Seismic anisotropy beneath the Northern Apennines (Italy) and its tectonic implications

Abstract

We examined shear wave splitting in SKS and S phases from 22 teleseisms at 10 temporary stations on a transect across the Northern Apenninic arc. The array, near 43øN, spans from Corsica Island across the Tyrrhenian region and the Apenninic belt to the Adriatic coast. We applied particle motion, covariance matrix decomposition, and cross correlation methods to estimate the polarization direction of the fast split - shear wave (q•) and the delay time between split phases (fit). Most of the analyzed shear waves show clear evidence of splitting. The q• in the Adriatic foreland and in the Apennines are approximately parallel to the strike of the mountain belt (NW-SE). The largest fit correspond to the highest elevations, suggesting that anisotropy is related to the compressional tectonics which built the Apennines, and that this tectonic compression involved at least the entire lithosphere. In the Tyrrhenian area we observe q• oriented about E-W, suggesting a reorientation of the mantle fabric due to astenospheric flow, responsible for the E-W post-orogenic extension observed at the surface.