1984年8月30日以来,在伊豆半岛以东近海持续发生了令人不安的震群。大岛和静冈县的网代等地每天都感觉到摇晃,如果把无感地震包括在内,到9月12日为止,两周内所发生的地震多达4,500余次。实际上,在包括该震群发生区域在内的伊豆半岛东侧,多年来震群活动一直频繁地发生。其中有几次并接着发生了酿成灾害的大震。因此,日本气象厅以及地震学者们加强了对该区域震群活动的监视。这 Since August 30, 1984, there have been disturbing swarm of swarms near the east of the Izu Peninsula. There is daily shaking in the Oshima and Shizuoka prefectures and other places. If no-sense earthquakes are included, as many as 4,500 earthquakes occur in two weeks until Sept. 12. In fact, earthquake swarm activities have been frequent for many years on the eastern side of the Izu Peninsula, including the area where the swarm occurred. Several times and followed by a major earthquake that caused disasters. As a result, the Japan Meteorological Agency and seismologists stepped up surveillance of earthquake swarm activities in the area. This