European Geotraverse: A seismic refraction profile across the Ligurian Sea

A seismic refraction profile was shot in the Ligurian Sea between Italy and Corsica in September 1983. The profile, which is part of the southern portion of the European Geotraverse, was shot using small dynamite charges, and the seismograms were recorded by ocean bottom seismometers and land stations, resulting in a number of partially overlapping reversed profiles.The refraction data were interpreted by means of the velocity-intercept and ray-tracing methods, using seismic reflection derived velocity-depth information for the sedimentary section. Refraction velocities of 4.8, 6.0 and 6.6 km s⁻¹ were calculated for the base of the sedimentary section, crystalline basement and lower crust, respectively. An upper mantle velocity of 7.4 km s⁻¹ was inferred using the refraction profiles recorded on Corsica.The interpretation of the data indicates a prominent high in the crystalline basement in the northern part of the profile, while the sedimentary section increases in thickness from about 1.5 km over the basement high to over 6 km between the basement high and Corsica, and includes a considerable thickness of pre-Miocene sediments.The crust-mantle boundary shows shoaling towards the centre of the profile, where a minimum crustal thickness of 16 km is reached. The model, therefore, is that of a stretched and thinned continental crust which was rifted in Oligo-Miocene times. The presence of a low-velocity upper mantle may be indicative of the present renewal of subcrustal activity under the Ligurian Sea.