2013年芦山M_S7.0地震序列S波分裂特征  

Characteristics of shear-wave splitting for the 2013 Lushan M_S7.0 earthquake sequence

作　　者：吴朋[1] 陈天长[1] 赵翠萍[2] 苏金蓉[1] 杨建思[3] 黄春梅[1] 刘莎[3] 李兴泉[1] 

机构地区：[1]四川省地震局,中国成都610041 [2]中国地震局地震预测研究所,中国北京100036 [3]中国地震局地球物理研究所,中国北京100081

出　　处：《地震学报》2016年第5期703-718,813,共16页Acta Seismologica Sinica

基　　金：地震科技星火计划(XH14046);地震预测研究所基本科研业务专项(2014IES010103);国家自然科学基金项目(41090292;41090291)共同资助

摘　　要：本文测定了2013年4月20日芦山MS7.0地震震源区及其附近台站的S波分裂参数,包括快波偏振方向和慢波延迟时间,最终得到了40个台站的S波分裂结果.结果显示:在地震主破裂区内观测到的快波优势取向为NE向,与余震分布的长轴方向一致;位于双石—大川断裂以西台站的快波偏振优势方向为NW向,与区域最大主压应力轴方向一致;位于荥经断裂附近台站的快波偏振优势方向为NW向,与该断裂走向一致.快波偏振优势方向随时间的变化结果显示:主震前位于地震破裂区附近的TQU和BAX台站的快波偏振优势方向均呈NE向;主震后TQU台站的快波偏振优势方向为近EW向,而BAX台站的快波偏振优势方向则不突出,反映出芦山地震主震前快波偏振方向受控于龙门山断裂带,而主震后受构造应力场的作用更加明显.此外,各台站的慢波延迟时间为1.25—5.40ms/km,在余震覆盖密集区域,台站的慢波延迟时间均大于3.0ms/km,反映出震源区的各向异性程度较强.芦山主震后,各台站的延迟时间随时间变化持续减小,反映出震源区地壳应力随余震活动逐渐减小.This paper measured the shear-wave splitting parameters,the polarization direction of fast shear-wave and the time delay of slow shear-wave,by using the seismic data recorded by the stations in the focal region and its adjacent areas of the MS7.0Lushan earthquake on April 20,2013.And then the shear-wave splitting results from 40 seismic stations were obtained,which indicates the crustal anisotropy in the studied area.The results show that the dominant polarization directions of fast shear-waves are in NE in the rupture zone,which is consistent with the strike of the major axis of aftershocks distribution.The dominant polarization directions of fast shear-waves in the west of Shuangshi--Dachuan fault are in NW in agreement with the directions of the regional principal compressive stress.And the dominant polarization directions of fast shear-waves,near Yingjing fault are in NW,which is consistent with the strike of Yingjing fault.It is also shown that the dominant polarization directions of fast shear-waves at the stations TQU and BAX around the rupture zone are in NE direction before the main shock,and the dominant polarization directions at the station TQU are almost in EW after the main shock,and the variation of polarization directions before and after the main shock is not obvious at the station BAX,which indicates the polarization directions of fast shear-waves are controlled by Longmenshan fault zone before the main shock,and mainly affected by tectonic stress field after the main shock.Furthermore,the time delay of slow shear-wave is in the range of 1.25—5.40 ms/km for all the stations,but more than 3.0ms/km in the region with dense aftershocks coverage,reflecting strong anisotropy in the source area.After the main shock,the delay time decreased continuously,suggesting the stress field became stable gradually in the source region.

关 键 词：芦山Ms7.0地震 S波分裂 快波偏振方向 慢波延迟时间 各向异性 

分 类 号：P315.31[天文地球—地震学]