2017年8月8日九寨沟7.0级地震前地磁垂直强度极化短期异常特征分析

对2017年8月8日九寨沟7.0级地震前后四川及其邻区地磁台站数据进行垂直强度极化方法计算, 使用5~100 s周期发现震前地磁极化计算结果存在如下的显著异常特征: ① 2017年3月震中附近地磁台站同步存在极化超阈值异常, 时间上显示为短期异常; ② 同步异常台站出现最大幅度的时间较一致; ③ 九寨沟地震发生在异常阈值线附近, 对该方法预测地点有一定指示意义; ④ 对比异常时段内的Dst指数, 认为此次同步超阈值异常不是空间电流体系所造成的; ⑤ 3月18日地磁台站出现极化异常的台站数量较多, 异常分布区域面积较大, 异常主要集中在西北地区可能反映了该区域的应力作用。

Analysis on Short-Term Characteristics of Geomagnetic Vertical Intensity Polarization Anomaly Before Jiuzhaigou 7.0 Earthquake on August 8, 2017

The vertical intensity polarization is calculated by using the geomagnetic data of Sichuan and its adjacent areas before and after the Jiuzhaigou M_S7.0 earthquake on August 8, 2017. The geomagnetic polarization results at 5~100 s frequency band before the earthquake have the following obvious abnormal characteristics: ① In March 2017, the geomagnetic stations near the epicenter synchronously showed polarization over threshold anomalies, which are short-term anomalies in time. ② The occurrence time of the maximum amplitude was consistent for abnormal stations. ③ The Jiuzhaigou earthquake occurred near the anomaly threshold line, which has a certain indication significance for the prediction location of this method. ④ Compared the Dst index in the abnormal period, it is considered that the synchronous anomalies over threshold were not caused by the space current system. ⑤ On March 18, there were more stations with polarization anomalies to cover a larger area, and the anomalies mainly concentrating in Northwest China may illustrate the stress effects in this region.