HR: 0800h
AN: T11A-0351    [Abstracts]
TI: Tsunami Waveform of the AD1703 Kanto Earthquake Reconstructed from the Deposit
AU: * Fujiwara, O
EM: o.fujiwara@aist.go.jp
AF: Active Fault Research Center, GSJ/AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Kamataki, T
EM: t.kamataki@aist.go.jp
AF: Active Fault Research Center, GSJ/AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Hirakawa, K
EM: hkazu@ees.hokudai.ac.jp
AF: Grad. Sch. Environmental Sci., Hokkaido Univ., Kita 10, Nishi 5, Kita-ku, Sapporo, 060-0810 Japan
AU: Irizuki, T
EM: irizuki@riko.shimane-u.ac.jp
AF: Disciplinary Fac. Sci.and Engineer., Shimane Univ., 1060 Nishikawatsu, Matsue, 690-8504 Japan
AU: Uchida, J
EM: utty@es.sci.kumamoto-u.ac.jp
AF: Grad. Sch. Sci. and Tech., Kumamoto Univ., 2-39-1 Kurokami, Kumamoto, 860-8555 Japan
AU: Abe, K
EM: abekohei@arsia.geo.tsukuba.ac.jp
AF: Grad. Sch. Life and Environmental Sciences, the Univ. of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8572 Japan
AU: Hasegawa, S
EM: shiro@sci.kumamoto-u.ac.jp
AF: Grad. Sch. Sci. and Tech., Kumamoto Univ., 2-39-1 Kurokami, Kumamoto, 860-8555 Japan
AB: We reconstructed tsunami waveforms of the AD 1703 Kanto earthquake from deposits sampled along Tokyo Bay. The tsunami deposit, identified in nine orientation-controlled cores, sampled with 30 cm wide Geoslicer, is about 60-70 cm thick and has the following characters indicating the very long wavelength and period of tsunami; 1) a cyclic succession of sand sheets, 2) mud drapes covering the sand sheets, and 3) repeated turnover of flow directions. At least six sand sheets, several to 15 cm thick and sometimes including gravels, separated by mud drapes comprise the tsunami deposit. Landward currents were reconstructed from sedimentary structures in many sand sheets. Each sand sheet shows a fining-upward sequence resulted from a waning high-density current. Mud drapes indicate the long stagnant stages of muddy water between the succeeding currents. Turnover of flow directions, landward and seaward, exhibited by imbrications of gravels in some sand sheets, shows a cycle of up-flows and return-flows. A cyclic succession of the sand sheets reflects the temporal change in physical conditions of tsunami waves. At least six major tsunami up-flows with long intervals are reconstructed from the succession. The tsunami amplitude was the largest for the second or third wave, because relatively coarse-grained and thick gravelly sand sheets are intercalated in the center of the tsunami deposit. A fining- and thinning-upward trend of sand sheets in the upper trace of the tsunami deposit indicates the waning stage of the tsunami. The reconstructed tsunami waveform share the common features with the 1923 Kanto Tsunami recorded on a tide gauge, such as extremely long period and largest amplitude in its middle part. A similar reconstruction of tsunami waveform may be possible for other types of tsunami deposits, such as mud-rich or clast-rich types (Kon_fno ed., 1961; Fujiwara et al., 2003; Tuttle et al., 2004). Synthesis of data from various depositional sites would be necessary, because the preservation of tsunami deposits is limited by physical conditions of depositional sites, such as insufficient sediment supply or erosion by succeeding waves.
DE: 1744 Tectonophysics
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 7221 Paleoseismology (8036)
SC: Tectonophysics [T]
MN: Fall Meeting 2005