A Probabilistic Assessment of Tsunami Hazard in the Indian Ocean

Brief description

The Indian Ocean Tsunami of December 26, 2004 made starkly evident the need for better information on tsunami hazard in the Indian Ocean. The tsunami threat faced by Indian Ocean countries consists of a complex mix of tsunami from local, regional and distant sources, whose effects at any particular location in the Indian Ocean are highly dependent on variations in sea floor shape between the source and affected coastlines, complicating tsunami disaster management and the design of tsunami warning systems for the Indian Ocean. In order to provide national governments in the Indian Ocean with the information they need to make informed decisions about tsunami mitigation measures, including development of a warning system, a comprehensive hazard and risk ass

In this presentation we discuss the results of this assessment. The study focused on tsunami caused by subduction zone earthquakes, because they are the most frequent source of large tsunami, and tsunami hazard is expressed as annual probability of a tsunami exceeding a given amplitude at a given offshore depth. Because so little is known about the recurrence rates of large megathrust earthquakes in the subduction zones bordering the Indian Ocean, it was decided to develop two hazard maps: a 'low-hazard' end member, based on only those earthquake sources of tsunami for which there is definite evidence, and a 'high-hazard' end member, based on all potential megathrust earthquake sources, including hypothetical ones for which there is no historical or geological evidence, that may affect Indian Ocean coastlines. The actual hazard lies somewhere between these two end members, and the difference between the low hazard and high hazard maps is a simple and effective way to express the uncertainty in the hazard assessment. This uncertainty reflects the lack of knowledge of tsunamigenic earthquake occurrence, and can only be reduced through a better understanding of earthquake and tsunami occurrence in the Indian Ocean.

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