Lessons learnt from the Indian Ocean Tsunami 2004: the role of surface and subsurface topography in deep water tsunami propagation

Abstract:

The Indian Ocean experienced its most devastating natural disaster through the action of a Tsunami, resulting from of an earthquake off the coast of Sumatra on 26^th of December 2004. This resulted in widespread damage both to property and human lives with over 250,000 deaths in the region and many millions homeless. Our understanding of tsunami generation and propagation has increased significantly over the past decade. In this presentation, results obtained from detailed analysis of sea level data from Western Australia and Sri Lanka together with numerical modelling are presented to highlight the effects of topography both at the surface and subsurface. The major effects are due to wave reflection and refraction. Examples of wave reflection include: impacts on Malaysia/Thailand, Sri Lanka and Western Australia due to wave reflection from Sri Lanka, Maldives and Mascarene Ridge, respectively. In the case of Sri Lanka, the maximum wave height recorded along the west coast during the 2004 tsunami was due to the reflected wave from Maldives impacting 3 hours after the arrival of the initial waves. Similarly, along the West coast of Australia highest waves occurred 15 hours after the arrival of the first wave. Here, based on travel times, we postulate that the waves were reflected from the Mascarene Ridge and/or the island of Madagascar (Figure 1b). The conclusions based on observations were verified using numerical model simulations using the MOST and ComMIT models. Numerical modelling using the MOST model indicated the role of offshore susurface topography on tsunami propagation through wave wave refraction. Examples of wave refraction included the effects of deep water seamounts (Venin Meinesz) and plateaus (Wallaby, Cuvier and Exmouth) on tsunami propagation along the West Australian coast. The tsunami waves are first scattered by the Venin Meinesz seamounts and were then refracted by the Wallaby and Cuvier plateaus resulting in waves being deflected onto the coast.