Rapid response to the M_w 4.9 earthquake of November 11, 2019 in Le Teil, Lower Rhône Valley, France

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics

Tectonic and geomorphic analysis of the Belledonne border fault and its extensions, Western Alps

International audienceIn the western Alps, the NE trending Belledonne fault system extends from the Mont Blanc massifs in the NE to the Vercors massif in the SW. It includes the Belledonne border fault, defined by an alignment of micro earthquakes (ML <= 3.5). Focal mechanisms and their respective depths indicate a crustal scale NE trending dextral strike-slip faulting. This study aims at better constraining the geometry, the fault kinematics and slip rate of the faults of the Belledonne fault system by using a multidisciplinary approach that includes tectonics, geomorphology and geophysics. New clues of potential Quaternary deformations are observed: 1 - the right-lateral offsets of morphologic markers (talwegs) along the NE trending Arcalod fault at the north-eastern termination of the Belledonne border fault; 2 - the left-lateral offset of the valley carved by the Isere glacier along the NW trending Brion fault, which is consistent with the fault kinematics deduced from the focal mechanisms. Stream network anomalies along the Belledonne border fault are related to glacial erosion processes rather than faulting. However, fault kinematics analysis along the Belledonne border fault allows us to determine a strike-slip tectonic regime characterized by horizontal ENE trending sigma 1 stress axis. It is consistent with the mean trend of the P and T axes deduced from the focal mechanisms. We display evidences that this stress state is Messinian to Quaternary in age and occurred after an Oligocene to Messinian strike-slip tectonic regime characterized by horizontal WNW trending sigma 1. Fault slip rates cannot be assessed because of the lack of morphologic features with constrained ages. However, it is likely that the presented geomorphic markers are older than Wurm. (C) 2015 Elsevier B.V. All rights reserved

Constraining recent fault offsets with statistical and geometrical methods: Example from the Jasneuf Fault (Western Alps, France)

International audienceWe propose two new approaches regarding recent fault offset measurements by studying the seismogenic potential of the Jasneuf Fault. The NE trending right-lateral strike-slip Jasneuf Fault is the southwestern extension of the Belledonne fault system in the Vercors Massif. This fault, which is located in an intraplate domain, does not show strongly associated seismicity but displays morphological anomalies that are related to recent faulting (right-lateral offset of Late Cenozoic cliffs, recent talwegs, and post Ganz scarps). The two methods that we use to quantify fault slip are as follows. 1 - Recursive measurements of stream offsets are conducted. This analysis reveals that a stream network can display characteristic distances between streams that can be mistakenly interpreted as long-term cumulative fault offsets. A comparison of the apparent stream offset values and stream spacing values is necessary to identify the true offsets. 2 - We propose a new method that enables us to determine the fault offset and kinematics by using recursive measurements of topographic apparent offsets to counter the lack of morphologic features that are used to determine piercing points or lines. This method enables us to define each possible slip vector for numerous artificial piercing points along a fault. The slip vector that is shared by these piercing points is the true slip vector. By applying these methodologies, we determine that the Jasneuf Fault has accumulated slip since the Messinian, which corresponds to an average slip rate of 0.13 +/- 0.03 mm year The extension of the fault is poorly constrained. Nevertheless, if we do not consider the potential aseismic (creep slip) component of the faulting, we calculate that this fault could generate Mw 5.7 earthquakes every similar to 500 years according to Wells and Coppersmith's scaling laws and by assuming that the faulting is limited to the sedimentary cover and the Vercors Plateau. (C) 2016 Elsevier B.V. All rights reserved

Présentation de MINERVE, une solution SIG sous réalité virtuelle.

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Deep oceanic submarine fieldwork with undergraduate students, an exceptional immersive experience (Minerve software)

We present the content and scripting of an active tectonic lab-session conceived for third year undergraduate students studying Earth Sciences at Observatoire des Sciences de l’Univers of Lyon. This session is based on a research project conducted on the submarine Roseau active fault in Lesser Antilles. The fault morphology is particularly interesting to map as this structure in the deep ocean is preserved from weathering. Thus high resolution models computed from Remotely Operated Vehicle videos (ROV) provide exceptional educational material to link fault morphology and coseismic displacement. This5class, composed of mapping exercises on GIS and virtual fieldwork, aims at providing basic understanding of active tectonics,and in particular active fault morphology. The work has been conducted either in a full remote configuration via 3D online models or in virtual reality (VR) in a dedicated room using the Minerve software. During the VR sessions, students were either alone in the virtual environment or participated as a full group, including the teacher (physically in the classroom or remotely, from another location), which is to our knowledge one of the first attempts of this kind in France. We discuss on the efficiency10of virtual fieldwork using VR based on feedback from teachers and students, and we conclude that VR is a promising tool to learn observational skills, subject to certain improvements which should be possible in the years to come

Performing submarine field survey without scuba gear using GIS-like mapping in a Virtual Reality environment

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