Indian Ocean tsunami recurrence from optical dating of tsunami sand sheets in Thailand

Abstract

Sand sheets deposited by the 2004 Indian Ocean tsunami and three Holocene tsunami predecessors in western Thailand have been dated by optically stimulated luminescence (OSL). Ages from the modern Indian Ocean tsunami sand sheet allow an assessment of the suitability of OSL to date tsunami-deposited sediment in tropical beach-ridge plain depositional environments. They show that, provided appropriate precautions are taken to correct for incomplete bleaching of sediments, OSL can provide a robust chronology of tsunami recurrence. Ages from the tsunami-deposited sand sheets underlying the 2004 tsunami deposits provide a chronology of the largest tsunamis in western Thailand over the late Holocene. Three sand sheets, likely deposited by tsunamis of similar magnitude to the 2004 event, were dated by luminescence to 380±50, 990±130–1410±190, and 2100±260years before AD 1950 (at 1-sigma precision). The youngest of these compares with previous radiocarbon ages of detrital bark high in buried soils (Jankaew et al., 2008), which suggest that the most recent large-scale predecessor to the 2004 tsunami occurred soon after 550–700cal BP. The OSL ages from the lower two sand sheets, provide constraint on tsunami recurrence that was not previously available from radiocarbon dating. The ages imply that between 350 and 1100years separate successive tsunamis on the Andaman coast of Thailand, with an average tsunami recurrence interval of around 550years. These results contribute to the growing body of research on tsunami recurrence in the Indian Ocean region and show that OSL can provide independent estimates of tsunami recurrence for hazard analysis, particularly in areas where suitable material for radiocarbon dating is unavailable.