Seismicity and crustal structure beneath the western Ligurian Sea derived from local earthquake tomography

In this paper, we present and comment on the results of a tomographic inver sion of P arrival times of local earthquakes to better understand the struc ture and features of the Ligurian Sea, an oceanic basin originated in the O ligocene-Miocene. This tomographic inversion is the last step in a long and careful revision of the data available for the Ligurian Sea. An accurate c atalogue derived from a controlled compilation of data from the numerous st ations monitoring seismic activity in this young oceanic basin has been use d for computation of a one dimensional (1D) reference model. A high-quality subset of the new catalogue has been used for the non-linear 3D tomographi c inversion by iteratively solving the coupled hypocenter-velocity problem in a least square sense. Careful analysis of the resolution capability of t he used data set has revealed the better-resolved features for interpretati on. The resulting 3D model shows a high-velocity layer extending from the north eastern side of the model, where it lays about 30 kin deep, to the southwes tern part where it shallows to 15 kin. The shallow part of this high-veloci ty body is located near the original area of the opening of the Ligurian Se a that took place between the Oligocene and early Miocene. Its velocity is comparable with that of an oceanic Moho (around 7.8 km/s). A lens-shaped high-velocity body, about 25 kin long, located at a depth of 8-15 kin, is interpreted as a series of ophiolitic bodies intruded into the upper crust. (C) 2001 Elsevier Science B.V. All rights reserved.