2021年5月21日云南漾濞M_(S)6.4地震总结

Summary of the Yangbi M_(S)6.4 earthquake in Yunnan on May 21,2021

2021年5月21日云南漾濞M_(S)6.4地震发生在滇西北地区维西—乔后断裂带附近,震源机制结果显示,此次地震是一次走滑型破裂事件,与区域构造特征一致。漾濞地震序列主震发生前3天震中附近有4级地震活动,主震后余震较为丰富,属于前震—主震—余震型地震序列。系统总结漾濞M_(S)6.4地震发生前出现的地震活动和地球物理观测异常发现,①地震活动:震前存在地震平静、丛集活跃、地震条带、Benioff应变比、地震发生率指数等异常;②地球物理观测:震前存在楚雄垂直摆NS向、弥渡水管NS向、楚雄基线等趋势性异常,以及龙陵水氡、水温和流量、洱源水温、红格地电阻率等短期异常。上述异常空间上主要分布在滇西至滇西北地区,对漾濞地震的发生具有指示意义。

On May 21,2021,the Yangbi M_(S)6.4 earthquake occurred near the Weixi-Qiaohou fault zone in Northwest Yunnan.The focal mechanism solution shows that the earthquake occurred on a strike-slip fault,which is consistent with the regional tectonic characteristics.There are several foreshocks with magnitude above MS 4.0 near the epicenter 3 days before the mainshock occurrence.The Yangbi earthquake sequence is a typical foreshock-mainshock-aftershock sequence with abundant aftershocks.We systematically summarized seismicity anomalies and geophysical anomalies preceding the mainshock.The results show that:(1)Seismicity anomalies:there are anomalies such as seismic quiescence,active seismic cluster,seismic belt,Benioff strain ratio,and seismicity rate index before the Yangbi earthquake;(2)Geophysical observations:there are trend anomalies such as NS component of Chuxiong vertical pendulum,NS component of Midu water tube,and Chuxiong baseline,as well as short-term anomalies such as Longling radon,water temperature,and fow,Eryuan water temperature,and Hongge apparent resistivity.These anomalies are mainly distributed from western to northwestern Yunnan and have indicative signifcance to the occurrence of the Yangbi M_(S)6.4 earthquake.