Seismic velocity structure and focal mechanism of the Umbria-Marche region (Central Italy) from local earthquake tomography

Abstract

Following the 26 September 1997 Colforito earthquakes, seismicity occurred for several months along a normal fault system composed by several adjacent NW trending segments distributed from Gualdo Tadino, in the north, to Sellano in the south. Earthquakes were recorded by several temporary seismic networks. We joined data collected from about 100 permanent and temporary seismic stations for a total complete dataset of several thousands of afstershocks. We present high resolution 3-D images of the Umbria-Marche region (central Italy) as derived from the inversion of P and S wave arrival times from $\sim$2000 crustal earthquakes belonging to the seismic crisis. Moreover, from the 3-D location of earthquakes, $\sim$600 focal mechanisms have been calculated by using the first polarities method.