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

Abstract

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.

A decade of seismicity in metropolitan France (2010–2019): the CEA/LDG methodologies and observations

“…The inverted depth lies around 1 km and the calculated moment magnitude is Mw 4.8 (Vallage et al, 2020), which is in agreement with other publications (Ritz et al, 2020;Cornou et al, 2021) and with rapid estimations from different French institutes such as OCA (Mw 4.9, 1 km) and IPGP (Mw 4.8, 3 km). The moment magnitude estimated from coda wave analysis at 14 LDG stations is slightly higher (Mw coda 5.2), in between the ML and the other moment magnitudes (Tab.…”

“…The very small number of aftershocks, only four recorded by the LDG stations in November, raised questions in the scientific community about the anthropogenic or tectonic origin of this event, also due to the close location of the event to a quarry (De Novellis et al, 2020;Cornou et al, 2021).…”

On rapid multidisciplinary response aspects for Samos 2020 M7.0 earthquake

“…On the contrary, as shown from DInSAR data, the eastern propagation of the rupture does not seem to have reached the land surface. This is critical as such information could assist several groups during their fieldwork and help assessment of damages as successfully done for other geohazard events (Cornou et al 2020). In fact, the above finding was confirmed after the relocation of post-seismic events, which showed the absence of very shallow aftershocks.…”

“…Since the initial development of spaceborne synthetic aperture radar (SAR) systems and the demonstration of the SAR interferometric capability, the technique has reached its maturity for the detection of earthquake-induced ground displacements (Cornou et al 2020;Bacques et al 2020), among other geohazards (Delgado Blasco et al 2019;Papageorgiou et al 2019;Aslan et al 2020;Cigna and Tapete 2020;Vassilakis et al 2020). In the last decade, Earth Observation (EO) satellite missions are providing a richness of data at improved spatial resolution and coverage, as well as reduced revisit time, while the latest generation of SAR sensors ensures the millimeter precision of interferometric measurements (Gisinger et al 2019).…”

EXCEPTIONAL GROUND MOTION DURING THE SHALLOW Mw 4.9 2019 LE TEIL EARTHQUAKE, FRANCE

“…Seismological, geodetical and field observations indicate a reverse-fault mechanism, a rupture area of about 4 km by 1.5 km, a hypocenter at about 1 km and surface rupture evidences (ref. [7][8] ). Such a shallow location is exceptional.…”