Effects Of Earthquake Location Errors On Share-wave Splitting Analysis And Crustal Seismic Anisotropy In The West Of Zhangjiako-bohai Sea Seismic Zone

Crustal seismic anisotropy is mainly caused by the stress-aligned fluid-saturated grain-boundary cracks. When share-wave travels through anisotropic media, it will split. The parameters of share-wave splitting are relative to the physical property of curst media and regional stress field. The polarization of fast shear-wave is consistent with the crack's direction, which reflects the direction of the principal compressive stress. Time delay of slow shear wave is correlated to the level of anisotropy.In the study of share-wave splitting, the errors of earthquake location have an impact on share-wave splitting reference. This paper discusses the factors that can influence on the accurate location and analyses the variety of the time delay which is caused by the depth location error. We compared the influences on normalized time delays which are made by different depth errors. The result of the quantitative analysis shows that the depth error can influence selecting waveform datas in the window of shear-wave and cause a great influence on the slow share-wave time delay.The west of Zhangjiako-Bohai See seismic zone is in the boundary of three tectonic units which are North China basin, Yanshan and Taihang uplift regions. Shanxi seismic zone and Zhangjiako-Bohai sea seismic zone interchange hear, and this region has complex geologic structure. There are some NE, ENE, NW, WNW stretching faults. GPS data and focal-mechanism show that the regional principal compressive stress is ENE (near E-W) directing.In this study, earthquakes which happened in Norht China regions from January 2006 to November 2009, were relocated using the double difference algorithm. The relocation results show that the earthquakes in North China are mainly concentrated in Zhangjiakou–Bohai sea seismic zone. The spatial distributions of hypocenters show WNW directing. But in the region of internal, hypocenters distribute along faults. In this thesis, the depth profiles were made and analyzed the relationships between faults depth structures and the distributions of hypocenters in Tangshan and Xingtai region.This paper shows the research of shear-wave splitting by applying waveform data from ZBnet-W seismic network and Heibei regional seismic network, and selecting SAM method as the tool to analyze crustal anisotropy in the west of Zhangjiako-Bohai sea seismic zone. The result of analyzing the data which are in shear-waves window show that there are two predominate polarization directions of fast shear-waves. One predominate polarization direction is 96.98°±17.19°which is consistent with the direction of regional compressive stress. This direction is also consistent with the regional blackground compressive stress which is the result of another study. The other predominate polarization direction is 32.00°±15.63°, which is consistent with the direction of fault in the north of Shanxi seismic zone.This research indicates that the polarizations directions of fast shear-waves, which close to the NE-NEN Shanxi earthquake belt, are consistent with trend of this belt. In addition, the polarization directions of fast shear-waves, which are located the junction of the local depression and uplift (the edge of Huai'an basin), put out two dominant directions. It is possibly attributed to the local complex geological tectonics around these stations. This result probably stems from the effect between the local compressive stress field and trend of partial strike-slip fault.In this paper, the result of shear-wave splitting analysis is in contrast with the conclusion between the GPS deformation data and local focal mechanisms. The characteristics of crustal anisotropy and distribution of stress field was preliminary discussed in the western of the Zhangjiakou-Bohai Fault Zone. In this area, the result demonstrates that the background stress field and the local geological structure will effect the polarization direction of the fast shear-wave splitting.