By Devin Powell
One of the most seismically shaky places on the planet got rattled again on April 11, when a magnitude 8.6 earthquake struck near the Indonesian island of Sumatra. A massive aftershock, magnitude 8.2, followed two hours later.
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The quake’s epicenter was located about 400 kilometers off the island’s west coast, near — but not on — the boundary where the piece of Earth’s crust that underlies Sumatra and parts of southeast Asia rubs against the plate beneath Australia. Vibrations detected around the world suggest the quake occurred at a depth of about 22 kilometers, though this number may change after further analysis.
“We know that this was a big, shallow earthquake,” says Don Blakeman, a geophysicist with the U.S. Geological Survey’s National Earthquake Information Center in Golden, Colorado. “We know that it was felt in mainland India.”