Precise absolute earthquake location under Somma-Vesuvius volcano, Geophys

The Somma–Vesuvius volcanic complex and surroundings are characterized by topo-graphic relief of over 1000 m and strong 3-D structural variations. This complexity has to be taken into account when monitoring the background volcano seismicity in order to obtain reliable estimates of the absolute epicentres, depths and focal mech-anisms for events beneath the volcano. We have developed a 3-D P-wave velocity model for Vesuvius by interpolation of 2-D velocity sections obtained from non-linear tomo-graphic inversion of the Tomoves 1994 and 1996 active seismic experiment data. The comparison of predicted and observed 3-D traveltime data from active and passive seismic data validate the 3-D interpolated model. We have relocated about 400 natural seismic events from 1989 to 1998 under Vesuvius using the new interpolated 3-D model with two different VP /VS ratios and a global search, 3-D location method. The solution quality, station residuals and hypocentre distribution for these 3-D locations have been compared with those for a representative layered model. A relatively high VP/VS ratio of 1.90 has been obtained. The highest-quality set of locations using the new 3-D model falls in a depth range of about 1–3.5 km belo