. (2017). Coda reconstruction from cross-correlation of a diffuse field on thin elastic plates. Physical Review E, 96(3).
Résumé: This study contributes to the evaluation of the robustness and accuracy of Green's function reconstruction from cross-correlation of strongly dispersed reverberated signals, with disentangling of the respective roles of ballistic and reverberated (“coda”) contributions. We conduct a suite of experiments on a highly reverberating thin duralumin plate, where an approximately diffuse flexural wave field is generated by taking advantage of the plate reverberation and wave dispersion. A large number of impulsive sources that cover the whole surface of the plate are used to validate ambient-noise theory through comparison of the causal and anticausal (i.e., positive-and negative-time) terms of the cross-correlation to one another and to the directly measured Green's function. To quantify the contribution of the ballistic and coda signals, the cross-correlation integral is defined over different time windows of variable length, and the accuracy of the reconstructed Green's function is studied as a function of the initial and end times of the integral. We show that even cross-correlations measured over limited time windows converge to a significant part of the Green's function. Convergence is achieved over a wide time window, which includes not only direct flexural-wave arrivals, but also the multiply reverberated coda. We propose a model, based on normal-mode analysis, that relates the similarity between the cross-correlation and the Green's function to the statistical properties of the plate. We also determine quantitatively how incoherent noise degrades the estimation of the Green's function.
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Noury, M., Philippon, M., Bernet, M., Paquette, J. - L., & Sempere, T. (2017). Geological record of flat slab-induced extension in the southern Peruvian forearc. Geology, 45(8), 723–726.
Résumé: The long-lived Andean subduction zone underwent several flat slab episodes and is therefore ideal to study the consequences of a complete cycle of slab flattening and steepening on the upper plate deformation pattern. In the modern Peruvian forearc (15 degrees-17 degrees S), slab flattening caused a Paleogene (52-30 Ma) landward migration of volcanic activity. Combining structural geology and a source-tosink thermochronological study, we show that the flat slab period is contemporaneous with uplift accommodated by large-scale crustal extension in the forearc. In this light, we argue that the study area is an ancient analog to the modern Mexican and northern Peruvian forearcs located above modern flat slab segments and currently under-going widespread extension.
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Ossorio, M., Stawski, T. M., Rodriguez-Blanco, J. D., Sleutel, M., Manuel Garcia-Ruiz, J., Benning, L. G., et al. (2017). Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum. Minerals, 7(8).
Résumé: Synchrotron-based small-and wide-angle X-ray scattering (SAXS/WAXS) was used to examine in situ the precipitation of gypsum (CaSO4 center dot 2H(2)O) from solution. We determined the role of (I) supersaturation, (II) temperature and (III) additives (Mg2+ and citric acid) on the precipitation mechanism and rate of gypsum. Detailed analysis of the SAXS data showed that for all tested supersaturations and temperatures the same nucleation pathway was maintained, i.e., formation of primary particles that aggregate and transform/re-organize into gypsum. In the presence of Mg2+ more primary particle are formed compared to the pure experiment, but the onset of their transformation/reorganization was slowed down. Citrate reduces the formation of primary particles resulting in a longer induction time of gypsum formation. Based on the WAXS data we determined that the precipitation rate of gypsum increased 5-fold from 4 to 40 degrees C, which results in an effective activation energy of similar to 30 kJ.mol(-1). Mg2+ reduces the precipitation rate of gypsum by more than half, most likely by blocking the attachment sites of the growth units, while citric acid only weakly hampers the growth of gypsum by lowering the effective supersaturation. In short, our results show that the nucleation mechanism is independent of the solution conditions and that Mg2+ and citric acid influence differently the nucleation pathway and growth kinetics of gypsum. These insights are key for further improving our ability to control the crystallization process of calcium sulphate.
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Pastier, A. - M., Dauteuil, O., Murray-Hudson, M., Moreau, F., Walpersdorf, A., & Makati, K. (2017). Is the Okavango Delta the terminus of the East African Rift System? Towards a new geodynamic model: Geodetic study and geophysical review. Tectonophysics, 712, 469–481.
Résumé: The Okavango Graben (OG) has been considered as the terminus of the southwestern branch of the East African Rift System (EARS) since the 1970s based on fault morphology and early seismic and geophysical data. Thus it has been assumed to be an incipient rifting zone, analogous to the early stage of mature rifts in the EARS. Recent geodetic data and geophysical studies in the area bring new insights into the local crust and lithosphere, mantle activity and fault activity. In this study, we computed the velocities for three permanent GPS stations surrounding the graben and undertook a review of the new geophysical data available for the area. The northern and southern blocks of the graben show an exclusively low strike-slip displacement rate of about lmmfyear, revealing the transtensional nature of this basin. The seismic record of central and southern Africa was found to be instrumentally biased for the events recorded before 2004 and the OG may not represent the most seismically active area in Botswana anymore. Moreover, no significant lithosphere and crustal thinning is found in the tectonic structure nor any strong negative Bouguer anomaly and surface heat flux. Thus the OG does not match the classical model for a rifting zone. We propose a new geodynamic model for the deformation observed west of the EARS based on accommodation of far-field deformation due to the differential extension rates of the EARS and the displacement of the Kalahari craton relative to the Nubian plate. (C) 2017 Elsevier B.V. All rights reserved.
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Perez-Munoz, A. M., Schio, P., Poloni, R., Fernandez-Martinez, A., Rivera-Calzada, A., Cezar, J. C., et al. (2017). In operando evidence of deoxygenation in ionic liquid gating of YBa2Cu3O7-X. Proceedings Of The National Academy Of Sciences Of The United States Of America, 114(2), 215–220.
Résumé: Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2): 027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO2 by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126): 1402-1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBa2Cu3O7-X (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics.
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Perfettini, H., & Molinari, A. (2017). A micromechanical model of rate and state friction: 1. Static and dynamic sliding. Journal Of Geophysical Research-Solid Earth, 122(4), 2590–2637.
Résumé: Rate and state friction has been extensively used to explain many features of the seismic cycle but the scaling of the experimentally derived parameters a, b and d(c) for real faults is problematic. The purpose of this paper is to present a micromechanical model for rate and state friction in which the contact between the two surfaces occur via plastic and elastic contacts. Shear deformation is accommodated in the bulk of cylindrical contacts rather than at the surface of the contact, as done classically. Assuming that the viscoplastic response is governed by the J(2) plastic flow theory, we retrieve the rate and state framework. Unlike previous works, we identify the state variable as representing the changes of plastic contact area. In our model, all macroscopic frictional parameters of the rate and state framework are related to the parameters of the elementary contacts. We provide a derivation of the aging evolution law for the state variable and propose a new evolution law that reconciles the aging, Linker-Dieterich and Nagata evolution laws. We discuss the scaling of the frictional parameters for active faults and landslides. The a and b parameters should have comparable value at fault scale since friction is mostly controlled by plastic contacts at large normal stress (typically hundreds of MPa). Our model predicts that the critical slip distance d(c) should be scale independent and controlled solely by the plastic contacts. Plain Language Summary The seismic cycle is controlled by the way friction evolves on active faults. We present here a micromechanical model, based on the idea that friction is accomodated by the plastic and elastic contacts on the fault interface. Our model allows the derivation of the rate and state friction laws, which have been widely used to model the seismic cycle. Our approach allows extrapolating laboratory results to the fault scale and suggests that laboratory experiments are suitable to describe fault dynamics. Our model presents an alternative to the reference Bowden and Tabor friction model, and allows, for the first time, the extrapolation of the frictional parameters derived in the laboratory to fault scale.
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Perron, V., Hollender, F., Bard, P. - Y., Gelis, C., Guyonnet-Benaize, C., Hernandez, B., et al. (2017). Robustness of Kappa (kappa) Measurement in Low-to-Moderate Seismicity Areas: Insight from a Site-Specific Study in Provence, France. Bulletin Of The Seismological Society Of America, 107(5), 2272–2292.
Résumé: Determination of the site component of kappa(kappa(0)) is important in the implementation of host-to-target adjustments for estimation of seismic hazard at hard-rock sites. Its evaluation through the classical approach of Anderson and Hough (1984), kappa(0AS), faces specific difficulties in low-to-moderate seismicity areas because the quantity and bandwidth of the usable data are generally limited. In such a context, measurements might have higher sensitivity to site amplification, frequency-dependent attenuation, the earthquake source, and the instrumental equipment. Here, the kappa(DS) displacement spectrum) approach of Biasi and Smith (2001) is compared with the kappa(AS) (acceleration spectrum) approach for three sites in an industrial area in Provence (southeastern France). A semiautomatic procedure is developed to measure individual values of kappa(r) that reduce interoperator variability and provide the associated uncertainty. We show that this uncertainty is mainly dependent on the bandwidth used to determine kappa(r). A good agreement is found between kappa(0AS) and kappa(0DS) for the two hard-rock sites, which yield similar to 30 ms. This highlights the kappa(DS) approach that is well adapted to low-magnitude events recorded at rock sites, and the use of velocimeters in low-tomoderate seismicity areas. The comparisons between these approaches are also used to infer the reliability of kappa measurements by addressing their sensitivity to site amplification, frequency-dependent attenuation, and the earthquake source. First, the impact of site amplification on kappa(0) estimates is shown to be very important and strongly frequency-dependent for stiff-soil sites, and non-negligible for hard-rock sites. Second, frequency-dependent attenuation cannot be ruled out for kappa, as indicated by comparison with the literature quality factor (Q) for the Alps. Finally, a source component for kappa(AS) is questionable from the comparison of kappa(rAS) evaluated for a cluster of events that shared the same path and site components.
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Philibosian, B., Sieh, K., Avouac, J. - P., Natawidjaja, D. H., Chiang, H. - W., Wu, C. - C., et al. (2017). Earthquake supercycles on the Mentawai segment of the Sunda megathrust in the seventeenth century and earlier. Journal Of Geophysical Research-Solid Earth, 122(1), 642–676.
Résumé: Over at least the past millennium, the Mentawai segment of the Sunda megathrust has failed in sequences of closely timed events rather than in single end-to-end ruptureseach the culmination of an earthquake supercycle. Here we synthesize the sixteenth- and seventeenth-century coral microatoll records into a chronology of interseismic and coseismic vertical deformation. We identify at least five discrete uplift events in about 1597, 1613, 1631, 1658, and 1703 that likely correspond to large megathrust ruptures. This sequence contrasts with the following supercycle culmination, which involved only two large ruptures in 1797 and 1833. Fault slip modeling suggests that together the five cascading ruptures involved failure of the entire Mentawai segment. Interseismic deformation rates also changed after the onset of the rupture sequence, as they did after the 1797 earthquake. We model this change as an altered distribution of fault coupling, presumably triggered by the similar to 1597 rupture. We also analyze the far less continuous microatoll record between A.D. 1 and 1500. While we cannot confidently delineate the extent of any megathrust rupture during that period, all evidence suggests that individual major ruptures involve only part of the Mentawai segment, often overlap below the central Mentawai Islands, often trigger coupling changes, and occur in clusters that cumulatively cover the entire Mentawai segment at the culmination of each supercycle. It is clear that each Mentawai rupture sequence evolves uniquely in terms of the order and grouping of asperities that rupture, suggesting heterogeneities in fault frictional properties at the similar to 100km scale.
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Piedrahita, V. A., Bernet, M., Chadima, M., Sierra, G. M., Marin-Ceron, M. I., & Toro, G. E. (2017). Detrital zircon fission-track thermochronology and magnetic fabric of the Amaga Formation (Colombia): Intracontinental deformation and exhumation events in the northwestern Andes. Sedimentary Geology, 356, 26–42.
Résumé: New detrital zircon-fission track (ZFT) and magnetic fabric data are presented to constrain the time of deposition, provenance and deformation of the of Lower and Upper members of the Amaga Formation in the Amaga Basin. The Amaga Basin is located in the northern Andes, between the Western and Central Cordilleras of Colombia. The Amaga Formation was deposited in a transpressive geodynamic context and is allegedly synchronous with tectonic events such as the Andean orogeny and the Panama-Choco Block collision with the northwestern South American Plate. Detrital ZFT data confirm an Oligocene age for the Lower Member and a middle-Miocene age for the Upper Member of the Amaga Formation. In addition to constraining the depositional age, the ZFT data presented in this study also reflect Paleocene-Eocene, late to early Oligocene and late to middle Miocene cooling in sediment source areas mainly located in the Central and Western Cordilleras of Colombia. These ages can be associated with regional exhumation events in the central and northern Andes of South America. Collisional stages of the Panama-Choco Block against northwestern South America, subduction of the Farallon-Nazca Plate and strike-slip reactivation periods of the Cauca-Romeral fault system, caused NW-SE compression and NE-SW simple shear in the Amaga Basin. This deformational regime, identified by magnetic fabric data, induces syn- and post-depositional deformation over the Amaga Formation. (C) 2017 Elsevier B.V. All rights reserved.
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Pinel, V., Carrara, A., Maccaferri, F., Rivalta, E., & Corbi, F. (2017). A two-step model for dynamical dike propagation in two dimensions: Application to the July 2001 Etna eruption. Journal Of Geophysical Research-Solid Earth, 122(2), 1107–1125.
Résumé: We developed a hybrid numerical model of dike propagation in two dimensions solving both for the magma trajectory and velocity as a function of the source overpressure, the magma physical properties (density and viscosity), and the crustal density and stress field. This model is used to characterize the influence of surface load changes on magma migration toward the surface. We confirm that surface loading induced by volcanic edifice construction tends both to attract the magma and to reduce its velocity. In contrast, surface unloading, for instance, due to caldera formation, tends to divert the magma to the periphery-retarding eruption. In both cases the deflected magma may remain trapped at depth. Amplitudes of dike deflection and magma velocity variation depend on the ratio between the magma driving pressure (source overpressure as well as buoyancy) and the stress field perturbation. Our model is then applied to the July 2001 eruption of Etna, where the final dike deflection had been previously interpreted as due to the topographic load. We show that the velocity decrease observed during the last stage of the propagation can also be attributed to the local stress field. We use the dike propagation duration to estimate the magma overpressure at the dike bottom to be less than 4 MPa. This approach can be potentially used to forecast if, where, and when propagating magma might reach the surface when having knowledge on the local stress field, magma physical properties, and reservoir overpressure.
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Pluymakers, A., Kobchenko, M., & Renard, F. (2017). How microfracture roughness can be used to distinguish between exhumed cracks and in-situ flow paths in shales. Journal Of Structural Geology, 94, 87–97.
Résumé: Flow through fractures in shales is of importance to many geoengineering purposes. Shales are not only caprocks to hydrocarbon reservoirs and nuclear waste or CO2 storage sites, but also potential source and reservoir rocks for hydrocarbons. The presence of microfractures in shales controls their permeability and transport properties. Using X-ray micro-tomography and white light interferometry we scanned borehole samples obtained from 4 km depth in the Pomeranian shales in Poland. These samples contain open exhumation/drying cracks as well as intact vein-rock interfaces plus one striated slip surface. At micron resolution and above tensile drying cracks exhibit a power-law roughness with a scaling exponent, called the Hurst exponent H, of 0.3. At sub-micron resolution we capture the properties of the clay interface only, with H = 0.6. In contrast, the in-situ formed veins and slip surface exhibit H = 0.4-0.5, which is deemed representative for in-situ fractures. These results are discussed in relation to the shale microstructure and linear elastic fracture mechanics theory. The data imply that the Hurst roughness exponent can be used as a microstructural criterion to distinguish between exhumation and in-situ fractures, providing a step forward towards the characterization of potential flow paths at depth in shales. 2016 Elsevier Ltd. All rights reserved.
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Pousse-Beltran, L., Vassallo, R., Audemard, F., Jouanne, F., Carcaillet, J., Pathier, E., et al. (2017). Pleistocene slip rates on the Bocono fault along the North Andean Block plate boundary, Venezuela. Tectonics, 36(7), 1207–1231.
Résumé: The Bocono fault is a strike-slip fault lying between the North Andean Block and the South American plate which has triggered at least five M-w>7 historical earthquakes in Venezuela. The North Andean Block is currently moving toward NNE with respect to a stable South American plate. This relative displacement at similar to 12mmyr(-1) in Venezuela (within the Maracaibo Block) was measured by geodesy, but until now the distribution and rates of Quaternary deformation have remained partially unclear. We used two alluvial fans offset by the Bocono fault (Yaracuy Valley) to quantify slip rates, by combining Be-10 cosmogenic dating with measurements of tectonic displacements on high-resolution satellite images (Pleiades). Based upon a fan dated at >79ka and offset by 1350-1580m and a second fan dated at 120-273ka and offset by 1236-1500m, we obtained two Pleistocene rates of 5.0-11.2 and <20.0mmyr(-1), consistent with the regional geodesy. This indicates that the Bocono fault in the Yaracuy Valley accommodates 40 to 100% of the deformation between the South American plate and the Maracaibo Block. As no aseismic deformation was shown by interferometric synthetic aperture radar analysis, we assume that the fault is locked since the 1812 event. This implies that there is a slip deficit in the Yaracuy Valley since the last earthquake ranging from similar to 1 to 4m, corresponding to a M-w 7-7.6 earthquake. This magnitude is comparable to the 1812 earthquake and to other historical events along the Bocono fault.
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Pradas del Real, A. E., Manuel Silvan, J., de Pascual-Teresa, S., Guerrero, A., Garcia-Gonzalo, P., Carmen Lobo, M., et al. (2017). Role of the polycarboxylic compounds in the response of Silene vulgaris to chromium. Environmental Science And Pollution Research, 24(6), 5746–5756.
Résumé: This work aims to investigate the nature and the specific mechanisms by which polycarboxylic compounds participate in the tolerance of Silene vulgaris to Cr with special attention given to the rhizosphere system. This knowledge is important to use this species in the implementation of phytoremediation technologies in Cr-polluted soils. According to the results, chromium is chelated and mobilized by the citric and malic acids in plant tissues, while oxalic acid might participate in the reduction and chelation of Cr in the rhizosphere. At the applied doses, the response of both exudation rate and root exudate composition (total polyphenols and quercitin) seems to involve a rearrangement in the lignification of the plant cell wall to immobilize Cr. Quercetin-3-dirhamnosyl-galactoside and apiin (apigenin-7-O-apiosyl-glucoside) have been identified as the major polyphenols in the root exudates of S. vulgaris. The increments found in the apiin concentration in root exudates seem to be related to the protection against Cr toxicity by chelation of Cr or by free radical scavenging. Though earlier response is detected in plant tissues, results from this work together with previous studies in S. vulgaris indicate that exudation might be a regulated mechanism of protection under Cr exposition in S. vulgaris that may involve mainly Cr reduction and chelation.
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Pradas del Real, A. E., Vidal, V., Carriere, M., Castillo-Michel, H., Levard, C., Chaurand, P., et al. (2017). Silver Nanoparticles and Wheat Roots: A Complex Interplay. Environmental Science & Technology, 51(10), 5774–5782.
Résumé: Agricultural soils are major sinks of silver nanoparticles in the environment, and crops are directly exposed to these emerging contaminants. A clear picture of their chemical transformations, uptake and transport mechanisms, and phytotoxic impacts is still lacking. In this work, wheat plants were exposed to pristine metallic (Ag-NPs) and sulfidized (Ag2S-NPs) silver nanoparticles and ionic Ag. Data on Ag distribution and speciation, phytotoxicity markers, and gene expression were studied. A multi-technique and multi-scale approach was applied, combining innovating tools at both the laboratory and synchrotron. Various chemical transformations were observed on the epidermis and inside roots, even for Ag2S-NPs, leading to an exposure to multiple Ag forms, which likely evolve over time. Genes involved in various functions including oxidative stress, defense against pathogens, and metal homeostasis were impacted in different ways depending upon the Ag source. This study illustrates the complexity of the toxicity pattern for plants exposed to Ag-NPs, the necessity of monitoring several markers to accurately evaluate the toxicity, and the interest of interpreting the toxicity pattern in light of the distribution and speciation of Ag.
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Precigout, J., Prigent, C., Palasse, L., & Pochon, A. (2017). Water pumping in mantle shear zones. Nature Communications, 8.
Résumé: Water plays an important role in geological processes. Providing constraints on what may influence the distribution of aqueous fluids is thus crucial to understanding how water impacts Earth's geodynamics. Here we demonstrate that ductile flow exerts a dynamic control on water-rich fluid circulation in mantle shear zones. Based on amphibole distribution and using dislocation slip-systems as a proxy for syn-tectonic water content in olivine, we highlight fluid accumulation around fine-grained layers dominated by grain-size-sensitive creep. This fluid aggregation correlates with dislocation creep-accommodated strain that localizes in water-rich layers. We also give evidence of cracking induced by fluid pressure where the highest amount of water is expected. These results emphasize long-term fluid pumping attributed to creep cavitation and associated phase nucleation during grain size reduction. Considering the ubiquitous process of grain size reduction during strain localization, our findings shed light on multiple fluid reservoirs in the crust and mantle.
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Ramdhan, M., Widiyantoro, S., Nugraha, A. D., Metaxian, J. - P., Saepuloh, A., Kristyawan, S., et al. (2017). Relocation of hypocenters from DOMERAPI and BMKG networks: a preliminary result from DOMERAPI project. Earthquake Science, 30(2), 67–79.
Résumé: Merapi volcano located in central Java, Indonesia, is one of the most active stratovolcanoes in the world. Many Earth scientists have conducted studies on this volcano using various methods. The geological features around Merapi are very attractive to be investigated because they have been formed by a complex tectonic process and volcanic activities since tens of millions of years ago. The southern mountain range, Kendeng basin and Opak active fault located around the study area resulted from these processes. DOMERAPI project was conducted to understand deep magma sources of the Merapi volcano comprehensively. The DOMERAPI network was running from October 2013 to mid-April 2015 by deploying 46 broad-band seismometers around the volcano. Several steps, i.e., earthquake event identification, arrival time picking of P and S waves, hypocenter determination and hypocenter relocation, were carried out in this study. We used Geiger's method (Geiger 1912) for hypocenter determination and double-difference method for hypocenter relocation. The relocation result will be used to carry out seismic tomographic imaging of structures beneath the Merapi volcano and its surroundings. For the hypocenter determination, the DOMERAPI data were processed simultaneously with those from the Agency for Meteorology, Climatology and Geophysics (BMKG) seismic network in order to minimize the azimuthal gap. We found that the majority of earthquakes occurred outside the DOMERAPI network. There are 464 and 399 earthquakes obtained before and after hypocenter relocation, respectively. The hypocenter relocation result successfully detects some tectonic features, such as a nearly vertical cluster of events indicating a subduction-related backthrust to the south of central Java and a cluster of events to the east of Opak fault suggesting that the fault has an eastward dip.
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Regard, V., Pedoja, K., De la Torre, I., Saillard, M., Cortes-Aranda, J., & Nexer, M. (2017). Geometrical trends within sequences of Pleistocene marine terraces: selected examples from California, Peru, Chile and New-Zealand. Zeitschrift Fur Geomorphologie, 61(1), 53–73.
Résumé: Elevations of the shoreline angles of marine terraces have long been used to infer Pleistocene sea levels and/or uplift rates. We attempt to use morphologic properties of sequences of marine terraces terrace width and slope in order to track if these constitute a pattern showing similar alternations at different sites and if this alternation is comparable to the signal from the sea level highstand succession duration and sea level for Middle-Late Pleistocene. To do so, we focus on sequences of marine terrace including more than 10 successive strandlines from San Clemente Island and Santa Cruz (both in California, USA). We generated and analyzed 30 topographic profiles in order to confirm the occurrence or lack of each terrace, and to characterize their width and slope. To complement the observation of tenuous trends, we used additional data from previous works at Point Reyes (California, USA), Altos de Talinay (central Chile), San Juan de Marcona (central Peru) and South Taranaki (Northern Island, New Zealand). These additional data strengthen the observations made at San Clemente and Santa Cruz and prove that the most prominent terrace observed is usually carved during the Marine Isotopic Stage 5 (MISS). Moreover, some terraces appear better expressed than the others: those formed during MIST, MIS9 plus one of those formed during MIS15, MIS17 or MIS19 highstands. The terraces formed during MIS11 are not preeminent, contrary to what expected from its long highstand duration.
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Renard, F., Cordonnier, B., Kobchenko, M., Kandula, N., Weiss, J., & Zhu, W. (2017). Microscale characterization of rupture nucleation unravels precursors to faulting in rocks. Earth And Planetary Science Letters, 476, 69–78.
Résumé: Precursory signals, manifestations of microscale damage that precedes dynamic faulting, are key to earthquake forecasting and risk mitigation. Detections of precursors have primarily relied on measurements performed using sensors installed at some distance away from the rupture area in both field and laboratory experiments. Direct observations of continuous microscale damage accumulated during fault nucleation and propagation are scarce. Using an X-ray transparent triaxial deformation apparatus, we show the first quantitative high resolution three-dimensional (3D) information about damage evolution of rocks undergoing brittle failure. The dynamic microtomography images documented a spectrum of damage characteristics and different fault growth patterns. The interplay between various deformation mechanisms can result in either a positive, negative, or constant net volume change. Consequently, changes in rock density and acoustic wave velocities before faulting are expected to vary in different tectonics settings, hence making failure forecasting intrinsically dependent on rock type at depth. (C) 2017 Elsevier B.V. All rights reserved.
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Renard, F., Putnis, C. V., Montes-Hernandez, G., & King, H. E. (2017). Siderite dissolution coupled to iron oxyhydroxide precipitation in the presence of arsenic revealed by nanoscale imaging. Chemical Geology, 449, 123–134.
Résumé: Siderite, the iron carbonate mineral, occurs in several geological environments and contributes to both the global iron and CO2 cycles. Under crustal conditions, this mineral may dissolve, releasing iron that becomes oxidized and then precipitates in the form of iron oxides and oxyhydroxides that have a high affinity for pollutants, such as arsenic. The process of siderite dissolution, dissolved iron oxidation, and oxyhydroxide precipitation is coupled in time and space. Here, we study the entire process using time-lapse in-situ atomic force microscopy. Natural siderite crystals were dissolved at room temperature in acidic aqueous solutions in the presence or absence of arsenic. The dissolution process, whose rate could be measured at a nanometer scale, occurred by the nucleation and growth of etch pits, the retreat of step edges, and the deepening of cleavage steps. Precipitation of iron oxyhydroxide phases coupled to siderite dissolution was imaged in-situ. Nucleated particles have an initial height of 1-2 nm after 1 minute reaction and then grow with time into aggregate precipitates 130-220 nm wide and up to 80 nm high after 24 h of reaction. Ex-situ stirred-flow reactor measurements confirm the same sequence of siderite dissolution and iron oxyhydroxide precipitation. The arsenic is adsorbed by iron oxyhydroxides and its presence does not change significantly the rate of dissolution-precipitation of the overall process. Results provide a basis for understanding and quantifying the interactions between reduced-iron minerals and aqueous-phase oxidants, as well as potential sequestration of toxic elements such as arsenic. (C) 2016 Elsevier B.V. All rights reserved.
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Retailleau, L., Boue, P., Stehly, L., & Campillo, M. (2017). Locating Microseism Sources Using Spurious Arrivals in Intercontinental Noise Correlations. Journal Of Geophysical Research-Solid Earth, 122(10), 8107–8120.
Résumé: The accuracy of Green's functions retrieved from seismic noise correlations in the microseism frequency band is limited by the uneven distribution of microseism sources at the surface of the Earth. As a result, correlation functions are often biased as compared to the expected Green's functions, and they can include spurious arrivals. These spurious arrivals are seismic arrivals that are visible on the correlation and do not belong to the theoretical impulse response. In this article, we propose to use Rayleigh wave spurious arrivals detected on correlation functions computed between European and United States seismic stations to locate microseism sources in the Atlantic Ocean. We perform a slant stack on a time distance gather of correlations obtained from an array of stations that comprises a regional deployment and a distant station. The arrival times and the apparent slowness of the spurious arrivals lead to the location of their source, which is obtained through a grid search procedure. We discuss improvements in the location through this methodology as compared to classical back projection of microseism energy. This method is interesting because it only requires an array and a distant station on each side of an ocean, conditions that can be met relatively easily.
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Revil, A. (2017). Comment on “Dependence of shear wave seismoelectrics on soil textures: a numerical study in the vadose zone” by FI Zyserman, LB Monachesi and L. Jouniaux. Geophysical Journal International, 209(2), 1095–1098.
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Revil, A. (2017). Transport of water and ions in partially water-saturated porous media. Part 1. Constitutive equations. Advances In Water Resources, 103, 119–138.
Résumé: I developed a model of cross-coupled flow in partially saturated porous media based on electrokinetic coupling including the effect of ion filtration (normal and reverse osmosis) and the multi-component nature of the pore water (wetting) phase. The model also handles diffusion and membrane polarization but is valid only for saturations above the irreducible water saturation. I start with the local Nernst Planck and Stokes equations and I use a volume-averaging procedure to obtain the generalized Ohm, Fick, and Darcy equations with cross-coupling terms at the scale of a representative elementary volume of the porous rock. These coupling terms obey Onsager's reciprocity, which is a required condition, at the macroscale, to keep the total dissipation function of the system positive. Rather than writing the electrokinetic terms in terms of zeta potential (the double layer electrical potential on the slipping plane located in the pore water), I developed the model in terms of an effective charge density dragged by the flow of the pore water. This effective charge density is found to be strongly controlled by the permeability and the water saturation. I also developed an electrical conductivity equation including the effect of saturation on both bulk and surface conductivities, the surface conductivity being associated with electromigration in the electrical diffuse layer coating the grains. This surface conductivity depends on the CEC of the porous material. (C) 2016 Elsevier Ltd. All rights reserved.
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Revil, A. (2017). Transport of water and ions in partially water-saturated porous media. Part 2. Filtration effects. Advances In Water Resources, 103, 139–152.
Résumé: A new set of constitutive equations describing the transport of the ions and water through charged porous media and considering the effect of ion filtration is applied to the problem of reverse osmosis and diffusion of a salt. Starting with the constitutive equations derived in Paper 1, I first determine specific formula for the osmotic coefficient and effective diffusion coefficient of a binary symmetric 1:1 salt (such as KCI or NaCI) as a function of a dimensionless number 8 corresponding to the ratio between the cation exchange capacity (CEC) and the salinity. The modeling is first carried with the Donnan model used to describe the concentrations of the charge carriers in the pore water phase. Then a new model is developed in the thin double layer approximation to determine these concentrations. These models provide explicit relationships between the concentration of the ionic species in the pore space and those in a neutral reservoir in local equilibrium with the pore space and the CEC. The case of reverse osmosis and diffusion coefficient are analyzed in details for the case of saturated and partially saturated porous materials. Comparisons are done with experimental data from the literature obtained on bentonite. The model predicts correctly the influence of salinity (including membrane behavior at high salinities), porosity, cation type (K+ versus Na+), and water saturation on the osmotic coefficient. It also correctly predicts the dependence of the diffusion coefficient of the salt with the salinity. (C) 2016 Elsevier Ltd. All rights reserved.
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Revil, A., & Soueid Ahmed, A. (2017). Comment on 'Electrical conductance of a sandstone partially saturated with varying concentrations of NaCl solutions' by R. Umezawa, N. Nishiyama, M. Katsura and S. Nakashima. Geophysical Journal International, 211(2), 1099–1103.
Résumé: Umezawa et al. investigated the dependence of the electrical conductivity of rocks with respect to the saturation of the water phase. Four issues can be underlined in their work: (1) The conductivity model they used mixes bulk and surface tortuosities in the same linear equation (i.e., between the conductivity and the conductivity of the pore water). This conflicts with the fact that the conductivity is a concave down increasing function of the pore water conductivity and bulk tortuosity is defined only at high salinity while surface tortuosity is defined only at very low salinity. (2) The specific surface conductance obtained by Umezawa et al. is too low and conflicts with independent evaluations obtained with double layer models for aluminosilicates and silicates. (3) The expression given for the resistivity index conflicts with the inclusion of a surface conductivity term in the conductivity equation.
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Revil, A., Soueid Ahmed, A., & Jardani, A. (2017). Self-potential: A Non-intrusive Ground Water Flow Sensor. Journal Of Environmental And Engineering Geophysics, 22(3), 235–247.
Résumé: The flow of the ground water in an aquifer or during pumping test generates an electrical current (called the streaming current), which is of advective nature. The resulting electrical field (streaming potential field, one of the components of the self-potential field) can be remotely measured at the ground surface or in boreholes. We first discuss the underlying physics of this electrokinetic effect and the role of the electrical double layer coating the surface of the grains. We show how the drag of the excess of electrical charge of the pore water by the flow is equivalent to a source current density. Then, we discuss the metrological aspects, the type of voltmeter and electrodes required to carry out good measurements in field conditions. Two applications are discussed in steady-state conditions. The first is dedicated to the flow of water in shallow aquifers. In this case, the streaming current and the conduction current are nearly balanced and, inside the aquifer, the electrical equipotentials mimic the hydraulic equipotentials. They have, however, the advantage to extend the shape of these hydraulic equipotentials up to the ground surface. The second case is related to the flow of water in the vadose zone, here again investigated in steady-state conditions. In this situation, the vadose zone is polarized and the ground surface electrical potential map reflects essentially the depth of the vadose zone. A case study is shown for a small watershed in the South of France. The resistivity tomography shows no contrast in resistivity between the vadose zone and the aquifer and the observed self-potential data are observed to be linearly correlated to the depth of the water table.
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Revil, A., Coperey, A., Shao, Z., Florsch, N., Fabricius, I. L., Deng, Y., et al. (2017). Complex conductivity of soils. Water Resources Research, 53(8), 7121–7147.
Résumé: The complex conductivity of soils remains poorly known despite the growing importance of this method in hydrogeophysics. In order to fill this gap of knowledge, we investigate the complex conductivity of 71 soils samples (including four peat samples) and one clean sand in the frequency range 0.1 Hz to 45 kHz. The soil samples are saturated with six different NaCl brines with conductivities (0.031, 0.53, 1.15, 5.7, 14.7, and 22 S m(-1), NaCl, 25 degrees C) in order to determine their intrinsic formation factor and surface conductivity. This data set is used to test the predictions of the dynamic Stern polarization model of porous media in terms of relationship between the quadrature conductivity and the surface conductivity. We also investigate the relationship between the normalized chargeability (the difference of in-phase conductivity between two frequencies) and the quadrature conductivity at the geometric mean frequency. This data set confirms the relationships between the surface conductivity, the quadrature conductivity, and the normalized chargeability. The normalized chargeability depends linearly on the cation exchange capacity and specific surface area while the chargeability shows no dependence on these parameters. These new data and the dynamic Stern layer polarization model are observed to be mutually consistent. Traditionally, in hydrogeophysics, surface conductivity is neglected in the analysis of resistivity data. The relationships we have developed can be used in field conditions to avoid neglecting surface conductivity in the interpretation of DC resistivity tomograms. We also investigate the effects of temperature and saturation and, here again, the dynamic Stern layer predictions and the experimental observations are mutually consistent. Plain Language Summary Geophysical methods are increasingly popular in agriculture. Usually, DC (DIrect Current) resistivity is the preferred method but the interpretation of resistivity data suffers a major flaw: the inability to distinguish between bulk and surface conductivity. This has yield to unrealistc interpretation schemes in hydrogeophysics and an abuse of Archie's law. We propose a way to cure this flaw by extending the DC resistivity method to what is called induced polarization. This paper is the first work entirely focused on the study of induced polarization of soils including a comparison with a mechanistic model and a study of the influence of both temperature and saturation.
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Revil, A., Le Breton, M., Niu, Q., Wallin, E., Haskins, E., & Thomas, D. M. (2017). Induced polarization of volcanic rocks-1. Surface versus quadrature conductivity. Geophysical Journal International, 208(2), 826–844.
Résumé: We performed complex conductivity measurements on 28 core samples from the hole drilled for the Humu'ula Groundwater Research Project (Hawai'i Island, HI, USA). The complex conductivity measurements were performed at 4 different pore water conductivities (0.07, 0.5, 1.0 or 2.0, and 10 S m(-1) prepared with NaCl) over the frequency range 1 mHz to 45 kHz at 22 +/- 1 degrees C. The in-phase conductivity data are plotted against the pore water conductivity to determine, sample by sample, the intrinsic formation factor and the surface conductivity. The intrinsic formation factor is related to porosity by Archie's law with an average value of the cementation exponent m of 2.45, indicating that only a small fraction of the connected pore space controls the transport properties. Both the surface and quadrature conductivities are found to be linearly related to the cation exchange capacity of the material, which was measured with the cobalt hexamine chloride method. Surface and quadrature conductivities are found to be proportional to each other like for sedimentary siliclastic rocks. A Stern layer polarization model is used to explain these experimental results. Despite the fact that the samples contain some magnetite (up to 5 per cent wt.), we were not able to identify the effect of this mineral on the complex conductivity spectra. These results are very encouraging in showing that galvanometric induced polarization measurements can be used in volcanic areas to separate the bulk from the surface conductivity and therefore to define some alteration attributes. Such a goal cannot be achieved with resistivity alone.
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Revil, A., Le Breton, M., Niu, Q., Wallin, E., Haskins, E., & Thomas, D. M. (2017). Induced polarization of volcanic rocks. 2. Influence of pore size and permeability. Geophysical Journal International, 208(2), 814–825.
Résumé: We investigate the relationship between complex conductivity spectra and both permeability and pore mean size and distribution of 22 core samples (21 volcanic rocks and 1 clayey sandstone). The volcanic core samples were extracted from a well bore drilled for the Humu'ula Groundwater Research Project in the Humu'ula saddle region between Mauna Kea and Mauna Loa volcanoes (Hawaii). The quadrature conductivity spectra of volcanic rocks exhibit a subtle, but generally detectable, relaxation frequency in the range 0.3 Hz to 45 kHz similar to the relaxation frequency observed for clayey sandstones. We find a fair relationship between this relaxation frequency and the pore size determined by mercury porosimetry. Combined with the intrinsic formation factor of the core samples, the relaxation frequency can be used as an indicator of the permeability of the material. The predicted values of the permeability are grossly consistent with the permeability values to air (in the range 0.001-100 mD) within two orders of magnitude. The measured permeability values are highly correlated to the peak of the pore size distribution determined from mercury porosimetry divided by the intrinsic formation factor. By fitting the complex conductivity spectra with the pore size distribution, we obtain the normalized chargeability of the core samples, which is, in turn, highly correlated to the measured cation exchange capacity.
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Revil, A., Mao, D., Shao, Z., Sleevi, M. F., & Wang, D. (2017). Induced polarization response of porous media with metallic particles – Part 6: The case of metals and semimetals. Geophysics, 82(2), E97–E110.
Résumé: We collected spectral induced polarization spectra with clean sand mixed with metallic particles (either silver, graphite, copper, steel, magnetite, or pyrite particles). The initial pore water conductivity was either 1500 or 1000 μS cm(-1) depending on the experiments (25 degrees C, NaCl). For each of the 15 experiments, we used a narrow and unimodal grain size distribution for the metallic particles. The resulting polarization spectra display clear polarization peaks in the phase and can be fitted with a Cole-Cole complex conductivity model. In addition to this, the chargeability scales with the volume content of the metallic particles in a way that is consistent with the theory of disseminated metallic particles in a weakly polarizable background. Similarly, the phase scales with the content of the metallic particles in a predictableway. The ColeCole relaxation time shows a rough dependence with the mean particle size. The trend between these two parameters can be used to determine an apparent diffusion coefficient for the charge carriers responsible for the polarization. Finally, we conducted a laboratory sandbox experiment in which we put a copper plate in tap water-saturated sand. We use an approach based on self-potential tomography and compactness to invert the secondary source current density from the secondary voltages associated with timedomain induced polarization. With this approach, we localized the copper plate and determined a value for the relaxation time that is consistent with the laboratory core sample experiments.
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Revil, A., Murugesu, M., Prasad, M., & Le Breton, M. (2017). Alteration of volcanic rocks: A new non-intrusive indicator based on induced polarization measurements. Journal Of Volcanology And Geothermal Research, 341, 351–362.
Résumé: Induced polarization is a geophysical method investigating the ability of rocks to store reversibly electrical charges under a slowly alternating electrical field. The material property of interest is a complex-valued electrical conductivity with an in-phase component associated with conduction and a quadrature component associated with polarization. We investigated the relationship between complex conductivity spectra over the frequency range 1 mHz-45 kHz and the specific surface area (SSA) of 28 volcanic core samples extracted from a wellbore drilled for the Humu'ula Groundwater Research Project in Hawaii. The specific surface area of these samples was determined through the Brunauer, Emmett and Teller (BET) method. Subcritical nitrogen adsorption experiments were conducted using two different instruments and the samples were prepared in both pellets and powder forms. The BET specific surface area is found to be highly correlated to the cation exchange capacity of the core samples measured by the cobalthexamine method. The in-phase conductivity itself can be decomposed as the sum of a bulk contribution associated with conduction in the bulk pore water and a surface conductivity associated with conduction in the electrical double layer coating the grains. The surface conductivity, the quadrature conductivity, and the normalized chargeability (defined as the difference between the in-phase conductivity at high and low frequencies) are observed to be linearly correlated to the specific surface area or the surface per volume ratio of the core samples, which can be considered as proxy of alteration. These trends are consistent with those shown by sedimentary rocks. This new data set demonstrates that the induced polarization method can be potentially used to image alteration in volcanic environments. (C) 2017 Published by Elsevier B.V.
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Revil, A., Sleevi, M. F., & Mao, D. (2017). Induced polarization response of porous media with metallic particles – Part 5: Influence of the background polarization. Geophysics, 82(2), E77–E96.
Résumé: Very often, ore bodies are found in altered porous materials that are rich in clay minerals. These altered rocks are in turn characterized by a relatively high normalized chargeability (product of the chargeability by the high frequency conductivity) or electrical quadrature conductivity with respect to clayfree materials. We have performed 36 experiments in which dispersed pyrite grains were mixed with a background host material composed of some pore water (NaCl, 500-1000 μS cm(-1) at 25 degrees C or tap water), Na-exchanged bentonite, and silica grains. The induced polarization spectra were obtained in the frequency range of 1 mHz to 45 kHz at room temperature (21 +/- 1 degrees C). The spectra of the background porous materials alone (i.e., without pyrite) were also measured. The normalized chargeability and the quadrature conductivity of the sand-clay mixtures are consistent with available theoretical relationships. These new data complete previous data sets showing a clear relationship among the normalized chargeability, quadrature conductivity, surface conductivity, and cation exchange capacity. Bentonite is characterized by very high quadrature and surface conductivities. The normalized chargeability and the quadrature conductivity of the sand-clay mixtures (no pyrite) increase with the clay content. In the presence of pyrite, the chargeability and the phase lag depend primarily on the volume content of pyrite in a predictable way. The Cole-Cole exponent, characterizing the particle size distribution of the pyrite grains, is independent of the clay content. Still, in the presence of pyrite, the magnitude of the phase peak and the phase peak frequency depend on the clay content in a way that is not explained by the current model. We have observed that the Cole-Cole relaxation time, in the presence of pyrite, is inversely proportional to the conductivity of the background material.
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Revillon, S., Guillou, H., Maury, R. C., Chauvel, C., Aslanian, D., Pelleter, E., et al. (2017). Young Marquesas volcanism finally located. Lithos, 294, 356–361.
Résumé: The Marquesas Island chain in Polynesia is quite unusual because the alignment of the islands on the Pacific oceanic plate (N40 degrees W) does not follow the plate motion in the region (N65 degrees W). The exact location of the active hotspot is unknown but has been predicted to underlie the Marquesas Fracture Zone Ridge. Nevertheless, no concrete evidence exists. Here, we document the occurrence on this ridge of fresh tephrites dated at similar to 921 a by the Ar-40-Ar-39 method. The lavas dredged on a small seamount have trace element contents and Sr, Nd, Pb isotopic compositions typical of the southwest Marquesas Islands, the Fatu Hiva group. This discovery demonstrates that the Marquesas plume is still active and it puts new constraints on its present location, It also supports McNutt et al.'s (1989) interpretation of the Marquesas Fracture Zone Ridge as a very young volcanic construction underlain by a hotspot. We suggest that the present location of the Marquesas plume is under the ridge, at its intersection with the isotopic divide known along the Marquesas chain. We attribute the presence of young volcanic products 190 km southwest of this location to preferential magma flow along the Marquesas Fracture lithospheric weakness zone. We also suggest that the puzzling general direction of the archipelago is the consequence of a persistent low magma flux over the past 5 Ma that could only find its way to the surface through multiple weak zones in the Pacific plate. (C) 2017 Elsevier B.V. All rights reserved.
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Rey, P. F., Mondy, L., Duclaux, G., Teyssier, C., Whitney, D. L., Bocher, M., et al. (2017). The origin of contractional structures in extensional gneiss domes. Geology, 45(3), 263–266.
Résumé: The juxtaposition of domains of shortening and extension at different scales in orogens has fueled many debates about driving forces and tectonic interpretations, including timing of deformation. At the orogen scale, gravitational collapse and mass transfer from orogenic plateaux to forelands explain some of these juxtapositions. At a regional scale, structures in gneiss domes are commonly contractional yet are coeval with regional extension and denudation. Here we use three-dimensional numerical experiments to show that crustal flow in orogenic domains does not necessarily conform to plate motion. We document contractional crustal flow associated with the formation of a gneiss dome in an orogenic pull-apart setting where localized extension and crustal thinning focus the exhumation of deep crust. We show that the flow field results in a complex strain pattern in which an extensional strain regime that is collinear with the direction of plate motion is partitioned into the shallow crust, whereas contractional structures and fabrics at a high angle to the direction of imposed transport develop in the deep crust. Advective mass transfer across regions of contrasting yet coeval strain regimes leads to a polyphase tectonic history. We observe structural features remarkably similar to those documented in some natural gneiss domes such as the Montagne Noire, which developed in a dextral pull-apart domain at the southern margin of the French Massif Central.
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Rey, P. F., Mondy, L., Duclaux, G., Teyssier, C., Whitney, D. L., Bocher, M., et al. (2017). The origin of contractional structures in extensional gneiss domes Reply. Geology, 45(6), E416.
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Roberge, M., Bureau, H., Bolfan-Casanova, N., Raepsaet, C., Surble, S., Khodja, H., et al. (2017). Chlorine in wadsleyite and ringwoodite: An experimental study. Earth And Planetary Science Letters, 467, 99–107.
Résumé: We report concentrations of Chlorine (Cl) in synthetic wadsleyite (Wd) and ringwoodite (Rw) in the system NaCl-(Mg,Fe)(2)SiO4 under hydrous and anhydrous conditions. Multi-anvil press experiments were performed under pressures (14-22 GPa) and temperatures (1100-1400 degrees C) relevant to the transition zone (TZ: 410-670 km depth). Cl and H contents were measured using Particle Induced X-ray Emission (PIXE) and Elastic Recoil Detection Analysis (ERDA) respectively. Results show that Cl content in Rw and Wd is significantly higher than in other nominally anhydrous minerals from the upper mantle (olivine, pyroxene, garnet), with up to 490 ppm Cl in anhydrous Rw, and from 174 to 200 ppm Cl in hydrous Wd and up to 113 ppm Cl in hydrous Rw. These results put constrains on the Cl budget of the deep Earth. Based on these results, we propose that the TZ may be a major repository for major halogen elements in the mantle, where Cl may be concentrated together with H2O and F (see Roberge et al., 2015). Assuming a continuous supply by subduction and a water-rich TZ, we use the concentrations measured in Wd (174 ppm Cl) and in Rw (106 ppm Cl) and we obtain a maximum value for the CI budget for the bulk silicate Earth (BSE) of 15.1 x 10(22) g Cl, equivalent to 37 ppm Cl. This value is larger than the 17 ppm Cl proposed previously by McDonough and Sun (1995) and evidences that the Cl content of the mantle may be higher than previously thought. Comparison of the present results with the budget calculated for F (Roberge et al., 2015) shows that while both elements abundances are probably underestimated for the bulk silicate Earth, their relative abundances are preserved. The BSE is too rich in F with respect to heavy halogen elements to be compatible with a primordial origin from chondrites Cl-like (carbonaceous chondrites CC) material only. We thus propose a combination of two processes to explain these relative abundances: a primordial contribution of different chondritic-like materials, including EC-like (enstatite chondrites), possibly followed by a distinct fractionation of F during the Earth differentiation due to its lithophile behavior compared to Cl, Br and l. (C) 2017 Elsevier B.V. All rights reserved.
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Rousset, B., Campillo, M., Lasserre, C., Frank, W. B., Cotte, N., Walpersdorf, A., et al. (2017). A geodetic matched filter search for slow slip with application to the Mexico subduction zone. Journal Of Geophysical Research-Solid Earth, 122(12), 10498–10514.
Résumé: Since the discovery of slow slip events, many methods have been successfully applied to model obvious transient events in geodetic time series, such as the widely used network strain filter. Independent seismological observations of tremors or low-frequency earthquakes and repeating earthquakes provide evidence of low-amplitude slow deformation but do not always coincide with clear occurrences of transient signals in geodetic time series. Here we aim to extract the signal corresponding to slow slips hidden in the noise of GPS time series, without using information from independent data sets. We first build a library of synthetic slow slip event templates by assembling a source function with Green's functions for a discretized fault. We then correlate the templates with postprocessed GPS time series. Once the events have been detected in time, we estimate their duration T and magnitude M-w by modeling a weighted stack of GPS time series. An analysis of synthetic time series shows that this method is able to resolve the correct timing, location, T, and M-w of events larger than M-w 6 in the context of the Mexico subduction zone. Applied on a real data set of 29 GPS time series in the Guerrero area from 2005 to 2014, this technique allows us to detect 28 transient events from M-w 6.3 to 7.2 with durations that range from 3 to 39days. These events have a dominant recurrence time of 40days and are mainly located at the downdip edges of the M-w>7.5 slow slip events.
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Roux, P., & Ben-Zion, Y. (2017). Rayleigh phase velocities in Southern California from beamforming short-duration ambient noise. Geophysical Journal International, 211(1), 450–454.
Résumé: Beamforming of ambient noise recorded by regional arrays of seismometers is presented as an alternative imaging approach to cross-correlations between pairs of sensors. The method is used to obtain phase velocities and propagation directions of Rayleigh surface waves around the first and second microseism peaks in southern California. The derived velocity maps and propagation directions correlate with major geological structures and changes of the coastal shape in the region. The results are consistent with and complementary to those obtained using cross-correlations of long-duration data between pairs of sensors. Significant advantages of the presented high-resolution adaptive beamforming method over point-to-point noise cross-correlations are the short time interval of required data (hours to days compared to a year) and robust performance with directive (rather than omnidirectional) noise propagation. Given the recent trend toward dense and large seismic arrays at various scales, the combination of beamforming and noise-correlation processing may provide an optimal strategy for performing noise-based tomography.
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Rovezzi, M., Lapras, C., Manceau, A., Glatzel, P., & Verbeni, R. (2017). High energy-resolution x-ray spectroscopy at ultra-high dilution with spherically bent crystal analyzers of 0.5 m radius. Review Of Scientific Instruments, 88(1).
Résumé: We present the development, manufacturing, and performance of spherically bent crystal analyzers (SBCAs) of 100 mm diameter and 0.5 m bending radius. The elastic strain in the crystal wafer is partially released by a “strip-bent” method where the crystal wafer is cut into strips prior to the bending and the anodic bonding process. Compared to standard 1 m SBCAs, a gain in intensity is obtained without loss of energy resolution. The gain ranges between 2.5 and 4.5, depending on the experimental conditions and the width of the emission line measured. This reduces the acquisition times required to perform high energy-resolution x-ray absorption and emission spectroscopy on ultra-dilute species, accessing concentrations of the element of interest down to, or below, the ppm (ng/mg) level. Published by AIP Publishing.
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Rupin, M., & Roux, P. (2017). A multi-wave elastic metamaterial based on degenerate local resonances. Journal Of The Acoustical Society Of America, 142(1), EL75–EL81.
Résumé: In this letter, an experimental and numerical study of the influence of symmetric resonators on Lamb waves that propagate in a thin metallic plate is reported. The resonators consist of a set of small, closely packed rods that pass through the plate from side to side to create a locally resonant metamaterial. Adjusting the symmetry of these rods creates degenerate flexural resonances that can be tuned to couple only with a given Lamb mode that is either symmetric (S0) or anti-symmetric (A0). This approach offers promising perspectives in the development of metamaterials for elastic waves that involve non-scalar interactions. (C) 2017 Acoustical Society of America
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Saade, M., Montagner, J. P., Roux, P., Shiomi, K., Enescu, B., & Brenguier, F. (2017). Monitoring of seismic anisotropy at the time of the 2008 Iwate-Miyagi (Japan) earthquake. Geophysical Journal International, 211(1), 483–497.
Résumé: We investigate temporal variations of the polarization anomaly of surface waves (Rayleigh and Love) relative to an isotropic medium, before and after the 2008 June 13, Iwate-Miyagi Nairiku earthquake (M-w = 6.9) in Japan, using passive image interferometry. We use continuous data records of 20 high-sensitivity three-component seismic stations (National Institute for Earth Sciences and Disaster Resilience-NIED Hi-net) from mid-2007 to the end of 2009. We compute cross-correlations of ambient seismic noise between each pair of stations, in the frequency range of 0.08-0.22 Hz. The temporal variations of the surface wave polarization show slow and weak variations due to seasonal changes to which rapid and strong variations are superposed at the time of the earthquake, and more surprisingly, also a month and a half before the earthquake. Strong changes in the polarization of surface waves might be related to changes in the distribution of crack orientation affecting seismic anisotropy.
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Saillard, M., Audin, L., Rousset, B., Avouac, J. - P., Chlieh, M., Hall, S. R., et al. (2017). From the seismic cycle to long-term deformation: linking seismic coupling and Quaternary coastal geomorphology along the Andean megathrust. Tectonics, 36(2), 241–256.
Résumé: Measurement of interseismic strain along subduction zones reveals the location of both locked asperities, which might rupture during megathrust earthquakes, and creeping zones, which tend to arrest such seismic ruptures. The heterogeneous pattern of interseismic coupling presumably relates to spatial variations of frictional properties along the subduction interface and may also show up in the fore-arc morphology. To investigate this hypothesis, we compiled information on the extent of earthquake ruptures for the last 500 years and uplift rates derived from dated marine terraces along the South American coastline from central Peru to southern Chile. We additionally calculated a new interseismic coupling model for that same area based on a compilation of GPS data. We show that the coastline geometry, characterized by the distance between the coast and the trench; the latitudinal variations of long-term uplift rates; and the spatial pattern of interseismic coupling are correlated. Zones of faster and long-term permanent coastal uplift, evidenced by uplifted marine terraces, coincide with peninsulas and also with areas of creep on the megathrust where slip is mostly aseismic and tend to arrest seismic ruptures. We conclude that spatial variations of frictional properties along the megathrust dictate the tectono-geomorphological evolution of the coastal zone and the extent of seismic ruptures along strike.
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Salameh, C., Bard, P. - Y., Guillier, B., Harb, J., Cornou, C., Gerard, J., et al. (2017). Using ambient vibration measurements for risk assessment at an urban scale: from numerical proof of concept to Beirut case study (Lebanon). Earth Planets And Space, 69.
Résumé: Post-seismic investigations repeatedly indicate that structures having frequencies close to foundation soil frequencies exhibit significantly heavier damages (Caracas 1967; Mexico 1985; Pujili, Ecuador 1996; L'Aquila 2009). However, observations of modal frequencies of soils and buildings in a region or within a current seismic risk analysis are not fully considered together, even when past earthquakes have demonstrated that coinciding soil and building frequencies leads to greater damage. The present paper thus focuses on a comprehensive numerical analysis to investigate the effect of coincidence between site and building frequencies. A total of 887 realistic soil profiles are coupled with a set of 141 single-degree-of-freedom elastoplastic oscillators, and their combined (nonlinear) response is computed for both linear and nonlinear soil behaviors, for a large number (60) of synthetic input signals with various PGA levels and frequency contents. The associated damage is quantified on the basis of the maximum displacement as compared to both yield and ultimate post-elastic displacements, according to the RISK-UE project recommendations (Lagomarsino and Giovinazzi in Bull Earthq Eng 4(4): 415-443, 2006), and compared with the damage obtained in the case of a similar building located on rock. The correlation between this soil/rock damage increment and a number of simplified mechanical and loading parameters is then analyzed using a neural network approach. The results emphasize the key role played by the building/soil frequency ratio even when both soil and building behave nonlinearly; other important parameters are the PGA level, the soil/rock velocity contrast and the building ductility. A numerical investigation based on simulation of ambient noise for the whole set of 887 profiles also indicates that the amplitude of H/V ratio may be considered as a satisfactory proxy for site amplification when applied to measurements at urban scale. A very easy implementation of this method, using ambient vibration measurements both at ground level and within buildings, is illustrated with an example application for the city of Beirut (Lebanon).
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Salcedo, M., Novais, A., Schleicher, J., & Costa, J. C. (2017). Optimization of the parameters in complex Pade Fourier finite-difference migration. Geophysics, 82(3), S259–S269.
Résumé: Complex Pade Fourier finite-difference migration is a stable one-way wave-equation technique that allows for better treatment of evanescent modes than its real counterpart, in this way producing fewer artifacts. As for real Fourier finite-difference (FFD) migration, its parameters can be optimized to improve the imaging of steeply dipping reflectors. The dip limitation of the FFD operator depends on the variation of the velocity field. We have developed a wide-angle approximation for the one-way continuation operator by means of optimization of the Pade coefficients and the most important velocity-dependent parameter. We have evaluated the achieved quality of the approximate dispersion relation in dependence on the chosen function of the ratio between the model and reference velocities under consideration of the number of terms in the Pade approximation and the branch-cut rotation angle. The optimized parameters are chosen based on the migration results and the computational cost. We found that by using the optimized parameters, a one-term expansion achieves the highest dip angles. The implementations were validated on the Marmousi data set and SEG/EAGE salt model data.
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Sanchez, D. F., Simionovici, A. S., Lemelle, L., Cuartero, V., Mathon, O., Pascarelli, S., et al. (2017). 2D/3D Microanalysis by Energy Dispersive X-ray Absorption Spectroscopy Tomography. Scientific Reports, 7.
Résumé: X-ray spectroscopic techniques have proven to be particularly useful in elucidating the molecular and electronic structural information of chemically heterogeneous and complex micro-and nanostructured materials. However, spatially resolved chemical characterization at the micrometre scale remains a challenge. Here, we report the novel hyperspectral technique of micro Energy Dispersive X-ray Absorption Spectroscopy (mu ED-XAS) tomography which can resolve in both 2D and 3D the spatial distribution of chemical species through the reconstruction of XANES spectra. To document the capability of the technique in resolving chemical species, we first analyse a sample containing 2-30 μm grains of various ferrous-and ferric-iron containing minerals, including hypersthene, magnetite and hematite, distributed in a light matrix of a resin. We accurately obtain the XANES spectra at the Fe K-edge of these four standards, with spatial resolution of 3 μm. Subsequently, a sample of similar to 1.9 billion-year-old microfossil from the Gunflint Formation in Canada is investigated, and for the first time ever, we are able to locally identify the oxidation state of iron compounds encrusting the 5 to 10 μm microfossils. Our results highlight the potential for attaining new insights into Precambrian ecosystems and the composition of Earth's earliest life forms.
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Sbaa, S., Hollender, F., Perron, V., Imtiaz, A., Bard, P. - Y., Mariscal, A., et al. (2017). Analysis of rotation sensor data from the SINAPS@Kefalonia (Greece) post-seismic experiment-link to surface geology and wavefield characteristics. Earth Planets And Space, 69.
Résumé: Although rotational seismology has progressed in recent decades, the links between rotational ground motion and site soil conditions are poorly documented. New experiments were performed on Kefalonia Island (Greece) following two large earthquakes (M-W = 6.0, M-W = 5.9) in early 2014 on two well-characterized sites (soft soil, V-S30 similar to 250 m/s; rock, V-S30 similar to 830 m/s, V-S30 being harmonic average shear-wave velocity between 0 and 30 m depth). These earthquakes led to large six-component (three translations and three rotations) datasets of hundreds of well-recorded events. The relationship between peak translational acceleration versus peak rotational velocity is found sensitive to the site conditions mainly for the rotation around the vertical axis (torsion; dominated by Love waves): the stiffer the soil, the lower the torsion, for a given level of translational acceleration. For rotation around the horizontal axes (rocking; dominated by Rayleigh waves), this acceleration/rotation relationship exhibits much weaker differences between soft and rock sites. Using only the rotation sensor, an estimate of the Love-to-Rayleigh energy ratios could be carried out and provided the same results as previous studies that have analyzed the Love-and Rayleigh-wave energy proportions using data from translational arrays deployed at the same two sites. The coupling of translational and rotational measurements appears to be useful, not only for direct applications of engineering seismology, but also to investigate the composition of the wavefield, while avoiding deployment of dense arrays. The availability of new, low-noise rotation sensors that are easy to deploy in the field is of great interest and should extend the use of rotation sensors and expand their possible applications.
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Schaeffer, N., Jault, D., Nataf, H. - C., & Fournier, A. (2017). Turbulent geodynamo simulations: a leap towards Earth's core. Geophysical Journal International, 211(1), 1–29.
Résumé: We present an attempt to reach realistic turbulent regime in direct numerical simulations of the geodynamo. We rely on a sequence of three convection-driven simulations in a rapidly rotating spherical shell. The most extreme case reaches towards the Earth's core regime by lowering viscosity (magnetic Prandtl number P-m = 0.1) while maintaining vigorous convection (magnetic Reynolds number Rm > 500) and rapid rotation (Ekman number E= 10(-7)) at the limit of what is feasible on today's supercomputers. A detailed and comprehensive analysis highlights several key features matching geomagnetic observations or dynamo theory predictions-all present together in the same simulation-but it also unveils interesting insights relevant for Earth's core dynamics. In this strong-field, dipole-dominated dynamo simulation, themagnetic energy is one order of magnitude larger than the kinetic energy. The spatial distribution of magnetic intensity is highly heterogeneous, and a stark dynamical contrast exists between the interior and the exterior of the tangent cylinder (the cylinder parallel to the axis of rotation that circumscribes the inner core). In the interior, the magnetic field is strongest, and is associated with a vigorous twisted polar vortex, whose dynamics may occasionally lead to the formation of a reverse polar flux patch at the surface of the shell. Furthermore, the strong magnetic field also allows accumulation of light material within the tangent cylinder, leading to stable stratification there. Torsional Alfven waves are frequently triggered in the vicinity of the tangent cylinder and propagate towards the equator. Outside the tangent cylinder, the magnetic field inhibits the growth of zonal winds and the kinetic energy is mostly non-zonal. Spatio-temporal analysis indicates that the low-frequency, non-zonal flow is quite geostrophic (columnar) and predominantly large-scale: an m = 1 eddy spontaneously emerges in our most extreme simulations, without any heterogeneous boundary forcing. Our spatio-temporal analysis further reveals that (i) the low-frequency, large-scale flow is governed by a balance between Coriolis and buoyancy forces-magnetic field and flow tend to align, minimizing the Lorentz force; (ii) the high-frequency flow obeys a balance between magnetic and Coriolis forces; (iii) the convective plumes mostly live at an intermediate scale, whose dynamics is driven by a threeterm MAC balance-involving Coriolis, Lorentz and buoyancy forces. However, small-scale (similar or equal to E-1/3) quasi-geostrophic convection is still observed in the regions of low magnetic intensity.
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Schmeling, H., & Arndt, N. (2017). Modelling komatiitic melt accumulation and segregation in the transition zone. Earth And Planetary Science Letters, 472, 95–106.
Résumé: Komatiites are probably produced in very hot mantle upwellings or plumes. Under such conditions, melting will take place deep within the upper mantle or even within the mantle transition zone. Due to its compressibility at such pressures, melt might be denser than olivine, but would remain buoyant with respect to a peridotitic mantle both above and below the olivine-wadsleyite phase boundary because of the presence of its higher temperature and denser garnet. We studied the physics of melting and melt segregation within hot upwelling mantle passing through the transition zone, with particular emphasis on the effect of depth-dependent density contrasts between melt and ambient mantle. Assuming a 1D plume, we solved the two-phase flow equations of the melt-matrix system accounting for matrix compaction and porosity-dependent shear and bulk viscosity. We assumed a constant ascent velocity and melt generation rate. In a first model series, the level of neutral buoyancy Z(neutr) is assumed to lie above the depth of onset of melting, i.e. there exists a region where dense melt may lag behind the solid phases within the rising plume. Depending on two non-dimensional numbers (accumulation number Ac, compaction resistance number Cr) we find four regimes: 1) time-dependent melt accumulation in standing porosity waves that scale with the compaction length. The lowermost of these waves broadens with time until a high melt accumulation zone is formed in steady state. During this transient solitary porosity waves may cross the depth of neutral density and escape. 2) steady-state weak melt accumulation near Zneutr, 3) no melt accumulation due to small density contrast or, 4) high matrix viscosity. In regime 4 the high mantle viscosity prevents the opening of pore space necessary to accumulate melt. In a second series, the rising mantle crosses the olivine-wadsleyite phase boundary, which imposes a jump in density contrast between melt and ambient mantle. A sharp melt porosity contrast develops and a large melt porosity accumulates immediately above the phase boundary. Both model series show 1) that not only melt density, but also porosity-dependent matrix viscosity controls the melt ascent or accumulation, 2) that there are parameter ranges and physical conditions which may lead to the accumulation of very large melt porosities (> degree of melting), 3) that in spite of melt being denser than olivine at some depths, in general these melts escape these regions and continue to percolate upward faster than the rising mantle. Melting and melt transport under the conditions predicted by the numerical modelling is able to reproduce the compositions of the main types of komatiite. Thus, the accumulation of large melt fractions, and sequential escape of melt from porosity waves, explains several puzzling features of the geochemical compositions of komatiites. (C) 2017 Elsevier B.V. All rights reserved.
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Schwartz, S., Gautheron, C., Audin, L., Dumont, T., Nomade, J., Barbarand, J., et al. (2017). Foreland exhumation controlled by crustal thickening in the Western Alps. Geology, 45(2), 139–142.
Résumé: In alpine-type collision belts, deformation of the foreland may occur as a result of forward propagation of thrusting and is generally associated with thin-skinned deformation mobilizing the sedimentary cover in fold-and-thrust belts. Locally, foreland deformation can involve crustal-scale thrusting and produce large-scale exhumation of crystalline basement resulting in significant relief generation. In this study, we investigate the burial and exhumation history of Tertiary flexural basins located in the Western Alpine foreland, at the front of the Digne thrust sheet (southeast France), using low-temperature apatite fission-track and (U-Th)/He thermochronology. Based on the occurrence of partially to totally reset ages, we document 3.3-4.0 km of burial of these basin remnants between ca. 12 Ma and 6 Ma, related to thinskinned thrust-sheet emplacement without major relief generation. The onset of exhumation is dated at ca. 6 Ma and is linked to erosion associated with significant relief development. This evolution does not appear to have been controlled by major climate changes (Messinian crisis) or by European slab breakoff. Rather, we propose that the erosional history of the Digne thrust sheet corresponds to basement involvement in foreland deformation, leading to crustal thickening. Our study highlights the control of deep-crustal tectonic processes on foreland relief development and its erosional response at mountain fronts.
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Schwartz, S., Zerathe, S., Jongmans, D., Baillet, L., Carcaillet, J., Audin, L., et al. (2017). Cosmic ray exposure dating on the large landslide of Sechilienne (Western Alps): A synthesis to constrain slope evolution. Geomorphology, 278, 329–344.
Résumé: The 60 x 10(6) m(3) Sechilienne landslide (Belledonne Massif, Western Alps) is located on the right bank of the East-West trending Romanche valley which is shaped by glacial and alluvial processes during the Quaternary. Its head scarp (>35 m high) was dated by Le Roux et al. (2009) using the cosmic ray exposure (CRE) method. Even though these previous results revealed that the initiation of the instability occurred several thousand years after ice down-wastage in the valley, the internal landslide evolution is not constrained. In this paper, we provide 63 additional Be-10 samples collected from the internal scarps and the main scarp, as well as on glacially polished rock surfaces. The aim is to constrain the global landslide kinematics (internal and head scarps) and its relationship with glacier retreat. Results from glacially polished surfaces point out that complex shielding processes (relict moraines, soil deposits and seasonal snow cover) might have affected rock dating. Despite scattering of the resulting ages, the dataset shows that the glacial retreat was achieved between 17.5 and 13 ka. Exposure ages obtained on gravitational scarps reveal that the landslide initiation occurred 8 to 6 ka ago. From the initiation until 2 ka the gravitational kinematics was slow (similar to 2 mm" year(-1)) and focused around the head scarp, leading to a general slope subsidence. After 2 ka, the exposure rates increased significantly (similar to 8 min. year(-1)) with the development of pervasive internal deformation of the landslide mass. This new scenario for the 58chilienne slope reflects a progressive rock-slope weakening since 8 ka, associated with a continuous activity of a deep-seated surface failure. (C) 2016 Elsevier B.V. All rights reserved.
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Sestu, M., Navarra, G., Carrero, S., Valvidares, S. M., Aquilanti, G., Perez-Lopez, R., et al. (2017). Whole-nanoparticle atomistic modeling of the schwertmannite structure from total scattering data. Journal Of Applied Crystallography, 50, 1617–1626.
Résumé: Schwertmannite is a poorly crystalline nanometric iron sulfate oxyhydroxide. This mineral shows a structural variability under different environments. Because of that, the determination of its structure and, consequently, of its physical-chemical properties is quite challenging. This article presents a detailed structural investigation of the structure of schwertmannite conducted under different approaches: X-ray absorption spectroscopy, Rietveld refinement, and a combined reverse Monte Carlo and Debye function analysis of the whole nanoparticle structure. The schwertmannite model presented here is, to the auhors' knowledge, the most complete model so far reported.
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Shao, Z., Revil, A., Mao, D., & Wang, D. (2017). Induced polarization signature of coal seam fires. Geophysical Journal International, 208(3), 1313–1331.
Résumé: Coal seam fires are a worldwide disaster of both ecological and economic importance. Their remote detection from the ground surface or using airborne techniques is required for developing efficient strategies to extinguish them. We investigate here the use of time-domain-induced polarization to localize coal seam fires. For laboratory experiments, we first introduce a modified time-domain-induced polarization methodology to quickly acquire and invert the secondary voltage distribution mapped after the shutdown of the primary current. A set of sandbox experiments is conducted in which coal is embedded into humidified sand. Raw coal alone generates significant induced polarization anomalies, above those shown by the sand. Even higher induced polarization anomalies are detected in presence of a coal seam fire. We postulate that the higher chargeability is due to the pyrolysis, which may enhance electronic polarization or the polarization associated with the cation exchange capacity (CEC) of the material. The position of the coal seam fire is well recovered inside the tank by inverting the secondary voltages in term of a source current density distribution. We also collected field data over a recognized coal seam fire in Colorado, USA. A chargeability anomaly (similar to 800 mV V-1) and a resistivity anomaly (similar to 1 Ohm m) are observed at the position of the coal seam fire. We propose a normalized burning front index (a scaled normalized chargeability) to image and localize, without ambiguity, the position of the coal seam fire in the subsurface. The 3-D reconstructed target is located below a negative self-potential anomaly (similarly to what is observed in laboratory experiments) and a temperature anomaly recorded at a depth of 30 cm.
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Shokouhi, P., Riviere, J., Guyer, R. A., & Johnson, P. A. (2017). Slow dynamics of consolidated granular systems: Multi-scale relaxation. Applied Physics Letters, 111(25).
Résumé: Dynamic acousto-elastic testing, a pump-probe scheme, is employed to investigate the recovery of consolidated granular media systems from the non-equilibrium steady state established by a pump strain field. This measurement scheme makes it possible to follow the recovery from the non-equilibrium steady state over many orders of magnitude in time. The recovery is described with a relaxation time spectrum that is found to be independent of the amplitude of the non-equilibrium steady state (pump amplitude) and of the environment in which samples reside. The non-equilibrium steady state and its slow recovery are the laboratory realization of phenomena that are found in many physical systems of practical importance. Published by AIP Publishing.
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Socquet, A., Valdes, J. P., Jara, J., Cotton, F., Walpersdorf, A., Cotte, N., et al. (2017). An 8month slow slip event triggers progressive nucleation of the 2014 Chile megathrust. Geophysical Research Letters, 44(9), 4046–4053.
Résumé: The mechanisms leading to large earthquakes are poorly understood and documented. Here we characterize the long-term precursory phase of the 1 April 2014 M(w)8.1 North Chile megathrust. We show that a group of coastal GPS stations accelerated westward 8months before the main shock, corresponding to a M(w)6.5 slow slip event on the subduction interface, 80% of which was aseismic. Concurrent interface foreshocks underwent a diminution of their radiation at high frequency, as shown by the temporal evolution of Fourier spectra and residuals with respect to ground motions predicted by recent subduction models. Such ground motions change suggests that in response to the slow sliding of the subduction interface, seismic ruptures are progressively becoming smoother and/or slower. The gradual propagation of seismic ruptures beyond seismic asperities into surrounding metastable areas could explain these observations and might be the precursory mechanism eventually leading to the main shock.
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Sorrel, P., Eymard, I., Leloup, P. - H., Maheo, G., Olivier, N., Sterb, M., et al. (2017). Wet tropical climate in SE Tibet during the Late Eocene. Scientific Reports, 7.
Résumé: Cenozoic climate cooling at the advent of the Eocene-Oligocene transition (EOT), similar to 33.7 Ma ago, was stamped in the ocean by a series of climatic events albeit the impact of this global climatic transition on terrestrial environments is still fragmentary. Yet archival constraints on Late Eocene atmospheric circulation are scarce in (tropical) monsoonal Asia, and the paucity of terrestrial records hampers a meaningful comparison of the long- term climatic trends between oceanic and continental realms. Here we report new sedimentological data from the Jianchuan basin (SE Tibet) arguing for wetter climatic conditions in monsoonal Asia at similar to 35.5 Ma almost coevally to the aridification recognized northwards in the Xining basin. We show that the occurrence of flash-flood events in semi-arid to sub-humid palustrine-sublacustrine settings preceded the development of coal-bearing deposits in swampylike environments, thus paving the way to a more humid climate in SE Tibet ahead from the EOT. We suggest that this moisture redistribution possibly reflects more northern and intensified ITCZ-induced tropical rainfall in monsoonal Asia around 35.5 Ma, in accordance with recent sea-surface temperature reconstructions from equatorial oceanic records. Our findings thus highlight an important period of climatic upheaval in terrestrial Asian environments similar to 2-4 millions years prior to the EOT.
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Stambouli, A. B., Zendagui, D., Bard, P. - Y., & Derras, B. (2017). Deriving amplification factors from simple site parameters using generalized regression neural networks: implications for relevant site proxies. Earth Planets And Space, 69.
Résumé: Most modern seismic codes account for site effects using an amplification factor (AF) that modifies the rock acceleration response spectra in relation to a “site condition proxy,” i.e., a parameter related to the velocity profile at the site under consideration. Therefore, for practical purposes, it is interesting to identify the site parameters that best control the frequency-dependent shape of the AF. The goal of the present study is to provide a quantitative assessment of the performance of various site condition proxies to predict the main AF features, including the often used short-and mid-period amplification factors, F-a and F-v, proposed by Borcherdt (in Earthq Spectra 10:617-653, 1994). In this context, the linear, viscoelastic responses of a set of 858 actual soil columns from Japan, the USA, and Europe are computed for a set of 14 real accelerograms with varying frequency contents. The correlation between the corresponding site-specific average amplification factors and several site proxies (considered alone or as multiple combinations) is analyzed using the generalized regression neural network (GRNN). The performance of each site proxy combination is assessed through the variance reduction with respect to the initial amplification factor variability of the 858 profiles. Both the whole period range and specific short- and mid-period ranges associated with the Borcherdt factors F-a and F-v are considered. The actual amplification factor of an arbitrary soil profile is found to be satisfactorily approximated with a limited number of site proxies (4-6). As the usual code practice implies a lower number of site proxies (generally one, sometimes two), a sensitivity analysis is conducted to identify the “best performing” site parameters. The best one is the overall velocity contrast between underlying bedrock and minimum velocity in the soil column. Because these are the most difficult and expensive parameters to measure, especially for thick deposits, other more convenient parameters are preferred, especially the couple (V-s30, f(0)) that leads to a variance reduction in at least 60%. From a code perspective, equations and plots are provided describing the dependence of the short-and mid-period amplification factors F-a and F-v on these two parameters. The robustness of the results is analyzed by performing a similar analysis for two alternative sets of velocity profiles, for which the bedrock velocity is constrained to have the same value for all velocity profiles, which is not the case in the original set.
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Stehly, L., & Boue, P. (2017). On the interpretation of the amplitude decay of noise correlations computed along a line of receivers. Geophysical Journal International, 209(1), 358–372.
Résumé: Measuring seismic wave attenuation is critical to the prediction of accurate ground motion and for earthquake hazard analysis. In the present article, we carefully investigate to what extent noise correlations can be used to unambiguously measure the attenuation of the Earth crust. More precisely, we explore the different ways to interpret the amplitude decay of noise correlations computed along two lines of broad-band receivers located nearby the French Pyrenees. To this end, we first study how the distribution of seismic noise sources affects the amplitude of noise correlations by computing of the noise-source kernels in PREM. Numerical experiments in a 2-D homogeneous medium are then used to interpret the amplitude decay of the noise correlations measured along two lines of broad-band receivers located in southwest France. We find that in the 5-10 s period band, where Rayleigh waves are sensitive to the upper-crust, the noise correlations have stronger amplitude decay along the northern Pyrenees than along the Aquitaine Basin. However this difference cannot be interpreted unambiguously as a contrast of attenuation as it is also possible to find a distribution of noise sources that explains our observations. This shows that even when considering a line of receivers, it is not possible to use noise correlations to measure the attenuation of the medium without making strong assumptions about or taking into account the distribution of the noise sources.
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Stepanov, R., & Plunian, F. (2017). Kinematic dynamo in a tetrahedron composed of helical Fourier modes (Vol. 208).
Résumé: It is generally believed that helicity can play a significant role in turbulent systems, e.g. supporting the generation of large-scale magnetic fields, but its exact contribution is not clearly understood. For example there are well-known examples of large scale dynamos produced by a flow which is pointwise non-helical. In any case a break of mirror symmetry seems to be always at the heart of the dynamo mechanism. A fruitful framework to analyze such processes is the use of helical mode decomposition. In pure hydrodynamics such framework has proved its availability in study of the processes responsible for helicity cascades. It has also been used in the analysis of MHD helical mode interactions. The present work deals with the kinematic dynamo problem, solving the induction equation within the framework of helical Fourier modes decomposition. We show that the simplest modes configuration leading to an unstable solution has the form of a tetrahedron. Then the dynamo is produced by only two scales flow. We find necessary conditions for such dynamo action, not certainly related to flow helicity. The results help to understand generic dynamo flows like the one studied by G.O. Roberts (1972).
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Strady, E., Quoc Tuc Dinh, Nemery, J., Thanh Nho Nguyen, Guedron, S., Nhu Sang Nguyen, et al. (2017). Spatial variation and risk assessment of trace metals in water and sediment of the Mekong Delta. Chemosphere, 179, 367–378.
Résumé: The Mekong Delta, is home to 17 million inhabitants and faces numerous challenges relating to climate change, environmental degradation and water issues. In this study, we assess trace metals concentrations (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Hg, Pb) in the water, suspended particulate matter and surface sediments of the Tien River, the Northern branch of the Mekong Delta, during both dry and rainy seasons. Metal concentrations in the dissolved and suspended particle phases remain in the low concentration range of the main Asian Tropical River. During transportation in the riverine part, we evidenced that V, Cr, Co, As and Pb are dominant in the particulate phase while Mo, Ni and Cu dominate in the dissolved fraction. In the salinity gradient, dissolved U, V, Mo exhibit conservative behaviour while Ni, Cu, As, Co and Cd showed additive behaviour suggesting desorption processes. In the surface sediment, metal concentrations are controlled by the particle-size, POC contents and Fe, Al and Mn – oxy(hydr)oxides. Calculated Enrichment Factor and Geoaccumulation Index evidenced As enrichment while the calculated mean effect range median quotients evidenced a low to medium ecotoxicological potential effects range in the surface sediments. (C) 2017 Elsevier Ltd. All rights reserved.
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Strady, E., Vu Bich Hanh Dang, Nemery, J., Guedron, S., Quoc Tuc Dinh, Denis, H., et al. (2017). Baseline seasonal investigation of nutrients and trace metals in surface waters and sediments along the Saigon River basin impacted by the megacity of Ho Chi Minh (Vietnam). Environmental Science And Pollution Research, 24(4), 3226–3243.
Résumé: The Saigon River, Southern Vietnam, crosses one of the most dynamic developing Megacity in Southeast Asia: Ho Chi Minh City (HCMC). The increased economic, industrial, and domestic developments may affect the environmental quality of water and halicutic resources. In this study, we evaluated the seasonal (dry and wet seasons) biogeochemical state of the Saigon River during two snapshot campaigns conducted along the river basin upstream from HCMC; the Saigon River was characterized by slightly acidic (pH 5.7-7.7) and oxygen-depleted water (dissolved oxygen (DO), 0.36-5.18 mg l(-1)). Nutrients (N-NH4 = 0.01-2.41, N-NO3 = 0.14-2.72, and P-PO4 = similar to 0-0.42 mg l(-1)), DOC (2.2-8.0 mg l(-1)), POC, and trace metal(oid) (As, Cd, Cr, Cu, Zn, and Hg) concentrations were low showing a good quality of the upstream river. In the urban center area, DO dropped to 0.03 mg l(-1) accompanied with a rise of nutrient concentrations (e.g., N-NH4, up to 17.7 mg l(-1)) likely originating from wastewater discharges. Trace metal concentrations also rose sharply (e.g., Cr and Hg rose up to 10-fold higher) in both water and sediments but remained under the World Health Organization (WHO) and Vietnamese concentration guidelines. In the downstream estuarine area, the intrusion of marine waters diluted water flowing from HCMC, leading water quality to return close to the state observed upstream from HCMC. In general, levels of nutrient and metal contaminations along the Saigon River during both seasons appear moderate regarding to Vietnamese and WHO guidelines although the urban area is highlighted as the major contributor for metal(oid) emissions. Finally, we showed that apart from wastewater and industrial discharges that affect the river quality, metal(oid) partitioning between solid and solution is controlled by the change in water geochemistry along the continuum during both seasons, such as DO (e.g., for As and Cr) and pH (e.g., for Pb) which drives their sorption/dissolution dynamics.
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Sucheras-Marx, B., Giraud, F., Lena, A., & Simionovici, A. (2017). Picking nannofossils: How and why. Journal Of Micropalaeontology, 36, 219–221.
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Sutherland, R., Townend, J., Toy, V., Upton, P., Coussens, J., Allen, M., et al. (2017). Extreme hydrothermal conditions at an active plate-bounding fault. Nature, 546(7656), 137–+.
Résumé: Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes(1). Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 +/- 15 degrees Celsius per kilometre(2,3). At temperatures above 300-450 degrees Celsius, usually found at depths greater than 10-15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional-mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades(4,5). The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 +/- 1 per cent above hydrostatic levels and an average geothermal gradient of 125 +/- 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.
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Svay, A., Perron, V., Imtiaz, A., Zentner, I., Cottereau, R., Clouteau, D., et al. (2017). Spatial coherency analysis of seismic ground motions from a rock site dense array implemented during the Kefalonia 2014 aftershock sequence. Earthquake Engineering & Structural Dynamics, 46(12), 1895–1917.
Résumé: The objective of studies presented in this paper is to analyse the spatial incoherency of seismic ground motions using signals from a velocimeter dense array located on a rock site, recording the aftershock sequence of the two M6 Kefalonia earthquakes that occurred in January/February 2014 (Kefalonia island, Greece). The analyses are carried out with both horizontal and vertical components of velocigrams for small separation distances of stations (<100m). The coherencies of seismic ground motions identified from strong motion windows are compared with those identified from coda parts of signals. It is realized that there is no significant difference between the coherencies estimated from those two parts of signals. The influence of earthquake event number on the result of coherencies and the dispersions of coherencies estimated from different earthquake events are presented. Finally, coherencies estimated from the dense array are compared with several coherency models proposed and widely used in the literature. The possibility of modifying some parameters of those existing coherency models to fit with in situ coherencies are discussed and presented. Copyright (c) 2017 John Wiley & Sons, Ltd.
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Tachikawa, K., Arsouze, T., Bayon, G., Bory, A., Colin, C., Dutay, J. - C., et al. (2017). The large-scale evolution of neodymium isotopic composition in the global modern and Holocene ocean revealed from seawater and archive data. Chemical Geology, 457, 131–148.
Résumé: Neodymium isotopic compositions (Nd-143/Nd-144 or epsilon(Nd)) have been used as a tracer of water masses and lithogenic inputs to the ocean. To further evaluate the faithfulness of this tracer, we have updated a global seawater epsilon(Nd) database and combined it with hydrography parameters (temperature, salinity, nutrients and oxygen concentrations), carbon isotopic ratio and radiocarbon of dissolved inorganic carbon. Archive epsilon(Nd) data are also compiled for leachates, foraminiferal tests, deep-sea corals and fish teeth/debris from the Holocene period (< 10,000 years). At water depths >= 1500m, property-property plots show clear correlations between seawater epsilon(Nd) and the other variables, suggesting that large-scale water mass mixing is a primary control of deepwater epsilon(Nd) distribution. At >= 200m, basin-scale seawater T-S-epsilon(Nd) diagrams demonstrate the isotopic evolution of different water masses. Seawater and archive epsilon(Nd) values are compared using property-property plots and T-S-epsilon(Nd) diagrams. Archive values generally agree with corresponding seawater values although they tend to be at the upper limit in the Pacific. Both positive and negative offsets exist in the northern North Atlantic. Applying multiple regression analysis to deep (>= 1500m) seawater data, we established empirical equations that predict the main, large-scale, deepwater epsilon(Nd) trends from hydrography parameters. Large offsets from the predicted values are interpreted as a sign of significant local/regional influence. Dominant continental influence on seawater and archive epsilon(Nd) is observed mainly within 1000 km from the continents. Generally, seawater and archive epsilon(Nd) values form gradual latitudinal trend in the Atlantic and Pacific at depths >= 600m, consistent with the idea that Nd isotopes help distinguish between northern/southern sourced water contributions at intermediate and deep water depths.
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Tavakoli F, B., Operto, S., Ribodetti, A., & Virieux, J. (2017). Slope tomography based on eikonal solvers and the adjoint-state method. Geophysical Journal International, 209(3), 1629–1647.
Résumé: Velocity macromodel building is a crucial step in the seismic imaging workflow as it provides the necessary background model for migration or full waveform inversion. In this study, we present a new formulation of stereotomography that can handle more efficiently long-offset acquisition, complex geological structures and large-scale data sets. Stereotomography is a slope tomographic method based upon a semi-automatic picking of local coherent events. Each local coherent event, characterized by its two-way traveltime and two slopes in common-shot and common-receiver gathers, is tied to a scatterer or a reflector segment in the subsurface. Ray tracing provides a natural forward engine to compute traveltime and slopes but can suffer from non-uniform ray sampling in presence of complex media and long-offset acquisitions. Moreover, most implementations of stereotomography explicitly build a sensitivity matrix, leading to the resolution of large systems of linear equations, which can be cumbersome when large-scale data sets are considered. Overcoming these issues comes with a new matrix-free formulation of stereotomography: a factored eikonal solver based on the fast sweeping method to compute first-arrival traveltimes and an adjoint-state formulation to compute the gradient of the misfit function. By solving eikonal equation from sources and receivers, we make the computational cost proportional to the number of sources and receivers while it is independent of picked events density in each shot and receiver gather. The model space involves the subsurface velocities and the scatterer coordinates, while the dips of the reflector segments are implicitly represented by the spatial support of the adjoint sources and are updated through the joint localization of nearby scatterers. We present an application on the complex Marmousi model for a towed-streamer acquisition and a realistic distribution of local events. We show that the estimated model, built without any prior knowledge of the velocities, provides a reliable initial model for frequency-domain FWI of long-offset data for a starting frequency of 4 Hz, although some artefacts at the reservoir level result from a deficit of illumination. This formulation of slope tomography provides a computationally efficient alternative to waveform inversion method such as reflection waveform inversion or differential-semblance optimization to build an initial model for pre-stack depth migration and conventional FWI.
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Teixeira, M. G., Donze, F., Renard, F., Panahi, H., Papachristos, E., & Scholtes, L. (2017). Microfracturing during primary migration in shales. Tectonophysics, 694, 268–279.
Résumé: In several geological environments, chemical reactions are coupled to rock deformation and the associated stresses induced locally interact with the far field loading. This is the case in immature shales that undergo burial and diagenesis, where the organic matter evolves with temperature into hydrocarbons which induces local volume expansion. At large scale, this mechanism is responsible for the transport of hydrocarbons from source to reservoir rocks, a process referred to as primary migration. However, how the interactions between local fluid production, microfracturing, and transport are coupled remain to be understood. Here, we analyze this coupling phenomenon by developing a discrete element model where the generation of local overpressures occurring in kerogen patches is simulated, while the surrounding rock is subjected to external loading. It is shown that, due to local fluid overpressure; microfracturing occurs and brings the fluids to migrate through the medium. The numerical results are confirmed by laboratory experiments where the network of microfractures induced in an immature Green River shale sample heated under small differential stress was imaged in three dimensions using X-ray microtomography. Moreover, the numerical simulations identify that the state of differential stress and the initial kerogen distribution constitute two key parameters that control the formation of the three-dimensional percolating microfracture network and could thus explain primary migration in shale rocks. (C) 2016 Elsevier B.V. All rights reserved.
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Thiede, R., Robert, X., Stuebner, K., Dey, S., & Faruhn, J. (2017). Sustained out-of-sequence shortening along a tectonically active segment of the Main Boundary thrust: The Dhauladhar Range in the northwestern Himalaya. Lithosphere, 9(5), 715–725.
Résumé: Competing hypotheses suggest that Himalayan topography is sustained and the plate convergence is accommodated either solely along the basal decollement, the Main Himalayan thrust (MHT), or more broadly, across multiple thrust faults. In the past, structural, geomorphic, and geodetic data of the Nepalese Himalaya have been used to constrain the geometry of the MHT and its shallow frontal thrust fault, known as Main Frontal thrust (MFT). The MHT flattens at depth and connects to a hinterland mid-crustal, steeper thrust ramp, located similar to 100 km north of the deformation front. There, the present-day convergence across the Himalaya is mostly accommodated by slip along the MFT. Despite a general agreement that in Nepal most of the shortening is accommodated along the MHT, some researchers have suggested the occurrence of persistent out-of-sequence shortening on interior faults near the Main Central thrust (MCT). Along the northwest Himalaya, in contrast, some of these characteristics of central Nepal are missing, suggesting along-strike variation of wedge deformation and MHT fault geometry. Here we present new field observations and seven zircon (U-Th)/He (ZHe) cooling ages combined with existing low-temperature data sets. In agreement with our previous findings, we suggest that the transect of cooling age patterns across the frontal Dhauladhar Range reveals that the Main Boundary thrust (MBT) is a primary fault, which has uplifted and sustained this spectacular mountain front since at least the late Miocene. Our results suggest that the MBT forms an similar to 40-km-long fault ramp before it soles into the MHT, and motion along it has exhumed rocks from depth of similar to 8-10 km. New three-dimensional thermokinematic modeling (using Pecube finite-element code) reveals that the observed ZHe and apatite fission track cooling ages can only be explained by sustained mean MBT slip rates between similar to 2.6 and 3.5 mm a(-1) since at least 8 Ma, which corresponds to a horizontal shortening rate of similar to 1.7-2.4 mm a(-1). We propose that the MBT is active today, despite a lack of definitive field or seismogenic evidence, and continues to accommodate crustal shorting by out-of-sequence faulting. Assuming that present-day geodetic shorting rates (similar to 14 +/- 2 mm a(-1)) across the northwest Himalaya have been sustained over geologic time scales, this implies that the MBT accommodated similar to 15% of the total Himalayan convergence since its onset. Furthermore, our modeling results imply that the MHT is missing a hinterland mid-crustal ramp further north.
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Thomas, F., Godard, V., Bellier, O., Shabanian, E., Ollivier, V., Benedetti, L., et al. (2017). Morphological controls on the dynamics of carbonate landscapes under a mediterranean climate. Terra Nova, 29(3), 173–182.
Résumé: The influence of the morphological setting on the denudation of carbonate landscapes and the respective contributions of mechanical and chemical weathering processes are still debated. We have addressed these questions by measuring Cl-36 concentrations in 40 samples from the Luberon mountain, SE France, to constrain the denudation of various landscape elements. We observe a clear contrast between the local denudation rates from the flat summit surface, clustered around 30mm/ka, and the basin-average denudation rates across the flanks, ranging from 100 to 200mm/ka. This difference highlights the transient evolution of the range, whose topography is still adjusting to previous uplift events. Such a pattern also suggests that carbonate dissolution is not the only driver of denudation in this setting, which appears to be significantly controlled by slope-dependent processes.
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Townend, J., Sutherland, R., Toy, V. G., Doan, M. - L., Celerier, B., Massiot, C., et al. (2017). Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone. Geochemistry Geophysics Geosystems, 18(12), 4709–4732.
Résumé: Fault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging-wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP-2). We present observational evidence for extensive fracturing and high hanging-wall hydraulic conductivity (similar to 10(-9) to 10(-7) m/s, corresponding to permeability of similar to 10(-16) to 10(-14) m(2)) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP-2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging-wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off-fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation.
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Toy, V. G., Niemeijer, A., Renard, F., Morales, L., & Wirth, R. (2017). Striation and slickenline development on quartz fault surfaces at crustal conditions: Origin and effect on friction. Journal Of Geophysical Research-Solid Earth, 122(5), 3497–3512.
Résumé: Fragments of optically flat silica discs embedded in synthetic gouge were deformed to examine the relationship between the development of striations and slickenlines, and deformation mechanisms, conditions, and fault rheology. Experiments were performed under hydrothermal conditions in a rotary shear apparatus at 100 degrees C or 450 degrees C, to shear strains of 2.02<<8.25. Slip hardening and softening prevail at low and high temperatures, respectively. In recovered samples, disc fragment surfaces are decorated by fine gouge, sometimes arranged in trails, pits, and scratch marks. Prominent groovesinferred slickenlineswith constant orientation, wavelength <10m, and amplitude <0.7m are only observed on disc fragments deformed at 450 degrees C. Some parts of the grooves below the original disc fragment surface contain scattered rounded beads of silica similar to 200nm diameter. Conversely, close examination of pits in 100 degrees C experiments reveals they contain angular particles <2m diameter. The 200nm diameter crystalline quartz can precipitate at 450 degrees C in only 250s, well within the time frame of the experiments but precipitation at 100 degrees C would take at least 8years. No systematic dislocation arrays were observed in the quartz disc fragments, but microfractures are sporadically present. This indicates that at both temperatures brittle failure generated microfractures and microcomminution occurred where gouge particles impacted disc fragment surfaces. These observations suggest formation of silica beads by precipitation from amorphous silica facilitates slip weakening, smoothing of the fault surface parallel to the slip vector, development of undulations perpendicular to the slip vector by a pressure solution creep mechanism, weakening, and maintenance of a constant slip direction.
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Toy, V. G., Sutherland, R., Townend, J., Allen, M. J., Becroft, L., Boles, A., et al. (2017). Bedrock geology of DFDP-2B, central Alpine Fault, New Zealand. New Zealand Journal Of Geology And Geophysics, 60(4), 497–518.
Résumé: Duringthesecondphaseof theAlpineFault, DeepFault Drilling Project (DFDP) in theWhataroa River, South Westland, New Zealand, bedrock was encountered in the DFDP-2B borehole from 238.5-893.2 m Measured Depth (MD). Continuous sampling and meso-to microscale characterisation of whole rock cuttings established that, in sequence, the borehole sampled amphibolite facies, Torlesse Composite Terrane-derived schists, protomylonites and mylonites, terminating 200-400 m above an Alpine Fault Principal Slip Zone (PSZ) with a maximum dip of 62 degrees. The most diagnostic structural features of increasing PSZ proximity were the occurrence of shear bands and reduction in mean quartz grain sizes. A change in composition to greater mica: quartz + feldspar, most markedly below c. 700 m MD, is inferred to result from either heterogeneous sampling or a change in lithology related to alteration. Major oxide variations suggest the fault-proximal Alpine Fault alteration zone, as previously defined in DFDP-1 core, was not sampled.
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Trela, J., Gazel, E., Sobolev, A. V., Moore, L., Bizimis, M., Jicha, B., et al. (2017). The hottest lavas of the Phanerozoic and the survival of deep Archaean reservoirs. Nature Geoscience, 10(6), 451–+.
Résumé: Large igneous provinces and some hotspot volcanoes are thought to form above thermochemical anomalies known as mantle plumes. Petrologic investigations that support this model suggest that plume-derived melts originated at high mantle temperatures (greater than 1,500 degrees C) relative to those generated at ambient mid-ocean ridge conditions (about 1,350 degrees C). Earth's mantle has also cooled appreciably during its history and the temperatures of modern mantle derived melts are substantially lower than those produced during the Archaean (2.5 to 4.0 billion years ago), as recorded by komatiites (greater than 1,700 degrees C). Here we use geochemical analyses of the Tortugal lava suite to show that these Galapagos-Plume-related lavas, which formed 89 million years ago, record mantle temperatures as high as Archaean komatiites and about 400 degrees C hotter than the modern ambient mantle. These results are also supported by highly magnesian olivine phenocrysts and Al-in-olivine crystallization temperatures of 1,570 +/- 20 degrees C. As mantle plumes are chemically and thermally heterogeneous, we interpret these rocks as the result of melting the hot core of the plume head that produced the Caribbean large igneous province. Our results imply that a mantle reservoir as hot as those responsible for some Archaean lavas has survived eons of convection in the deep Earth and is still being tapped by mantle plumes.
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Trinh, P. T., Brossier, R., Metivier, L., Virieux, J., & Wellington, P. (2017). Bessel smoothing filter for spectral-element mesh. Geophysical Journal International, 209(3), 1489–1512.
Résumé: Smoothing filters are extremely important tools in seismic imaging and inversion, such as for traveltime tomography, migration and waveform inversion. For efficiency, and as they can be used a number of times during inversion, it is important that these filters can easily incorporate prior information on the geological structure of the investigated medium, through variable coherent lengths and orientation. In this study, we promote the use of the Bessel filter to achieve these purposes. Instead of considering the direct application of the filter, we demonstrate that we can rely on the equation associated with its inverse filter, which amounts to the solution of an elliptic partial differential equation. This enhances the efficiency of the filter application, and also its flexibility. We apply this strategy within a spectral-element-based elastic full waveform inversion framework. Taking advantage of this formulation, we apply the Bessel filter by solving the associated partial differential equation directly on the spectral-element mesh through the standard weak formulation. This avoids cumbersome projection operators between the spectral-element mesh and a regular Cartesian grid, or expensive explicit windowed convolution on the finite-element mesh, which is often used for applying smoothing operators. The associated linear system is solved efficiently through a parallel conjugate gradient algorithm, in which the matrix vector product is factorized and highly optimized with vectorized computation. Significant scaling behaviour is obtained when comparing this strategy with the explicit convolution method. The theoretical numerical complexity of this approach increases linearly with the coherent length, whereas a sublinear relationship is observed practically. Numerical illustrations are provided here for schematic examples, and for a more realistic elastic full waveform inversion gradient smoothing on the SEAM II benchmark model. These examples illustrate well the efficiency and flexibility of the approach proposed.
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Valentin, J., Capron, A., Jongmans, D., Baillet, L., Bottelin, P., Donze, F., et al. (2017). The dynamic response of prone-to-fall columns to ambient vibrations: comparison between measurements and numerical modelling. Geophysical Journal International, 208(2), 1058–1076.
Résumé: Seismic noise measurements (ambient vibrations) have been increasingly used in rock slope stability assessment for both investigation and monitoring purposes. Recent studies made on gravitational hazard revealed significant spectral amplification at given frequencies and polarization of the wave-field in the direction of maximum rock slope displacement. Different properties (resonance frequencies, polarization and spectral ratio amplitudes) can be derived from the spectral analysis of the seismic noise to characterize unstable rock masses. The objective here is to identify the dynamic parameters that could be used to gain information on prone-to-fall rock columns' geometry. To do so, the dynamic response of prone-to-fall columns to seismic noise has been studied on two different sites exhibiting cliff-like geometry. Dynamic parameters (main resonance frequency and spectral ratio amplitudes) that could characterize the column decoupling were extracted from seismic noise and their variations were studied taking into account the external environmental parameter fluctuations. Based on this analysis, a two-dimensional numerical model has been set up to assess the influence of the rear vertical fractures identified on both sites on the rock column motion response. Although a simple relation was found between spectral ratio amplitudes and the rock column slenderness, it turned out that the resonance frequency is more stable than the spectral ratio amplitudes to characterize this column decoupling, provided that the elastic properties of the column can be estimated. The study also revealed the effect of additional remote fractures on the dynamic parameters, which in turn could be used for detecting the presence of such discontinuities.
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Van Lichtervelde, M., Grand'Homme, A., de Saint-Blanquat, M., Olivier, P., Gerdes, A., Paquette, J. - L., et al. (2017). U-Pb geochronology on zircon and columbite-group minerals of the Cap de Creus pegmatites, NE Spain. Mineralogy And Petrology, 111(1), 1–21.
Résumé: The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group minerals (CGM), which are present in the different types of pegmatites from type I (K-feldspar pegmatites, least evolved) to type IV (albite pegmatites, most evolved) and therefore allow dating the different pegmatitic pulses. In a type III pegmatite where zircon and CGM are co-genetically associated in the same sample, both minerals were dated using zircon and tantalite reference materials, respectively, to avoid laser-induced matrix-dependent fractionation. In one sample, xenotime genetically associated with zircon was also dated. Two ages were obtained for type I and three ages for type III pegmatites. Three of these 5 ages range from 296.2 +/- 2.5 to 301.9 +/- 3.8 Ma and are allocated to the primary magmatic stage of crystallization and therefore to the emplacement event. Two younger ages (290.5 +/- 2.5 and 292.9 +/- 2.9 Ma) obtained on secondary zircon and xenotime, respectively, are interpreted as late post-solidus hydrothermal remobilization. There is no age difference between type I and type III pegmatites. The mean 299 Ma primary magmatic age allows the main late Carboniferous deformation event to be dated and is also synchronous with other peraluminous and calc-alkaline granites in the Pyrenees. However, the youngest ages around 292 Ma imply that tectonics was still active in Early Permian times in the Cap de Creus area.
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Veylon, G., Luu, L. - H., Merckle, S., Bard, P. - Y., Delvallee, A., Carvajal, C., et al. (2017). A simplified method for estimating Newmark displacements of mountain reservoirs. Soil Dynamics And Earthquake Engineering, 100, 518–528.
Résumé: In the present article we propose a new simplified method for assessing the seismic performance of large mountain reservoirs. The pseudo-empirical regression model is established on the basis of decoupled dynamic analyses performed on 7 accelerograms applied to 33 structural and geotechnical configurations. We study the influence of embankment geometries and mechanical properties on the prediction of earthquake-induced permanent displacements estimated by Newmark analyses. We also discuss the relevance of our model by carrying out comparisons with existing simplified models and with post-seismic field observations on earth dams. A regression analysis using parameters of interest provides a pseudo-empirical predictive equation to carry out rapid, preliminary assessments of the seismic performance of mountain reservoirs.
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Vidal, J., & Cebron, D. (2017). Inviscid instabilities in rotating ellipsoids on eccentric Kepler orbits. Journal Of Fluid Mechanics, 833, 469–511.
Résumé: We consider the hydrodynamic stability of homogeneous, incompressible and rotating ellipsoidal fluid masses. The latter are the simplest models of fluid celestial bodies with internal rotation and subjected to tidal forces. The classical problem is the stability of Roche-Riemann ellipsoids moving on circular Kepler orbits. However, previous stability studies have to be reassessed. Indeed, they only consider global perturbations of large wavelength or local perturbations of short wavelength. Moreover many planets and stars undergo orbital motions on eccentric Kepler orbits, implying time-dependent ellipsoidal semi-axes. This time dependence has never been taken into account in hydrodynamic stability studies. In this work we overcome these stringent assumptions. We extend the hydrodynamic stability analysis of rotating ellipsoids to the case of eccentric orbits. We have developed two open-source and versatile numerical codes to perform global and local inviscid stability analyses. They give sufficient conditions for instability. The global method, based on an exact and closed Galerkin basis, handles rigorously global ellipsoidal perturbations of unprecedented complexity. Tidally driven and libration-driven elliptical instabilities are first recovered and unified within a single framework. Then we show that new global fluid instabilities can be triggered in ellipsoids by tidal effects due to eccentric Kepler orbits. Their existence is confirmed by a local analysis and direct numerical simulations of the fully nonlinear and viscous problem. Thus a non-zero orbital eccentricity may have a strong destabilising effect in celestial fluid bodies, which may lead to space-filling turbulence in most of the parameters range.
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Vidal, O., Rostom, F., Francois, C., & Giraud, G. (2017). Global Trends in Metal Consumption and Supply: The Raw Material-Energy Nexus. Elements, 13(5), 319–324.
Résumé: The consumption of mineral resources and energy has increased exponentially over the last 100 years. Further growth is expected until at least the middle of the 21st century as the demand for minerals is stimulated by the industrialization of poor countries, increasing urbanization, penetration of rapidly evolving high technologies, and the transition to low-carbon energies. In order to meet this demand, more metals will have to be produced by 2050 than over the last 100 years, which raises questions about the sustainability and conditions of supply. The answers to these questions are not only a matter of available reserves. Major effort will be required to develop new approaches and dynamic models to address social, economic, environmental, geological, technological, legal and geopolitical impacts of the need for resources.
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Vignon, V., Mugnier, J. - L., Vassallo, R., Srivastava, P., Malik, M. A., Jayangondaperumal, R., et al. (2017). Sedimentation close to the active Medlicott Wadia Thrust (Western Himalaya): How to estimate climatic base level changes and tectonics. Geomorphology, 284, 175–190.
Résumé: The Medlicott-Wadia Thrust (MWT) is one of the major active out-of-sequence thrusts in the Himalaya. Studies on Quaternary terraces in its vicinity have been performed using sedimentological, geomorphic and geochrono-logical methods. We focus on the Riasi zone, south of the Pir Panjal range, in the Jammu and Kashmir region of India. The sedimentary units of Quaternary landforms have been mapped as a function of their location with respect to the thrust faults, their relative chronology, and their lithology. Three aggrading sedimentary units, five thin units above strath surfaces at the footwall of the fault system, and seven thin units above strath surfaces at its hangingwall are identified. The terraces have been dated by combining Optically Stimulated Luminescence (OSL) on fine-grained deposits and cosmogenic-nuclide dating (Be-10) on sandstone pebbles sampled along depth profiles throughout the alluvial units. Three major allostratigraphic units were defined with upper surface ages estimated at similar to 4, similar to 15, and 36 +/- 3 ka; the two older allostratigraphic units are encased terraces at the hangingwall but superposed sedimentary units at the footwall. They are related to phases of elevation of the river level (respectively 30 and 60 m) at similar to 36-38 and 14-15 ka and to a phase of extensive lateral incision before similar to 4 ka. These units present vertical offsets induced by the MWT of 50, 190, and 375 m, respectively. By taking the aggradation/incision rates at the footwall of the MWT into account, we found that the uplift of the hangingwall remains uniform since 361 a, with a value of similar to 10 mm/yr. Therefore, the aggradation/incision events observed in the Riasi area cannot be ascribed to variations in the tectonic rates and are most likely driven by climatic fluctuations. The high uplift rate is possibly local and related to the Chenab recess, which affects the Himalayan frontal structure. Our results indicate that the MWT is an active growth fault, and one of the main emergences of the active Indian/ Asian plate boundary in Western Himalaya. (C) 2016 Elsevier B.V. All rights reserved.
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Vogeli, N., Najman, Y., van der Beek, P., Huyghe, P., Wynn, P. M., Govin, G., et al. (2017). Lateral variations in vegetation in the Himalaya since the Miocene and implications for climate evolution. Earth And Planetary Science Letters, 471, 1–9.
Résumé: The Himalaya has a major influence on global and regional climate, in particular on the Asian monsoon system. The foreland basin of the Himalaya contains a record of tectonics and paleoclimate since the Miocene. Previous work on the evolution of vegetation and climate has focused on the central and western Himalaya, where a shift from C3 to C4 vegetation has been observed at similar to 7 Ma and linked to increased seasonality, but the climatic evolution of the eastern part of the orogen is less well understood. In order to track vegetation as a marker of monsoon intensity and seasonality, we analyzed delta C-13 and 8180 values of soil carbonate and associated delta C-13 values of bulk organic carbon from previously dated sedimentary sections exposing the syn-orogenic detrital Dharamsala and Siwalik Groups in the west, and, for the first time, the Siwalik Group in the east of the Himalayan foreland basin. Sedimentary records span from 20 to 1 Myr in the west (Joginder Nagar, Jawalamukhi, and Haripur Kolar sections) and from 13 to 1 Myr in the east (Kameng section), respectively. The presence of soil carbonate in the west and its absence in the east is a first indication of long-term lateral climatic variation, as soil carbonate requires seasonally arid conditions to develop. delta C-13 values in soil carbonate show a shift from around -10 parts per thousand to -2 parts per thousand at similar to 7 Ma in the west, which is confirmed by delta C-13 analyses on bulk organic carbon that show a shift from around -23 parts per thousand to -19 parts per thousand at the same time. Such a shift in isotopic values is likely to be associated with a change from C3 to C4 vegetation. In contrast, delta C-13 values of bulk organic carbon remain at 23 parts per thousand o in the east. Thus, our data show that the current east -west variation in climate was established at similar to 7 Ma. We propose that the regional change towards a more seasonal climate in the west is linked to a decrease of the influence of the Westerlies, delivering less winter precipitation to the western Himalaya, while the east remained annually humid due to its proximity to the monsoonal moisture source. (C) 2017 Elsevier B.V. All rights reserved.
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Vogeli, N., van der Beek, P., Huyghe, P., & Najman, Y. (2017). Weathering in the Himalaya, an East-West Comparison: Indications from Major Elements and Clay Mineralogy. Journal Of Geology, 125(5), 515–529.
Résumé: Studying past weathering regimes is important for a better understanding of the influence of climate on weathering, erosion, and runoff. The Himalayan foreland basin contains a record of tectonics and paleoclimate since Miocene times. Spanning the entire mountain range, the Mio-Pliocene detrital Siwalik Group allows studies to directly compare the western and eastern Himalaya within similar sedimentary settings. In this study, we use major elements and clay mineralogy to reconstruct the weathering regime along strike since Miocene times. We studied previously dated Dharamsala (pre-Siwalik) and Siwalik sections in the western (Joginder Nagar, Jawalamukhi, and Haripur Kolar) and eastern (Kameng) Himalaya in order to constrain variations in weathering regimes along strike. The compilation of the three sections in the west makes for one of the longest continuous sedimentary records in the Himalaya, spanning over 20 My. The K/Al ratio is used as a reliable weathering proxy and shows a trend toward more intense weathering over time in both the west and the east, but with sediments in the western Himalaya generally more weathered than those in the east, despite higher precipitation in the east. Clay minerals and major elements indicate similar lateral variations in weathering. More intense weathering in the west is linked to a more seasonal climate, permitting weathering of sediments during the dry season, whereas higher runoff in the east leads to more rapid erosion and sediment transport, inhibiting extensive weathering.
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Volkov, D., Voisin, C., & Ionescu, I. R. (2017). Determining Fault Geometries From Surface Displacements. Pure And Applied Geophysics, 174(4), 1659–1678.
Résumé: We introduce a new algorithm for determining the geometry of active parts of faults. This algorithm uses surface measurements of displacement fields and local modeling of the Earth's crust as a half-space elastic medium. The numerical method relies on iterations alternating non-linear steps for recovering the geometry and linear steps for reconstructing slip fields. Our algorithm greatly improves upon past attempts at reconstructing fault profiles. We argue that these past attempts suffered from either the restrictive assumption that the geometry of faults can be derived using only uniformly constant slips or that they relied on arbitrary assumptions on the statistics of the reconstruction error. We test this algorithm on the 2006 Guerrero, Mexico, slow slip event (SSE) and on the 2009 SSE for the same region. These events occurred on a relatively well-known subduction zone, whose geometry was derived from seismicity and gravimetric techniques, see Kostoglodov et al. (Geophys Res Lett 23(23): 3385-3388, 1996), Pardo and Suarez (J Geophys Res 100(B7): 357-373, 1995), Singh and Pardo (Geophys Res Lett 20(14): 1483-1486, 1993), so our results can be compared to known benchmarks. Our derived geometry is found to be consistent with these benchmarks regarding dip and strike angles and the positioning of the North American Trench. In addition, our derived slip distribution is also consistent with previous studies (all done with an assumed fixed geometry), see Larson et al. (Geophys Res Lett 34(13), 2007), Bekaert et al. (J Geophys Res: Solid Earth 120(2): 1357-1375, 2015), Radiguet et al. (Geophys J Int 184(2): 816-828, 2011, J Geophys Res 2012), Rivet et al. (Geophys Res Lett 38(8), 2011), Vergnolle et al. (J Geophys Res: Solid Earth 115(B8), 2010), Walpersdorf et al. Geophys Res Lett 38(15), 2011), to name a few. We believe that the new computational inverse method introduced in this paper holds great promise for applications to blind inversion cases, where both geometry and slip distribution are unknown.
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Volkov, D., Voisin, C., & Ionescu, I. R. (2017). Reconstruction of faults in elastic half space from surface measurements. Inverse Problems, 33(5).
Résumé: We study in this paper a half-space linear elasticity model for surface displacements caused by slip along underground faults. We prove uniqueness of the fault location and (piecewise-planar) geometry and of the slip field for a given surface displacement field. We then introduce a reconstruction algorithm for the realistic case where only a finite number of surface measurements are available. After showing how this algorithm performs on simulated data and assessing the effect of noise, we apply it to measured data. The data were recorded during slow slip events in Guerrero, Mexico. Since this is a well studied subduction zone, it is possible to compare our inferred fault geometry to other reconstructions (obtained using different techniques) found in the literature.
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Wang, C., Ma, B., Xu, S., Li, D., He, S., Zhao, Y., et al. (2017). Visible-light-driven overall water splitting with a largely-enhanced efficiency over a Cu2O@ZnCr-layered double hydroxide photocatalyst. Nano Energy, 32, 463–469.
Résumé: Overall water splitting through solar radiation is highly attractive for alternative energy utilization. Herein, we designed and fabricated a Cu2O@ZnCr-layered double hydroxide (LDH) core-shell photocatalyst to achieve a high-performance, visible-light overall water splitting. The Cu2O@ZnCr-LDH nanostructure exhibits a high activity (with H-2 and O-2 production rate of 0.90 and 0.44 μmol h(-1), respectively) under visible-light without any sacrificial agent and co-catalyst, which is among the highest level of reported photocatalysts under the same conditions. Both experimental and computational investigations demonstrate that the Cu2O@ZnCr-LDH heterostructure fully exploits the synergistic effect of Cu2O and ZnCr-LDH, in terms of band structure matching. Most significantly, the S2O3 2-group in the gallery of ZnCr-LDH acts as an effective mediator between these two individual components, which not only inhibits the photocorrosion of Cu2O but also accelerates the immigration of photo-induced electron-hole pairs. Therefore, this work provides a deep insight for the design and preparation of visible-light-responsive photocatalysts, which show promising applications in photochemical reactions and energy conversion.
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Wang, Q. - Y., Brenguier, F., Campillo, M., Lecointre, A., Takeda, T., & Aoki, Y. (2017). Seasonal Crustal Seismic Velocity Changes Throughout Japan. Journal Of Geophysical Research-Solid Earth, 122(10), 7987–8002.
Résumé: Noise-based crustal seismic velocity changes are known to be affected by environmental perturbations, such as rainfall, atmospheric pressure loading, and temperature changes. Similar to geodetic observations, these external perturbations can mask the effects of tectonic and volcanic processes. In this study, we benefit from the dense Hi-net short-period seismic network that covers the entire Japan to measure continuous changes in seismic velocities over a few years, using noise-based seismic monitoring. Some strong seasonal seismic velocity changes are observed in both southern Japan (Kyushu Island) and northern Japan (Hokkaido Island). Decreasing of seismic velocities in summer in southern Japan can be clearly explained by a model of increased crustal fluid pore pressure associated with high rainfall. In northern Japan, it is necessary to adopt a more complex model to explain the observed seismic velocity variations, which takes into account precipitation, snow depth, and sea level changes. Moreover, western and eastern Hokkaido Island show very different responses to these different external perturbations. The models developed are used to remove the seasonal components of the seismic velocity changes. The minimum remaining detectable seismic velocity change reduces to 10(-5), which allows detection of crustal responses to small earthquakes that are previously hidden in the strong seasonal perturbations.
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Wang, W., Godard, V., Liu-Zeng, J., Scherler, D., Xu, C., Zhang, J., et al. (2017). Perturbation of fluvial sediment fluxes following the 2008 Wenchuan earthquake. Earth Surface Processes And Landforms, 42(15), 2611–2622.
Résumé: Quantifying the removal of co-seismic landslide material after a large-magnitude earthquake is central to our understanding of geomorphic recovery from seismic events and the topographic evolution of tectonically active mountain ranges. In order to gain more insight into the fluvial erosion response to co-seismic landslides, we focus on the sediment fluxes of rivers flowing through the rupture zone of the 2008 M-w 7.9 Wenchuan earthquake in the Longmen Shan of the eastern Tibetan Plateau. Over the post-seismic period of 2008-2013, we annually collected river sediment samples (0.25-1mm) at 19 locations and measured the concentration of cosmogenic Be-10 in quartz. When compared with published pre-earthquake data, the Be-10 concentrations declined dramatically after the earthquake at all sampling sites, but with significant spatial differences in the amplitude of this decrease, and were starting to increase toward pre-earthquake level in several basins over the 5-year survey. Our analysis shows that the amplitude of Be-10 decrease is controlled by the amount of landslides directly connected to the river network. Calculations based on Be-10 mixing budgets indicate that the sediment flux of the 0.25-1mm size fraction increased up to sixfold following the Wenchuan earthquake. Our results also suggest that fluvial erosion became supply limited shortly after the earthquake, and predict that it could take a few years to several decades for fluvial sediment fluxes to go back to pre-earthquake characteristics, depending on catchment properties. We also estimate that it will take at least decades and possibly up to thousands of years to remove the co-seismic landslide materials from the catchments in the Longmen Shan. Copyright (c) 2017 John Wiley & Sons, Ltd.
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Wang, Y., Zhu, L., Shi, F., Schubnel, A., Hilairet, N., Yu, T., et al. (2017). A laboratory nanoseismological study on deep-focus earthquake micromechanics. Science Advances, 3(7).
Résumé: Global earthquake occurring rate displays an exponential decay down to similar to 300 km and then peaks around 550 to 600 km before terminating abruptly near 700 km. How fractures initiate, nucleate, and propagate at these depths remains one of the greatest puzzles in earth science, as increasing pressure inhibits fracture propagation. We report nanoseismological analysis on high-resolution acoustic emission (AE) records obtained during ruptures triggered by partial transformation from olivine to spinel in Mg2GeO4, an analog to the dominant mineral (Mg,Fe)(2)SiO4 olivine in the upper mantle, using state-of-the-art seismological techniques, in the laboratory. AEs' focal mechanisms, as well as their distribution in both space and time during deformation, are carefully analyzed. Microstructure analysis shows that AEs are produced by the dynamic propagation of shear bands consisting of nanograined spinel. These nanoshear bands have a near constant thickness (similar to 100 nm) but varying lengths and self-organize during deformation. This precursory seismic process leads to ultimate macroscopic failure of the samples. Several source parameters of AE events were extracted from the recorded waveforms, allowing close tracking of event initiation, clustering, and propagation throughout the deformation/transformation process. AEs follow the Gutenberg-Richter statistics with a well-defined b value of 1.5 over three orders of moment magnitudes, suggesting that laboratory failure processes are self-affine. The seismic relation between magnitude and rupture area correctly predicts AE magnitude at millimeter scales. A rupture propagation model based on strain localization theory is proposed. Future numerical analyses may help resolve scaling issues between laboratory AE events and deep-focus earthquakes.
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Webb, A. A. G., Guo, H., Clift, P. D., Husson, L., Mueller, T., Costantino, D., et al. (2017). The Himalaya in 3D: Slab dynamics controlled mountain building and monsoon intensification. Lithosphere, 9(4), 637–651.
Résumé: Tectonic models for the Oligocene-Miocene development of the Himalaya mountain range are largely focused on crustal-scale processes, and developed along orogen-perpendicular cross sections. Such models assume uniformity along the length of the Himalaya, but significant along-strike tectonic variations occur, highlighting a need for three-dimensional evolutionary models of Himalayan orogenesis. Here we show a strong temporal correlation of southward motion of the Indian slab relative to the overriding Himalayan orogen, lateral migration of slab detachment, and subsequent dynamic rebound with major changes in Himalayan metamorphism, deformation, and exhumation. Slab detachment was also coeval with South Asian monsoon intensification, which leads us to hypothesize their genetic link. We further propose that anchoring of the Indian continental subducted lithosphere from 30 to 25 Ma steepened the dip of the Himalayan sole thrust, resulting in crustal shortening deep within the Himalayan orogenic wedge. During the subsequent similar to 13 m.y., slab detachment propagated inward from both Himalayan syntaxes. Resultant dynamic rebound terminated deep crustal shortening and caused a rapid rise of the mountain range. The increased orography intensified the South Asian monsoon. Decreased compressive forces in response to slab detachment may explain an observed similar to 25% decrease in the India-Eurasia convergence rate. The asymmetric curvature of the arc, i.e., broadly open, but tighter to the east, suggests faster slab detachment migration from the west than from the east. Published Lu-Hf garnet dates for eclogite facies metamorphism in the east-central Himalaya as old as ca. 38-34 Ma may offer a test that the new model fails, because the model predicts that such metamorphism would be restricted to middle Miocene time. Alternatively, these dates may provide a case study to test suspicions that Lu-Hf garnet dates can exceed actual ages.
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Weide, D. M., Fritz, S. C., Hastorf, C. A., Bruno, M. C., Baker, P. A., Guedron, S., et al. (2017). A similar to 6000 yr diatom record of mid- to late Holocene fluctuations in the level of Lago Winaymarca, Lake Titicaca (Peru/Bolivia). Quaternary Research, 88(2), 179–192.
Résumé: A multidecadal-scale lake-level reconstruction for Lago Winaymarca, the southern basin of Lake Titicaca, has been generated from diatom species abundance data. These data suggest that similar to 6500 cal yr BP Lago Winaymarca was dry, as indicated by a sediment unconformity. At similar to 4400 cal yr BP, the basin began to fill, as indicated by the dominance of shallow epiphytic species. It remained somewhat saline with extensive wetlands and abundant aquatic plants until similar to 3800 cal yr BP, when epiphytic species were replaced by planktic saline-indifferent species, suggesting a saline shallow lake. Winaymarca remained a relatively shallow lake that fluctuated on a multidecadal scale until similar to 1250 cal yr BP, when freshwater planktic species increased, suggesting a rise in lake level with a concomitant decrease in salinity. The lake became gradually fresher, dominated by deep, freshwater species from similar to 850 cal yr BP. By similar to 80 cal yr BP, saline-tolerant species were rare, and the lake was dominated by freshwater planktic diatoms, resembling the fresh and deep lake of today. These results reveal a more dynamic and chronologically specific record of lake-level fluctuations and associated ecological conditions that provide important new data for paleoclimatologists and archaeologists, to better understand human-environmental dynamics during the mid- to late Holocene.
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Weiss, J. (2017). Exploring the “solid turbulence” of sea ice dynamics down to unprecedented small scales. Journal Of Geophysical Research-Oceans, 122(8), 6071–6075.
Résumé: Sea ice decline is an essential player, as well as an emblematic signature, of global warming. Besides sea surface temperature rising, sea ice drift, and deformation play a major role on the observed negative mass balance, thus calling for a deeper understanding of sea ice mechanics. Over the last decades, drifters and satellite data allowed a detailed characterization of sea ice kinematics, however limited by relatively coarse space (approximate to 10 km) and time (similar to day) resolutions. A new work allows bridging the gap between these large scales and fundamental ice physics and mechanics.
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Weiss, J., & Dansereau, V. (2017). Linking scales in sea ice mechanics. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 375(2086).
Résumé: Mechanics plays a key role in the evolution of the sea ice cover through its control on drift, on momentum and thermal energy exchanges between the polar oceans and the atmosphere along cracks and faults, and on ice thickness distribution through opening and ridging processes. At the local scale, a significant variability of the mechanical strength is associated with the microstructural heterogeneity of saline ice, however characterized by a small correlation length, below the ice thickness scale. Conversely, the sea ice mechanical fields (velocity, strain and stress) are characterized by long-ranged (more than 1000 km) and long-lasting (approx. few months) correlations. The associated space and time scaling laws are the signature of the brittle character of sea ice mechanics, with deformation resulting from a multi-scale accumulation of episodic fracturing and faulting events. To translate the short-range-correlated disorder on strength into long-range-correlated mechanical fields, several key ingredients are identified: long-ranged elastic interactions, slow driving conditions, a slow viscous-like relaxation of elastic stresses and a restoring/healing mechanism. These ingredients constrained the development of a new continuum mechanics modelling framework for the sea ice cover, called Maxwell-elasto-brittle. Idealized simulations without advection demonstrate that this rheological framework reproduces the main characteristics of sea ice mechanics, including anisotropy, spatial localization and intermittency, as well as the associated scaling laws. This article is part of the themed issue 'Microdynamics of ice'.
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Wellington, P., Brossier, R., Hamitou, O., Phuong-Thu Trinh, & Virieux, J. (2017). Efficient anisotropic dip filtering via inverse correlation functions. Geophysics, 82(4), A31–A35.
Résumé: We have developed a computational framework that allows an efficient, spatially variant correlation filter for anisotropic dip filtering. The approach is based on the Laplace correlation function, for which there exists analytical expressions for the correlation kernel and its inverse kernel in the 1D case. An extension to higher dimensions by adding orthogonal 1D inverse functions provides a linear equation whose solution is identical to applying a Bessel filter. We have found that a good approximation of the Laplace filter function is obtained by applying a cascade of Bessel filters. We implement such an inverse operator on regular grids with a finite-difference stencil, giving a sparse matrix for the linear equation, which can be solved efficiently through a conjugate-gradient algorithm. Computing such a correlation operation by solving the linear system involving the inverse operator is significantly faster than applying the correlation function via convolution or windowed convolution: Solving the linear system is as fast as applying often-used tensorized 1D convolutions.
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Williams, E. G., Tippmann, J. D., Rakotonarivo, S. T., Waters, Z. J., Roux, P., & Kuperman, W. A. (2017). Experimental estimation of in vacuo structural admittance using random sources in a non-anechoic room. Journal Of The Acoustical Society Of America, 142(1), 103–109.
Résumé: Identification of unexploded ordinance buried in the sediment in the littoral waters throughout the world is a problem of great concern. When illuminated by low-frequency sonar some of these targets exhibit an elastic response that can be used to identify them. This elastic behavior is embodied and identified by a quantity called the in vacuo structural admittance matrix Y-s, a relationship between the sonar-induced forces and resulting vibration on its surface. When it is known it can be combined with surface impedances to predict the three-dimensional bistatic scattering in any fluid-like media and for any burial state (depth and orientation). At the heart of this is the measurement of Ys and it is demonstrated in this paper that this can be accomplished by studying the target in a simple (acoustically unaltered) in-air laboratory environment. The target chosen in this study is a thick spherical shell that was illuminated by a nearly spatially isotropic array of remote loudspeakers. Ys is constructed from ensemble averages of the cross-correlations of eight collocated accelerometers and microphones placed on the surface of the object. The structural admittance determined from the data showed excellent agreement with theory.
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Woodruff, W. F., Lewan, M. D., Revil, A., & Torres-Verdin, C. (2017). Complex electrical conductivity changes associated with hydrous pyrolysis maturation of the Woodford Shale. Geophysics, 82(2), D85–D106.
Résumé: Hydrous closed-system pyrolysis experiments were performed on five pairs of chert cubes from the Woodford Shale aliquots under uniaxial confinement at various prescribed thermal maturities. These thermal maturities represent each of the phases of organic-matter (OM) catagenesis under hydrous conditions: immature kerogen at low thermal stress (125 degrees C for 72 h), low and peak bitumen generation with increasing thermal stress (300 degrees C and 330 degrees C for 72 h), cracking of bitumen to oil and gas at higher thermal stresses (330 degrees C and 360 degrees C for 72 h), and cracking of some oil at the highest experimental conditions (400 degrees C for 72 h). We measured the spectra of the complex electrical conductivity tensor (in the frequency range 10 mHz to 45 kHz) of these 10 aliquots to capture the effects of thermal maturation by hydrous pyrolysis. Results indicate that surface conduction of polar-rich bitumens has a significant effect on their complex electrical conductivity. The OM of a source rock is considered a negligible cause of cation-exchange capacity (CEC), whose parameters influence surface and quadrature conductivity components of the complex electrical conductivity tensor. Part of this CEC was reactivated during the hydrous closed-system pyrolysis experiments. The conspicuous absence of a decrease in electrical conductivity with bitumen and oil generation in the chert cubes recovered from the hydrous-pyrolysis experiments does not agree with the observed increases of well-log resistivity in the natural maturation of some source rocks. Contraction of OM at the contacts with mineral grains is considered a partial cause of this discrepancy, which occurs during the cooling of the experiments to room temperature when no mechanical compaction is applied. Mineral-grain supported rocks such as the chert we studied appear to be especially prone to such a phenomenon.
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Wright, S., Su, S., Scolan, H., Young, R. M. B., & Read, P. L. (2017). Regimes of Axisymmetric Flow and Scaling Laws in a Rotating Annulus with Local Convective Forcing. Fluids, 2(3).
Résumé: We present a numerical study of axisymmetric flow in a rotating annulus in which local thermal forcing, via a heated annular ring on the outside of the base and a cooled circular disk in the centre of the top surface, drives convection. This new configuration is a variant of the classical thermally-driven annulus, where uniform heating and cooling are applied through the outer and inner sidewalls respectively. The annulus provides an analogue to a planetary circulation and the new configuration, with its more relaxed vertical thermal boundary conditions, is expected to better emulate vigorous convection in the tropics and polar regions as well as baroclinic instability in the mid-latitude baroclinic zone. Using the Met Office/Oxford Rotating Annulus Laboratory (MORALS) code, we have investigated a series of equilibrated, two dimensional axisymmetric flows across a large region of parameter space. These are characterized in terms of their velocity and temperature fields. When rotation is applied several distinct flow regimes may be identified for different rotation rates and strengths of differential heating. These regimes are defined as a function of the ratio of the horizontal Ekman layer thickness to the non-rotating thermal boundary layer thickness and are found to be similar to those identified in previous annulus experiments. Convection without rotation is also considered and the scaling of the heat transport with Rayleigh number is calculated. This is then compared with existing work on the classical annulus as well as horizontal and Rayleigh-Benard convection. As with previous studies on both rotating and non-rotating convection the system's behaviour is found to be aspect ratio dependent. This dependence is seen in the scaling of the non-rotating Nusselt number and in transitions between regimes in the rotating case although further investigation is required to fully explain these observations.
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Wu, Y., Karimi, K., Maloney, C. E., & Teitel, S. (2017). Anomalous stress fluctuations in athermal two-dimensional amorphous solids. Physical Review E, 96(3).
Résumé: We numerically study the local stress distribution within athermal, isotropically stressed, mechanically stable, packings of bidisperse frictionless disks above the jamming transition in two dimensions. Considering the Fourier transform of the local stress, we find evidence for algebraically increasing fluctuations in both isotropic and anisotropic components of the stress tensor at small wave numbers, contrary to recent theoretical predictions. Such increasing fluctuations imply a lack of self-averaging of the stress on large length scales. The crossover to these increasing fluctuations defines a length scale l(0), however, it appears that l(0) does not vary much with packing fraction phi, nor does l(0) seem to be diverging as phi approaches the jamming phi(J). We also find similar large length scale fluctuations of stress in the inherent states of a quenched Lennard-Jones liquid, leading us to speculate that such fluctuations may be a general property of amorphous solids in two dimensions.
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Yamazaki, T., Kimura, Y., Vekilov, P. G., Furukawa, E., Shirai, M., Matsumoto, H., et al. (2017). Two types of amorphous protein particles facilitate crystal nucleation. Proceedings Of The National Academy Of Sciences Of The United States Of America, 114(9), 2154–2159.
Résumé: Nucleation, the primary step in crystallization, dictates the number of crystals, the distribution of their sizes, the polymorph selection, and other crucial properties of the crystal population. We used timeresolved liquid-cell transmission electron microscopy (TEM) to perform an in situ examination of the nucleation of lysozyme crystals. Our TEM images revealed that mesoscopic clusters, which are similar to those previously assumed to consist of a dense liquid and serve as nucleation precursors, are actually amorphous solid particles (ASPs) and act only as heterogeneous nucleation sites. Crystalline phases never form inside them. We demonstrate that a crystal appears within a noncrystalline particle assembling lysozyme on an ASP or a container wall, highlighting the role of heterogeneous nucleation. These findings represent a significant departure from the existing formulation of the two-step nucleation mechanism while reaffirming the role of noncrystalline particles. The insights gained may have significant implications in areas that rely on the production of protein crystals, such as structural biology, pharmacy, and biophysics, and for the fundamental understanding of crystallization mechanisms.
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Yu, C. Q., Day, E. A., de Hoop, M. V., Campillo, M., & van der Hilst, R. D. (2017). Mapping Mantle Transition Zone Discontinuities Beneath the Central Pacific With Array Processing of SS Precursors. Journal Of Geophysical Research-Solid Earth, 122(12), 10364–10378.
Résumé: We image mantle transition zone (MTZ) discontinuities beneath the Central Pacific using similar to 120,000 broadband SS waveforms. With a wave packet-based array processing technique (curvelet transform), we improve the signal-to-noise ratio of SS precursors and remove interfering phases, so that precursors can be identified and measured over a larger distance range. Removal of interfering phases reveals possible phase shifts in the underside reflection at the 660, that is, (SS)-S-660, which if ignored could lead to biased discontinuity depth estimates. The combination of data quantity and improved quality allows improved imaging and uncertainty estimation. Time to depth conversions after corrections for bathymetry, crustal thickness, and tomographically inferred mantle heterogeneity show that the mean depths of 410 and 660 beneath the Central Pacific are 420 +/- 3 km and 659 +/- 4 km, respectively. The mean MTZ thickness (239 +/- 2 km) is close to global estimates and suggests an adiabatic mantle temperature of similar to 1,400 degrees C for the Central Pacific. Depth variations of the 410 and 660 appear to be relatively small, with peak-to-peak amplitudes of the order of 10-15 km. The 410 and 660 are weakly anticorrelated, and MTZ is thinner beneath Hawaii and to the north and east of the hotspot and thicker southwest of it. The relatively small discontinuity topography argues against the presence of large-scale (more than 5 degrees wide) thermal anomalies with excess temperatures over 200 K across the transition zone. The data used cannot exclude stronger thermal anomalies that are of more limited lateral extent or that are not continuous across the MTZ.
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Zamboni, D., Trela, J., Gazel, E., Sobolev, A. V., Cannatelli, C., Lucchi, F., et al. (2017). New insights into the Aeolian Islands and other arc source compositions from high-precision olivine chemistry. Lithos, 272, 185–191.
Résumé: The Aeolian arc (Italy) is characterized by some of the strongest along-the-arc geochemical variations in the planet, making it an ideal location to study the effect of subducting components in modifying the mantle source of island arc melts. Here, we use high-precision element concentrations in primitive phenocrystic olivine from basalts along the arc to elucidate the effects of mantle source modification by the.subduction process. Olivines from this arc have Ni concentrations and Fe/Mn ratios that show similarity to peridotite sources that melted to produce mid-ocean ridge basalts. Nevertheless, they also have systematically lower Ca concentrations and Fe/Mn ratios that broadly overlap with olivines from the available global arc array. These phenocrysts also do not show significant variations in Ca as a function of olivine forsterite content. The global data suggest that all olivines crystallizing from island-arc melts have suppressed Ca concentrations and Fe/Mn ratios, relative to olivines derived from melts at intraplate and mid-ocean ridge settings suggesting elevated H2O concentrations and higher oxidation state of the equilibrium melts. Based on olivine chemistry, we interpret a predominantly peridotite source (fluxed by subduction fluids) beneath the Aeolian Arc and also for other examples of arc-related lavas. (C) 2016 Elsevier B.V. All rights reserved.
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Zanda, B., & Lewin, E. (2017). The Chondritic Assemblage. Meteoritics & Planetary Science, 52, A402.
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Zanetta, P. - M., Leroux, H., Le Guillou, C., Zanda, B., Hewins, R. H., Lewin, E., et al. (2017). A New Method For Modal Abundance, Chemistry And Density Determination Of Fine Grained Matrices Of Primitive Chondrites. Meteoritics & Planetary Science, 52, A403.
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Zerathe, S., Blard, P. - H., Braucher, R., Bourles, D., Audin, L., Carcaillet, J., et al. (2017). Toward the feldspar alternative for cosmogenic Be-10 applications. Quaternary Geochronology, 41, 83–96.
Résumé: The possibility of quantifying surface processes in mafic or volcanic environment using the potentialities offered by the in situ-produced cosmogenic nuclides, and more specifically by the in situ-produced Be-10, is often hampered by the rarity of quartz minerals in the available lithologies. As an alternative to overcome this difficulty, we explore in this work the possibility of relying on feldspar minerals rather that on quartz to perform in situ-produced Be-10 measurements in such environments. Our strategy was to cross-calibrate the total production rate of Be-10 in feldspar (P-10fsp) against the total production rate of He-3 in pyroxene (P-3px) by measuring He-3 and Be-10 in cogenetic pyroxene (He-3(px)) and feldspar (Be-10(fsp)). The samples were collected from eight ignimbritic boulders, exposed from ca 120 to 600 ka at elevations ranging from 800 to 2500 m, along the preserved rock-avalanche deposits of the giant Caquilluco landslide (18 degrees S, 70 degrees W), Southern Peru. Along with data recently published by Blard et al. (2013a) at a close latitude (22 degrees S) but higher elevation (ca. 4000 m), the samples yield a remarkably tight cluster of He-3(px) – Be-10(fsp) total production ratios whose weighted-mean is 35.6 +/- 0.5 (1 sigma). The obtained weighted mean He-3(px) – Be-10(fsp) total production ratio combined with the local He-3(py) total production rate in the high tropical Andes published by Martin et al. (2017) allows to establish a total SLHL Be-10 in situ-production rate in feldspar mineral (P-10fsp) of 3.57 +/- 0.21 at.g(-1).yr(-1) (scaled for the LSD scaling scheme, the ERA40 atm model and the VDM of Lifton, 2016). Despite the large elevation range covered by the whole dataset (800-4300 m), no significant variation of the He-3(px) – Be-10(fsp) total production ratios in pyroxene and feldspar was evidenced. As an attempt to investigate the effect of the chemical composition of feldspar on the total Be-10 production rate, major and trace element concentrations of the studied feldspar samples were analyzed. Unfortunately, giving the low compositional variability of our dataset, this issue is still pending. (C) 2017 Elsevier B.V. All rights reserved.
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Zhang, P., Salman, O. U., Zhang, J. - Y., Liu, G., Weiss, J., Truskinovsky, L., et al. (2017). Taming intermittent plasticity at small scales. Acta Materialia, 128, 351–364.
Résumé: The extreme miniaturization in modern technology calls for deeper insights into the non-conventional, fluctuation dominated mechanics of materials operating at microscale. For instance, both experiments and simulations show that sub-micron face-centered-cubic (FCC) crystals exhibit high yield strength accompanied by intermittent, power law distributed strain fluctuations. At macro-scales, the same bulk materials show bounded, uncorrelated fluctuations. Both anomalous strength and intermittency appear therefore as size effects: while the former is highly desirable, the latter is detrimental because stochastic dislocation avalanches interfere with forming processes and endanger structural stability. In this paper we quantify the coexistence of correlated and uncorrelated fluctuations in compressed Al alloys micro pillars, demonstrate that the partition between the two is determined by sample size, and propose quantitative strategies allowing one to temper plastic intermittency by artificially tailored disorder. Our experimental results are rationalized using a theoretical framework that quantifies the competition between external (size related) and internal (disorder related) length scales. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Zhang, Y. - Z., Replumaz, A., Leloup, P. H., Wang, G. - C., Bernet, M., van der Beek, P., et al. (2017). Cooling history of the Gongga batholith: Implications for the Xianshuihe Fault and Miocene kinematics of SE Tibet. Earth And Planetary Science Letters, 465, 1–15.
Résumé: Using thermochronological data and thermokinematic modeling, we constrain the timing of late Miocene exhumation of the northern portion of the Gongga batholith, located in Southeast Tibet along the Xianshuihe Fault (XF). We show that rapid exhumation started in the north of the Gongga batholith at similar to 9 Ma at a rate of similar to 1.85 km/Myr and slowed down since similar to 4 Ma. A magmatic pulse occurring during the early Pliocene (similar to 4 Ma) has overprinted the rapid Miocene exhumation phase in some parts of the batholith, which record mainly early Pliocene post-magmatic cooling. Slow exhumation since similar to 4 Ma is consistent with the present-day lower relief observed in the centre of the batholith, which contrasts with the rugged high peaks located to the south. We propose that the northern segment of the XF, the Yalahe fault, which is not active at present, was active between 9 and 4 Ma, forming a restraining bend that focused exhumation south of it. Since similar to 4 Ma, the Selaha and the Zheduotang faults form the present-day restraining bend south of which the highest part of the massif is located, including the Gongga Shan that rises more than 3000 m above the mean elevation of the plateau. In the north of the batholith, similar peaks have been removed since the Miocene by local relief reduction at high elevations. Considering that the onset of motion along the XF is contemporaneous with the onset of rapid exhumation recorded along the Kangding transect at similar to 9 Ma and a total offset of similar to 62 km documented for the XF, the average slip rate of the XF is similar to 7 mm/yr since 9 Ma. (C) 2017 Elsevier B.V. All rights reserved.
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Zuluaga, C. A., Amaya, S., Uruena, C., & Bernet, M. (2017). Migmatization and low-pressure overprinting metamorphism as record of two pre-Cretaceous tectonic episodes in the Santander Massif of the Andean basement in northern Colombia (NW South America). Lithos, 274, 123–146.
Résumé: The core of the Santander Massif in the northern Andes of Colombia is dominated by migmatitic gneisses with a <1.71 Ga protolith and was affected by continuous interactions of oceanic plates to the west and the northwestern corner of the South American continental plate. The exposed metamorphic core of the massif offers a unique opportunity to understand the tectonic evolution of northwestern South America. We present new metamorphic petrology and geochemistry data from the Bucaramanga Gneiss in the Santander Massif to document part of this tectonic evolution from late Proterozoic to Jurassic times. Metapelitic migmatite gneiss, quartz-feldspathic gneiss, and amphibolite from the Bucaramanga Gneiss recorded metamorphic peak conditions in the range of 660-850 C-circle at pressures of> 7.5 kbar. Lithologies are overprinted by low-pressure metamorphism, related to extensive Jurassic intrusions and linked with growth of cordierite and equilibration of low-pressure mineral assemblages, recorded metamorphic conditions are <750 C-circle and <6.5 kbar. Observed leucosomes display significant compositional variations and can be grouped in three groups: i) Group One leucosomes with high total REE content, high LREE/HREE, and negative Eu anomaly, ii) Group Two leucosomes with low total REE, low LREE/HREE, and positive Eu anomalies, and iii) Group Three leucosomes with relatively low LREE/HREE and strong positive Eu anomaly. Geochemical data support the interpretation that Group Two leucosomes crystallized from melts originated in a partial melting event affecting mostly pelitic and quartz-feldspathic lithologies with fluid-present melting reactions. The evaluation of mesosomes (amphibolite, pelitic and quartz-feldspathic rocks) as potential protoliths or restites indicates that at least two pelitic samples of the analyzed lithologies have characteristics consistent with the occurrence of fluid-present melting reactions involving quartz and feldspar. The leucosomes produced by crystallization of modified partial melts contrast with several other leucosomes that were injected; however, in some cases the melts crystallized as injected leucosomes show consistent geochemistry with partial melting of lithologies geochemically similar to the ones observed in the unit. The migmatization and the low pressure metamorphic overprint are related here to two main tectonic events: an early Paleozoic tectonic pulse produced by subduction of the oceanic crust of the Iapetus Ocean beneath northwestern Gondwana, and an Upper Triassic to Lower Jurassic tectonic pulse produced by subduction of oceanic crust of the proto-Pacific ocean beneath western Pangaea. (C) 2017 Elsevier B.V. All rights reserved.
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