Data from the CASN(Capital Area Seismograph Network),NSNC(National Seismograph Network of China),and IRIS(Incorporated Research Institutions for Seismology) are compared with data from a temporary North China Seismic Array to obtain the background orientation of the horizontal crustal principal compressive stress at NE 95.1°±15.4° in North China.Data are corrected for disturbances of faults and irregular tectonics,and are used to constrain the fast SKS polarization at NE 110.2°±15.8° in North China.Individual station analyses suggests that there is consistently more than 10° difference between the polarizations of fast shear-wave in the crust and those of fast SKS phases.Azimuthally anisotropic phase velocities of Rayleigh waves at different periods also indicate an orientation change for fast velocity with depth.It suggests the crust-mantle coupling in North China follows neither the simple decoupling model nor the strong coupling model.Instead,it is possibly some inhomogeneous combination of two models or some gradual-change model of physical characteristics.This study shows that anisotropy in the crust and mantle could be multiply characterized more correctly and crust-mantle coupling could be analyzed further,if increasing near-field shear-wave splitting data that indicate crustal anisotropy,combined with the azimuthal anisotropy of Rayleigh waves,besides the result of SKS splitting travelling through lithosphere and surface GPS measurements.
The rocks in the crust are pervaded by stress-aligned fluid-saturated microcracks, and the complex fault tectonics and stress control the configuration of the microcracks, however shear-wave splitting could indicate this kind of characteristics. In this paper, Capital Area Seismograph Network (CASN), the widest scope and highest density of regional seismograph network presently in China, is adopted to deduce the principal compressive stress field distribution pattern from polarizations of fast shear- waves, based on shear-wave splitting analysis. The principal compressive stress in capital area of China is at NE85.7°± 41.0° in this study. Compared with the results of principal compressive stress field in North China obtained from other methods, the results in this study are reliable in the principal com- pressive stress field distribution in capital area. The results show that it is an effective way, although it is the first time to directly obtain crustal stress field from seismic anisotropy. It is effectively applied to the zones with dense seismograph stations.
