Seismic Structure Beneath Mt. Vesuvius From Receiver Function Analysis and Local Earthquakes Tomography: Evidences for Location and Geometry of the Magma Chamber

The recognition and localisation of magmatic fluids are pre-requisites for evaluating the volcano hazard of the highly urbanized area of Mt. Vesuvius. Here we show evidence and constraints for the volumetric estimation of magmatic fluids underneath this sleeping volcano. We use Receiver Functions for teleseismic data recorded at a temporary broad band station installed on the volcano to constrain the S-wave velocity structure in the crust. Receiver Functions are analyzed and inverted using the Neighbourhood Algorithm approach. The 1D S-velocity profile is jointly interpreted and discussed with a new Vp and Vp/Vs image obtained by applying double difference tomographic techniques to local earthquakes. Seismologic data define the geometry of an axial, cylindrical high Vp, high Vs body consisting of a shallow solidified materials, probably the remnants of the caldera, and ultramafic rocks paving the crustal magma chamber. Between these two anomalies, we find a small region where the shear wave velocity drops, revealing the presence of magma at relatively shallow depths. The volume of fluids (30 km3) is sufficient to contribute future explosive eruptions.