Several location methods for underwater shots in the Gulf of Genoa (Western Mediterranean): Structural implications

Abstract During the EGT survey, 50 underwater shots were detonated on a N-S section through the Gulf of Genoa running from the northern margin (44.12°N) towards Corsica (42.90°N) along the 9°E meridian. The aim of this work is, in a first stage, to establish the propagation model of regional phases in this region and. consequently, to improve the location of epicentres, and afterwards, to refine our structural knowledge of this complex crustal area. The relocation of these shots was carried out with arrival times of seismic signals recorded at land stations. We have used different location methods all of which led to similar crustal models. They reveal a low P n -velocity area in the northern Ligurian Sea and in the Gulf of Genoa, with a 20 km thick crust. In the southern part, approximately south of latitude 43°7N, a 4 km thick oceanic crust covered by 8 km of sediments is clearly confirmed. Using these models, a significant improvement of epicentre locations was obtained. These improvements to propagation models lead to the two main structural conclusions: 1. (1) in the southern part of the investigated area, the spread of an oceanic-type domain as far as the foot of the continental margin, 2. (2) a sharp transition between the two domains of different stretching rate — the northern one. with a Moho depth of about 20 km, and the southern one, with an average Moho depth of about 14 km. These observations substantiate the presence of a transform margin between the rifted Gulf of Genoa and the oceanic-type Ligurian Basin.