Lithosphere - Asthenosphere Structure Beneath Central - Southern Apennines (Italy) From Nonlinear P-Wave Tomography

We present new results for the P-wave velocity structure beneath the Central-Southern part of the Italian peninsula, obtained by inverting an improved dataset and extending the usual linearized approach of traveltime tomography to non-linear tomography. The data used in the imaging are the relative arrival times of over 5000 P-phases, accurately handpicked from teleseismic waveforms recorded by the Italian seismic network in the last decade. Data from a temporary array of ten stations deployed in southern Italy in the frame of an ongoing passive experiment (Saptex) were also included to provide a more complete and homogeneous ray geometry. The tomographic model is computed by means of an iterative sequence of linearized inversions incorporating a 3-D minimum travel time ray-tracing. At each iteration, a weighted damped least square solution is determined by using the singular value decomposition (SVD) method to better test the spatial resolution of the reconstructed anomalies. Beneath central Apennines the tomograms reveal a continuous, SW-dipping high-velocity body, from ~ 150 km down to ~ 500 km. At shallower depths, a pronounced low-velocity zone is recognized from the uppermost mantle beneath the Apenninic belt down to ~ 200 km below the Tyrrhenian area. This feature is proposed to affect the seismic structure of the downgoing slab, weakening its velocity signature. Beneath southern Apennines, high-velocity anomalies are reconstructed in the uppermost mantle of the Apulian foreland and below the belt between ~ 100 and ~ 400 km. Low-velocity regions, interpreted as due to asthenospheric upwelling, are recovered above or across the fast structures, as at the southeastern end of the Apennines where a possible complete slab breakoff is suggested.