Crustal and uppermost mantle structure in Italy fron the inversion of P-wave arrival times: geodynamic impliations

In this paper we present a 3-D image of the P-wave velocity structure in the crust and uppermost mantle beneath Italy, obtained by inverting P-wave arrival times of crustal earthquakes. We used about 48 000 arrival times at stations close to the epicentres (within 200 km) to mitigate the effects of both reading errors and intrinsic complexity for long-distance ray paths due to the scale of heterogeneities in the Earth structure beneath Italy. Whereas two of the inverted layers (located in the lower crust and beneath the Moho) are well resolved by the data, the upper crustal layer has regions of relatively poor resolution beneath the central Apennines, due to the sparse station spacing. We made several attempts, varying the Moho geometry, to obtain reliable and stable results without introducing too complex and unconstrained a priori information. One of the most important results is the discovery of low-velocity anomalies at 38 km depth beneath the northern Apenninic and Calabrian arcs, which we interpret as subducted crustal material of the Adriatic and Ionian lithospheres. In the lower crust beneath the entire Apennines, a pronounced low-velocity belt is present, suggesting high temperatures in front of the bent Adriatic lithosphere. Based on our results and on those previously obtained from seismic tomography, we propose a model for the geodynamic evolution of the Apenninic system in which the present-day scenario reflects lateral heterogeneities in the subducting Ionian (oceanic) and Adriatic (continental) lithosphere.