Double surface rupture and hydraulic recharge of a three-fault system during the Mw 4.9 earthquake of 11 November 2019 at Le Teil (France)

Abstract

The Mw 4.9 earthquake of 11 November 2019 at Le Teil (France) occurred at a very shallow depth (about 1 km) inducing the surface rupture of La Rouvière fault, nearby of a limestone quarry. Thanks to satellite differential interferometry, we detected the existence of the secondary surface rupture of the quasi-parallel Bayne Rocherenard fault. A newly processed seismic cross-section allowed us to construct a local 3D fault system. Assuming that the earthquake was triggered by the transient increase in hydraulic pressure following heavy rainfall before the event, our numerical 3D simulations demonstrate that the hydraulic pressure gradient is maximum just before the earthquake at the intersection of the two faults, the most probable place of the hypocenter. This hydraulic effect is about two and a half times larger than the cumulative effect of mechanical stress release due to the mass removal from the surface quarry over the two past centuries.