An earthquake with M6.6 occurred about 50 km southeast off Kikai-jima which is located near Amami-Oshima in Kagoshima prefecture at 19 : 37 October 18, 1995. About 16 hours after the event, an another earthquake with M6.5 occurred in the same region. Seismic intensity of 5 in the JMA scale was recorded at Takigawa in Kikai-jima for the two earthquakes. Focal mechanisms of the two earthquakes were normal fault-type, and they were estimated to have had occurred within the Philippine Sea plate. Tsunamis were observed at Pacific coasts in southwest Japan. Tsunami waves were higher than usual at Kikai-jima, relative to seismic magnitude, at the two earthquakes. Characteristics of the seismic activity before and after the near Amami-Oshima earthquake are summarized as follows :
1. Preceding seismic activity and foreshocks were observed.
2. Another earthquake with almost the same magnitude succeeded after a short interval.
3. Following characteristic patterns were recognized in seismicity :
Seismicity was decreased noticeably in the northeastern part of the aftershock area just before larger shocks over M5. While conspicuous decrease in seismicity was observed in the southwestern part of the aftershock area after the earthquake of M6.5.
