Paleotsunami History of Northwestern Aceh Province, Sumatra, Indonesia
Our multi-disciplinary project explores the paleotsunami record in northwestern Aceh Province, Sumatra. We are focusing on an extraordinary sedimentary deposit in a coastal limestone cave that contains a series of tsunami deposits separated by guano, and offer a nearly complete mid-Holocene record of tsunamis. Our investigations will be incorporated into tsunami hazard modelling and risk assessment along the western Sumatra coast.
Our studies are motivated by our paleoseismic investigations of coastal wetlands of northwestern Aceh Province (see map below). Here we have documented a record of abrupt sea-level changes due to coseismic subsidence accompanied by tsunami inundation [Dura et al., 2011 and Grand Pre et al., 2012]. These prior studies suggest that evidence for abrupt sea level change is only preserved in conditions of long term rising sea level. They found evidence for three tsunamigenic earthquakes occurred during conditions of sea level rise between 4500 and 7000 years ago with an average recurrence of approximately 1000 years.
Detailed investigations of lithology and micro- and macrofossil assemblages suggest a lack of stratigraphic preservation of subsidence in the late Holocene (4500 years to present) because of the net emergence of the coast of northwest Sumatra [Dura et al., 2011; Kelsey et al., 2011; Horton et al., 2005]. Our work in northwestern Aceh Province targets depocenters, such as coastal caves, as a promising alternative approach for constructing a complete Holocene paleoseimic record for the Aceh portion of the Sunda subduction zone, and has demonstrated the remarkably high preservation of tsunamigenic sand deposits within the relatively sheltered cave interior.