A Ligurian (Western Mediterranean Sea) geophysical transect revisited

Data from a new deep-penetration seismic reflection line (LISA cruise 1995) , onland seismic recording (LISA) and marine ESPs (expanding spread profile s, CROC II cruise 1981) are integrated to study the crustal structure of th e north Ligurian basin. The correlation of these different seismic data, lo cated along an Antibes-Ile Rousse transect, provides accurate information o n the nature of the crust. On the Provencal margin, the multichannel seismi c (MCS) profile LISA01 shows a major step in the basement. This structure i s associated with a crustal change, corresponding to the ocean boundary. On the Corsica margin, we do not observe such a structure and the ocean bound ary is constrained by magnetic anomalies. These anomalies are identical to those observed on the Provencal margin above the main basement structure, O n the MCS line, the Messinian salt and the bottom water multiple obscure th e crustal image below 7 s two-way traveltime (TWTT). Nevertheless, the ESPs provide information about the crust below 7 s TWTT. These ESPs were reproc essed and analysed by matching traveltime and amplitude variations in the X -T and tau -p domains. The main result is the identification of a transitio nal zone on the continental margin (Provencal and Corsica mar-gin) characte rized by a layer with velocities of 7.2-7.3 km s(-1) in the lower crust. Re cordings from land stations on the Corsica margin define the geometry of th is layer. In the centre of the basin, the oceanic crust is about 6 km thick . From the Corsica margin to the centre of the basin, the Moho depth decrea ses from 18 to 13 km. The velocity model deduced from offshore data is cons istent with the ESP velocity model and MCS line LISA01. The combined analys is of these data allows us to propose a new boundary of the oceanic crust i n the north Ligurian basin.