HR: 1340h
AN: S53A-1041    [Abstracts]
TI: Observed and Simulated High Amplitude Tsunami Offshore of Northern Banda Aceh During the 2004 Sumatra Earthquake
AU: * Ando, M
EM: ando@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road, Sec. 2 Nankang, Taipei, 115, Taiwan
AU: Nakamura, M
EM: mnaka@sci.u-ryukyu.ac.jp
AF: Faculty of Science, University of Ryukyus, Nishihara, Okinawa, Nishihara, 903-0213, Japan
AU: Hayashi, Y
EM: hayashi@seis.nagoya-u.ac.jp
AF: Graduate School of Envirometal Sciences, Nagoya University, Furocho, Chikusa, Nagoya, 464-8601, Japan
AU: Ishida, M
EM: ishida@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, Showa, Kanazawa, Yokohama, 236-0001, Japan
AB: Several isolated high waves were observed about 0.5 to 20 km away from the west coast of northern Sumatra based from the interviews undertaken with fishermen who were on their fishing vessels when the December 2004 Sumatra earthquake occurred. The fishermen were on their wooden boats powered by motor engine manned by one to 20 crew members. Most of them felt the earthquake shocks and some of the crews immediately recognized the shaking phenomena as an earthquake based on their previous experiences. About half of interviewees had difficulties in controlling their boats during the shaking, which lasted about 10 to 15 min. About 5 to 15 minute after the shaking their boats were struck by the 10-20m high waves. Moreover, their boats, located more than several km off the coast of northern Sumatra, were struck repeatedly by more or less isolated high waves. Based from these interviews it is ascertained that tsunami can also pose danger even offshore when the tsunami amplitudes are high and water depths are shallower than about 50m. These observations also provided new evidence that the 2004 tsunami is already high enough to damage or overturn ships offshore. We simulated tsunami waves using a source model of the 2004 earthquake by Fujii and Satake (2007). Since the seafloor topography is not clear for both continental shelf and slope in northern Sumatra, the depth of 150m at 30 km off the coast varying gently towards the coast is presumed. This depth is assumed based on the type of fish caught in the area that are likely to live near the rocky seafloor at depths around 50m. For the numerical analysis, the non-linear long wave equation and the non-linear dispersive long wave equation were used for depths deeper and shallower than 150m, respectively. As a result, at depths around 20m, dispersive short- period solitary waves with height of 6-8m were generated that are similar to the waves that struck the fishing vessels. However, the tsunami waves that the fishermen encountered were as high as 10-20m. This means that the incoming tsunami in the shallower depths was higher than the wave heights derived from Fujii and Satakefs model.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 4564 Tsunamis and storm surges
DE: 7215 Earthquake source observations (1240)
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2007 Fall Meeting