HR: 1340h
AN: T13C-1384    [Abstracts]
TI: Fault-slip derived paleotsunami compared with historical descriptions: simulation of the 1596 Keicho-Bungo tsunami based on the paleoseismic study of submarine faults in Beppu Bay, Japan
AU: Shimazaki, K
EM: nikosh@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: * Okamura, M
AF: Faculty of Science, Kochi University, 2-5-1 Akebono, Kochi, 780-8520 Japan
AU: Ishibe, T
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Matsuoka, H
AF: Faculty of Science, Kochi University, 2-5-1 Akebono, Kochi, 780-8520 Japan
AU: Chida, N
AF: Oita University, 700 Dannohara, Oita, 870-1192 Japan
AB: High-resolution shallow-water profiling survey revealed recent activity of submarine fault which was newly found to fill a gap between two subaerial faults, the Asamigawa and the Funai faults running on the southern coast of Beppu Bay. Historical records suggest that this activity on the north-dipping normal fault corresponds to the M7.3 Keicho-Bungo earthquake of September 1, 1596. Our previous profiling survey and correlation study of core samples show that the event caused vertical offset on south-dipping normal faults in the central and northern parts of the bay. Thus it is most likely that the Keicho-Bungo event simultaneously ruptured the faults on the both sides of the Beppu Graben. Furthermore core samples obtained from the both sides of the newly found submarine fault suggest repeated occurrence of this simultaneous rupturing. A comparison of vertical offsets of two prominent ash layers on Beppu Bay faults whose total length exceeds 230km, shows almost linear relationship between the two offsets, indicating characteristic behavior of the fault slip distribution. This enables us to estimate co-seismic fault slip of the Keicho-Bungo earthquake on faults without core samples. On the basis of the estimated fault slip, vertical deformation of the ocean bottom, or the initial height of the tsunami was calculated. A comparison of the simulated tsunami height on the coast and historical description of the 1596 tsunami indicates that the Keicho-Bungo earthquake ruptured not only the Beppu Bay faults, but also the westernmost segment of the Median Tectonic Line active fault zone.
DE: 7221 Paleoseismology
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting