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Three earthquakes in three days. More than coincidence?

First came an earthquake in Colorado. Then Virginia's quake shook the US from South Carolina to New England. Finally, San Francisco had a rattler as well. Are they connected?

By Staff writer / August 24, 2011

Office workers gather on a sidewalk after their building was evacuated following an earthquake in New York on Tuesday. The 5.8 magnitude earthquake centered northwest of Richmond, Va., shook much of the east coast from Washington, D.C., to New York City and Rhode Island.

Mark Lennihan/AP

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Colorado, Virginia, California: three earthquakes across the United States in three days. Aside from the apocalyptic questions some are raising, was this more than an earth-trembling coincidence? Or was there some scientific connection between these three events?

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First there was the magnitude 5.3 earthquake near Trinidad, Colo., the largest earthquake in the state since 1973. Then a magnitude 5.8 quake centered in Mineral, Va., jarred a region from Charleston, S.C. to Boston. Finally, there was a relatively mild 3.6 rattler in the San Francisco area Tuesday night.

What’s going on here?

Experts say that while the Colorado and East Coast earthquakes were unusual, the first one did not trigger the second. Nor did the San Francisco quake have anything to do with the two that preceded it.

“They really are unrelated,” says Meredith Nettles, a seismologist at Columbia University. “There really is no causal connection.”

“This is pure coincidence,” concurs San Diego State University seismologist Tom Rockwell.

“That’s because small earthquakes don’t change the state of stress very much in the crust of the earth, so the effects will be only local,” he says.

While this week’s earthquakes made news – with earthquake tremors and hurricane Irene on the way, some people in North Carolina wondered if a plague of locusts was next – the earth’s shake-rattle-and-roll is going on all around us almost constantly.

In just the past week in the US alone, there were about 700 earthquakes perceptible to detection equipment. And as the US Geological Survey puts it, “there's a 100 percent chance of an earthquake today” somewhere in the world.

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