1978年日本宫城县近海发生7.4级强震前约1个月,东北大学女川地磁观测所观测到地磁明显的短周期变化。 1.序言 在地面观测点观测到的地磁短周期变化(如湾扰、地磁脉动等周期小于1小时的变化),是地球外部原因产生的变化和它在地球内部感应电流所引起的变化的总和,因此地磁短周期 In 1978, about a month before the M 7.4 earthquake occurred off the coast of Miyagi Prefecture in Japan, the obvious short-period change of geomagnetism was observed by the Nuchuang Geomagnetic Observatory, Northeastern University. 1. INTRODUCTION The observed short-period changes in geomagnetic (such as changes in the bay disturbances and geomagnetic pulsations less than one hour) observed at terrestrial observation points are the sum of the changes caused by causes outside the Earth and the changes induced by its induced currents inside the Earth , So geomagnetic short cycle