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Magnitude-7.8 earthquake strikes off Indonesia

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(CNN) -- A magnitude-7.8 earthquake struck Wednesday off the coast of Indonesia, the U.S. Geological Survey reported.

The quake was centered in the Indian Ocean about 410 miles (660 kilometers) southwest of Muara Siberut and roughly 500 miles west-southwest of Padang, which is on the west coast of Sumatra, the Asian archipelago nation's largest island.

The USGS indicated the earthquake struck 15 miles deep.

The Pacific Tsunami Warning Center, a U.S. government agency, tweeted about a "potential tsunami threat."

Australia's Bureau of Meteorology sounded a similar alarm, issuing a tsunami warning for the Cocos Islands, which are about 530 miles south-southeast of the quake's epicenter.

Large earthquakes are relatively common in and around Indonesia, which is part of the Ring of Fire, an arc of fault lines circling the Pacific Basin that is prone to frequent earthquakes and volcanic eruptions.

Two earthquakes, one a magnitude 7.1 and the other a 7.0, struck in November 2014.

More recently, on February 12 of this year, a magnitude-6.5 earthquake struck the Indonesian island of Pulau Sumba.

Neither of those did significant damage, though that's not always the case.

In December 2004, a magnitude-9.1 quake struck off the west coast of Northern Sumatra and the tsunamis it generated killed upwards of 225,000 people in India, Sri Lanka, Indonesia, Thailand, Malaysia, Somalia, Kenya, Tanzania and Bangladesh. That quake, which lasted between 500 and 600 seconds, released an amount of energy equal to a 100-gigaton bomb.

More than 1,300 people were killed three months later following an 8.7 earthquake and subsequent tsunami on the same fault line. Another quake, this one a 6.3, killed some 5,750 people in May 2006, and there have been a number of other deadly incidents since.

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