Crustal anisotropy beneath the Yunnan region and dynamic implications

In this study, we chose high-quality Pms (Moho-converted) phases from the receiver functions which were obtained by using the time-domain iterative deconvolution of waveforms. These waveform data were recorded by the 21 temporary seismic stations in the Yunnan region during 2010 and 2011, which were deployed by the Institute of Crustal Dynamics, CEA. Using the transverse energy minimal method, we obtained the crustal anisotropy beneath the Yunnan region from the 283 pairs of splitting parameters with high signal-to-noise ratios and unambiguous Pms phases. Our results show that delay times between fast and slow Pms range from 0. 125 to 0. 40 s with an average of 0. 25 s, and the strength of anisotropy is related to the tectonics. The Yangtze and Baoshan blocks show a relative stronger anisotropy, whereas the Simao block has a weaker one, suggesting the different effects of the lower crustal flow. Except for the region (stations YNL04 and YNL12) where the orientations of the Red River and Lancang River faults change rapidly, the polarization direction of the fast wave is approximately parallel to the orientation of faults, implying that the large-scale faults may control the deformation of the lower crustal flow. Distinguished from other blocks, the Tengchong block shows a scatter-shaped direction in the fast polarization, possibly suggesting that the upwelling flow has been obstructed when it meets the upper crust.