Articles présents dans Web of Knowledge

Résumé: During an induced polarization survey, both electrical conductivity and chargeability can be imaged. Recent petrophysical models have been developed to provide a consistent picture of these two parameters in terms of water and clay contents of soils. We test the ability of this method at a test site in which a controlled artificial leakage can be generated in an embankment surrounding an experimental basin. 3D tomography of the conductivity and normalized chargeability are performed during such a controlled leakage. Conductivity and induced polarization measurements were also performed on a core sample from the site. The sample was also characterized in terms of porosity and cation exchange capacity. Combining the 3D survey and these laboratory measurements, a 3D tomogram of the relative variation in water content (before leakage and during leakage) was estimated. It clearly exhibits the ground water flow path through the embankment from the outlet of the tube used to generate the leak to the bottom of the embankment. In addition, a self-potential survey was performed over the zone of leakage. This survey evidences also the projection of the ground water flow path over the ground surface. Both methods are found to provide a consistent picture. A 2.5D time lapse tomography of the electrical conductivity and normalized chargeability was also performed and evidences the position of the preferential flow paths below the profile. These results confirm the ability and efficiency of induced polarization to provide reliable information pertaining to the detection of leakages in dams and embankments.

Résumé: The self-potential method can be used to detect and monitor anomalous seepages in dams and embankments. In such a case, an electrical field of electrokinetic nature (i.e., associated with pore water flow) can be measured using a set of non-polarizable electrodes typically located at the ground surface or in some wells. This field can be in turn related to the pattern of groundwater flow. We built an experimental dam to investigate to which extent the self-potential method can help characterizing seepages in dams. We first use the finite element method to simulate the ground water flow in a heterogeneous porous and permeable material by solving the groundwater flow equation. The resulting groundwater flow solution is then used to compute the electrical potential distribution by solving the corresponding elliptic partial differential equation. In a preliminary experiment, we could not measure any self-potential anomaly associated with the infiltration of water in the dam. Our numerical simulations showed that the magnitudes of the self-potential anomalies were controlled by (1) the nature of the flow regime (viscous laminar versus inertial laminar flow regimes) and (2) the presence of insulating Polyvinyl Chloride (PVC) tubes located at the end of the preferential flow channels in the structure of the dam. Thanks to these numerical simulations, we added sand at the entrance of the infiltration area in order to reduce the effects of the PVC tubes and to restrain the flow regime to the viscous laminar flow regime. New experiments allowed for detecting a self-potential anomaly with an amplitude of around -9 mV consistent with that obtained through numerical modelling with a finite element simulator. This comparison was used to test the accuracy of the modelling approach and define the strengths and weaknesses of the self-potential method to determine preferential seepages in earth dam structures.

Résumé: The analysis of surface wave dispersion curves (DCs) is widely used for near-surface S-wave velocity (VS) reconstruction. However, a comprehensive characterization of the near-surface requires also the estimation of P-wave velocity (VP). We focus on the estimation of both VS and VP models from surface waves using a direct data transform approach. We estimate a relationship between the wavelength of the fundamental mode of surface waves and the investigation depth and we use it to directly transform the DCs into VS and VP models in laterally varying sites. We apply the workflow to a real data set acquired on a known test site. The accuracy of such reconstruction is validated by a waveform comparison between field data and synthetic data obtained by performing elastic numerical simulations on the estimated VP and VS models. The uncertainties on the estimated velocity models are also computed.

Résumé: Geophysical exploration in unconventional geothermal reservoir is challenging because of the lack of structures with specific geophysical signature such as a clay cap above volcanic geothermal reservoirs. The combination of several geophysical methods such as magnetotelluric (MT), gravity and seismic methods provides complementary insight into the geothermal reservoir. We present a joint inversion approach of ambient noise surface wave and gravity constrained by the 3D distribution of electrical resistivity. The method is applied to analyze the potential of unconventional deep geothermal resources in the French Massif Central (FMC). We coupled the resistivity, density and shear wave velocity with a linear correlation. We characterized the common properties in relation to the geological domains down to about 10-15 km. We validated the proposed approach on a synthetic model derived from models obtained from each independent geophysical method. The joint inversion limited the non-uniqueness of the gravity and the ambient noise tomography inversion and allow to recover the features of the synthetic models. We applied the method to real field data acquired in the Sioule Valley, Massif Central, France. The joint features observed in the geophysical models suggest a deep heat source associated with a possible shallow (similar to 6-8 km) brittle ductile transition. A large fault zone, the Pongibaud Fault zone, seems to become listric and connect the surface to this transition zone to possibly constitute a permeable path for water circulation.

Résumé: Iron Oxide Nanoparticles (IONPs) present unique properties making them one of the most used NPs in the biomedical field. Nevertheless, for many years, growing production and use of IONPs are associated with risks that can affect human and the environment. Thus, it is essential to study the effects of these nanoparticles to better understand their mechanism of action and the molecular perturbations induced in the organism. In the present study, we investigated the toxicological effects of IONPs (gamma-Fe2O3) on liver, lung and brain proteomes in Wistar rats. Exposed rats received IONP solution during 7 consecutive days by intranasal instillation at a dose of 10 mg/kg body weight. An iTRAQ-based quantitative proteomics was used to study proteomic variations at the level of the three organs. Using this proteomic approach, we identified 1565; 1135 and 1161 proteins respectively in the brain, liver and lung. Amon them, we quantified 1541; 1125 and 1128 proteins respectively in the brain, liver and lung. Several proteins were dysregulated comparing treated samples to controls, particularly, proteins involved in cytoskeleton remodeling, cellular metabolism, immune system stimulation, inflammation process, response to oxidative stress, angiogenesis, and neurodegenerative diseases.

Résumé: We characterize and monitor subsidence of the Bursa Plain (southern Marmara region of Turkey), which has been interpreted as resulting from tectonic motions in the region. We quantify the subsidence using Interferometric Synthetic Aperture Radar (InSAR) time-series analysis. The Stanford Method for Persistent Scatterers InSAR package (StaMPS) is employed to process series of Sentinel 1 A-B radar images acquired between 2014 and 2017 along both ascending and descending orbits. The vertical velocity field obtained after decomposition of line-of-sight velocity fields on the two tracks reveals that the Bursa plain is subsiding at rates up to 25 mm/yr. The most prominent subsidence signal in the basin forms an east-west elongated ellipse of deformation in the east, and is bounded by a Quaternary alluvial plain undergoing average vertical subsidence at similar to similar to 10 mm/yr. Another localized subsidence signal is located 5 km north of the city, following the Bursa alluvial fan, and is subsiding at velocities up to 25 mm/yr. The comparison between temporal variations of the subsiding surface displacements and variations of the water pressure head in the aquifer allows estimation of the compressibility of the aquifer, It falls in the range of0.tic5x10-6-2x10-6 Pa-1, which corresponds to typical values for clay and sand sediments. We find a clear correlation between subsidence patterns and the lithology, suggesting a strong lithological control over subsidence. In addition, the maximum rate of ground subsidence occurs where agricultural activity relies on groundwater exploitation. The InSAR time series within the observation period is well correlated with changes in the depth of the ground water. These observations indicate that the recent acceleration of subsidence is mainly due to anthropogenic activities rather than tectonic motion.

Résumé: Peat layers within alluvial sediments are considered effective arsenic (As) sinks under reducing conditions due to the binding of As(III) to thiol groups in natural organic matter (NOM) and the formation of As-bearing sulfide phases. However, their possible role as sources of As for anoxic groundwaters remains unexplored. Here, we perform laboratory experiments to provide evidence for the role of a sediment peat layer in releasing As. Our results show that the peat layer, deposited about 8,000 years ago in a paleomangrove environment in the nascent Mekong Delta, could be a source of As to porewater under reducing conditions. X-ray absorption spectroscopy (XAS) analysis of the peat confirmed that As was bound to NOM thiol groups and incorporated into pyrite. Nitrate was detected in peat layer porewater, and flow-through and batch experiments evidenced the release of As from NOM and pyrite in the presence of nitrate. Based on poisoning experiments, we propose that the microbially mediated oxidation of arsenic-rich pyrite and organic matter coupled to nitrate reduction releases arsenic from this peat. Although peat layers have been proposed as As sinks in earlier studies, we show here their potential to release depositional- and/or diagenetically-accumulated As.

Résumé: In this Letter, we report on the effects of a vorticity filament on the coherent backscattering cone. Using ultrasonic waves in a strongly reverberating cavity, we experimentally show that the discrete number of loops of acoustic paths around a pointlike vortex located at the center of the cavity drives the cancellation and the potential rebirth of the coherent backscattering enhancement. The vorticity filament behaves, then, as a topological anomaly for wave propagation that provides some new insight between reciprocity and weak localization.

Résumé: Potassium (K) is an essential plant nutrient mainly present in the crystal structure of K-bearing soil minerals (K-feldspars, micas). To assess the evolution of (clay) mineralogy due to K+ release from these minerals in continuously cultivated soils, samples were collected from long-term (1904-2014) field experiments submitted to contrasting crop rotations and amendments, with and without fertilisation. Soil samples were size-fractionated and mineralogy of the silt fraction and of clay subfractions was determined quantitatively by modelling X-ray diffraction (XRD) patterns. Clay subfractions were also analysed for their cation exchange capacity (CEC). Mineralogical data indicate the stability of clay mineralogy and the increased abundance of the finest clay subfraction at the expense of coarser ones, regardless of agronomic practices or amount of K removed by plants. This increase is accompanied by an increase in the bulk clay CEC owing to the major contribution of the finest clay subfraction to this parameter. Mineral dissolution, rather than alteration of mineral phases from coarse clay subfractions, most likely supplements K for plant nutrition in this soil. Dissolution is favoured over cation exchange owing to the dioctahedral character of micas and to their fine-grained granulometry. The observed longterm mineralogical resilience also indicates that part of plant nutrition is obtained from subsoil in a non K-limited context, whereas K supply through K-feldspar dissolution appears marginal.

Résumé: We present a new automated earthquake detection and location method based on beamforming (or back projection) and template matching and apply it to study the seismicity of the Southwestern Alps. We use beamforming with prior knowledge of the 3-D variations of seismic velocities as a first detection run to search for earthquakes that are used as templates in a subsequent matched-filter search. Template matching allows us to detect low signal-to-noise ratio events and thus to obtain a high spatiotemporal resolution of the seismicity in the Southwestern Alps. We describe how we address the problem of false positives in energy-based earthquake detection with supervised machine learning and how to best leverage template matching to iteratively refine the templates and the detection. We detected 18,754 earthquakes over 1 year (our catalog is available online) and observed temporal clustering of the earthquake occurrence in several regions. This statistical study of the collective behavior of earthquakes provides insights into the mechanisms of earthquake occurrence. Based on our observations, we infer the mechanisms responsible for the seismic activity in three regions of interest: the Ubaye valley, the Brianconnais, and the Dora Maira massif. Our conclusions point to the importance of fault interactions to explain the earthquake occurrence in the Brianconnais and the Dora Maira massif, whereas fluids seem to be the major driving mechanism in the Ubaye valley.

Résumé: The strength of the lithosphere may be constrained qualitatively by field observations on localized vs distributed modes of deformation and by the mineral assemblages formed during deformation. The internal deformation of the Bielsa basement unit of the Pyrenean Axial zone is investigated through structural, microstructural and thermometric data. In this area, shortening is widely distributed as attested by the folded attitude of the interface between the basement and its sedimentary Triassic cover. Shortening is estimated around 1.7 km (13%) from a regional balanced cross-section and should be considered in pre-Pyrenean reconstructions. Shortening probably occurred before strain localization on crustal ramps as suggested by zircon fission-track analysis. Distributed shortening is characterized at small-scale by low-temperature mylonites and cataclasites. In thin-section, feldspar originally present in the magmatic protolith is partially to totally sericitized. This transformation led to significant weakening of the rock and took place in the 250-350 degrees C temperature range. Sericitization is ubiquitous, even in un-deformed granodiorites. This shows that the weakening effect of sericitization not only occurs in ultra-mylonites, ultra-cataclasites and phyllonites but also more generally in the upper crust early during the shortening history, with implications for the shortening style. Estimates of the geothermal gradient suggest that Inherited thermicity may also have influenced the style of shortening. We propose that the upper crust was very weak before or at the onset of its shortening due to high-thermal gradients and fluid circulation that induced large-scale sericitization in greenschist fades conditions. This has strong implications on the rheological evolution of the upper crust submitted to metamorphic alteration in the greenschist fades and below.

Résumé: Thermal and mechanical models of magma reservoir growth need to be reconciled with deformation patterns and structural relationships observed at active magma systems. Geophysical observations provide a series of short time-scale snap-shots (10(0)-10(2) years) of the long-term growth of magmatic bodies (10(3)-10(6) years). In this paper, we first review evidence for the growth of magmatic systems along structural features and the associated deformation patterns. We then define three distinct growth stages, (1) aligned melt pockets, (2) coalesced reservoirs, (3) highly evolved systems, which can be distinguished using short-term surface observations. We use two-dimensional thermal models to provide first-order constraints on the time scales and conditions associated with coalescence of individual magma bodies into large-scale reservoirs. We find that closely spaced intrusions (less than 1 km apart) can develop combined viscoelastic shells over time scales of 10s kyr and form laterally extensive mush systems over time scales of 10-100 kyr. The highest temperatures and melt fractions occur during a period of thermal relaxation after melt injection has ceased, suggesting that caldera-forming eruptions may preferentially occur long after the main intrusive activity. The coalescence of eruptible melt-rich chambers only occurs for the highest melt supply rates and deepest systems. Thus, these models indicate that, in most cases, conductive heat transfer alone is not sufficient for a full coalescence of magma chambers and that other processes involving mechanical ruptures and mush mobilization are necessary; individual melt lenses can remain isolated for long periods within growing mush systems, and will only mix during eruption or other catastrophic events. The long-term history of the magmatic system is therefore critical in determining rheological structure and hence short-term behaviour. This framework for the development of magmatic systems in the continental crust provides a mechanical basis for the interpretation of unrest at the world's largest volcanoes. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.

Résumé: The compression of liquid nickel and cobalt has been investigated up to 102 and 83 GPa, respectively, by x-ray absorption spectroscopy at the Ni and Co K edges, using laser-heated diamond anvil cell. A shortening of about 8%-10% of the metal bond distances is observed in the pressure range considered and the experimental results are confirmed by theoretical calculations. Ab initio quantum molecular dynamics calculations have been performed, providing a model pair distribution function for cobalt, used as a starting model in the extended x-ray absorption fine structure analysis. The specific volume of the liquid has also been estimated and compared to calculations in the literature. This work sets the basis for x-ray absorption spectroscopy studies of liquid metals under extreme conditions with potentially important implications for the understanding of Earth and planetary interiors.

Résumé: Temporal changes of seismic velocities generated at the subsurface by the 2011 M-w 9 Tohoku earthquake in Japan are analyzed using interferometry and autocorrelation of waveforms recorded by surface and borehole sensors at the KiK-net station IBRH16. Spectral ratios and interferometry of data recorded in moving time windows at the surface and a depth of 300 m exhibit clear time delays and reduction of the predominant frequency during the strong ground motion followed by partial recovery in the waveform coda. Converting the time-delay evolution to velocity changes implies about 30% velocity reduction in the structure between the two sensors. Calculating temporal evolution with autocorrelation of data at the surface sensor in the moving time window indicates about 50% velocity reduction, reflecting changes of shallower material below the station. Computing autocorrelations of data recorded by the surface sensor with the Stockwell transform allows monitoring temporal changes with higher resolution that approaches the sampling rate of the waveforms. Using this technique, we estimate about 60% drop of seismic velocity below the surface sensor during strong ground motion followed again by partial recovery in the coda. These results provide fundamental information on in situ dynamic properties of soils and damaged shallow rocks that complement laboratory measurements, with important implications for constitutive equations of material degradation and healing and nonlinear site effects.

Résumé: Vapor-dominated hydrothermal systems are characterized by localized and elevated heat and gas flux. In these systems, steam and gas ascend from a boiling water reservoir, steam condenses beneath a low-permeability cap layer, and liquid water descends, driven by gravity (heat pipe model). We combine magnetic, electromagnetic, and geoelectrical methods and CO2 flux and subsurface temperature measurements in the Solfatara Plateau Thermal Area in the Yellowstone Caldera to address several fundamental questions: (1) What are the structural and/or lithological controls on heat and mass transport in vapor-dominated areas? (2) What is the geometry and size of convecting multiphase thermal plumes? (3) Are thermal plumes associated with subsurface rock alteration and demagnetization? Magnetic and electromagnetic data inversions suggest an asymmetric 50- to 100-m thick basin of glacial deposits with the thickest part adjacent to the margin of a rhyolite flow. The 3-D electrical conductivity model in the glacial basin reveals a narrow vertical conductor interpreted as a focused multiphase plume, which coincides at the ground surface with the heat and CO2 flux maxima. The magnetic data suggest that destruction of magnetic minerals due to rock alteration associated with the hydrothermal plume occurs mainly near the ground surface. We propose a model where the buoyant multiphase plume forms in response to decompression, boiling, and phase separation of pressurized thermal groundwater that discharges from the brecciated base of a rhyolite flow into the basin of glacial deposits. Results from multiphase groundwater flow and heat transport numerical simulations corroborate the first-order characteristics of this model.

Résumé: The present work aims at establishing an earthquake catalog for seismic hazard assessment in Lebanon. This catalog includes two different parts: historical earthquakes and instrumental earthquakes. The first part of the article describes the work done on the period 31 B.C.E. to the end of the nineteenth century. Numerous studies published in the last 30 yr, devoted to pre-instrumental earthquakes in Lebanon, had not been included in any parametric earthquake catalog. A thorough and critical review of these studies was devised to check their respective interpretations of available earthquake records in terms of seismic parameters (date, location, and size) and to select for each earthquake the most reliable interpretation. The second part provides the details on the selection of instrumental solutions for the period 1900-2015 and for magnitudes >= 4. From global instrumental earthquake catalogs, we build a unified earthquake catalog for Lebanon and bordering regions. A selection scheme is applied for the choice of the best location and the best magnitude among solutions available. The number of events in the catalog is relatively small, and all earthquakes can be checked one by one. The earthquake catalog is homogenized in moment magnitude. For 89% of the events, an M-w proxy was calculated from the original magnitude, applying conversion equations. The merging of the historical and instrumental periods highlights a specificity of this zone: the instrumental seismicity (1900-2015) corresponds to a relatively quiet period for Lebanon. The historical part, covering 2000 yr, includes similar periods of quiescence, as well as much more active periods with destructive earthquakes.

Résumé: The interaction between ultramafic rocks and hot seawater at slow-spreading mid-oceanic ridges triggers hydrothermal redox reactions which are known to produce magnetite and H-2 under appropriate pressure and temperature conditions. Steel slags share some common properties with ultramafic rocks. They are composed of anhydrous and refractory minerals formed at temperatures exceeding 1,200. C and they contain ferrous iron in comparable amounts. Consequently, when submitted to hydrothermal conditions both types of materials, natural and anthropogenic, are prone to form magnetite and H-2 according to the simplified redox reaction: 3[FeO] + H2O => Fe3O4 + H-2 (1) where [FeO] is the ferrous iron component of the corresponding material that can be present under different mineralogical forms. Since H-2 and magnetite are two valuable products for applications in new technologies, the hydrothermal treatment of steel slags can be seen as a way to valorize a byproduct of the steel industry, a few tenths of a billion tons of which are produced yearly. The hydrothermal behavior of steel slags which arise from basic oxygen furnace (BOF) operations and that of olivine (Mg, Fe) 2SiO(4), the main mineral constituent of abyssal peridotites, are described here based on data from the literature. The thermochemical characteristics of Reaction 1 are reviewed for both types of materials in the perspective of optimizing a process that would valorize BOF steel slags for the production of nanomagnetite (and high-purity H-2). In particular, the kinetics effect of temperature, pH and solution-to-solid mass ratio on the hydrothermal oxidation of wustite (FeO), considered here as an analog of the ferrous-iron component of steel slags, are modeled. The possible role of additives (impurity) on the hydrothermal oxidation of wustite through the catalysis of the water-splitting reaction is discussed. Finally, the lack of kinetics constraints on nanomagnetite growth under hydrothermal conditions in a wide range of pH is identified as a major gapin the understanding of two important issues: (1) the catalysis of abiotic molecules in the course of serpentinization reactions, and (2) the tailoring of the size of the magnetite produced by hydrothermal treatment of BOF steel slags.

Résumé: Single-phase maricite, NaFePO4, was synthesized from a mixture of monosodium phosphate and iron oxalate at 750 degrees C and atmospheric pressure. Thermal treatment of synthetic maricite in air led to its oxidative decomposition into Na3Fe23+(PO4)(3) NASICON and alpha-Fe2O3, which started at temperatures slightly below 225 degrees C. Intergrowth of the two reaction products is found to occur at the nanoscale without identified crystallographic relationship with the maricite precursor. Electrochemical activity of the reaction product is confirmed with the reversible insertion of one Na at 2.55 V versus Na+/Na-0.

Résumé: We analyzed pumice from the February 11, 2010 Vulcanian explosion that immediately followed a large dome collapse at Soufriere Hills volcano. We obtained pre-explosive values of porosity, pressure, and depth by combining textural analyses and glass water content determinations. Our data suggest that the February 2010 explosion evacuated the upper 3 km of the conduit from the dense magma (<= 10 vol% porosity) it contained. The low porosity distribution in the volcanic conduit implies that the magma rising from the reservoir had time to extensively degas during emplacement. We use a conduit flow model to characterize the effects of permeability on ascent conditions. Model input parameters were fitted to match our pre-explosive porosity data, which yielded first-order constraints on conduit radius, mass flux, outgassing efficiency, and permeability. This parametric study suggests that efficient lateral gas escape is necessary to explain the low pre-explosive porosities. Steady-state solutions fitting the observed range of dome extrusion rate in the month preceding the February 11 event suggest permeabilities < 10(-13) m(2) deeper than 500 m, which are values typical of crack-supported permeability. Conversely, solutions with parameters consistent with bubble-supported permeability imply transient flow conditions prior to the February 11 event. The transient conditions imply that our data represent a snapshot of the porosity distribution within the conduit that does not preclude the temporary presence of much higher porosities in the conduit. Such unsteady conduit flow conditions are consistent with the irregular but active dome growth in the month prior to the February 11 event. (C) 2019 Elsevier B.V. All rights reserved.

Résumé: The timing and mechanisms of uplift in southeastern Tibet remain disputed. To address this debate, we conducted structural and morphological analyses of the Yulong thrust belt; we also reconstruct the cooling and exhumation history of the Jianchuan basin in the hanging wall of the thrust system using inverse thermal modeling of apatite fission-track and (U-Th)/He thermochronology data. Our results provide evidence for 2.3-3.2km of rapid exhumation in the Jianchuan basin between 28 and 20Ma, followed by limited exhumation of less than 0.2km since then. The magnitude of basin exhumation is consistent with the present-day topographic step of 1.8-2.4km across the Yulong and Chenghai thrust belts, as shown by morphometric analysis. We thus infer that the present-day morphology of the southeastern margin of Tibet results partly from thrusting along the Yulong thrust belt during the Late Oligocene-Early Miocene. This structure may be the southwest continuation of the Longmen Shan thrust belt, offset by the Xianshuihe fault in the Late Miocene. On a regional scale, the approximate synchronicity of exhumation in the hanging walls of the Yalong-Yulong and Longmen Shan thrust systems indicates that widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene-Early Miocene. Plain Language Summary The timing and mechanisms for the high-elevation, low-relief landscape in southeastern Tibet remain at the center of debate. Using apatite fission track and apatite (U-Th)/He thermochronology and thermal modeling, this study sheds new lights on this issue by reconstructing the cooling and exhumation history of the Jianchuan basin, western Yunnan. One major finding is that the Jianchuan basin experienced rapid exhumation during 28-20Ma at a rate of 0.57-0.80km/Myr, coinciding with the absence of coeval sedimentation within the basin. Furthermore, morphometric and structural analyses point out a reasonable causal link between production of the topographic relief in the SE Tibet, exhumation of the Jianchuan basin, and thrusting of the Yalong thrust belt. These results allow us to propose a regional-scale tectonic scenario of widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene-Early Miocene.

Résumé: Silicic magma bodies are formed by repeated injections of mobile magma and reside as a crystal-rich mush. Numerical studies of open-system events have revealed the complexity of mixing and rheological behavior. This is associated with the dilation of the crystal network and the possible occurrence of a lubricated regime. Lubrication forces are hydrodynamic interactions occurring when neighboring crystals have relative motion. The effect of such dissipative forces has not yet been explored in the case of magmatic mush. Here, we investigate the effects of lubrication on mush dynamics and on magma transport. First, we propose scaling relationships to assess the relative importance of the forces controlling the motion of one crystal within a mush by adding lubrication terms into the Basset-Boussinesq-Oseen equation that describes crystal motion in a viscous melt. We then investigate lubrication effects at the macroscopic scale with computational fluid dynamics with discrete element modeling (CFD-DEM) simulations that include these forces. We explore two cases: crystal mush sedimentation and the injection of a crystal-free magma inside a mush. We perform all simulations twice, with and without lubrication forces, and compare the results. At the grain scale, we show that three dimensionless numbers and the crystal content can describe the competition between viscous drag, buoyancy, and lubrication. Two of these numbers (Stokes and Froude numbers) have been previously employed in the context of dilute suspensions. The third is a new form of the Sommerfeld number that measures the importance of lubrication. At the macroscopic scale, simulation pairs (with and without lubrication forces) exhibit very similar behavior when in steady state. The duration of the transient regime preceding steady state, however, is increased when lubrication forces are included. Lubrication causes an apparent bulk strain hardening followed by softening at the initiation of the mush motion. Our results show that lubrication opposes dilation and the initiation of motion within the magmatic mush during this transient phase. Our results highlight the control that the crystal network exerts on magma transport and provide a novel way to evaluate when lubrication matters. (C) 2019 Elsevier B.V. All rights reserved.

Résumé: Explosive eruptions that occur with little or no precursory unrest (less than a month) pose the greatest hazards from volcanoes to nearby populations. Here we focus on the preeruptive conditions for these explosive events, their triggers and how these eruptions evolve. We concentrate on Kelud volcano, where we have conducted a set of petrological experiments to understand preeruptive storage conditions for several recent eruptions. For the 2014 explosive eruption, we combine this with an analysis of interferometric synthetic aperture radar measured deformation. Our data suggest that both explosive and effusive eruptions at Kelud are sourced from a magma storage system at 2-4 km. However, explosive eruptions are fed by magma stored under relatively cool (similar to 1000 degrees C) and water-saturated conditions, whereas effusive eruptions are fed by slightly hotter (similar to 1050 degrees C), water-undersaturated magmas. We propose that the initial phase of the 2014 eruption was triggered by volatile overpressure, which then fostered top-down decompression tapping discrete magma bodies. By compiling a global data set of monitoring signatures of explosive eruptions, we show that the onset of unrest rarely points to the shallow ascent of magma to the surface, as ascent mostly occurs in a matter of hours or minutes. We relate the timescale of preeruptive unrest to eruption triggering mechanisms, with yearly/decadal periods of unrest relating to magma injection events (which may or may not precede a magmatic eruption), whereas internal triggering (e.g., second boiling) of an already present, cooling magma body can lead to explosive eruptions with little warning.

Résumé: Precession of planets or moons affects internal liquid layers by driving flows, instabilities and possibly dynamos. The energy dissipated by these phenomena can influence orbital parameters such as the planet's spin rate. However, there is no systematic study of these flows in the spherical shell geometry relevant for planets, and the lack of scaling law prevents convincing extrapolation to celestial bodies. We have run more than 900 simulations of fluid spherical shells affected by precession, to systematically study basic flows, instabilities, turbulence and magnetic field generation. We observe no significant effects of the inner core on the onset of the instabilities. We obtain an analytical estimate of the viscous dissipation, mostly due to boundary layer friction in our simulations. We propose theoretical onsets for hydrodynamic instabilities, and document the intensity of turbulent fluctuations. We extend previous precession dynamo studies towards lower viscosities, at the limits of today's computers. In the low viscosity regime, precession dynamos rely on the presence of large-scale vortices, and the surface magnetic fields are dominated by small scales. Interestingly, intermittent and self-killing dynamos are observed. Our results suggest that large-scale planetary magnetic fields are unlikely to be produced by a precession-driven dynamo in a spherical core. But this question remains open as planetary cores are not exactly spherical, and thus the coupling between the fluid and the boundary does not vanish in the relevant limit of small viscosity. Moreover, the fully turbulent dissipation regime has not yet been reached in simulations. Our results suggest that the melted lunar core has been in a turbulent state throughout its history. Furthermore, in the view of recent experimental results, we propose updated formulas predicting the fluid mean rotation vector and the associated dissipation in both the laminar and the turbulent regimes.

Résumé: This study presents centrifuge tests analysis of nonlinear soil?structure interactions and the reciprocal influence of the soil and the structure. Weak and strong motions were considered and applied to several centrifuge setups, implemented ?with? or ?without? buildings. For each setup, the response of the site was analyzed using arrays of accelerometers located in the soil and buildings, using time and frequency domain methods. We conclude that the presence of buildings may strongly modify the nonlinear soil response in the free field and the simplified relationships linking the contribution of each motion to the overall soil?structure system response were discussed.

Résumé: Low-temperature DSC on a wide range of opal-A and opal-CT samples was carried out to estimate the proportion of crystallisable water and to determine the size of water-filled cavities. A wide range of crystallisable water contents in the range 4.9 to 41.9% of the water contained in opals were observed, although the proportion of crystallisable water did not correlate with structure. Pore size and pore size distribution were estimated from the melt temperature depression and heat flow data, respectively. Opal-CT was observed to have smaller water-filled pores (radii < 2 nm) than opal-A (radii from 2.5 to 4.9 nm), suggesting that molecular water may be contained between nanograins in the microstructural units (spheres or lepispheres). A narrower pore size distribution was calculated for opal-CT, and no melting of the crystallisable water was observed where bulk water would be expected to melt, suggesting the absence of larger voids. The melting peaks for opal-A, on the other hand, transitioned into the melting of bulk water suggesting the presence of significantly larger water-filled pores, an observation consistent with the microstructure observed in SEM micrographs.

Résumé: Determining the timing and extent of past glaciations in Tibet is essential to reconstruct regional paleoclimate and understand how atmospheric circulation varies due to the high altitude low latitude Tibetan Plateau. In SE Tibet, geomorphological field observation of glacial deposits shows two main imbricated moraines. We apply statistical analyses to a compilation of eight new Be-10 cosmogenic exposure ages from two moraine crests at GMX site and 128 previously published but recalculated exposure ages from 30 additional crests in the region. The results show that ages from the sharpest inner moraines range from 14-25 ka, corresponding to the full range of Marine oxygen Isotope Stage (MIS)-2 (i.e., Last Glacial Maximum, LGM) with less than 2% of older outliers. The outer moraines have a fundamentally different distribution with scattered ages from 10 to 200 ka, obtained using the same method of sampling, dating, and age modeling proven robust for dating the LGM inner moraines, therefore excluding a methodologic artifact. This large scatter prevents the application of any statistical analysis to the age distribution. At a site with well-developed and preserved imbricated moraines (Cuopu), the outer moraine's oldest ages are MIS-6, with the oldest one being at the MIS-6/MIS-7 limit, identical to what is observed in the regional compilation. Following our observations for the LGM moraines where <2% of older outliers are present, the outer moraines in SE Tibet could not be younger than MIS-6. This implies that no glacial advance occurred during MIS-3 which is surprising because MIS-3 moraines have been reported to be the most extensive elsewhere in the Himalayan-Tibetan orogen. Indeed, glaciers are sensitive to both precipitation increase and temperature decrease but whether one factor is prevalent remains debated especially on the Tibetan Plateau. Considering negligible erosion of the boulders, as observed in the field at Cuopu, the most conservative interpretation of our observations is that the true emplacement age of the outer moraines external to the LGM moraines is MIS-6. In that case, glacial advances in SE Tibet correlate with the two coldest periods of the Northern Hemisphere cooling cycles, MIS-2 and MIS-6, indicating that these glaciers are mostly sensitive to a decrease in temperature. (C) 2018 Elsevier B.V. All rights reserved.

Résumé: Recent advancements in seismic data acquisition and computational power have enhanced the deployment of dense seismic monitoring networks. The growing volume of recorded data requires the development of automated techniques to monitor and image zones of seismicity. We have developed an automatic detection and localization method that demands minimal a priori information for retrieval of the spatial distribution of subsurface noise sources (including, but not limited to, microseismic activity), in a reservoir and in the near vicinity during a hydraulic fracturing treatment. This method is based on matched-field processing (MFP), which takes advantage of the phase coherence that is recorded at dense arrays of sensors to localize noise sources. MFP is applied with a distributed set of patch arrays in the context of geophysics exploration. The MFP approach is applied to ambient noise recordings, and it provides results that are consistent with the classic localization methods applied to high-amplitude microseismic signals (in particular, using the relative template-based method). Furthermore, MFP provides enhanced sensitivity of detection and spatially extended information about structural heterogeneities. MFP opens a route to continuous, automatic, statistics-based, and high-sensitivity reservoir monitoring and imaging for geophysics exploration. Potential applications can also be envisaged for seismic monitoring of volcanic and geyser activities, and for other types of hydrothermal activity.

Résumé: We investigate the thermal dependence of the complex conductivity of nine porous materials in the temperature range +20 degrees C to -10 or -15 degrees C. The selected samples include three soils, two granites, three clay-sands mixes, and one graphitic tight sandstone. A total of 12 experiments is conducted with one sample tested at three different salinities. Our goal is to use this database to extend the dynamic Stern layer polarization model in freezing conditions. We observe two polarization mechanisms, one associated with the effect of the change in the liquid water content and its salinity upon the polarization of the porous material. A second mechanism, at higher frequencies (>10 Hz), is likely associated with the polarization of ice. At low frequencies and above the freezing point, the in-phase and quadrature conductivities depend on temperature in a predictable way. This dependence is due to the dependence of the mobility of the charge carriers with temperature. Below the freezing point, the in-phase and quadrature conductivity follow a brutal decay with temperature. This dependence is modeled through an exponential freezing curve function. We were also able to determine how the (apparent) formation factor and surface conductivity change with temperature and water content below the freezing point. Our model is able to replicate the data at low frequencies and predicts correctly the fact that the ratio between the normalized chargeability and the surface conductivity is independent of the water content and temperature and equals a well-defined dimensionless number R.

Résumé: Understanding fluid flow in rocks is crucial to quantify many natural processes such as ground water flow and naturally triggered seismicity, as well as engineering questions such as displacement of contaminants, the eligibility of subsurface waste storage, geothermal energy usage, oil and gas recovery and artificially induced seismicity. Two key parameters that control the variability of fluid flow and the movement of dissolved chemical species are (i) the local hydraulic conductivity, and (ii) the local sorption properties of the dissolved chemical species by the solid matrix. These parameters can be constrained through tomography imaging of rock samples subjected to fluid injection under constrained flow rate and pressure. The neutron imaging technique is ideal to explore fluid localization in porous materials due to the high but variable sensitivity of neutrons to the different hydrogen isotopes. However, until recently, this technique was underused in geology because of its large acquisition time. With the improved acquisition times of newly set-up neutron beamlines, it has become easier to study fluid flow. In the current set of experiments, we demonstrate the feasibility of in-situ 2D and 3D time-lapse neutron imaging of fluid and pollutant percolation in rocks, in particular that of cadmium salt. Cadmium is a hazardous compound that is found in many electronic devices, including batteries and is a common contaminant in soil and groundwater. It also exhibits higher contrast in neutron attenuation with respect to heavy water, and is therefore an ideal tracer. Time-lapse 2D radiographies and 3D neutron tomographies of the samples were acquired on two neutron beamlines (ILL, France and SINQ, Switzerland). We performed two sets of experiments, imbibition and injection experiments, where we imaged in-situ flow properties, such as local permeability and interactions between cadmium and the solid rock matrix. Our results indicate that even within these cm-scale porous rocks, cadmium transport follows preferential pathways, and locally interacts within the limestone samples. Our results demonstrate that the use of neutron imaging provides additional insights on subsurface transport of pollutants.

Résumé: Chronologies of lake-sediment records covering the last centuries to millennia are usually based on both short-lived radionuclides and radiocarbon dating. However, beyond the range of short-lived radionuclides, age model accuracy often suffers from large radiocarbon uncertainties. For high-altitude records, this issue is even more prominent as terrestrial plant fragments for radiocarbon dating are often lacking due to the sparse vegetation in such environments. In this study, we evaluate the potential of the geomagnetic field secular variations as a complementary tool to establish more robust age-depth relationships. Our palaeomagnetic study, applied to five high-altitude lakes from the western European Alps, first shows that recent unconsolidated sediments can carry stable remanent magnetization. The analysis of the magnetic parameters indicates that low-coercivity pseudo-single domain magnetite grains carry the natural magnetization. Nevertheless, the quality of palaeomagnetic secular variation records varies from one lake to another. This quality can be illustrated through the calculation of the declination/inclination maximum angular variations and their comparison to the expected value. Compared with available models, the declination variations are usually too large and the inclination too high. We discuss the validity of palaeosecular variation (PSV) of the Earth's magnetic field regarding rock magnetism, magnetization processes and possible deformation during coring. From a magnetic point of view, the quality of data is variable, but the characteristic remanent magnetization direction is consistent at site level between neighbouring lakes and with the reference curve, suggesting that geomagnetic field secular variations are approximately recorded. Finally, we attempt to correlate the declination/inclination variations of the characteristic remanent magnetization measured in the five records to the reference geomagnetic model to provide additional chronological markers for age-depth modelling. These stratigraphic chrono-markers appear in systematic agreement with our previous chronological data and enable a reduction of dating uncertainties up to 30% when including these chrono-markers in the age-depth modelling. This agreement supports the interpretation that PSV may have been recorded more or less accurately depending on the studied lake. Therefore, coupled with a comprehensive understanding through other analysis (sedimentology, dating, geochemistry), PSV can be used to improve the age models in the more favourable cases.

Résumé: We present the results of a numerical modeling study of the Pyrenees Mountains investigating the spatio-temporal variation in lithospheric flexure in response to the developing orogen, with the aim of setting constraints on paleotopography. We employ a finite-element method to model the 3D flexural deformation of the lithosphere beneath the Pyrenean orogen since the onset of convergence in the Late Cretaceous. Using subsurface and structural data, we describe the evolving geometry of both the northern Aquitaine and southern Ebro foreland basins at the Paleocene (early orogenic phase), the end-and mid-Eocene (peak orogenic phase), the Oligocene (late orogenic phase), and the present (post-orogenic phase). The flexural modeling provides insight into how both the rigidity of the lithosphere and the paleotopographic load have varied over the course of orogenesis to shape the basin geometry. Employing a 3D continuous-plate model, we find that the overriding European plate has slightly higher rigidity than the underthrusting Iberian plate. The best-fit model results for the modern setting produce a root mean -square error (RMSE) of 458 m using effective elastic thickness (T-e) values of 23 and 16 km for the European and Iberian plates, respectively. We also test a broken-plate model, which produces a similar RMSE but predicts higher T-e (32 km for the European plate and 26 km for the Iberian plate). The broken plate model results indicate minimal vertical plate-boundary forces are necessary to reproduce the observed basin geometry. Flexural modeling results suggest that the topographic load doubled from the Paleocene to the Oligocene, and achieved modern topography by the end of the Eocene. The topography remained relatively stable throughout the Oligocene and Neogene, with only limited growth and decay. These results have implications for surface processes and foreland-basin development of the Pyrenean Orogen, tectonic inheritance, and the geodynamic evolution of Western Europe. (C) 2019 Elsevier B.V. All rights reserved.

Résumé: The Mohr-Coulomb criterion is widely used in geosciences and solid mechanics to relate the state of stress at failure to the observed orientation of the resulting faults. This relation is based on the assumption that macroscopic failure takes place along the plane that maximizes the Coulomb stress. Here, this hypothesis is assessed by simulating compressive tests on an elastodamageable material that follows the Mohr-Coulomb criterion at the mesoscopic scale. We find that the macroscopic fault orientation is not given by the Mohr-Coulomb criterion. Instead, for a weakly disordered material, it corresponds to the most unstable mode of damage growth, which we determine through a linear stability analysis of its homogeneously damaged state. Our study reveals that compressive failure emerges from the coalescence of damaged clusters within the material and that this collective process is suitably described at the continuum scale by introducing an elastic kernel that describes the interactions between these clusters.

Résumé: The upper part of the Ubaye Valley (French Alps) is characterized by alternating mainshock-aftershock sequences and swarms. Particularly, during the 2012-2015 crisis, four mainshocks with Ml>3.5 occurred. We here focus on the aftershocks of the largest one (Ml=4.8, 7 April 2014), in order to better understand the involved processes behind this peculiar seismic behavior. We use template matching detection, waveform classification, and double-difference relocations to analyze this seismicity, on average and at the scale of the clusters that compose it. Most event sources are aligned along a plane consistent with the mainshock fault (N165, 65 degrees W), but occurred on conjugate structures. A few clusters of seismicity are also observed far from the mainshock source. Our analysis shows that distinct, spatially separated processes are at play. While coseismic stress transfer explains the seismicity close to the mainshock source, fluid-pressure diffusion and distant stress triggering are required to generate events farther away. The overall distributions in time and magnitude followed a slow Omori's decay and a Gutenberg-Richter relationship, respectively. However, these classical responses arise from the superposition of very different behaviors, associated with different processes at depth. Plain Language Summary Earthquakes have regularly shaken the upper part of the Ubaye valley, near the town of Barcelonnette in the Southwestern French Alps, for nearly 20years. The earthquake behavior is peculiar, as swarms of numerous low magnitude events alternate with larger earthquakes, such as the Ml 4.8 one occurring on 7 April 2014. To understand this dual behavior, we performed an in-depth analysis of the aftershock of this event. The seismicity mainly aligns on a plane consistent with the mainshock fault (N165, 65 degrees W). However, most of the events occurred on branching structures, belonging to the damaged zone of this fault, or on some other small faults far away. While the average behavior of this aftershock sequence is close to a standard one, we show that two different processes occurred at depth. Events occurring close to the mainshock are triggered by coseismic stress transfer, while fluid-pressure diffusion are likely required to explain the seismicity further away. Such dual process should be considered for seismic hazard assessment.

Résumé: On active volcanoes, ambient noise-based seismic interferometry can be a very useful monitoring tool as it allows to detect very slight variations in seismic velocity associated with magma transported toward the surface. However, the classical cross-station approach occasionally fails to detect seismic velocity changes related to eruptive activity, even on very active, well-instrumented volcanoes such as Mt. Etna. In this work, we explored an improved ambient noise-based monitoring strategy by performing the autocorrelation of seismic noise recorded at Mt. Etna volcano, by three stations located close to the active summit craters, during April 2013-October 2014. Such an interval was chosen because of the number and variety of eruptions. In place of the classical cross-correlation, we implemented the phase cross-correlation of each component with itself, which does not require normalization of the signals. The detected seismic velocity variations were very consistent for all three stations throughout the study period, mainly ranging between 0.3 and -0.2%, and were time-related to both sequences of paroxysmal eruptions and more effusive activities. In particular, we observed seismic velocity decreases accompanying paroxysmal eruptions, suggesting an intense pressurization within the plumbing system, which created an area of extensional strain with crack openings. In addition, seismic velocity variations over time were analyzed in the light of ground deformation data recorded by GPS stations and volcanic tremor centroid locations and displayed a particularly strong correlation with the former. Finally, we showed that, although the investigated frequency band (1-2 Hz) contained most of the volcanic tremor energy, our results did not indicate a particular contamination of seismic velocity variation measurements by variations of tremor sources. Ultimately, our investigation highlights a better way to implement noise-based seismic monitoring techniques. The near-field sensitivity of the autocorrelation helped improve our understanding of the relationship between variations of seismic velocity, ground deformation and the pressurization dynamics of volcanic plumbing systems which, in turn, allows for better monitoring implementations of seismic interferometry on other volcanoes.

Résumé: Recent studies using satellite data have shown a growing interest in detecting and anticipating landslide failures. However, their value for an actual landslide prediction has shown variable results. Therefore, the use of satellite images for that purpose still requires additional attention. Here, we study the landslide of the Tunnel du Chambon in the French Alps that ruptured in July 2015, generating major impacts on economic activity and infrastructures. To evaluate the contribution of very high-resolution optical satellite images to characterize and potentially anticipate the landslide failure, we conduct here a retro analysis of its evolution. Two time periods are analyzed: September 2012 to September 2014, and May to July 2015. We combine Pleiades optical images analysis and geodetic measurements from in situ topographic monitoring. Satellite images were correlated to detect pre-failure motions, showing 1.4-m of displacement between September 2012 and September 2014. In situ geodetic measures were used to analyze motions during the main activity of the landslide in June and July 2015. Topographic measurements highlight different areas of deformations and two periods of strong activity, related to the last stage of the tertiary creep and to anthropic massive purges of unstable masses. The law of acceleration toward the rupture observed in June and July 2015 over the topographic targets also fits well the satellite observation between 2012 and 2014, showing that the landslide probably already entered into tertiary creep 2.5 years before its failure.

Résumé: Local site effects due to geotechnical conditions modify seismic motions on surface. This implies that during a given earthquake, buildings located on soft sites may experience a higher damage than similar buildings resting on nearby rock sites. The aim of this study is to provide an estimation of the influence of site conditions on the buildings damage distribution. We combine an approach adapted from the Hazus methodology for the assessment of building damage, with the Borcherdt non linear site amplification factors, that enable to characterize the high and low frequency amplification as a function of V-S30 (the average shear wave velocity in the upper 30m) and ground motion levels. Analysis of obtained results indicates that, seismic damage expressed by the normalized mean damage index depends not only on seismic shaking level and building typology but also on site conditions through the shear wave velocity proxy. A regression relationship is established between the seismic damage and both shaking levels and site conditions, aiming at presenting a simple, rapid tool for estimating this damage at urban areas. An index, the damage increase ratio, is proposed to quantify the increase of damage resulting from site effects, and its dependence on loading level and site conditions are quantified and discussed for the main building typologies present in Algeria. Depending on the building typology, the overall damage may vary within a range of 2-5 for moderate shaking (0.1g) between hard rock and very soft soil, and within a range 1-1.5 for strong shaking (0.5g). The reduction of the impact of site conditions with increasing shaking level is directly linked with the nonlinear soil behavior.

Résumé: Seismic noise interferometry is an exciting technique for studying volcanoes, providing a continuous measurement of seismic velocity changes (dv/v), which are sensitive to magmatic processes that affect the surrounding crust. However, understanding the exact mechanisms causing changes in dv/v is often difficult. We present dv/v measurements over 10 years in central Iceland, measured using single-station cross-component correlation functions from 51 instruments across a range of frequency bands. We observe a linear correlation between changes in dv/v and volumetric strain at stations in regions of both compression and dilatation associated with the 2014 Baroarbunga-Holuhraun dike intrusion. Furthermore, a clear seasonal cycle in dv/v is modeled as resulting from elastic and poroelastic responses to changing snow thickness, atmospheric pressure, and groundwater level. This study comprehensively explains variations in dv/v arising from diverse crustal stresses and highlights the importance of deformation modeling when interpreting dv/v, with implications for volcano and environmental monitoring worldwide.

Résumé: Lobate stony landforms occur on steep slopes at high latitudes on Mars. We demonstrate active boulder movement at seven such sites. Submeter-scale boulders frequently move distances of a few meters. The movement is concentrated in the vicinity of the lobate landforms but also occurs on other slopes. This provides evidence for a newly discovered, common style of activity on Mars, which may play an important role in slope degradation. It also opens the possibility that the lobate features are currently forming in the absence of significant volumes of liquid water. Plain Language Summary Tongue-shaped lobes of boulders occur on steep slopes at high latitudes on Mars. Boulders in those lobes, as well as on nearby slopes, commonly move short distances. Several processes could contribute to moving the boulders, but liquid water is probably not involved. This is a new type of active surface process on Mars and may be an important contributor to forming the lobes or changing steep slopes.

Résumé: Spatial variability of earthquake ground motion (SVEGM) refers to the differences in amplitude and phase between recordings of the same earthquake at different locations. In the near-surface, geological processes (sedimentation, erosion) and anthropogenic activities can lead to small scale spatial heterogeneities of soil mechanical properties, which may affect SVEGM. In this paper, the effect of shallow 2D spatial variability of the shear wave velocity (Vs) on the surface ground motion is assessed through a set of numerical experiments, using a simple 2D velocity structure (a sedimentary layer over a half-space). Non-linearity or damping are not considered in the wave propagation calculation in order to solely focus on the effects of soil elastic property variability. Vs is modeled as a random field using the EOLE method (Expansion Optimal Linear Estimation) and considering three statistical parameters: the coefficient of variation, and the horizontal and vertical auto correlation distances. Seismic ground motions are numerically simulated for a plane wave excitation with SV polarization. Modeling results clearly highlight the scattering of surface waves by ground heterogeneities, leading to large spatial variations in surface ground motion. We computed surface ground motion indicators (resonance frequency, spectral amplification, Arias intensity and duration) and we showed that their spatial variability is mainly controlled by the Vs coefficient of variation. A comparison between 2D and 1D ground motion probabilistic modeling shows that the 1D probabilistic approach may correctly reproduce average fundamental resonance frequencies and corresponding amplification. However, the 1D approach significantly under-predicts both ground motion amplification at higher frequencies and related variabilities, as well as Arias intensities and inferred durations, which are all controlled by the generation of locally diffracted surface waves.

Résumé: We use two-dimensional thermomechanical models to investigate the potential role of rapid filling of foreland basins in the development of orogenic foreland fold-and-thrust belts. We focus on the extensively studied example of the Western European Alps, where a sudden increase in foreland sedimentation rate during the mid-Oligocene is well documented. Our model results indicate that such an increase in sedimentation rate will temporarily disrupt the formation of an otherwise regular, outward-propagating basement thrust-sheet sequence. The frontal basement thrust active at the time of a sudden increase in sedimentation rate remains active for a longer time and accommodates more shortening than the previous thrusts. As the propagation of deformation into the foreland fold-and-thrust belt is strongly connected to basement deformation, this transient phase appears as a period of slow migration of the distal edge of foreland deformation. The predicted pattern of foreland-basin and basement thrust-front propagation is strikingly similar to that observed in the North Alpine Foreland Basin and provides an explanation for the coeval mid-Oligocene filling of the Swiss Molasse Basin, due to increased sediment input from the Alpine orogen, and a marked decrease in thrustfront propagation rate. We also compare our results to predictions from critical-taper theory, and we conclude that they are broadly consistent even though critical-taper theory cannot be used to predict the timing and location of the formation of new basement thrusts when sedimentation is included. The evolution scenario explored here is common in orogenic foreland basins; hence, our results have broad implications for orogenic belts other than the Western Alps.

Résumé: An exhaustive biostratigraphic study based on the calcareous nannofossil content from Lower and Middle Jurassic Lusitanian Basin sections in Portugal is here presented. Located at the strategic intersection of important Jurassic water masses during a period of drastic environmental changes, the Lusitanian Basin conveyed mixed phytoplanktonic communities in its surface waters. Approximately 800 m of exceptionally continuous Lower and Middle Jurassic series bearing detailed ammonite biostratigraphy and two Global Stratotype Section and Point are studied. Vertical and lateral ubiquity of calcareous nannofossils in marine sediments and rapid evolutionary rate and radiation make this fossil group a remarkable biostratigraphic tool. Nearly 100 bioevents are acknowledged in similar to 24 Myr time span this work refers to, bridging 11 nannofossil zones and 29 subzones. A thorough revision of the existing literature referring to Early and Middle Jurassic calcareous nannofossil biostratigraphy is presented, and causes and implications for zonal marker discrepancies discussed under a palaeoceanographic and Jurassic nannofossil evolution angle. In order to create a solid biostratigraphic frame and to compare it with C and O stable isotopic trends, brachiopod calcite shells were analysed for geochemistry. This work yields for the first time a very detailed and inclusive biostratigraphic scheme for the Early and Middle Jurassic epochs.

Résumé: This study, which complements a first mineralogical work, presents detailed petrographic and chemical data on the sequences of clay infillings commonly found in serpentine veins of reactivated faults from the New Caledonian peridotite formation. Chemical trends and transfers established from the outer serpentine fringe to the inner clay infilling, as well as from the white (deweylite) to the greenish (garnierite) parts of the veins, enable us to decipher the processes and conditions involved in the redistribution of Mg and Ni along reactivated faults. As commonly reported from studies of peridotite formations worldwide, two main chemical trends are distinguished. In New Caledonia, these trends belong to distinct periods of tectonic activities associated with the dislocation and early alteration of the ophiolite nappe. They result from two kinds of Ni-ore-forming processes and reveal a significant decrease in the mobility of Ni over time. The first process relates the step-by-step alteration of serpentine species into talclike (TL) minerals to the sequential leaching of Mg and Fe, together with their local replacement by Ni in octahedral sites of the newly formed TL minerals. The TL minerals are thus considered as the main Ni-bearing phases (pimelite) of the ore. The large-scale redistribution of Mg and Ni during a first period of tectonic activity and alteration leads to the differentiation of white (Ni-free) and olive-green (Ni-rich) clay infillings along the reactivated faults. The second process belongs to a second period of tectonic activity and alteration where most of the serpentine species have been converted into TL minerals without major Ni enrichment (formation of a second sequence of milky white and turquoise clay infillings). Redistribution of Mg and Ni occurs over shorter distances from the transition of Mg-rich to Ni-rich clay infillings (or breccias). It results from oscillatory phenomena and self-organised precipitation processes leading to cyclic and inverse Mg and Ni variations in alternating bands of contrasted optical anisotropy. The early redistribution of Ni and the significant decrease in the mobility of this element from the first to the second period of tectonic activity provide better constraints on an alternative model for the genesis of the Ni-silicate ore.

Résumé: Passive seismic interferometry allows to track continuously the weak seismic velocity changes in any medium by correlating the ambient seismic noise between two points to reconstruct the Green's function. The ballistic surface waves of the reconstructed Green's functions are used to monitor the changes of water table induced by a controlled experiment in the Crepieux-Charmy (France) exploitation field. Viscoelastic numerical modelling of the monitoring experiment reproduces quite satisfactorily the sensitivity of the surface waves to the water table previously observed with seismic noise data. This numerical approach points out that this sensitivity is controlled by mode mixing of Rayleigh waves. It also made it possible to identify the refracted P wave and to extract its anticorrelated sensitivity to water table variations. Depending on the offset between receivers, it was observed numerically that the interferences between the different waves (with different velocities) composing the seismic wavefield slightly affect the quantitative sensitivity to water table changes. This suggests the use of an optimal spatial and temporal observation window for which wave interference is minor and does not blur the quantitative response to water table variations. We were thus able to determine the relationship between velocity and water table variations for all waves involved. From numerical computations, we identify a weak signal-to-noise ratio phase in the noise correlograms, with a anticorrelated sensitivity to the water table: the reconstructed refracted waves.

Résumé: The observation of a transient slip 1month before the rupture of the 2011 Tohoku earthquake is a conandrum since the area was supposedly fully coupled. A better understanding of the mechanisms at work during the preseismic phase is thus fundamental. However, the configuration of the Pacific plate and the location of the Tohoku rupture zone 200km from the coast make it difficult to detect microseismic events. In this study, we use a multidimensional template matching (MDTM) technique to detect earthquakes that are hidden in the noise. The temporal distribution of these 395 newly detected earthquakes provides new insights on the slip history of the megathrust earthquake epicentral zone. The detected events can be separated into two groups: 187 low-frequency detections (below 5Hz) that well recorded the episodes of earthquake migration prior to the Tohoku earthquake and 208 high-frequency detections (above 10Hz) that occurred close to the rupture zones of the M >= 4.8-6 earthquakes that struck between the 9 March 2011 M7.3 foreshock and the 30 November 2010 Tohoku-Oki earthquake. The seismic rate of these high frequency detection events starts to increase on 30 November 2010 until the Tohoku earthquake.

Résumé: We present a measurement of K-shell transitions in H-like gold (Au78+) using specially developed transmission type crystal spectrometers combined with Ge(i) microstrip detectors. The experiment has been carried out at the Experimental Storage Ring at GSI in Darmstadt. This is a first high-resolution wavelength-dispersive measurement of a K-shell transition in a high-Z H-like ion, thus representing an important milestone in this field. Ideas on possible future improvements are discussed as well.

Résumé: The alteration of chromian spinel is a key process during serpentinization and metamorphism of ultramafic rocks controlled by oxygen fugacity (fO(2)) and Fe2+<-> Fe3+ exchange during fluid-rock interaction. Chromian spinel alteration is better recorded in less permeable chromitite than in peridotites where extensive fluid-rock interaction frequently overprints the record of earlier stages of alteration. To shed light on that process we have studied the distribution of Fe2+ and Fe3+ in variably altered chromian spinel grains from a set of chromitite samples from the same mining district using synchrotron-based microscopic chemical imaging and spatially resolved X-ray absorption near edge structure spectroscopy. Our results show that early stages of alteration do not involve changes in Cr3+ and Fe2+ contents or in Fe speciation but only depletion in Al3+ and Mg2+ resulting in the formation of porous chromite. With ongoing alteration Fe3+ migrates into porous chromite mainly along fracture walls and fracture zones as well as along grain boundaries. Sheared-type chromitites record the maximum rates of fluid-rock interaction because in these chromitite-types the accommodation of deformation on porous chromite allowed higher rates of diffusion of Fe3+ and Fe2+ (a magnetite component with Fe3+/Fe-total=0.66) into the newly formed neoblasts. In porous chromite-type texture (all the original chromite grains fully transformed to porous chromite) the deformation and accompanying diffusion processes result in the formation of homogenous ferrian chromite grains. In contrast, in partly altered-type texture (chromite grains with original cores surrounded by porous chromite), such processes are only restricted to the porous rims, giving rise to zoned chromian spinel-ferrian chromite grains.

Résumé: Coalescence during bubble nucleation and growth in crystal-free rhyolitic melt was experimentally investigated, and the percolation threshold, defined as the porosity at which the vesicular melt first becomes permeable, was estimated. Experiments with bubble number densities between 10(14) and 10(15)m(-3) were compared to four suites of rhyolitic Plinian pumices, which have approximately equal bubble number densities. At the same total porosity, Plinian samples have a higher percentage of coalesced bubbles compared to their experimental counterparts. Percolation modeling of the experimental samples indicates that all of them are impermeable and have percolation thresholds of approximately 80-90%, irrespective of their porosity. Percolation modeling of the Plinian pumices, all of which have been shown to be permeable, gives a percolation threshold of approximately 60%. The experimental samples fall on a distinct trend in terms of connected versus total porosity relative to the Plinian samples, which also have a greater melt-bubble structural complexity. The same holds true for experimental samples of lower bubble number densities. We interpret the comparatively higher coalescence within the Plinian samples to be a consequence of shear deformation of the erupting magma, together with an inherently greater structural complexity resulting from a more complex nucleation process.

Résumé: Linking volcano-seismic signals with subsurface processes is crucial to improve the forecasting of volcanic eruptions. One of the most enigmatic signals is shallow volcanic tremor, a highly periodic ground vibration that is typically sourced beneath the crater of active volcanoes, is long lasting (from minutes to years), appears during unrest periods, and frequently precedes eruptions. In this paper, we demonstrate that shallow tremor can be produced by periodic pressure oscillations emerging spontaneously beneath permeable media (e.g., fractured magma caps). These pressure oscillations are the result of three concurrent processes: (a) the transient porous flow of gases through the permeable cap; (b) the temporary accumulation of these gases beneath the cap, forming a gas pocket; and (c) the random supply of volatiles from deeper levels. For highly permeable media (>= 10(-12) m(2); realistic for shallow volcanic edifices), the pressure in subsurface gas pockets is governed by the equation of a linear oscillator; hence, under proper conditions, periodic pressure oscillations emerge during the transfer of gases from the Earth's interior to the surface. Our model is consistent with geophysical data showing that the tremor source is localized at a fixed region and can explain the main characteristics of ground vibrations, including frequency gliding, variations of seismic amplitude prior to eruptions, and the different types of tremor observed. For thin permeable caps (<100 m), we find that different eruption mechanisms (e.g., magma ascent vs. cap sealing) leave distinct footprints in the tremor properties, thus opening new perspectives to forecast the type and style of impending eruptions.

Résumé: Imaging via pre-stack depth migration (PSDM) of reflection towed-streamer multichannel seismic (MCS) data at the scale of the whole crust is inherently difficult. This is because the depth penetration of the seismic wavefield is controlled, firstly, by the acquisition design, such as streamer length and air-gun source configuration, and secondly by the complexity of the crustal structure. Indeed, the limited length of the streamer makes the estimation of velocities from deep targets challenging due to the velocity-depth ambiguity. This problem is even more pronounced when processing 2-D seismic data due to the lack of multi-azimuthal coverage. Therefore, in order to broaden our knowledge about the deep crust using seismic methods, we present the development of specific imaging workflows that integrate different seismic data. Here we propose the combination of velocity model building using (i) first-arrival tomography (FAT) and full-waveform inversion (FWI) of wide-angle, long-offset data collected by stationary ocean-bottom seismometers (OBSs) and (ii) PSDM of short-spread towed-streamer MCS data for reflectivity imaging, with the former velocity model as a background model. We present an application of such a workflow to seismic data collected by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and the Institut Francais de Recherche pour l'Exploitation de la Mer (IFREMER) in the eastern Nankai Trough (Tokai area) during the 2000-2001 Seize France Japan (SFJ) experiment. We show that the FWI model, although derived from OBS data, provides an acceptable background velocity field for the PSDM of the MCS data. From the initial PSDM, we refine the FWI background velocity model by minimizing the residual move-outs (RMOs) picked in the pre-stack-migrated volume through slope tomography (ST), from which we generate a better-focused migrated image Such integration of different seismic datasets and leading-edge imaging techniques led to greatly improved imaging at different scales. That is, large to intermediate crustal units identified in the high-resolution FWI velocity model extensively complement the short-wavelength reflectivity inferred from the MCS data to better constrain the structural factors controlling the geodynamics of the Nankai Trough.

Résumé: The longevity of zoo animals is increasing due to continuous improvement in husbandry and veterinary medicine. However, increasing age is correlated to a higher prevalence of neoplasia. Despite tremendous improvement in diagnoses and monitoring capacities, cancers are still a challenge for veterinarians within the global zoo community. The recent use of copper isotopes as biomarkers for neoplasia in both human and veterinary medicine is a promising and cost-effective diagnostic tool. Two hundred and twenty-nine serum samples from 10 different species of wild felids under human care were processed through mass spectrometry to determine the ratio of heavy and light copper isotopes (Cu-65/Cu-63). The results of this preliminary study exhibit an important variability between felid species, with a ratio ranging between -1.71 and 0.63. Additionally, copper isotopes seem to be a promising diagnostic tool in monitoring cancer in wild animals, as in human medicine, where the isotopic ratio decreases significantly with time in the presence of a tumor.

Résumé: Volcano acoustic signals contain valuable information on shallow magmatic and hydrothermal processes. In some cases, the detection of acoustic waves is the only clear evidence of the occurrence of volcanic explosions. Their study is thus complementary to that of seismic signals. For this reason, acoustic sensors are more and more frequently integrated in volcano monitoring systems as well as in temporary instrumental deployments. We have developed a broadband, robust and low-cost infrasound sensor designed for the detection and analysis of acoustic waves on volcanoes. It is based on a microelectromechanical differential pressure transducer (MEMS). The reference pressure is balanced with the atmospheric pressure through a pneumatic high-pass filter. Its low corner frequency, usually set to 60 mHz, can be adjusted from a few to tens of mHz. Its amplitude range is +/- 240 Pa and its sensitivity is 20 mV Pa-1, with a noise level <0.05 Pa RMS. The power consumption is 42 mW (3.5 mA with 12 V voltage). A direct output of the MEMS also provides a signal with sensitivity of about 500 μV Pa-1 and range +/- 1245 Pa. This sensor is not sensitive to mechanical vibrations. The instrumental response of each infrasound sensor is carefully measured from 1 mHz to >100 Hz using two specially designed calibration systems which deliver sinusoidal pressure variations. The mechanical elements of the sensor are produced by 3D printer and filled with epoxy resin which guarantees high robustness in the aggressive environment of most volcanoes. The sensor dimensions (26x45x80 mm) and weight (100 g) makes it very easy to handle and install. (C) 2019 Elsevier B.V. All rights reserved.

Résumé: Volcanismis one of the major natural processes emitting mercury (Hg) to the atmosphere, representing a significant component of the global Hg budget. The importance of volcanic eruptions for local-scale Hg deposition was investigated using analyses of Hg, inorganic elemental tracers, and organic biomarkers in a sediment sequence from Lake Chungara (4520 m a.s.l.). Environmental change and Hg deposition in the immediate vicinity of the Parinacota volcano were reconstructed over the last 2700 years, encompassing the pre-anthropogenic and anthropogenic periods. Twenty eruptions delivering large amounts of Hg (1 to 457 μg Hg m(-2) yr(-1) deposited at the timescale of the event) were locally recorded. Peaks of Hg concentration recorded after most of the eruptions were attributed to a decrease in sedimentation rate together with the rapid re-oxidation of gaseous elemental Hg and deposition with fine particles and incorporation into lake primary producers. Over the study period, the contribution of volcanic emissions has been estimated as 32% of the total Hg input to the lake. Sharp depletions in primary production occurred at each eruption, likely resulting from massive volcaniclastic inputs and changes in the lake-water physico-chemistry. Excluding the volcanic deposition periods, Hg accumulation rates rose from natural background values (1.9 +/- 0.5 μg m(-2) yr(-1)) by a factor of 2.3 during the pre-colonial mining period (1400-900 yr cal. BP), and by a factor of 6 and 7.6, respectively, during the Hispanic colonial epoch (400-150 yr cal. BP) and the industrial era (similar to 140 yr cal. BP to present). Altogether, the dataset indicates that lake primary production has been the main, but not limiting, carrier for Hg to the sediment. Volcanic activity and climate change are only secondary drivers of local Hg deposition relative to the magnitude of regional and global anthropogenic emissions. (C) 2019 Elsevier B.V. All rights reserved.

Résumé: The presence of multiscale interactions means that the complex urban wavefield must be observed and analyzed in order to understand seismic ground motion in urban environments. Originally called site-city interaction, the interactions between soil and structures, structures and soil, and between structures contribute to the modification of urban seismic ground motion. This may affect the lateral variability of the ground motion observed in relation to earthquake damage, the characterization of site effects in urban areas, and also the response of civil engineering structures designed without consideration of the immediate urban environment. The METACity-Quito experiment was designed to take accurate measurements of the effects of the resonator array formed by structures in the seismic wavefield, in the manner of an urban metamaterial. Current applications in the fields of physics, acoustics and, more recently, geophysics have shown the existence of forbidden bands, that is, frequencies at which seismic energy vanishes. This concept could help to understand the heterogeneous distribution of damage in urban areas as well as to imagine the future design of seismic-proof cities.

Résumé: The 1000 km-long suture zone of the Dahomeyide belt, exposed from Southeast Ghana to South Mali, corresponds to a narrow and lithologically diverse area with symptomatic coronitic HP granulitic massifs. Based on a review of published petrological, geochemical and geochronological data along the Dahomeyide belt we propose a global scenario for the closure of the Pharusian ocean between the West African craton (WAC) and the Benino-Nigerian shield during the end of the Neoproterozoic. The onset of a long-lived oceanic subduction by 800-780 Ma is recorded by early magmatism in the Amalaoulaou intra-oceanic arc in Mali, contemporary to the Gourma and Adrar des Iforas to the North, and in Brazil to the South. The first occurrence of tonalitic plutons dated at 720 Ma, and the development of a forearc system around 650 Ma mark the onset of active margin subduction beneath the Benino-Nigerain shield and its northward prolongation in Mali. Oceanic subduction beneath the active margin ended between 640 and 630 Ma with the onset of subduction of the WAC continental margin while subduction related magmatism continues till ca. 600 Ma on the upper plate. During a short period between 620 and 610 Ma, the forearc system and the tip of the active continental margin were buried synchronously. The positive Bouguer anomaly observed to the East of the suture zone, in Benin, and not beneath the suture zone itself supports the occurrence of a massive mafic body at the base of the crust that could correspond to the underplated buried forearc. Ultimately, the exhumation and partial amphibolitization of the suture zone and a shift from a calc-alkaline magmatism to anatectic magmatism along with the onset of strike-slip faulting in the upper plate marks the transition from continental subduction to continental collision between 610 and 580 Ma. This work highlights the importance of the Pharusian suture zone s.l. To our knowledge, it represents a unique example in the world in where the forearc system is buried and partly exhumed at the transition from subduction to collision.

Résumé: Sorption isotherms remain a major tool to describe and predict the mobility of pollutants in natural and anthropogenic environments, but they are typically determined by independent batch experiments. In the present study, the sequestration of As(III), Cr(VI) and competitive As(III)-Cr(VI) on/in 6L-ferrihydrite, siderite and goethite nanostructured minerals was reinvestigated using stirred flow-through reactor experiments. Herein, sorption isotherms were particularly determined from breakthrough curves for inert and reactive tracers monitored simultaneously in a single percolation experiment. In complement, X-ray absorption spectroscopy (XAS) was used to identify As sorption sites on 6L-ferrihydrite and goethite. As expected, the minerals have high potential to remove As and Cr from water (siderite = ferrihydrite (about 60 mg/g) > goethite (20 mg/g)). As and Cr sorption isotherms were modelled with a Langmuir model, and with a sigmoidal Hill model in the case of the competitive sorption. XAS measurements have revealed that As(III) was partially oxidized (up to 22%) in the competitive system with chromate oxyanion Cr(VI). As(III) sorbed on ferrihydrite and goethite adopted edge sharing and corner sharing complex geometries. Nowadays, a new class of adsorbing phases is being developed for wastewater treatment, including engineered nanostructured materials and nanocomposites. The use of flow through reactor experiments as a high throughput method, combined with XAS, should be considered as efficient screening methods to test their sorbing properties on various contaminants.

Résumé: We present a Bayesian method to map contemporary rates of relative sea level change using a joint inversion of vertical trends from tide gauges, GPS time series, and satellite radar altimetry measurements. Tide gauge measurements constrain rates of relative sea level change on decadal to secular time scales at a few hundred sites sparsely distributed along coastlines. Predicting the rates of relative sea level change from historical tide gauge measurements is difficult due to the paucity and uneven distribution of sites with high quality records. Since the late twentieth century, deployments of GPS stations have enabled accurate determination of the rates of vertical land motion. A series of satellite radar altimetry missions provide continuous and global monitoring of geocentric sea level changes since the launch of TOPEX/Poseidon in 1992. By combining these three observations types into a single Bayesian inversion, we construct continuous maps of rates of relative sea level change, geocentric sea level change, and vertical land motion assuming linear trends, with robust estimates of uncertainties at regional scales. Cross-validation tests show that reliable predictions of relative sea level changes are still provided where only GPS and satellite altimetry data are used, suggesting this method is viable for studying potential sea level risk for communities where historical tide gauge data are not available. Our results provide spatially and temporally consistent estimates of the various contributions to relative sea level changes.

Résumé: Receiver function analysis is widely used to make quantitative inferences about the structure below a seismic station. As these observables are mainly sensitive to traveltimes of phases converted and reflected at seismic discontinuities, the resulting inverse problem is highly non-linear, the solution non-unique, and there are strong trade-offs between the depth of discontinuities and absolute velocities. To overcome this difficulty, we propose to measure the misfit between the predicted and observed data with an optimal transport distance instead of the conventional least-squares distance, a strategy that has shown its assets in the context of full waveform inversion. This approach views a seismogram as a distribution of 'mass'. The optimal transport distance between two waveforms is the minimal cost of transporting one waveform onto the other. We test the optimal transport approach on the inversion of a radial P-wave receiver function. We also show how it can be applied to measure the cross-convolution distance between the radial and vertical components, thus avoiding the need for deconvolution associated with the calculation of the receiver function. The resulting misfit function is minimized with a local optimization algorithm to constrain the receiver-side structure. The benefits of this methodology are studied in simple synthetic tests and with real data. In particular, we show that with its increased sensibility to time-shifts, the optimal transport distance reduces the number of local minima in the misfit function, which, in the case of a linearized inversion, significantly reduces the dependency to the starting model and results in a better convergence towards the solution model. A joint inversion of the P-wave receiver function and surface wave dispersion curves is performed at the Hyderabad station in India.

Résumé: Deformation microstructures of albitic plagioclase and K-feldspar were investigated in mylonitic pegmatites from the Austroalpine basement south of the western Tauern Window by polarized light microscopy, electron microscopy and electron backscatter diffraction to evaluate feldspar deformation mechanisms at greenschist facies conditions. The main mylonitic characteristics are alternating almost monophase quartz and albite layers, surrounding porphyroclasts of deformed feldspar and tourmaline. The dominant deformation microstructures of K-feldspar porphyroclasts are intragranular fractures at a high angle to the stretching lineation. The fractures are healed or sealed by polyphase aggregates of albite, K-feldspar, quartz and mica, which also occur along intragranular fractures of tourmaline and strain shadows around other porphyroclasts. These polyphase aggregates indicate dissolution-precipitation creep. K-feldspar porphyroclasts are partly replaced by albite characterized by a cuspate interface. This replacement is interpreted to take place by interface-coupled dissolution-precipitation driven by a solubility difference between K-feldspar and albite. Albite porphyroclasts are replaced at boundaries parallel to the foliation by fine-grained monophase albite aggregates of small strain-free new grains mixed with deformed fragments. Dislocation glide is indicated by bent and twinned albite porphyroclasts with internal misorientation. An indication of effective dislocation climb with dynamic recovery, for example, by the presence of subgrains, is systematically missing. We interpret the grain size reduction of albite to be the result of coupled dislocation glide and fracturing (low temperature plasticity). Subsequent growth is by a combination of strain-induced grain boundary migration and formation of growth rims, resulting in an aspect ratio of albite with the long axis within the foliation. This strain-induced replacement by nucleation (associated dislocation glide and microfracturing) and subsequent growth is suggested to result in the observed monophase albite layers, probably together with granular flow. The associated quartz layers show characteristics of dislocation creep by the presence of subgrains, undulatory extinction and sutured grain boundaries. We identified two endmember matrix microstructures: (i) alternating layers of a few hundred micrometres' width, with isometric, fine-grained feldspar (on average 15 μm in diameter) and coarse-grained quartz (a few hundred micrometres in diameter), representing lower strain compared to (ii) alternating thin layers of some tens of micrometres' width composed of fine-grained quartz (<20 μm in diameter) and coarse elongated albite grains (long axis of a few tens of micrometres) defining the foliation, respectively. Our observations indicate that grain size reduction by strain-induced replacement of albite (associated dislocation glide and microfracturing) followed by growth and granular flow simultaneous with dislocation creep of quartz are playing the dominating role in formation of the mylonitic microstructure.

Résumé: We study temporal changes of seismic velocity (dv/v) in the crust around the central section of the San Jacinto fault zone (SJFZ), Southern California. Focusing on a 200-day-long period around April 2010, our analysis resolves two tens-of-days-long successive episodes of reduced velocities that are compatible with signals from the long base strainmeter at the Pinon Flat Observatory. The imaged dv/v sequences are proxies for evolving material properties in the crust surrounding the SJFZ. The temporal and the spatial coincidence of the observed dv/v patterns with the occurrence of two proposed creep episodes suggest that the relative velocity changes reflect the response to deep creep events that follow the M7.2 El Mayor-Cucapah earthquake and the M5.4 Collins Valley earthquake that occurred 94days later on the San Jacinto fault. The main slip during the creep events was proposed to occur below 10-km depth. Wavefield properties suggest sensitivity to medium changes above this source zone, in the top 10km. The distribution of the obtained dv/v reductions shows a strong difference between large values to the west of the SJFZ and significantly smaller amplitudes to the east. The similarity to the seasonal velocity change pattern implies that the results are likely controlled by the contrast of mechanical properties across the fault, such as fault-perpendicular shear modulus variations. Our analysis extends the spectrum of methods that can be used to study earthquake interaction, fault zone rheology and dynamics, triggering, and the interplay between creep episodes and earthquakes. Plain Language Summary Motion along geologic fault zones not only occurs during small and large potentially devastating earthquakes. Some faults creep aseismically, which means the slip motion is too slow to generate earthquake waves. To develop a more complete understanding of fault behavior, it is important to detect and locate such creep transients. A particularly interesting problem is how earthquakes and episodic creep events, which tend to occur in a zone below the earthquakes, interact with each other. Creep events are usually detected using satellite-based methods. In this study we applied the most modern ambient seismic wavefield analysis techniques to first detect and locate changes in the rock properties around a continental strike slip fault, the San Jacinto fault, Southern California, that are caused by two successive deep creep events along that fault. These results are supported by data from a colocated deformation meter that picked up signals from the same creep events that are thought to be triggered, initiated by the two earthquakes indicated in the title. The observed deformation patterns-they are not uniform along and across the fault-and their temporal evolution can help us better understand the processes that happen on and off faults in earthquake-prone regions.

Résumé: The controlled crystallisation of struvite (MgNH4PO4 center dot 6H(2)O) is a viable means for the recovery and recycling of phosphorus (P) from municipal and industrial wastewaters. However, an efficient implementation of this recovery method in water treatment systems requires a fundamental understanding of struvite crystallisation mechanisms, including the behavior and effect of metal contaminants during struvite precipitation. Here, we studied the crystallisation pathways of struvite from aqueous solutions using a combination of ex situ and in situ time-resolved synthesis and characterization techniques, including synchrotron-based small- and wide-angle X-ray scattering (SAXS/WAXS) and cryogenic transmission electron microscopy (cryo-TEM). Struvite syntheses were performed both in the pure Mg-NH4-PO4 system as well as in the presence of cobalt (Co), which, among other metals, is typically present in waste streams targeted for P-recovery. Our results show that in the pure system and at Co concentrations < 0.5 mM, struvite crystals nucleate and grow directly from solution, much in accordance with the classical notion of crystal formation. In contrast, at Co concentrations >= 1 mM, crystallisation was preceded by the transient formation of an amorphous nanoparticulate phosphate phase. Depending on the aqueous Co/P ratio, this amorphous precursor was found to transform into either (i) Co-bearing struvite (at Co/P < 0.3) or (ii) cobalt phosphate octahydrate (at Co/P > 0.3). These amorphous-to-crystalline transformations were accompanied by a marked colour change from blue to pink, indicating a change in Co2+ coordination in the formed solid from tetrahedral to octahedral. Our findings have implications for the recovery of nutrients and metals during struvite crystallisation and contribute to the ongoing general discussion about the mechanisms of crystal formation.

Résumé: The pygeodyn package is a sequential geomagnetic data assimilation tool written in Python. It gives access to the core surface dynamics, controlled by geomagnetic observations, by means of a stochastic model anchored to geo-dynamo simulation statistics. The pygeodyn package aims to give access to a user-friendly and flexible data assimilation algorithm. It is designed to be tunable by the community by different means, including the following: the possibility to use embedded data and priors or to supply custom ones; tunable parameters through configuration files; and adapted documentation for several user profiles. In addition, output files are directly supported by the package webgeodyn that provides a set of visualization tools to explore the results of computations.

Résumé: The mechanisms triggering intermediate and deep earthquakes have puzzled geologists for several decades. There is still no consensus concerning whether such earthquakes are triggered by brittle or ductile mechanisms. We performed a deformation experiment on a synthetic lawsonite-bearing blueschist at a confining pressure of 3 GPa and temperatures from 583 to 1,073 K. After deformation, the recovered sample reveals conjugated shear fractures. Garnet crystals are dissected and displaced along these narrow faults and reveal micro- and nanostructures that resemble natural pulverization structures as well as partial amorphization. Formation of such structures at low confining pressures is known to require high tensile stresses and strain rates and is explained by the propagation of a dynamic shear rupture. The absence of shearing in the pulverized wall rock is taken as evidence that these structures pre-date the subsequent heat-producing frictional slip. In analogy to observations at low pressure we infer that the garnet structures in our experiment result from rapid propagation of a shear fracture even at the high pressure exerted on the sample and thus suggest that brittle deformation is possible at lower crustal to upper mantle depths. (C) 2019 Elsevier B.V. All rights reserved.

Résumé: The Barremian-Aptian interval is considered a turning point in the extensional evolution of the passive Atlantic margin of Morocco. The biostratigraphy and sedimentology study of the coarse-grained clastic deposits of the Essaouira-Agadir Basin (Bouzergoun Fm) indicates that they are entirely late Barremian (Sartousiana p.p. to Sarasini p.p. Zones) and suggests that most of them were deposited in a shallow marine environment, locally impacted by substantial fluvial influences. Facies evolution and the identification of discontinuity surfaces subdivide the unit into seven depositional sequences, two of which are marked by coarse-grained deposits and numerous indications of synsedimentary instability, and are interpreted as tectonically enhanced. These late Barremian tectonic events are interpreted as related to the abrupt uplift of the West Moroccan Arch, a long-lived, NNE-trending positive structure, located east of the Essaouira-Agadir Basin. (C) 2018 Elsevier Ltd. All rights reserved.

Résumé: Rock rheology and density have first-order effects on the lithosphere's response to plate tectonic forces at plate boundaries. Changes in these rock properties are controlled by metamorphic transformation processes that are critically dependent on the presence of fluids. At the onset of a continental collision, the lower crust is in most cases dry and strong. However, if exposed to internally produced or externally supplied fluids, the thickened crust will react and be converted into a mechanically weaker lithology by fluid-driven metamorphic reactions. Fluid introduction is often associated with deep crustal earthquakes. Microstructural evidence, suggest that in strong highly stressed rocks, seismic slip may be initiated by brittle deformation and that wall-rock damage caused by dynamic ruptures plays a very important role in allowing fluids to enter into contact with dry and highly reactive lower crustal rocks. The resulting metamorphism produces weaker rocks which subsequently deform by viscous creep. Volumes of weak rocks contained in a highly stressed environment of strong rocks may experience significant excursions toward higher pressure without any associated burial. Slow and highly localized creep processes in a velocity strengthening regime may produce mylonitic shear zones along faults initially characterized by earthquake-generated frictional melting and wall rock damage. However, stress pulses from earthquakes in the shallower brittle regime may kick start new episodes of seismic slip at velocity weakening conditions. These processes indicate that the evolution of the lower crust during continental collisions is controlled by the transient interplay between brittle deformation, fluid-rock interactions, and creep flow.

Résumé: The postseismic deformation consecutive to the April 25, 2015 Gorkha earthquake (Mw 7.9) is estimated in this paper based on a cGNSS network installed prior to the earthquake and supplemented by 6 cGNSS stations installed after the main shock. Postseismic displacement are obtained from daily time series corrected for interseismic deformation and seasonal variations. The maximum postseismic displacement is found north of the rupture area, where locally it reached 100 mm between the date of the earthquake and late 2016. The post-seismic deformation affects the northern part of the rupture area but not the southern part, along the southern part of the Main Himalayan Thrust (MHT). Three hypotheses for the mechanisms controlling postseismic deformation are tested through numerical simulations of the postseismic time series: (i) viscous relaxation, (ii) afterslip, or (iii) a combination of these two mechanisms. We can exclude postseismic deformation controlled by viscous relaxation of a thick deformation zone along the northern and lower flat of the MHT. However, it is impossible to discriminate between postseismic deformation controlled by either afterslip along the MHT (northern part of the rupture zone, crustal ramp, and lower flat of the MHT) or a combination of afterslip along the MHT (northern part of the rupture zone, crustal ramp) and viscous relaxation controlled by a thin (similar to 3-4 km thick) low-viscosity body centered on the lower flat of the MHT. The occurrence of afterslip along the northern part of the upper flat of the MHT and its longitudinal variations have been established thanks to the densification of GNSS network by our team presented in this paper.

Résumé: Microscale heterogeneities influence failure mechanisms in the crust. To track the microstructural changes in rock samples when loaded until failure, we employed a novel experimental technique that couples dynamic X-ray microtomography imaging with a triaxial deformation apparatus. We studied the brittle failure of Carrara marble under triaxial compression. Dynamic tomographic data revealed the spatial organization of microfractures and damage increments characterizing the precursory activity toward catastrophic failure. We quantified the emergence of scaling relationships between microstructural parameters, including total damage volume, incremental damage volume, the largest connected microfracture, and the applied differential stress. The total volume of microfractures accumulated from the beginning of the experiment as well as the incremental damage showed power law increase. The growth of the largest connected microfracture was related to differential stress as a power law with divergence at failure. The microfracture volume increments were distributed according to a power law with an upper cutoff that itself spanned the entire volume toward failure. These characteristic features of brittle failure in Carrara marble under compression are in agreement with theoretical models that consider failure as a critical phase transition. We also observed that, very close to failure, several power law relationships broke down, which we interpret to be related to the coalescence of the largest microfractures in a finite size volume. Scaling laws and associated exponents computed from our data are compared with predictions made from theoretical and numerical models. Our results show that precursors of macroscopic brittle failure in Carrara marble follow predictable trends.

Résumé: The engines of surface deformation in the Anatolia-Aegean region are a matter of debate, including the origin of the high elevations of the Anatolian plateau. Recent publications based on geological and thermomechanical modelling emphasize the role of dynamic topography in the plateau uplift. However, quantitative estimates of the contribution of dynamic topography are affected by large uncertainties due to insufficient knowledge of the crustal structure, in particular crustal thickness and density. To reduce these uncertainties, we provide a new accurate crustal thickness map of the Anatolia-Aegean domain computed from a large volume of broadband seismic data. In addition, we display high-resolution seismic sections of the internal structure of the crust in Western and Central Anatolia. Density contrasts are derived from the same seismic data set and Bouguer gravity anomaly computed from the EGM2008 model. Our crustal thickness model is highly correlated with the topography suggesting that the Anatolian plateau is close to isostatic equilibrium. The average density difference between crust and upper mantle computed from our crustal model and Bouguer gravity anomaly is low compared to the global average, approximate to 0.315 x10(3)kgm(-3). The ratio of surface elevation to crustal thickness is lower than average, 1/9.4, which also indicates a low-density crust. Differences between isostatic topography and observed topography are overall small (<500m). The east-to-west gradients of crustal thickness and topography changes are nearly constant in between the Taurides and Pontides at the northern and southern borders of Anatolia. The observed constant crustal thickness gradient may indicate a low viscosity lower crust supported by the thin mantle lithosphere evidenced by seismic tomography beneath the Anatolian plateau. We propose that viscous flow in the lower crust has smoothed out lateral changes in the crustal structure expected for such a heterogeneous collage of continental fragments. This flow may originate from gravitational potential energy differences between Eastern Anatolia (thick crust, high elevations) and the Aegean Sea (thin crust, low elevations), suggesting that gravity plays an integral part in the westward escape of Anatolia.

Résumé: Smectite-type clays play a critical role in the trapping of fluids within soil and atmospheric nanoparticles. The hydrodynamics of cation-saturated smectite nanopores are well documented. However, little is known about the influence of small organic compounds. Here we investigate the effects of carbohydrates (glucose and cellobiose), representing an important class of organic compounds, on the hydration and nanopore structures of montmorillonite, a prototypical smectite. To achieve the same amount of adsorbed water, higher relative humidity was required in the presence of the adsorbed carbohydrates than with the clay alone. The decrease in the characteristic micropore water adsorption with the clay-carbohydrate aggregates implied that water adsorption was constrained within the clay nanopore regions. The presence of carbohydrates promoted water retention as a function of gradual decrease in moisture content. Moisture-dependent X-ray diffraction patterns determined that, relative to the mineral alone, greater nanopore sizes were preserved in the presence of the carbohydrates, despite severe dehydration that is expected to induce clay nanopore collapse. Fourier-transform infrared spectroscopy captured disruption in the population of exchangeable waters within the carbohydrate-populated clay nanopores, with some agreement with the measured water-desorption profiling. These new findings demonstrate that carbohydrates can restructure smectite interlayer nanopores and water trapping dynamics.

Résumé: In aquatic environments, the benthic water column exhibits strong concentration gradients of various substances. They result from transfers and chemical reactions that may occur both within this layer, and at the sediment-water interface (SWI). Characterization of these gradients yields important information for the quantification of such processes and transfers. However, it is difficult to actually sample these gradients in the field, since turbulence decreases their vertical scale. This article describes a sampler designed to collect simultaneously 16 discrete water column samples at a centimeter-scale vertical resolution. This small device (40 x 40 x 60 cm) is reliable, safe to handle, and easily deployed from a small boat using a cable or a Scuba diver. It is made of materials compatible with trace element and dissolved gases work, and simultaneously draws samples from various heights above the SWI into 60 mL syringes. The altitude of the sample inlets is field-adjustable. Sampling artifacts are minimized by in situ flushing of tubing dead volumes, by rapid and simultaneous sample collection, and by sampling an undisturbed water-column. Thus, this device can contribute to the characterization of vertical concentration gradients in benthic water-columns. Such gradients of various compounds and metals from two coastal sites (Quiberon Bay and Berre Lagoon) are shown, illustrating the sampler's usefulness to describe and investigate processes in the benthic zone.

Résumé: We use high-resolution Pleiades optical satellite imagery to study the distribution and magnitude of fault slip along the Milun fault surface rupture, which broke during the 2018 Hualien earthquake (M-w 6.4) in eastern Taiwan. Correlation of pre- and postearthquake stereo Pleiades images reveals detailed 3D surface displacements along the 8-km-long Milun fault, with maximum similar to 1 m left-lateral offsets across the fault. Along the northern section of the Milun fault, our correlation results indicate a localized deformation zone, with offset values slightly larger than the maximum offsets reported in the field (similar to 77 cm). To the south, the left-lateral offsets become increasingly distributed, producing arctangent shapes in displacement profiles crossing the fault. In places, the deformation zone reaches widths of 200 + m and can be explained by a shallow east-dipping fault rupture extending from 2 to 3 km depth to 70-120 m below the surface. A very shallow coseismic rupture on the Milun fault is consistent with a shallow locking depth interpreted from previous geodetic analyses from the interseismic period. Despite a few highly discontinuous and irregular surface ruptures reported along the southern section of the fault, our results suggest the main fault slip (up to 1 m) stopped at very shallow depths below the surface, in which similar to 60% of the deformation may be accommodated as off-fault deformation (OFD). In this upper similar to 100 m of the crust, OFD may be promoted by a significant change in material strength, as the fault crosses from bedrock and/or consolidated sediments into weaker, water-rich, poorly consolidated alluvial sediments.

Résumé: In mountainous environments, slow-moving landslides (velocities <100m/year) are a major concern for local populations. Rainfall is often the dominant forcing, and often result in major changes in kinematics which can mask smaller signals related to internal forcings. We focus here on a major (>40Mm(3)) slow-moving landslide in the desert of southern Peru and take advantage of this arid environment to study the internal processes affecting landslide kinematics. We first estimate the ground displacement from time series analysis of Landsat-8 images, spanning a 5.7-year period. Systematic artifacts in the optical time series are shown to correlate with topography, as well as vary seasonally. We apply a novel procedure for correcting these artifacts, which significantly reduces noise in the resulting time series, thereby allowing us to precisely resolve landslide displacements. We find landslide velocities of up to 35m/year, with complex nonlinear interannual pattern, including a period of rapid acceleration. We validate our optically derived time series using Global Navigation Satellite System field measurements and find uncertainties (root-mean-square error) on the moving mass of 1.12 to 1.55m. Sudden acceleration of the landslide body after March 2016 may originate from a mass collapse due to retrogression of the headscarp. By coupling sparse 3-D Global Navigation Satellite System measurements with dense 2-D optical time series data, we show that the headscarp retrogression acts like a wedge, resulting in domino-like tilting of the downward blocks, and accelerates basal sliding over 2years. These observations reveal that the dynamics of this retrogressive landslide are predominantly controlled by sediment supply and that succession of retrogressive and advancing motions is a self-entrainment process.

Résumé: Phyllosilicates are abundant materials both on Earth and Mars, and the weathering of these minerals is an essential part of a wide variety of geochemical cycles. Alteration mainly takes place at the solution-mineral interface and needs to be fully understood in order to correctly model global water-rock interactions. To directly link the physicochemical solution properties to the dominant surface processes controlling phyllosilicate alteration, we used a custom-built hydrothermal atomic force microscope to study in situ the surface reactivity of biotite, phlogopite, and muscovite in contact with aqueous solutions for a broad range of temperatures and pH values. On the basis of our microscopic observations correlated with previously obtained macroscopic dissolution rates, we have constructed a tentative weathering diagram for mica minerals connecting the dominant surface mechanisms and bulk dissolution behavior to the physicochemical solution properties (pH, T, and speciation). The resulting diagram can be divided into two main areas: low-grade weathering occurring at low temperatures and mildly acidic to neutral pH and high-grade weathering taking place at high temperatures and low pH, separated by a transition zone. Each of these areas is characterized by a series of chemical and physical surface processes, which can be related directly or indirectly to incongruent and congruent bulk dissolution. The transition temperatures and pH values depend on the type of mica, with biotite being the most reactive one and muscovite the least reactive one. It is noteworthy that for close to neutral pH conditions the presence of NH4+ shifts the transitions from low- to high-grade weathering to a significantly lower temperature.

Résumé: We tackle the challenging problem of efficient and accurate seismic traveltime computation in 3D anisotropic media by applying the fast-sweeping method to a discontinuous Galerkin (DG)-based eikonal solver. Using this method leads to a stable and highly accurate scheme, which is faster than finite-difference schemes for a given precision, and with a low computational cost compared to the standard Runge-Kutta DG formulation. The integral formulation of the DG method also makes it easy to handle seismic anisotropy and complex topographies. Several numerical tests on complex models, such as the 3D SEG advanced modeling model, are given as illustration, highlighting the efficiency and the accuracy of this new approach. In the near future, these results will be used together with accurate solvers for seismic amplitude and take-off angle computation to revisit asymptotic inversion (traveltime/slope tomography) and imaging approaches (quantitative migration involving amplitudes and angles).

Résumé: We analyzed 21 rockfalls that occurred in limestone cliffs of the Chartreuse Massif (French Alps). These rockfalls were detected both by Terrestrial Laser Scanning or photogrammetry and by a local seismological network. The combination of these methods allowed us to study relations between rockfall properties (location of detachment and impacts areas, volume, geometry, and propagation) and the induced seismic signal. We observed events with different propagation modes (sliding, mass flow, and free fall) that could be determined from digital elevation models. We focused on events that experienced a free fall after their detachment. We analyzed the first parts of the seismic signals corresponding to the detachment phase and to the first impact. The detachment phase has a smaller amplitude than the impact phase, and its amplitude and duration increases with rockfall volume. By measuring the time delay between the detachment phase and the first impact, we can estimate the free-fall height. We found a relation E-s = aE(p)(b) between the potential energy of a rockfall E-p and the seismic energy Es generated during an impact, with a = 10(-8) and b = 1.55 and with a correlation coefficient R-2 = 0.98. We can thus estimate both the potential energy of a block and its free-fall height from the seismic signals. By combining these results, we obtain an accurate estimate of the rockfall volume. The relation between the E-p and E-s was tested on different geological settings and for larger range of volumes using Yosemite, Mount Granier rockfalls, and with a data set of controlled releases of blocks (Hibert et al., 2017, https://doi.org/10.5194/esurf-5-283-2017, https://www.earth-surf-dynam.net/5/283/2017/).

Résumé: Assessing the impact of Quaternary glaciation at the Earth's surface implies an understanding of the long-term evolution of alpine landscapes. In particular, it requires simultaneous quantification of the impact of climate variability on past glacier fluctuations and on bedrock erosion. Here we present a new approach for evaluating post-glacial bedrock surface erosion in mountainous environments by combining terrestrial cosmogenic nuclide Be-10 (TCN) and optically stimulated luminescence (OSL) surface exposure dating. Using a numerical approach, we show how it is possible to simultaneously invert bedrock OSL signals and Be-10 concentrations into quantitative estimates of post-glacial exposure duration and bedrock surface erosion. By exploiting the fact that OSL and TCN data are integrated over different timescales, this approach can be used to estimate how bedrock erosion rates vary spatially and temporally since glacier retreat in an alpine environment.

Résumé: Fibrous particles interact with cells and organisms in complex ways that can lead to cellular dysfunction, cell death, inflammation, and disease. The development of conductive transparent networks (CTNs) composed of metallic silver nanowires (AgNWs) for flexible touchscreen displays raises new possibilities for the intimate contact between novel fibers and human skin. Here, we report that a material property, nanowire-bending stiffness that is a function of diameter, controls the cytotoxicity of AgNWs to nonimmune cells from humans, mice, and fish without deterioration of critical CTN performance parameters: electrical conductivity and optical transparency. Both 30- and 90-nm-diameter AgNWs are readily internalized by cells, but thinner NWs are mechanically crumpled by the forces imposed during or after endocytosis, while thicker nanowires puncture the enclosing membrane and release silver ions and lysosomal contents to the cytoplasm, thereby initiating oxidative stress. This finding extends the fiber pathology paradigm and will enable the manufacture of safer products incorporating AgNWs.

Résumé: Localizing leaks of water and fluids from storage tanks and water reservoirs with geomembranes is an important task for a variety of environmental applications and water resources applications. The minimally intrusive mise-a-la-masse method is used to detect leaks with the current injected inside the reservoir and a return current electrode located remotely. We test a new approach for the inversion of the voltage data using sandbox experiments and numerical modeling. A method similar to the self-potential inversion method is proposed to inverse the voltages recorded around the tank or reservoir. A global objective function with a data misfit term and regularization term is minimized to invert the voltages. In the inversion process, a depth-weighting matrix is used to strengthen the depth resolution of the current source, and the minimum support method is used to avoid oversmoothed results in terms of leak detection. The distributions of electrical current density on the walls of reservoir indicate the position of leaks. The results show that the inversion method with source compaction accurately identifies the location of single leaks. For two separated leaks, there is an obvious bias for the deeper hole and the bias increases with its depth. For three holes, the source compaction method generally identifies the location of the three leaks when their depth ranges are similar. When one of the leaks becomes deeper, localization of the deeper one becomes more difficult. The influence of the size of the leak on the inversion results is also investigated. The inversion algorithm overestimates the depth of small leaks while it slightly underestimates the depth of large leaks. For a leak having the form of a crack, the inversion results using the source compaction method agree with the position of the leak and its shape.

Résumé: We study here a mesoscopic metasurface made of a randomly distributed set of long vertical metallic rods attached to a thin elastic plate. The A(0) Lamb wave propagation is strongly affected by the local change in apparent stiffness of the plate induced by the low-quality factor resonance of the rods. At the resonance, the plate-plus-rods system is allowed to move freely, and plate waves can penetrate into the metamaterial. At the antiresonance, the plate behaves in terms of waves as if it was clamped by the rods in the metamaterial region, which induces large-frequency band gaps. Between the resonant and antiresonant frequencies, the continuous change in effective rigidity results in a continuous change in reflectivity. In the present paper, we aim at measuring the corresponding complex impedance of the metasurface in terms of amplitude and phase. Experimental data are presented to estimate the effective impedance of a locally resonant metasurface, in agreement with theoretical prediction and numerical simulation.

Résumé: Yttrium belongs to the rare earth elements (REEs) together with lanthanides and scandium. REEs are commonly used in modern technologies, and their limited supply has made it necessary to look for new alternative resources. Acid mine drainage (AMD) is a potential resource since it is moderately enriched in REEs. In fact, in passive remediation systems, which are implemented to minimize the environmental impacts of AMD, REEs are mainly retained in basaluminite, an aluminum hydroxysulfate precipitate. In this study, the solid and liquid speciation and the local structure of yttrium are studied in high-sulfate aqueous solutions, basaluminite standards, and samples from remediation columns using synchrotron-based techniques and molecular modeling. Pair distribution function (PDF) analyses and ab initio molecular dynamics density functional theory models of the yttrium sulfate solution show that the YSO4+ ion pair forms a monodentate inner-sphere complex. Extended X-ray absorption fine structure (EXAFS) and PDF analyses show that Y is retained by basaluminite, forming a monodentate inner-sphere surface complex on the aluminum hydroxide surface. EXAFS of the column samples shows that more than 72% of their signal is represented by the signal of basaluminite with which YSO4+ forms an inner-sphere complex. The atomic view of the REE configuration in AMD environments could facilitate a deeper research of REE recovery from waste generated in AMD remediation systems.

Résumé: The deep geological disposal concept is widely accepted by the scientific community for the storage of high activity level nuclear waste. It uses a multi-barrier system to isolate radioactive waste from the hydrosphere and biosphere for hundreds of centuries. The multiple barriers include, from the waste to near-and far-field: metal (e.g., iron or copper) and/or concrete canisters/casks containing the radioactive waste, cement, clay (e.g., smectites) buffer and/or backfill materials, and naturally occurring host rocks (e.g., claystone and granite). The mobility of radionuclides (RNs) is a key issue regarding the safety assessment of nuclear waste repositories, especially for the soluble and mobile RNs, such as I-129, Cl-36, (235,) U-238, Se-79, and Tc-99. Among them, U-235,U- 238, Se-79, Mo-99, and Sb-125 are some of the redox-sensitive RNs whose mobility largely depends on their speciation, i.e., their oxidation states. The interactions of these redox-sensitive RNs with the components of each of the barriers is complex, and it needs to be fully understood for a correct safety assessment. Much progress has been made in the recent years in getting a fundamental understanding of the migration of redox-sensitive RNs in geological media. Here, an overview of the major achievements is presented. In general, the electron donors in repositories can be steel (i.e., zero valent iron), steel reaction products when in contact with groundwater (producing H-2), steel corrosion products (e.g., magnetite, green rust, and ferrous oxyhydroxides), Fe(II)-sulfides (e.g., pyrite, chalcopyrite, and mackinawite), Fe(II)-bearing clays (e.g., Fe-bearing smectites) in claystone, or Fe (II)-bearing mica minerals (e.g., biotite) in granites. All these phases can sorb redox-sensitive RNs and drive reductive immobilization processes. For U and all the redox-sensitive RN oxyanions, the resulting reduced products are the most stable and least soluble phases, such as FeSe2 for Se or UO2 for U, which may be favorably formed in the presence of a high solubility of electron donors and fast reaction kinetics. However, with slow reaction kinetics, metastable reduced mixed species in intermediate oxidation states such as Se(0) and hyper-stoichiometric uranium oxides are produced. In order to characterize the RN-bearing phases and the uptake and reduction pathway, powerful molecular-scale tools such as X-ray photoelectron spectroscopy (XPS) or X-ray absorption spectroscopy (XAS) are commonly used. Here, we provide a comprehensive perspective on the studies addressing interactions of redox-sensitive RNs with the above-mentioned potential barrier.

Résumé: Volcano monitoring and eruption forecasting are based on the observation and joined interpretation of several precursory phenomena. It is thus important to detect new types of precursor and to study their relationship with forthcoming eruptions. In the last years, variations of seismic velocity have been observed in some volcanoes, mainly basaltic, before eruptions. In this paper, we look for velocity variations and waveform decorrelations before the 2014 eruptive sequence of the andesitic Ubinas volcano in Peru. We compute velocity changes by using seismic ambient noise cross-correlation (between pairs of stations) and cross-components correlation (between vertical and horizontal components of single stations), as well as coda wave interferometry of seismic multiplets. With these different approaches, we show that the major explosions that occurred from 13 to 19 April were preceded by a clear velocity decrease and waveform decorrelation. The amplitude of velocity change is generally larger on single-station cross-components correlation than on two-station cross-correlation in all the frequency ranges tested (between 0.1 and 8 Hz). We highlight an apparent anisotropy of velocity change in single station cross-components correlation, with larger amplitudes when correlating vertical and tangential components than using vertical and radial components with respect to the crater. The Mw = 8.1 Iquique earthquake on 1 April 2014 produced also a marked co-seismic velocity drop detected in a high frequency range(3-5 Hz) in both single-station cross-components correlation and cross-correlations. We locate in the horizontal plane and in depth the velocity perturbation and the structural change related with decorrelation. During the main phase of eruptive activity, the velocity decrease at low frequency (0.1-1 Hz) appears to affect the whole edifice mainly at depth of about 1 to 3 km below the surface. The structural perturbation is more concentrated on the south flank of the volcano, a zone that corresponds to an ancient collapse. We suggest that the observed velocity variations are due to the dilatation of the edifice and to microfracturation induced by magma pressurization. The structural change may be locally enhanced by a possible zone of material weakness in the southern sector. The co-seismic velocity perturbation is located mostly in the southeast flank, at depth smaller than 0.5 to 1 km, and may be related to the presence of the hydrothermal system of the volcano. (C) 2019 Elsevier B.V. All rights reserved.

Résumé: This paper presents a new method based on recent optimization technique to detect slow-moving landslides (<150m/year) in time series of displacement field generated by satellite images. Sparse optimization is applied simultaneously on the 3-D data set in space as well as in time. The proposed method takes into account the distinctive signal physical properties in space and time, by enforcing a sparse representation by blocks in space, but a continuing and monotonous representation in time of the landslides. As a result, we show that a mixed l(1,2)-norm is the most suitable norm for this detection problem, compared to pure l(1)-norm or l(2)-norm. Moreover, an outlier estimation step is included that sets apart the Gaussian noise from locally sparse processing errors in the data. The performance of this approach is tested by applying it both on synthetic data and on a time series of displacements fields over 16 dates in the Colca Valley, Peru. This detection presents commission and omission errors for landslides of 29% and 14%, respectively, using a medium resolution (10 m) data set of optical satellite images. It detects all important landslides, already known from field investigations. Moreover, it also points out other smaller or unknown landslides, increasing the existing slow-moving landslide inventory by +50%.

Résumé: Thiol functional groups in natural organic matter form strong complexes with Hg(II) and other soft metal cations and therefore are an important component of sulfur and metal cycling in the environment. However, characterizing thiol reactivity is difficult because natural organic molecules are complex both in composition and molecular structure. Here, reactivity was assessed by calculating the Gibbs free energies of thiolation and thiol deprotonation reactions for model structures considered to form during abiotic sulfurization of natural organic matter. Gaussian calculations were performed at the CCSD(T) level of theory. Thiol addition is predicted to be faster by as much as 8 orders of magnitude on unsaturated cyclic structures rich in ketone and ether linkages than on open-chain carbonyl structures. The RIC, values of thiols added to carboxyl-rich alicyclic molecules are predicted to be above 10, whereas plc values of thiols bonded to lignin-derived polyhydroxyphenols are predicted to be between 2 and 6. Reactivity of thiols with Hg(II) was evaluated by monitoring the kinetics of transformation of Hg(SR)(2) complexes to nanoparticulate metacinnabar in dissolved organic matter with different chemical compositions under oxic conditions using high-energy-resolution X-ray absorption near-edge structure spectroscopy (HR-XANES). The most rapid transformation occurred in the material with the greatest quinone carbon (ketone) and polyphenol contents, consistent with the predicted low pK(a) values of thiolated ketones near phenolic hydroxyl groups. The slowest transformation occurred in the material with the least amount of cyclic ketone structures despite having the highest amount of thiols. These results indicate that the sulfur atoms in thiolated ketones are those that are most reactive and removed during the alkyl transfer reaction considered to nucleate metacinnabar and that the concentration of the low-pK(a) thiols controls the transformation rate.

Résumé: The Central Paratethys was a large-scale Oligo-Miocene epicontinental sea located in Central and Eastern Europe. It was separated from the Mediterranean by the Alpine orogenic belt. The Paratethys progressively flooded the Pannonian back-arc basin that formed during the early to middle Miocene. Along the southern margin of the basin, the maximum extension of the Paratethys onto the flanks of the Dinarides Mountains occurred during the middle Miocene (Badenian). We have studied the most complete middle Miocene (BadenianSarmatian) Paratethys section located at this southern margin. It comprises a > 1.5 Myr long, continuous marine depositional sequence, which is highly relevant for our understanding of the interplay between global climatic and regional geodynamic perturbations in this semi-isolated epicontinental basin. The investigated record is particularly important to assess the impact of the Middle Miocene Climate Transition, the Langhian-Serravallian glacial Mi-3b event, the syn-rift climax of the Pannonian Basin and the Badenian Salinity Crisis. Moreover, we present the first high resolution age model for the regional Badenian stage based on integrated biomagnetostratigraphy. According to our age model, the marine flooding reached the area at similar to 14.15 Ma, during the regional Badenian stage. Open marine conditions persisted until similar to 12.6 Ma when the extinction of the fully marine fauna marks the beginning of the regional Sarmatian stage. Sea-level fluctuations are reflected in the section by four transgressive regressive cycles coinciding roughly with 400-kyr-eccentricity periods. The largest sea-level fall occurred after the first cycle and corresponds to the end of the Middle Miocene Climate Transition marked by glacial event Mi-3b. Elsewhere in the Pannonian Basin, this marked drop in base-level triggered deposition of evaporites during the Badenian Salinity Crisis. At Ugljevik however, there are no evaporites and the short-term Mi-3b regression was followed by a transgression and re-establishment of deeper marine conditions at 13.76 Ma, i.e. during the earliest Serravallian. Diversified planktonic and benthic assemblages suggest fully marine conditions with a persistent connection to the Mediterranean at this time. Such conditions prevailed until the mid Serravallian (latest Badenian) when sediment input increased and coastal environments prograded seawards. The Badenian/Sarmatian boundary roughly coincided with a 400-kyr-eccentricity as well as with a 1.2-Myr obliquity minimum.

Résumé: To describe the energy transport in the seismic coda, we introduce a system of radiative transfer equations for coupled surface and body waves in a scalar approximation. Our model is based on the Helmholtz equation in a half-space geometry with mixed boundary conditions. In this model, Green's function can be represented as a sum of body waves and surface waves, which mimics the situation on Earth. In a first step, we study the single-scattering problem for point-like objects in the Born approximation. Using the assumption that the phase of body waves is randomized by surface reflection or by interaction with the scatterers, we show that it becomes possible to define, in the usual manner, the cross-sections for surface-to-body and body-to-surface scattering. Adopting the independent scattering approximation, we then define the scattering mean free paths of body and surface waves including the coupling between the two types of waves. Using a phenomenological approach, we then derive a set of coupled transport equations satisfied by the specific energy density of surface and body waves in a medium containing a homogeneous distribution of point scatterers. In our model, the scattering mean free path of body waves is depth dependent as a consequence of the body-to-surface coupling. We demonstrate that an equipartition between surface and body waves is established at long lapse-time, with a ratio which is predicted by usual mode counting arguments. We derive a diffusion approximation from the set of transport equations and show that the diffusivity is both anisotropic and depth dependent. The physical origin of the two properties is discussed. Finally, we present Monte Carlo solutions of the transport equations which illustrate the convergence towards equipartition at long lapse-time as well as the importance of the coupling between surface and body waves in the generation of coda waves.

Résumé: We have studied porphyritic olivine-rich chondrules of the carbonaceous chondrite Kaba (CV3) by combined high-resolution X-ray mapping, quantitative electron microprobe analyses, and oxygen isotopic analyses via secondary ion mass spectrometry. These chondrules contain smaller inner-chondrule olivine grains characterized by low refractory element (Ca, Al, Ti) contents, and larger outer-chondrule olivine crystals that are enriched in refractory elements and show complex Ti and Al oscillatory zonings. Our 0 isotopic survey revealed that many of the inner-chondrule olivines are O-16-richer than the relatively isotopically uniform outer-chondrule olivines. Inner-chondrule olivine crystals only a minority of which may be derived from earlier generations of chondrules are likely mostly inherited from nebular condensates similar to AOAs, as they share similar isotopic and chemical features and are thus interpreted as relict grains. Still, being O-16-poorer than most AOAs, they may have experienced significant exchange with a O-16-poor reservoir prior to chondrule formation (even if to a lesser degree than relicts in CM2 and ungrouped C2 chondrites). Subsequent incomplete melting of the relict grains produced Ca-Al-Ti-rich melts that engulfed the remaining relict olivine grains. The complex Ti and Al zoning patterns in outer chondrule (host) olivines, in particular the systematic dilution near the margin, seem to reflect gas-melt interactions (with e.g. SiO (g), Mg (g)) which also buffered the O isotopic composition of chondrule hosts. Together, these results demonstrate that important episodes of recycling of nebular condensates occurred in the solar protoplanetary disk. (C) 2018 Elsevier Ltd. All rights reserved.

Résumé: This paper studies the Porat Formation (Fm.), which was deposited along the NE margin of the Dacian Basin part of the East Carpathian foreland (ECF) during the Pliocene and Early Pleistocene. We use a review of stratigraphic data in combination with lithofacies and sedimentary architecture analysis to interpret the Porat Fm. as a large sandy alluvial basin ilia with an aggradational structure, consisting of cyclic successions of shallow sandy high-energy braided rivers. Aggradation of the Porat Fan was governed by subsidence of the Dacian Basin, along with a northerly supply of water and sediment from the Carpathians. Along the southern margin of the area the fan entered the Reni lzmail-Trough, which formed the periodically active gateway between the Black Sea and Dacian basins. Along this trough, the Porat Fm. is developed in a different facies, discerned as the Dolynske Member (Mb.1), which accumulated in the channel of a large river interpreted as the paleo-Danube. According to mammal stratigraphy of the Porat Fm. this continental-scale river had reached the area by the Gelasian to early Calabrian. The Porat alluvial mull indicates a stable water supply from the Carpathians, which explains the ecologically mixed fauna in its deposits: moistened forested alluvial plain-valleys were present between the zonally semi-arid steppe interfluves. The Porat Fm. and the previously studied late Miocene Balta Fm. are key elements for further in-depth study of the terrestrial evolution (tectonic sedimentary relief) of the ECF and north-western Black Sea coastal regions.

Résumé: Centuries of work have highlighted the importance of several characteristics on fracture propagation. However, the relative importance of each characteristic on the likelihood of propagation remains elusive. We rank this importance by performing dynamic X-ray microtomography experiments that provide unique access to characteristics of evolving fracture networks as rocks are triaxially compressed toward failure. We employed a machine learning technique based on logistic regression analysis to predict whether or not a fracture grows from 14 fracture geometry and network characteristics identified throughout four experiments on crystalline rocks in which thousands of fractures propagated. The characteristics that best predict fracture growth are the length, thickness, volume, and orientation of fractures with respect to the external stress field and the distance to the closest neighboring fracture. Growing fractures tend to be more clustered, shorter, thinner, volumetrically smaller, and dipping closer to 30-60 degrees from the maximum compression direction than closing fractures.

Résumé: To constrain the impact of preexisting mechanical weaknesses on strain localization culminating in macroscopic shear failure, we simulate triaxial compression of layered sedimentary rock using three-dimensional discrete element method simulations. We develop a novel particle packing technique that builds layered rocks with preexisting weaknesses of varying orientations, roughness, and surface area available for slip. We quantify how the geomechanical behavior, characterized by internal friction coefficient, mu(o), and failure strength, sigma(F), vary as a function of layer orientation, theta, interface roughness, and total interface area. Failure of the simulated sedimentary rocks mirrors key observations from laboratory experiments on layered sedimentary rock, including minima sigma(F) and mu(o) for layers oriented at 30 degrees with respect to the maximum compressive stress, sigma(1), and maxima sigma(F), and mu(o) for layers oriented near 0 degrees and 90 degrees to sigma(1). The largest changes in sigma(F), (66%) and mu(o) (20%) occur in models with the smoothest interfaces and largest interface area. Within the parameter space tested, layer orientation exerts the most significant impact on sigma(F), and mu(o). These simulations allow directly linking micromechanical processes observed within the models to macroscopic failure behavior. The spatial distributions of nucleating microfractures, and the rate and degree of strain localization onto preexisting weaknesses, rather than the host rock, are systematically linked to the distribution of failure strengths. Preexisting weakness orientation more strongly controls the degree and rate of strain localization than the imposed confining stress within the explored parameter space. Using the upper and lower limits of mu(o) and sigma(F), obtained from the models, estimates of the Coulomb shear stress required for failure of intact rock within the upper seismogenic zone (7 km) indicates that a rotation of 30 degrees of sigma(1) relative to the weakness orientation may reduce the shear stress required for failure by up to 100 MPa.

Résumé: Satellite Image Time Series (SITS) are large datasets containing spatiotemporal information about the surface of the Earth. In order to exploit the potential of such series, SITS analysis techniques have been designed for various applications such as earthquake monitoring, urban expansion assessment or glacier dynamic analysis. In this paper, we present an unsupervised technique for browsing SITS in preliminary explorations, before deciding whether to start deeper and more time consuming analyses. Such methods are lacking in today's analyst toolbox, especially when it comes to stimulating the reuse of the ever growing list of available SITS. The method presented in this paper builds a summary of a SITS in the form of a set of maps depicting spatiotemporal phenomena. These maps are selected using an entropy-based ranking and a swap randomization technique. The approach is general and can handle either optical or radar SITS. As illustrated on both kinds of SITS, meaningful summaries capturing crustal deformation and environmental phenomena are produced. They can be computed on demand or precomputed once and stored together with the SITS for further usage.

Résumé: Most frequently arsenic is nominally monovalent (As1-) in pyrite (FeS2) and substituted for S. Nominally trivalent arsenic (As3+) has been reported previously in hydrothermal Peruvian pyrite and was considered to be substituted for Fe based on the negative correlation between the concentrations of the two elements. Here, we provide the first observation of the incorporation of As3+ in goldfieldite [Cu-12(As,Sb,Bi)(2)Te2S13] and As5+ in colusite [Cu26V2(As,Sb)(4)Sn2S32] inclusions in As1--pyrite from high-sulfidation deposits in Peru. This information was obtained by combining spatially resolved electron probe (EPMA), synchrotron-based X-ray fluorescence (SXRF), and absorption spectroscopy (micro-XANES and micro-EXAFS) with new high energy-resolution XANES spectroscopy (HR-XANES). The two Cu sulfide inclusions range from several to one hundred micrometers in size, and the As3+/As5+ concentration varies from a few parts per million (ppm) to a maximum of 17.33 wt% compared to a maximum of 50 ppm As1- in pyrite. They also contain variable amounts of Sn (18.47 wt% max), Te (15.91 wt% max), Sb (8.54 wt% max), Bi (5.53 wt% max), and V (3.25 wt% max). The occurrence of As3+/As5+-containing sulfosalts in As1--containing pyrite grains indicates that oxidizing hydrothermal conditions prevailed during the late stage of the mineralization process in the ore deposits from Peru. From an environmental perspective, high concentrations of potentially toxic As, contained in what appear to be non-As-bearing pyrite, may pose a heretofore unrecognized threat to ecosystems in acid mine drainage settings. More generally, the combination of techniques used in this study offers a new perspective on the mineralogy and crystal chemistry of hazardous elements in pyrite, such as highly toxic and little studied thallium.

Résumé: The foundations of a new micromechanical model of rate and state friction are established. Based on the assumption that the relative sliding of two material surfaces is accommodated by the viscoplastic deformation of junctions in their entire volume, the model parameters are characterized in terms of loading conditions, geometrical contact characteristics and rheological properties of the bulk material. A relationship is established between the state parameter of the friction law and the mean microscopic normal stress exerted on the real contact area. Original results are obtained for the transition from stable to unstable slip regimes and applications to geological faults are considered. (C) 2018 Elsevier Ltd. All rights reserved.

Résumé: We use 1 month of continuous seismic waveforms from a very dense seismic network to image with unprecedented resolution the shallow damage structure of the San Jacinto fault zone across the Clark fault strand. After calculating noise correlations, high apparent velocity arrivals coming from below the array are removed using a frequency-wavenumber filter. This is followed by a double-beamforming analysis on multiple pairs of subarrays to extract phase and group velocity information across the study area. The phase and group velocity dispersion curves are regionalized into phase and group velocity maps at different frequencies, and these maps are inverted using a neighbourhood algorithm to build a 3-D shear wave velocity model around the Clark fault down to approximate to 500m depth. The model reveals strong lateral variations across the fault strike with pronounced low-velocity zones corresponding to a local sedimentary basin and a fault zone trapping structure. The results complement previous earthquake- and seismic noise-based imaging of the fault zone at greater depth and clarify properties of structural features near the surface.

Résumé: The Cenozoic history of crustal deformation, surface uplift, and erosion of the central Colorado Plateau (southwestern USA) is distinct from and relatively poorly understood compared with surrounding regions in the North American Cordillera, including the Grand Canyon region and the southwestern Plateau margin. Here, we present new apatite thermochronologic results from Paleozoic-Mesozoic sandstones sampled in the Canyonlands region-the interior of the Colorado Plateau in southeastern Utah. The apatite (U-Th-Sm)/He (He) ages are highly dispersed, with both positive-slope and negative-slope age-effective U (eU) trends. Samples with apatite He results suitable for thermal history modeling are from the Abajo and La Sal mountains intrusive complexes and the Permian, Triassic, and Jurassic rocks sampled near the Colorado River at Lees Ferry, Arizona, and Hite, Utah. Samples with the richest thermal history information have positive-slope apatite He age-[eU] trends, with ages ca. 10 to 5 Ma at [eU] < 10 ppm and ca. 25 to 20 Ma at [eU] > 60 ppm. Modeled thermal histories that best predict this pattern require two periods of rock cooling: one during the middle Cenozoic ca. 30 to 20 Ma and the other since the latest Miocene ca. 6 Ma. The most recent cooling documents the transition from a slowly eroding Miocene landscape to recent rapid erosion that likely postdates 6 Ma and the integration of the modern Colorado River. Middle Cenozoic rock cooling can be attributed to either similar to 1 km of erosion between ca. 25 and 15 Ma, as previous workers have suggested in other parts of the Colorado Plateau region, or relaxation of a geothermal gradient transiently doubled by magmatism associated with the vigorous magmatic flare-up that swept through the region ca. 34 to 20 Ma. The ambiguity of using middle Cenozoic rock cooling as a proxy for erosion in this region means that this event should be described using a nongenetic term: the Middle Cenozoic Cooling Event.

Résumé: Strong volcanic signals simultaneously recorded in polar ice sheets are commonly assigned to major low-latitude eruptions that dispersed large quantities of aerosols in the global atmosphere with the potential of inducing climate perturbations. Parent eruptions responsible for specific events are typically deduced from matching to a known volcanic eruption having coincidental date. However, more robust source linkage can be achieved only through geochemical characterisation of the airborne volcanic glass products (tephra) sometimes preserved in the polar strata. We analysed fine-grained tephra particles extracted from layers of the AD 1259 major bipolar volcanic signal in four East Antarctic ice cores drilled in different widely-spaced locations on the Antarctic Plateau. The very large database of glass-shard geochemistry combined with grain size analyses consistently indicate that the material was sourced from multiple distinct eruptions. These are the AD 1257 mega-eruption of Samalas volcano in Indonesia, recently proposed to be the single event responsible for the polar signal, as well as a newly-identified Antarctic eruption, which occurred in northern Victoria Land in AD 1259. Finally, a further eruption that took place somewhere outside of Antarctica has also contributed to tephra deposition. Our high-resolution, multiple-site approach was critical for revealing spatial heterogeneity of tephra at the continental scale. Evidence from ice-core tephra indicates recurrent explosive activity at the Antarctic volcanoes and could have implications for improved reconstruction of post-volcanic effects on climate from proxy polar records. (C) 2019 Elsevier Ltd. All rights reserved.

Résumé: One of the major applications to be interested by the processes controlling the nucleation (and growth) of minerals are the concrete and the gypsum industries. The available theoretical framework, i.e. classical nucleation theory (CNT), has several shortcomings which limit its ability to describe the complex crystallisation pathways. To address the apparent contradiction rising from CNT in the presence of nucleation retarding polymers (i.e. increase of the interfacial energy vs. formation of emerging nucleus surface-polymer bonds), we have performed induction time experiments to study the effect of various polymers on the nucleation of gypsum (CaSO4 center dot 2H(2)O), and in parallel determined the interfacial energy between aqueous solutions of the same polymers and different faces of macroscopic gypsum crystals by means of contact angle measurements. Based on the collected data, we show that added polymers mainly alter the kinetics of the reaction and do not significantly affect the thermodynamic properties of the system.

Résumé: Since the end of 2013, the region around the two volcanoes Masaya and Momotombo, which includes the Nicaraguan capital Managua, has shown an unusually high seismic and volcanic activity. In December 2015, the Momotombo volcano erupted after 110 years of quiescence. Since mid-December 2015, the Masaya volcano has also shown gradually increasing activity, including the formation of a lava lake in its main crater. By adding 30 broadband stations, we had temporarily (December 2016-March 2017) densified the permanent Nicaraguan seismic network around these volcanoes to study the local seismicity and image the subsurface structure. During the observation period, we observed an overall low level of seismicity. Recorded events around Momotombo likely consist of aftershocks of the M5.5 earthquake that struck this area on September, 26th, 2016. At Masaya, we did not observe volcano-tectonic events. Using the continuous waveform recordings, we perform a 3D ambient seismic noise tomography that reveals a first image of the subsurface velocity structure below the Masaya and Momotombo volcanoes. While Momotombo shows a typical elongated low shear-wave velocity anomaly that reaches depths of about 8 km, Masaya does not show indications of a deep plumbing system. At Masaya, we have indications of a shallow (0-3 km) magmatic chamber, offset to the west and not directly below the active Santiago vent, where the crater lake is located At greater depth (3-8 km) a low velocity anomaly towards the northeast coincides in location with a modelled positive gravity anomaly and could indicate the presence of a former intrusive body. With this study we want to trigger further interest in the diverse tectonic and volcanic features of Nicaragua. Future, long-term seismic imaging and monitoring projects are of critical interest for the estimation of seismic and volcanic risks in Managua and the surroundings. (C) 2019 Elsevier B.V. All rights reserved.

Résumé: The 2018 Klauea eruption was a complex event that included deformation and eruption at the summit and along the East Rift Zone. We use ambient seismic noise interferometry to measure time-lapse changes in seismic velocity of the volcanic edifice prior to the lower East Rift Zone eruption. Our results show that seismic velocities increase in relation to gradual inflation of the edifice between 1 March and 20 April. In the 10 days prior to the 3 rd of May eruption onset, a rapid seismic velocity decrease occurs even though the summit is still inflating. We confirm that intereruptive velocity change is correlated with surface deformation, while the velocity decrease prior to eruption is likely due to accumulating damage induced by the pressure exerted by the magma reservoir on the edifice. The accumulating damage and subsequent decrease in bulk edifice strength may have facilitated increased transport of magma from the summit reservoir to the Middle East Rift Zone.

Résumé: The variety of coral reefs morphologies highlights their sensitivities to several forcings; fossil reefs stack in sequences that are accordingly diverse. In order to understand their genesis and architectures, we devised a numerical approach, accounting for Quaternary sea level oscillations, vertical land motion, initial slope, wave erosion, and reef growth. We first test our model on the subsiding sequence of Hawaii and on the uplifting sequence of Wangi-Wangi (Sulawesi) that bears active barriers. We then construct a parametric study that we analyze based on a comprehensive yet compact description of sequences as barcodes, that depict the vertical distribution of a few geometrical characteristics (number, width, and height of the terraces and barriers). We find that geological factors suffice to explain the variety of architectures of reefal sequences at first order, regardless of additional ecosystemic processes. Vertical land motion and foundation slopes are the prime players, while reef growth rates only play a minor role. Barriers may develop both in uplift and subsidence mode, and their preservation attests for the erosional power. Last, we reappraise the genesis of sequences and find that sequences do not fingerprint discrete events of sea level oscillations but a continuous process harrowed by stochastic events: Major sea level fluctuations can be overrepresented by several terraces or conversely absent; reoccupations may yield composite terraces representing multiple events. Overall, sequences shall not be regarded as stacks of reef bodies forming during sea level highstands, which implies that the commonly assumed bijective relationship between sea level highstands and terraces shall be abandoned.

Résumé: Mercury (Hg) concentration in fish of the Gulf of the Mexico (GoM) is a major concern due to the importance of the GoM for U.S. fisheries. The Deepwater Horizon (DWH) oil spill in April 2010 in the northern GoM resulted in large amounts of oil and dispersant released to the water column, which potentially modified Hg bioaccumulation patterns in affected areas. We measured Hg species (methylmercury (MMHg) and inorganic Hg (IHg)) concentrations, and light (C, N and S) and Hg stable isotopes in muscle and liver tissues from tilefish (Lopholatilus chamaleonticeps) sampled in 2012 and 2013 along the shelf break of the northeastern GoM. Fish located close to the mouth of the Mississippi River (MR) and northwest of the DWH well-head (47 km) showed significantly lower Hg levels in muscle and liver than fish located further northeast of the DWH (>109 km), where 98% of tilefish had Hg levels in the muscle above US consumption advisory thresholds (50% for tilefish close to the DWH). Differences in light and Hg stable isotopes signatures were observed between these two areas, showing higher delta N-15, and lower delta Hg-202, Delta Hg-199 and delta S-34 in fish close to the DWH/MR. This suggests that suspended particles from the MR reduces Hg bioavailability at the base of the GoM food chains. This phenomenon can be locally enhanced by the DWH that resulted in increased particles in the water column as evidenced by the marine snow layer in the sediments. On the other hand, freshly deposited Hg associated with organic matter in more oligotrophic marine waters enhanced Hg bioaccumulation in local food webs. Comparing Hg isotopic composition in liver and muscle of fish indicates specific metabolic response in fish having accumulated high levels of MMHg. (C) 2019 Published by Elsevier B.V.

Résumé: The cumulative effects of periodic redox cycling on the mobility of As, Fe, and S from alluvial sediment to groundwater were investigated in bioreactor experiments. Two particular sediments from the alluvial floodplain of the Mekong Delta River were investigated: Matrix A (14 m deep) had a higher pyrite concentration than matrix B (7 m deep) sediments. Gypsum was present in matrix B but absent in matrix A. In the reactors, the sediment suspensions were supplemented with As(III) and SO42-, and were subjected to three full-redox cycles entailing phases of nitrogen/CO2, compressed air sparging, and cellobiose addition. Major differences in As concentration and speciation were observed upon redox cycling. Evidences support the fact that initial sediment composition is the main factor controlling arsenic release and its speciation during the redox cycles. Indeed, a high pyrite content associated with a low SO42- content resulted in an increase in dissolved As concentrations, mainly in the form of As(III), after anoxic half-cycles; whereas a decrease in As concentrations mainly in the form of As(V), was instead observed after oxic half-cycles. In addition, oxic conditions were found to be responsible for pyrite and arsenian pyrite oxidation, increasing the As pool available for mobilization. The same processes seem to occur in sediment with the presence of gypsum, but, in this case, dissolved As were sequestered by biotic or abiotic redox reactions occurring in the Fe-S system, and by specific physico-chemical condition (e.g. pH). The contrasting results obtained for two sediments sampled from the same core show that many complexes and entangled factors are at work, and further refinement is needed to explain the spatial and temporal variability of As release to groundwater of the Mekong River Delta (Vietnam). (C) 2019, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

Résumé: Viscoelastic full-waveform inversion is recognized as a challenging task for current acquisition deployment at the crustal scale. We have developed an efficient formulation based on a time-domain spectral-element method on a flexible Cartesian-based mesh. We consider anisotropic elastic coefficients and isotropic attenuation. Complete gradient expressions including the attenuation contribution spread into those of elastic components are given in a consistent way. The influence of attenuation on the P-wave velocity reconstruction is illustrated through a toy configuration. The numerical implementation of the forward problem includes efficient matrix-vector products for solving second-order elastodynamic equations for 3D geometries: An original high-order integration for topography effects is performed at nearly no extra cost. Combined adjoint and forward field recomputation from the final state and previously saved boundary values allows the estimation of misfit gradients for density, elastic parameters, and attenuation factors with no I/O efforts. Two-level parallelism is implemented over the sources and domain decomposition, which is necessary for a realistic 3D configuration. The misfit gradient preconditioning is performed by a so-called Bessel filter using an efficient differential implementation based on finite-element ingredients on the forward mesh instead of the often-used, costly convolution approach. A 3D synthetic illustration is provided on a subset (2 x 7 x 3 km) of the SEG Advanced Modeling (SEAM) Phase II Foothills model with 4 lines of 20 sources. The structurally based Bessel filter and a simple data hierarchy strategy considering early body waves before all waves including surface waves allow a precise reconstruction of the P- and S-wavespeeds while keeping a smooth density description.

Résumé: In hydrodynamic and MHD (magnetohydrodynamic) turbulence, formal expressions for the transfer rates rely on integrals over wavenumber triads (k, p, q) satisfying k + p + q = 0. As an example S-E(uu) (k vertical bar p, q) denotes the kinetic energy transfer rate to the mode k, from the two other modes in the triad, p and q. However as noted by Kraichnan (Phys. Rev., vol. 111, 1958, pp. 1747-1747), in S-E(uu) (k vertical bar p, q), what fraction of the energy transferred to the mode k originated from p and which from q is unknown. Such an expression is thus incongruent with the customary description of turbulence in terms of two-scale energy exchange. Notwithstanding this issue, Dar et al. (Physica D, vol. 157 (3), 2001, pp. 207-225) further decomposed these transfers into separate contributions from p-to-k and q-to-k, thus introducing the concept of mode-to-mode transfers that they applied to MHD turbulence. Doing so, they had to set aside additional transfers circulating within each triad, but failed to calculate them. In the present paper we explain how to derive the complete expressions of the mode-to-mode transfers, including the circulating transfers. We do it for kinetic energy and kinetic helicity in hydrodynamic turbulence, for kinetic energy, magnetic energy and magnetic helicity in MHD turbulence. We find that the degree of non-uniqueness of the energy transfers derived from the induction equation is a priori higher than the one derived from the Navier-Stokes equations. However, separating the contribution of magnetic advection from magnetic stretching, the energy mode-to-mode transfer rates involving the magnetic field become uniquely defined, in striking contrast to the hydrodynamic case. The magnetic helicity mode-to-mode transfer rate is also found to be uniquely defined, contrary to kinetic helicity in hydrodynamics. We find that shell-to-shell transfer rates have the same properties as mode-to-mode transfer rates. Finally calculating the fluxes, we show how the circulating transfers cancel in accordance with conservation laws.

Résumé: Investigation of Holocene extents of mountain glaciers along with the related naturally-driven climate conditions helps improve our understanding of glacier sensitivity to ongoing climate change. Here, we present the first Holocene glacial chronology in the Mont-Blanc massif (Argentiere glacier) in the French Alps, based on 25 in situ-produced cosmogenic Be-10 dates of moraines and glacial bedrocks. The obtained ages from mapped sequences of moraines at three locations reveal that the glacier retreated from its Lateglacial extent and oscillated several times between similar to 11.7 ka and similar to 10.4 ka, i.e. during the Younger Dryas/Early Holocene (YD/EH) transition, before substantially retreating at similar to 10.4 ka. Climate conditions corresponding to the past extents of Argentiere glacier during the YD/EH transition (similar to 11 ka) and the Little Ice Age (LIA) were modelled with two different approaches: by determining summer temperature differences from reconstructed ELA-rises and by using a Positive Degree Day (PDD) mass-balance model. The ELA-rise reconstructions yield a possible range of temperatures for the YD/EH transition that were lower by between 3.0 and 4.8 degrees C compared to the year 2008, depending on the choice of the ELA sensitivity to temperature. The results from the PDD model indicate temperatures lower by similar to 3.6-5.5 degrees C during the YD/EH transition than during the 1979-2002 period. For the LIA, our findings highlight the role of local precipitation changes, superimposed on the dominant temperature signal, in the detailed evolution of the glacier. Overall, this study highlights the challenge that remains in accurately inferring paleoclimate conditions from past glacier extents. (C) 2019 Elsevier Ltd. All rights reserved.

Résumé: During the Albian, the hyperextension of the Pyrenean passive margin led to a hyperthinning of the continental crust and the subsequent subcontinental mantle exhumation. The giant Trimouns talc-chlorite deposit represents the most prominent occurrence of Albian metasomatism in the Pyrenees, with the occurrence of the largest talc deposit worldwide. Consequently, this deposit, which is located on a fault zone and a lithological contact, represents one of the major drains at the scale of the Pyrenees and one of the best geological targets in order to determine the origin(s) of the fluid(s) that circulated during this period. Talc-chlorite ore is characterized by the presence of brines trapped in dolomite, quartz, and calcite fluid inclusions in the vicinity of the talc-rich zone. Considered as being responsible for the formation of talc, these fluids may be interpreted in several ways: (i) primary brines expelled from Triassic evaporites, (ii) secondary brines produced through halite leaching by diagenetic/metamorphic fluids, and (iii) brines derived from seawater serpentinization of mantle rocks. Stable isotope analyses (delta C-13, delta O-18, delta D, and delta Cl-37) and Cl/Br ratio measurements in fluid inclusions and their host minerals were carried out in order to determine the origin of the fluid(s) involved in the formation of the ore deposit. The data are consistent with a primary brine origin for the mineralizing fluid, which could have been expelled from the Triassic levels. Other hypotheses have been tested, for example, the production of brines via the seawater concentration during serpentinization. The geochemical proxies used in this study provide equivocal results. The first hypothesis is by far the most realistic one considering the numerous occurrences of Trias formations nearby, their deformation during the extension, and the drainage of the expulsed brines as evidenced by the high-salinity fluid inclusions found all around the deposit. Alternatively, the exhumation of the mantle is considered as a major source of heat and stress that favored brine migration along the major shear zones. Our results fit well with brine circulation in a hyperextensional geodynamic context, which is related to the formation of the talc-chlorite ore, the thinning of the continental crust, and the exhumation of the subcontinental mantle, in accordance with recent works.

Résumé: The relatively short eruption period of Merapi volcano is the reason for many earth scientists to investigate the processes that occur both beneath the surface and at the top of the volcano. The DOMERAPI seismic network consisting of 53 seismic stations was installed to understand the characteristics of the main magma reservoir under the volcano with a period of data recording from October 2013 to mid-April 2015. A total of 464 earthquakes were detected by DOMERAPI seismic network with the majority of the earthquake occured outside the seismic network because the volcano was inactive at that time. The earthquakes are used to delineate the main magma reservoir beneath the volcano. The main magma reservoir was identified at a depth of 15 km below mean sea level (MSL,) which is characterized by high Vp, a high Vp/Vs ratio and low Vs. The existence of shallow magma reservoirs related to fluid percolation was also clearly identified in this study which was at a depth of less than 5 km below MSL which was characterized by low Vp, a high Vp/Vs ratio and low Vs. The existence of deep magma reservoir was not identified in this study because of the limited resolution of seismic data.

Résumé: Gravimetric methods are expected to play a decisive role in geophysical modeling of the regional crustal structure applied to geoneutrino studies. GIGJ (GOCE Inversion for Geoneutrinos at JUNO) is a 3-D numerical model constituted by 46x10(3) voxels of 50x50x0.1km, built by inverting GOCE (Gravity field and steady-state Ocean Circulation Explorer) gravimetric data over the 6 degrees x4 degrees area centered at the JUNO (Jiangmen Underground Neutrino Observatory) experiment, currently under construction in the Guangdong Province (China). The a priori modeling is based on the adoption of deep seismic sounding profiles, receiver functions, teleseismic P wave velocity models, and Moho depth maps, according to their own accuracy and spatial resolution. The inversion method allowed for integrating GOCE data with the a priori information and some regularization conditions through a Bayesian approach and a stochastic optimization. GIGJ fits the highly accurate and homogeneously distributed GOCE gravity data with a 1 mGal standard deviation of the residuals, compatible with the observation accuracy. GIGJ provides a site-specific subdivision of the crustal layers masses, of which uncertainties include estimation errors, associated to the gravimetric solution, and systematic uncertainties, related to the adoption of a fixed sedimentary layer. A consequence of this local rearrangement of the crustal layer thicknesses is a 21% reduction and a 24% increase of the middle and lower crust geoneutrino signal, respectively. The geophysical uncertainties of geoneutrino signals at JUNO produced by unitary uranium and thorium abundances distributed in the upper, middle, and lower crust are reduced by 77%, 55%, and 78%, respectively. The numerical model is available at this site (http://www.fe.infn.it/radioactivity/GIGJ).

Résumé: Understanding the approach to faulting in continental rocks is critical for identifying processes leading to fracturing in geomaterials and the preparation process of large earthquakes. In situ dynamic X-ray imaging and digital volume correlation analysis of a crystalline rock core, under a constant confining pressure of 25 MPa, are used to elucidate the initiation, growth, and coalescence of microfractures leading to macroscopic failure as the axial compressive stress is increased. Following an initial elastic deformation, microfractures develop in the solid, and with increasing differential stress, the damage pervades the rock volume. The creation of new microfractures is accompanied by propagation, opening, and closing of existing microfractures, leading to the emergence of damage indices that increase as powers of the differential stress when approaching failure. A strong spatial correlation is observed between microscale zones with large positive and negative volumetric strains, microscale zones with shears of opposite senses, and microscale zones with high volumetric and shear strains. These correlations are attributed to microfracture interactions mediated by the heterogeneous stress field. The rock fails macroscopically as the microfractures coalesce and form a geometrically complex 3D volume that spans the rock sample. At the onset of failure, more than 70% of the damage volume is connected in a large fracture cluster that evolves into a fault zone. In the context of crustal faulting dynamics, these results suggest that evolving rock damage around existing locked or future main faults influences the localization process that culminates in large brittle rupture events.

Résumé: An experimental work is undertaken to understand the effect of the differential pressure (in the range 3-20.7 MPa) upon the complex conductivity of sedimentary rocks. We use five sandstone core samples from outcrops and a sandstone analog built from sintered glass beads. The spectra were fitted with a Cole-Cole complex conductivity model and the four Cole-Cole parameters were plotted as a function of the differential stress (in the range 3-20.7 MPa). The Cole-Cole relaxation times are analysed in terms of the evolution of the pore size with the differential pressure. Neither the relaxation time nor the Cole-Cole exponent show a strong dependence with the differential pressure indicating that the distribution of the relaxation times remains here roughly the same when the differential stress increases. More specifically, the Cole-Cole exponent does not describe the entire distribution of relaxation times, but the broadness of this distribution. Since the relaxation times are related to the pore sizes, this means that the pore sizes do not depend on the differential pressure in this case. The chargeability is essentially independent of the differential pressure and close to the upper value that can be reached in rocks without metallic particles. This also means that the conductivity of these rocks is dominated by their surface conductivity contribution considering the low pore water salinity used in this work. These results are interpreted thanks to the Stern layer polarization model. The Stern layer denotes the inner part of the electrical double layer coating the surface of the grains. The predictions of this model are mostly consistent with the data.

Résumé: We consider a mixture made of dispersed metallic particles immersed into a background material saturated by an electrolyte. Below the freezing temperature (typically 0 degrees C to -4 degrees C), a fraction of the liquid water in the pore space is transformed into ice, whereas the salt remains segregated into the liquid-pore water solution. Our goal is to understand how freezing affects the complex conductivity (induced polarization) of such mixtures. Complex conductivity measurements (96 spectra) are performed in a temperature-controlled bath equipped with a high-precision impedance meter. We cover the temperature range from +20 degrees C to -15 degrees C to -18 degrees C and the frequency range from 10-2 Hz to 45 kHz. The spectra are fitted with a double Cole-Cole complex conductivity model. A finite-element model is used to further analyze the mechanisms of polarization by considering an intragrain polarization mechanism for the metallic particles and a change of the conductivity of the background material modeled with an exponential freezing curve. This curve is used to relate the liquid water content to the temperature. In the context of freezing, we test all the aspects of the intragrain polarization model developed in the previous papers of this series, at least for a weakly polarizable background material. The Cole-Cole exponent and the chargeability are observed to be essentially independent of temperature including in freezing conditions. This means that all the relaxation times of the system follow the same temperature dependence and that the chargeability is controlled by the volume fraction of metal. The instantaneous conductivity (high-frequency conductivity) and the relaxation times depend on the temperature in a predictable way, and their product can be considered to be essentially temperature independent. The analytical and numerical models can reproduce the inverse relationship between the relaxation time and the instantaneous conductivity.

Résumé: The Historic Sanctuary of Machu Picchu (Cusco, Peru) is one of the most important archaeological monuments in Peru and worldwide. Machu Picchu is classified as a UNESCO World Heritage site and at risk from climatic change. However, the seismic centennial history of Peru reports large earthquakes generated both along the subduction zone (Mw8) and on active crustal faults along the Andean Cordillera (Mw7). It is therefore important to know if Machu Picchu is located in an area of seismic hazard and then to take measures to mitigate potential seismic hazards. Due to the short historical earthquake catalogue (< 500 years) and the absence of significant recent instrumental seismicity in the site's vicinity (radius of < 30 km), our knowledge about the seismic hazard in Machu Picchu is limited. The earthquakes of 1650 and 1950 affected Cusco city and surrounding areas, but without damage descriptions in Machu Picchu (80 km away) (Silgado Ferro 1978). In this study, we make the first attempt to use the analysis of earthquake archaeological effects (EAEs) and their differentiation from the effects generated by slope movements (creep) to investigate the past occurrence of strong earthquakes at the site. The application of geological structural analysis to the deformations observed in Machu Picchu shows two directions of the mean ground movement: N020 degrees E and N110 degrees E. Two earthquakes that affected Machu Picchu during its construction generated these directions. This kind of data should be used in the future to protect this important archaeological site.

Résumé: Episodic tremor and accompanying slow slip are observed at the down-dip edge of subduction seismogenic zones. While tremors are the seismic signature of this phenomenon, they correspond to a small fraction of the moment released; thus, the associated fault slip can be quantified only by geodetic observations. On continental strike-slip faults, tremors have been observed in the roots of the Parkfield segment of the San Andreas fault. However, associated transient aseismic slip has never been detected. By making use of the timing of transient tremor activity and the dense Parkfield-area global positioning system network, we can detect deep slow slip events (SSEs) at 16-km depth on the Parkfield segment with an average moment equivalent to M-w 4.90 +/- 0.08. Characterization of transient SSEs below the Parkfield locked asperity, at the transition with the creeping section of the San Andreas fault, provides new constraints on the seismic cycle in this region.

Résumé: In this paper we study the enstrophy transfers in helical turbulence using direct numerical simulation. We observe that the helicity injection does not have significant effects on the inertial-range energy and helicity spectra (similar to k(-5/3)) and fluxes (constants). We also calculate the separate contributions to enstrophy transfers via velocity-to-vorticity and vorticity-to-vorticity channels. There are four different enstrophy fluxes associated with the former channel or vorticity stretching, and one flux associated with the latter channel or vorticity advection. In the inertial range, the fluxes due to vorticity stretching are larger than that due to advection. These transfers too are insensitive to helicity injection.

Résumé: We introduce a site factor computation method for a region by extending the site-specific and probabilistic site amplification approach in Bazzuro and Cornell (2004). The site-factor exceedance probability is estimated from the exceedance probabilities of the reference rock ground motion and the soil amplification conditioned on the reference rock ground motion. The former probability is represented by regional hazard curves. The latter probability is computed from soil amplification models. The proposed method is capable of yielding site factors for a target exceedance probability. This property does not exist in the current code-based site factors. Given a site class, if the site factors and the reference rock spectrum possess the same exceedance probability the resulting spectrum would have the same probability of exceedance. The use of such probabilistically consistent earthquake demands would be more relevant for probability-based seismic design and assessment. Owing to the use of hazard curves, the proposed method can account for regional seismicity in the computation of site factors.

Résumé: Drastic paleogeography changes in the Indonesian archipelago over the Plio-Pleistocene, either in response to sea level oscillations or vertical land motion, enabled the periodic emergence of the Sunda shelf. When emerged, this wide continental platform in the heart of the Maritime Continent may have modified regional and global climate systems. We investigate the effect of the exposure of the Sunda shelf on climate dynamics using a set of numerical simulations with (i) atmosphere-land surface and (ii) fully coupled general circulation models. We first explore the impact of convection schemes on the rainfall regime simulated over the Maritime Continent and show how they could explain the discrepancies among previous studies. We further depict a robust and common mechanism that prevails. We show that diurnal heating of the surface of the continental platform enhances low-level convergence and local convection, and fosters local precipitations. This effect, to a second order, is modulated by the radiative effect and increased turbulent heat flux driven by vegetated surface properties such as albedo or roughness. Increasing precipitations over the exposed platform also impacts freshwater export into seawater, making salinity of the Indian Ocean and Indonesian Throughflow highly dependent on the routing scheme over the exposed shelf.

Résumé: A triplet of M-w similar to 6 earthquakes on 2017 December 1-12 occurred similar to 50 km north of Kerman, Iran, in an area of mountainous topography where several major right-lateral strike-slip fault systems-the Gowk, Nayband, Lakar Kuh and Kuh Banan faults-converge. Here we assess their source parameters and surficial expression using regional and teleseismic waveforms and arrival times, synthetic aperture radar interferometry, optical satellite image correlation and field observations. All three main shocks occurred on shallow reverse faults associated with the southern termination of the Lakar Kuh right-lateral strike-slip fault. The first two main shocks on 1 December and 12 December (08: 43 UTC) likely ruptured and reruptured a previously unrecognized, blind, NE-dipping fault beneath the Mian Kuh range. Slip in both earthquakes extends much further along strike than down dip, hinting at structural or stratigraphic controls on rupture dimensions. The thirdmain shock on 12 December (21: 41 UTC) is perhaps the most interesting of the three events. It ruptured a conjugate SW-dipping thrust in the hangingwall of the first fault, generating a sinuous fault scarp in the alluvial plain north of the Mian Kuh range, consistent with its unusually shallow centroid depth of similar to 2 km. Its high ratio of net surface slip (average similar to 1.5 m and maximum similar to 2.5 m) to length (similar to 7 km) and its narrow down-dip width (similar to 6 km) implies a very high stress drop. The surface rupture aligns along-strike with larger scarps that contain uplifted and incised fan surfaces in their hangingwalls, but this subtle expression of active faulting had not been fully recognized prior to these earthquakes. The clustering in space and time of large, shallow earthquakes on hidden faults is of broad concern for seismic hazard assessment in mountainous parts of Iran and in other collisional settings.