Shear-wave splitting at central Tien Shan: Evidence for rapid variation of anisotropic patterns



At active collisional belts, the fast polarization axis of shear-wave splitting is generally aligned parallel to the strike of the belt, which has been proposed to indicate mantle strain that is coherent with crustal deformation. A notable exception is central Tien Shan, where anomalous patterns of splitting have previously been observed. We here analyze shear-wave splitting of SKS phases across north central Tien Shan using digital data from the Kyrgyzstan Broadband Seismic Network (KNET). We find a pattern of short-wavelength anisotropic heterogeneity that supports complex mantle flow due to small-scale convection. The along-strike variations in mantle structure contrast with the coherent pattern of crustal shortening, and indicate that mantle flow is not directly coupled to crustal deformation in this region.