Institut des Sciences de la Terre

The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth’s magnetic field.

Nanoscale zero-valent iron (NZVI) was synthesized and tested for the removal of As(III), which is a highly toxic, mobile, and predominant arsenic species in anoxic groundwater. We used SEM-EDX, AFM, and XRD to characterize particle size, surface morphology, and corrosion layers formed on pristine NZVI and As(III)-treated NZVI. AFM results showed that particle size ranged from 1 to 120 nm. XRD and SEM results revealed that NZVI gradually converted to magnetite/maghemite corrosion products mixed with lepidocrocite over 60 d. Arsenic(III) adsorption kinetics were rapid and occurred on a scale of minutes following a pseudo-first-order rate expression with observed reaction rate constants (K(obs)) of 0.07-1.3 min(-1) (at varied NZVI concentration). These values are about 1000x higher than K(obs) literature values for As(III) adsorption on micron size ZVI. Batch experiments were performed to determine the feasibility of NZVI as an adsorbent for As(III) treatment in groundwater as affected by initial As(III) concentration and pH (pH 3-12). The maximum As(III) adsorption capacity in batch experiments calculated by Freundlich adsorption isotherm was 3.5 mg of As(III)/g of NZVI. Laser light scattering (electrophoretic mobility measurement) confirmed NZVI-As(III) inner-sphere surface complexation. The effects of competing anions showed HCO3-, H4SiO4(0), and H2P04(2-) are potential interferences in the As(III) adsorption reaction. Our results suggest that NZVI is a suitable candidate for both in-situ and ex-situ groundwater treatment due to its high reactivity.

Abstract In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.

cubic meters of rock and glacier ice collapsed from the steep north face of Ronti Peak. The rock and ice avalanche rapidly transformed into an extraordinarily large and mobile debris flow that transported boulders greater than 20 meters in diameter and scoured the valley walls up to 220 meters above the valley floor. The intersection of the hazard cascade with downvalley infrastructure resulted in a disaster, which highlights key questions about adequate monitoring and sustainable development in the Himalaya as well as other remote, high-mountain environments.

Abstract Geophysics provides a multidimensional suite of investigative methods that are transforming our ability to see into the very fabric of the subsurface environment, and monitor the dynamics of its fluids and the biogeochemical reactions that occur within it. Here we document how geophysical methods have emerged as valuable tools for investigating shallow subsurface processes over the past two decades and offer a vision for future developments relevant to hydrology and also ecosystem science. The field of “hydrogeophysics” arose in the late 1990s, prompted, in part, by the wealth of studies on stochastic subsurface hydrology that argued for better field‐based investigative techniques. These new hydrogeophysical approaches benefited from the emergence of practical and robust data inversion techniques, in many cases with a view to quantify shallow subsurface heterogeneity and the associated dynamics of subsurface fluids. Furthermore, the need for quantitative characterization stimulated a wealth of new investigations into petrophysical relationships that link hydrologically relevant properties to measurable geophysical parameters. Development of time‐lapse approaches provided a new suite of tools for hydrological investigation, enhanced further with the realization that some geophysical properties may be sensitive to biogeochemical transformations in the subsurface environment, thus opening up the new field of “biogeophysics.” Early hydrogeophysical studies often concentrated on relatively small “plot‐scale” experiments. More recently, however, the translation to larger‐scale characterization has been the focus of a number of studies. Geophysical technologies continue to develop, driven, in part, by the increasing need to understand and quantify key processes controlling sustainable water resources and ecosystem services.

Surface complexation models are commonly used to predict the mobility of trace metals in aquifers. For arsenic in groundwater, surface complexation models cannot be used because the database is incomplete. Both carbonate and ferrous iron are often present at a high concentration in groundwater and will influence the sorption of arsenic, but the surface complexation constants are absent in the database of Dzombak and Morel. This paper presents the surface complexation constants for carbonate and ferrous iron on ferrihydrite as derived for the double-layer model. For ferrous iron the constants were obtained from published data supplemented by new experiments to determine the sorption on the strong sites of ferrihydrite. For carbonate the constants were derived from experiments by Zachara et al., who employed relatively low concentrations of carbonate. The double-layer model, optimized for low concentrations, was tested against sorption experiments of carbonate on goethite at higher concentration by Villalobos and Leckie, and reasonable agreement was found. Sorption was also estimated using linear free energy relations (LFER), and results compared well with our derived constants. Model calculations confirm that sorption of particularly carbonate at common soil and groundwater concentrations reduces the sorption capacity of arsenic on ferrihydrite significantly. The displacing effect of carbonate on sorbed arsenate and arsenite has been overlooked in many studies. It may be an important cause for the high concentrations of arsenic in groundwater in Bangladesh. Sediments containing high amounts of sorbed arsenic are deposited in surface water with low carbonate concentrations. Subsequently the sediments become exposed to groundwater with a high dissolved carbonate content, and arsenic is mobilized by displacement from the sediment surface.

Surface wave methods gained in the past decades a primary role in many seismic projects. Specifically, they are often used to retrieve a 1D shear wave velocity model or to estimate the V S,30 at a site. The complexity of the interpretation process and the variety of possible approaches to surface wave analysis make it very hard to set a fixed standard to assure quality and reliability of the results. The present guidelines provide practical information on the acquisition and analysis of surface wave data by giving some basic principles and specific suggestions related to the most common situations. They are primarily targeted to non-expert users approaching surface wave testing, but can be useful to specialists in the field as a general reference. The guidelines are based on the experience gained within the InterPACIFIC project and on the expertise of the participants in acquisition and analysis of surface wave data.

The Neighborhood Algorithm (NA) is a popular direct search inversion technique. For dispersion curve inversion, physical conditions between parameters V s and V p (linked by Poisson's ratio) may limit the parameter space with complex boundaries. Other conditions may come from prior information about the geological structure. Irregular limits are not natively handled by classical search algorithms. In this paper, we extend the NA formulation to such parameter spaces. For problems affected by non‐uniqueness, the ideal solution is made of the ensemble of all models that equally fits the data and prior information. Hence, a powerful exploration tool is required. Exploiting the properties of the Voronoi cells, we show that a dynamic scaling of the parameters during the convergence to the solutions drastically improves the exploration.

Hydration of the <1 μm size fraction of SWy-1 source clay (low-charge montmorillonite) was studied by modeling of X-ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Li-, Na-, K-, Mg-, Ca-, and Sr-saturated specimens. The quantitative description of smectite hydration, based on the relative proportions of different layer types derived from the fitting of experimental XRD patterns, was consistent with previous reports of smectite hydration. However, the coexistence of smectite layer types exhibiting contrasting hydration states was systematically observed, and heterogeneity rather than homogeneity seems to be the rule for smectite hydration. This heterogeneity can be characterized qualitatively using the standard deviation of the departure from rationality of the 00l reflection series (ξ), which is systematically larger than 0.4 Å when the prevailing layer type accounts for ~70% or less of the total layers (~25% of XRD patterns examined). In addition, hydration heterogeneities are not distributed randomly within smectite crystallites, and models describing these complex structures involve two distinct contributions, each containing different layer types that are interstratifed randomly. As a result, the different layer types are partially segregated in the sample. However, these two contributions do not imply the actual presence of two populations of particles in the sample.

Recent experimental observations of the onset of calcium carbonate (CaCO3) mineralization suggest the emergence of a population of clusters that are stable rather than unstable as predicted by classical nucleation theory. This study uses molecular dynamics simulations to probe the structure, dynamics, and energetics of hydrated CaCO3 clusters and lattice gas simulations to explore the behavior of cluster populations before nucleation. Our results predict formation of a dense liquid phase through liquid-liquid separation within the concentration range in which clusters are observed. Coalescence and solidification of nanoscale droplets results in formation of a solid phase, the structure of which is consistent with amorphous CaCO3. The presence of a liquid-liquid binodal enables a diverse set of experimental observations to be reconciled within the context of established phase-separation mechanisms.

Other| January 01, 1977 Evolution tectonique du systeme alpin en Mediterranee; poinconnement et ecrasement rigide-plastique Paul Tapponnier Paul Tapponnier Author Universite des Sciences et Techniques du Languedoc, Departement des Sciences de la Terre, Montpellier, France Search for other works by this author on: GSW Google Scholar Bulletin de la Société Géologique de France (1977) S7-XIX (3): 437–460. https://doi.org/10.2113/gssgfbull.S7-XIX.3.437 Article history first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Paul Tapponnier; Evolution tectonique du systeme alpin en Mediterranee; poinconnement et ecrasement rigide-plastique. Bulletin de la Société Géologique de France 1977;; S7-XIX (3): 437–460. doi: https://doi.org/10.2113/gssgfbull.S7-XIX.3.437 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin de la Société Géologique de France Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Using buoy data from the International Arctic Buoy Program, we found that the sea ice mean speed has substantially increased over the last 29 years (+17% per decade for winter and +8.5% for summer). A strong seasonal dependence of the mean speed is also revealed, with a maximum in October and a minimum in April. The sea ice mean strain rate also increased significantly over the period (+51% per decade for winter and +52% for summer). We check that these increases in both sea ice mean speed and deformation rate are unlikely to be consequences of a stronger atmospheric forcing. Instead, they suggest that sea ice kinematics play a fundamental role in the albedo feedback loop and sea ice decline: increasing deformation means stronger fracturing, hence more lead opening, and therefore a decreasing albedo. This accelerates sea ice thinning in summer and delays refreezing in early winter, therefore decreasing the mechanical strength of the cover and allowing even more fracturing, larger drifting speed and deformation, and possibly a faster export of sea ice through the Fram Strait. The September minimum sea ice extent of 2007 might be a good illustration of this interplay between sea ice deformation and sea ice shrinking, as we found that for both winter 2007 and summer 2007 exceptionally large deformation rates affected the Arctic sea ice cover.

Isotopic fingerprinting has long been used to trace magmatic processes and the components that contribute to magmas. Recent technological improvements have provided an opportunity to analyze isotopic compositions on the scale of individual crystals, and consequently to integrate isotopic and geochemical tracing with textural and petrographic observations. It has now become clear that mineral phases are commonly not in isotopic equilibrium with their host glass/groundmass. Isotopic ratios recorded from core to rim of a mineral grain reflect the progressive changes in the magma composition from which the mineral crystallized. The sense of these changes and the relationship between isotopic composition and petrographic features, such as dissolution surfaces, can be used to constrain magma evolution pathways involving open system processes such as magma mixing, contamination and recharge.

Selenium is a natural trace element that is of fundamental importance to human health. The extreme geographical variation in selenium concentrations in soils and food crops has resulted in significant health problems related to deficient or excess levels of selenium in the environment. To deal with these kinds of problems in the future it is essential to get a better understanding of the processes that control the global distribution of selenium. The recent development of analytical techniques and methods enables accurate selenium measurements of environmental concentrations, which will lead to a better understanding of biogeochemical processes. This improved understanding may enable us to predict the distribution of selenium in areas where this is currently unknown. These predictions are essential to prevent future Se health hazards in a world that is increasingly affected by human activities.

Abstract Ambient vibrations are nowadays considerably used worldwide for numerous types of engineering applications and scientific research. Geopsy and its companion tools are part of that landscape. Since the first release of the program package in 2005, as outcome of the European Union project Site Effects aSsessment from AMbient noisE, Geopsy has become a mature multiplatform open-source package (released under GNU Public License version 3) that has already been recognized as a reference tool for analyzing ambient vibration data in the context of site characterization studies. The community of users has grown from a core group of researchers up to thousands of seismologists and engineers on every career level and on all continents. The versatility of geopsy allows for the processing of all kinds of data needed in site characterization studies, that is, from single station single trace to three-component array recordings. In all of the aforementioned cases, the steps from field acquisition to the production of publication-ready figures are covered and supported by user-friendly graphical user interfaces or corresponding command-line tools for the automation of the complete processing chain. To avoid black-box usage, a number of lower-level tools guarantee maximum flexibility in accessing and controlling processing results at any stage of the analysis.

Critical concepts from three different fields, elasticity, plasmonics and metamaterials, are brought together to design a metasurface at the geophysical scale, the resonant metawedge, to control seismic Rayleigh waves. Made of spatially graded vertical subwavelength resonators on an elastic substrate, the metawedge can either mode convert incident surface Rayleigh waves into bulk elastic shear waves or reflect the Rayleigh waves creating a "seismic rainbow" effect analogous to the optical rainbow for electromagnetic metasurfaces. Time-domain spectral element simulations demonstrate the broadband efficacy of the metawedge in mode conversion while an analytical model is developed to accurately describe and predict the seismic rainbow effect; allowing the metawedge to be designed without the need for extensive parametric studies and simulations. The efficiency of the resonant metawedge shows that large-scale mechanical metamaterials are feasible, will have application, and that the time is ripe for considering many optical devices in the seismic and geophysical context.

Research Article| January 01, 2002 Quantitative Speciation of Heavy Metals in Soils and Sediments by Synchrotron X-ray Techniques Alain Manceau; Alain Manceau 1Environmental Geochemistry Group LGIT, University J. Fourier and CNRS, 38041 Grenoble Cedex 9, France2Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California, 94720, U.S.A. Search for other works by this author on: GSW Google Scholar Matthew A. Marcus; Matthew A. Marcus 2Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California, 94720, U.S.A. Search for other works by this author on: GSW Google Scholar Nobumichi Tamura Nobumichi Tamura 2Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California, 94720, U.S.A. Search for other works by this author on: GSW Google Scholar Author and Article Information Alain Manceau 1Environmental Geochemistry Group LGIT, University J. Fourier and CNRS, 38041 Grenoble Cedex 9, France2Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California, 94720, U.S.A. Matthew A. Marcus 2Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California, 94720, U.S.A. Nobumichi Tamura 2Advanced Light Source, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California, 94720, U.S.A. Publisher: Mineralogical Society of America First Online: 09 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2002) 49 (1): 341–428. https://doi.org/10.2138/gsrmg.49.1.341 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alain Manceau, Matthew A. Marcus, Nobumichi Tamura; Quantitative Speciation of Heavy Metals in Soils and Sediments by Synchrotron X-ray Techniques. Reviews in Mineralogy and Geochemistry 2002;; 49 (1): 341–428. doi: https://doi.org/10.2138/gsrmg.49.1.341 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Human societies have, in all ages, modified the original form of metals and metalloids in their living environment for their survival and technical development. In many cases, these anthropogenic activities have resulted in the release into the environment of contaminants that pose a threat to ecosystems and public health. Examples of local and global pollution are legion worldwide, and the reader of the environmental science literature is forever faced with ever more alarming reports on hazards due to toxic metals. For example, extensive mining and associated industrial activities have introduced large amounts of metal contaminants in nature at the local,... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

[1] Despite remarkable successes achieved by Differential InSAR, estimations of low tectonic strain rates remain challenging in areas where deformation and topography are correlated, mainly because of the topography‐related atmospheric phase screen (APS). In areas of high relief, empirical removal of the stratified component of the APS may lead to biased estimations of tectonic deformation rates. Here we describe a method to correct interferograms from the effects of the spatial and temporal variations in tropospheric stratification by computing tropospheric delay maps coincident with SAR acquisitions using the ERA‐ Interim global meteorological model. The modeled phase delay is integrated along vertical profiles at the ERA‐I grid nodes and interpolated at the spatial sampling of the interferograms above the elevation of each image pixel. This approach is validated on unwrapped interferograms. We show that the removal of the atmospheric signal before phase unwrapping reduces the risk of unwrapping errors in areas of rough topography. Citation: Jolivet, R.,

Abstract The Early Palaeozoic Orogen of SE China consists of three litho‐tectonic elements, from top to bottom: a sedimentary Upper Unit, a metamorphic Lower Unit and a gneissic basement. The boundaries between these units are flat lying, south directed, ductile decollements. The lower one is coeval with an amphibolite facies metamorphism (M1). The belt is reworked by migmatite–granite domes, high‐temperature metamorphism (M2) and granitic plutons related to post‐orogenic crustal melting. We date here the syn‐M1 ductile shearing at 453 ± 7 Ma by U‐Th/Pb method on monazite. Previous ages and our new 40 Ar/ 39 Ar ages of biotites and muscovites show that the metamorphic rocks experienced syn‐M2 exhumation from 440 to 400 Ma. The Early Palaeozoic Orogen of SE China is an intracontinental belt in which decollements accommodated the north‐directed subduction of the Cathaysian continent. This orogen is an example of intracontinental subduction that was not preceded by oceanic subduction.

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