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Abstract: One- and two-dimensional V P models were obtained by TomoVes experiment, all characterized by low V P in the uppermost 500 m and a sharp discontinuity at about 2–3 km beneath the volcano. Large amplitude late arrivals were identified as P- to S-phases converted at the top, between 8 and 10 km deep, of a low-velocity layer with a dramatic drop of V S, from approximately 3.6 km/s to less than 1.0 km/s. Here, we synthesize the interpretation of Rayleigh wave dispersion measurements, made by several authors, to delineate the extent of such anomalous layer of hot, partially molten, crust material. Our non-linear inversion of broad-band dispersion measurements evidences a main feature of Somma-Vesuvius deep structure consisting of low V S layers at about 8–10 and 20 km of depth. The depth of the shallower low-velocity layer and the V S value above it are in agreement with TomoVes results, but the V S velocity reduction is of about 10%. If we assume V S equal to 1.0 km/s in our non-linear inversion, a thickness not greater than 0.35 km results. The volume occupied by this very low-velocity layer, sill-shaped, is compatible with the size of Mt. Vesuvius cone, but it develops above a much larger hot mass, which could be the parental source as the erupted products are only few percent of magma chamber. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]