Reconstruction of the coastal impact of the Indian Ocean tsunami on December 26, 2004

Abstract:

The aim of this study is to reconstruct the coastal impact of the Indian Ocean tsunami on coastal areas of Thailand based on amateur videos. The purpose of such reconstructions is to provide quantitative data needed to verify computer simulations of tsunamis which are used to guide mitigation efforts during the critical time interval following a potentially tsunamigenic earthquake.

More than ten years have passed since the tsunami catastrophe in Thailand 2004, and there are almost no visible signs left from the damage it caused. Many of the buildings in Thailand were rebuilt precisely as they were before the catastrophe. This allowed us to use amateur videos made a decade ago, during the tsunami to estimate tsunami height, direction and velocity. We also made an analogue experiment in a lab at Stockholm University to examine how the tsunami was affected entering a narrow passage (e.g. a street).

The results of this study is an overview of tsunami height data and velocity. Our tsunami height results show an average and standard deviation of (6.8+/-0.1 m) and are remarkably uniform across the 100 km x 100 km study area although the height is increasing slightly on its way north. Tsunami velocity is also increasing on its way north while the velocity is decreasing on its way east. Based on these observations, which are unexpected because the velocity and height are more powerful in the northern parts which are further away from the epicentre than the southern parts of the study area, we interpret that this is a result of that the southern parts are shielded by the northern parts of Sumatra. Our analogue experiment showed that tsunami height and velocity are essentially unaffected by entering a narrow passage (e.g. a street) perpendicular to the beach. This indicates that measurements done in this environment are indeed reliable because it avoids the influence of back flow as the tsunami hits a barrier.