华北成组地震前地电阻率小波能谱分析
Wavelet Power Spectrum Analysis of Geo-resistivity Prior to Earthquake Groups in North China

应用小波变换方法处理了华北地区中强成组地震前后震中附近台站的地电阻率观测数据，研究地电阻率小波能谱及相对变化特征。结果表明小波能谱在震前中期阶段地电阻率出现异常，与成组地震活动中地电阻率出现破年变异常相符。中强震前或成组地震过程中地电阻率出现明显小波相对能谱增大异常，能较好的识别地电阻率短临变化。
In this paper, we investigate the Tangshan M7.8, Datong M5.9, and Zhangbei M6.2 earthquake groups, each of which includes three to four earthquakes of the same magnitude. The case study results of these earthquake groups in north China show that stations near earthquake epicenters can record a significant rate of earth resistivity anomalies, which are characterized by a wide spatial distribution and long duration. We applied the wavelet transform method to analyze the geo-resistivity data observed prior to the occurrence of the earthquake groups to study the wavelet power geo-resistivity spectrum and its relative variation. The results suggest that the wavelet power spectrum can well reflect changes in the geo-resistivity, and is an effective method for extracting short-term geo-resistivity anomalies. In the mid-term stage prior to earthquakes, the wavelet power spectra of geo-resistivity are abnormal. The relative wavelet power spectra show obvious increases prior to moderate earthquakes or an earthquake group, which can well identify short-term and impending changes in geo-resistivity.