Holocene coastal evolution of southwest Thailand-implications for the site-specific preservation of palaeotsunami deposits

摘要

Summary. The reconstruction of tsunami recurrence in southwest Thailand, where the historical record is short, is predominantly based on sedimentary evidence of prehistoric events stored in coastal geo-archives. Since geological palaeotsunami records are dependent on the deposition and preservation of tsunami deposits, the existence of near-shore geoarchives suitable for preservation, which is primarily controlled by coastal evolution, has considerable influence on the length and completeness of local archives. Based on sediment drill cores this study reconstructs Holocene changes in palaeogeography for three coastal sections along the west coast of Thailand to evaluate the influence of coastal evolution on local tsunami records. The patterns of palaeotsunamis archived on Phra Thong Island (four events within the last 3,000 years) and at Ban Bang Sak (up to three events within the period 1,200-2,000 cal BP and another event at 500-700 cal BP) can be explained by the time windows provided by the evolution of favourable environments. At Pakarang Cape, instead, only one prehistoric tsunami at 1,000-1,200 cal BP is archived, although a back-reef lagoon, which proved to be a suitable environment for preservation, was persistent for several millennia.