应用小波变换提取张北地震的震磁效应

以1998年1月10日的张北地震为例，应用小波变换及傅里叶分析，分析震中附近的6个地磁台站在地震前后共6个月的地磁场三分量分钟值采样数据.发现各个地磁台站记录的地磁场Z分量在张北地震前三个月内出现不同程度的异常现象，这种现象的出现频率随着离发震时间越近而越来越高，出现的地点由南向北迁移.地磁场H和D分量没有此类异常出现.用这6个地磁台出现异常时同一频率所对应的振幅值绘出等值曲线，得到的图形是稳定的四象限分布，震中基本上位于0～3nT的等值线上.结果表明小波分析是提取地震磁效应的有效工具，同时也证实了地震磁效应的客观存在.

Wavelet analysis as a tool for revealing geomagnetic precursors of the Zhangbei earthquake

We study the minutely geomagnetic field values of six months recorded by six observatories around the epicenter by wavelet and FFT (Fast Fourier Transform) analysis in order to reveal the geomagnetic precursors of the Zhangbei earthquake, which occurred on Jan. 10, 1998 It is found that abnormal frequency structure of vertical (Z) component appeared before the Zhangbei earthquake and transferred from south to north. The occurrence rate of the abnormal frequency structure increased as the time approached to the earthquake occurrence. However, no similar phenomenon is found for horizontal (H) and deviation (D) components. The space distribution of amplitudes in different observatories is close to steady four quadrant pattern in those days with abnormal frequency structure, and the epicenter is located at contours of 0～3nT. The results indicate that the geomagnetic precursors do exist, and wavelet analysis is effective for revealing such precursor.