SciDev.Net

The 2004 Indian Ocean tsunami may not have been the first of its size

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[BANGKOK] A tsunami of a similar size to the 2004 Indian Ocean tsunami might have occurred in the same region around 600 years ago, according to two studies published in Nature last week (30 October).

The two international teams found sand sheets — layers of sandy sediment rushed inland and dropped by a tsunami — beneath the layers deposited in 2004 at research sites in Thailand's Phra Thong Island, 125 kilometers north of Phuket, and in Aceh, Indonesia.

The sheets travelled as far inland as the 2004 layers and are similar in thickness, suggesting tsunami events similar to that in 2004. Both studies identified a sand layer around 600 years old — which could represent the most recent tsunami prior to 2004.

"Based on the extent of the sand layers, similar sediment characteristics and the occurrence in both countries, we think that the tsunami that occurred 600 years ago was possibly similar to the tsunami in 2004," Katrin Monecke, a researcher at the US-based University of Pittsburgh and a team leader for the Aceh study, told SciDev.Net.

The longer the intervals between tsunami events, the more stress that can build up at the plate boundary — and the larger the earthquake will be. Six hundred years is relatively long for the region, says Monecke.

These new findings will help improve coastal planning, education and tsunami preparedness for the people along the shorelines, she says. "In order to prepare for a natural disaster, you have to know how often it occurs and how large it might be."

Kruawun Jankaew, a geologist from Chulalongkorn University and lead author of the Thailand study, told SciDev.Net, "We have to think about the best ways to deal with the disaster. Long-term education may give us a more sustainable solution, as the interval times of the disaster span are quite long."

Jankaew says education will help people to learn how to best help themselves, by reading natural signs such as the rapid recession of water before a tsunami, for example.

"Our recent findings are just the first step," says Monecke, adding that the researchers need to find similar layers on other shores around the Indian Ocean region to fully understand the tsunami hazard. 

Link to Monecke paper in Nature