HR: 11:05h
AN: T41E-04    [PDF]
TI: Seismicity along the Nankai trough seismogenic zone: results from micro-seismicity observations using ocean bottom seismographs
AU: * Obana, K
EM: obanak@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marince Science and Technology Center, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Kodaira, S
EM: kodaira@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marince Science and Technology Center, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 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: 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: Suyehiro, K
EM: suyehiro@jamstec.go.jp
AF: Deep Sea Research Department, Japan Marince Science and Technology Center, 2-15, Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Kaneda, Y
EM: kaneday@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marince Science and Technology Center, 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AB: Along the Nankai Trough, southwestern Japan, the Philippine Sea plate is subducting beneath the Eurasian plate with a convergence rate of about 4 cm/year. Large interplate thrust earthquakes that are caused by the subduction of the Philippine Sea plate have occurred repeatedly. Records of the great earthquakes can be seen in historical documents since the seventh century and the recurrence interval between them is about 100-200 years. Most recent events are the 1944 Tonankai and 1946 Nankai earthquakes occurred in the eastern and the western part of the Nankai trough, respectively. On the other hand, current seismicity is very low and hypocenters are not determined accurately by the land seismic network. Many seismic surveys using controlled sources have been conducted to obtain crustal structure at the Nankai trough seismogenic zone. We performed micro-seismicity observations using ocean bottom seismographs at the coseismic slip area of the 1944 Tonankai and 1946 Nankai earthquakes. Hypocenters were determined using 2- or 3-D realistic velocity structure based on the results of the seismic surveys. Off cape Muroto, fault area of the 1946 Nankai earthquake, several micro earthquake clusters locate around the plate interface. The seaward limit of the seismicity is characterized by clusters of earthquakes with very similar waveforms. These clusters locate about 30-45 km landward from the deformation front and coincide with the stepping down of the decollement. These earthquakes are considered to occur at small asperities in the aseismic-seismogenic transition zone of the plate interface. Off Kii peninsula, the rupture area of the 1944 Tonankai earthquake, seismicity is locally active near the axis of the Nankai trough. Although the depths of these earthquakes are not constrained well, they are considered to be shallower than the Moho of the subducting oceanic crust. On the other hand, micro-seismicity in the rupture area of the 1944 Tonankai earthquake is very low. The recent GPS survey shows a fully coupled plate interface along the Nankai trough seismogenic zone. Analyses of the seismic and tsunami waves show a uniform distribution of the coseismic slip during the 1944 Tonankai Earthquake. These facts imply an existence of a large asperity with a uniform interplate coupling off Kii Peninsula.
DE: 7230 Seismicity and seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting