1995年武定6.5级地震余震的S波分裂  

Shear-wave Splitting of the aftershocks for the 1995 Earthquake of Yunnan Wuding

作　　者：李白基[1] 秦嘉政[1] 钱晓东[1] 

机构地区：[1]云南省地震局,昆明650041

出　　处：《地震研究》2002年第2期108-114,共7页Journal of Seismological Research

基　　金：云南省科学技术厅"十五"重点攻关项目资助课题 ( 2 0 0 1NG46 )

摘　　要：1995年 10月 2 4日云南武定发生MS6 5地震。分析田心三分向数字记录 ,从 77个余震中获得 45个余震的S波分裂数据。快速S波偏振有两个优势取向 ,分别为N32°E和N94°E ,二者与震源应力场的主压应力方向N140°E相差甚大 ,不是应力场导致的EDA裂隙系各向异性结果。武定地震发生在近南北走向的汤朗—易门断裂被次级的北西向断裂交切的地区。快S波N32°E偏振方向与汤朗—易门断裂走向接近 ,且又与震源S波固有偏振方向相同 ,难以辨别是构造抑或是应力引起的各向异性结果。分析认为 ,N94°E偏振方向是北西向断层系各向异性产生。两个偏振方向是在同一台站观测到 。An M S=6.5 earthquake occurred in Wuding County,Yunnan Province,on October 24,1995.Analyzing the 3-component digital seismograms recorded at station Tianxin,the data of shearwave splitting for 45 out of 77 aftershocks have been obtained.There are two preferred polarization directions from the fast shear wave,N32°E and N94°E respectively.Both deviate much from the direction of the principal compression stress axis,N140°E,of the source stress field.They were not resulted from the anisotropy of the stress-induced cracks(EDA).The earthquake of Wuding occurred in an area in which the Tanlang-Yimen fault system with northsouth strike is intersected by a secondary fault system oriented north-west.The polarization direction for the fast shear wave,N32°E,approximates the strike of the Tanlang-Yimen fault system and coincides with the intrinsic direction of the shear wave radiated from the seismic source.It is hard to distinguish the results between structure-and stress-induced anisotropy.the polarization of N94°E is very likely to be the result from the anisotropy of the north-west fault system.Both preferred polarizations of the fast shear wave observed at the station suggest that two anisotropic medium bodies with different property are in the source area beneath some depth.

关 键 词：S波分裂 地震断层 构造各向异性 主压应力 武定地震 1995年 余震 

分 类 号：P315.3[天文地球—地震学]