High-frequency Coastal Overwash Deposits from Phra Thong Island, Thailand

Abstract

The 26th December 2004 Indian Ocean Tsunami (IOT) emanated from an Mw 9.2 earthquake that generated a 1600 km-long rupture along the Sumatran Megathrust and generated tsunami waves up to 30 m high. The IOT directly impacted the Bay of Bengal and east Africa, with over 283,000 people perishing. At the time, this catastrophic event was considered unprecedented and sparked intense investigations to test this claim. It is now believed that four pre-2004 IOT events have occurred in the last 2500 years, recurring every 550 to 700 years. Much of this information comes from Phra Thong Island, Thailand, where a sequence of four stacked sandsheets separated by organic units has been recognised and compared to the 2004 IOT event. Recently, ground-penetrating radar on Phra Thong Island identified a region that could not be explained by the known stratigraphy. The stratigraphy of the area was investigated from auger cores and pits, and several previously-unrecognised sandsheets were identified and compared to the known tsunami sandsheets. The proximity of the newly-recognised sandsheets to the palaeo-coastline of Phra Thong Island does not preclude the impacts of localised storms in sandsheet emplacement or that tsunamigenic earthquake recurrence may have been more frequent in the past.

Could tsunami risk be underestimated using core‐based reconstructions? Lessons from ground penetrating radar

“…Gouramanis et al . (, ) and Premasiri et al . () investigated the 2004 Indian Ocean tsunami deposits and possible predecessors using GPR in Thailand and Sri Lanka.…”

“…For example, wetlands are likely to preferentially preserve the sedimentary evidence of past tsunamis but may also blanket a palaeotopography that can confound the search for good evidence. In fact, based on their GPR survey results, Gouramanis et al (2017) discovered more sand sheets than had been previously recognized at Phra Thong Island, Thailand.…”

“…In fact, based on their GPR survey results, Gouramanis et al . () discovered more sand sheets than had been previously recognized at Phra Thong Island, Thailand.…”

“…Koster and Reicherter (2014) reconstructed the local palaeotopography in southern Spain by using GPR-acquired depth information of the base of palaeotsunami deposits. Gouramanis et al (2015Gouramanis et al ( , 2017 and Premasiri et al (2015) investigated the 2004 Indian Ocean tsunami deposits and possible predecessors using GPR in Thailand and Sri Lanka. GPR can also be used in palaeotsunami research to determine the most appropriate survey sites.…”

Archaeological evidence that a late 14th-century tsunami devastated the coast of northern Sumatra and redirected history

“…To the contrary, the great 2004 earthquake and tsunami could have been anticipated if paleotsunami and paleogeodetic research had occurred in the years before the disaster. Following the 2004 tsunami, a flurry of such research greatly changed what we know about the long-term history of tsunami in the eastern Indian Ocean ( 2 – 14 ). Discoveries of sand deposits in swales behind Thai and Acehnese beach ridges revealed the predecessor of the 2004 event most likely occurred between about 1300 and 1500 CE ( 5 , 9 ) ( Fig.…”