Géoazur

The East Antarctic Ice Sheet (EAIS) contribution for future global sea level rise and climate change is source of uncertainty, and it appears essential to reconstruct its past fluctuations. Previous works reveal geomorphic and chronological evidence that the ice sheet extended to the continental shelf break during LGM (Last Glacial Maximum; ~20 ka). However, still little is known about its response to the major climate and oceanic transitions following the LGM. In this study, we reconstruct (1) a chronology of ice-sheet fluctuations, (2) ice-sheet past erosion efficiency and (3) ice-sheet thinning during the late-Pleistocene to Holocene time-period, in Terre Adélie (East Antarctica). Newly obtained exposure ages for coupled 10Be-26Al support a scenario of glacial fluctuations at global, regional and local scales. Inland nunataks reveal some long-term exposure with apparent exposure ages ~150 ka, while coastal areas record a past ice-sheet thinning after ~20 ka. Ages measured on erratic boulders of Archipel Pointe Géologie record the final episode of a regional deglaciation around ~15 ka. Slightly inland, in Lacroix sector, erratic boulders record a more recent local ice-sheet oscillations around ~1.5 ka. In contrast, exposure ages obtained on glacially-polished bedrock are characterised by spatially-variable inheritance, suggesting that past ice sheet retreat history is characterised by variations in erosion efficiency. Finally, our results also suggest some potential previous geomorphological inheritance from the hot Pliocene phase.

The Statewide California Earthquake Center (SCEC) sequence of earthquake and aseismic slip (SEAS) group has regularly developed and published benchmarks along the years to follow recent development in the modeling of sequences of aseismic slip and earthquakes, as well as progress in numerical methods. These benchmarks, as well as the results from the different groups are publicly available at: https://strike.scec.org/cvws/seas/. It provides both reference solutions for code verification and a framework for systematic comparison of different modeling approaches. Every group is welcomed to join this Community driven comparison.Recent efforts have focused on adding physics to better reproduce earthquake cycle by considering 2-dimensional fault (Jiang et al., 2022), improve our understanding of fluid injection processes (Lambert et al., 2025), and the effect of free surface and dipping fault (Erickson et al., 2023).To follow up these developments, the SCEC SEAS group is designing two new benchmarks, that will be released to the community soon:[1] A generalization of our benchmark about fluid injection (BP6) from a 2-dimensional domain to 3-dimensional domain. In this benchmark pore fluid diffuses along a 2-dimensional fault, modifying the effective normal traction through one-way hydromechanical coupling. The fluid is injected for 10 hours on a rate strengthening faut and then shut off. The benchmark is designed to admit an analytical formulation for pore fluid diffusion while avoiding numerical singularities that may occurred with point source injection. For this reason, fluid is injected along a Gaussian profile.[2] An updated version of our previous dipping fault benchmark (BP3), in a two-dimensional medium with a free surface. Previous version assumed that the normal traction along the fault was constant. This is obviously a strong assumption, because the normal traction should increase with depth. However, this has proven to be difficult to simulate numerically as the system is going stiffer with lower normal traction. This benchmark therefore aims at providing a more realistic simulation of a dipping fault with a free surface by introducing depth dependent normal traction while also testing the ability of different numerical code to circumvent the problem of stiffness. This benchmark will be a joint benchmark with CRESCENT (Cascadia Region Earthquake Science Center).This contribution will present the design of these forthcoming benchmarks and will provide an opportunity for the community to discuss about future benchmarks and directions for SEAS code comparison efforts.

The increasing occurrence of injection-induced earthquakes has raised public concern and highlighted the importance of understanding subsurface processes to assess induced seismic hazards and risks. A feature of natural faults that has not received sufficient attention in induced seismicity modeling is their geometric roughness. We develop a simple physics-based model to investigate how fault roughness can control induced seismicity during fluid injection.The first approach to modeling along-fault stresses prior to injection is to project the background stress tensor onto the rough fault. In this case, our models and theoretical analysis show that the apparent diffusivity of seismicity fronts can deviate significantly from the hydraulic diffusivity. Faults with realistic roughness generally display slow seismicity migration, producing apparent diffusivities far below the hydraulic values. Thus, seismicity fronts often lag behind the pressure front, especially at low background stresses and small roughness amplitudes. Only in the rare case of very rough faults stressed very close to failure, apparent diffusivity can exceed the hydraulic diffusivity, leading to seismicity fronts that outpace pressure fronts. The second approach to modeling along-fault stresses prior to injection is to simulate stress evolution after multiple tectonic rupture cycles. This ongoing work explores the resulting stress heterogeneity after multiple tectonic rupture cycles and examines whether seismicity migration follows the same trend as in the first approach, i.e., whether seismicity migration is generally slower than the pressure front on rough faults.Apart from seismicity migration, the magnitude-frequency statistics are also analyzed. Along this single rough fault the frequency-magnitude distribution is bimodal. These results demonstrate how fault roughness and stress conditions control the induced seismicity through their influence on the criticality of the fault and stress transfer, and link long-term fault loading processes with short-term seismicity migration patterns in fluid injection scenarios.

A barita é um mineral de ganga comum em sistemas hidrotermais de baixa temperatura. Na área do Seival, a cronologia relativa dos minerais indica que a barita, a calcita e a pouca hematita estão associadas aos estágios hidrotermais de baixa temperatura (< 157° C) de uma mineralização epitermal da Bacia do Camaquã, Cinturão Dom Feliciano, Neoproterozoico. Interpretações anteriores de dados geoquímicos sugeriram que o enriquecimento de Cu nos sulfetos está relacionado à albitização e à cloritização, mas não determinam as origens ou as condições de cristalização da barita. O conteúdo de Ba, S e suas condições de precipitação foram examinados e foi observado um conteúdo menor de Ba no plagioclásio alterado que possui composição de albita, do que na porção menos alterada que possui composição de andesina-labradorita. Além disso, a análise de elementos de terras raras (ETRs) de barita e plagioclásio sugere que a composição elementar da barita na área de Seival veio de material vulcânico (magmático) com influência de água meteórica em vez de água do mar. Os diferentes padrões de ETRs da barita mostram dois grupos relacionados a duas fontes magmáticas de ETRs. Essas diferentes fontes de S, Ba e ETRs foram interpretadas como alteração dominante de rochas vulcanogênicas locais, como rocha piroclástica e fluxos de lava andesítica ou, menos provavelmente, dique lamprofírico.

ABSTRACT Water is essential for life on earth. This is true in the present as it was in the past. Water scarcity and concomitant climate change are increasingly seen as the main threat to human economies across large areas of the world. The Peruvian Andes faced a similar threat during the Medieval Climate Anomaly (c. ad 750–1250). In response, past indigenous communities invested in hydraulic engineering to offset water scarcity due to retreating tropical glaciers. Then as now, the main solution was to build microdams along the headwaters of the Cordilleras. Ancient microdams existed alongside watershed management strategies that incorporated wetland and aquifer protection, terracing and canals. All these constructions, including the dams, were the product of millennia‐long engineering projects that integrated these technologies with their immediate environs. European colonisation in the sixteenth century and concomitant population decline led to their abandonment. Modern microdam construction is now destroying the remaining vestiges of these past hydraulic technologies. In documenting and studying these features, the Past Water Futures project led by Kevin Lane has compiled a geographic database of ancient dams in the Cordillera Negra region, Department of Ancash, Peru. We began by systematising all existing data, documenting both recent and ancient dams and compiling information from previous surveys undertaken by both the Peruvian government agencies and varied research projects. Thereafter, we conducted a survey employing digital imagery (recent and historical), testing out a series of locational parameters including elevation, geology and other aspects. Finally, we selected several hotspots to undertake ground survey of the dams, including a photographic and photogrammetric record of the structures.

Abstract Understanding the seismicity and hydromechanical processes during hydraulic stimulation in hectometer-scale in situ experiments is crucial for bridging the gap between laboratory studies, decameter-scale in situ experiments, and large-scale geothermal projects. These insights can help to optimize the use of geothermal energy. A key example of this is the Bedretto Underground Laboratory in Switzerland, where multiple hydraulic stimulation experiments were conducted between 2021 and 2023 at a hectometer scale. In this study, we present modifications of standard seismic event processing techniques for mesoscale experiments, enabling the accurate detection and location of picoseismic events at these scales. We differentiate between the needs of seismic catalogs for rapid hazard assessment, which require real-time detection of large-magnitude events, and postprocessed catalogs, which are essential for detailed analysis of activated fracture networks, for which a complete seismic catalog is essential. In addition, we evaluate the impact of picking accuracy, background 1D velocity model, and network coverage on the final event locations within a mesoscale underground 3D seismic network, a novelty in experimental seismology.

International audience

Abstract Ever since the discovery of the invasive soft coral species Xenia umbellata (Anthozoa, Octocorallia, Malacalcyonacea, Xeniidae) on the reefs of southwestern Puerto Rico, ongoing surveys have documented its spread and potential impacts on native marine fauna. During benthic surveys conducted by scientific divers from Puerto Rico’s DNER and the Department of Marine Sciences at UPRM, colonies of xeniid soft corals were observed with morphological and color characteristics distinct from those of X. umbellata . Morphological and genetic barcoding analyses of four gene regions confirmed the presence of a second invasive xeniid species, Latissimia ningalooensis , in the southern reefs of Puerto Rico. Originally described in Western Australia, L. ningalooensis has recently been reported in southeastern Brazilian waters, marking its expansion into the Atlantic. The discovery of a second xeniid species in Puerto Rico following the recent introduction of X. umbellata , is both surprising and concerning. Highly disturbed reefs, such as those along the southern coast of Puerto Rico and the wider Caribbean, seem highly susceptible to invasive species. Recent reports of invasive soft corals and other marine species in Puerto Rico highlight the potential for some species to become a regional issue, requiring coordinated management actions across the Caribbean.

The Pokupsko earthquake in Oct. 1909 (Ms 5.7) and, more recently, the Petrinja earthquake in Dec. 2020 (Mw 6.4), both occurring along the same Petrinja-Pokupsko Fault system, induced soil liquefaction phenomena in the alluvial plain of the Kupa river (Croatia). While surface evidence of liquefaction was limited in the 1909 event, the 2020 earthquake triggered more extensive and well-developed liquefaction features along the riverbanks. These features included sand blows, fissures, ground settlements, and lateral spreading, highlighting the increased susceptibility of the alluvial deposits to seismic shaking in the 2020 event. The use of remote sensing techniques enhances the understanding of the spatial distribution of liquefaction occurrences and their subsequent impacts. Drone surveys and a high-resolution Digital Elevation Model (0.5 m resolution) reveal that liquefaction is concentrated within the lowest Holocene terrace and specific areas shaped by fluvial processes. Of particular note is the higher density of sand blows observed in the convex sections of river meanders and the increased lateral spreading at the inflection zones of meanders, where point bar formations become tightened.Lateral spreading along the Kupa river can also be mapped and quantified from optical image correlation of high-resolution aerial images (30 cm resolution) taken before and after the 2020 Petrinja earthquake. These data show that lateral spreading locally exceeds 1 m of displacement toward the river and is generally confined to within 200 m of the riverbanks. On a smaller scale, geological and geotechnical surveys in different sites along the Kupa river point to other conditions influencing liquefaction occurrences and their effects. Soundings and sampling have shown that all sand blows originate from point bars buried between 3 m and 6 m below the surface covered by silty sediments. The soil strength and the thickness of this covering sediment layer are key parameters controlling the occurrence of sand blows. In addition, OSL and 14C dating indicate possible paleo-liquefaction for a sand dyke sealed below the upper part of the aforementioned cover. This combined approach facilitates the identification and detailed characterization of the areas most susceptible to liquefaction in 2020 and historically along the Kupa river. However, in these regions, the surface cover may impede the emergence of liquefied soils to the surface or mask their presence.