2019年甘肃张掖5.0级、夏河5.7级地震前地磁低点位移时空分布特征

2019年甘肃张掖5.0级、夏河5.7级地震前中国大陆均有明显的“地磁低点位移”现象出现，2次地震震中均位于低点位移线出现明显转折的区域。通过对2次低点位移异常日中国大陆地磁台站低点时间进行梯度法分析，研究了2次中强地震震中位置与低点时间高梯度带分布间的关系。研究结果表明：①在2次低点位移异常日都同步出现了地磁垂直分量低点时间高梯度带分布；②2次中强地震震中位置均位于低点位移线出现明显转折处和低点时间高梯度带1.0 h/（°）等值线附近；③利用低点时间梯度法对低点位移异常进行分析有利于改进原有异常识别方法，较少虚报率。

Characteristics of spatio-temporal distribution of geomagnetic low-point displacement before the 2019 M 5.0 Zhangye and M 5.7 Xiahe earthquakes

Apparent geomagnetic low-point displacement appeared in mainland china before the M 5.0 Zhangye earthquake and M 5.7 Xiahe earthquake in Gansu Province in 2019, the epicenters of these two earthquakes are located near the position where the low-point displacement line turned obviously. The relationship between earthquakes epicenters and the distribution of high gradient zones of low-point time is studied through analyzing the low-point time of the Chinese mainland's geomagnetic stations. The results show that:① The distribution of high gradient zone of the low-point time of geomagnetic vertical component appears synchronously in the two dates with low point displacement anomalous before these earthquakes; ② The epicenters of these two moderate to strong earthquakes are located at the obvious turning point of the low-point displacement line and near the 1.0 h/(°) contour line of the high gradient zone of low-point time; ③ Analyzing the low-point displacement anomaly by using the low-point time gradient method is helpful to improve the original identification, and shall reduce the misstatement rate.