海底地震計による1995年奄美大島近海地震の余震観測 Aftershock Observation of the 1995 Amami-Oshima-Kinkai Earthquake Using Ocean Bottom Seismometers
On October 18, 1995, an earthquake with magnitude <I>M</I>j 6.7 occurred in the central part of Ryukyu Arc at 28°1.7'N, 130°23.0' E and 38 km in depth. The next day, another earthquake with magnitude <I>M</I>j 6.6 occurred in the same area. The hypocenter parameters were determined by Japan Meteorological Agency (J.M.A.). For the purpose of investigating the aftershock activities finely, we put an array of twenty-two ocean bottom seismometers (OBSs) covering the area of aftershocks. The OBS observation started on October 28, ten days after the occurrence of the <I>M</I>j 6.7 event, and continued about four weeks.<BR>In this study, we relocated hypocenters of the aftershocks using the data of eighteen OBSs. The results give us detailed view of the hypocenter distribution as follows : <BR>Most of aftershocks occurred (1) on the fault of <I>M</I>j 6.7 event, and (2) in the focal area of <I>M</I>j 6.6 (October 19, 1995). Considering the distributions of (1) and (2), we identified one of the nodal planes of the CMT solutions as the fault plane of <I>M</I>j 6.7 event and <I>M</I>j 6.6 event. For both events, the strike is almost parallel to the trench axis. Dip angle of the <I>M</I>j 6.7 event is almost vertical. Therefore, it is obvious that this event is not a low-angle thrust-type interplate earthquake but an intraplate event.
地學雜誌 106(4), 514-524, 1997-08-25
Tokyo Geographical Society