Deep reflection seismic images of the crustal thinning in the eastern Pyrenees and western Gulf of Lion

Abstract

The results of the MCS LISA seismic survey in the Mediterranean Sea and the wide angle data recorded by the onland stations during this experiment are merged and compared with the ray tracing modeling and the deep structure known from previous refraction studies. The results are very good, arriving at a new deep seismic image of the crustal structure. The LISA seismic profile 26, shown is this publication, crosses in strike line a deep basin close to the eastern Pyrenees. The shallow part of the seismic profile is poorly imaged but, thanks to the very good ELF seismic profiles crossing the LISA survey, the acoustic basement and a decollement level can be drawn. The deep part of the LISA profile data has a much better quality than the shallow part and reveals a high velocity (7.1 km/s) lower crust, overlying a shallow Moho interpreted at 8 s TWTT. The wide angle reflections enable the comparison between the ray tracing measured by distance and the seismic image measured by time thereby making the relationship between the continent and the continental shelf clearly delineated for the first time. The thinning of the thickened crust of the eastern Pyrenees does not occur at the shore but inland at the western boundary of the Roussillon basin. However, the central part of the Gulf of Lion continental shelf forms a deep basin that overlies a thinned crust. The age of the thinning is discussed in the general context of the convergence and divergence of the European and Iberian plates including the Sardinia-Corsica block. The geometry of the transfer faults is studied and shown as not steep and to have normal and strike-slip components.