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Rupture of the 1949 Khait Earthquake on a Cryptic Fault: Implications for Earthquake Hazard
No full textInternational audienceAbstract The 1949 M w 7.6 Khait earthquake, Tajikistan, was one of the most destructive of the Pamir—Tien Shan region, killing over 7,000 people by building collapse and landsliding. It occurred at the transition between the Pamir and Tien Shan mountain ranges, which converge along the narrow Vashkh river valley. Therefore, it is important in understanding the tectonic and structural development at the junction of these two major mountain ranges, as well as yielding important information regarding hazard and risk to local populations and infrastructure. Although widespread landsliding and intensities of shaking were recorded, no surface ruptures were mapped, and the earthquake epicenter and source are poorly known. To determine the location, magnitude, and focal mechanism of the 1949 earthquake we combine calibrated earthquake relocations with body‐wave amplitude ratios from digitized paper seismograms. Our analysis shows that the earthquake nucleated within the Tien Shan basement with strike slip kinematics. Using high‐resolution digital elevation models and orthophotos derived from high‐resolution satellite imagery, we identify earthquake ruptures within the epicentral zone consistent with NW‐SE right‐lateral faulting. Relocated aftershocks and later seismicity also follow a NW‐SE trend through the Tien Shan north of the Vakhsh river. Mapping tectonically offset moraines dated in previous literature, we find a Vakhsh Fault slip rate of only half the present day strain accumulation rate derived from GNSS. Our results suggest a significant proportion of the regional deformation may occur away from the geomorphologically well expressed Vakhsh and Darvaz faults, and on faults with little prior expression of activity
Journées de sensibilisation régionale à la géothermie profonde en Hauts-de-France – 22 & 23 février 2024
No full textInternational audienc
Predicting the steady-state infiltration rates of agricultural soils of the Mediterranean region from their soil surface conditions
No full textInternational audienceKnowledge of soil infiltration properties is essential for managing water resources. Here, we present and evaluate an expert-based classification of soil surface conditions (SSCs) for predicting steady infiltration rates in Mediterranean soils. The classification distinguishes 9 SSC classes. To identify the SSC classes, an identification chart is proposed that uses five easy-to-observe soil surface descriptors (SSDs), namely, the soil cover percentages of clods, surface crusts, rock fragments, herbaceous vegetation and litter. To evaluate the classification, we gathered a dataset including infiltration measurements by rainfall simulations and observations of 12 different SSDs at 273 plots across southern France and Tunisia. The plots represent a range of Mediterranean crops and land uses, including vineyards, wheat, barley, chickpeas, rangeland and fallow land. The expert classification was compared with a statistically derived classification based on a regression tree approach and calibrated with the observational dataset. Variance analysis revealed that the expert SSC classification and the fitted statistical classification explained 73 % and 79 % of the variance in infiltration rates, respectively. A cross-validation test showed that the expert classification is more precise and robust than the statistical classification for predicting soil infiltration rates. The expert classification exhibited a root mean square error (RMSE) of 5.2 mm/h, much smaller than the RMSE values of current pedotransfer functions for predicting soil hydraulic conductivity. Soil surface cover characteristics, proved to be more important proxies for discriminating soil infiltration capacity than permanent topsoil properties, such as soil texture and soil types. To conclude, the expert classification provides an easy and accurate way to estimate the soil infiltration capacity of agricultural fields
Immobilization of a chiral rhodium catalyst on carbon nanotubes <i>via</i> non-covalent interaction for heterogeneous asymmetric hydrogenation
No full textInternational audienceA new chiral rhodium complex containing a diphosphine ligand with a pyrene tag, Rh-(2S,4S)-PPM-pyrene, was synthesized. Its immobilization was achieved through non-covalent π-π stacking interaction between pyrene units of the ligand and multiwalled carbon nanotubes, leading to a hybrid material that was characterized by a set of analysis techniques. Strong adsorption of the complex onto the CNTs enabled an asymmetric hydrogenation of dimethyl itaconate under heterogeneous conditions. This hybrid catalyst showed reduced activity and enantioselectivity compared to its free complex but exhibited good stability for recycling.</div
Separating faces in ARMS metabarcoding improves marine biodiversity monitoring: a comparison across protocols, experimental designs, and photographic surveys
No full textMonitoring marine biodiversity requires approaches that capture its full complexity through space and time. DNA metabarcoding coupled with Autonomous Reef Monitoring Structures (ARMS) is increasingly used for this purpose, yet most applications still pool all sessile fractions and rarely benchmark molecular ouputs against photographic observations. Here, we combined photographic analysis with cytochrome c oxidase I (COI) metabarcoding across ten north-western Mediterranean sites to test, compare, and refine ARMS-based monitoring protocols. We first optimized laboratory procedures (DNA extraction and polymerase choice) and applied the control-driven, replicate-aware VTAM pipeline to minimize false positives and ensure full traceability. We then conducted the first face-by-face comparison of α- and β-diversity between imaging and eDNA in which each individual ARMS face was metabarcoded separately rather than pooled. Metabarcoding detected ∼15× higher site-level richness and revealed stronger correlations with geographic distance and environmental gradients, whereas photography provided complementary information on macro-taxa and surface cover. For metabarcoding, processing each face separately yielded much higher richness and markedly stronger β-diversity–distance correlations than with the NOAA pooling protocol, demonstrating that pooling inflates sampling variance resulting in a loss of the ecological signal. Grouping faces into five structural categories offered a more operational alternative while further increasing α-diversity and strengthening β-diversity correlations. Overall, our results show that retaining ARMS microhabitat structure is critical for maximizing metabarcoding performance. Using five structural sessile fractions per ARMS combined with a control-driven bioinformatic workflow provides a reproducible, scalable framework for long-term eDNA monitoring and early detection of biodiversity change
Extreme sensitivity of the northeastern Gulf of Lion (western Mediterranean) to subsurface heatwaves: physical processes and insights into effects on gorgonian populations in the summer of 2022
No full textInternational audienceIn the summer of 2022, atmospheric conditions characterized by persistent anticyclonic anomalies caused an extreme marine heatwave in the western Mediterranean Sea. Time series of temperature profiles at various points along the northeastern coast of the Gulf of Lion (NW Mediterranean Sea) showed exceptional temperatures down to depths of 30 m, which led to massive mortality of benthic species. A hydrodynamic numerical simulation was used to analyze the physical processes responsible for this subsurface heatwave in a region where the climatology in summer is characterized by northerly winds inducing upwelling alternating with low winds. Firstly, the recurrence of heatwaves limited to the surface was demonstrated, triggered when upwelling stopped and warm water from the Northern Current intruded onto the shelf. More importantly, in August and early September 2022, two episodes of southerly and easterly winds of 8 to 10 m s−1 occurred. The oceanic response to these winds was an alongshore cyclonic current advecting warm water onto the shelf and a downwelling of this warm water to depths of the order of 30 to 40 m. A large part of the Gulf of Lion coast was warmed by these events. However, the northeastern part of the shelf, on either side of the city of Marseille, was by far the area most affected at depth due to the combination of the proximity of the warm surface waters of the Ligurian coast advected by wind-induced currents and the local acceleration of the wind by the continental topography, which intensifies the downwelling of these surface waters. These events are rare in summer, but their impact on the rich benthic ecosystems that characterize the region is dramatic and will only increase with the warming trend in surface waters, which is already close to 1 °C, as seen over the last decade
High‐Frequency Harmonic Tremor Associated With a Water‐Filled Crevasse at Tête Rousse Glacier, Mont‐Blanc Massif
No full textInternational audienceAbstract Tête Rousse glacier is a small polythermal glacier in the Mont‐Blanc massif (French Alps) that released a large outburst flood in 1892 when a water‐filled intraglacial cavity suddenly drained. A new water‐filled cavity was detected again in the central part of the glacier by a geophysical campaign in 2007. It has been pumped three times since to avoid another catastrophic flood. The volume of water in this central reservoir has decreased recently but recent geophysical surveys suggested that significant volumes of water could be stored in the upper part of the glacier. Here, we describe a seismic tremor signal detected in May 2022 probably generated by a water‐filled reservoir within the glacier. The tremor started on 15 May a few days after temperature first increased above 0°C. Tremor amplitude was stronger in the evening and is correlated with water level measured in a crevasse about 230 m downglacier. The time delay between temperature and tremor or water level is consistent with the time needed for water to infiltrate within the snow and into the glacier. We used different methods to locate this signal both from amplitude decay and from P and S waves arrival times. Both methods provide a similar location near the northern boundary of the glacier. Ground penetrating radar surveys performed in May 2024 have since detected a water‐filled reservoir near this location. These results validate our interpretation of this seismic tremor being produced by changes in water‐level in this reservoir
Massive Mg-rich fluid release across the brucite + serpentine reaction in subduction zones
No full textInternational audienceIn subduction zones, serpentinized oceanic mantle is expected to dehydrate above 600 °C due to antigorite breakdown (Atg-out reaction). Analysis of compilatory bulk composition of serpentinites shows that brucite (Brc) should also be an important hydrous component, capable of carrying water to depth. The Atg + Brc = Ol + H2O reaction (R1) which occurs at lower temperature than Atg-out, is thus highly relevant for fluid release in subduction zones. Depending on the initial composition of the serpentinized mantle, R1 can produce more water than the Atg-out reaction. The consideration of most recent thermochemical data for brucite and serpentine solid-solutions shows that the R1 reaction proceeds in a narrow temperature range (< 10 °C), implying relatively high dehydration rates. Thermochemical modeling also shows that the fluid released during R1 is highly magnesian ([Mg]/[Si] > 100), i.e., likely to promote Mg metasomatism. In parallel, metamorphic olivine veins formed according to R1 in the Zermatt-Saas meta-ophiolite were examined. They are interpreted as magnesium-rich segregations resulting from the interaction between an Mg-rich fluid and the host serpentinite for around a hundred years. Furthermore, they are crosscut by brucite veinlets formed at R1 conditions or higher, which confirms, in agreement with thermodynamical modeling, that R1 is not a brucite-out reaction. Finally, P-T conditions of R1 were found to coincide with the location of Low Frequency Earthquakes recorded in the Mexican, Nankai and Cascadian subductions; this indirectly supports the role played by R1 as a significant source of fluid in subduction zones
An empirical analysis of the determinants of food insecurity among smallholder farmers in Eastern Rwanda
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/615956/) * Autres projets (id;sigle;titre): DCI-ENV/2017/387-627;;(EU) Regreening Africa//International audienceBackground: Food insecurity is one of the most pressing problems confronting households in sub-Saharan Africa (SSA). It is particularly acute in low income areas across the continent. Despite Rwanda's economic progress, food insecurity persists especially in rural areas, necessitating empirical evidence to inform targeted interventions that address the complex interplay of socio-economic, environmental and policy factors affecting household food insecurity. Factors affecting food insecurity vary, and obtaining context-specific information is necessary for designing relevant interventions. This empirical study analyzes factors affecting the probability of experiencing severe food insecurity in Eastern Rwanda and discusses how land restoration strategies like agroforestry may contribute to it. Panel data collected in 2018 and 2022 from 1100 randomly selected households are analyzed using both descriptive statistics and a correlated random effects probit model. Results: The findings show a generally high level of food insecurity, with sample households having average food insecurity experience scale scores of 6.02 in 2018 and 5.73 in 2022. Moreover, 63% and 60% of the households experienced severe food insecurity in the two periods, respectively. The empirical results show that farming practices and household socio-economic characteristics played a more significant role in food insecurity status. Households that cultivated different crops had a lower probability of experiencing severe food insecurity and larger households were more likely to experience severe food insecurity. However, agroforestry-related variables were not statistically significant in reducing the probability of severe food insecurity experience in the study area. Conclusion: The study concludes that food insecurity in the study area is high. To address the prevailing situation, efforts to reduce food insecurity should focus on solutions that could increase food production in the short term, such as improving household socio-economic status, diversifying crop production and market-focused production. However, these need to be aligned with local needs and ecological conditions. Agroforestry interventions should focus on integrating suitable tree species into farming systems, and future studies should account for the time dimension to accurately capture long-term effects of such interventions. Moreover, experimental studies to enable rigorous impact analysis of agroforestry interventions are recommended