HR: 1340h
AN: S23B-0234    [Abstracts]
TI: Long Term Ocean Bottom Seismographic Observation on the Rupture Areas of the Tonankai and Nankai Earthquakes
AU: * Yamada, T
EM: yamada@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kanazawa, T
EM: kanazawa@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Shinohara, M
EM: mshino@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sakai, S
EM: coco@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Mochizuki, K
EM: kimi@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Nakahigashi, K
EM: kazuo@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: The Nankai trough, which runs off the coast of the southwestern part of Japan, is widely known for its systematic activity of large earthquakes with the estimated magnitudes as large as 8. The recurrence periods are approximately 100 years after 1361, and the latest events are the 1944 Tonankai and the 1946 Nankai earthquakes. However, the number of smaller earthquakes observed by the on-land seismic stations is very small, and the location had not been resolved precisely. We start earthquake monitoring on the estimated rupture areas of the Tonankai and the Nankai earthquakes using ocean bottom seismometers, which are pop-up types with the life of one year continuous recording. We deployed 9 OBSs and start observation in 2003. We tried to retrieve them, redeployed 9 OBSs and deployed new 14 OBSs in 2004. In 2005, 23 OBSs were retrieved and redeployed. Moreover, we performed urgent aftershock observation of the 2004 Off Kii-Peninsula earthquake (Mw7.4) occurred on September 5, 2004. In this presentation, we focus the first observation with 9 OBSs. This network covered the boundary zone between the Tonankai and the Nankai earthquake rupture areas. The spatial intervals among OBSs were about 20 km. Earthquakes are located after correction of sedimentary layer estimated from active source data. One seismicity group, which locates near trench axis, is about 20km deep. The other seismicity, which locates along subducting plate, may be in the uppermost mantle within the subducting Philippine Sea Plate, and exist over 60km from trench axis. This work is a part of the Research on the Tonankai and Nankai earthquakes funded by the Ministry of Education, Culture, Sports, Science, and Technology, Japan.
UR: http://www.eri.u-tokyo.ac.jp/nankai/index.html
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: Fall Meeting 2005