Upper Mantle Structure of the Alps, Appennines and Adria Regions as Revealed by Shear Wave Splitting: Results from the CIFALPS Project

The structure of the upper mantle beneath the Alps and the Apennines has been extensively studied in the past, and several studies have been focused on the seismic anisotropic properties to delineate the strain distribution in the litho-asthenospheric region. However, Northern Apennines, Alps and surrounding regions are often studied separately, and a joint interpretation of the Alps-Apennines transition zone is still lacking. In this perspective, the China-Italy-France Alps seismic survey (CIFALPS) provided an improved image of the crust and upper mantle beneath the southwestern Alps and the Alps-Apennines transition zone. Here, we present the SKS shear wave splitting results obtained from the analysis of teleseismic data recorded by 55 temporary seismic stations along the CIFALPS profile. The strain-induced lattice preferred orientation of olivine minerals within the upper mantle, expressed by the analysis, confirms the NW trending fast polarization directions parallel to the strike of the orogen, in good agreement with the results of previous studies all along the Alpine chain. Instead, a scattering in the distribution of new shear wave splitting measurements is evidenced in the Po Plain, where the coexistence of both NNE-SSW and E-W directions provides new insights on upper mantle deformation in the complex transition zone between the Alps and the Apennines.