HR: 0800h
AN: S31C-0567    [Abstracts]
TI: Discovery Of Pre-2004 Tsunami Deposits On Simeulue Island, Southern Aceh Province, Indonesia
AU: * Fujino, S
EM: shige-fujino@aist.go.jp
AF: Geological Survey of Japan, AIST, Central 7, 1-1-1, Higashi, Tsukuba, 305-8567, Japan
AU: Sieh, K
EM: sieh@gps.caltech.edu
AF: Tectonics Observatory, California Institute of Technology, MC 170-25 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Meltzner, A J
EM: meltzner@gps.caltech.edu
AF: Tectonics Observatory, California Institute of Technology, MC 170-25 1200 E. California Blvd., Pasadena, CA 91125, United States
AU: Yulianto, E
EM: ekoy001@yahoo.com
AF: Research Center for Geotechnology, LIPI, Kompleks LIPI Bld 70, Jl. Sangkuriang, Bandung, 40135, Indonesia
AU: Whitlow, K
EM: WhitlowK@cwu.EDU
AF: Department of Geological Sciences, Central Washington University, 400 E. University Way Bouillon 203, Ellensburg, WA 98926, United States
AU: Putra, A
AU: Satake, K
EM: kenji.satake@aist.go.jp
AF: Geological Survey of Japan, AIST, Central 7, 1-1-1, Higashi, Tsukuba, 305-8567, Japan
AB: Presumably, megathrust earthquakes and tsunamis occurred repeatedly along the Sunda megathrust before 2004 and 2005. To determine its past tsunami history, we conducted field surveys on Simeulue Island, which straddles the boundary of the 2004 and 2005 ruptures. Shallow excavations exposed paleo-tsunami deposits at two coastal lowland sites in southern Simeulue Island. The paleo-tsunami deposits at the Inor|Naibos and Busong Bay sites appear as laterally continuous sand layers in terrestrial sedimentary successions. Two paleo-tsunami layers exist at Busong Bay; the younger one is bounded by peat layers and the older one separates peat and underlying muddy sediment that was probably deposited in an inter-tidal or sub-tidal environment. Both tsunami deposits are rich in coral clasts. A fresh, uneroded coral boulder from the upper tsunami layer yielded a U/Th age that is consistent with emplacement in 1861, the year of an historical great (M`8.5) earthquake there. The lower tsunami layer may have been emplaced during an earlier uplift event around A.D. 1799, documented by an uplifted coral microatoll at the site. This interpretation is consistent with the sedimentary facies change from mud to peat across the lower tsunami layer, which probably represents an environmental change due to uplift. The single tsunami layer at the Inor|Naibos site demarcates a sedimentary facies change. As at Busong Bay, it is accompanied by coral boulders, which we think are likely to yield U/Th ages consistent with deposition contemporaneous with one of the layers at Busong Bay.
DE: 8100 TECTONOPHYSICS
SC: Seismology [S]
MN: 2007 Fall Meeting