Average shear wave velocity models of the crustal structure at Mt. Vesuvius

Some Mt. Vesuvius events recorded in 1989–1999 period at Osservatorio Vesuviano (OSVE)-INGV stations have been processed by means of frequency time analysis (FTAN) method. The group velocities of the fundamental mode of Rayleigh-wave have been extracted in the period range 0.3–2 s. Group velocity data, in the period range 10–35 s, and phase velocity data in the period range 25–100 s, obtained in previous studies, have been considered as well, at the inversion stage. Average Vs models for the uppermost 30 km of the crust have been obtained by means of the hedgehog non-linear inversion method. The limestone horizon, calibrated in the Trecase well, close to the FTC station, is characterized by Vs varying in the range 2.40–3.05 km/s, and is about 2–3 km deep. A main feature of Somma-Vesuvius crustal structure is represented by low Vs (2.45–3.05 km/s) around 10 km of depth. This low-velocity layer is absent at a distance of about 15 km from the crater, i.e. outside of the volcano, and can be explained by the local presence of partially melted material. A deeper low Vs layer is found below all stations, constituted by mantle or a mélange of crustal and mantle material with about 10% of partially melted material. It is a regional feature and can be interpreted as magmatic reservoir of Campania active volcanoes.