Analyzing the characteristics of the upper mantle anisotropy beneath the northeastern North China Craton based on SKS wave splitting

Based on teleseismic events recorded at 52 broadband temporary seismic stations in the Hebei Seismic Network, the SKS wave splitting parameters, including the polarization orientation of the fast shear wave and the delay time between the fast and slow waves at each station, were determined, and then, the structure of the upper mantle anisotropy beneath the northeastern North China Craton (NCC) was acquired. The results of this study reveal that the fast wave directions are basically in the NWW direction with a mean value of N99.2°E±15.4°, and the delay times are about 0.93±0.11 s, corresponding to a 107±13 km thick anisotropic layer. The research results imply that the anisotropy beneath the northeastern NCC mainly resides in the upper mantle, and most of it may reside in the asthenosphere. The results show that the anisotropy parameters of the Eastern Blocks (ENCC) and the Trans-North China Orogen (CNCC) are relatively consistent, indicating that the differences in the characteristics of the upper mantle anisotropy beneath the northeastern NCC are smaller. The deformation model of the crust and upper mantle could be both a simple asthenosphere flow model and vertical coherent deformation model based on comparison of the direction of the absolute plate movement, regional lithospheric extension, the crustal fast wave, and velocity field of China based on global positioning system (GPS) data.