2024年1月23日乌什MS7.1地震前柯坪地电阻率异常变化

Apparent Resistivity Anomalies at Keping Seismic Station before the Wushi MS7.1 Earthquake on January 23,2024

摘要:

2024年1月23日新疆乌什发生M_S7.1地震,震中400km范围内仅有柯坪一个地电阻率观测站,该站距离此次地震的震中约90km。2023年4月开始,柯坪站EW和NS两个测道相较于2021—2022年同期,开始出现年变化幅度减小。截至乌什M_S7.1地震发生,EW和NS测道观测数据去年变化后,最大下降幅度分别为0.6%和0.5%。采用断层虚位错模式分析了地震前震中周围的应力和变形的空间分布特征,计算结果显示柯坪站位于地震前挤压变形增强的区域,与地电阻率的下降型异常变化相符。此次地震前,地电阻率的各向异性变化与实验研究、理论分析和震例总结给出的特征一致。根据异常的各向异性变化,推测最大主压应力方位为320°,与震源机制解给出的P轴方位330°较为相近。因此,柯坪站地电阻率的异常变化与乌什M_S7.1地震的晚期孕育过程之间可能存在“介质变形-电阻率变化”机制上的联系。

Abstract:

On January 23,2024,an M_S7.1 earthquake struck Wushi County,Xinjiang. Within a 400km radius of the epicenter,only one apparent resistivity station, Keping, is in operation,located approximately 90km from the epicenter. Analysis of the EW and NS monitoring arrays at the Keping station revealed a decline in the amplitude of annual variations beginning in April 2023,when compared to the corresponding periods in 2021 and 2022. By the time the Wushi M_S7.1 earthquake occurred,the maximum decline in monitoring data, after removing annual variations using the Fourier sliding method, was 0.6% and 0.5% for the EW and NS arrays,respectively. To further investigate the pre-seismic stress and deformation characteristics in the vicinity of the epicenter,a fault virtual dislocation model was applied. The results indicate that the Keping station was located in a region of enhanced compressive deformation before the earthquake,consistent with the observed decline in apparent resistivity. Additionally,the anisotropic variations in apparent resistivity prior to the earthquake align with patterns observed in experimental research,theoretical analyses,and past earthquake case studies. Based on these anisotropic changes,the azimuth of the maximum principal compressive stress was estimated to be 320°,closely matching the P-axis azimuth of 330° derived from the focal mechanism solution. These findings suggest a potential mechanical relationship between the apparent resistivity anomalies at the Keping station and the late-stage seismogenic process of the Wushi M_S7.1 earthquake in 2024,following a “deformation-resistivity change” mechanism.