Seismic Anisotropy in the Crust in Northwestern Capital Area of China

Abstract

Abstract Seismic anisotropy is obtained in the crust in northwestern capital area by shear‐wave splitting analysis, using the SAM technique. The seismic data was recorded at the Capital Area Seismic Network from Jan. 2002 to Dec. 2003. The results at 14 stations in all, every of which has at least 3 records available or more, are statistically discussed in this paper. The statistical results show that the average polarization of fast shearwaves is NE69.9 ° ±44.5 ° and the time delay of slow shear‐waves is 4.44±2.93 (ms/km). The average polarization of fast shear‐waves of NE69.9 ° ±44.5° suggests the direction of maximum horizontal principal compressive stress in this area. The most predominant polarization direction of fast shear‐wave suggests the tectonic implication of horizontal principal compressive stress at the direction NWW or nearly E‐to‐W, which exposes the Zhangjiakou‐Penglai depression fault zones with strike NWW. According to the polarization of fast shear‐wave, this study verifies that the predominant polarizations of fast shear‐wave at stations on active faults are consistent with fault strike. Possibly, both the Nankou‐Sunhe fault and Xiadian fault are two active faults while the Babaoshan fault is possibly a less active fault. The polarizations of fast shear‐wave in the North China Basin show the complexity, consistent with the complicated pattern of regional principal compressive stress controlled locally, induced by many faults crossing in the depression zone within the basin. This study also suggests that the quick change of time delays of slow shear‐waves is possibly related to the temperature change in deep crust.