Tsunami of 26 December 2004

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This tsunami, with its death toll of at least 225 000, was not only the most deadly since the eruption of Krakatau in 1883, but highly significant scientifically. The rupture occurred on the Sumatra subduction zone, where the Indian tectonic plate descends beneath the Eurasian plate, and which was believed to be locked or so slow-moving that rupture was highly unlikely. The occurrence has called attention to similar, potentially hazardous locations in the North Atlantic, Indian, and Pacific Oceans and the necessity for warning systems to cover those areas. Some estimates of the accompanying earthquake suggest that its magnitude was as high as 9.3, the largest since the Alaskan earthquake of 1964. The propagation of the waves across all the world's ocean basins was observed in detail by satellite instrumentation, generally confirming the accuracy of current computer simulations, but also revealing that wave-heights and travel distances were greatest along mid-ocean ridges. The extremely high waves (exceeding 30 m in northern Sumatra) were produced by displacement of the sea-floor by as much as 8 m in places, extending for 1 200 km along the plate boundary. The rupture occurred beneath deep water, and the fault continued to slip after the initial seismic event, increasing the amount of water displaced and the consequent size of the waves. A magnitude-8.7 shock farther south on the same fault on 28 March 2005 which occurred below shallow water produced much smaller (although still destructive) waves with a run-up of c.4 m.

Subjects: Meteorology and Climatology.

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