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Abstract:
Active and past subduction systems influence the interpretation and understanding of current tectonics and velocity structures of the upper mantle of the Alps and Apennines. Computational advances over the years made it possible to identify remnant and active slabs up to great depths. 824 stations were used in this study to calculate splitting intensities in an automated process. Compared to SKS measurements, more stable fast polarisation directions were recovered with a pattern paralleling the strike of the mountain belts and a clockwise rotation in the Alps. While strong anisotropy has been recovered over the bulge of the Alps and Apennines chain, weaker anisotropy has been found beneath the Po plain, the eastern sector of the Apennines, in the western sector of Sicily and the external European domain. On the other hand it is still difficult to get reliable depth-dependent anisotropy, therefore we adopted the tomographic method relying on the inversion of splitting intensity (SI). Since it is linearly related to the elastic perturbations of the medium through the 3-D sensitivity kernels, SI can be easily inverted, providing the basis for a better interpretation of shear wave splitting measurements. The anisotropic tomography models obtained so far allowed us to recover the most prominent splitting patterns and see some changes with depth, especially for the strength of anisotropy. Directional changes often seem to be related to the slab domain or dimension (e.g. Central Italy or Sicily).
