地磁垂直分量Z日变幅逐日比及其与磁暴和地震的关系

地磁垂直分量Z日变幅逐日比是基于变化磁场在地球电导率的作用下会产生一个与变化磁场相反的感应磁场, 该感应磁场不仅包含了外空磁场的信息, 还包含了地下电导率的信息。 因此, 相对于地磁场其他成分来说Z分量更多地反应了地下活动的变化, 逐日比是利用前后两日地磁Z分量日变幅相比来提取该异常现象, 但磁暴可能会对逐日比异常判定产生影响。 我们取1984年至今江苏区域范围达到逐日比异常判定指标的29个事件结合磁暴以及该异常事件之后和地震的对应关系进行统计分析。 研究发现, 无磁暴时逐日比异常和预测范围内地震对应关系达到0.77, 有磁暴时逐日比异常和地震对应关系为0.25。 综合分析认为逐日比异常事件发生后, 若该日无磁暴或者Dst指数小于异常第二日, 那么该异常为地震前兆的可能性大概为0.8, 反之则该异常有可能是磁暴的影响而不是来自于地下活动的影响, 需结合其他前兆分析方法进行综合分析, 该研究增强了逐日比异常判定地震地磁前兆信息的可靠性。

Daily Variation Ratio of Geomagnetic Z Component and its Relationship with Magnetic Storms and Earthquakes

Daily variation ratio of geomagnetic vertical component (Z) is important in the study of earthquake precursor analysis. The variation magnetic field makes an induced magnetic field because of the earth conductivity, and the induced magnetic field includes information from outer magnetic field and underground electrical conductivity, so the geomagnetic field Z component reflects more changes of underground activity than other components. We collected data of Jiangsu area since 1984 and got 29 events of anomalies with day by day ratio, and then carried out a statistical analysis on the relation between them by combining geomagnetic storm and the earthquake after the abnormal events. The study has found that the anomaly event of day by day ratio and earthquake have a good correlation without geomagnetic storm, with coefficient of 0.77, while the corresponding relationship drops to 0.25 with geomagnetic storm. Combining all of the abnormal events, we consider that, after the abnormal event of day by day ratio, the possibility of the abnormal event of day by day ratio being an earthquake precursor will be 0.8 if there is no geomagnetic storm on that day or the Dst index is smaller than that on the second day. Otherwise, the abnormality maybe be caused by geomagnetic storm rather than the influence of underground activity.