Low shear-velocity zone in the Neapolitan-area crust between theCampi Flegrei and Vesuvio volcanic areas

Some Vesuvio earthquakes recorded at OV-INGV stations in the Campi Flegrei volcanic area have been processed by FTAN (frequency–time analysis) method. The group velocities of Rayleigh-wave fundamental mode have been extracted in the period range 0.7–3 s. Regional group and phase velocity data have been considered as well at the inversion stage. Average shear wave velocity models for the uppermost 73 km of the lithosphere below the Neapolitan area, midway between Campi Flegrei and Vesuvio volcanic areas, have been obtained by the hedgehog nonlinear inversion method. The resulting structural models are characterized by the presence of the carbonate horizon at about 3 km depth. A main feature is represented by low Vs velocities around 9 km depth. This low-velocity layer, already found below both Campi Flegrei and Vesuvio, can be reasonably interpreted as a magmatic reservoir of Campania active volcanoes.