Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

62 PATA Days 2024 1 2 T H I N T E R N AT I O N A L I N Q U A M E E T I N G O N PA L E O S E I S M O L O G Y , A C T I V E T E C T O N I C S A N D A R C H A E O S E I S M O L O G Y ( PATA ) , O C T O B E R 6 T H - 1 1 T H , 2 0 2 4 , L O S A N D E S , C H I L E K E Y W O R D S Neotectonics, Offshore geophysics, Stable Continental Region, Channel Islands, France (1) Institut de Radioprotection et Sûreté Nucléaire, Fontenay-Aux-Roses, France. (2) Université du Havre Normandie, Le Havre, France (3) Université de Bretagne Occidentale, Brest, France (4) Université de Caen, CNAM-INTECHMER, Caen, France *Email: stephane.baize@irsn.fr Stéphane Baize (1) Tassadit Kaci (2) Juliette Thomas (1, 3) Léa Lubert (1, 3) David Graindorge (3) Anne Duperret (2) Bernard Le Gall (3) Yann Méar (4) Johann Brochon (3) Emmanuel Poizot (4) OFFSHORE INVESTIGATION OF NEOTECTONIC FAULTS IN AN INTRAPLATE AREA, BETWEEN THE NORMAN COAST AND THE CHANNEL ISLANDS A B S T R A C T We present preliminary results on neotectonics in an intraplate area of NW Europe, namely the domain between the Channel Islands and the Norman coast. Thanks to offshore geophysics, we illuminate the sea bottom geology with an unprecedented resolution, together with the deep structure and the post- Eocene sedimentary formations. We document the presence of neotectonic faults which, considering their length, could cause significant earthquakes. I N T R O D U C T I O N The evaluation of seismic hazard in Stable Continental Region is a challenge because seismological data are lacking and represent only a partial sample of seismicity that characterizes an area. One way to overcome this incompleteness is to study the activity of faults over sufficiently long periods to better assess their seismogenic potential. This is particularly relevant for the safety of nuclear sites (IAEA, 2022) and, in this case, the Plio-Quaternary period is recommended. The Cotentin Peninsula, Normandy, Western France, includes two major nuclear sites along its shoreline, a nuclear power plant with several reactors (Flamanville) and a major plant for treatment and recycling of nuclear fuel (La Hague) (Figure 1). This area has experienced several historical damaging earthquakes, corresponding to moderate events (e.g. Baumont et al., 2023). The preliminary results presented here are part of the characterization of faults presenting evidence of post- eocene deformation, most likely during the Neogene by correlation with knowledge on land (Sainteny- Marchésieux basin, SM). These faults, here qualified as neotectonic, could potentially be taken into account as sources of further significant earthquakes.