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SKS Wave Splitting of the Northeastern Margin of the Qinghai Tibet Plateau

PAN Yu-hang;PU Ju;CHENG Jian-wu;CHEN Ji-feng;Lanzhou Institute of Seismology,CEA;  
Based on the teleseismic SKS phase recorded by 43 permanent broadband stations in Gansu Province in the northeastern margin of the Qinghai-Tibetan plateau,this study obtains the splitting parameters of the fast-wave polarization direction and delay times at each station using the minimum energy and rotation-correlation methods.The results can be summarized as follows.In the southeastern region of Tarim Basin,the fast-wave polarization sites exists obvious angle with the strike of regional faults,and coincides with the subduction direction from Tarim Basin to Qaidam Basin.This result reveals that the upper mantle deformation is mainly affected by ancient tectonic movement.The anisotropy observed may be considered "fossil" anisotropy.Because of crust-mantle delamination,decoupling between the crust and mantle occurs in this area.In the Qilian-Hexi Corridor region,fast-wave polarization shows a NW-SE trend,consistent with the strike direction of the main faults in this region.Comparison of the fast-wave directionwith the direction of lithospheric extension and GPS-observed velocity reveal that the deformation model of the crust and upper mantle may be vertically coherent deformation.In the northern fringe fault of the western segment of the Qinling mountains,slow-wave time delays exert significant anisotropy in the vicinity.This phenomenon could indicate upper mantle deformation,which is caused by both deformation of the lithosphere and flow of the asthenosphere.In the Ordos block,the fast-wave direction shows a NW-SE trend,which suggests that the movement of deep material exists motion of flow around the Tibetan plateau.Collision between plates causes thickening and uplifting of the western China crust and eastward extrusion of material in the northeastern margin of the Qinghai-Tibetan plateau.Different regional stations present different levels of anisotropy in the northeastern margin of the Qinghai-Tibetan plateau,which further proves the complexity of tectonic deformation in its northeastern margin.According to the splitting parameters of SKS waves,the anisotropic characteristics of the study region are analyzed to investigate dynamic processes in the area.
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