SKS-wave splitting and upper mantle structure: Results in the Southern Apennines

Abstract

Shear wave splitting measures at six temporary stations in the Southern Apennines are computed analyzing fifteen events recorded during the spring and summer 1996, with magnitude greater than 5.8. The splitting parameters were measured using Silver and Chan's (1991) method only on SKS and SKKS phases. Evidence for strong seismic anisotropy was found at all the stations: delay times δt are generally larger than 1.5 s and fast directions φ are quite variable in different geodynamic domains. NW-SE φ average directions are found at stations on the mountain belt while at stations on the foredeep and foreland φ is on average N-S. Changes in splitting parameters may be related to upper mantle structure, and particularly to the geometry of a fragmented lithosphere subducting beneath the Apennines.