Lithospheric VS models in the Campanian Plain (Italy) by integrating Rayleigh wave dispersion data from noise cross-correlation functions and earthquake recordings

Abstract

Cross-correlation functions of long noise recordings with two broadband stations and earthquake recordings in the Campanian Plain have been processed with frequency time analysis to extract the fundamental mode of Rayleigh waves. Group velocities have been combined with regional group and phase velocity data in the non-linear inversion, with Hedgehog method, in order to get average shear wave velocity models for lithospheric structures extending to 73km of depth.The structural model below the central part of the Campanian Plain is characterized by a covering of pyroclastics and alluvial sediments, about 2km thick, on the carbonate platform with VS ranging from 2.30–2.40 to 2.85–3.15km/s. However, the presence of lava bodies within the carbonates cannot be excluded in the light of the same density and seismic velocities. At greater depths, a main feature is represented by a sharp increment of velocity around 8–9km of depth (VS of 3.85km/s), which can be attributed to the presence of metamorphic rocks, overlying a low VS layer (5% velocity reduction), at about 14–15km of depth. Such structural model resembles those found below the quiescent Roccamonfina and Colli Albani volcanoes, and can be interpreted as the signature of a cooling magma chamber.Moreover, a low VS layer is detected at 8–9km of depth towards the Apennines and at 6km of depth in the southernmost part of the Campanian Plain, nearby Mt. Vesuvius. Such low velocity layer seems to be a regional feature since it has been found below Roccamonfina in the North, Campi Flegrei, bay of Napoli and Mt. Vesuvius in the South, and can be explained by the widespread presence of partially melted material below the whole Campanian area.