More aftershocks may come from East Coast quake

WASHINGTON Fri Aug 26, 2011 4:00pm EDT

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WASHINGTON (Reuters) - Even as the East Coast faces a fresh natural disaster in Hurricane Irene, there could still be aftershocks from the 5.8 magnitude quake that shook the region Tuesday, a U.S. Geological Survey specialist said on Friday.

Associate Coordinator of the USGS Earthquake Hazards Program Michael Blanpied, who is also a seismologist, said Tuesday's quake was a close call.

"Had it landed right beneath an urban area, it really could have been quite dangerous," he said in a live, online chat hosted by the U.S. Department of the Interior. Blanpied said the quake was felt by the largest number of people of any in the country's history.

Despite its widespread impact, the quake caused no deaths.

Earthquakes strike every U.S. state, said Blanpied, but Tuesday's was the biggest event in the East in decades.

The East Coast falls in the middle of a massive tectonic plate whose fault-lined edges start at the West Coast's feared San Andreas and stretch east to the center of the Atlantic.

Only two earthquakes of 5.0 or more have struck in the Virginia part of this plate in 100 years, said Blanpied.

"In some cases, we don't even know the fault that caused the earthquake and that's the case with Tuesday's quake," he said.

"What we can do given that absence of knowledge is look at the rate at which earthquakes occur ... to say what the hazard is, and it's that information about safety that can give us the building code provisions to make safe structures."

The nation's capital was one of the places the quake was strongly felt. Damage included cracks in the Washington Monument that has forced its temporary closure.

A quake of 5.3 magnitude struck in Colorado the night before the East Coast temblor, also in an area where such seismic activity is relatively rare.

"We do know that earthquakes can 'talk' to each other," said Blanpied, but he added it was "probably just happenstance" that the Colorado and East Coast quakes occurred over a short period.

He added that aftershocks are manifestations of the 'talking' phenomenon, warning that aftershocks from Tuesday's quake could reach 5.0 but would become less likely and powerful with time.

"During an earthquake you generally have very little time to react," said Blanpied, suggesting the safest place to go is under a heavy piece of furniture.

"What you don't want to do is rush from inside the building to outside, because that's one of the least safe places, due to objects falling."

(Editing by Jerry Norton)

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