Application of polarization method to geomagnetic data from the station Chengdu
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摘要: 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.Abstract: 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≥5.0 earthquakes 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≥5.0 earthquakes 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.
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Keywords:
- geomagnetic field /
- polarization method /
- ULF electromagnetic emission
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图 1 2010—2015年成都台周边满足式(1) 的ML≥5.0地震震中分布图
F1:灌县—安县断裂;F2:映秀—北川断裂;F3:汶川—茂汶断裂;F4:龙泉山断裂
Figure 1. Epicentral distribution of ML≥5.0 earth-quakes satisfying equation (1) around the station Chengdu from 2010 to 2015
F1: Guanxian-Anxian fault; F2: Yingxiu-Beichuan fault; F3: Wenchuan-Maowen fault; F4: Longquanshan fault
图 2 成都台地磁极化值变化
(a)极化值5日滑动平均值;(b)极化值傅里叶拟合; (c)极化值与傅里叶拟合残差5日滑动平均值
Figure 2. The variations of polarization value of the station Chengdu
(a) Five days moving average of polarization value; (b) The Fourier fitting values of polarization value; (c) Five days moving average of residuals between polarization value and Fourier fitting
表 1 成都台磁场极化值高值异常与ML≥5.0地震对应情况统计
Table 1 Statistics of corresponding relation between the high value of polarization anomaly at the station Chengdu and ML≥5.0 earthquakes
异常出现时间 异常持续时间/d 异常幅值 对应地震 发震时间间隔/d 震中距
/km震源深度
/km震源机制 2010-01-04 3 0.83 虚报 2010-05-13 5 0.60 汶川ML5.2 12 38.7 20.5 逆冲 2010-07-09 4 0.47 虚报 2011-10-26 4 0.36 青川ML5.6 6 230 21.5 逆冲 彭州ML5.2 61 51 25.5 逆冲 2012-06-19 3 0.37 虚报 2013-01-02 3 0.39 三台ML5.1 49 141 29.5 走滑 2013-04-02 4 0.45 芦山MS7.0 18 100 17.5 逆冲 漏报 理县MS4.9 104 22.5 走滑 漏报 梓潼ML5.2 150 21.5 走滑 2014-11-16 5 0.33 康定MS6.3 6 211 20.5 走滑 -
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