Publication Date:
1983-01-01
Description:
An earthquake swarm that occurred east of the Kii Peninsula near the Nankai trough was investigated using seismic data from four pop-up type OBSs, four telemetering OBSs, and one land seismic observation station. The addition of the pop-up type OBSs was most effective in the analysis of the swarm. We analysed the daily frequency of earthquakes, the b-value, S-P time distribution, and hypocenter distribution. Here we discuss the swarm activity with regard to recent seismicity around the area, to submarine active tectonic lines, to oceanic topography, and to block boundaries along the Nankai trough. The swarm activity was largely divided into two periods, and seemed to consist of six or seven sequences of foreshocks-mainshock-aftershocks or mainshock-aftershocks. The earlier activity occurred in a deeper region (at a depth of about 17 km), the later one in a shallower region (about 5 km). The epicenter was distributed in a region no larger than 8 km x 8 km. The b-value seems to have decreased before the largest earthquake. The swarm seems to have occurred at a submarine active tectonic line near the Nankai trough. © 1983, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan. All rights reserved.
Print ISSN:
0022-3743
Electronic ISSN:
1884-2305
Topics:
Geosciences
Permalink