Reconstructions of the coastal impact of the 2004 Indian Ocean tsunami in the Khao Lak area, Thailand

Abstract

Khao Lak, SW Thailand was severely affected by the tsunami on 26 December 2004. Here we present reconstructions of its coastal impact in this area. These are based on (1) eyewitness reports alone and (2) eyewitness reports supported by videos and photos of the tsunami and the damage it caused, field measurements, and satellite imagery. On the basis of eyewitness reports, we estimated that the sea began retreating at 1000 local time (LT) and, based also on photos, that the tsunami arrived at 1026–1029 LT. On the basis of videos of the tsunami, we estimated an offshore wave direction of 083 ± 3° and on the basis of the paths by which eyewitnesses were carried, we estimated an onshore direction of 088 ± 6°. On the basis of videos, we calculated that the velocity of the wavefront on its final approach was 33 ± 4 km/h. We obtained tsunami heights of 7.3 ± 0.8 m (relative to ground level) on the basis of eyewitness reports and 8.0 ± 0.6 m (relative to mean sea level) on the basis of field and photographic data. On the basis of eyewitness reports and photos, we concluded that Khao Lak experienced at least two main waves with a period >40 min. From eyewitness reports and satellite imagery, we measured maximum inundation ≤0.5 km in the southern part of the area, which is confined by a steeply sloping hinterland, and ≤1.5 km in the more gently sloping northern part. Comparison between these reconstructions supports the reliability of eyewitness reports as a source of quantitative data, and comparison with the numerical simulation by Ioualalen et al. (2007) supports the validity of the simulation.