中强地震前地磁极化异常特征及其与后续地震的关系

基于国家地磁台网中心的地磁秒采样数据, 采用地磁垂直强度极化法, 计算了2019年1月1日至2020年7月31日全国各地磁台站的极化值, 对2019年中国大陆西部(110°E以西)极化异常进行了分析, 研究了2020年于田M_S6.4等中强地震前地磁极化异常变化特征及其与后续地震的关系。 研究发现: ①地磁极化异常具有空间成组特征, 即空间上多个地区可以同时出现地磁极化异常; 地磁极化异常一般被认为是震前震源区发生断层蠕动或岩石破裂导致的电磁辐射, 这意味着震前可能会有多个地区同时发生断层蠕动或岩石破裂, 这一现象似乎表明有一个“力源”在主导多区域同时发生断层蠕动或岩石破裂。 ②地磁极化异常的后续地震具有成组特征, 即一个地区出现极化异常后可能发生多次地震。 该现象对日常会商分析具有重要参考意义, 即此类异常发生预期地震后可能还会有类似地震的发生。 ③以往的一些研究认为地磁极化异常一般在震前2—3个月出现, 但本研究发现极化异常出现后10个月在异常区域仍然会发生地震, 这表明电磁辐射异常可能不仅仅是短临异常, 还可能具有中期指示意义, 即断层蠕动或岩石破裂发生时间可能在震前近1年左右便已开始。 这一发现对目前许多类似地震电磁异常研究仅仅分析异常后3个月左右内地震提出了挑战。

Characteristics of Geomagnetic Vertical Intensity Polarization Anomalies before Moderate Strong Earthquakes and Their Relationship with Subsequent Earthquakes

Based on the 1-second sampling data from the national geomagnetic network center, using the method of geomagnetic vertical intensity polarization, we calculated the geomagnetic polarization values of stations in China from January 1, 2019 to July 31, 2020. The polarization anomalies in the western China (west of 110°E) in 2019 are analyzed, and the characteristics of geomagnetic polarization anomalies before moderate earthquakes such as Yutian M_S6.4 earthquake and its relationship with earthquakes are studied. The results show that, ① the geomagnetic polarization anomalies have the characteristics of spatial grouping, that is, the polarization anomalies can occur simultaneously in multiple regions. Geomagnetic polarization anomalies are generally considered to be electromagnetic radiation caused by fault creep or rock rupture in the source area before the earthquake. This means that fault creep or rock rupture may occur in multiple areas at the same time before the earthquake. It seems to indicate that there is a force source of that causes fault creep or rock rupture in multiple areas at the same time. ② Earthquakes have group characteristics after geomagnetic polarization anomalies, that is, multiple earthquakes may occur after polarization anomalies in one region. And this phenomenon is of great reference significance for routine consultation and analysis. The subsequent earthquakes may occur after the expected earthquake. ③ Some previous studies demonstrated that geomagnetic polarization anomalies generally appeared 2~3 months before the earthquakes, but we found that earthquakes would still occur in the abnormal area 10 months after the polarization anomalies. It indicates that the electromagnetic radiation anomalies may not only be short-term anomalies, but may also have mid-term indication, that is, fault creeping or rock rupture may have started nearly 1 year before the earthquakes. This discovery poses a challenge to many current studies of similar electromagnetic anomalies that only to be connected with earthquakes within 3 months.