2017年11月23日重庆武隆5.0级地震前地磁谐波振幅比异常研究

近年来，地磁谐波振幅比方法在国内得到较广泛的应用，并成为一种较为有效的地震预测方法。本文利用谐波振幅比方法，对2017年11月23日重庆武隆5.0级地震震中附近台站的地磁三分量数据进行计算，并分析了各台站10~60min周期谐波振幅比值异常特征。研究发现，异常台站几乎均位于震源机制解的拉张区(P波向下的区域)，具有象限分布特征；异常台站NS向谐波振幅比值变化存在分层现象，短周期(浅部)的变化与长周期(深部)变化成相反相位，从电磁学机理看，浅部与深部之间存在EW向的面电流；近震中台站的异常低点时间存在由长周期(深部)向短周期(浅部)迁移的现象。

Variation of the Geomagnetic Harmonic Wave Amplitude Ration before the Wulong MS5.0 Earthquake

On November 23, 2017, M_S5.0 earthquake occurred in Wulong, Chongqing. In this paper, we calculated the three component data of the geomagnetic station by using the harmonic amplitude ratio method, and obtained the ratio of 10~60min period harmonic amplitude, and then discussed the variation characteristics of the deep resistivity before the earthquake. The results show that the distance of anomalies of geomagnetic harmonic amplitude ratio before wulong M_S5.0 earthquake is less than 280km, where the stations with anomalies are concentrated in space and distributed on the side of the epicenter of the earthquake. On the projection of the source mechanism solutions, the anomalies are all located in the region under the initial p-wave movement, with a quadrant distribution feature. The Y_ZHy harmonic amplitude ratio of the stations with anomalies are characterized of decreasing variation similar to the anomalous resistivity. In the process of descending change, the harmonic amplitude ratio of Y_ZHx and Y_ZHy show different turning points. Y_ZHx experienced two asynchronous transitions, in which the first about 1.8~2 years before the earthquake, and the second about 1 year before the earthquake. Y_ZHy of the stations within 100km from the epicentre of the earthquake appeared the phenomenon of transition time from deep to shallow in the transition process. Y_ZHy anomaly amplitude shows that the anomaly amplitude of 20~60min generally decreases with the increase of the epicenter and increases with the increase of the period. The amplitude of Y_ZHx anomaly does not change with the epicenter or the period.