Since the occurrence of the Tangshan Ms7.8 earthquake,Guye—Luanxian area has been a frequently occurrence of aftershocks.The fault and geological structure are very complex in Guye—Luanxian area.What are the differences in the fragmentation degree of these faults?The problems are concerned by seismologists.To answer these questions,by using the waveform records of the mobile seismic network densely deployed in the Guye—Luanxian area from August 2020 to July 2021,we study the anisotropy of the upper crust in Guye—Luanxian area according to the principle of shear wave splitting.The following conclusions are obtained:(1)The average polarization direction of fast shear wave in Guye—Luanxian area is NE86.2°±27.8°,the average time delay of slow shear wave in this area is 2.37±1.25 ms·km-1.The first dominant polarization direction of fast shear wave is ENE,which is consistent with the direction of principal compressive stress of regional background,the second dominant direction is NE direction,which reveals the tectonic significance that the faults in this area are mainly developed in NE direction.(2)The polarization direction of fast shear wave near the Tangshan fault zone shows the second dominant direction in NE direction,which is consistent with the fault strike.The time delay of slow shear wave of stations near the fault is higher,and the difference of time delay in stations is smaller,which indicates that the regional anisotropy is stronger,and the fragmentation degree along the NE direction is stronger and homogeneity.(3)The polarization direction of fast shear wave near Luanxian—Leting fault and Lulong fault shows complexity,indicating that the intersection of two active faults produces a complex crustal fracture structure in the crust.The time delay of slow shear wave in stations near the fault is higher,and the time delay difference of each station is larger,which indicates that the regional anisotropy and fragmentation degree are stronger,and the fragmentation is heterogeneity.(4)The polarization direction of fast shear wave at stations near the Fengtai—Yejituo fault and Zhenzizhen fault is consistent with the direction of regional principal compressive stress.The slow shear wave time delay of stations near the fault is the smallest,indicating that the Fengtai—Yejituo fault and Zhenzizhen fault have no influence on the polarization direction of fast shear wave at nearby stations,regional anisotropy and fragmentation degree are weaker,and may be indicating closure of fracture internal cracks in the faults.Moreover,we also discussed whether the tip effect on the Tangshan fault after the 1976 Tangshan Ms7.8 earthquake has an impact on the stress field in the northern segment of the Tangshan fault zone.The results of this study not only reflect the relationship between the complexity of fault distribution and crustal anisotropy,but also reveal the difference of crustal anisotropy on faults with different degrees of fragmentation.
关键词
古冶—滦县地区/地壳各向异性/剪切波分裂/构造应力/断裂破碎程度
Key words
Guye—Luanxian area/Crustal anisotropy/Shear-wave splitting/Tectonic stress/Fragmentation degree in the fault
维普
万方数据