| In the last few years, dense passive seismic experiments have been conducted in southern
Italy with the goal of better understanding its deep structure and seismotectonic. Such
deployments, along with the ongoing improvement of the Italian national network, increased
significantly the coverage of recording sites, making available large datasets of local,
regional, and teleseismic events for high-resolution lithospheric studies. In this study the
upper mantle velocity structure to a depth of 550 km is investigated by integrating the
teleseismic waveforms recorded by the permanent network in the last two decades with those
collected from the continuous records of the temporary arrays (2001 ÷ 2008). The dataset
consists of 7355 P wave relative arrival time residuals picked from a selection of 239, Mw
-¥ 5.5 events recorded at epicentral distances between 25Ë and 95Ë . A recently
developed iterative nonlinear tomographic procedure based on a subspace inversion
scheme and incorporating a robust wavefront tracking method, is used to obtain the
solution model. The resultant tomographic images show a pattern of P -wavespeed
anomalies that better defines the geometry of the subduction system along the southern
Apenninic arc from central Italy to Sicily. Beneath the Southern Apennines the
main features of the model is represented by a SW-ward dipping high-velocity
anomaly which extends from below 100 km to about 300 km depth. Below the
Calabrian Arc the subducting Ionian slab is imaged clearly in the upper mantle
down to at least 350 km depth. Pronounced low-velocity anomalies are visible
around the southwestern boundary of the downgoing lithosphere, depicting a possible
asthenospheric flow from the African mantle to the Southern Tyrrhenian back arc basin. |