The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthqu...The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthquakes.In this study,we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region.We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area.Although some stations returned a polarization direction of NNW-SSE.a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area.The polarization directions of the fast shear wave were highly consistent throughout the study-area.This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults.The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures.The mean delay time between fast and slow shear waves was 3.83 ms/km.slightly greater than the values obtained in other regions of Sichuan.This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.展开更多
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 t...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.展开更多
基金This work is jointly supported by the National Natural Science Foundation of China(No.41904057)the National Key Research and Development Program of China(No.2018YFC1503402).
文摘The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthquakes.In this study,we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region.We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area.Although some stations returned a polarization direction of NNW-SSE.a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area.The polarization directions of the fast shear wave were highly consistent throughout the study-area.This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults.The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures.The mean delay time between fast and slow shear waves was 3.83 ms/km.slightly greater than the values obtained in other regions of Sichuan.This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.
基金the National Natural Science Foundation of China (Grant No. 40674021)IES-CEA Project (Grant No. 2007-13)
文摘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.
