P-wave deep velocity structure of the Southern Tyrrhenian Subduction Zone from nonlinear teleseismic traveltime tomography

A new 3-D model for the P-wave velocity structure of the Southern Tyrrhenia n Subduction Zone (STSZ) is determined from nonlinear inversion of relative arrival times of teleseismic events. The data used in the imaging are the travel time residuals of both direct, P and PKPdf, and secondary pP, sP, Pc P, PKPbc phases,computed with respect to the global 1-D velocity model ak13 5. 2308 teleseismic waveforms were collected for this study from 109 events recorded by the Italian National Seismic Network (RSNC) during 1988-1998. The velocity perturbation field is reconstructed gradually by means an iter ative sequence of linearized inversions, incorporating a 3-D minimum travel time ray tracing. The tomographic images reveal a broad high-velocity zone dominating the pattern of lateral variations beneath the Southern Tyrrheni an Sea and Calabria. This fast structure extends laterally for a maximum of similar to 350 km, from northern Sicily to southern Campania, and vertical ly for at least 400 km, from the uppermost mantle down to 500 km depth. Bel ow 350 km the geometry of the depicted slab is characterized by horizontal deflection of the subducting lithosphere towards the central Tyrrhenian bas in.