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

Abstract

In this paper, we present and comment on the results of a tomographic inversion of P arrival times of local earthquakes to better understand the structure and features of the Ligurian Sea, an oceanic basin originated in the Oligocene±Miocene. This tomographic inversion is the last step in a long and careful revision of the data available for the Ligurian Sea. An accurate catalogue derived from a controlled compilation of data from the numerous stations monitoring seismic activity in this young oceanic basin has been used 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 tomographic inversion by iteratively solving the coupled hypocenter-velocity problem in a least square sense. Careful analysis of the resolution capability of the used data set has revealed the better-resolved features for interpretation. The resulting 3D model shows a high-velocity layer extending from the northeastern side of the model, where it lays about 30 km deep, to the southwestern part where it shallows to 15 km. The shallow part of this high-velocity body is located near the original area of the opening of the Ligurian Sea 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 km long, located at a depth of 8±15 km, is interpreted as a series of ophiolitic bodies intruded into the upper crust.