EGU24-9479, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Aftershock sequence and source characteristics of the June 16, 2023 MW=4.9 La Laigne earthquake, western France

Mickaël Bonnin1,2, Marion Alloncle1, Maxime Bes de Berc3, Éric Beucler1,2, Damien Fligiel2, Marc Grunberg4, Céline Hourcade1, Clément Perrin1,2, Olivier Sèbe5, Jérôme Vergne3,4, and Dimitri Zigone3,4
Mickaël Bonnin et al.
  • 1Laboratoire de Planétologie et Géosciences (LPG), Nantes Université, CNRS-6112, Nantes, France
  • 2Observatoire des Sciences de l’Univers Nantes Atlantique (Osuna), Nantes Université, CNRS-3281, Nantes, France
  • 3Institut Terre et Environnement de Strasbourg (ITES), Université de Strasbourg, CNRS-7063, ENGEES, Strasbourg, France
  • 4École et Observatoire des Sciences de la Terre (EOST), Université de Strasbourg, CNRS-830, Strasbourg, France
  • 5CEA-DAM, Bruyères-le-Châtel, Arpajon, France

On June 16, 2023 at 16h38 UTC, a moderate earthquake of magnitude MW=4.9 stroke western France south of Niort city, near the small village of La Laigne (Charente Maritime). The shaking has been widely felt in the whole NW France and macroseismic intensity (EMS98) of VII was reached at the epicenter. Such an event is relatively rare in continental France and represents the second largest event in the western France in the last century. The epicentral region is located at the northern termination of the Aquitaine basin where 300 m of Mesozoic sediments covers the variscan basement. The focal mechanism obtained from waveform inversion corresponds to a pure dextral strike-slip motion or a pure senestrial strike-slip motion along a EW or NS striking fault plane, respectively.

The fault that ruptured on June 16 is not known. To gain insight on its characteristics, teams of Nantes (Osuna and LPG), of Strasbourg (EOST and ITES) and of the CEA deployed between June 17 and June 22, 2023 for approximately one month, a network of 3-components stations composed of 12 MEMS accelerometers, 104 five hertz geophones and 5 broadband velocimeters in a 40 by 30 km region around the epicenter, with a station inter-distance of approximately 4 km.

We present is this study the first results derived from this unique experiment. In particular, we show that the aftershock sequence (more than 600 events recorded) highlights a planar rupture zone of about 5.4 km2, trending NS and strongly dipping to the East (75°), located between 2 and 5 km depth. Site effect analysis allows us to better understand large ground motion distributions over the area and their link with macroseismic intensities. The installed array also allows us to infer a preliminary 3D VS model of the region. We show the extent to which a dense temporary network is mandatory for studying the fine structure of the fault plane in a region where previous knowledge of active geological structures is limited.

How to cite: Bonnin, M., Alloncle, M., Bes de Berc, M., Beucler, É., Fligiel, D., Grunberg, M., Hourcade, C., Perrin, C., Sèbe, O., Vergne, J., and Zigone, D.: Aftershock sequence and source characteristics of the June 16, 2023 MW=4.9 La Laigne earthquake, western France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9479,, 2024.