重庆武隆M5.0地震前地磁异常特征分析

Analysis of Magnetic Anomalies before the Wulong M5.0 Earthquake in Chongqing

摘要:

选取恩施台、涪陵江东台、石柱黄水台以及武隆仙女山台2012年1月至2017年11月地磁数据进行异常分析，得到各个台站的地磁谐波振幅比和加卸载响应比计算结果，并结合2017年11月23日重庆武隆M5.0地震震中附近地质构造背景分析地震前后地磁异常现象。分析结果认为大部分地磁谐波振幅比变化特征类似于地电阻率的变化特征，表现为“下降-转折-上升”过程。本次地震大致发生在转折上升的初期阶段，其中震中距较小的台站地磁谐波振幅比变化趋势不同步，但变化幅度大致相同，而震中距较大的台站地磁谐波振幅比变化趋势较为同步，变化幅度较大。此外，研究还表明震前地磁加卸载响应比异常高值在时空分布上与震中位置具有很好的对应关系。

Abstract:

The geomagnetic data of Enshi station, Jiangdong station in Fuling, Huangshui station in Shizhu, and Xiannushan station in Wulong from January 2012 to November 2017 were selected and the anomalies were analyzed. Then the calculation results of geomagnetic harmonic amplitude ratio and load/unload response ratio of each station were obtained. The geomagnetic anomalies before and after the Wulong, Chongqing M5.0 earthquake on November 23, 2017 were analyzed by combining with the geological structure background near the earthquake epicenter. The analysis results indicated that the variation characteristics of most harmonic wave amplitude ratios are similar to those of earth resistivity, showing a process of "down-turning-recovery". The M5.0 earthquake occurred in the early stage of turning upward. During the earthquake, the changing trend of geomagnetic harmonic amplitude ratios of stations with small epicentral distance are not synchronous, but their change amplitudes are roughly the same; the changing trend of geomagnetic harmonic amplitude ratios of stations with large epicentral distance are relatively synchronous, and their change amplitudes are large. In addition, the study also showed that the temporal and spatial distribution of abnormal high value of geomagnetic load/unload response ratio before the earthquake has a good corresponding relationship with the epicenter position.Keywords: geomagnetism; harmonic wave amplitude ratio; Wulong earthquake; tectonic setting