HR: 1340h
AN: S13A-1048    [Abstracts]
TI: Spatial Distribution and Sedimentary Facies of the 2007 Solomon Islands Tsunami Deposits
AU: * Nakamura, Y
EM: nyugo@mail.sci.hokudai.ac.jp
AF: Institute of Seismology and Volcanology, Hokkaido University, N10W8, Kita-ku, Sapporo, 060-0810, Japan
AU: Nishimura, Y
EM: yns@mail.sci.hokudai.ac.jp
AF: Institute of Seismology and Volcanology, Hokkaido University, N10W8, Kita-ku, Sapporo, 060-0810, Japan
AU: Woodward, S
EM: smwoodwa@kent.edu
AF: Department of Geology, Kent State University, 221 McGilvrey Hall, Lincoln And Summit Streets, Kent, OH 44242, United States
AB: We conducted a field survey of the extent of damage, crustal deformation, and onshore deposits caused by 2007 Solomon Islands tsunami in Ghizo and adjacent islands in the western Solomon Islands, from 13th to 18th April, 2007. Our survey team was comprised of six Japanese and one American researcher. Three of us, the authors, mainly investigated tsunami deposits in three villages (Titiana, Suva, and Pailongge) in southern Ghizo Island. One member of our team re-investigated the deposits in June 2007. The tsunami generated sheet-like deposits of coral beach sand on the flat plain in Titiana. Beside the sea coast, the tsunami wave eroded ground surfaces and formed small scarps at 30 m from the sea. Just interior of the scarps, tsunami deposits accumulated up to 9 cm in thickness. The thickness decreased with distance from the sea and was also affected by microtopography. No sandy tsunami deposits were observed on the inland area between 170 m and 210 m from the sea. The upper boundary of inundation was recognized at about 210 m from the sea because of accumulation of driftwood and floating debris. In Suva and Pailongge, the outline of sand-sheet distribution is the same as it in Titiana. The tsunami had a maximum thickness of 10 cm and two or three sand layers are separated by thin humic sand layers. These humic layers were likely supplied from hillslopes eroded by the tsunami and transported by return-flows. These successions of deposits suggest that tsunami waves inundated at least two times. This is consistent with the number of large waves told by eyewitnesses. In the Solomon Islands, the plentiful rainfall causes erosion and resedimentation of tsunami deposits. Furthermore, the sedimentary structures will be destroyed by chemical weathering in warm and moist environment, and bioturbation by plants, animals, and human activities. The sedimentary structures had been preserved till the end of June 2007, but had already been penetrated by plant roots and sandpipes of crabs. We believe that the knowledge of weathering process of tsunami deposits is important for interpretation of sedimentary structures of paleo-tsunami deposits.
DE: 4564 Tsunamis and storm surges
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: 2007 Fall Meeting