2021年5月21日云南漾濞M_(S)6.4地震序列的时空演化  

TEMPORAL AND SPATIAL EVOLUTION OF THE 2021 YANGBI(YUNNAN CHINA)M_(S)6.4 EARTHQUAKE SEQUENCE

作　　者：王凯英[1] 金明培[2] 黄雅 党文杰 李文涛 卓燕群[1] 何昌荣[1] WANG Kai-ying;JIN Ming-pei;HUANG Ya;DANG Wen-jie;LI Wen-tao;ZHUO Yan-qun;HE Chang-rong(State Key Laboratory Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;Yunnan Earthquake Agency,Kunming 650011,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [2]云南省地震局,昆明650011

出　　处：《地震地质》2021年第4期1030-1039,共10页Seismology and Geology

基　　金：国家重点研发计划项目(2018YFC1503303)资助。

摘　　要："亚失稳"研究试验区滇西北短周期测震台网测得的2021年5月21日云南漾濞6.4级地震序列显示,主震发生前约3d内在破裂区北西段依次出现相邻区域的前震时空丛集;后续临震时段(主震前约1h)的前震从破裂区中心开始对称地向两端快速扩展,随后爆发主震。不同时段的前震空间分布显示了地震进入短临阶段后断层不同部位破裂的时空迁移及快速扩展,扩展速度由前震丛集过程的约5km/d提高至临震时段的约96km/d;主震震中位于前震丛集的边缘、最终破裂区的北西端,主震后余震向SE迁移,约0.5h后扩展至整个破裂带,最终破裂带长度> 20km,显示了本次地震的单向传播特征;该台网建立以来,漾濞地区的小地震活动显示本区域近3a时段内b值平稳(为0.9~1.1),6.4级主震前b值异常持续下降至0.6以下,反映了漾濞地震前存在显著的应力增加过程。In 2018,a short-period seismic network was set up in Eryuan area of Yunnan Province to carry out continuous field observation of the sub-instability process of the earthquake.The relevant data of the Yangbi M_(S)6.4 earthquake sequence are mainly from the waveforms recorded by this network,combined with some other stations from Yunnan regional seismic network.The Yangbi earthquake sequence shows that the events in this area began to occur intensively on May 18.A total of 2000 earthquakes with M>0.1 were recorded from May 18 to 23,including 770 foreshocks.Seismicity analysis shows that two clusters of foreshocks occurred successively in the adjacent area of the main earthquake in the northwest segment of the rupture strip within 3 days,then in the subsequent impending period(within 1 hour before the main shock)about 60 events spread symmetrically from the center of the fracture zone to the ends.The spatial distribution of foreshocks in different periods shows the spatial migration of local fractures and accelerated expansion prior to the main shock.The spreading speed is about 5km/d from foreshock clustering process to 96km/d in impending earthquake period.The epicenter of the main shock is located at the edge of the cluster foreshocks and the northwest end of the final rupture zone.Subsequent aftershocks extend southeastward to the whole fracture zone in about half an hour,and the final fracture zone is more than 20 kilometers long,showing unilateral propagation of the rupture.Since 2018,b-value in the Yangbi area has been stable(0.9~1.1)for the past three years.After March this year,the b-value abnormally decreased to 0.6 before the main shock,reflecting that there was a significant process of continuous increase of local stress before the Yangbi earthquake.The identification of short-term precursors and somehow definite information is one of the focus problems in earthquake prediction research.On the basis of the experimental results,Ma Jin proposed the theory of seismic meta-instability stage based on the char

关 键 词：漾濞6.4级地震 前震时空丛集 震前快速扩展 单向传播 震前 b值下降 

分 类 号：P315.2[天文地球—地震学]