The 2004 and 1861 Tsunami Deposits on Simeulue Island, Western Sumatra

Katherine Frances Whitlow
November 2007


Megathrust earthquakes and associated tsunamis along the subduction zone along western Sumatra represent a significant seismic hazard that is not well understood. I present the results of mapping, paleoseimologic, and geochronologic studies of tsunami deposits exposed on Simeulue Island, western Sumatra, to document the timing of past tsunamis. Three field sites were targeted to conduct these studies: Inor, Busong Bay, and Langi Bay. Stratigraphic relationships, geochronologic data, and grain size analyses from these field sites show evidence of a tsunami that occurred in 1861 following a Mw ~8.5 earthquake. A wood fragment collected from an excavation at Inor yielded an age of 1640-1960 A.D. A coral boulder from an excavation at Busong Bay yielded an age of 1868±19 years. The 2004 tsunami deposit was also exposed in excavations at the three field sites. Identifying tsunami deposits and characterizing their stratigraphic and depositional settings will help to further understand tsunami inundation and preservation in the geologic record.

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