HR: 0800h
AN: S11A-1010    [Abstracts]
TI: Large earthquakes along the Nankai trough, the 1944 Tonankai earthquake (Mw 8.0) and two 2004 Tonankai-oki earthquakes (Mw 7.2 and 7.4)
AU: * Tanioka, Y
EM: tanioka@eos.hokudai.ac.jp
AF: Institute of Seismology and Volcanology, Hokkaido University, N10W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Kusunose, T
EM: s010113w@ec.hokudai.ac.jp
AF: Institute of Seismology and Volcanology, Hokkaido University, N10W8 Kita-ku, Sapporo, 060-0810 Japan
AU: Baba, T
EM: babat@jamstec.go.jp
AF: JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Hasegawa, Y
EM: yhasegaw@mri-jma.go.jp
AF: Meteorological Research Institue, 1-1 Nagamine, Tsukuba, 305-0052 Japan
AB: Great interplate earthquakes have repeatedly occurred along the Nankai trough with an interval of about 120 years. The most recent events were the 1944 Tonankai and 1946 Nankai earthquakes. Recently, two large compressional outer-rise earthquakes occurred off the source region of the 1944 Tonankai earthquake near the Nankai trough on Sept. 5, 2004 (GMT). First, the detailed slip distribution of the 1944 Tonankai earthquake is estimated using the tsunami waveform inversion in this paper. Second, the tsunamis from two recent outer-rise earthquakes are analyzed to discuss the relation between the great interplate event and the large outer-rise events. The slip distribution of the 1944 Tonankai earthquake has been already estimated using the tsunami waveform inversion by several researchers. The slip estimation in this paper is improved by using smaller size of subfaults, 25 km x 25 km, and larger number of subfaults, 72 subfaults. We also use smoothness constraints for the discrete Laplacian to stabilize the inversion. Appropriate weights for the smoothness constraints are determined using the Akaike Bayesian information criterion. The results show that the largest slip of 3.7m is occured at the subfault off Shima peninsula. The large slip region, $>$1m, are elongated to the southwest-northeast direction from the subfault where the largest slip is estimated. The total seismic moment is 1.3 x 10$^{20}$ Nm (Mw 8.0) by assuming that the rigidity is 5 x 10$^{10}$ N/m$^{2}$. The two 2004 Tokachi-oki outer-rise earthquakes generated the moderate tsunamis. Those tsunamis were observed at several tide gauge stations and ocean bottom pressure gauges. The tsunami heights of the second event are about twice as large as those of the first event. This is consistent with the magnitudes of two events because the Harvard CMT moment magnitudes of the first and second events are 7.2 and 7.4, respectively.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7215 Earthquake parameters
DE: 4564 Tsunamis and storm surges
SC: Seismology [S]
MN: 2004 AGU Fall Meeting