Earth plate breakup caused earthquake

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SALT LAKE CITY, Sept. 27 (UPI) -- A large earthquake in the Indian Ocean in April was part of a crustal plate breakup, a phenomenon not observed before, seismologists say.

The April 11 quake, felt from India to Australia and throughout South Asia and Southeast Asia, was caused by at least four undersea fault ruptures southwest of Sumatra, Indonesia, within a 2-minute, 40-second period, they said.

Writing in the journal Nature, scientists from the University of Utah and University of California, Santa Cruz, said the magnitude-8.7 quake, and an 8.2 quake 2 hours later, were part of the breakup of the Indian and Australian subplates along a yet-unclear boundary beneath the Indian Ocean west of Sumatra and southeast of India.

The breakup was part of a process that started roughly 50 million years ago and will go on for millions more, they said.

"We've never seen an earthquake like this," study co-author Keith Koper, a geophysics professor at the University of Utah, said. "This is part of the messy business of breaking up a plate. This is a geologic process. It will take millions of years to form a new plate boundary and, most likely, it will take thousands of similar large quakes for that to happen."

Seismic analysis shows the quakes "involve rupture of a very complex network of faults, for which we have no documented precedent in recorded seismic history," the researchers wrote in the Nature article.