The study on the frequency of past giant earthquakes in the Indian Ocean region shows that Sri Lanka, and much of the Indian Ocean, is affected by large tsunamis at highly variable intervals, from a few hundred to more than one thousand years.

The findings suggest that the accumulation of stress in the region could generate even larger tsunamis than the one that resulted from the 2004 magnitude-9.2 Sumatra earthquake.

Researchers from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science and the University of Peradeniya in Sri Lanka collected and analysed 22 sediment cores from Karagan Lagoon, Hambantota in southeastern Sri Lanka, to expand the historical record of giant earthquakes along the Sumatra-Andaman subduction zone, where the India-Australian plate and Eurasian plate meet.

Using sand deposited in the lagoon during the 2004 Indian Ocean tsunami and seven older paleo-tsunami deposits as proxies for large earthquakes in the region, the scientists reconstructed the timeline for mega-earthquakes along the Indian Ocean's plate boundary from Myanmar to Indonesia, assuming that the tsunamis were all generated by large earthquakes.

"In Sri Lanka, coastal lagoons were inundated by this tsunami and others that occurred over thousands of years," said Gregor Eberli, professor of Marine Geosciences and director of UM's CSL — Centre for Carbonate Research.

"These lagoons are ideal repositories for tsunami sand layers because after deposition, the tsunami sands were sealed with mud," said Eberli.

The December 26, 2004 magnitude-9.2 Sumatra earthquake resulted in a transoceanic tsunami, with wave heights up to 100 feet in some places, which impacted much of the Indian Ocean region, researchers said.

The resulting tsunami killed over 200,000 people in fourteen countries, including India, and inundated coastal communities.

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