From: RICHARD A. KERR, Science
Published December 24, 2013 08:04 AM

Tsunami threat to Sumatra continues

A great offshore earthquake, like the one that killed hundreds of thousands when it struck off Indonesia's Sumatra coast in December 2004, would seem to offer a small measure of solace to survivors: The offshore tectonic fault that caused the temblor should require many centuries to recharge. Now, it appears such optimism is unwarranted. Three speakers here at the fall meeting of the American Geophysical Union earlier this month warned that the Indian Ocean coast of northern Sumatra could suffer another tsunami disaster in as few as 60 years.

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That sobering news came in three talks by paleoseismologists—researchers who literally dig up records of past earthquakes and tsunamis-associated with Nanyang Technological University's Earth Observatory of Singapore. Charles Rubin, Kerry Sieh, Jessica Pilarczyk, and their colleagues had been reading the millennia-long histories of past tsunamis in three kinds of geologic records and determining the age of each tsunami recorded there using radioactive carbon-14 dating.

The most novel record was found in a cave located 200 meters from the present-day coastline. Only the far-reaching inland surge of a tsunami can carry sand into this cave, where it can then be deposited layer by layer, tsunami by tsunami. Conveniently enough for the researchers, tsunami deposits in this cave are demarcated by dark layers of guano deposited between tsunamis by the cave’s resident bats. Other records were retrieved from tsunami deposits in coastal wetlands and exposed in eroding sea cliffs.

Taken together, the new records paint a disconcerting picture of highly erratic tsunami recurrence.

Fisherman photo via Shutterstock.

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