Thin-bed Ground-penetrating radar analysis of preserved modern and palaeotsunami deposits from Phra Thong Island, Thailand

Ground-penetrating radar (GPR) is a well-established technique for investigating the sub-surface stratigraphy in sandy coastal environments. GPR is most commonly applied in sandy coastal settings to determine the environmental evolution of an area. Several studies have used GPR to investigate the impact of storms through the identification of erosional scarps and very few have used GPR to investigate coastal overwash deposits. Here we present GPR profiles collected from a swale near the west coast of Phra Thong Island, Thailand, a key site where the 2004 Indian Ocean Tsunami and three earlier tsunamis deposited 5 to 20 cm thick, sandy deposits that are easily distinguished by intervening organic mud layers. We utilised 100, 500 and 1000 MHz antennas to image the spatial continuity of the sand-mud interface. The 100 MHz antennas demarcate the contact between the swale and underlying beach ridge stratigraphy, whereas the 1000 MHz antennas were poor at resolving the swale's internal stratigraphy. The 500 MHz antennas resolved the tsunami sand-organic mud contacts as evidenced from auger cores collected along the profiles. The 500 MHz profiles show where the 2004 tsunami partially scoured the back of the beach ridge and deposited sands over the back-beach environment. Our results confirm the utility of GPR to characterise sandy overwash deposits in muddy environments, which has applications for a range of coastal and fluvial settings around the globe.