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

66 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 This basin includes several sequences, limited by erosion surfaces and characterized by hummocky to chaotic seismic facies, evoking deposits of high energies (fluvial or coastal environment). They are found on maximum thicknesses of 50-60 meters. More recently, in 2022, we used other seismic sources to image the La Hague Deep area with, on the one hand, a sparker- type seismic source and, on the other hand, a shallow water multi-trace streamer. The process included an analysis in variable velocity, carried out at tight intervals on each profile: this heavy work significantly improved the amplitude of the reflectors and reduced that of the so-called multiple reflector. This allows imaging of deep interfaces and it improved recognition of sedimentary and tectonic features. Finally, the preliminary results allow to clarify the structure of the ancient basement and to show that some faults intersect the post-Eocene fills, probably Neogene. The latter are particularly developed in the Hague Deep (H) off the peninsula, with thicknesses of nearly 75 meters (Figure 4). The seismic facies are comparable to those of the Ecréhous basin, evoking high energy deposits arranged in a few seismo- stratigraphic sequences. One fault is particularly noteworthy: the LHOF. Besides the bathymetric data show that it extends over 10 km with a remarkable morphological signature, Fig. 4: Portion of a seismic section from the EMECHAT campaign performed in 2022. This illuminates the seismic facies of suspected Neogene deposits and basement, together with the LHOF signature at depth. See Figure 2 for location.