HAL-BRGM, les publications scientifiques en libre accès du BRGM
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A Comprehensive Analysis of Seismic Site Effects in the Grenoble Basin (French Alps)
No full textInternational audienceThe Grenoble basin, located in the French Alps, is a region of significant interest for seismic hazard assessment due to its thick sedimentary layers and surrounding high massifs, leading to 2D/3D complex wave propagation patterns. With the aim to develop suitable strategies for seismic microzonation in alpine valleys, this study focuses on the seismic response of the basin using state-of- the-art 3D simulations performed with the EFISPEC3D spectral element method code for frequencies up to 5 Hz. These simulations aim to capture the intricate interactions between geological features, including lateral heterogeneity and basin geometry, which are not considered in traditional 1D microzonation approaches.A primary goal of this research is to compare synthetic seismic data derived from 1D and 3D models with observed data to identify the limitations of 1D approach to provide a robust estimation of the site effects. Particular attention is paid to the analysis of fundamental frequencies and seismic wave amplification. While central regions of the basin exhibit consistent fundamental frequencies across 1D and 3D models, discrepancies arise at the edges due to the presence of complex lateral heterogeneities.The study further investigates aggravation factors such as Peak Ground Velocity (PGV), Peak Ground Acceleration (PGA), and Arias Intensity, revealing significant amplification in the central areas of the basin when using 3D models. In contrast, edge zones tend to show neutral or slightly de-amplified responses. These findings underscore the importance of incorporating 3D effects into seismic hazard assessments to improve the accuracy of microzonation strategies.Future work aims to refine seismic hazard maps by leveraging machine learning techniques to automate the classification of zones based on response spectra and frequency-dependent amplification
Corrosion Behavior of X65 API 5L Carbon Steel Under Simulated Storage Conditions: Influence of Gas Mixtures, Redox States, and Temperature Assessed Using Electrochemical Methods for up to 100 Hours
No full textInternational audienceIn the context of the deep geological disposal of high-level and intermediate-level long-lived radioactive waste in France, the Callovian–Oxfordian (Cox) clay formation has been selected as a natural barrier. Thus, understanding the corrosion phenomena between the carbon steel used (API 5L X65) for the waste lining tubes and the Cox pore water, as well as its possible future evolutions, is of great importance. A controlled laboratory experiment was conducted using robust handmade API 5L X65 carbon steel electrodes in synthetic Cox pore water under equilibrium with three distinct gas atmospheres, simulating oxic, anoxic, and sulfide-rich environments at 25 °C and 80 °C, in a batch-type electrochemical cell. The experimental methodology involved linear polarization resistance (LPR) cycles, electrochemical impedance spectroscopy (EIS), and Tafel extrapolation at regular intervals over a period of 70 to 100 h to elucidate corrosion mechanisms and obtain corrosion current densities. At the same time, the fluid’s key geochemical parameters (temperature, pH, and redox potential) were monitored for temporal variation. This study, with results showing high corrosion rates under the three conditions investigated at two temperatures, underscores the importance of controlling the immediate environment of the containment materials to prevent exposure to variable conditions and to ensure that corrosion remains controlled over the long term
Thermochronology of the Western Alps (Pelvoux Massif) Reveals the Longterm Multiphase Tectonic History of the European Paleomargin
No full textInternational audienceThe Variscan and Alpine long‐term thermal evolution of the European paleomargin in the external Western Alps is still unknown, although important for reconstructing the geodynamic evolution of this orogen. Here we combine zircon fission track and apatite fission track and U‐Pb double dating analyses of the Pelvoux massif in the Western Alps. Apatite U‐Pb ages of <310 Ma and >320 Ma define a bimodal age distribution that reflects differential cooling across the East Variscan Shear Zone. QTQt thermal history modeling reveals a two‐stage rifting evolution on the European paleomargin, initiated with the Alpine Tethys rifting episode during the Early Jurassic and reactivated during the Cretaceous Valais rifting event, leading to peak temperatures of ∼350°C at 90 Ma. The subsequent cooling records a pre‐Priabonian phase of exhumation between 80 and 50 Ma that is related to N‐S oriented Pyrenean shortening. It is followed by Alpine collision‐related burial of the Pelvoux massif from below the foreland basin and the Penninic Frontal Thrust at around 30–25 Ma
“The bigger picture beyond the pump”: Engaging farmer’s in Collaborative Groundwater Management in California
No full textInternational audienceIn response to the limitations of the "open-access" groundwater management regime, exacerbated by climate change, many countries are shifting towards a regulated access paradigm (Rouillard et al., 2021). This new governance approach ranges from "state-centered" to forms of "collaborative management" or "comanagement" (Molle, Closas, 2020), where farmers must now cooperate with stakeholders representing diverse interests (drinking water supply, protection of groundwater-dependent ecosystems, etc.). In California, the Sustainable Groundwater Management Act (SGMA) of 2014 embodies this shift (Harter, 2020), with the creation of Groundwater Sustainability Agencies (GSAs), responsible for developing sustainable management plans that engage a wide variety of stakeholders. Based on a qualitative survey (~50 respondents) conducted in 2023-24 in two groundwater basins in north California, we examine how this new governance model effectively involves farmers in the development of communities of interest and collective action for sustainable groundwater management. Our analysis focuses on two key aspects: First, we evaluate the social learning outcomes of the participatory process, examining how this experience is able to foster a shared and renewed understanding of an invisible and complex resource, deeply intertwined with socio-economic, political and cultural dimensions. Specifically, we investigate how the process facilitated the co-construction of a common vision regarding groundwater dynamics, the interdependencies between groundwater and surface water, and between uses and the relationships among various uses and users - capturing the "bigger picture beyond the pump". Additionally, we examine how this collaborative effort was able to build new forms of cooperation, grounded in mutual recognition of legitimacy, and the creation of shared values. Second, we explore how this process challenges the notions of collectives and communities of interest within the agricultural sector itself. Participation reshapes relationships among farmers - between large and small farms, and between farmers with different practices and environmental sensitivities. It redefines forms of collective action within the farming community, reinforcing or creating coalitions of interests, and elaborating new strategies to protect farmer’s “water rights”, in the face of evolving political dynamics and shifting power relations
3D Characterization of Aquifers in the Cenozoic Sedimentary Formations of the Paris Basin
No full textEGU 2025 Session ESSI4.7 - Geological mapping and modellingInternational audienceCharacterization of Aquifers in the Cenozoic Sedimentary Formations of the Paris BasinThe objective of this study is to synthesize the geological and hydrogeological characteristics of the main aquifers in the Paris Basin within the Cenozoic sedimentary formations. This work is part of the multi-annual scientific program RGF (Référentiel Géologique de la France, https://rgf.brgm.fr/page/bassin-parisien), which aims to update the representation and mapping of French geology on a national scale. The program also funds several PhD projects in collaboration with the academic community, focusing on the geometry, distribution of petrophysical properties, modeling, and mapping of key Cenozoic geological formations in the basin. Particular emphasis is placed on the major aquifers as part of this modeling effort.</p
How Stiff Was Armorica During the Variscan Orogeny? A Reappraisal of the “Bretonian” Phase in Central Brittany
No full textInternational audienceIn collision belts, the upper plate is generally less deformed than the lower one that underwent syn-metamorphic ductile shearing, and frequently late-collisional crustal melting. Concerning the Variscan orogeny, it is widely accepted that the Armorica microcontinent represented the upper plate of the collision system. In France, the Central-North-Armorican Domain belonged to this upper plate whose southern margin in the Pontivy-Coray area exposes metamorphic rocks. There, structural and metamorphic studies indicate that an early tectono-metamorphic event (M0-M1) with biotite-garnetstaurolite-kyanite assemblage, crystallized at 0.9 GPa and 500 • C, is characterized by a top-to-the NW shearing. This event was followed by an HT event (M2) at ca 800-900 • C, coeval with a domal structure. In micaschists, monazite yields an LA-ICP-MS age at 351 Ma ascribed to M2. M0-M1-M2 events developed before the Late Carboniferous pluton emplacement at ca 315 Ma (M3 event). The tectono-metamorphic succession documents that Armorica was not a rigid block but underwent a synmetamortphic ductile deformation during the Famennian-Tournaisian (360-355 Ma) collision redefined here as the late episode of the "Bretonian orogenic phase", whereas the pre-Famennian Bretonnian episode is ascribed to oceanic subduction. These new data allow us to reassess the geodynamic evolution of this part of the Variscan orogen
Performance of All-Solid-State MoOx pH Sensors Prepared via Thermal Oxidation for Robust Applications
No full textInternational audienceIn this study, we investigated the morphology, chemical composition and pH measurement performance of MoO x electrodes prepared via thermal oxidation and submitted to hydration in milliQ water. Surface analysis using SEM-EDS and XPS revealed that the hydrated MoO x film is composed of different oxidation states of Mo (Mo (IV), Mo (V) and Mo (VI)), influencing its electrochemical behavior. A hydration period of 45 days was required for the electrode to achieve a response approaching the Nernstian model (-58 mV/pH), while extended hydration of up to 70 days enhanced its stability and sensitivity. The electrode's performance was assessed under various conditions, including in the presence and absence of oxygen and in anaerobic conditions with the presence of sulfides. Oxygen absence increased sensitivity and lowered the experimental standard potential (E 0 Exp ) due to the effect of oxygen vacancies. Low sulfide concentrations had minimal impact on electrode performance, although higher concentrations may slightly decrease the electron transfer efficiency due to the complex formation. The pH sensing mechanisms of MoO x electrodes are also discussed
Monitoring the mean high water shoreline along the meso-macrotidal Cap Ferret sand spit, SW France, using the satellite-derived wet/dry sand line
No full textInternational audienceBuilding long shoreline position databases is critical to improve knowledge on past coastal dynamics and predict future changes. Several satellites acquiring recurrent optical images over land and coastal areas have been commissioned since the 1980s. This has allowed the implementation of various satelliteimagery-based shoreline detection algorithms for sandy coasts, which rely on the waterline delineation. However, the detection accuracy decreases with increasing tidal range at sites exhibiting a non-uniform intertidal profile slope. This generally forces to exclude satellite images acquired near low tide at meso and macrotidal coasts. This communication explores the ability of the wet sand/dry sand line extracted from satellite images to reproduce the mean high water shoreline along the km-scale meso-macrotidal Cap Ferret sand spit, SW France. The results show that satellite-derived wet/dry line provides a consistent proxy of the mean high water shoreline, with almost no influence of low water levels at image acquisition time. However, the use of satellite-derived waterline to retrieve the MHW shoreline should still be preferred for images acquired at high water levels
Impacts of wastewater irrigation on Mediterranean soil and food: A three-year case study in Italy
No full textInternational audienceWater supply for irrigation is a limiting factor for agriculture in Mediterranean countries. A strategy for increasing water availability proposes to use low quality water for irrigation to avoid irrigation with precious and high cost potable water. A drawback about using waste water is the potential heavy metal accumulation in soil and foodstuff. In this study, primary or secondary treated municipal wastewater went through supplementary cleaning steps with a low-cost device and was used to irrigate tomatoes and potatoes in an experimental field in Italy. We monitored heavy metals in soil, food and processed food during three years. We measured no accumulation neither in soil, nor in food after this period. Variations of metal concentrations in soil and food were mainly due to common farm practices such as fertilisation and pesticide applications. This study demonstrates that irrigation with wastewater is achievable with a low-cost treatment device that can be used elsewhere to decrease pressure on water resources