Morphology of the Andaman outer shelf and upper slope of the Thai exclusive economic zone

Following the devastating 2004 tsunami that hit the southwestern coast of Thailand, the need for detailed bathymetric data of the Andaman Sea outer shelf became evident in order to better predict tsunami wave propagation and coastal impact. Bathymetric data and subbottom profiler records covering the outer shelf and upper slope of the Thai exclusive economic zone (EEZ) were collected onboard Thai RV Chakratong Tongyai in 2006 and 2007. The data cover an area of approximately 3000 km2 between 500 and 1600 m water depth. The soundings allowed generating a final bathymetric grid with 50 m grid cell spacing. The outer shelf is rather smooth and slightly inclined southward, while the upper slope is strongly dissected by gullies. Several previously unknown features are identified including mud-domes, pockmarks, three large plateaus surrounded by moats, gas-charged sediment on subbottom profiler records, and only few indications for small submarine landslides on the upper slope. The largest of these possibly translational submarine landslides involved 2.2 × 107 m3 of sediment. This slide would have generated a tsunami wave of less than 0.12 m wave height. Considering the entire data, there is no evidence that landslides have been the source of tsunami waves in recent geological time.

► We present a new detailed multibeam bathymetry and subbottom profilers.
► The Andaman Sea outer slope within Thai EEZ was investigated for the first time.
► The slope inclines westward and southward with gradient higher than 4° further north.
► Previously unknown features are identified such as mud-dome and plateaus.
► One location of translational submarine landslide is studied.