渤海7.4级地震前区域地磁场的异常变化

本文利用《中国地磁图》和我国地磁台网资料分析研究了1969年7月18日渤海7.4级强震前的地磁场变化,给出了有利于渤海地震发生的中长期背景性异常及变化磁场的短临异常变化图形。中国地磁图展示了几年乃至十年尺度的地球基本磁场的大区域变化特征以及与我国强震活动的主体地区的联系,显示了渤海地震前的背景性异常。地磁变化场垂直分量“低点位移”及幅相法异常则显示出渤海地震前华北地区出现的小区域的短临地磁异常。

ANOMALOUS VARIATION OF REGIONAL GEOMAGNETIC FIELD BEFORE THE BOHAI SEA EARTHQUAKE (7.4M_S)

By use of the map of geomagnetic field of China and the geomagnetic data of the networkin China,the variation of geomagnetic field before the Bohai Sea earthquake (7.4Ms) of July 18,1969 is analysed,giving the maps of medium-long term background anomalous variation andshort-imminent anomalous variation of magnetic field.The maps of geomagnetic field of Chinashow a characteristic of large range variation in space of basic magnetic field of the earth with aperiod of several years or decades and its correlation with the large earthquake activities in ma-jor areas of earthquakes as well as the background anomaly before the Bohai Sea earthquake.The lowest point shift of vertical component of geomagnetic variation and the anomaly deter-mined by the amplitude-phase method show a short-imminent anomaly of geomagnetic varia-tion in small range in North China before the Bohai Sea earthquake.