2022年1月8日青海门源MS6.9地震前地磁垂直强度极化异常变化特征

基于甘青川地区的14个地磁台站秒采样资料，对2022年1月8日青海门源M_S6.9地震前地磁垂直强度极化异常的时空变化特征进行分析研究。计算结果显示，在2021年10月底出现了地磁极化超阈值高值异常变化，异常台站主要分布在青海、甘肃和四川地区，异常出现后73天发生了门源地震，震中位于极化高值异常阈值线附近。研究还发现，此次地磁极化异常具有一定的时空变化特征，时间上，不同台站极化异常具有较好的时间同步性；空间上，极化异常高值区呈现出沿震中附近出现后不断扩展最终再向震中收缩的特点。此外，各地磁极化异常台站的归一置零极化值、异常持续时间与震中距存在较好的负相关性，异常台站距离地震震中越近，其归一置零极化值越高，异常持续时间也越长，这一特征符合地震电磁扰动信号的衰减特征。根据极化异常和地震的时空关系分析认为，此次地磁极化高值异常对应了之后在异常高值区边缘发生的门源M_S6.9地震。

Characteristic of geomagnetic vertical intensity polarization anomaliesbefore the Menyuan, Qinghai MS6.9 earthquake on January 8, 2022

Based on the 1-second sampling data of 14 geomagnetic stations in Gansu, Qinghai, and Sichuan areas, we analyzed the temporal and spatial variation characteristics of the geomagnetic vertical intensity polarization anomalies before Menyuan, Qinghai M_S6.9 earthquake on January 8, 2022. The results show that there were high value anomalies of geomagnetic vertical intensity polarization at the end of October 2021. The anomalous stations are mainly distributed in Qinghai, Gansu, and Sichuan areas. The Menyuan earthquake occurred 73 days after the occurrence of anomalies, and the epicenter was near the anomaly threshold line of high polarization. It is also found that the geomagnetic polarization anomalies have certain temporal and spatial variation characteristics. In terms of time, the polarization anomalies of different stations have good time synchronization; spatially, the anomalous high-value area of polarization shows the characteristics of appearing near the epicenter, then expanding continuously, and finally shrinking toward the epicenter. In addition, the normalized zero polarization value, the anomaly duration, and the epicentral distance of anomalous stations show a negative correlation. As the epicenter distance of abnormal stations decreases, the normalized zero polarization value becomes higher and the anomaly duration becomes longer. It is consistent with the attenuation characteristic of the seismic electromagnetic signal. According to the spatial-temporal relationship between polarization anomalies and earthquakes, the high-value anomaly of geomagnetic polarization corresponds to the subsequent Menyuan M_S6.9 earthquake.