运用地磁低点位移、地磁加卸载响应比和地磁Z分量日变幅逐日比3种地磁分析方法，分析了2008年5月12日汶川8.0级地震前的地磁前兆异常现象。研究发现，运用上述3种方法，汶川地震前出现多次异常，地震发生在异常预测线集中交汇区域。综合分析结果显示，地磁多方法综合分析可以有效提升地震预测的精确性。文章还讨论了地磁日变化畸变异常机理问题。

In this paper, we use five geomagnetic analysis methods including geomagnetic low-value displacement, geomagnetic daily value spatial correlation and spatial correlation of daily variation of geomagnetic vertical component, geomagnetic load-unload response ratio and daily ratio of geomagnetic vertical component amplitude to analyze the geomagnetic precursor anomalies before the Wenchuan M_S8.0 earthquake on May 12, 2008. The study found that:three methods of geomagnetic low-value displacement, geomagnetic load-unload response ratio of geomagnetic vertical component amplitude and daily ratio of geomagnetic vertical component amplitude had abnormal phenomena before the Wenchuan M_S8.0 earthquake. And the earthquake occurred in the joint region of the prediction lines. The analysis shows that comprehensive analysis by multiple methods can effectively improve the accuracy of earthquake prediction. The mechanism of the geomagnetic abnormal diurnal variation is also discussed.

P315

中国地震局青年震情跟踪课题（2018010417）资助