Exceptional ground motion during the shallow Mw 4.9 2019 Le Teil earthquake, France

Abstract

An unusually damaging Mw 4.9 earthquake occurred on November 11, 2019 in the south east of France within the lower Rhône river valley, an industrial region that hosts several operating nuclear power plants. The hypocentre of this event occurred at an exceptionally shallow depth of about 1 km. Here we use far-field seismological observations to demonstrate that the rupture properties are consistent with those commonly observed for large deeper earthquakes. In the absence of strong motion sensors in the fault vicinity, we perform numerical predictions of the ground acceleration on a virtual array of near-fault stations. These predictions are in agreement with independent quantitative estimations of ground acceleration from in-situ observations of displaced objects. Both numerical and in-situ analyses converge toward estimates of an exceptional level of ground acceleration in the fault vicinity, that locally exceeded gravity, and explain the unexpectedly significant damage.

EMS98 intensities distribution of the “Le Teil” earthquake, France, 11 November 2019 (Mw 4.9) based on macroseismic surveys and field investigations

“…In this small area, a shaking of intensity VIII cannot be excluded due to the high damage on the four houses of vulnerability A or B, but cannot be confirmed according to the EMS98 due to the very low density of buildings, which limits the statistical approach. A strong seismic motion could occur here due to the proximity of the surface rupture (400 to 700 m away), and it is also possible that the ground motion was highly variable inside the district [see more discussion in Causse et al, 2021]. In the opposite way, unless a more thorough survey is made on the slightly damaged buildings in the south of Viviers, the occurrence of parts of intensity VI in the locality cannot be excluded.…”

“…Two cemeteries are also present in the intensity-VII part of the municipality; a few displacements of small objects have been observed there, but no displacement of funeral slabs [Causse et al, 2021].…”

“…These disorders on modern houses are observed only along the road linking La Rouvière and Mélas districts (i.e., over a distance of only 1300 m, about ten modern houses with D1 damage, two with D2, one with D3). It should be noted that the cemetery on this road had numerous fallen steles, and funeral slabs that had tipped over or been displaced by several centimetres [Figure 8h; measurements available in Causse et al, 2021]. Another cemetery located in the Mélas district also showed some displaced slabs and fallen steles, and the mausoleums are heavily cracked.…”

New perspectives in studying active faults in metropolitan France: the “Active faults France” (FACT/ATS) research axis from the Resif-Epos consortium

“…On November 11th, 2019, the Mw 4.9 Le Teil earthquake occurred on the northeastern termination of the CFS along a segment called the La Rouvière fault (LRF). This very shallow (1-1.5 km) moderate magnitude and reverse-faulting event inverted an Oligocene normal fault which was not assessed to be potentially active [see Jomard et al, 2017], causing surface rupture and strong ground shaking [Ritz et al, 2020, Causse et al, 2021, Vallage et al, 2021 (Figure 12A).…”

Seismic swarms in Tricastin, lower Rhône Valley (France): review of historical and instrumental seismicity and models

“…Southeastern France is a region of moderate but shallow seismic activity, sometimes affected by locally 2 Laurent Bollinger et al 2020, Causse et al, 2021.…”