云南漾濞县6.4级地震前地电场异常回溯性分析

Retrospective analysis of geoelectric field anomalies before the Yangbi M_(S)6.4 earthquake in Yunnan Province

针对2021年5月21日云南漾濞M_(S)6.4地震,采用滑动相关性方法和地电场优势方位角方法,开展震中周围200 km范围内地电场台站地震异常的统计特征分析和优势方位角的回溯性研究,发现:(1)通过对漾濞M_(S)6.4震中周围历史地震事件的统计分析,认为该区域地电场地震异常现象通常在震前约20(±5)天开始出现,如弥渡、祥云和洱源台;(2)漾濞M_(S)6.4地震前,洱源和祥云台地电场优势方位角在震前约15天或更早时间开始出现异常变化现象;(3)当地电场台站与地震事件处于同一发震断层(或断裂带)时,其观测到地震异常的可能性更大。此外,结合研究区域已有大地电磁测深结果,对地震反映敏感的地电场台站测区下方电性结构特征进行了初步探索,认为当测区位于电阻率边界上时,更易观测到地震地电场异常变化现象,相关研究结论将有望为地电场台站的选址建设、地震异常分析等工作提供技术支撑。

On May 21,2021,an M_(S)6.4 earthquake occurred in Yangbi County,Yunnan Province.In this paper,we analyzed the statistical characteristics of earthquake anomalies from the geoelectric field stations within 200 km around the epicenter with the shifting correlation method and the dominant azimuthαof geoelectric field.The conclusions are as follows:(1)The statistical analysis results of historical events around the epicenter showed that the abnormal phenomena of geoelectric field usually appeared about 20(±5)days before the earthquake,such as Midu,Xiangyun and Eryuan stations;(2)The dominant azimuthαof geoelectric field at Eryuan and Xiangyun stations began to change about 15 days or earlier before the Yangbi M_(S)6.4 earthquake;(3)When the local geoelectric field station is on the same seismogenic fault(or fracture zone)with the seismic event,it is more likely to observe the earthquake anomaly.In addition,based on the existing magnetotelluric sounding results in the study area,the electrical structure characteristics under geoelectric field stations sensitive to earthquake are preliminarily explored.We found that when the survey area is located on the resistivity boundary,it is easier to observe the abnormal changes of seismic electric field.The findings of the study are expected to provide a technical support for the site selection of geoelectric field stations and the analysis of seismic anomalies.