Azimuthal anisotropy of Rayleigh wave in Qinling and its adjacent areas

We retrieved Rayleigh-wave group velocity dispersion from earthquake waveforms and inter-station Green’s functions cross-correlated from noises recorded by our 59 portable broadband seismic stations and hundreds of national and provincial stations of China Earthquake Administration in Qinling and its adjacent areas. Using the dispersion data and the previously published Rayleigh wave dispersions, we invert for isotropic group velocities and azimuthal anisotropies beneath Qinling and its adjacent areas for the periods of 10—50 s by 2-D surface wave tomography. The results show that the distribution of isotropic group velocities and the azimuthal anisotropies in the period of 10 s is obviously correlated with the crustal tectonics in the entire study region. The fast-propagation direction for the Rayleigh waves in the periods of 10—50 s beneath the Sichuan and Ordos basins are mostly near N-S. Unlike previous studies, the fast direction for all the periods from 10 s to 50 s beneath Qinling and Daba mountains and adjacent areas is near E-W which is nearly parallel to the strike of the regional tectonics. The fast-propagation direction from surface waves are consistent with that by previous SKS splitting analyses beneath the Qinling and Daba mountains, indicating that the deformation at the depths of the whole crust beneath the Qinling and Daba mountains are similar, even down to the lithospheric base. However, the Rayleigh wave fast-propagation directions beneath Sichuan and Ordos basins are different from fast-wave directions inferred from previous SKS analyses, indicating that the uplifting and extending of Tibetan Plateau did not reform the crust but the lithospheric upper mantle beneath the two basins.