Activity of the 1995 Amami-Oshima-Kinkai Earthquakes

An earthquake of MJMA 6.7 occurred at 19 : 37 on October 18, 1995 at about 50 km southeast of Kikai-jima in the central part of Ryukyu-islands, Japan. About 16 hours after this event, another large earthquake of MJMA 6.6 occurred in the same area. We relocate hypocenters of two large events and their aftershocks using JMA data by considering the station corrections, which are obtained by joint using the temporary observation data of ocean bottom seismometers (OBS) and JMA data. The relocated hypocentral distribution obtained by joint using of OBS and JMA data show the possibility that two large events occurred on the adjacent faults. The events during four days after the MJMA 6.7 event occurred in the region of about 70 km in length in NNE-SSW direction and the epicentral area is divided into two sub-regions, NNE and SSW sub-regions. The aftershock activity of the MJMA 6.7 event is predominant in the SSW sub-region until 7 : 00 a.m. on the next day. After 7 : 00 a.m., the activity increases in the NNE sub-region and the MJMA 6.6 event at 11 : 41 a.m. on October 19 and its aftershocks occurred in this region. On the other hand, the activity in SSW sub-region becomes low in this period. Such the alternative rise and fall activities in two sub-regions are thought to be caused by the interraction of stresses on the different faults. Therefore, the present activity is concluded to be constituted by two foreshockmainshock-aftershock sequences occurred on the adjacent faults in a short time interval.