Upper crust seismic anisotropy in the central orogenic belt of North China Craton revealed by shear-wave splitting

Using the near-field local seismic data from temporary and permanent seismic network in the central orogenic belt of the North China Craton, we obtain the anisotropic parameters at 55 stations by the shear-wave splitting (SWS) analysis from a total of 534 individual measurements. The results show that the polarization of fast shear-wave (PFS) at most stations is parallel to the direction of the regional compressive stress (EW) , while it at some stations is consistent with the strike of fault or the trend of major geological structures, indicating that the anisotropic mechanism is influenced by faults, geological structure, and the regional compressive stress. The predominant PFS in Shanxi Graben is in NE direction. However, the PFS in the north of the intersection area of the Shanxi Graben and the Zhang-Bo Seismic Belt is in WNW orientation, but the rose diagram of PFS orientations in the south is complicated, with the predominant PFS in NE direction. The predominant PFS in the intersection of Taihang Mountain uplifting and North China Basin is in NE orientation, and the secondary dominant PFS is in nearly EW direction, reflecting the complex anisotropic characteristics in the North China. The time delay of the Shanxi Graben gradually decreases from south to north. The biggest difference between subzones is 0. 2 ms . km(-1). The time delay of the intersection area of Taihang Mountain uplifting and North China Basin, and the north of the intersection area of the Shanxi Graben and the Zhang-Bo Seismic Belt are relatively small, indicating that the upper crust deformation in this area is relatively weak and strong seismic activity is to the disadvantage of strain accumulation. Our results also suggest that the extent of crust-mantle coupling cannot be explained by the simple relationship of decouple or couple.