Group velocity tomography and regionalization in Italy and bordering areas

More than 200 group velocity dispersion curves (109 new dispersion data and 101 collected from literature) of the fundamental mode of Rayleigh waves, in the period range from 10 to 35 s, have been processed to obtain tomographic maps, for the Italian peninsula and bordering areas. We compute average dispersion relations over a 1°×1° grid, and, since the lateral resolving power of our data set is of about 200 km, we group the cells of the grid according to their dispersion curves. In this way and without any a priori geological constraints, we define seven different regions, each characterised by a distinctive mean group velocity dispersion curve. The resulting regionalization can be easily correlated with the main tectonic features of the study area and mimics a recently proposed structural sketch. Average models of the shear wave velocity in the crust and in the upper mantle for a few selected regions are presented. The very low S-wave velocity values found in the uppermost upper mantle of the southern Tyrrhenian basin are consistent with a large percentage of partial melting, in agreement with the presence of the Vavilov-Magnaghi and Marsili huge volcanic bodies.