2010年山西河津4.8级地震地磁垂直分量日变化低点时间空间分布特征

2010年1月11-24日，华北地区出现7次地磁低点位移异常。异常结束1天后研究区内发生2010年1月24日山西河津4.8级地震。采用实测低点时间减去理论低点时间的方法剔除低点时间经度效应，并以剔除经度效应后低点时间为0 h的等值线作为低点位移分界线，山西河津4.8级地震震中处于1月16日、17日、19日、22日地磁低点位移分界线上。低点位移异常日期间，华北地区存在显著的高梯度带，该文采用梯度值定量描述低点时间空间变化程度。在正常日期间，华北地区未出现梯度值大于1 h/（°）的区域，在异常日期间，出现梯度值大于1 h/（°）的区域，河津4.8级地震多位于高梯度区边缘。

Spatial Distribution Characteristics of Low-point Time of Geomagnetic Vertical Component Diurnal Variation before the Hejin M4.8 Earthquake of 2010

Geomagnetic low-point displacement anomalies occurred in North China from January 11 to 24, 2010, and the Hejin M4.8 earthquake occurred in the study area on January 24, 2010, after the ending of the anomalies. In this paper, the longitudinal effect of low-point time is removed by subtracting theoretical low-point time from measured low-point time, and the isoline whose low-point time is 0 h after removing the longitudinal effect is used as the low-point displacement boundary. The epicenter of Hejin M4.8 earthquake is located at the boundary of geomagnetic low-point time on January 16, 17, 19, and 22. The gradient value is used to describe the spatial distribution characteristics of low-point time. During the abnormal dates, there appears high gradient area in North China, whose gradient are greater than 1 h/(°), and the Hejin M4.8 earthquake is generally located at the edge of the high gradient area.