2017年阿拉善左旗5.0级地震地磁垂直分量日变化低点时间时空演化特征

2017年4月21日中国大陆出现地磁低点位移异常，异常出现后43天，于6月3日在低点位移分界线附近发生阿拉善左旗5.0级地震。文中采用克里格方法对中国大陆低点时间数据进行插值处理，获取地磁异常的4月21日和正常的4月7日Z分量低点时间等值线，结果显示：①异常日期间蒙宁陕交汇处存在低点时间等值线高梯度区，地震发生于高梯度区域边缘；②若以低点时间13 h的等值线作为低点位移分界线，则该分界线穿过震中位置；③异常日期间，震中距500 km范围以内分界线两侧台站Z分量日变形态差异性大，存在显著的分区特征。

Temporal and spatial evolution characteristics of diurnal variation low-point time of the geomagnetic vertical component of the Alashan Zuoqi M 5.0 earthquake in 2017

On April 21, 2017, a geomagnetic low-point displacement anomaly occurred in mainland China. 43 days after the anomaly occurred, an M 5.0 earthquake occurred near the boundary of low-point displacement on June 3 in Alashan Zuoqi. In this paper, the Kriging method is used to interpolate the low-point time over the Chinese mainland. The low-point time contour maps of the vertical component of the geomagnetic field on April 21 and April 7 are obtained. The results show that:① There is a high gradient area of low-point time isoline at the intersection of Mongolia, Ningxia, and Shaanxi during the anomalous date, and the earthquake occurs at the edge of the high gradient area; ② If the isoline at 13 o'clock of the low-point time is used as the demarcation line of the low-point displacement, the demarcation line will pass through the epicenter; ③ Statistical analysis of daily deformations of geomagnetic vertical components during anomalous dates shows that there are significant differences in daily deformations of geomagnetic vertical components between stations on both sides of the boundary within 500 km of epicentral distance, and there are significant zoning characteristics.