The Le Teil earthquake provides new insights on seismic risk in France
and Western Europe

Date:
August 27, 2020
Source:
CNRS
Summary:
On 11 November 2019, a magnitude 5 earthquake occurred near
the village of Le Teil in the Rho^ne River Valley in southern
France producing an unexpected surface rupture with ground
displacement. For the first time in France, scientists had
the opportunity to use all modern seismological, geodetical,
and geological techniques available to study this historically
unprecedented seismic event.



FULL STORY ==========================================================================
On 11 November 2019, a magnitude 5 earthquake occurred near the village
of Le Teil in the Rho^ne River Valley in southern France producing an unexpected surface rupture with ground displacement.


==========================================================================
For the first time in France, the CNRS, IRSN, IRD, Universite'
de Montpellier, Universite' Co^te d'Azur and Terradue (1) had the
opportunity to use all modern seismological, geodetical (2), and
geological techniques available to study this historically unprecedented seismic event. The data, published on 27 August 2020 in Communications
Earth & Environment, reveals that the earthquake was caused by the
reactivation of the ancient La Rouvie`re fault. The fault formed during
an extensional tectonic period some 20-30 million years ago during the Oligocene epoch, and was no longer considered to be active.

During the Le Teil earthquake, the fault experienced a reverse faulting movement (compression) with an average surface displacement of about
10cm both vertically and horizontally. Scientists estimate that the
event nucleated at a shallow focal depth of approximately 1km, which
explains why the rupture along the fault was able to reach the surface
and cause considerable damage despite the moderate-magnitude (3) (the
accurate position of the earthquake's focus is presently being studied
by another research team).

The results raise the possibility that other faults could be reactivated
in France and Western Europe and produce surface displacements, whereas
the risk of earthquakes with surface rupture was until now considered
as highly improbable. To better assess the probability of such events,
several teams of scientists in France are performing palaeoseismological investigations looking for evidence of past earthquakes along such faults.

Notes: (1) Members of Ge'osciences Montpellier (CNRS/Universite' de Montpellier/ Universite' des Antilles), Ge'oazur (CNRS/Observatoire de la
Co^te d'Azur/IRD/ Universite' Co^te d'Azur), Isterre (CNRS/IRD/Universite' Grenoble Alpes/ Universite' Savoie Mont Blanc/Universite' Gustave Eiffel) laboratories participated in this study, along with IRSN (France) and
the company Terradue (Italy).

(2) Geodesy is the study, usually with the aid of satellite observations,
of the shape and deformations of the surface of the Earth.

(3) Only 10% of earthquakes of this magnitude cause surface rupture.


========================================================================== Story Source: Materials provided by CNRS. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Jean-Franc,ois Ritz, Ste'phane Baize, Matthieu Ferry, Christophe
Larroque, Laurence Audin, Bertrand Delouis, Emmanuel Mathot. Surface
rupture and shallow fault reactivation during the 2019 Mw 4.9 Le
Teil earthquake, France. Communications Earth & Environment, 2020;
1 (1) DOI: 10.1038/s43247-020-0012-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200827141252.htm

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