Lithosphere-Asthenosphere and Volcanism in the Tyrrhenian Sea and surroundings - Struttura

Since the beginning of the 1980s seismic tomography studies have helped to unravel the deep structure and to constrain the kinematic models of tectonic evolution of Italy. In this chapter I describe the main features of the upper mantle structure beneath the Tyrrhenian – Apennine system obtained by jointly analysing the tomographic results with the distribution of subcrustal earthquakes. A new three-dimensional P-wave velocity model is also presented to give the most recent advancement in this research field. The model is computed by applying a non linear inversion algorithm on an improved data set of high-quality teleseismic arrival times recorded at the National Seismic Network and by the stations of a temporary passive array deployed in southern Italy. The resulting picture indicates a remarkable alongstrike complexity of the subduction system below the Tyrrhenian – Apennine region, with at least three basic types of lithospheric sinking. The recognized slabs are characterized by significant differences in the geometry, continuity at depth, velocity contrasts with respect to the surrounding mantle, and reology. In the uppermost mantle the seismic structure is furtherly complicated by the presence of prominent low – velocity regions interpreted as asthenospheric upwelling in front of the downgoing lithosphere.