The 2019 Le Teil surface-rupturing earthquake along the La Rouvière Fault within the Cévennes fault system (France): What does paleoseismology reveal?

¹ Géosciences Montpellier, Univ. Montpellier, CNRS, Univ. Antilles, Montpellier, France
² Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Fontenay-aux-roses, France
³ EDF-DIPNN-DI-TEGG, Aix-en-Provence, France
⁴ Département Analyse Surveillance Environnement, CEA, DAM, DIF, 91297 Arpajon, France
⁵ ISTerre, Université de Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, IFSTTAR, Grenoble, France
⁶ Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, IRD, Géoazur, 250 rue Albert Einstein, Sophia Antipolis 06560 Valbonne, France
⁷ Aix Marseille Univ., CNRS, IRD, INRAE, Collège De France, CEREGE, Aix‑en‑Provence, France

^* Corresponding author: jean-francois.ritz@umontpellier.fr

Résumé

The 2019-11-1, Mw4.9 Le Teil earthquake occurred within the NE termination of the Cévennes faults system (CFS) in southern France, along the La Rouvière fault (LRF), an Oligocene normal fault which was not known to be potentially active. This shallow moderate magnitude reversefaulting event produced a 5 km-long surface rupture and strong ground shaking. No evidence of previous quaternary activity was observed in the morphology, raising the question whether the fault had been reactivated for the first time since the Oligocene or had broken the surface in the past without being detected in the morphology. To address this issue, we carried out paleoseismological investigations to analyze and characterize evidences of paleo-ruptures in Quaternary deposits. We discovered that at least one event prior 2019, occurred between 13.5 and 3.3 ka within the central part of the fault segment that broke in 2019, and that a possible earlier surfacerupturing event occurred within the northern part of this segment during the 16th century. Further investigations coupling sub-surface geophysical investigations and trenching are now carried out within the southern and northern segments of the LRF as well as along the other fault segments of the CFS.