7.8 Indonesian Earthquake hits near Sumatra - April 7, 2010 - Triggers Tsunami Warnings

A major earthquake has shaken Indonesia's northwest island of Sumatra, prompting a brief tsunami warning and sending residents rushing for higher ground.

The U.S. Geological Survey says a 7.7 magnitude earthquake occurred at sea about 215 kilometers northwest of the Indonesian island of Sumatra.

The quake was felt throughout northern Sumatra and in Malaysia. Local news reports say that patients from some area hospitals were evacuated and that some residents fled to high ground in case of a tsunami. Electricity in some areas was cut off but so far no major damage has been reported.

The Indonesia Meteorology and Geophysics Agency issued a tsunami warning following the quake, but lifted it two hours later.

Susan Potter, a geophysicist with the U.S. Geological Survey, says because the earthquake originated deep below the surface of the earth, the chances of it producing a major tsunami are low.

"This earthquake occurred at approximately 31 kilometers. To be an extremely shallow earthquake, it would be around 10 kilometers or so," said Potter. "An extremely large earthquake above the magnitude eight that was an extremely shallow depth, around a depth of 10 kilometers, would be prime candidate for creating, I am not saying definitely a large tsunami, but perhaps a regional tsunami or a tsunami in general. So the deeper the earthquake occurs, the less likely it is to cause a large scale tsunami."

Earthquakes are common in this region. Indonesia is located on the Pacific Ocean's so-called Ring of Fire, where the continental plates meet. A 9.1 magnitude quake off Aceh in December 2004 triggered a tsunami that killed more than 200,000 people around the Indian Ocean.

Stephen Almsteier has been a development worker in Aceh for the last five years. He says he has felt hundreds of earthquakes in this region and that this last one, and the aftershocks that followed, were not that strong.

"Obviously after several years here we're kind of used to aftershocks. People react in a different way," said Almsteier. "Once I realized that the aftershock was over I didn't leave my room, but obviously enough people here are very traumatized and some people did leave their houses and rooms in the center of town."

The U.S. Geological Survey says earthquakes of magnitude 7 and above occur on average 17 times a year.

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