Azimuthal Anisotropy Of Rayleigh Wave In Qinling And Adjacent Area

Qinling Mountains, one of the active tectonic zones, locates among the Tibetan Plateau, the North and South China blocks. The information of crustal/lithospheric azimuthal anisotropy beneath Qinling Mountains and its surrounding region is helpful for understanding the interaction between the North and South China blocks, especially the influence of the extending of the Tibetan Plateau on the two blocks. In addition to the previously published Rayleigh-wave dispersions, we retrieved Rayleigh-wave group-velocity dispersion from earthquake waveforms and inter-station Green functions cross-correlated from continuous waveforms recorded by our59portable broadband seismic stations and hundreds of national and provincial stations of China Earthquake Administration in Qinling and adjacent area. Using the dispersion data, we invert for isotropic group velocities and azimuthal anisotropies beneath Qinling Mountains and its adjacent regions for the periods of7-45s by2-D surface-wave tomographic inversion. The results show that the distribution of isotropic group velocities and the azimuthal anisotropies at period7s is obviously correlated with crustal tectonics in the entire study region. The fast-propagation direction for the Rayleigh waves at the periods of7-45s beneath the Sichuan and Ordos basins are mostly near N-S. Different from previous studies, the fast-propagation direction for all the periods from7s to45s beneath Qinling and Daba Mountains and adjacent area is near E-W which is nearly paralleling to the strike of the regional tectonics. The fast-propagation direction from surface waves are the same as that revealed by previous SKS splitting analyses beneath the Qinling and Daba Mountains, indicating that the both the crust and lithosphere beneath the Qinling and Daba Mountains occurred similar deformations. However, the Rayleigh wave fast-propagation directions beneath Sichuan and Ordos basins are different from those determined by previous SKS analyses, indicating that the extending of Tibetan Plateau did not reform the crust but the lithospheric upper mantle of the two basins.