极化方法在成都地磁台的应用研究

Application of polarization method to geomagnetic data from the station Chengdu

以成都台FHDZ-M15地磁组合观测系统产出的秒采样观测数据为研究对象,应用极化方法提取该台站附近几次中强震前的超低频(ULF)磁异常信号.成都台极化值长期曲线具有一定的年变化特征,利用傅里叶拟合消除周期变化后,对残差进行分析.结果显示,极化值增高现象与其后2个月内台站周边区域的ML≥5.0地震有很好的对应关系,高值异常持续3—5日,与外空场活动无关,且逆冲型地震前的极化值异常幅值高于走滑型地震.

Based on the 1-second sampling data derived from FHDZ-M15 digital recording geometry of the station Chengdu,we applied polarization method to analyzing the possible ultra-low frequency electromagnetic phenomena associated with ML≥5.0earthquakes surrounding the station.It was shown that the long-term curve of the polarization value of the station Chengdu exhibits annual variations.By applying the Fourier fitting,the periodic annual variations were eliminated,and the analysis results on residuals between polarization values and fitting ones indicate that the increasing of the polarization value has a close relationship with ML≥5.0earthquakes which would happen in two months,and the appearance duration of the high value was one day to five days.Meanwhile,there was no correlation between the ultra-low frequency electromagnetic phenomena and the space current activity;the abnormal amplitude of polarization value before the thrust earthquake is higher than that of the strike-slip type.