Earthquake Tomography in the Larderello Geothermal Area

Abstract

A 3D velocity structure model of the Larderello geothermal area has been constructed by analyzing seismic data recorded by the Enel network of Larderello and using two different techniques: - the analysis of teleseismic travel time residuals of more than 100 - a joint hypocenter-velocity inversion of local earthquake arrival The inversion of these data showed a sharp low velocity zone in the center of the geothermal area, characterized by a of P wave velocity. The velocity model obtained from the 3D inversion of teleseismic and local earthquakes is supported by further geophysical data. Peaks of the seismic reflector known as the "K horizon" are in agreement with P wave velocity anomalies at depth of 4-8 Furthermore, the 2D gravimetric model shows a deep low density body (d = 2.55 while the resistivity model shows an analogous conductive body (resistivity The convergence of these elements supports the hypothesis that the velocity anomaly is related to an intrusive, still partially molten body, that might be the heat source of the Larderello geothermal area.