2020年7月12日唐山古冶M_(S)5.1地震前延庆地电场变化  

Anomaly analysis of apparent resistivity in Yanqing area before the July 12,2020,Guye M_(S)5.1 earthquake

作　　者：王丽红[1] 董鸿燕[1] 武敏捷[1] 王同利[1] 李菊珍[1] 岳晓媛[1] WANG Lihong;DONG Hongyan;WU Minjie;WANG Tongli;LI Juzhen;YUE Xiaoyuan(Beijing Earthquake Agency,Beijing 100080,China)

机构地区：[1]北京市地震局,中国北京100080

出　　处：《地震地磁观测与研究》2024年第2期68-75,共8页Seismological and Geomagnetic Observation and Research

基　　金：北京市地震局科技项目(项目编号:BJWC-2023010)。

摘　　要：采用日均值曲线形态、日均值一阶差分及优势方位角法,对2020年7月12日唐山古冶M_(S)5.1地震前北京延庆地震台地电场异常变化进行分析。该台2套地电场日均值具有较为清晰、稳定的年变,存在季节性变化,自2020年5月开始出现年变畸变或年变幅改变,表明在地震孕育过程中台站所在区域地下构造活动由平稳到逐渐加剧。地电场日均值一阶差分在震前1-3个月呈高频突跳或丛集异常变化,震后逐渐平稳。日均值一阶差分可反映日均值突跳、阶跃和快速明显的趋势变化,对缓慢渐变过程反映弱。方位角背景值中间值约为70°,与延庆台所在区域主压应力轴平均值74.45°相当,代表了该区域的主要裂隙方向。方位角的改变,可以反映地震孕育过程中一定范围内地下应力应变活动。方位角自2020年5月跳变范围收窄,变化幅度约为45°,异常开始至发震约3个月。应用方位角法,可以提取台站周边300 km范围内M_(S)5左右地震地电场短期异常变化。Using the daily mean curve shape,the daily mean first-order difference,and the dominant azimuth method,the abnormal changes of the Beijing Yanqing station electric field before the July 12,2020 earthquake are analyzed.The daily mean values of the two sets of geoelectric fields in Yanqing have relatively clear and stable annual variation,with seasonal variation,and annual distortion or annual variation amplitude change since May 2020,indicating that the underground tectonic activities in the area where the stations are located have changed from stable to gradually intensified during the earthquake preparation process.The daily mean first-order difference showed high-frequency sudden jump or cluster anomaly 1 to 3 months before the earthquake and became gradually stable after the earthquake.The first-order difference of the daily mean value of the ground electric field can reflect the sudden,step,and rapid trend change of the daily mean value,but it is weak to reflect the slow gradual change.The median of the background value of the azimuth is about 70°,which is equivalent to the average value of the principal compressive stress axis in the Yanqing platform region of 74.45°,representing the main fracture direction in this region.The change of azimuth angle can reflect the underground stress-strain activity in a certain range during earthquake preparation.The range of azimuth jump has narrowed since May 2020,with a change of about 45°.It took three months from the beginning of the anomaly to the earthquake.Using the azimuth method,the geoelectric field short-term abnormal changes of M_(S)5 earthquakes within 300 km around the station can be extracted.

关 键 词：地电场 一阶差分 方位角 古冶地震 

分 类 号：P31[天文地球—固体地球物理学]