基于幅相法的地磁低点位移异常可靠性分析方法

地磁低点位移法和幅相法都是地震短临阶段的预报方法, 两者均是通过提取地磁垂直分量日变化中的畸变信息对地震的发生给出预测意见, 低点位移法可以提取反相位畸变异常的持续时间, 但虚报率高, 无法确定每次异常的可靠性。而幅相法可以为异常提供定量判定依据。为应对低点位移法虚报率较高的不足, 本文应用幅相法计算2008年至2018年间出现的159次低点位移异常, 提取反映地磁反相位畸变程度的瞬时差值面积均值S_x及残差C, 并以此作为判断震前低点位移异常可靠性的标准。结果显示, 使用本文给出的标准可以将低点位移法的异常报对率从39%提高到70%, 证明了基于幅相法的低点位移异常可靠性分析方法的有效性, 提高了低点位移法的实用性。统计结果还显示不同地区震前异常具有不同的特征, 如新疆、 西藏与川滇地区震前异常的S_x、 C的变化范围和均值存在差异。

Validity Analysis of Geomagnetic Low-point Displacement Based on Amplitude-phase Method

Geomagnetic low-point displacement method and amplitude-phase method are frequently used for short term earthquake forecasting, both of which are based on distortions in diurnal variation of the geomagnetic vertical component. Low-point displacement method is able to extract the duration of anti-phase anomalous distortion, but this method is always with higher false rate and the reliability of each anomaly cannot be determined. In order to deal with this problem, the amplitude-phase method is used to 159 anomalies occurring during 2008 to 2018, and the transient difference area S_x and error C standing for the extent of anti-phase distortions are extracted as a standard to validate the low-point displacement anomalies before earthquakes. The results show that the criteria suggested in this paper makes the accuracy of low-point displacement anomalies related to earthquakes rise from 39% to 70%. It demonstrates the effectiveness of amplitude-phase method and its actual application ability. The statistical results also exhibit the regional differences, in which the ranges and mean values of S_x and C differ before the earthquakes in Xinjiang, Tibet, Yunnan and Sichuan regions.