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Résumé: The paleoseawater temperature record from the oxygen isotope compositions of fossil foraminifera tests may be biased by up to about 1 degrees C due to grain-boundary diffusion alone, according to isotope exchange experiments on foraminifera tests. The oxygen isotopic compositions of fossil foraminifera tests constitute a continuous proxy record of deep-ocean and sea-surface temperatures spanning the last 120 million years. Here, by incubating foraminifera tests in O-18-enriched artificial seawater analogues, we demonstrate that the oxygen isotopic composition of optically translucent, i.e., glassy, fossil foraminifera calcite tests can be measurably altered at low temperatures through rapid oxygen grain-boundary diffusion without any visible ultrastructural changes. Oxygen grain boundary diffusion occurs sufficiently fast in foraminifera tests that, under normal upper oceanic sediment conditions, their grain boundaries will be in oxygen isotopic equilibrium with the surrounding pore fluids on a time scale of <100 years, resulting in a notable but correctable bias of the paleotemperature record. When applied to paleotemperatures from 38,400 foraminifera tests used in paleoclimate reconstructions, grain boundary diffusion can be shown to bias prior paleotemperature estimates by as much as +0.86 to -0.46 degrees C. The process is general and grain boundary diffusion corrections can be applied to other polycrystalline biocarbonates composed of small nanocrystallites (<100 nm), such as those produced by corals, brachiopods, belemnites, and molluscs, the fossils of which are all highly susceptible to the effects of grain boundary diffusion.

Résumé: In seismology, the rupture mechanisms of an earthquake, a glacier stick-slip and a landslide are not directly observed, but inferred from surface measurements. In contrast, laboratory experiments can illuminate near field effects. The near field reflects the rupture mechanism but is highly attenuated in the case of real-world surface data. We directly image the elastic wave-field of a nucleating rupture non-invasively in its near-field with ultrasound speckle correlation. Our imaging yields the particle velocity of the full shear wave field at the source location and inside the 3D frictional body. We experimentally show that a strong bimaterial contrast, as encountered in environmental seismology, yields a unidirectional or linear force mechanism for pre-rupture microslips and decelerating supershear ruptures. A weak contrast, characteristic for earthquakes, generates a double-couple source mechanism for sub-Rayleigh ruptures, sometimes preceded by slow deformation at the interface. This deformation is reproduced by the NF of a unidirectional force.

Résumé: Background Strategies to reduce the environmental impact of health care are often limited to greenhouse gas emissions. To broaden their scope, our aim was to determine the evolution of the resource footprints, dependency, and efficiency of health-care systems and to determine the relationship between this evolution and their Healthcare Access and Quality (HAQ) index.Methods We carried out an input-output analysis of 49 health-care systems from 1995 to 2015. We harmonised the EXIOBASE v3.8.2 database-providing data for 49 world regions-to the World Health Organization Health Expenditures Database. We then performed a panel data analysis to understand the relationship between Healthcare Access and Quality index and energy footprint per capita of health-care systems. EXIOBASE3 does not provide measurement errors so it was not possible to propagate the uncertainties as can be done with other input-output databases.Findings Health-care systems' footprint increased over the past two decades, reaching 7% of global non-metallic minerals footprint, 4% of global metal ores footprint, and 5% of global fossil fuels footprint in 2013. This increase was mostly due to China, rising from 7% of the non-metallic minerals footprint in 1995 to 45% in 2013. 80% of the health-care systems studied were dependent at more than 50% on fossil fuel imports. The energy footprint per capita was correlated exponentially with the HAQ index but some countries performed much better than others at a given energy footprint. Health-care systems have not become more efficient between 2002 and 2015.Interpretation Health-care systems' resources footprint are exponentially linked to their HAQ. Both prevention and efficiency measures will be needed to change this relationship. If it is not enough, high-income countries will have to choose between further reducing the resource consumption of their health-care systems or shifting the efforts to other sectors, health being considered an incompressible need. We call for the creation of a HAQE (health-care access, quality, and efficiency) index that would add resource efficiency to access and quality when ranking health-care systems.Funding The Shift Project.Copyright (c) The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND IGO license.

Résumé: The role of volatile exsolution in triggering volcanic eruption is re-evaluated using numerical simulations of a growing and solidifying magma chamber. The modelled magma chamber is silicic, emplaced at about 2 Kbar, and H2O-saturated. The rate of volume additions to the chamber by the release of volatiles is controlled by cooling and solidification and is significantly lower than magma infilling rates. Thus, the increase in volume due to volatile exsolution is unlikely to be the primary cause of magma chamber failure unless the magma chamber is already on the brink of failure. However, the formation of buoyant H2O rich layers within the mush that sur-rounds the magma chamber makes the system gravitationally unstable. If the host rock is not permeable and volatiles accumulate, their buoyancy might overcome the strength of the wall resulting in dyke injection and possibly an eruption. Eruptions that are triggered or facilitated by volatiles exsolution are associated to the presence of mush in the chamber and are expected to be crystal-rich. Triggering of eruption by volatiles buoyancy explains the common occurrence of large ranges of crystals ages and protracted crystal residence times at low temperature.

Résumé: Wang et al. (2023) propose that rocks adjacent to the Panzhihua intrusion are not marbles and skarns, but carbonatites. If true, this interpretation could have important implications for models explaining the origin of the large Fe-Ti ore deposits in the intrusion. We reject this interpretation for two principal reasons: 1) the objects described as “mantle xenoliths”, and considered, incorrectly, as diagnostic of carbonatite, are in fact deformed and altered mafic/ultramafic intrusions; 2) the concentrations of incompatible trace elements in the marbles are low and typical of metasedimentary rocks, not carbonatite.

Résumé: We report here a slow-moving landslide complex of the lateral spreading type revealed by Sentinel-1 interferometric time-series analysis. Located along the western coast of the Aral Sea, with a >150-km length and 3-km width, a giant active landslide complex, slides with a constant velocity of up to 60 mm/year. Systematic subsidence up to 5 mm/year is also observed along narrow strips of terraces that appear to result from rotations of fault-bounded blocks. The landslide deformation velocity does not correlate with the annual variations of the water level in the southwestern lake of the Aral Sea during the observation period of 2014-2022, indicating a long-term forcing of this landslide that is rather interpreted to be caused by the long-term sea-level drop. The lateral spreading involves the competent limestone beds lying horizontally on plastic clay-and evaporite-rich layers. We propose a conceptual model for the kinematic of landslides that appear to be controlled by the attitude of bedding, lithological sequence, hydrogeology, and low angle faults.

Résumé: Thermochronological data are essential to constrain thermal and exhumation histories in active mountain ranges. In the Central Andes, bedrock outcrops are rare, being blanketed by widespread late Palaeogene-Neogene and younger volcanic formations. For this reason, the exhumation history of the Western Cordillera (WC) in the Peruvian Andes has only been investigated locally along the mountain range. Dense thermochronological data are only available in canyons of the Arequipa (16 degrees S) and Cordillera Negra regions (10 degrees S). We present new apatite (U-Th)/He and fission-track data from the 1 km deep Canete Canyon (13 degrees S), where the Oligo-Miocene deposits are preserved lying conformably on an Eocene palaeo-topographic surface. Thermal modelling of thermochronological data indicate that the 30-20 Ma ignimbrite deposits overlying the bedrock were thick enough to cause burial reheating. We demonstrate that burial associated with thick volcanic formations should be taken into account when interpreting thermochronological data from the WC or in similar volcanic-arc settings.

Résumé: Nuweiba is located on the western coast of the Gulf of Aqaba (GoA), which represents the southern part of the Gulf of Aqaba – Dead Sea transform fault (GoA-DST). The GoA is characterized by high seismic activity and is the source of the November 22, 1995, Nuweiba earthquake, with a moment magnitude of Mw 7.3. This seismic unrest caused extensive damage in the city of Nuweiba due to the strong shaking caused by the earthquake. In addition, soil amplification triggered by the thick soft-sediments of the Wadi Watir delta beneath the city amplified the destructive power of the event. Therefore, an assessment of the effect of the Wadi Watir sediments on the ground motion at Nuweiba is very important for future construction, seismic hazard assessment, and seismic risk mitigation. Accordingly, the goal of the current study is to define the amplification characteristics of the Wadi Watir deposits using microtremor and surface wave data sets. The horizontal-to-vertical spectral ratio (HVSR) technique is applied to the microtremor data and Multichannel Analysis of Surface Waves (MASW) is applied to the surface wave data. The data are processed to obtain the distribution of the fundamental resonance frequency (F0), the depth of the geophysical bedrock using joint inversion of the Rayleigh wave dispersion curve and ellipticity peak, the shear wave velocity structure, the time-averaged shear-wave velocity in the topmost 30 m (Vs30), and the shear wave transfer function. The results of the HVSR show that F0 in the northern part of the city is 4.2-5.2 Hz and 0.5-0.8 Hz in the middle of the city. Bedrock depth is found to be in the range of 27 and 199 m. The one-dimensional velocity structure obtained from the MASW measurements has resolved two sedimentary layers within the upper 15 m. The Vs30 ranges between 207 and 556 m/s, according to the Vs30 the soil in the study area is categorized into soil classes B and C according to Eurocode 8. The obtained shear wave transfer functions show that the highest amplification factors are observed in the middle part of the study area.

Résumé: Experiments accessing extreme conditions at x-ray free electron lasers (XFELs) involve rapidly evolving conditions of temperature. Here, we report time-resolved, direct measurements of temperature using spectral streaked optical pyrometry of x-ray and optical laser-heated states at the High Energy Density instrument of the European XFEL. This collection of typical experiments, coupled with numerical models, outlines the reliability, precision, and meaning of time dependent temperature measurements using optical emission at XFEL sources. Dynamic temperatures above 1500 K are measured continuously from spectrally- and temporally-resolved thermal emission at 450-850 nm, with time resolution down to 10-100 ns for 1-200 μs streak camera windows, using single shot and integrated modes. Targets include zero-pressure foils free-standing in air and in vacuo, and high-pressure samples compressed in diamond anvil cell multi-layer targets. Radiation sources used are 20-fs hard x-ray laser pulses at 17.8 keV, in single pulses or 2.26MHz pulse trains of up to 30 pulses, and 250-ns infrared laser single pulses. A range of further possibilities for optical measurements of visible light in x-ray laser experiments using streak optical spectroscopy are also explored, including for the study of x-ray induced optical fluorescence, which often appears as background in thermal radiation measurements. We establish several scenarios where combined emissions from multiple sources are observed and discuss their interpretation. Challenges posed by using x-ray lasers as non-invasive probes of the sample state are addressed. (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/5.0142196

Résumé: Extended and sufficiently dense seismic networks capture spatiotemporal properties of the continuously recorded wavefields and can be used to compute the level of their coherence at different frequencies via the analysis of the network covariance matrix, which has been successfully used to study volcanic seismicity. Here, we present an application of the covariance matrix method in a subduction zone environment. We show that most coherent signals identified through the covariance matrix analysis are related to regional earthquakes with the wavefield properties affected by the scattering, which depends on the source location. Tectonic tremors, on the other hand, are not characterized by a high level of coherence. We compare real data results with a set of synthetic tests aimed at mimicking the properties of seismic sources and the main features of wave propagation. We conclude that highly coherent volcanic tremor wavefields could be produced in two ways: by a spatially localized group of monochromatic seismic sources or by a single source located in a highly heterogeneous medium. In both cases, the stability of the source position is a necessary condition to reproduce the observations in volcanoes. On the other hand, the low coherence of tectonic tremor wavefields can be explained by a spatially extended distribution of sources, in agreement with large portions of the subduction interface being nearly simultaneously involved in the episodes of slow deformation. In addition to earthquakes, weak and nearly continuous seismic signals known as “seismic tremors” are observed in the vicinity of active volcanoes and large seismic faults. They are related to slow processes that lead to accumulation of energy released during catastrophic events such as large eruptions and earthquakes. The exact mechanisms generating seismic tremors remain elusive. Possible physical processes include variations of the fluid pressure, slow deformation and rupturing of rocks. In order to better understand possible analogies and differences between seismic tremors occurring in the volcanic and the tectonic environments, we compare observations from the Kyuchevskoy group of volcanos in Kamchatka, Russia and from the Nankai subduction zone in Japan. We apply a mathematical formalism called “network-based covariance matrix analysis” that is based on correlating signals recorded by a network of seismographs. Our results show significant differences between the distribution of sources of volcanic and tectonic tremors. For the former, the sources are found to be very localized in space and stable in time while the latter are generated by a spatially broad and variable in time distribution of sources, in agreement with large portions of the subduction interface being nearly simultaneously involved in the episodes of slow earthquakes. We compare deep volcanic and tectonic tremors continuously recorded by regional-scale seismic networksVolcanic tremor wavefields are characterized by high level of spatial coherence across the networkLow level of coherence of tectonic tremor wavefields can be explained by a spatially extended distribution of their sources

Résumé: The objective of this study was to evaluate the rate of foliar absorption of magnesium (Mg) salts with different deliquescence and efflorescence relative humidity values (DRH and ERH, also known as point of deliquescence (POD) and point of efflorescence (POE), respectively) when supplied to leaves of model plants with different wettability properties. For this purpose, a greenhouse pot experiment was conducted with lettuce (very wettable), broccoli (highly unwettable) and leek (highly unwettable). Foliar sprays contained 0.1% surfactant plus 100 mM Mg supplied as MgCl2 & BULL;6H(2)O, Mg(NO3)(2)& BULL;6H(2)O or MgSO4 & BULL;7H(2)O. Leaf Mg concentrations were determined 1 and 7 days after foliar application. Anion concentrations were also measured in lettuce where a significant foliar Mg absorption was detected. Leaf wettability, leaf surface free energy and fertilizer drop deposit appearance onto the foliage were assessed. It is concluded that despite including a surfactant in the spray formulation, leaf wettability plays a major role in foliar Mg absorption.

Résumé: On 2013 September 24, an earthquake of magnitude M-w 7.7 occurred on the Hoshab Fault in southern Pakistan, south of the 650-km-long Chaman Fault, within the eastern Makran accretionary wedge. This earthquake was caused predominantly by strike-slip faulting. To quantify the post-seismic deformation following this large earthquake, we used ascending and descending Sentinel-1 data over the period 2014 November-2017 December. The deformation time-series over these 3 years shows that the post-seismic deformation was not linear over the time. To determine the mechanisms that may have driven post-seismic deformation, such as after-slip or a combination of after-slip and viscous relaxation, we explored some models, including after-slip only, and a combination of after-slip and viscous relaxation, to identify the best fit between the observed and simulated deformation time-series. Our results indicate that after-slip was the main mechanism controlling the post-seismic deformation. The introduction of a basal flat fault in the modelling improves the fit between the model results and the time-series obtained from the satellite images This basal fault is located at a depth of 18 km, has a northward dip of 7 degrees and corresponds to the basal decollement level of the Makran accretionary prism.

Résumé: The present experimental study explores the effects of temperature and sulfur in Cd aqueous geo-chemistry under reduced conditions. Greenockite CdS solubility is measured in H2O-H2S-HClO4-NaHS solutions at 25-80 degrees C as a function of pH and sulfur concentration. Based on solubility product measurements in highly acid solutions, the standard thermodynamic properties of greenockite (CdS) are revised, and the recommended value of Delta(integral)G(298.15)(0) for greenockite CdS(s) is -151.5 +/- 0.3 kJ mol(-1). The stability of greenockite (CdS) is higher than predicted by calculations using previous literature data. At 80 degrees C, the stability constants for Cd-HS complexes are measured for the first time, the values are 10(-5.65 +/- 1.00) for CdS(s) + H+ = CdHS+, 10(-6.00 +/- 0.40) for CdS(s) + H2S(aq)0 = Cd(HS)(2(aq))(0), 10(-3.87 +/- 0.10) for CdS(s) + H2S(aq)0 + HS- = Cd(HS)(3)(-), and 10(-3.53 +/- 0.20) for CdS(s) + H2S(aq)0 + 2HS- = Cd(HS)(4)(2-). Modeling of Cd behavior at 3-200 degrees C shows that Cd-HS species are more important than previously believed. The fraction of Cd(HS)(n)(2-n) (n = 1-4) complexes increases with m H2S and decreases with T. Thus, in euxinic marine environments with m H2S >= 10(-5), Cd speciation changes from Cd-Cl to Cd-HS. This speciation change is expected to affect Cd isotope fractionation and should be accounted for when applying Cd isotopic signature as a paleo tracer in marine sediments. The new thermodynamic data are indispensable for modeling Cd behavior in response to pH, T, and m H2S. As a function of these parameters, sulfur has the main control on Cd geochemistry being the main factor of Cd precipitation at low m H2S and favoring Cd mobilization at high m H2S.

Résumé: The age of brittle deformation in the superficial part of orogens is generally constrained by relative, cross-cutting structural relationships. However, it becomes possible to decipher the timing of fault activity by a combination of methods based on U-Pb dating and stable isotope composition of calcite-filled fault and veins. This methodology is applied to constrain the timing of deformation of the frontal part of an orogenic system, through the example of the Tertiary development of subalpine massifs fold and thrust belt (composed by Bauges, Chartreuse, Vercors massifs). The architecture of the massifs is well constrained, but the chronology and the nature of involved fluids is unknown. Clumped isotope Delta 47 analysis shows a significant variation of fluid temperature from 54 degrees C to the west up to 149 degrees C for the internal Vercors thrust to the east. These temperature estimates highlight a deep underthrusting with a significant exhumation of the eastern Vercors (4-6 km), while a shallow underthrusting at a depth of around 2 km is estimated for the central Vercors. Carbon and oxygen stable isotope analyses, reveal three fluid signatures corresponding to heated fluids from meteoric or basin-derived origin, which interacted at various extents with the host-rock. These data are in agreement with a low altitude frontal belt, and with a progressive reequilibration of downwards infiltrating fluids with the composition of the host-rocks. The successfully dated calcites are those exhibiting the highest fluid-rock ratios, which allowed U enrichment in a mainly uranium-poor rock environment. In-situ U-Pb calcite dating was performed on fault mirrors of main thrusts and on fractured pebbles of the underthrusted molasses of eight major thrusts. Preserved Oligocene ages of extensional veins related to pre-Alpine rifting demonstrate that U-Pb calcite is a robust method to characterize multiple superimposed events of a whole mountain building history. Furthermore, the presence of multiple deformation events in the same location point out the importance of inherited structures on the strain localization processes. Thrust related U-Pb on calcite ages on an E-W section between the Vercors and Chartreuse massifs record a major Miocene shortening phase, and the timing of strain propagation towards the foreland. The oldest thrust dated at 15 Ma, corresponds to the activation of the most internal preserved thrust mobilizing 149 degrees C fluids. In the central subalpine massifs, ages range from 14 Ma (Chartreuse) to 12 Ma (Vercors) mobilizing 54 degrees C fluids. On the western part, the initiation of the most external thrust has been dated between 10 Ma and 7 Ma. These geochronological constraints are consistent with an 'in-sequence' westward propagation of the deformation between 15 Ma and 7 Ma and contemporaneous with the exhumation of the Belledonne External Crystalline Massif and the development of flexural basin sedimentation. Paleostress calculations indicate a threestage evolution of the subalpine nappe stack. Reverse and strike-slip deformations are interpreted as a diffuse tectonic reactivation in an 'hors-sequence' mode from 10 Ma to present in a broadly similar stress field.

Résumé: Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for Holocene eruptions, but the size and state of its magma chamber remain poorly constrained. We report high spatial resolution U-Th-Pb zircon ages, co-registered with oxygen and hafnium isotopic values, span similar to 0.6 Ma in each lava, documenting magmatic initiation that forms the current edifice. The best-fit thermochemical modeling constrains magmatic fluxes at 1.2 km(3)/1000 year by hot (900 degrees C), initially zircon-undersaturated dacite into a vertically extensive magma body since similar to 0.6 Ma, whereas a volcanic episode with eruptible magma only extends over the past 0.2 Ma, matching the age of oldest lavas. Simulations explain the total magma volume of similar to 180 km(3), temporally oscillating delta O-18 and epsilon Hf values, and a wide range of zircon age distributions in each sample. These data provide insights into the current state (similar to 200 km(3) of melt in a vertically extensive system) and the potential for future activity of Elbrus calling for much-needed seismic imaging. Similar zircon records worldwide require continuous intrusive activity by magmatic accretion of silicic magmas generated at depths, and that zircon ages do not reflect eruption ages but predate them by similar to 10(3) to 10(5) years reflecting protracted dissolution-crystallization histories.

Résumé: Active felsic magmatism has been rarely probed in situ by drilling but one recent exception is quenched rhyolite sampled during the 2009 Iceland Deep Drilling Project (IDDP). We report finding of rare zircons of up to similar to 100 μm in size in rhyolite glasses from the IDDP-1 well products and the host 1724 AD Viti granophyres. The applied SHRIMP U-Th dating for both the IDDP and the Viti granophyre zircons gives zero-age (+/- 2 kyr), and therefore suggests that the IDDP-1 zircons have crystallized from an active magma intrusion rather than due to the 20-80 ka post-caldera magmatic episodes recorded by nearby domes and ridges. Ti-in-zircon geothermometer for Viti granophyre reveals zircon crystallization temperatures similar to 800 degrees C-900 degrees C, whereas IDDP-1 rhyolite zircon cores show Ti content higher than 100 ppm, corresponding to temperatures up to similar to 1,100 degrees C according to the Ti-in-zircon thermometer. According to our thermochemical model at such elevated temperatures as 1,100 degrees C, rhyolitic magma cannot be saturated with zircon and zircon crystallization is not possible. We explain this controversy by either kinetic effects or non-ideal Ti incorporation into growing zircons at low pressures that start to grow from nucleus at temperatures similar to 930 degrees C. High temperatures recorded by IDDP-1 zircon together with an occurrence of baddeleyite require that the rhyolite magma formed by partial melting of the host granophyre due to basaltic magma intrusion. Zr concentration profiles in glass around zircons are flat, suggesting residence in rhyolitic melt for >4 years. In our thermochemical modeling, three scenarios are considered. The host felsite rocks are intruded by: 1) a basaltic sill, 2) rhyolite magma 3) rhyolite sill connected to a deeper magmatic system. Based on the solution of the heat conduction equation accounting for the release of latent heat and effective thermal conductivity, these data confirm that the rhyolite magma could be produced by felsic crust melting as a result of injection of a basaltic or rhyolite sill during the Krafla Fires eruption (1975 AD).

Résumé: We introduce a new polarized radiative transfer model able to compute the polarization measured by a virtual instrument in a given nocturnal environment recreating real world conditions (1-dimensional atmospheric and aerosol profiles, 3-dimensional light sources with complex and widespread geometries, terrain obstructions). Initially developed to address the issue of aurorae and nightglow polarization, the model has potential applications in the context of light pollution, or aerosols and air pollution measurements in night time conditions. We provide the physical assumptions behind the model together with the main points regarding its numerical implementation, together with the inherent constraints and liberties it brings. The model, based on single scattering equations in the atmosphere, is first tested on a few simple configurations to assess the effect of several key parameters in controlled environments. The model outputs are then compared to field measurements obtained in four wavelengths at mid-latitude in a dark valley of the French Alps, 20 km away from the closest city. In this context where the nightglow emissions are supposedly stationary and widespread, a convincing fit between the model predictions and observations is found in three wavelengths. This confrontation of ground-based records with our modeling constitutes a proof of concept for the investigation of our polarized environment in nocturnal conditions, in the presence of localized and/or extended sources. It calls for further investigations. In particular we discuss the future need for inter-calibrating the sources and the polarimeter in order to optimally extract the information contained in such measurements, and how multiple-scattering (not implemented in the present study) could impact our observations and their interpretation.

Résumé: Sea ice is a heterogeneous, evolving mosaic of individual floes, varying in spatial scales from meters to tens of kilometers. Both the internal dynamics of the floe mosaic (floe-floe interactions), and the evolution of floes under ocean and atmospheric forcing (floe-flow interactions), determine the exchange of heat, momentum, and tracers between the lower atmosphere and upper ocean. Climate models do not represent either of these highly variable interactions. We use a novel, high-resolution, discrete element modeling framework to examine ice-ocean boundary layer (IOBL) turbulence within a domain approximately the size of a climate model grid. We show floe-scale effects could cause a marked increase in the production of fine-scale three-dimensional turbulence in the IOBL relative to continuum model approaches, and provide a method of representing that turbulence using bulk parameters related to the spatial variance of the ice and ocean: the floe size distribution and the ocean kinetic energy spectrum. Sea ice is a complex broken mosaic of individual pieces, called floes. These floes control how heat and momentum move between the atmosphere and ocean. But these floes interact with each other as well as with the upper ocean and lower atmosphere, and this means that these exchanges can be complexly related to both types of processes: floe-floe and floe-flow. Using experiments that explicitly evolve sea ice floes interacting with each other and the upper ocean, we develop a formulation for how momentum is transferred between the ice and ocean as a function of simple parameters of the ice-ocean system that may be available to climate models. Discrete element model results show floe-size-dependent ice-ocean boundary layer (IOBL) stress-driven turbulenceIOBL turbulence is driven both by floe collisional velocity and by floe-scale ocean variabilityWe present a framework for a scale-aware parameterization of IOBL turbulence using bulk parameters

Résumé: The 2015 moment magnitude M-w = 8.3 Illapel earthquake is the largest mega-thrust earthquake that has been recorded along the Chilean subduction zone since the 2010 M-w = 8.8 Maule earthquake. Previous studies indicate a rupture propagation from the hypocentre to shallower parts of the fault, with a maximum slip varying from 10 to 16 m. The amount of shallow slip differs dramatically between rupture models with some results showing almost no slip at the trench and other models with significant slip at shallow depth. In this work, we revisit this event by combining a comprehensive data set including continuous and survey GNSS data corrected for post-seismic and aftershock signals, ascending and descending InSAR images of the Sentinel-1A satellite, tsunami data along with high-rate GPS, and doubly integrated strong-motion waveforms. We follow a Bayesian approach, in which the solution is an ensemble of models. The kinematic inversion is done using the cascading capability of the AlTar algorithm, allowing us to first get a static solution before integrating seismic data in a joint model. In addition, we explore a new approach to account for forward problem uncertainties using a second-order perturbation approach. Results show a rupture with two main slip patches, with significant slip at shallow depth. During the rupture propagation, we observe two regions that are encircled by the rupture, with no significant slip, westward of the hypocentre. These encircling effects have been previously suggested by back-projection results but have not been observed in finite-fault slip models. We propose that the encircled regions correspond to zones where the yield stress largely exceeds the initial stress or where fracture energy is too large to be ruptured during the Illapel earthquake. These asperities may potentially break in the future and probably already broke in the past.

Résumé: On Sept. 19th, 2021, a volcanic eruption began on the island of La Palma (Canary Islands, Spain). The pre-eruptive episode was characterized by seismicity and ground deformation that started only 9.5 days before the eruption. In this study, we applied seismic interferometry to the data recorded by six broadband seismic stations, allowing us to estimate velocity variations during the weeks preceding the eruption. About 9.5 days before the eruption, we observed a reduction in the seismic velocities is registered next to the eruptive centers that opened later. Furthermore, this zone overlaps with the epicenters of a cluster of volcano-tectonic earthquakes located at shallow depth (< 4 km) and detached from the main cluster of deeper seismicity. We interpret the decrease in seismic velocities and the occurrence of such a shallow earthquake cluster as the effect of hydrothermal fluid released by the ascending magma batch and reaching the surface faster than the magma itself.

Résumé: La Palma island is located in the NW of the Canary Islands and is one of the most volcanically active of the archipelago, therefore the existence of geothermal resources on the island is highly probable. The main objective of this work is to detect velocity anomalies potentially related to active geothermal reservoirs on La Palma island, by achieving a high-resolution seismic velocity model of the first few kilometres of the crust using Ambient Noise Tomography (ANT). The obtained ANT model is merged with a recent local earthquake tomography model. Our findings reveal two high-velocity zones in the island's northern and southern parts, that could be related to a plutonic intrusion and old oceanic crust materials. Conversely, four low-velocity zones are imaged in the southern part of the island. Two of them can be related to hydrothermal alteration zones located beneath the Cumbre Vieja volcanic complex. This hypothesis is reinforced by comparing the S-wave velocity model with the seismicity recorded during the pre-eruptive phase of the 2021 Tajogaite eruption, which revealed an aseismic volume coinciding with these low-velocity zones. Another low-velocity zone is observed in the southern part of the island, which we interpret as highly fractured rocks which could favour the ascent of hot fluids. A last low-velocity zone is observed in the central part of the island and associated with loose deposits generated by the Aridane valley mega landslide.

Résumé: The release of engineered nanomaterials (ENMs) during manufacturing, use and disposal of nano-enabled products (NEPs) is a potential route of environmental nanopollution. To date, there is limited knowledge on the ecological impact of ENMs incorporated in NEP matrices and how they compare to pristine nanoparticles. Here, we examined the fate and effect of silver nanowires (AgNWs) embedded in a cellulose matrix for the production of printed paper electronics (PPE) (nano)technologies. The fate and impact of fragmented AgNWs-PPE was monitored for 21 days in freshwater mesocosms mimicking a pond ecosystem. The Ag release and AgNWs-PPE behavior in water was further characterized in abiotic batch incubations. Qualitative and quantitative analyses were carried out to estimate the Ag partitioning between the environmental compartments and the aging of AgNWs-PPE as well as bioaccumulation and behavioral responses in biota. In contaminated pond mesocosms, the NEP cellulose/polyvinylidene chloride matrix resulted in rapid settling of the Ag on the sediments and prevented Ag release into the water column. The highest aqueous concentration measured corresponded to less than 0.5% of the total Ag introduced. The AgNWs-PPE fragments accumulated at the water sediment interface, where they were rapidly (bio)degraded and became bioavailable for benthic organisms. Aquatic snails accumulated a significant fraction of the Ag (1.4 +/- 0.5%) and displayed enhanced burrowing behavior in comparison to controls. In batch experiments, alteration of the ENM morphology was evident at the NEP surface. Here, the colocalization of Ag and S clusters suggests aging via sulfidation, similar to other pristine Ag ENMs. However, the cellulose matrix prevented weathering of the AgNWs within the NEP, which presented a near-pristine state even after 21 days of incubation. Overall, these results indicate that the fate and impact of Ag embedded in the AgNWs-PPE were driven by the cellulose matrix. In particular, given the specific properties and behavior of paper-based (nano)products, these may constitute a unique category when evaluating NEP environmental impact. The data gathered in this study can help in defining the environmental fate of such materials and provide useful information to address future studies focused on ENM environmental fate and risk assessment in a life-cycle perspective. The fate and impact of silver nanowires incorporated in a paper-based nano-enabled product (NEP) was investigated in freshwater mesocosms.

Résumé: In this paper, physics-based numerical simulation (PBS) is employed to render a broad-band (0-10 Hz) realization of the near-field seismic response of the experimental nuclear site of Cadarache, located nearby the active Middle Durance Fault (southeastern France). The sensitivity of the earthquake numerical model to geological features is investigated by comparison with geophysical measurements and past aftershock and by highlighting the amplification induced by the soft sediments below Cadarache. The blind prediction of an M(W)6 target earthquake is approached by synthesizing four different finite-fault scenarios. The outcome is compared to the standard ground motion prediction equations (GMPEs), unveiling a possible GMPE overestimation of the pseudospectral acceleration ordinates at short natural periods, supporting the actual need to integrate synthetic and empirical predictions when direct observations are not available.

Résumé: The reactivity of Fe(II) sorbed on clay edges towards U(VI) reduction is investigated at pH 6.0 using Fe-free synthetic montmorillonite (MONT), Fe-poor natural montmorillonite (Fe-MONT) and Fe-rich natural nontronite (NAu-2). Partial reduction of U(VI) by sorbed Fe(II) only occurred on MONT but neither on Fe-MONT nor NAu-2. In the former case, the formation of a hydrated uranyl silicate (soddyite)-like phase is demonstrated by U L-III-edge EXAFS spectroscopy. Fe-57 Mossbauer spectrometry reveals that in this case 10% of the total sorbed Fe(II) was oxidized before- and an additional 6% after-addition of U(VI). The lack of reactivity towards U(VI) of Fe(II) sorbed on Fe-MONT or NAu-2 is likely due to inter-valence charge transfer (IVCT) between surface Fe(II) and structural Fe(III). The present study demonstrates that the reactivity of clay sorbed Fe2+ towards U(VI) strongly depends on the nature of clay and correspondingly on the oxidation state of sorbed Fe.

Résumé: Localization of passive Radio-Frequency Identification (RFID) tags has been used to monitor landslide surface displacement since 5 years. This method, applied on slow displacements lower than 1cm per day, allows a high spatio-temporal resolution at a relatively low cost. With the feedback of the previous years, this paper proposes to summarize the various challenges encountered with the long-term outdoor RFID localization method, and presents data-processing solutions that were implemented to overcome these challenges. We propose a complex-smoothing unwrapping algorithm, a multi-frequency merging operation, as well as multi-tag and multi-antenna phase combining method. The concept of an unwrapping reference guide is presented and applied with groups of tags showing coherent displacements, or with absolute reference measurements. These approaches allow a higher data availability up to 38% for one site over multiple years, and a better phase unwrapping. Earth surface displacement monitoring with RFID proves to be a robust and accurate solution, with four equipped sites across France and Switzerland.

Résumé: Continuous data streams from translational and rotational seismometers installed in TAIPEI 101 enable monitoring of the natural frequencies on different time scales. Using the 2014 seismic data recorded on the 90th floor of this high-rise building and the meteorological data from a weather station located just 1 km away, we explored the characteristics and controlling factors of the ambient vibrations in TAIPEI 101. Using the random decrement technique, the three modal frequencies in translation were identified as 0.15 Hz (F1), 0.43 Hz (F2), and 0.78 Hz (F3). For rotation around the vertical axis, the modal frequencies were 0.23 Hz (R1), 0.59 Hz (R2), and 0.93 Hz (R3). In translation, TAIPEI 101 exhibits a trend of increasing modal frequency with increasing temperature but decreasing modal frequency with increasing wind velocity. The trend with temperature is reversed in rotation motion. The different frequency versus temperature relationship seen for rotational and translational motion demonstrates the importance of introducing rotational motion analysis into structural health monitoring. The change in modal frequencies were also found to decrease with growing amplitude. It is intriguing that F1 exhibits a weaker dependency with amplitude with respect to the higher modes, which may be associated with the suppression of F1 vibration caused by the damper installed in TAIPEI 101. Other than long-term (seasonable) variation, we also highlight the hourly variation of the first-mode amplitude throughout a day by comparing with weather and mobility data. Other than the atmospheric conditions that strongly influence the modal frequencies in long-term behavior, we found that human activities may play an important role in the short-term vibration characteristics of the building.

Résumé: Forecasting hanging glacier instabilities remain challenging as sensing technology focusing on the ice surface fails to detect englacial damage leading to large-scale failure. Here, we combine icequake cluster analysis with coda wave interferometry constraining damage growth on Switzerland's Eiger hanging glacier before a 15,000 m(3) break-off event. The method focuses on icequake migration within clusters rather than previously proposed “event counting.” Results show that one cluster originated from the glacier front and migrated by 13.9(+/- 1.2) m within 5 weeks before the break-off event. The corresponding crevasse extension separates unstable and stable ice masses. We use the measured source displacement for damage parametrization and find a 90% agreement between an analytical model based on damage mechanics and frontal flow velocities measured with an interferometric radar. Our analysis provides observational constraints for damage growth, which to date is primarily a theoretical concept for modeling englacial fractures.

Résumé: Understanding the interactions between surface and deep Earth processes is important for research in many diverse scientific areas including climate, environment, energy, georesources and biosphere. The TOPO-EUROPE initiative of the International Lithosphere Program serves as a pan-European platform for integrated surface and deep Earth sciences, synergizing observational studies of the Earth structure and fluxes on all spatial and tem-poral scales with modelling of Earth processes. This review provides a survey of scientific developments in our quantitative understanding of coupled surface-deep Earth processes achieved through TOPO-EUROPE. The most notable innovations include (1) a process-based understanding of the connection of upper mantle dynamics and absolute plate motion frames; (2) integrated models for sediment source-to-sink dynamics, demonstrating the importance of mass transfer from mountains to basins and from basin to basin; (3) demonstration of the key role of polyphase evolution of sedimentary basins, the impact of pre-rift and pre-orogenic structures, and the evo-lution of subsequent lithosphere and landscape dynamics; (4) improved conceptual understanding of the tem-poral evolution from back-arc extension to tectonic inversion and onset of subduction; (5) models to explain the integrated strength of Europe's lithosphere; (6) concepts governing the interplay between thermal upper mantle processes and stress-induced intraplate deformation; (7) constraints on the record of vertical motions from high -resolution data sets obtained from geo-thermochronology for Europe's topographic evolution; (8) recognition and quantifications of the forcing by erosional and/or glacial-interglacial surface mass transfer on the regional magmatism, with major implications for our understanding of the carbon cycle on geological timescales and the emerging field of biogeodynamics; and (9) the transfer of insights obtained on the coupling of deep Earth and surface processes to the domain of geothermal energy exploration.Concerning the future research agenda of TOPO-EUROPE, we also discuss the rich potential for further ad-vances, multidisciplinary research and community building across many scientific frontiers, including research on the biosphere, climate and energy. These will focus on obtaining a better insight into the initiation and evolution of subduction systems, the role of mantle plumes in continental rifting and (super)continent break-up, and the deformation and tectonic reactivation of cratons; the interaction between geodynamic, surface and climate processes, such as interactions between glaciation, sea level change and deep Earth processes; the sensitivity, tipping points, and spatio-temporal evolution of the interactions between climate and tectonics as well as the role of rock melting and outgassing in affecting such interactions; the emerging field of bio-geodynamics, that is the impact of coupled deep Earth – surface processes on the evolution of life on Earth; and tightening the connection between societal challenges regarding renewable georesources, climate change, nat-ural geohazards, and novel process-understanding of the Earth system.

Résumé: The low-temperature alteration (< 150 degrees C) of ophiolites by infiltrated meteoric waters removes atmospheric CO2 through mineral carbonation and is assumed to generate H-2 and possibly CH4 according to so-called serpentinization reactions. This overall alteration pattern is primarily constrained by the chemical composition of alkaline springs that are issued in several ophiolites worldwide. Here we report on the fingerprint, as veinlet mineralization, of the reactive percolation of such meteoric waters in the New Caledonia ophiolite (Massif du Sud). The mineralization which resulted from carbonation and serpentinization reactions, is young (< 2 Ma) and formed at a temperature of ca. 95 degrees C. It is mainly composed of lizardite, dolomite, magnetite +/- pyroaurite. Thermochemical simulation of mineral-water equilibria shows that the percolating aqueous fluid was alkaline and H-2 bearing. The delta C-13 of dolomite is exceptionally high, between 7.1 and up to 17.3 parts per thousand, and is interpreted as evidence of low-temperature methanogenesis. Overall, the percolating fluid had a chemical composition similar to that of the waters issued today in the (hyper)alkaline springs of the Massif du Sud. The studied veinlets are thus interpreted as a sample of the plumbing system that fed an ancient Quaternary alkaline spring in the area.

Résumé: Slow slip events (SSEs) originate from a slow slippage on faults that lasts from a few days to years. A systematic and complete mapping of SSEs is key to characterizing the slip spectrum and understanding its link with coeval seismological signals. Yet, SSE catalogues are sparse and usually remain limited to the largest events, because the deformation transients are often concealed in the noise of the geodetic data. Here we present a multi-station deep learning SSE detector applied blindly to multiple raw (non-post-processed) geodetic time series. Its power lies in an ultra-realistic synthetic training set, and in the combination of convolutional and attention-based neural networks. Applied to real data in Cascadia over the period 2007-2022, it detects 78 SSEs, that compare well to existing independent benchmarks: 87.5% of previously catalogued SSEs are retrieved, each detection falling within a peak of tremor activity. Our method also provides useful proxies on the SSE duration and may help illuminate relationships between tremor chatter and the nucleation of the slow rupture. We find an average day-long time lag between the slow deformation and the tremor chatter both at a global- and local-temporal scale, suggesting that slow slip may drive the rupture of nearby small asperities. A deep learning detector applied to raw multi-station geodetic time series data from 2007 to 2022 is able to identify slow slip events in the Cascadia region and finds that they are each associated with periods of greater tremor activity

Résumé: In the Apennine Mountains of the Italian Peninsula, GPS data display 3-4 mm/yr of divergent motion oriented N50 degrees E between the Adriatic and Tyrrhenian coastlines. However, the mechanisms driving this extension remain debated and along-strike variations of extension within the actively deforming belt remain poorly constrained. Here, we derived the first large-scale extensional and vertical velocity field for the Apennines by multi-temporal InSAR analysis of 7 years of Sentinel-1 data at the scale of the entire range, improving the spatial resolution and vertical accuracy of existing GPS measurements. The results reveal along-strike variations of extensional rates and gradients, with extension concentrated on single fault systems in the north, consistent with the loci of seismicity and recent moderate earthquakes, and distributed throughout the central Apennines, where the range is widening. Vertical surface displacements do not resolve any active long-wavelength uplift of the orogenic belt and, on average, show more subsidence than uplift relative to the Tyrrhenian and Adriatic coasts. This work provides the first InSAR-based geodetic map of differential extension and uplift within the Italian Peninsula. Our results are compatible with a pure shear extensional model of the crust, driven by both boundary and gravitational forces.

Résumé: The fossil record of Quaternary reef systems, as expressed in uplifted regions by sequences of stacked terraces, has been extensively used either to understand their morphodynamics or to unravel sea level variations. Yet, because these two aspects are intimately linked, Quaternary reef analysis is often underdetermined because the analysis often focuses on single sequences, along one-dimensional profiles. Here, we take advantage of the lateral variations of coral reef sequences by documenting the morphological variations of the reef sequence on Sumba Island. Near Tambolaka, northwest Sumba, we analysed a reef transect, topography, and associated sedimentological record to obtain a precise coral reef stratigraphy and geomorphic patterns that can be compared with the well-documented eastern counterpart. In Tambolaka, the reef sequence displays four lower layers of bedded chalky limestone units with a weakly cemented sandy matrix, which we attribute to the Middle Miocene to Pliocene Wakabukak formation based on calcareous nannofossils and planktonic foraminifers. The uppermost layer is a calcretized reefal limestone unit with a well-lithified sandy matrix, which we attribute to the Plio-Pleistocene reef sequence of the Kalianga formation. Seven marine terraces imprint the regional morphology, four of which we correlate with Marine Isotope Stage (MIS) 5e, MIS 7e, MIS 9e, and MIS 11c terraces of Cape Laundi, northeast Sumba. When scrutinized at the light of numerical models of reef development, these results indicate that the morphodynamics of reefal sequences is strongly impacted by the tectonic evolution. The geodynamic context sets both the extrinsic conditions of reef development, such as the morphology of the basement and hydrodynamics, and the intrinsic properties, in particular reef growth rate. While the morphodynamic evolution of the sequence is at first-order representative of the interplay between uplift rates and sea level oscillations, the detailed assemblage of the reef units drastically varies along the coastline.

Résumé: Using logging data and samples collected by the four expeditions of the International Ocean Discovery Program NanTroSEIZE drilling campaign that occupied Site C0002 in the Nankai margin located southwest of Japan, we determined effective porosity and sonic velocity profiles down to 3 km below the seafloor in the accretionary prism, above the seismogenic plate interface. We measured cation exchange capacity to differentiate clay-bound water content from effective porosity, which is representative of compaction. The decrease in effective porosity with depth is fitted with a single exponential decay, which suggests hydrostatic conditions for most of the borehole. The Erickson-Jarrard template was adapted to account for the actual clay-bearing nature of the sediments. We used this improved P-wave velocity-effective porosity relationship to fill shipboard data gaps and predict P- and S-wave velocity profiles at Site C0002.

Résumé: This work aims to construct a synthetic database of human and economic seismic losses. For weak-to-moderate magnitude and older earthquakes, the catalogs of losses are incomplete, which limits the creation of probabilistic based loss models. Furthermore, the number of earthquakes involving losses has increased in recent years, following a non-stationary Poisson distribution with a rate proportional to the exposed population and GDP. First, this study involved defining a series of empirical models (from definition of magnitude to losses) tested by the likelihood method applied to data from 377 earthquakes with variables related to exposure (exposed population and exposed GDP) and consequences (economic losses, number of fatalities and injuries). For these 377 earthquakes, the spatial variation of the hazard was deduced from USGS ShakeMaps and the social and economic losses evaluated were made stationary by taking into account exposure evolving over time. We then built a synthetic database of seismic losses from the ISC-GEM catalog of epicenters, which is assumed to be complete and homogeneous since 1967 for magnitudes > 5. The combination of the 377 events and the synthetic data indicates that earthquakes of magnitudes [5.5; 6.9] represent 36% of all economic losses, 56% of all fatalities, and 71% of injuries. An occurrence model was then designed to predict the evolution of losses over the next years.

Résumé: Changes in magma properties and transport geometry can have a direct impact on volcanic activity. However, such variations can be difficult to track during eruptions. We report previously undetected very long-period (VLP) signals at Piton de la Fournaise that can be used to probe changes in magma transport. Source analysis of VLP events during the August-October 2015 eruption indicates a source depth of about 0.9-1.2 km and points to the resonance of the magma dike feeding the eruption. The evolution of the resonance period reveals a shortening of the dike when the magma flux decreases at the end of the eruption. VLP events are actually quite frequent at Piton de la Fournaise: all eruptions analyzed in this study exhibit VLP signals that are indicative of rapid drops in lava discharge. This work encourages the detection of VLP signals to monitor changes in magma flow during volcanic eruptions, and anticipate the corresponding evolution in effusive activity.& COPY; 2023 Elsevier B.V. All rights reserved.

Résumé: In the Mexican subduction zone, slow slip events of various duration, from a few days to several months have previously been identified in the regions of Guerrero and Oaxaca. They occur along with microseismicity: low-frequency earthquakes and tectonic tremors. In this study, we analyzed a 10-year long tremor catalog covering multiple SSE cycles, to identify periods of high tremor activity. We then used the temporal information of these tremor bursts to decompose GNSS time series. Surface velocities estimated for tremor and non-tremor periods are then inverted to locate slip rates on the plate interface. Combining the detected microseismicity information and GNSS time series, we show that large slow slip events are made of clusters of short-lasting slip events occurring at tremor times and located updip of the tremor area. This analysis also allowed us to unveil low amplitude transients in between large slow slip events, that last 8 – 9 days, occurring at tremor times and locations, in both Guerrero and Oaxaca regions. Finally, we show that the plate locking amplitude in between short and large slow slip events increases by a factor up to 0.5 at the location of tremors. & COPY; 2023 Elsevier B.V. All rights reserved.

Résumé: Hydrothermal alteration of chromitite bodies in the form of pods (from a few centimeters to a few tens of meters in thickness) from the central sector of the Sabzevar ophiolite belt (NE Iran) was examined down to the nanoscale. The main Cr-spinel alteration feature corresponds to homogeneous cores (primary Cr-spinel) either rimmed by or locally replaced by heterogeneous domains composed of spinel grains with little or no inclusions / pores. The chemical evolution of spinel in response to hydrothermal alteration is found to follow two distinct chemical trends: (i) in the massive and semi-massive chromitites, the trend consists in the progressive increase of Cr without Fe3+ incorporation; (ii) in serpentinized dunites containing disseminated Cr-spinel grains, the increase in Cr occurs in conjunction with Fe3+ incorporation. These two trends involve a decrease in the spinel Mg/(Mg + Fe2+) ratio. Nanoscale observation using transmission electron microscopy (TEM) shows that porous ferrian Crspinel which are poorer in Al and Mg and richer in Cr and Fe than the primary Cr-spinel, contains relicts of the primary Cr-spinel as well as intercalated platelets of newly formed magnetite and lizardite/chlorite. Automated crystal orientation mapping reveals that the (001) and (111) planes of newly formed lizardite/chlorite and Crspinel/magnetite, respectively, are parallel. The replacement of the primary Cr-spinel by porous ferrian Crspinel and magnetite is found to be isomorphic. The pores, ranging from 2 to 15 μm in size, may act as pathways for the aqueous solutions involved in the serpentinization process, which fed the crystallization of alteration minerals in the pores. The two different compositional trends in chromite grains from massive/semimassive chromitite and hosted in serpentinized dunite are best explained, using mass-balance calculation, by considering the influence of the Cr-spinel/(Cr-spinel+olivine) initial ratio in the rock (XChr) and the dissolution of Mg at a water-to-rock ratio (w/r) above one. In general, at the cm-to-meter scale, Al and Fe exchange between chromitites and their serpentinized dunite envelope was not observed in the central sector of the Sabzevar ophiolite belt; however, such Al and Fe transfer is clearly observed in other parts of this ophiolite belt, where hydrothermal alteration of podiform chromitites produced magnetite ores. Comparatively, the small extend of chromitite alteration observed here, likely reflects the product of lesser fluid-rock interaction with w/r ratio close to one instead of >103 estimated for the magnetite ores based on the magnitude of the Al transfer to their dunite envelope.

Résumé: The Earth's magnetic field at the core-mantle boundary is the gradient of a harmonic potential function if the mantle is electrically insulating, and the horizontal components of the field can be derived from its radial component in the mantle. Therefore, these components give no further observational information on the core dynamics. However, it can still be envisioned that the horizontal components of the induction equation at Earth's core surface yield further knowledge on the fluid motions at the top of the core independently of the observations. Here, we show that they provide a linear relationship between the surface velocity and the surface shear (strain shear) that depends on the mantle electrical conductivity. This offers a protocol to calculate the surface shear that we validate with synthetics obtained from dynamo simulations in the limit of a weak mantle conductance. First, using numerical simulations with stress-free boundary condition at the core surface, we retrieve the expected relationship between the horizontal flow u(Sigma) and the shear, u(Sigma)=r partial derivative(r)u(Sigma). Next, we investigate simulations with no-slip boundary condition and insulating mantle, and we obtain the same relationship, even though the shear is not imposed as a boundary condition. Finally, we calculate the flow shear at the top of the core from a magnetic field model based on satellite measurements. The application to geophysical data indicates larger values of the surface flow shear than in the synthetic case, suggesting a possible role of the mantle electrical conductivity. The surface flow shear, in the simulations, much differs from the radial shear in the flow, deeper in the core, which is influenced by the mostly quasi-geostrophic geometry. This implies that we cannot rely on the relationship between the flow and the radial shear for quasi-geostrophic motions to exploit the horizontal components of the induction equation and gain further information on the flow at the Earth's core surface.

Résumé: Using lake-sediment cores to document past seismicity requires a comprehensive understanding of possible lateral variations in depositional processes. This study aims to reveal the lateral variations in earthquake-induced event deposits throughout Lake Iznik, a large lake located on the middle strand of the North Anatolian Fault. Based on stratigraphic, sedimentological and geochemical analyses of 14 sediment cores from two subbasins across the lake, five different types of event deposits (T1-T5) were identified and characterised. One event deposit type (T5) is restricted to a delta mouth, characterised by the occurrence of authigenic Fe-Mn carbonates and interpreted to result from flood events. The four other types of event deposits are characterised by their synchronicity between cores and their age consistency with historical earthquakes and are interpreted to be likely generated by earthquakes. The locally prominent 1065 CE historical earthquake that ruptured the sub-lacustrine Iznik Fault produced at least three different types of event deposits. One deposit type (T2) is only observed for this very local earthquake, implying that the type of event deposit might also depend on ground-motion parameters. At the lake scale, the occurrence of various event deposits depends on the flow distance from the source of sediment destabilisations to the coring site.

Résumé: Numerical experiments of seismic wave propagation in a laterally homogeneous layered medium explore subsurface imaging at subwavelength distances for dense seismic arrays. We choose a time-reversal approach to simulate fundamental mode Rayleigh surface wavefields that are equivalent to the cross-correlation results of three-component ambient seismic field records. We demonstrate that the synthesized 2-D spatial autocorrelation fields in the time domain support local or so-called focal spot imaging. Systematic tests involving clean isotropic surface wavefields but also interfering body wave components and anisotropic incidence assess the accuracy of the phase velocity and dispersion estimates obtained from focal spot properties. The results suggest that data collected within half a wavelength around the origin is usually sufficient to constrain the used Bessel functions models. Generally, the cleaner the surface wavefield the smaller the fitting distances that can be used to accurately estimate the local Rayleigh wave speed. Using models based on isotropic surface wave propagation we find that phase velocity estimates from vertical-radial component data are less biased by P-wave energy compared to estimates obtained from vertical-vertical component data, that even strong anisotropic surface wave incidence yields phase velocity estimates with an accuracy of 1 per cent or better, and that dispersion can be studied in the presence of noise. Estimates using a model to resolve potential medium anisotropy are significantly biased by anisotropic surface wave incidence. The overall accurate results obtained from near-field measurements using isotropic medium assumptions imply that dense array seismic Rayleigh wave focal spot imaging can increase the depth sensitivity compared to ambient noise surface wave tomography. The analogy to elastography focal spot medical imaging implies that a high station density and clean surface wavefields support subwavelength resolution of lateral medium variations.

Résumé: The local ground motion amplification related to the geology at a specific site (i.e. the so-called site effects) may be classically quantified through the SSR (standard spectral ratio) technique applied on earthquake recordings. However, such a quantification might be challenging to carry out in low-to-moderate seismicity regions. Methods based on background ambient noise, such as noise-based standard spectral ratio (SSRn), might be of great interest in these areas. But noise-derived amplification is particularly sensitive to local anthropogenic sources, which may introduce biases in the evaluation of site effects by dominating the geological effects, especially for frequencies higher than 1 Hz. A hybrid approach (SSRh), developed to reduce biases in noise-based spectral ratios by combining classical earthquake-based spectral ratio (SSR) and SSRn, was recently introduced and relies on a site reference. We here investigate the applicability of SSRn and SSRh in a heavily industrialized environment in the Tricastin Valley (south-east France), where critical facilities are located. We continuously recorded ambient noise from 2020 February to March on a 400-sensor seismic array covering an area of about 10 km by 10 km. We demonstrate that SSRn and SSRh computed below 1 Hz are able to reproduce amplification factors provided by SSR. By contrast, at frequencies higher than 1 Hz, SSRn strongly deviates from SSR. SSRh shows closer results to SSR but presents a dependence to the choice of the local site reference, thereby questioning the possibility to use SSRh blindly to estimate the local amplification in our context. These discrepancies reflect the impact of local anthropogenic sources. We therefore introduced a two-step workflow to mitigate the influence of local sources. The first step is to define a characteristic time window to optimally isolate significant transient signals. The second step consists in selecting the time segments that do not contain these transients with a clustering-based approach. By applying this workflow, we were able to remove some strong anthropogenic transient signals likely to be generated by local sources at some sites and therefore to locally improve the amplification assessment through noise-based spectral ratios. However, stationary sources, whose impact cannot be removed through our procedure, remain a major issue. This study provides some insights into the application of SSRn and SSRh in noisy industrialized areas, especially regarding the impact of local noise sources. It illustrates the difficulty of having a procedure for mitigating the impact of these sources that is efficient everywhere inside such a complex anthropized environment, where different types of sources (including stationary sources) cohabit.

Résumé: The Tibetan Plateau was formed by intense Cenozoic shortening (up to 1,100 km) of a composite “proto-Tibet,” itself the product of a long Paleozoic and Mesozoic history of accretion of Gondwana-derived continental fragments and volcanic arcs against the Asian continental margin. The difficult access and the scarcity of outcrops have long limited the possibilities of studying these Mesozoic suture zones in the heart of the Plateau. In this work, we present new U-Pb and 40Ar/39Ar ages from the highly deformed units of the Yushu melange, along the Jinsha Suture in the northeastern Qiangtang terrane. Early Triassic (c. 253 Ma) to Middle Jurassic ages (c. 165 Ma) complement the existing data set and help to refine the chronology of the Paleo-Tethyan oceanic subductions which have structured the northeastern part of the Qiangtang terrane. The Yushu melange records at least three successive tectono-magmatic events. The opening of a back-arc basin during the northward Paleo-Tethyan subduction along the Longmu Co-Shuanghu Suture during Early to Middle Triassic; then its closure during the southward subduction of the Songpan-Ganze Ocean along the Jinsha Suture in Late Triassic. Finally, a shortening phase related to the continental collision of the Songpan-Ganze and Qiangtang blocks from Late Triassic to Early-Middle Jurassic. No evidence for any high- or mid-temperature Cenozoic reactivation of the Jinsha suture in our study area is recorded.

Résumé: At andesitic volcanoes, effusive lava flows and dome emplacement alternate with explosive, sometimes very destructive events. It is thus crucial to obtain quantitative information on the dome volume emplaced as well as on the extrusion rate. However, steep slopes and continuous activity make it difficult to install field instruments near many volcano summits. In this study, we take advantage of two high resolution remote-sensing datasets, Pleiades (optical acquisitions in tri-stereo mode) and TanDEM-X (radar acquisitions in bistatic mode), to produce twenty Digital Elevation Models (DEMs) over the summit area of Merapi volcano, Indonesia, between July 2018 and December 2019. We calculate the difference in elevation between each DEM and a reference DEM derived from Pleiades images acquired in 2013, in order to track the evolution of the dome in the crater. Uncertainties are quantified for each dataset by a statistical analysis of areas with no change in elevation. We show that the DEMs derived from Pleiades and TanDEM-X data are consistent with each other and provide good spatiotemporal constraints on the evolution of the dome. Furthermore, the remote-sensing estimate of the lava volume is consistent with local drone measurements carried out by BPPTKG at the time of dome growth. From our DEMs, we show that the dome growth was sustained by a relatively small effusion rate of about 0.0336 +/- 0.0067 m(3).s(-1)(2900 +/- 580 m(3)/day) from August 2018 to February 2019, when it reached a height of 40 m (+/- 5 m) and a volume of 0.64 Mm(3) (+/- 0.03 Mm(3)). The lava dome initially grew radially, and then extended asymmetrically to the northwest and southeast starting in October 2018. From February 2019 onwards, the dome elevation remained constant, but lava was continuously emitted. Lava supply was balanced by destabilization southwards downhill producing an accumulation zone of 400 m long and maximum 15 m (+/- 5 m) high with a volume of 0.37 Mm(3) (+/- 0.29 Mm(3)). The measured accumulation rate between February and September 2019 is 0.0094 +/- 0.001 m(3).s(-1)(810 +/- 90 m(3)/day). In late 2019, several minor explosions partially destroyed the center of the dome. This study highlights the strong potential of the joint use of TanDEM-X and Pleiades DEMs to quantitatively monitor domes at andesitic stratovolcanoes.

Résumé: Herein, we discuss amplitude-frequency noise models for high-quality accelerometric monitoring of a civil engineering building and the benefits of seismic building monitoring policies in weak-to-moderate seismic regions. Since 2004, the city hall building in Grenoble (French Alps) has been monitored continuously. First, accelerometric data from one continuous year are used to derive broadband noise models for the bottom and top of the building. The noise models are compared with (1) the noise sensitivity of the high-gain accelerometer installed in the building and low-cost sensor sensitivity models; (2) the typical earthquake response curves given by Clinton and Heaton (2002); and (3) the earthquakes recorded in the Northern Alps. Then, using earthquakes data, this study highlights threshold values for signal-to-noise ratio ( >= 3 or 9 dB) recordings of earthquake as a function of magnitude and distance for weak-to-moderate earthquakes. We present a preliminary cost-benefit analysis of instrumentation for such regions according to seismic hazard and instrumentation quality. For weak-to-moderate seismic regions like Grenoble area, the capability of high-dynamic accelerometers to record low-amplitude ground motions and building responses is confirmed and encouraged to enable high-quality observation of building response over a broad range of frequencies. Bearing in mind that full-scale building test data are of greater interest for improving our understanding of building response than even the most sophisticated models, the recording of weak-to-moderate earthquakes in building must be broadened using high dynamic instruments to obtain more comprehensive and advanced results.

Résumé: We provide a detailed 3D characterization of the geometry evolution and dissolution rate mapping at the surface of four carbonate samples, namely a calcite spar crystal, two limestone rock fragments, and an aragonite ooid, using time-lapse X-ray micro-tomography during dissolution experiments at pH 4.0. Evaluation of the retreat and mapping of the reaction rates at the whole surface of the samples reveals a large spatial variability in the dissolution rates, reflecting the composition and the specific contributions of the different regions of the samples. While crystal edges and convex topographies record the highest dissolution rates, the retreat is slower for flat surfaces and in topographic lows (i.e., concave areas), suggesting surface-energy related and/or diffusion-limited reactions. Microcrystalline aragonite has the highest rate of dissolution compared to calcite. Surprisingly, rough microcrystalline calcite surface dissolves globally more slowly than the {1014} faces of the calcite spar crystal. The presence of mineral impurities in rocks, through the development of a rough interface that may affect the transport of species across the surface, may explain the slight decrease in reactivity with time. Finally, a macroscopic stochastic model using the set of detachment probabilities at corner, edge, and face (terrace) sites obtained from kinetic Monte Carlo simulations is applied at the spar crystal scale to account for the effect of site coordination onto reactivity. Application of the model to the three other carbonate samples is discussed regarding their geometry and composition. The results suggest that the global dissolution process of carbonate rocks does not reflect only the individual behavior of their forming minerals, but also the geometry of the crystals and the shape of the fluid-mineral interface.

Résumé: We study the 2020 M-w 6.8 Calama earthquake sequence that occurred within the subducting oceanic Nazca plate. The main shock is modelled via waveform inversion using a dynamic rupture model, while detection and location techniques are used to better characterize its aftershock sequence. We analyse the local seismotectonic and thermal context of the subducting Nazca plate to understand the trigger mechanism of this earthquake and how it compares with other significant earthquakes in the vicinity. The stress drop and the related dynamic rupture parameters of the Calama main shock are similar to those of the nearby 2007 M-w 6.8 Michilla and 2015M(w) 6.7 Jujuy intraslab earthquakes, which occurred to the west (trenchwards) and to the east (under the backarc) of the Calama earthquake, respectively. The sequences of these three events were located using a 3-D tomographic velocity model. While the Michilla earthquake sequence occurred within the oceanic crust at temperatures of similar to 250 degrees C, the Calama sequence occurred within the upper lithospheric mantle at similar to 350 degrees C and exhibited a smaller aftershock productivity than Michilla. Additionally, the 3-D tomographic model shows intermediate V-P/V-S ratios (1.72-1.76) in the region of the Calama earthquake. This indicates a less hydrated environment that could be responsible for the smaller aftershock productivity of the Calama earthquake.

Résumé: Investigating spatio-temporal changes in crustal structure is a key to understanding the dynamic processes in the earth's crust associated with large earthquakes and volcanic activities. The dense seismic network in the northeast part of Japan (Tohoku region) allows us to apply seismic interferometry to continuous records of ambient noise data for studying crustal changes related to the 2008 Mw 6.9 Iwate-Miyagi Nairiku earthquake and the 2011 Mw 9.0 Tohoku-oki earthquake. We track changes in both seismic scattering properties and velocities over five years and spatially localize them based on the coda wave decorrelation and travel time sensitivity kernels calculated from the solution of the radiative transfer equation. The 2008 Iwate-Miyagi Nairiku earthquake caused significant changes in both seismic scattering properties and seismic velocities in the vicinity of the epicenter subjected to dynamic or/and static stress perturbations. Changes in scattering properties associated with the 2011 Tohoku-Oki earthquake around some active volcanoes in the Tohoku region are likely related to geofluid migrations triggered by strong vibrations during the large earthquake. The decrease in seismic velocity exists mainly along the eastern coastal region and extends to the central Quaternary volcanic chains under the combined dynamic and static stress changes by the earthquake. The waveform correlation is possibly sensitive to the fluid content and might be a useful indicator of fluid migration in the crust. This is the first comprehensive demonstration and comparison of the spatio-temporal changes of seismic scattering properties and velocities at long-term and regional scales under the influence of two large earthquakes.& COPY; 2023 Elsevier B.V. All rights reserved.

Résumé: Borehole accelerometers are designed to record strong ground movements at depth. They have become an important complement to surface accelerometers for seismic and earthquake engineering applications. Borehole accelerometers present several imple-mentation challenges, including their coupling with the geological environment. One possible coupling solution is the use of small glass beads, which are placed inside the borehole casing with the purpose of filling in any empty space between the sensor and the casing walls. We carried out a test on a shaking table, over a wide range of peak ground accelerations (PGA from 0.17 to 1.64g), allowing the comparison of the sig-nals between a surface accelerometer and a borehole accelerometer coupled through the glass beads. These tests show that there is almost no difference between the surface and borehole accelerometer signals between 0.5 and 25 Hz, and only very small differences outside this band (0.2-0.5 Hz and 25-80 Hz). Furthermore, experience from multiple ver-tical accelerometric arrays show that an installation using glass beads is “reversible”, that is, 30 yr after the initial installation it can still be possible to easily extract the acceler-ometers for repair or replacement, without any problems or damage to the sensors.

Résumé: Solidification of the cores of small planets and moons is thought to occur in the “iron snow” regime, in which iron crystals form near the core-mantle boundary and fall until re-melting at greater depth. The resulting buoyancy flux may sustain convection and dynamo action. This regime of crystallization is poorly understood. Here we present the first laboratory experiments designed to model iron snow. We find that solidification happens in a cyclic pattern, with intense solidification bursts separated by crystal-free periods. This is explained by the necessity of reaching a finite amount of supercooling to re-initiate crystallization once the crystals formed earlier have migrated away. When scaled to planetary cores, our results suggest that crystallization and the associated buoyancy flux would be strongly heterogeneous in time and space, which eventually impacts the time variability and geometry of the magnetic field. In small planets or moons with iron core, solidification proceeds from the top down, producing solid iron crystals at the top of the core. These crystals then fall until they melt at deeper depth, where the temperature is larger. By analogy with snow in the atmosphere, this regime is called iron snow. It creates motions in the liquid core and provides energy for generating a magnetic field. However, the key aspects of this regime remain largely unknown. Using analog laboratory experiments, we have found that solidification occurs in a cyclic pattern, with periods of intense crystal formation followed by quiet periods with no crystals. This happens because crystallization needs a certain amount of cooling below the solidification temperature to be triggered, during which all crystals have risen and melted. Applied to planetary cores, it means that the iron snow would be heterogeneous in space and time, with intermittent and localized crystals falling. This would affect the shape and strength of the planet's magnetic field. We have carried out an experimental study of the dynamics of iron snowOur experiments present crystallization cycles, with intense solidification bursts separated by quiet periodsThis cyclic pattern is controlled by thermal diffusion and by the amount of supercooling required for crystallization

Résumé: East Africa hosts significant reserves of untapped geothermal energy. Exploration has focused on geologically young (<1 Ma) silicic calderas, yet there are many sites of geothermal potential where there is no clear link to an active volcano. The origin and architecture of these systems are poorly understood. Here, we combine remote sensing and field observations to investigate a fault-controlled geothermal play located north of Lake Abaya in the Main Ethiopian Rift. Soil gas CO2 and temperature surveys were used to examine permeable pathways and showed elevated values along a similar to 110 m high fault, which marks the western edge of the Abaya graben. Ground temperatures are particularly elevated where multiple intersecting faults form a wedged horst structure. This illustrates that both deep penetrating graben bounding faults and near-surface fault intersections control the ascent of hydrothermal fluids and gases. Total CO2 emissions along the graben fault are similar to 300 t d (-1); a value comparable to the total CO2 emission from silicic caldera volcanoes. Fumarole gases show d(13)C of -6.4%0 to -3.8%0 and air-corrected He-3/He-4 values of 3.84-4.11 R-A, indicating a magmatic source originating from an admixture of upper mantle and crustal helium. Although our model of the North Abaya geothermal system requires a deep intrusive heat source, we find no ground deformation evidence for volcanic unrest or recent volcanism along the graben fault. This represents a key advantage over the active silicic calderas that typically host these resources and suggests that fault-controlled geothermal systems offer viable prospects for geothermal exploration.

Résumé: Earthquake simulations at the urban scale usually focus on estimating the damages to the built environment and the consequent losses without fully taking into account human behavior in crisis. Yet, human behavior is a key element for improving crisis disaster management; therefore, it is important to include it in seismic crisis simulations. In this study, an agent-based model for the simulation of pedestrian evacuation during earthquakes at the city scale is developed following an interdisciplinary approach. The model recreates the urban conditions using Geographic Information System (GIS) and a synthetic population, in addition to the earthquake consequences on the urban fabric. Moreover, the model integrates realistic human behaviors calibrated using quantitative survey results. We simulate pedestrian outdoor mobility with the different constraints that affect it such as the topography and the presence of debris. The simulator is applied to the case of Beirut, Lebanon. A what-if approach is adopted to analyze the population's safety in case of earthquakes in Beirut, particularly the open spaces' capacity to provide shelters and the effect of debris and realistic human behaviors on people's safety. The simulation results show that less than 40% of the population is able to arrive at an open space within 15 min after an earthquake. This number is further reduced when some open spaces are locked. Debris and realistic human behaviors significantly delay the arrivals to safe areas and, therefore, should not be neglected in earthquake simulations.

Résumé: Various earthquake models predict that aseismic slip modulates the seismic rupture process but actual observations of such seismic-aseismic interaction are scarce. We analyze seismic and aseismic processes during the 2014 Iquique earthquake sequence. High-rate Global Positioning System displacements demonstrate that most of the early afterslip is located downdip of the M 8.1 mainshock and is accompanied by decaying aftershock activity. An intriguing secondary afterslip peak is located similar to 120 km south of the mainshock epicenter. The area of this secondary afterslip peak likely acted as a barrier to the propagating mainshock rupture and delayed the M 7.6 largest aftershock, which occurred 27 hr later. Interevent seismicity in this secondary afterslip area ended with a M 6.1 near the largest aftershock epicenter, kicking the largest aftershock rupture in the same area. Hence, the interevent afterslip likely promoted the largest aftershock nucleation by destabilizing its source area, favoring a rate-dependent cascade-up model. Subduction zone faults host both fast (regular earthquakes, seismic) and slow (aseismic) slip. Simulation models predict that slow slip can affect fast slip processes. We explored such an interaction taking place during the 2014 Iquique earthquake offshore northern Chile using observation data of crustal deformation by Global Positioning System and earthquakes. We discovered that the fast mainshock slip was terminated by a slowly slipping fault zone, which prevented the simultaneous occurrence of the largest aftershock. Furthermore, afterslip, one type of slow slip following the mainshock, helped the occurrence of the largest aftershock 27 hr after the mainshock. Therefore, the sequential occurrence of large earthquakes can be controlled by slowly slipping faults. Global Positioning System captured crustal deformation during 27 hr between the 2014 Iquique mainshock and its largest aftershockThe mainshock and the largest aftershock areas are separated by an aseismic area, likely preventing both from rupturing as a single eventThe largest aftershock nucleation is a mixture of seismicity and decelerating afterslip, favoring a rate-dependent cascade-up model

Résumé: The biophysical foundations of socio-economic systems are underrepresented in the vast majority of macroe-conomic models. This lack is particularly troublesome when considering the links between energy, matter and the economy in the context of the energy transition. As a remedy, we present here a biophysical stock-flow consistent macroeconomic model calibrated at the global scale, that combines detailed bottom-up estimates for the high capital intensity of renewable energies and the decreasing energy return on investment (EROI) of fossil fuels. We find that the completion of a global energy transition scenario compatible with the 1.5 degrees C objective of the Paris Agreement leads to a decrease of the system's EROI and to high investment share, employment and inflation trends, characteristic of a “war economy”. Our results further indicate that a slower growth rate eases the transition, and call for further work on post-growth scenarios studies.

Résumé: A new diamond anvil cell experimental approach has been implemented at the European x-ray Free Electron Laser, combining pulsed laser heating with MHz x-ray diffraction. Here, we use this setup to determine liquidus temperatures under extreme conditions, based on the determination of time-resolved crystallization. The focus is on a Fe-Si-O ternary system, relevant for planetary cores. This time-resolved diagnostic is complemented by a finite-element model, reproducing temporal temperature profiles measured experimentally using streaked optical pyrometry. This model calculates the temperature and strain fields by including (i) pressure and temperature dependencies of material properties, and (ii) the heat-induced thermal stress, including feedback effect on material parameter variations. Making our model more realistic, these improvements are critical as they give 7000 K temperature differences compared to previous models. Laser intensities are determined by seeking minimal deviation between measured and modeled temperatures. Combining models and streak optical pyrometry data extends temperature determination below detection limit. The presented approach can be used to infer the liquidus temperature by the appearance of SiO2 diffraction spots. In addition, temperatures obtained by the model agree with crystallization temperatures reported for Fe-Si alloys. Our model reproduces the planetary relevant experimental conditions, providing temperature, pressure, and volume conditions. Those predictions are then used to determine liquidus temperatures at experimental timescales where chemical migration is limited. This synergy of novel time-resolved experiments and finite-element modeling pushes further the interpretation capabilities in diamond anvil cell experiments.

Résumé: Northwestern South America is a plate boundary zone where the Nazca, Caribbean and South American plates interact to produce a wide area of active continental deformation from the Gulf of Guayaquil (latitude 3 & DEG;S) to Venezuela. Previous studies have identified a & SIM;2000-km-long continental sliver, referred as the North Andean Sliver (NAS), squeezed between the Nazca, Caribbean and South American plates and escaping at & SIM;1 cm yr(-1) northeastward with respect to South America. Subduction of the Nazca Plate beneath the NAS has produced a sequence of large and great earthquakes during the 20th century along the coast of Ecuador and Colombia. Large crustal earthquakes up to magnitude 7.7 have been documented along the proposed eastern boundary of the NAS. However, active tectonics data, historical and recent earthquakes all indicate active fault systems within the NAS, possibly resulting from the interaction of several tectonic blocks. Here, we derive an extensive horizontal velocity field using continuous and episodic GNSS data from 1994 to 2019.9, covering northern Peru, Ecuador, Colombia, Panama and Venezuela. We model the GNSS velocity field using a kinematic elastic block approach that simultaneously solves for rigid tectonic block rotations and interseismic coupling along the subduction interfaces and along major crustal faults. In contrast to previous results that considered a single rigid NAS, our dense GNSS velocity field demonstrates that the NAS undergoes significant internal deformation and cannot be modelled as single rigid block. We find that block kinematics in the northern Andes are well described by the rotation of 6 tectonic blocks, showing increasing eastward motion from south to north. The Eastern boundary of the sliver is defined by a right-lateral transpressive fault system accommodating 5.6-17 mm yr(-1) of motion. Fragmentation of the NAS occurs through several fault systems with slip rates of 2-4 mm yr(-1). Slow reverse motion is found across the sub-Andean domain in Ecuador and northern Peru at 2-4 mm yr(-1), marking a transitional area between the NAS and stable South America. In contrast, such a transitional sub-Andean domain does not exist in Colombia and western Venezuela. At the northwestern corner of Colombia, fast (& SIM;15 mm yr(-1)) eastward motion of the Panama block with respect to the NAS results in arc-continent collision. We propose that the Uramita fault and Eastern Panama Deformed Zone define the current Panama/NAS boundary, accommodating 6 and 15 mm yr(-1) of relative motion, respectively. A fraction of the Panama motion appears to transfer northeastward throughout the San Jacinto fold belt and as far east as longitude & SIM;75 & DEG;W. Along the Caribbean coast, our model confirms, slow active subduction at & SIM;4.5 mm yr(-1) along the South Caribbean Deformed Belt offshore northern Colombia and a relatively uniform rate of & SIM;1-2 mm yr(-1) offshore northern Venezuela. Along the Nazca/NAS subduction interface, interseismic coupling shows a first-order correlations between highly locked patches and large past earthquake ruptures. These patches are separated by narrow zones of low/partial coupling where aseismic transients are observed. Compared to previous studies, our interseismic coupling model highlights the presence of deep coupling down to 70 km in Ecuador.

Résumé: The Indian collision has deformed the eastern Asian continent in a multifaceted way, uplifting Tibet and surrounding mountains, activating >= 1,000 km-long strike-slip faults, and opening Tertiary rifts and oceanic basins up to approximate to 3,000 km away from the Himalayas. Modeling such broad-scale tectonics has been challenging. While continent-scale, lithospheric deformation appears to have been primarily taken-up by long, narrow, inter-connected shear-zones with large offsets, the contribution of processes such as channel-flow, collapse, delamination, etc horizontal ellipsis has remained contentious. Here, based on increasing (4)G (Geological, Geophysical, Geochronological, Geodetic) evidence including kinematic and timing constraints on the main mechanisms at play, we use Discrete Element (DE) Modeling to simulate and further understand the evolution of 3D strain across east Asia since the onset of collision, approximate to 55 Ma ago. The planar, 50 million km(2), 125 km-thick models are scaled for gravity. The approach permits mega-fault generation and evolution without pre-arranged initial settings. The results provide insight into fault birth, propagation and motion, as well as mountain building and plateau growth. They corroborate that continental crustal thickening across Tibet alternated with the extrusion of large blocks that rifted apart in the far field. Remarkably, without changes in boundary conditions or indentation rate, the DE model also vindicates slip reversal along initial strike-slip shear zones. To better understand the Tertiary, three-dimensional tectonics of South-Eastern Asia, mostly a result of the north-eastwards penetration of “rigid” India since approximate to 55 Ma, we use a Discrete Element Modeling approach. The technique permits the generation and evolution of large faults without initial pre-setting. The model results substantiate the northwards growth of 4/5 Tibet sub-plateaus, atop south-dipping, subducted lithospheric slabs. Two long strike-slip faults, comparable to the Ailao-Shan-Red River and Altyn Tagh-Haiyuan shear zones, successively propagate to the eastern boundary of the model, where they generate extensional basins similar to the South China Sea and North China Rifts. They isolate two stable blocks (approximate to Sunda and South China). Remarkably, without changes in indentation rate, the activation of the northern shear zone triggers slip reversal on the southern one, as observed along Yunnan's Red River faults since the Miocene. On the west side of Sunda, the model generates faults comparable to the Sagaing fault and triangular basins similar to the Andaman and Mergui basins. Finally, the model suggests that crustal thickening across Tibet alternated with strike-slip faulting. The main discrepancy between tectonic observations and model results is the striking difference in strike-slip fault orientation, likely due to age-dependent lithospheric strength.

Résumé: Calcium carbonate and cadmium-rich fluid interactions have been studied at the nano and microscale with fluid flow and static fluid conditions for three forms of CaCO3: calcite in single crystals of Iceland Spar, calcite in a polycrystalline Carrara marble, and aragonite single crystals. Atomic Force Microscopy (AFM) showed the nanoscale effect of cadmium on CaCO3 dissolution and growth under flow-through conditions at ambient tem-perature, with the modification of calcite dissolution behaviour and simultaneous precipitation of a Cd-rich phase on all the different samples. Hydrothermal experiments at 200 degrees C revealed that the reactivity of single calcite crystals is passivated by epitaxial growth of the less soluble Cd-rich endmember of the (Ca,Cd)CO3 solid -solution on the sample surface due to the similar crystallographic structures of calcite and otavite (CdCO3). Conversely, the presence of grain boundaries in Carrara marble or the change of crystallographic structure and reaction-induced fracturing in aragonite allowed, to some extent, the pseudomorphic replacement of Carrara marble and aragonite samples by a porous (Ca,Cd)CO3 solid-solution phase of variable composition. These phenomena have been observed in solutions undersaturated with respect to all solid phases and are the result of an interface-coupled dissolution-precipitation mechanism where the dissolving CaCO3 provides ions to super-saturate the mineral-fluid interfacial layer, leading to the precipitation of a Cd-containing phase on the samples' surfaces. This coupled dissolution-precipitation mechanism could potentially be used as a remediation process to sequester cadmium from contaminated effluents.

Résumé: The exhumation of bedrock is controlled by the interplay between tectonics, surface pro-cesses, and climate. The highest exhumation rates of centimeters per year are recorded in zones of highly active tectonic convergence such as the Southern Alps of New Zealand or the Himalayan syntaxes, where high rock uplift rates combine with very active surface processes. Using a combination of different thermochronometric systems including trapped-charge ther-mochronometry, we show that such rates also occur in the Hida Mountain Range, Japanese Alps. Our results imply that centimeter per year rates of exhumation are more common than previously thought. Our thermochronometry data allow the development of time series of exhumation rate changes at the time scale of glacial-interglacial cycles, which show a four-fold increase in baseline rates to rates of -10 mm/yr within the past -65 k.y. This increase in exhumation rate is likely explained by knickpoint propagation due to a combination of very high precipitation rates, climatic change, sea-level fall, range-front faulting, and moderate rock uplift. Our data resolve centimeter-scale sub-Quaternary exhumation rate changes, which show that in regions with horizontal convergence, coupling between climate, surface processes, and tectonics can exert a significant and rapid effect on rates of exhumation.

Résumé: Wet chemistry C-S-H precipitation experiments were performed under controlled conditions of solution supersaturation in the presence and absence of gluconate and three hexitol molecules. Characterization of the precipitates with SAXS and cryo-TEM experiments confirmed the presence of a multi-step nucleation pathway. Induction times for the formation of the amorphous C-S-H spheroids were determined from light transmittance. Analysis of those data with the classical nucleation theory revealed a significant increase of the kinetic prefactor in the same order as the complexation constants of calcium and silicate with each of the organics. Finally, two distinct precipitation regimes of the C-S-H amorphous precursor were identified: i) a nucleation regime at low saturation indexes (SI) and ii) a spinodal nucleation regime at high SI where the free energy barrier to the phase transition is found to be of the order of the kinetic energy or less.

Résumé: Multiple-step nucleation pathways have been observed during mineral formation in both inorganic and biomineral systems. These pathways can involve precursor aqueous species, amorphous intermediates, or metastable phases. Despite the widespread occurrence of these processes, elucidating the precise nucleation steps and the transformation mechanisms between each step remains a challenging task. Using a suite of potentiometric, microscopic, and spectroscopic tools, we studied the nucleation pathway of SrSO4 as a function of the physico-chemical solution parameters. Our observations reveal that below a threshold supersaturation, nucleation is driven by bound species, akin to the prenucleation cluster model, which directly leads to the formation of the stable phase celestine, SrSO4. At higher supersaturations, this situation is altered, with nucleation dominated by the consumption of free ions. Importantly, this change in nucleation mechanism is coupled to the formation of a hemihydrate metastable phase, SrSO4 & BULL; 1/2H(2)O, which eventually transforms into celestine, adhering to Ostwald's rule of stages. This transformation is a solution-mediated process, also occurring in the presence of a fluid film and is controlled by the physico-chemical parameters of the surrounding environment. It proceeds through the dissolution of the metastable phase and the de novo crystallization of the final phase. Overall, our results reveal that ion association taking place during the prenucleation stage dictates whether the nucleation pathway goes through an intermediate phase or not. This also underlines that although Ostwald's rule of stages is a common process, it is not a prerequisite for mineral formation-even in systems where it can occur.

Résumé: The significant weight of the building sector in global material demand has been addressed in several publications, but a lack of consideration of the energy-materials nexus was identified. To fill this gap, we developed a stock-flow dynamic model from 1950 to 2100, using scenarios of the International Energy Agency and the Shared Socioeconomic Pathways of the academic literature. We find that (i) the increasing stocks in the less developed countries results in a rise of the inflows; (ii) strong inequalities are observed in the in-use stocks per capita of materials in the SSPs, despite optimistic material intensities projection, (iii) a growing materials demand translates into larger final energy demand of material production, which could question the feasibility of some low-energy demand scenarios, and that (iv) the recycled concrete aggregated display a significant potential to enhance the reduction of accumulated concrete stocks in landfills and green concrete could decrease the energy demand of concrete production. We furthermore highlight the crucial temporal aspect of policies to successfully implement these solutions, as long lifetimes are observed in the building sector.

Résumé: The amount of water contained in a snowpack, known as snow water equivalent (SWE), is used to anticipate the amount of snowmelt that could supply hydroelectric power plants, fill water reservoirs, or sometimes cause flooding. This work introduces a wireless, non-destructive method for monitoring the SWE of a dry snowpack. The system is based on an array of low-cost passive radiofrequency identification (RFID) tags, placed under the snow and read at 865- 868 MHz by a reader located above the snow. The SWE was deduced from the phase delay of the tag's backscattered response, which increases with the amount of snow traversed by the radiofrequency wave. Measurements taken in the lab-oratory, during snowfall events and over 4.5 months at the Col de Porte test field, were consistent with reference mea-surements of cosmic rays, precipitation and snow pits. SWE accuracy was +/- 18 kg m(-2) throughout the season (averaged over three tags) and +/- 3 kg m(-2) during dry snowfall events (averaged over data from two antennas and four or five tags). The overall uncertainty compared to snow weighing was +/- 10 % for snow density in the range 61-390 kg m(-3). The main limitations observed were measurement bias caused by wet snow (biased data were discarded) and the need for phase unwrapping. The method has a number of advantages: it al-lows for continuous measurement (1 min sampling rate in dry snow), it can provide complementary measurement of tag temperature, it does not require the reception of external data, and it opens the way towards spatialized measurements. The results presented also demonstrate that RFID propagation-based sensing can remotely monitor the permittivity of a low-loss dielectric material with scientific-level accuracy.

Résumé: The eastern margin of the Tibetan Plateau has given rise to much debate about mechanisms of plateau uplift and evolution and, in particular, the role of the lower crust in crustal thickening. Knowledge of the middle to lower crust conditions is critical for evaluating various models of crustal deformation, but data on crustal evolution through time are lacking. Here, we turn to the Gongga Shan granite, an intrusion along the Xianshuihe fault in easternmost Tibet that directly records local Cenozoic crustal conditions. We present 124 U-Pb samples from the Gongga Shan granite (GSG) that prove that the crust has been stepwise producing partial melt from 56 Ma to 4 Ma. According to the age distribution, the GSG can be separated into four major groups with ages of 4-10 Ma, 12-20 Ma, 25-40 Ma, and 43-56 Ma. Combining the timing information with geophysics and low-temperature thermochronology data, we suggest that events younger than 10 Ma may indicate the onset of recent crustal channel flow in the middle to lower crust. In contrast, the youngest 4 Ma ages indicate the ongoing partial melting of the middle crust. The 12-20 Ma events could be related to an earlier stage of crustal channel flow, consistent with the regional large-scale crustal channel flow in central Tibet.

Résumé: The Trans-Mexican Volcanic Belt is an active continental volcanic arc related to subduction along the Middle America trench. It is characterized by intra-arc extension resulting into several major arc-parallel active fault systems and tectonic basins. The Acambay graben, one of the largest of these basins, is located near Mexico City, in the central part of this province. In 1912, a M 6.9 earthquake ruptured the surface along the northern border of the graben together with at least two other faults. In this paper, we analyze the paleoseismic history of the southern border of the Acambay Graben, with new observations made in one natural outcrop and four paleoseismological trenches excavated across branches of the Venta de Bravo Fault at the site where it overlaps with the Pastores Fault. We present evidence of at least two paleo-earthquakes that occurred between 12,190 +/- 175 and 5,822 +/- 87 cal year BP and between 647 +/- 77 and 250 cal year BP. On one of these branches, we estimate a minimum slip-rate value between 0.1 and 0.23 mm/year for the last 12 ka and a mean recurrence interval of 8.5 +/- 3 ka. By considering several likely rupture lengths along the Venta de Bravo and Pastores faults, we calculated a maximum possible magnitude of M-w 7.01 +/- 0.27. Finally, by correlating events recorded along different faults within the Acambay Graben, we discuss several possible rupture coalescent scenarios and related consequences for Mexico City.

Résumé: This paper provides an explicit geometric and coordinate-free formulation of incremental discrete mechanics in the framework of potentially non integrable hypoelasticity. First, the general framework is developed in order to tackle hypoelasticity as an Ehresmann connection on the cotangent bundle T*M. Two types of incremental evolutions may be distinguished, the weak or integrable incremental evolutions and the strong or non integrable incremental evolutions, according to the nature of the hypoelastic constitutive law. The geometric structure of the double tangent bundle TT*M is fully used in order to get the geometric counterpart kappa of the so-called tangent stiffness matrix. Subject to specific conditions in TT*M, the incremental evolution is then a well-founded question. An hypoelastic four-grains granular system illustrates in detail these general results.

Résumé: The 2021 M-w 7.4 Maduo earthquake (eastern Tibetan Plateau), with a surface deformation zone that is characterized by multiple distinct surface rupture segments separated by segments with no surface ruptures, provides an excellent opportunity to constrain the strain threshold (minimum strain) for the formation of surface ruptures. Through sub-pixel correlation of pre- and post-event SPOT-6/7 satellite images (pixel = 1.5 m), we derive surface displacement and shear-strain fields of the Maduo earthquake. By quantifying the minimum shear strain along the surface rupture segments and the maximum shear strain along the segments with no surface ruptures, we estimate a rupture strain threshold, which ranges from 0.8% to 1.8% and appears to decrease with structural maturity of the causative fault. This threshold is generally consistent with a rupture strain limit (0.5%-1.5%) of intact rocks from laboratory measurements, and is higher than a commonly-assumed strain threshold (0.5%) for inelastic deformation.

Résumé: The uncommon association of ammonium sulfates identified in the Pastora abandoned mine is the result of a complex mineral evolution. By means of dissolution-(re)crystallization reactions operating during long periods of time, ammonium minerals “adapt” to local spatiotemporal changes in physico-chemical conditions. We found that during such an evolution, seasonal variations in temperature and humidity, the relative solubility of mineral species, and the presence of organic matter play an important role. In addition, our study shows the existence of “mineral niches” and “mineral seasonality,” which can be explained on the basis of the “mineral ecology” concept introduced by Hazen et al. (2015). Our investigation of the formation of hydrated sulfates, particularly of ammonium sulfates, might be of importance for identifying the existence of life in mineral formation environments.

Résumé: Understanding the mechanical behavior of rocks is crucial in subsurface activities, including storage of carbon dioxide and hydrogen gases, which both rely on shale caprocks as potential sealing barriers. Several current large-scale initiatives focus on potential carbon storage in North Sea aquifers. The Draupne Formation contains a series of shale layers interbedded with sandstone layers, the overall thickness of which varies in the range from tens to hundreds of meters. Injection of carbon dioxide into the underlying sandstone reservoirs leads to changes in the surrounding stress field, which can result in fault reactivation or the creation of microfractures, and thus, alter the performance of the shale caprock. Time-resolved microcomputed tomography (4D μCT) has, in recent years, become a powerful technique for studying the mechanical properties of rocks under stress conditions similar to those prevailing in geological reservoirs. Here, we present results from experiments performed on Draupne shale using a triaxial rig combined with 4D μCT based on synchrotron radiation. Detailed mechanical analysis of the tomography datasets by digital volume correlation reveals the three-dimensional pattern of the temporally evolving deformation field. Intermittent bursts of deformation at different locations within the specimen are observed, which eventu-ally evolve into a major fracture plane extending laterally across the whole sample. This study suggests that the pseudolinear-elastic-appearing behavior in the macroscopic stress-strain relationship previously reported for Draupne shale samples could consist of a series of irreversible processes occurring at various weak points within the sample. The combination of 4D μCT imaging with strain analysis enables in situ investigations of deformation processes via quantification of shear and volumetric strains within the sample, thus providing an improved understanding of the fracture dynamics of shales.

Résumé: In the recent years, the seismological community has adopted deep learning (DL) models for many diverse tasks such as discrimination and classification of seismic events, identification of P- and S-phase wave arrivals or earthquake early warning systems. Numerous models recently developed are showing high accuracy values, and it has been attested for several tasks that DL models perform better than the classical seismological state-of-art models. However, their performances strongly depend on the DL architecture, the training hyperparameters, and the training data sets. Moreover, due to their complex nature, we are unable to understand how the model is learning and therefore how it is making a prediction. Thus, DL models are usually referred to as a 'black-box'. In this study, we propose to apply three complementary techniques to address the interpretability of a convolutional neural network (CNN) model for the earthquake detection. The implemented techniques are: feature map visualization, backward optimization and layer-wise relevance propagation. Since our model reaches a good accuracy performance (97%), we can suppose that the CNN detector model extracts relevant characteristics from the data, however a question remains: can we identify these characteristics? The proposed techniques help to answer the following questions: How is an earthquake processed by a CNN model? What is the optimal earthquake signal according to a CNN? Which parts of the earthquake signal are more relevant for the model to correctly classify an earthquake sample? The answer to these questions help understand why the model works and where it might fail, and whether the model is designed well for the predefined task. The CNN used in this study had been trained for single-station detection, where an input sample is a 25 s three-component waveform. The model outputs a binary target: earthquake (positive) or noise (negative) class. The training database contains a balanced number of samples from both classes. Our results shows that the CNN model correctly learned to recognize where is the earthquake within the sample window, even though the position of the earthquake in the window is not explicitly given during the training. Moreover, we give insights on how a neural network builds its decision process: while some aspects can be linked to clear physical characteristics, such as the frequency content and the P and S waves, we also see how different a DL detection is compared to a visual expertise or an STA/LTA detection. On top of improving our model designs, we also think that understanding how such models work, how they perceive an earthquake, can be useful for the comprehension of events that are not fully understood yet such as tremors or low frequency earthquakes.

Résumé: A review of the localities in continental rocks where H2-rich gases have been reported, showed that they are mainly located near orogenic gold deposits. Two types of geomorphological features known as markers of gas venting in sed-imentary basins were also systematically observed near orogenic gold deposits on satellite images. They consist in both barren ground depressions and high densities of small (<20 m in diameter) circular-and comet-shaped white spots in 32 and 7 localities, respectively. Point pattern analysis revealed that the white spots are self-organized, and similar to previously described vegetation patterns associated with termite mounds and fairy circles. We proposed a geochemical model to account for this relationship between orogenic gold deposits, H2 emanations and geomorphological features. Fe-carbonates are ubiquitous mineral products associated with gold mineralization. They can further dissolve in the presence of aqueous fluid due to their high reactivity below 200 degrees C to produce magnetite and up to-1 mol H2 per kg of rock along with-3 mol/kg CO2. This process induces a solid volume decrease of 50 %. Therefore, we propose that Fe-carbonate dissolution is (1) the primary source of H2 in orogenic gold deposit areas, and (2) involved in the formation of the geomorphological structures reported here, providing a new framework to understand their seem-ingly complex formation. Ground depressions and white spots are possible tools for gold exploration. Actually, we identified four new areas where we suspect possible orogenic gold deposits. The association between H2-rich gas and ground depressions was also made near other formations containing Fe-carbonates such as iron formations and carbonatites. This suggests that H2 production through Fe-carbonate dissolution is not restricted to gold deposits. The global H2 production in crustal rocks associated with Fe-carbonate alteration is estimated to 3 x 105 mol/yr.

Résumé: Two boreholes of an experimental site located in the Cher region (France) were investigated via Full Waveform Acoustic Logging (FWAL). The acoustic tool used for the FWAL experiments is a flexible monopole tool holding two pairs of piezoelectric receivers and a magnetostrictive transducer. The tool was modified to perform both active and passive FWAL. To our knowledge, this change is a novelty. For passive acoustic logging, several runs were recorded to obtain a set of acoustic noise sections from which noise Root Mean Squared (RMS) amplitude logs and spectral amplitude logs in different frequency bandwidths were computed. The acoustic logs resulting from passive acoustic monitoring were compared with P-wave acoustic velocity, core data, and a flowmeter log. It is shown that: (1) the distribution of noise frequencies in the 0-5 kHz is strongly correlated with the variations of the flowmeter, (2) the distribution of noise frequencies and noise RMS amplitude is correlated with the lithology (core description), and the P-wave velocity log. As the noise is simultaneously recorded by two receivers of the tool, an interference noise section was elaborated by correlating and summing pairs of acoustic traces at each depth. This procedure, which can be interpreted as an interferometry analysis, points out the presence of low-frequency waves identified as Stoneley waves. It is shown that the Stoneley wave velocity obtained in passive mode can be used to estimate the shear velocity of the formation.

Résumé: We search for earthquake swarms along the Chilean subduction, from -18 degrees to -39 degrees of latitude, 2003-2020 by developing an objective, model-based method that detects potential swarms as anomalous changes in earthquake rate. A set of 16 swarms is obtained after careful inspection of the candidate swarms; this assessment allows to reject cases for which model errors, rather than 'true' anomalous rate changes, are likely the cause of the detection. Averaging the activity over these 16 episodes, we find indirect evidence for a mostly aseismic driving mechanism, and a mean aseismic to seismic ratio estimated to range between 40 and 90 when using the seismicity rate as a proxy for slip. All the swarms are found in the 20-50 km depth range with the notable exception of one 60-100-km-deep swarm that occurs several days after the 2010 Maule earthquake and downdip of it. The dominant depth range (20-50 km) is in agreement with previous studies that suggest this range to be a transition zone from the shallower, locked part of the subduction, to the freely slipping interface at greater depth and intraslab earthquake activity. The swarms can be separated into three spatial groups, two of which being related to a subducting oceanic ridge. This structural control by fluid-rich geological features is modulated by stress control, that is swarms cluster in time with intermediate to large ruptures, both prior and following them, pointing to a close interplay between seismic slip and aseismic deformation in specific, well separated segments of the Chilean subduction.

Résumé: We have developed a 2D distributional-finite-difference (DFD) algorithm for modeling the propagation of seismic waves in heterogeneous media in the time domain. We revisit the classic staggered finite-difference algorithm by substituting the standard finite-difference operators with the recently introduced DFD operators with the methodological differences we underline. We find that the DFD operators improve the simulation accuracy while maintaining the simple structure of the finite-difference algorithm. Thanks to its weak formalism, the newly developed algorithm accurately and naturally accounts for the free surface, which is a substantial improvement for finite-difference approaches. Moreover, we develop an efficient factorization for the DFD operators. It limits the computational cost of the proposed algorithm to twice that of the finite-difference algorithm. Numerical examples demonstrate that the extra computational burden is well compensated by the superior accuracy of the DFD operators.

Résumé: Solute transport in multiphase flow through porous media plays a central role in many natural systems and geoengineering applications. The interplay between fluid flow and capillary forces leads to transient flow dynamics and phase distributions. However, it is not known how such dynamic flow affects the dispersion of transported species. Here, we use highly resolved numerical simulations of immiscible two-phase flow to investigate dispersion in multiphase flows. We show that repeated activation and deactivation of different flow pathways under the effect of capillary forces accelerates the spreading of solutes compared to single phase flow. We establish the transport laws under dynamic multiphase flows by linking the dispersion coefficient to the Bond number, the ratio of the force driving the flow and the surface tension. Our results determine the controlling factors for solute dispersion in porous media, opening a range of applications for understanding and controlling transport in porous geological systems.

Résumé: Outer Albanides experienced a seismic sequence starting on 21 September 2019, with an M-w 5.6 earthquake, considered a foreshock, and culminated with the main shock on 26 November 2019, followed by a paramount aftershock activity. We propose a model for the coseismic slip distribution using InSAR, permanent, and campaign GNSS measurements. We tested two hypotheses: an earthquake on a thrust plane with the direction N160 degrees and along with a back thrust. By varying the depth and dip angle for the first hypothesis and only the dip angle for the second hypothesis, we concluded the optimal solution is a blind thrust at a 15-km depth dipping eastward 40 degrees, a maximum slip of 1.4 m and an M-w 6.38. A GNSS time-series obtained after 2020 shows two slow slip events (SSEs): the first one is 200 d after the main shock up to 26 d, and the second one is 300 d after the main shock up to 28 d. We tested three hypotheses: SSE along the basement thrust where the main shock has been localized, SSE along the flat formed by the detachment layer of the cover, and SSE along these two faults. We concluded that SSE occurred along the detachment layer or along the two faults.

Résumé: Determining how fracture network development leads to macroscopic failure in heterogeneous materials may help estimate the timing of failure in rocks in the upper crust as well as in engineered structures. The proportion of extensile and shear deformation produced by fracture development indicates the appropriate failure criteria to apply, and thus is a key constraint in such an effort. Here, we measure the volume proportion of extensile and shear fractures using the orientation of the fractures that develop in triaxial compression experiments in which fractures are identified using dynamic in situ synchrotron X-ray imaging. The fracture orientations transition from shear to extensile approaching macroscopic, system-size failure. Numerical models suggest that this transition occurs because the fracture networks evolve in order to optimize the total mechanical efficiency of the system. Our results provide a physical interpretation of the empirical internal friction coefficient in rocks. Fracture networks transition from shear to extensile immediately before macroscopic failure in order to optimize the total mechanical efficiency of the system, according to synchrotron observations and modeling of triaxial compression experiments on granite.

Résumé: An increasing number of bacteria has been shown to form intracellular amorphous calcium carbonates (ACC), as previously observed for biomineralizing eukaryotes. Yet, the short-range order of these bacterial intracellular ACC remains largely unexplored. Because ACC in bacteria is easily lost upon sample preparation, the use of in situ techniques is required to probe ACC within intact cells at the atomic scale. Here, we show the application of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies to study the calcium (Ca) speciation and coordination environment in intact cells of diverse ACC-forming cyanobacteria. Our results show that XANES was effective in detecting ACC in intact cells. Between 60 and 85% of the total Ca in ACC-forming cyanobacteria strains is contained in the ACC phase and the rest in a single phase or a mixture of amorphous phases, possibly Ca complexed by organic molecules. Moreover, the short-range order of cyanobacterial ACC was different from eukaryotic ACC. This short-range order was similar to monohydrocalcite. These findings shed light on the fate of cyanobacterial ACC and the role of ACC-forming cyanobacteria in the Ca biogeochemical cycle.

Résumé: The involvement of meteoric water in orogens dynamics through surface processes is well known as for example in the Himalayas where erosion, resulting of the interplay between climate and tectonics shapes the most spectacular landscapes on the planet. But what about more internal and deepest surface fluid infiltration? Here we report analysis of the delta 18O(water) and delta D(water) of extracted water from fluid inclusions hosted into Cenozoic quartz veins sampled in the core of the Himalayan range, near the Main Central Thrust and the South Tibetan Detachment. Isotopic and microthermometric values suggest a meteoric origin for the fluids trapped in the quartz of syn-to post-kinematic veins formed between 10 to 20 km depth. Moreover, the isotopic compositions obtained in this study on quartz fluid inclusions water collected along a transect across the Himalayan range evolved with the topography in a similar manner than the modern meteoric water. Considering the age of formation of the quartz veins between 18 and 12 Ma, we deduce that the morphology of the Himalayan topographic front was already shaped during the Miocene but located further north. (c) 2023 Elsevier B.V. All rights reserved.

Résumé: We use seismic waveform data from the AlpArray Seismic Network and three other temporary seismic networks, to perform receiver function (RF) calculations and time-to-depth migration to update the knowledge of the Moho discontinuity beneath the broader European Alps. In particular, we set up a homogeneous processing scheme to compute RFs using the time-domain iterative deconvolution method and apply consistent quality control to yield 112 205 high-quality RFs. We then perform time-to-depth migration in a newly implemented 3D spherical coordinate system using a European-scale reference P and S wave velocity model. This approach, together with the dense data coverage, provide us with a 3D migrated volume, from which we present migrated profiles that reflect the first-order crustal thickness structure. We create a detailed Moho map by manually picking the discontinuity in a set of orthogonal profiles covering the entire area. We make the RF dataset, the software for the entire processing workflow, as well as the Moho map, openly available; these open-access datasets and results will allow other researchers to build on the current study.

Résumé: This paper presents numerous new data on the geochemical composition of olivine, clinopyroxene, and leucite phenocrysts, as well as spinel inclusions in olivine and quench glass from lamproites of Gaussberg volcano (East Antarctica). Most of the olivine phenocrysts in the Gaussberg lamproites are high Mg varieties (Fo(89-91)) with elevated Ni contents (up to 4900 ppm) and high Ni/Co ratios. According to data of about 320 clinopyroxene analyses, two groups of diopsidic phenocrysts have been established. Group I consists mainly of high-Mg varieties (Mg#>80), while group II clinopyroxenes are less magnesian (Mg# 52-80). The main difference between the clinopyroxenes of the two groups is the elevated contents of Al2O3, FeO and reduced TiO2, Cr2O3, and NiO in the compositions of group II compared to group I, as well as different contents of trace elements, which may reflect their crystallization from different types of primary melts. According to the study of similar to 550 grains of leucite phenocrysts in the Gaussberg lamproites, it was shown that they correspond to the ideal stoichiometry of leucite K[AlSi2O6] and are enriched in Na2O (0.05-0.35 wt %), but depleted in K2O (19.9-20.9 wt %) compared to leucites from lamproites of other provinces. The BaO content reaches 0.3 wt %, SrO -0.04 wt %. The iron content in most leucite phenocrysts varies within 0.7-1.2 wt % Fe2O3, but some grains have the low Fe2O3 contents (<0.5 wt %). In leucite microlites of the groundmass and rims of phenocrysts, the Fe2O3 content can reach 2.4 wt %, which may indicate more oxidized conditions at lava eruption. Based on the study of natural samples, existing experimental data and numerical models, the order and conditions of crystallization of the Gaussberg lamproites were obtained. Crystallization proceeded in the following order: chromian spinel. chromian spinel + olivine -> olivine + leucite (+/- chromian spinel) -> olivine + leucite + clinopyroxene (+/- chromian spinel). The near-liquidus assemblage represented by high-Mg olivine phenocrysts with inclusions of Cr-spinel was formed in the temperature range from 1180 to 1250 degrees C. Further crystallization of the melt with the formation of an association of olivine+leucite+clinopyroxene phenocrysts could occur at pressures below 2 GPa and temperatures of 1070-1180 degrees C, corresponding to the presence of water in the magmatic system. Estimates of the redox conditions of crystallization of lamproites obtained using different oxybarometers vary in a wide range from QFM-0.5 to QFM+2.3. The elevated Ni contents in liquidus olivines of Gaussberg indicate the high nickel contents in the source. It is shown that the formation of ultra-alkaline magmas in the Gaussberg volcano area is likely related to melting of the continental lithosphere, which was heterogeneous and included both the peridotite mantle and hydrous pyroxenite fragments.

Résumé: In this study we report on the petrography, major and trace element and mineral chemistry, platinum-group elements and Re-Os isotope systematics of depleted ultramafic rock suites from the Itmurundy Block in the North Balkhash ophiolite zone in Kazakhstan. Represented mainly by variably serpentinized harzburgites and dunites, our samples are characterized by low whole-rock Al2O3 (0.33-0.86 wt%), CaO (0.51-0.86 wt%) and Na2O (0.07-0.25 wt%) concentrations, and high-Mg olivine (Fo = 91-92) and orthopyroxene (Mg# = 92-93) contents, together with moderately high spinel Cr-numbers (Cr# = 63-68). They are depleted in incompatible elements (sigma REE, Nb, Sc) and enriched in compatible elements, such as Cr (up to 2817 ppm) and Ni (up to 2327 ppm), representing highly refractory mantle residues derived from a forearc mantle wedge. They underwent 19-23% hydrous partial melting to produce boninitic melts.Os- 187/Os-188 values vary from 0.1202 to 0.12599, and Re-187/Os-188 ratios from 0.230 to 0.316. The Re-Os model ages (T-MA) and maximum Re depletion model age (T-RD) were calculated based on the obtained data. Re-Os isotope systematics suggests that the analysed peridotites formed in two stages: a first stage around 1.5 Ga and a later stage around 668-589 Ma.

Résumé: Seismic barriers are fault portions that promote earthquake rupture arrest and fault segmentation. Despite their fundamental role in controlling the maximum magnitude of earthquakes, the nature of seismic barriers is still uncertain. A common interpretation of barriers as having velocity-strengthening friction-steady-state friction that increases with increasing slip velocity-is only partially consistent with the thermal control of friction observed in laboratory experiments, which implies that most relevant materials in subduction channels are velocity-weakening at seismogenic depths. Here we examine the possibility of velocity-weakening barriers by conducting earthquake cycle simulations along a velocity-weakening megathrust segmented by lateral variations of frictional properties and normal stress. We show that velocity-weakening fault segments display a wide range of behaviours, including permanent barrier behaviour. They can be locked during long periods and release their slip deficit either seismically or aseismically. We quantify the efficiency of velocity-weakening barriers in arresting ruptures using a non-dimensional parameter based on fracture mechanics theory that can be constrained by observations on natural faults. Our results provide a theoretical framework that could improve physics-based seismic hazard assessment. Velocity-weakening seismic barriers in subduction zones display a range of behaviours consistent with geologic structural control on earthquake seismicity, according to earthquake cycle simulations along a megathrust.

Résumé: The fundamental frequency plays a primary role in the dynamic assessment of Cultural Heritage towers. Local and global features may impact its value: geometric, material features, interaction with the soil and adjacent buildings, aging, the construction phase, and repairs. A database is assembled to study the relationship between the fundamental frequency and the slender masonry structure features. Empirical and physics-based approaches were developed to assess the fundamental frequency from different sources of information. A Rayleigh-Ritz approach is proposed and compared with a 3D finite element model. A sensitivity analysis is then performed to quantify the contribution of each feature. As expected, it is shown that the height of the tower contributes the most to the fundamental frequency. The other tower features have a second-order impact on both the fundamental frequency and the mode shape. A comparison between the different approaches shows that the Rayleigh-Ritz drastically minimizes the difference between numerical and experimental frequencies when all information is available. Empirical relations are a good compromise when less information is available.

Résumé: In the perspective of an upcoming seasonally ice-free Arctic, understanding the dynamics of sea ice in the changing climate is a major challenge in oceanography and climatology. In particular, the new generation of sea ice models will require fine parameterization of sea ice thickness and rheology. With the rapidly evolving state of sea ice, achieving better accuracy, as well as finer temporal and spatial resolutions of its thickness, will set new monitoring standards, with major scientific and geopolitical implications. Recent studies have shown the potential of passive seismology to monitor the thickness, density and elastic properties of sea ice with significantly reduced logistical constraints. For example, human intervention is no longer required, except to install and uninstall the geophones. Building on this approach, we introduce a methodology for estimating sea ice thickness with high spatial and temporal resolutions from the analysis of icequake waveforms. This methodology is based on a deep convolutional neural network for automatic clustering of the ambient seismicity recorded on sea ice, combined with a Bayesian inversion of the clustered waveforms. By applying this approach to seismic data recorded in March 2019 on fast ice in the Van Mijen Fjord (Svalbard), we observe the spatial clustering of icequake sources along the shoreline of the fjord. The ice thickness is shown to follow an increasing trend that is consistent with the evolution of temperatures during the 4 weeks of data recording. Comparing the energy of the icequakes with that of artificial seismic sources, we were able to derive a power law of icequake energy and to relate this energy to the size of the cracks that generate the icequakes.

Résumé: Following laboratory experiments and friction theory, slow slip events and seismicity rate accelerations observed before mainshocks are sometimes interpreted as evidence of a nucleation phase. However, such precursory observations still remain scarce and are associated with different time and length scales, raising doubts about their actual preparatory nature. We study the 2017 Valparaiso Mw = 6.9 earthquake, which was preceded by aseismic slip accompanied by an intense seismicity, suspected to reflect its nucleation phase. We complement previous observations, which have focused only on precursory activity, with a continuous investigation of seismic and aseismic processes from the foreshock sequence to the post-mainshock phase. By building a high-resolution earthquake catalog and searching for anomalous seismicity rate increases compared to aftershock triggering models, we highlight an over-productive seismicity starting within the foreshock sequence and persisting several days after the mainshock. Using repeating earthquakes and high-rate GPS observations, we highlight a transient aseismic perturbation starting 1-day before the first foreshock and continuing after the mainshock. The estimated slip rate over time is lightly impacted by large magnitude earthquakes and does not accelerate toward the mainshock. Therefore, the unusual seismic and aseismic activity observed during the 2017 Valparaiso sequence might be interpreted as the result of a slow slip event starting before the mainshock and continuing beyond it. Rather than pointing to a possible nucleation phase of the 2017 Valparaiso mainshock, the identified slow slip event acts as an aseismic loading of nearby faults, increasing the seismic activity, and thus the likelihood of a large rupture. Both laboratory experiments and friction theory show that earthquakes do not begin abruptly but are preceded by an accelerating slip associated with a seismicity increase. On the field, however, such precursory observations still remain scarce and are associated with different characteristic time and length scales, raising doubts that they actually reflect the same nucleation phenomena. We study the 2017 Valparaiso M = 6.9 earthquake, which was preceded by both a slow slip and an intense seismicity suspected to reflect such nucleation phase. We complement previous studies, that have focused only on precursory activity, with a continuous investigation of seismic and slow slip before and after the mainshock. Using refined earthquake detection tools, we highlight a seismicity excess starting before and persisting several days after the mainshock. Using repeating earthquakes and high-resolution GPS, we show that the slow slip does not accelerate toward the mainshock, but continues after it. Therefore, rather than pointing to a possible accelerating nucleation phase of the Valparaiso mainshock, we suggest that the slow slip drives an enhanced seismic activity that is not mainshock-directed. Within such slow-slip driven seismicity, the probability of triggering a large earthquake (subsequently considered as the mainshock) is increased. We use a high resolution seismic catalog and GPS to investigate seismic and aseismic process before and after the Valparaiso mainshockAn unusually high seismicity and a slow slip event is continuously observed from the foreshock sequence up to days after the mainshockRather than a nucleation phase of the mainshock, the slow slip event acts as an aseismic loading of nearby faults during the entire sequence

Résumé: Four previously unrecognized neotectonic fault scarps in southwest Namibia are described. These relatively straight, simple but segmented structures are 16-80 km long and have measured vertical separations of 0.7-10.2 m. We estimate that each is capable of producing earthquakes of M-w 6.4 or greater, indicating that large earthquakes may occur despite limited cumulative displacement. There is strong evidence that some of these scarps were formed by repeated earthquakes. Comparison with aeromagnetic and geological maps reveal that the normal faults reactivate major crustal weaknesses that are orientated north-south and northwest-southeast and perpendicular to the local gravitational potential energy gradient. The presence of these structures in an area with a limited record of instrumental seismicity suggests that the M-max of this region may be much larger than generally assumed. They highlight the necessity of incorporating information from fault studies into probabilistic seismic hazard assessments in this region, in a similar way to other stable continental regions such as Australia. The fact that such major structures have gone hitherto unrecorded suggests significant further research is needed to characterize these sources of hazard. The identification of an apparent cluster of large magnitude neotectonic earthquakes in the area may be related to the exceptional preservation potential of scarps rather than indicating an area of comparatively rapid deformation. If this interpretation is correct, then these scarps represent an important indication of the potential seismic hazard across the region, and the occurrence of infrequent large-magnitude seismicity on similar structures should be considered throughout southwestern Africa.

Résumé: Most of water reservoirs are underground and therefore challenging to monitor. This is particularly the case of karst aquifers which knowledge is mostly based on sparse spatial and temporal observations. In this study, we propose a new approach, based on a supervised machine learning algorithm, the Random Forests, and continuous seismic noise records, that allows the prediction of the underground river water height. The study site is a karst aquifer in the Jura Mountains (France). An underground river is accessible through an artificial shaft and is instrumented by a hydrological probe. The seismic noise generated by the river is recorded by two broadband seismometers, located underground (20 m depth) and at the surface. The algorithm succeeds in predicting water height thanks to signal energy features. Even weak river-induced noise such as recorded at the surface can be detected and used by the algorithm. Its efficiency, expressed by the Nash-Sutcliffe criterion, is above 95 per cent and 53 per cent for data from the underground and surface seismic stations, respectively.

Résumé: Granular materials are now known to be an illustration of complex materials as they display emergent macroscopic properties when loaded. An initially homogenous response can bifurcate into a heterogeneous one with the appearance of a rich variety of structured kinematical patterns. The shear banding that ensues illustrates a symmetry-breaking transition with multiple choices of macroscopic behaviours, a common feature of dynamical complex systems. Even though the phenomenon has been studied for decades, this regime transition remains mostly mysterious in geomaterials, with no convincing arguments that could link it to the underlying microscopic mechanisms. The paper investigates this issue by invoking the fundamental minimum entropy production theorem established by Prigogine in the past century to seek any connection with the second-order work theory in the mechanics of failure. A general equation linking the derivatives of the entropy of a mechanical system to the second-order work is thus inferred, which leads to a thermodynamic interpretation of bifurcations in the failure behaviour of granular materials under a given loading. This is verified through discrete element simulations that highlight the fundamental role played by the elastic energy stored within a granular material before a bifurcation occurs, which also corresponds to a minimization of the entropy production. The analysis suggests a new interpretation of the intriguing shear banding phenomenon as a bifurcation with the emergence of ordered dissipative structures germane to nonequilibrium thermodynamics of open systems.

Résumé: We explored the potential of fibre optics coupled with distributed acoustic sensing (DAS) to measure the thickness and Young's modulus of an ice layer, using the properties of guided seismic waves. During two winter seasons (2020 and 2021), an optical fibre was deployed over one of the frozen Roberts Mountain lakes (at 2400 m a.s.l) near Grenoble (France) and we measured both the continuous ambient seismic noise as well as signals generated by active sources (hammer), with a DAS interrogator. Following a Bayesian scheme, we inverted the dispersion curves of longitudinal and flexural guided waves retrieved from the analysis of active shot gathers and obtained Young's modulus E = 3.4 +/- 0.1 GPa and ice thickness h = 47 +/- 1 cm from the second-year data. The ice thickness was consistent with field measurements. Field observations of porous and/or fracture ice may explain the relatively low effective Young's modulus (relative to pure ice), which may also be affected by a snow layer not included in the model. The drastic improvements in the inversion results between the two years are related to better coupling conditions (drone deployment before early freezing), more appropriate acquisition parameters (2 m gauge length), and the upper snow layers (less thick and less heterogeneous in the second year). Moreover, we were able to use the non-dispersive low-frequency noise associated with gravity waves to estimate the lake depth H = 5 m which is compatible with independent observations. The use of DAS to record guided seismic waves could then appear as a relevant tool for monitoring environments like floating ice shelves and sea ice.

Résumé: There is no doubt that nanotechnology and nanoscience open new doors to new applications and products that can potentially revolutionize the practice field and how we conserve built heritage materials. However, we are living at the beginning of this era and the potential benefits of nanotechnology to specific conservation practice needs are not always fully understood. This opinion/review paper aims to present reflections and answer a question that we are often asked when working directly with stone field conservators: why should we use a nanomaterial instead of a conventional product? Why does size matter? To answer this question, we revise the basic concepts of nanoscience with implications for the built heritage conservation field.

Résumé: Contaminant removal from (waste)waters by magnetite is a promising technology. In the present experimental study, a magnetite recycled from the steel industry waste (zero-valent iron powder) was used to investigate the sorption of As, Sb and U in phosphate-free and-rich suspensions, i.e. as a remediation for the acidic phospho-gypsum leachates derived from the phosphate fertilizer industry. The results showed up to 98% U removal under controlled pH conditions, while phosphate did not hinder this immobilisation. In contrast, the results confirmed the limited uptake of As and Sb oxyanions by magnetite in presence of phosphate as the competing anion, displaying only 7-11% removal, compared to 83-87% in the phosphate-free sorption experiments. To limit this wastewater problem, raw ZVI anaerobic oxidation was examined as mechanism to increase the pH and as a source of Fe2+ in a first step, and in a second step to remove phosphate via vivianite precipitation, therefore prior to the reaction with magnetite. UV-Vis, XRD and SEM-EDS showed that vivianite precipitation is feasible at pH > 4.5, mainly depending on the phosphate concentration. The higher the [PO43-], the lower is the pH at which vivianite precipitates and the higher the % removal of phosphate from solution. It is anticipated that an optimum 3-steps design with separate reactors controlling the conditions of ZVI oxidation, followed by vivianite precip-itation and finally, reaction with magnetite, can achieve high contaminant uptake in field applications.

Résumé: The 43 BCE eruption of Okmok Volcano has been proposed to have had a significant climate cooling impact in the Northern Hemisphere. In this study, we quantify the climate cooling potential of the Okmok II eruption by measuring sulfur concentration in melt inclusions (up to 1,606 ppm) and matrix glasses and estimate a total of 62 +/- 16 Tg S released. The proportion reaching the stratosphere (2.5%-25%, i.e., 1.5-15.5 Tg S) was constrained by physical modeling of the caldera-collapse eruption. Using the NASA Goddard Institute for Space Studies E2.2 climate model we found a linear response between cooling and stratospheric sulfur load (0.05-0.08 degrees C/Tg S). Thus, the 1-2 degrees C of cooling derived from proxy records would require 16-32 Tg sulfur injection. This study underscores the importance of combining approaches to estimate stratospheric S load. For Okmok II, we find all methods are consistent with a range of 15-16 Tg S. Gaseous sulfur released in explosive volcanic eruptions can reflect incoming solar radiation in the stratosphere and cool the Earth's surface. Here, we calculate the total amount of sulfur released in the 43 BCE caldera-forming eruption of Okmok Volcano, Alaska by measuring the concentration of sulfur dissolved in magma prior to the eruption. We find that the total sulfur load from the Okmok II eruption is one of the largest in the last 2,500 years, and we use climate models to simulate cooling and precipitation anomalies associated with total or partial injection of volcanic sulfur into the stratosphere. However, the estimated sulfur load is larger than that predicted by sulfur signals preserved in ice cores, and physical modeling of the eruption suggests that only a proportion of the sulfur released reached stratospheric altitudes. Further, comparison of temperature reconstructions from tree ring and cave deposit proxies with climate model results show the cooling associated with the eruption requires only a fraction of the total sulfur load. Thus, we propose that only a quarter of the total sulfur released in the eruption made it to the stratosphere, responsible for 1-2 degrees C of cooling in the year following the eruption. Petrologic evidence suggests a total of 62 Tg S was released in the caldera-forming eruption of Okmok Volcano in 43 BCEClimate models respond linearly to stratospheric sulfur loads. 1-2 degrees C cooling from proxy records suggests 16-32 Tg S injectionA physical model constrains the proportion of stratospheric sulfur to 2.5%-25%; thus we find a common range for all methods of 15-16 Tg S

Résumé: Coastal boulder deposits (CBDs), named huracanolitos in Cuba, found along rocky shores, result from storms, tropical cyclones or tsunamis. Despite being important indicators for coastal hazard assessment, determining the mode of emplacement of CBDs (storm/hurricane or tsunami) is not easy. We present, for the first time in English, data about CBDs along the shores of the Cuban Archipelago. More specifically, we focused on a CBD, that is, to our knowledge, the largest one ever described on Cuba Island. Located on a low-lying coral reef terrace on the SE shore of the island, the reefal limestone CBD is emplaced seaward of the ruins of the Bucanero resort. The resort was built in 1989, endured hurricanes Ivan (2004) and Dennis (2005) and, in October 2012, was destroyed by Hurricane Sandy. As observed on Corona and Landsat satellite images since 1962, the CBD was not moved, neither by hurricane Flora (1963) nor Sandy (2012), both associated with important storm surges and powerful swells. We determined the CBD volume with open-source structure from motion photogrammetry as 82.6 m(3). Then, we estimated from a sample its density as 2550 kg/m(3). Finally we calculated its weight as 210.6 tons. We calculated the minimum flow velocity responsible for the emplacement of the CBD 33 +/- 2 m inland-6.83 +/- 0.54 m/s and 7.26 +/- 0.51 m/s. Such flow velocities are compatible with those of both tsunamis and hurricanes. Because of the greater frequency of hurricanes than tsunamis in the area, we propose that a tropical cyclone generated the extreme surge and wave that emplaced the Bucanero CBD. Such CBDs demonstrate that on Cuba's south coast, we can expect marine flooding exceeding the flooding during the major hurricanes of recent decades.

Résumé: We consider a model where an unstable frictional region, governed by rate and state friction, interacts with a viscous zone with Newtonian rheology. The system is loaded at distance with a constant velocity. Pore pressure variations are considered and we show that the model of Segall and Rice (1995, ) relating porosity changes to variations of the state variable could be derived considering viscoplastic deformation of a population of identical asperities. We perform a linear stability analysis in the case of a constant pore pressure in agreement with the full numerical results. For a given value of the viscosity of the viscous region, stable slip is promoted at low normal stress and unstable slip at high normal stress. Near the transition from stable to unstable slip, modest acceleration of slip, resembling slow slip events (SSE) are observed. We show that our model can reproduce real SSE sequences in the Guerrero subduction zone which are the largest worldwide. The best fit parameters suggest that SSEs happen in areas of low effective normal stress (for the frictional region) and low viscosity (for the viscous region). In our model, SSEs happen in a regime where the viscous region is able to counteract the instability of the frictional one. We show that considering a rate strengthening rheology or a non newtonian one leads to the same linear stability results. Our work shows that a simple model with homogeneous spatial properties can lead to complex dynamics, covering a wide range of observed sliding modes, from steady-state creep to seismic slip and SSEs.

Résumé: Detrital Be-10 from continental river sands or submarine sediments has been extensively used to determine the average long-term denudation rates of terrestrial catchments, based on the assumption that the rate of cosmogenic nuclide production by the interaction of source rocks with cosmic radiation balances out the loss of these nuclides by surface denudation. However, the Be-10 signal recorded in sediments may be affected at the source by the response time of mountainous catchments to high-frequency forcings. In addition, transient sediment storage in piedmonts, alluvial plains and lakes or near the coast may also induce a difference between the erosive signal and its record in the sedimentary sink. Consequently, a significant part of the signal recorded in shallow-water sediments can be lost, as deep marine sediments may simultaneously record a signal coming from newly eroded source rocks along with one coming from the destabilization of previously deposited sediments. In this paper, we use the landscape evolution model Badlands to simulate erosion, deposition and detrital Be-10 transfer from a source-to-sink sedimentary system (the Var River catchment, southern French Alps) over the last 100 kyr. We first compare model-based denudation rates with the ones that would be extracted from the Be-10 record of local continental sediments (equivalent to river sands) and from sediments deposited offshore over time in order to examine if this record provides an accurate estimate of continental denudation rates. Then, we examine which conditions (precipitation rate, flexure, ice cover) satisfy published measured river incision rates and Be-10 concentration in submarine sediments. Our results, based on the Var catchment cosmic ray exposure dating and modelling indicate that, while river sands do accurately estimate the average denudation rate of continental catchments, this is much less the case for deep submarine sediments. We find that deep-sea sediments have a different and often much smoother Be-10 signature than continental ones and record a significant time lag with respect to imposed precipitation rate changes, representing the geomorphological response of the margin. A model which allows us to fit both measured Be-10 concentration in marine sediments and river incision rates on land involves an increase in precipitation rates from 0.3 to 0.7myr(-1) after 20 ka, suggesting more intense precipitation starting at the end of the Last Glacial Maximum.

Résumé: Hyperextended rift systems are characterized by extreme crustal thinning and mantle exhumation associated with extensional detachment faults. These faults cut through thinned continental crust, reaching the underlying mantle and allowing for seawater to infiltrate and react with the crustal and mantle rocks. Hydrothermal fluid systems linked to detachment faults result in fluid-rock reactions occurring along the detachments, resulting in the breakdown and alteration of minerals, loss of elements and strain weakening in both mantle and crustal rocks. We present new geological observations and geochemical data from the modern Iberia and fossil Alpine Tethys Ocean Continent Transition and the West Pyrenean Mauleon hyperextended rift basin. We show evidence for a km-scale fluid flow along detachment faults and discuss the conditions under which fluid flow and mass transfer occurred. Convective fluid systems are of major importance for mass transfer between the mantle, crustal and marine reservoirs. We identified gains in Si, Mg, Fe, Mn, Ca, Ni, Cr and V along extensional detachment faults that we relate to channelized, hydrothermal crust- and mantle-reacted fluid systems migrating along detachments in the hyperextended continental crust. The observation that fault rocks of extensional detachment and syn-extensional sedimentary rocks are enriched in mantle-derived elements such as Cr, Ni and V enables us to define the pathways of fluids, as well as to estimate their age relative to detachment faulting and sedimentation. Because all three examples show a similar mass transport of elements along detachment systems at km-scale, we conclude that these examples are linked to convective fluid systems that may affect the thermal state of the lithosphere, as well as the rheology and chemistry of rocks in hyperextended systems, and may have implications for ore mineral exploration in hyperextended rift systems.

Résumé: Infrastructures are critical for the functioning of society. Due to globalization, damages between different components of infrastructure systems can cross international boundaries, resulting in broad economic and social impacts. Hence, it is fundamental to develop powerful tools for the assessment of infrastructure risk, considering a wide spectrum of uncertainties. Past studies covering infrastructure risk assessment are limited to a few countries, partly because for assessing the infrastructure risk, issues due to the complexity of the systems, like paucity and heterogeneity of the data and methods, the consideration of dependencies between components and systems, modeling of ground shaking in terms of scenario and probabilistic approach, taking into account site effects, spatial variability and cross correlation of ground motion at the urban scale, as well as consideration of risk metrics tailored to infrastructure, still remain partially or not properly answered. Moreover, the presently available infrastructure risk assessment tools are not sufficiently illustrative, user-friendly, and comprehensive to meet actual needs. To this end, the paper making an overview of these issues proposes a comprehensive approach that leverages the main strength of existing infrastructure risk methodologies, integrating them into a powerful open-source tool and providing common platform from hazard to risk analysis that will serve for global and easy usage. The methodology and its implementation are illustrated through a test-bed study of the water supply network of the city of Thessaloniki in Greece, considering an M-w 6.5 scenario of the 1978 Thessaloniki earthquake and an event based probabilistic approach and, simultaneously evaluating the sensitivity of cross spatial correlation.

Résumé: The Lesser Antilles subduction zone marks the convergence between the Caribbean Plate and the oceanic Atlantic part of the America Plate. A specificity of this subduction is the development of a huge accretionary prism, the Barbados complex. As other subduction zones, the Lesser Antilles one has the potential to produce megathrust-associated earthquakes and related tsunamis. This study evaluates the potential hazard of tsunami scenarios along this eastern boundary of the Caribbean Plate, taking into account its specificities. We define six scenarios along the Lesser Antilles subduction zone including three M-w 7.5, 8.0 and 8.5 earthquake models, in both northern and southern parts of the arc. We incorporate in tsunami simulations the effect of sediment amplification in tsunami generation. In the southern half, the thick sediments pile, related to tectonic accretion, appears much more effective than the much thinner accumulation characterizing the northern half. The bed shear stress is also computed in this study as it is an important factor in sediment transport which can show the potential locations for sediment movement by tsunamis. Our results indicate the ability of scenario earthquakes to produce powerful tsunamis. The impacts of northern scenarios on Guadeloupe could be severe (maximum tsunami wave height of > 5 m ), whereas the impacts from southern scenarios are relatively less strong (maximum wave amplitude of < 5 m ). The tsunami waves produced by M-w 8.0 and 8.5 appear able to inundate the coast of Sainte-Anne, Guadeloupe, up to 2 km . The distributions of bed shear stress from northern scenarios suggest that the offshore Leeward Islands could be potentially prone to sediment transport as possible tsunami deposits have been found in the region in former geological studies.

Résumé: Mountaineering is a sport highly dependent on the conditions of the physical environments in which it takes place. As a result, mountaineers have to deal with major glacial and periglacial hazards, such as those affecting the two main routes used to climb Mont Blanc (4808 m a.s.l.; Western European Alps): rockfalls in the Grand Couloir du Gouter on the Voie Royale and serac falls on the NNW slope of Mont Blanc du Tacul on the Trois Monts route. Hazards in these two sectors and the number of climbers were measured using a multi-sensor system and automatic photographic acquisition, respectively. On the first site, which has a very high accident rate with an average of 3.7 deaths per year, 17,768 passages were recorded during the summer of 2019 and 2,648 seismic signals were classified as rockfalls affecting the Grand Couloir. The average risk of death associated with these rockfalls, the frequency of which depends on temperatures and the presence of liquid water in the ground, is estimated at 1.7 x 10-4. At Tacul, where an average of 0.6 deaths occur each year, 6,770 passages were recorded during the summer of 2017, as well as 31 serac falls unrelated to temperatures. The risk of death is 8.3 x 10-5. The risk is also quantified for each track made on the glacier. The results obtained makes it possible to specify the risks experienced by climbers and to promote risk reduction strategies.

Résumé: Tectonics exerts a strong control over the morphology of Earth's surface that is apparent in active mountain belts. In lowland areas, subtle processes like lithospheric flexure and isostatic rebound can impact Earth surface dynamics, hydrologic connectivity, and topography, suggesting that geomorphic and hydrologic analyses can shed light on underlying lithospheric properties. Here we examine the effect of lithospheric flexure on the geomorphology, hydrology, and river water chemistry of the Rio Bermejo fluvial system in the east Andean foreland basin of northern Argentina. Results show that proximal to the mountain front, foredeep basin subsidence causes sedimentation along a braided channel belt that is superelevated relative to the surrounding flood basin. During floods, water flows from the superelevated channel into the groundwater reservoir, causing a net loss of discharge with distance downstream. Further downstream, forebulge uplift forces channel narrowing, high lateral migration rates, and incision up to 13 m into older river deposits. This incision locally allows groundwater flow into the river, causing a similar to 20% increase in river solute load. Groundwater emerges from the forebulge into the backbulge, predominantly as spring-fed channels. Here, channel migration rates decrease, suggesting a switch from net uplift to subsidence that reduces the depth to the groundwater table. This analysis shows that subtle lithospheric flexure can have significant effects on river channel morphology that determine hydrologic flow paths, and ultimately influence geochemical and ecological patterns. We suggest that these effects may elucidate lithospheric properties that are otherwise inferred from bulk geophysical observations.

Résumé: The ability of numerical sea ice models to reproduce localized deformation features associated with fracture processes is key for an accurate representation of the ice dynamics and of dynamically coupled physical processes in the Arctic and Antarctic.Equally key is the capacity of these models to minimize the numerical diffusion stemming from the advection of these features to ensure that the associated strong gradients persist in time, without the need to unphysically re-inject energy for re-localization.To control diffusion and improve the approximation quality,we present a new numerical core for the dynamics of sea ice that is based on higher-order finite-element discretizations for the momentum equation and higher-order discontinuous Galerkin methods for the advection. The mathematical properties of this core are discussed, and a detailed description of an efficient shared-memory parallel implementation is given. In addition, we present different numerical tests and apply the new framework to a benchmark problem to quantify the advantages of the higher-order discretization. These tests are based on Hibler's viscous-plastic sea ice model, but the implementation of the developed framework in the context of other physical models reproducing a strong localization of the deformation is possible.

Résumé: The Late Glacial (14 700-11 700 cal BP) is a key climate period marked by rapid but contrasted changes in the Northern Hemisphere. Indeed, regional climate differences have been evidenced during the Late Glacial in Europe and the northern Mediterranean. However, past climate patterns are still debated since temperature and precipitation changes are poorly investigated towards the lower European latitudes. Lake Matese in southern Italy is a key site in the central Mediterranean to investigate climate patterns during the Late Glacial. This study aims to reconstruct climate changes and their impacts at Matese using a multi-proxy approach including magnetic susceptibility, geochemistry (XRF core scanning), pollen data and molecular biomarkers like branched glycerol dialkyl glycerol tetraethers (brGDGTs). Paleotemperatures and paleo-precipitation patterns are quantitatively inferred from pollen assemblages (multi-method approach: modern analogue technique, weighted averaging partial least-squares regression, random forest and boosted regression trees) and brGDGT calibrations. The results are compared to a latitudinal selection of regional climate reconstructions in Italy to better understand climate processes in Europe and in the circum-Mediterranean region. A warm Bolling-Allerod and a marked cold Younger Dryas are revealed in all climate reconstructions inferred from various proxies (chironomids, ostracods, speleothems, pollen, brGDGTs), showing no latitudinal differences in terms of temperatures across Italy. During the Bolling-Allerod, no significant changes in terms of precipitation are recorded; however, a contrasted pattern is visible during the Younger Dryas. Slightly wetter conditions are recorded south of 42(?) N, whereas dry conditions are recorded north of 42(?) N. During the Younger Dryas, cold conditions can be attributed to the southward position of North Atlantic sea ice and of the polar frontal jet stream, whereas the increase in precipitation in southern Italy seems to be linked to relocation of Atlantic storm tracks into the Mediterranean, induced by the Fennoscandian ice sheet and the North European Plain. By contrast, warm conditions during the Bolling-Allerod can be linked to the northward position of North Atlantic sea ice and of the polar frontal jet stream.

Résumé: We confirm the presence of interannual oscillations of period about 5.9 and 8.5 years in the Earth's length of day (LOD), better visible after subtracting the atmospheric contribution. Continental water mass redistribution and oceanic angular momentum contribute to a lesser extent, and are furthermore mostly compensated by sea level variations. We show, using a continuous wavelet transform analysis of synthetic oscillators embedded into a random correlated noise, the limits of isolating damped signals presenting nearby periods in time series of limited duration. In particular, we emphasize the possibility that a previously documented 7.3-year oscillation could be an artefact associated with the restricted available time span covered by LOD data. Finally, we perform a wavelet coherence analysis between geodetically observed LOD changes and their prediction from geomagnetically inferred core flow models. It confirms an origin from the fluid outer core for the two signals around 5.9 and 8.5 years. A convincing coherence is also found around 3.5 and 5 years, which may reveal signatures of higher harmonics of torsional modes or of quasi-geostrophic magneto-Coriolis modes.

Résumé: The Magallanes-Fagnano Fault is an active left-lateral strike-slip fault that cuts across Tierra del Fuego, forming the boundary between the South American and the Scotia plates. This fault may trigger strong earthquakes, as documented by the occurrence of two M-w >= 7.5 in December 1949. However, this region is characterized by one of the shortest historical archives in the world and by a growing population. The geological record is therefore needed in order to characterize the seismic information over a longer time scale and to improve the seismic hazard assessment. We conducted extensive field work, neotectonic mapping and excavated two paleoseismic trenches across one of the sharpest tectonic scarps in the Eastern onshore portion of the fault. Using scarp-derived colluvial wedges, cross-cutting relations, and 28 radiocarbon samples, we document evidences of at least six paleo-earthquakes during the Holocene. Paleoseismic record is particularly accurate for the last two thousand years, for which period we determine an average recurrence interval of 1080 +/- 150 years. For repeated earthquakes of same magnitude as the 1949 event, this recurrence interval is compatible both with the known geodetic and geomorphic slip rates. However, “paired earthquakes” in less than one or two centuries may also occur, suggesting that fault behavior could be characterized by irregular seismic cycles. Plain Language Summary The Magallanes-Fagnano Fault is a main active fault in Tierra del Fuego, at the southern tip of South America. This remote region has one of the shortest historical seismic record in the world. However, this fault may trigger strong earthquakes as occurred in 1949 and the surrounding population has been massively growing since. We therefore studied the paleo-earthquake history of the fault to improve the seismic hazard assessment. We analyzed and dated the disrupted sediments in two trenches excavated across the fault to establish a paleo-earthquake calendar. We document evidences of at least six paleo-earthquakes during the last ten thousand years. Paleoseismic record is particularly accurate for the last two thousand years, for which period we determine a recurrence interval of 1080 +/- 150 years. However, “paired” major earthquakes in less than one or two centuries may also occur, suggesting that fault behavior could not be based on regular seismic cycles.

Résumé: The long-term diversification of the biosphere responds to changes in the physical environment. Yet, over the continents, the nearly monotonic expansion of life started later in the early part of thePhanerozoiceon1 thanthe expansion in the marine realm, where instead the number of genera waxed and waned over time2. A comprehensive evaluation of the changes in the geodynamic and climatic forcing fails to provide a unified theory for the long-term pattern of evolution of life on Earth. Here we couple climate and plate tectonics models to numerically reconstruct the evolution of the Earth's landscape over the entire Phanerozoic eon, which we then compare to palaeo-diversity datasets from marine animal and land plant genera. Our results indicate that biodiversity is strongly reliant on landscape dynamics, which at all times determine the carrying capacity of both the continental domainand theoceanic domain. In the oceans, diversity closely adjusted to the riverine sedimentary flux that provides nutrients for primary production. On land, plant expansion was hampered by poor edaphic conditions until widespread endorheic basins resurfaced continents with a sedimentary cover that facilitated the development of soil-dependent rooted flora, and the increasing variety of the landscape additionally promoted their development.

Résumé: The unusually high number of volcanoes in the Ecuadorian Arc, located in the deformation zone of the continental North Andean Sliver, coincides with the projection of the major oceanic structures observed in the Nazca Plate, such as the Carnegie Ridge and the Grijalva fracture zone. Although the relationship between this tectonic setting and volcanism has been widely discussed in the literature, their temporal relationship has not been thoroughly investigated due to the lack of geochronological data. We present here 20 new K-Ar and 2 40Ar/39Ar ages obtained for 7 volcanoes of the central segment of the Ecuadorian arc, which together with previous data show that volcanism in this area started at -1.3 Ma. A notable increase in volcanic activity occurred since -0.6 Ma, when the formation of a dozen volcanoes occurred in a relatively small area of the central segment. While this arrangement of volcanoes, here referred to as a “volcanic cluster”, appears to be controlled by crustal tectonic structures, the order of onset of these volcanoes and their eruptive activity does not show clear migration patterns over time. However, the presence of older volcanoes in the north of the central segment suggests a possible southward extension of volcanism between -1.3 and – 0.6 Ma. Finally, based on the cumulative bulk volumes calculated for the volcanic edifices over time, we infer that the magmatic productivity rate has been roughly constant during the last -550 kyr in this area.

Résumé: The inference of fluid motion below the core-mantle boundary from geomagnetic observations presents a highly non-unique inverse problem. We propose a new method that provides a unique local estimate of the velocity field, assuming quasi-geostrophic flow in the core interior (which implies equatorial mirror symmetry) and negligible magnetic diffusion. These assumptions remove the theoretical underdetermination, enabling us to invert for the flow at each point of a spherical grid representing the core surface. The unreliable reconstruction of small-scale flows, which arises because only large-scale observations are available, is mitigated by smoothing the locally estimated velocity field using a Gaussian process regression. Application of this method to synthetic data provided by a state-of-the-art geodynamo simulation suggests that using this approach, the large-scale flow pattern of the core surface flow can be well reconstructed, while the flow amplitude tends to be underestimated. We compare these results with a core flow inversion using a Bayesian framework that incorporates statistics from numerical geodynamo models as prior information. We find that whether the latter method provides a more accurate recovery of the reference flow than the local estimation depends heavily on how realistic/relevant the chosen prior information is. Application to real geomagnetic data shows that both methods are able to reproduce the main features found in previous core flow studies.

Résumé: The 15 May 2020 Mw 6.5 Monte Cristo Range earthquake (MCRE) in Nevada, United States, is the largest instrumental event in the Mina deflection-a zone of east-trending left-lateral faults accommodating a right step between northwest-trending right-lateral faults of the Walker Lane. The MCRE ruptured a highly distributed faulting area with muted geomorphic expressions, motivating us to characterize the behavior of an earthquake on a structurally immature fault system. Inverse modeling of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) displacements reveals left-lateral slip on an east-striking, eastern fault and left-lateral-normal slip on an east-northeast-striking, western fault. Unusually, the two faults cross one another and ruptured together in the mainshock. The maximum slip of 1 m occurs at 8-10 km depth, but less than 0.1 m of slip reaches the surficial model fault patches, yielding a pronounced shallow slip deficit (SSD) of 91%. Relocated hypocenters indicate that the mainshock initiated at 9 km depth and that aftershocks span depths of 1-11 km, constraining the local seismogenic thickness. Our new field observations of fracturing and pebble-clearing in the western MCRE characterize a third, shorter, northern fault that is at the resolution limit of the InSAR-GNSS modeling. The segmented and intersecting fault geometry, off-fault aftershocks with variable mechanisms, distributed surface fractures, limited long-term geomorphic offsets, and a 600-700 m (cumu-lative) bedrock offset are all characteristic of a structurally immature fault system. However, the large SSD is not unusual for an earthquake of this magnitude, and a larger compilation of InSAR models (28 Mw >= 6:4 strike-slip events) shows that SSDs correlate with magnitude rather than structural maturity. This study demonstrates the importance of integrating geodesy, seismology, and field observations to capture the full complexity of large earth-quakes, and further suggests that seismic hazard assessments in shattered crustal regions consider the potential for multi-and cross-fault rupture.

Résumé: Site-specific seismic hazard assessment involves the prior knowledge of (1) the input ground motion at the local bedrock and (2) the site response. In this article and its companion, we address the deconvolution approach to obtain a reference ground-motion model, which consists of removing site effects from surface ground-motion recordings. Laurendeau et al. (2018) applied this approach on the KiK-net network with site response from 1D SH-wave (1DSH) simulations, calculated using the VS profiles available for most sites. Indeed, this approach presents several limitations with 1DSH site response if it is considered to be applied to other networks, especially in the European context. First, the approach requires identification of sites with dominant 1D effects. Second, it needs the presence of accurately measured VS profiles. In this context, we propose to derive deconvolved ground-motion models using site response from generalized inversion techniques () for two main reasons. The first reason is that the GIT delivers empirical site response for all types of sites, conditioned by the presence of sufficient amount of data, and the second is that it reduces the need for VS profiles. We focus on the estimation of site effects from different approaches and present a methodology to obtain reliable site terms from GIT based on the experience from previous studies. We also introduce and detail the difference between absolute and relative site response, which mainly depends on the chosen reference. We estimate and compare site response for the KiK-net stations with different methods, that is, empirical and theoretical 1DSH. We also conclude a list of 1D sites based on comparisons between theoretical and empirical estimates of site response. The results obtained in this article will be the primary input for the deconvolution approach applied in the companion article.

Résumé: The spin state of Fe can alter the key physical properties of silicate melts, affecting the early differentiation and the dynamic stability of the melts in the deep rocky planets. The low-spin state of Fe can increase the affinity of Fe for the melt over the solid phases and the electrical conductivity of melt at high pressures. However, the spin state of Fe has never been measured in dense silicate melts due to experimental challenges. We report detection of dominantly low-spin Fe in dynamically compressed olivine melt at 150 to 256 gigapascals and 3000 to 6000 kelvin using laser-driven shock wave compression combined with femtosecond x-ray diffraction and x-ray emission spectroscopy using an x-ray free electron laser. The observation of dominantly low-spin Fe supports gravitationally stable melt in the deep mantle and generation of a dynamo from the silicate melt portion of rocky planets.

Résumé: The Cretaceous marine sedimentary record is characterized by time intervals rich in organic matter correlating with positive carbon isotope excursions, often called oceanic anoxic events. The Weissert Event corresponds to the first such event in the Cretaceous during the Valanginian stage. The associated palaeoenvironmental perturbations, which include increasing marine surface water primary productivity, are hypothesized to have been triggered by volcanic activity from large igneous provinces, and the source of nutrients is not well constrained (continental runoff v. oceanic upwelling). We present isotope ratios of Pb, Sr and Nd, together with concentrations of major and trace elements, for sediments from the central Moroccan margin to test these hypotheses. We demonstrate that the nutrient input was dominated by continental weathering. The source of sedimentary material remained stable during the Valanginian interval and originated from an old source, probably the African Sahara region. The radiogenic isotope signatures do not show a significant contribution of volcanic products from any known Valanginian large igneous province to the geochemical budget of sediments deposited on the central Moroccan margin. Although this does not preclude an impact of volcanic activity on the composition of seawater, it demonstrates that the erupted volumes were not sufficient to affect the deposited sediments.

Résumé: In this study, we investigated the high-pressure (HP) metamorphism of the Precambrian continental crust exposed in the Zheltau terrane in South Kazakhstan (Koyandy complex) and the Chu-Kendyktas terrane in the North Tien Shan of Kyrgyzstan (Aktyuz, Kemin and Kokdzhon complexes) within the SW part of the Central Asian Orogenic Belt. HP quartz-feldspar lithologies of the Koyandy complex consist of migmatized kyanite-bearing garnet-mica paragneisses, garnet-kyanite paragneisses and their derivatives associated with eclogites. Paragneisses demonstrate prograde evolution involving mica dehydration melting and producing magnesium-rich garnet, kyanite and K-feldspar at the near-peak to retrograde stages at pressures of 15-18.5 kbar and temperatures of 800-870(degrees)C. The widespread growth of micas in these rocks reflects lower stages of retrogression at P = 10-12 kbar and T = 720-770(degrees)C. The age distributions of the cores of detrital zircon grains from the paragneisses indicate a predominance of Neoproterozoic and minor occurrence of Mesoproterozoic and Palaeoproterozoic sources of their protoliths. The ages of similar to 487-485 Ma obtained from the zircon rims of the paragneisses reflect the timing of their HP metamorphic re-equilibration. These age clusters are consistent with the age estimates obtained from the rims of zircons in the eclogite-bearing garnet gneisses of the adjacent Aktyuz complex in the North Tien Shan. The P-T paths and zircon ages obtained from the high-grade quartz-feldspar gneisses of the Zheltau and Chu-Kendyktas terranes are thus interpreted to indicate involvement of the crustal material derived from the Precambrian basement (magmatic zircons aged ca. 844 Ma) and its Ediacaran-Cambrian sedimentary cover (detrital zircons with maxima at 1 Ga and 800-600 Ma) in the latest Cambrian subduction processes induced by the closure of the oceanic basins assigned to the Palaeo-Asian Ocean.

Résumé: Recent geophysical campaigns in the Alps produce images with seismic property variations along the slab of sufficiently fine resolution to be interpreted as rock transformations. Since the reacting European lower crust is presumed responsible for the variations of velocities at the top of the Alpine slab, we sampled local analogs of the lower crustal lithologies in the field and modeled the evolution of equilibrium seismic properties during burial, along possible pressure-temperature paths for the crustal portion of the slab. The results are then compared to the range of the S-wave velocities obtained from the S-wave velocity tomography model along the CIFALPS transect. The velocity increase from 25 to 45 km within the slab, in the tomographic model is best reproduced by the transformation of specific lithologies in the high-pressure granulite facies along a collisional gradient (30 degrees C/km). Although the crust is certainly not completely homogeneous, the best candidates for the rocks that make up the top of the Alpine dip crustal panel are a kinzigite from Monte San Petrone, a gneiss from the Insubric line, and blueschist mylonite from Canavese. While they may not represent the entirety of the crust, they are sufficient to explain the tomographic velocity of the Alpine slab. A lateral lithological contrast inherited from the Variscan orogeny is not required. Eclogitization, suggested as the first-order transformation in convergence zones, could be a second-order transformation in collisional wedges. These results also imply a partially re-equilibrated thermal gradient, consistent with the Alpine thermal state data at depth. Tomography, that is, imaging of deep geological structures based on seismic wave travel to time anomalies, is now so sensitive that it allows us to see changes in the properties of rocks buried at depth beneath mountain belts. In the Alps, the European plate is imaged down to 80 km and shows a sharp velocity increase close to 30 km depth. By calculating the bulk seismic wave velocities on exhumed analogs sampled throughout the Western Alps, the present study proposes to interpret the velocity jump as the consequence of the transformation of the European lower crust from amphibolite to granulite (the high-temperature metamorphic rocks produced during a collision) rather than the usually admitted transformation to eclogite (the higher pressure metamorphic rocks produced during subduction). This has implications regarding the present-day thermal structure of the Alps: the Western Alps are not a frozen subduction zone but a collision zone exposing subduction-related rocks and structures at the surface only. The lower crustal top of the European Alpine slab is mostly composed of felsic to intermediate rocksThe transformation of hydrated rocks into HP granulites along a collision gradient reproduces the slab tomographic velocity increase at 30 kmThe often-supposed eclogitization produces velocities that are significantly higher than the crustal top of the European Alpine slab

Résumé: We investigated the state of the arc background mantle (i.e. mantle wedge without slab component) by means of olivine CaO and its Cr-spinel inclusions in a series of high-Mg# volcanic rocks from the Quaternary Trans-Mexican Volcanic Belt. Olivine CaO was paired with the Cr# [molar Cr/(Cr + Al) *100] of Cr-spinel inclusions, and 337 olivine+Cr-spinel pairs were obtained from 33 calc-alkaline, high-K and OIB-type arc front volcanic rocks, and three monogenetic rear-arc basalts that lack subduction signatures. Olivine+Cr-spinels display coherent elemental and He-O isotopic systematics that contrast with the compositional diversity of the bulk rocks. All arc front olivines have low CaO (0.135 +/- 0.029 wt %) relative to rear-arc olivines which have the higher CaO (0.248 +/- 0.028 wt %) of olivines from mid-ocean ridge basalts. Olivine He-3/He-4-delta O-18 isotope systematics confirm that the olivine+Cr-spinels are not, or negligibly, affected by crustal basement contamination, and thus preserve compositional characteristics of primary arc magmas. Variations in melt H2O contents in the arc front series and the decoupling of olivine CaO and Ni are inconsistent with controls on the olivine CaO by melt water and/or secondary mantle pyroxenites. Instead, we propose that low olivine CaO reflects the typical low melt CaO of high-Mg# arc magmas erupting through thick crust. We interpret the inverse correlation of olivine CaO and Cr-spinel Cr# over a broad range of Cr# (similar to 10-70) as co-variations of CaO, Al and Cr of their (near) primary host melts, which derived from a mantle that has been variably depleted by slab-flux driven serial melt extraction. Our results obviate the need for advecting depleted residual mantle from rear- and back-arc region, but do not upset the larger underlying global variations of melt CaO high-Mgy# arc magmas worldwide, despite leading to considerable regional variations of melt CaO at the arc front of the Trans-Mexican Volcanic Belt.

Résumé: At physiological levels, the trace element selenium plays a key role in redox reactions through the incorporation of selenocysteine in antioxidant enzymes. Selenium has also been evaluated as a potential anti-cancer agent, where selenium nanoparticles have proven effective, and are well tolerated in vivo at doses that are toxic as soluble Se. The use of such nanoparticles, coated with either serum albumin or the naturally occurring alkaline polysaccharide chitosan, also serves to enhance biocompatibility and bioavailability. Here we demonstrate a novel role for selenium in regulating histone methylation in ovarian cancer cell models treated with inorganic selenium nanoparticles coated with serum albumin or chitosan. As well as inducing thioredoxin reductase expression, ROS activity and cancer cell cytotoxicity, coated nanoparticles caused significant increases in histone methylation. Specifically, selenium nanoparticles triggered an increase in the methylation of histone 3 at lysines K9 and K27, histone marks involved in both the activation and repression of gene expression, thus suggesting a fundamental role for selenium in these epigenetic processes. This direct function was confirmed using chemical inhibitors of the histone lysine methyltransferases EZH2 (H3K27) and G9a/EHMT2 (H3K9), both of which blocked the effect of selenium on histone methylation. This novel role for selenium supports a distinct function in histone methylation that occurs due to a decrease in S-adenosylhomocysteine, an endogenous inhibitor of lysine methyltransferases, the metabolic product of methyl-group transfer from S- adenosylmethionine in the one-carbon metabolism pathway. These observations provide important new insights into the action of selenium nanoparticles. It is now important to consider both the classic antioxidant and novel histone methylation effects of this key redox element in its development in cancer therapy and other applications.

Résumé: In this study, we investigated phase transformations of CaTiO3 perovskite using x-ray diffraction at high pressure and high temperature up to 170 GPa and 4500 K in a laser-heated diamond-anvil cell. We report a high-pressure dissociation of CaTiO3 into CaO-B2 and CaTi2O5 with a monoclinic P2/m structure, instead of the expected transformation of the orthorhombic distorted perovskite structure into a post-perovskite phase. We propose that this transition may be favored by the B1 to B2 phase change of CaO at around 60 GPa. In order to provide additional information on the high pressure properties of CaTiO3 perovskite, we measured its melting temper-ature using CO2 laser heated diamond anvil cell up to 55 GPa yielding a fit of the melting curve to a Kraut-Kennedy empirical law according to: Tm (K) = 2188 * [1 + 4.23 * (Delta V/V0)]. To provide some further insight into the thermodynamic properties of CaTiO3, we determined the P-V-T equation of state of the orthorhombic mineral perovskite, fitted by using a third order Birch-Murnaghan equation of state and a Berman thermal expansion model. The fit of the data yields to K0 = 180.6(4) GPa, K ' 0 = 4 (fixed), partial differential K/ partial differential T =-0.022(1) GPa K-1, alpha 1 = 3.25(5) x 10-5 K-1, alpha 2 = 1.3(1) x 10-8 K-2

Résumé: Understanding radionuclides mass transfer mechanisms in monazite (LREEPO4) and the resulting features, from the micro- to the nanoscale, is critical to its use as a robust U-Th-Pb geochronometer. A detailed multiscale characterisation of discordant monazite grains from a granulite which records a polymetamorphic history explores the mechanisms of Th and Pb mobility in crystals. Some monazite grains display Th-rich linear features (0.1-1 μm thick) forming a regular network throughout the grain. They are interpreted as resulting from fluid ingress along crystallographically controlled pathways. Nanoscale features termed 'clusters' (o < 10 nm) are composed of radiogenic Pb (Pb*) +/- Si +/- Ca and are localised within monazite lattice defects. Their formation results from the competition, over millions of years, of both radiation damage production allowing element mobility (by diffusion) and accumulation in defects and alpha-healing inducing their trapping. Nanophases (o = 0.02-1 μm) containing Pb* are present in all grains and correspond to galena (PbS) or sesquioxide of Pb (Pb2O3). They are associated with a chemically varied suite of amorphous silicate (+/- Al, Mg, Fe) phases or sulphur (e.g. FeS). They are interpreted as precipitates within monazite crystals. They are formed during replacement mechanism of monazite through fluid interactions. Two generations of Pb*-bearing nanophases exist supported by previous geochronological data. The shielding effect of garnet and rutilated quartz (host minerals), limiting fluid access, induces plentiful Pb*-bearing nanophases precipitation (fluid saturation enhanced) and limits Pb*-loss at the grain scale. This multiscale study provides new insights for interpretations of meaningless geochronological information, thanks to nanoscale investigations.

Résumé: The pathways through which cadmium (Cd) is taken up and loaded into cacao beans (nibs) are yet to be revealed. Previous work suggested that Cd loading into cacao nibs may occur via direct xylem uptake rather than phloem-mediated redistribution from the leaves. A stable isotope (108Cd) pulse-chase experiment was set up to identify the pathways of Cd loading into cacao nibs. The topsoil beneath two mature cacao trees in the field was enriched in 108Cd via surface irrigation with a spiked solution. The increase in 108Cd isotopic abundance (IA) in the plant tissues was followed up for 548 days after spiking. The 108Cd IA in the plant tissues increased from natural abundance (0.89 %) to 7.0 % (tree A) and 10.1 % (tree B) at equilibrium. The tracer was taken up in the plant tissues in the order immature leaves > mature leaves > nibs in both trees, while tracer uptake in flowers and cherelles was less consistent between the trees. Half of the equilibrium 108Cd IA was reached in the nibs at 191 days after spiking, significantly later than corresponding values for mature (151 days) and immature leaves (117 days). Pod maturation from flower stage takes about 6 months with most Cd entering the nibs at the last stage of development. The rather slow rise in the 108Cd IA in the nibs compared to the leaves hence suggests that Cd in cacao nibs likely originates from phloem-redistribution from the stem, branches or mature leaves and not from direct root-to-nib transport via the xylem.

Résumé: Creep of shale controls the stability of fault gouge in sedimentary rocks, aseismic deformation in the upper crust, and several engineering operations, such as proppant embedment, reservoir subsidence, and wellbore stability during unconventional shale gas exploitation. However, measuring the creep properties of shale is challenging due to the multi-scale structure of this rock. Here, our goal is to assess how creep parameters measured at the core sample scale depend on those measured at the nanoscale in shales. We selected three clay-rich and quartzrich shale samples and conducted a series of experiments on shale samples at two scales: nanoindentation creep measurements on thin sections, and uniaxial creep tests on core samples. The creep parameters, including creep displacement (Delta h), indentation creep (CIT), creep strain rate sensitivity (m), contact creep modulus (C), and viscoelastic parameters (E1, E2, eta 1, and eta 2) of the Burgers' model, were calculated by fitting the nanoindentation creep data of each single-phase component of shale matrix. From these data, we upscale the creep parameters (E1, E2, and C) of shale matrix to those of the bulk shale. Upscaled E2 and C values based on the Mori-Tanaka scheme are found to be relatively close to those measured in previous microindentation study on Longmaxi shale and are consistent with our measurements in uniaxial creep tests on core samples of clay-rich shale and quartz-rich shale. The upscaling value of the elastic parameters, E1, is almost twice larger than the results from uniaxial creep test. We interpret this difference as due to low elastic stiffness along grain contacts of the shale that nanoindentation measurements underestimate. Our results show a consistency of some creep parameters upscaled from nanoindentation data and those measured at a macroscopic scale on core samples.

Résumé: Quantitative estimation of seismic risk over a region requires both an underlying probabilistic seismic hazard model and a means to characterise shallow site response over a large scale. The 2020 European Seismic Risk Model (ESRM20) builds on the 2020 European Seismic Hazard Model (ESHM20), requiring additional information to firstly parameterise the local site condition across all of Europe, and subsequently determine its influence on the prediction of seismic ground motion. Initially, a harmonised digital geological database for Europe is compiled, alongside a model of topographic/bathymetric elevation and a database of 30 m averaged shearwave velocity measurements ( V-S30), in order to produce separate 30 arc-second maps of inferred V-S30 based on topography and on geology. We then capitalise on a large database of seismic recording stations in Europe for which site to-site ground motion residuals (delta S2S(S)) have been determined with respect to the shallow crustal ground motion model used in the ESHM20. These residuals allow us to incorporate site amplification functions into the European GMM calibrated upon either observed or inferred V-S30, or on the European geology and topography models. We present the resulting pan-European seismic site amplification model and assess its impact on seismic hazard and risk compared against other approaches. The new site amplification model fulfils the requirements of the ESRM20 and, providing uncertainty is fully propagated, yields estimates of seismic hazard and risk at a large space scale that may be comparable to other methods often applied at local/urban scale where better-constrained site information is available.

Résumé: Goethite and pyrite are common iron minerals in oxic or anoxic environments, respectively, both minerals being major reservoirs for Nickel, a bio-essential element. Mineral transformation between goethite and pyrite is frequent owing to the alternation of oxic and anoxic conditions in sulfate-rich environments. This mineral transformation has been amply studied, but the effect of Ni on this transformation and its fate along it remain poorly understood. Sulfidation of Ni-free and Ni-containing (through adsorption or isomorphic substitution) goethites was thus studied experimentally by reacting goethite with dissolved S(-II) (molar Fe:S & AP;1:1). X-ray diffraction and associated Rietveld refinement, thermogravimetric analysis, scanning/transmission electron microscopy, X-ray absorption spectroscopy, and wet chemistry were used to monitor mineralogical evolutions and unravel Ni association with reaction products. After 44 days of sulfidation, about half of initial goethite converted to iron sulfides: thermodynamically stable pyrite (67%-93%) with minor contents of mackinawite (2%-15%) and greigite (5%-25%). Although the overall content of iron sulfides formed was essentially independent of Ni presence, Ni hampered the conversion from metastable iron sulfides (i.e., mackinawite and greigite) to pyrite (67%-78% vs. 93%, in the presence and absence of Ni, respectively). Pyrite formation from metastable sulfide precursors yielded a uniform Ni distribution in newly formed pyrite, regardless of the initial Ni association with goethite. Although no Ni was released to solution during pyrite formation, Ni incorporation to pyrite results in an increased risk of release to the environment as iron sulfides will be oxidized when exposed to air and water in supergene environments, leading to highly acidic conditions favoring Ni solubility and mobility.

Résumé: Plane-wave theory based on the Zoeppritz's equations and its various approximations have been extensively utilized in seismic processing and interpretation. However, localized sources used in field acquisition usually generate spherical wave. As a zero-order approximation of spherical reflected wave, plane reflected wave varies with seismic offset, which can only use amplitude information of multiple pre-critical offsets to estimate elastic parameters. While, the change of spherical wavefront curvature across reflected interfaces causes the amplitude and phase of spherical reflected wave to vary with seismic frequency and offset. Therefore, in addition to conducting conventional amplitude variation versus with offset inversion using a single frequency of multiple offsets, spherical reflected wave makes frequency-dependent inversion using multiple low frequencies of a single offset possible. Herein, we derive the integral expression of spherical wave reflection coefficient from the general solution of wave equation and verify the consistency of displacements of reflected wave simulated by numerical integral and finite difference method in elastic medium. Subsequently, we analyze and investigate the feasibility of frequency-dependent inversion using spherical wave reflection coefficient of a single offset in synthetic data with a planar reflection interface. Combining a global optimal algorithm, low frequency-dependent inversion based on spherical wave reflection coefficient can offer accurate velocity and density parameters for further seismic interpretation.

Résumé: Passive seismic interferometry has become a popular technique towards monitoring. The method depends on the relative stability of background seismic sources in order to make repeatable measurements of subsurface properties. Such stability is typically assessed by examining the similarity of cross-correlation functions through time. Thus, techniques that can better assess the temporal similarity of cross-correlation functions may aid in discriminating between real subsurface processes and artificial changes related variable seismic sources. In this study, we apply agglomerative hierarchical clustering to cross-correlation functions computed using seismic networks at two volcanoes. This allows us to form groups of data that share similar characteristics and also, unlike common similarity measures, does not require a defined reference period. At Piton de la Fournaise (La Reunion island), we resolve distinct clusters that relate both to changes in the seismic source (volcanic tremor onset) and changes in the medium following volcanic eruptions. At Mt Ruapehu (New Zealand), we observe a consistency to cross-correlation functions computed in the frequency band of volcanic tremor, suggesting tremor could be useful as a repeatable seismic source. Our results demonstrate the potential of hierarchical clustering as a similarity measure for cross-correlation functions, suggesting it could be a useful step towards recognizing structure in seismic interferometry data sets. This can benefit both decisions in processing and interpretations of observed subsurface changes.

Résumé: Solid iron-silicon alloys play an important role in planetary cores, especially for planets that formed under reducing conditions, such as Mercury. The CsCl (B2) structure occupies a considerable portion of the Fe-Si binary phase diagram at pressure and temperature conditions relevant for the core of Mercury, yet its thermodynamic and thermoelastic properties are poorly known. Here, we report in situ X-ray difraction measurements on iron-silicon alloys with 7-30 wt% Si performed in laser-heated diamond-anvil cells up to similar to 120 GPa and similar to 3000 K. Unit-cell volumes of the B2 phase at high pressures and high temperatures have been used to obtain a composition-dependent thermal equation of state of this phase. In turn, the thermal equation of state is exploited to determine the composition of the B2 phase in hcp+B2 mixtures at 30-100 GPa and to place constraints on the hcp+B2/B2 phase boundary, determined to vary between similar to 13-18 wt% Si in the considered pressure and temperature range. The hcp+B2/B2 boundary of Fe-Si alloys is observed to be dependent on pressure but weakly dependent on temperature. Our results, coupled with literature data on liquid equations of state, yield an estimation of the density contrast between B2 solid and liquid under Mercury's core conditions, which directly relates to the buoyancy of the crystallizing material. While the density contrast may be large enough to form a solid inner core by the gravitational sinking of B2 alloys in a Si-rich core, the density of the B2 solid is close to that of the liquid at solidus conditions for Si concentration approaching similar to 10 wt% Si.

Résumé: Correctly interpreting phase events thanks to data processing techniques based on correlation or deconvolution has been the focus of numerous studies in the field of high-resolution seismic imaging using full-waveform inversion. To mitigate the non-convexity of the misfit function and the risk to converge towards non-informative local minima, correlation and deconvolution techniques make it possible to focus on phase information instead of amplitude information and to design more convex misfit function, alleviating the dependency of the full-waveform inversion process on the accuracy of initial models. Such techniques however rely on the assumption that phase events can be compared one by one, or that all the phase events are shifted in time in a similar way. This assumption is not satisfied in practice, which limits the effectiveness of these correlation/deconvolution-based methods. To overcome this issue, we propose to account for the non-stationary relation between observed and predicted data through a local in-time deconvolution technique, based on time-frequency analysis of the signal using a Gabor transform. This makes it possible to estimate instantaneous time-shift between locally coherent phase events. This strategy generalizes the conventional normalized deconvolution technique, which has been popularized under the name of adaptive waveform inversion. To support the introduction of our novel method, we compare it with four misfit functions based respectively on classical cross-correlation, penalized cross-correlation, penalized deconvolution, and adaptive waveform inversion. We analyse the behaviour of these methods on specific scenarios, and then propose a comparison on 2-D synthetic benchmarks. We show how our 'localized' adaptive waveform inversion applies in these realistic tests and overcomes some of the limitations of the aforementioned techniques.