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Good Question: Why Are East Coast Quakes So Rare?

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(credit: CBS) Jason DeRusha
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MINNEAPOLIS (WCCO) – A 5.8 earthquake is mild by west coast standards, but on the east coast, it is weird stuff.

It’s the same situation with Colorado, which had a large earthquake on Monday. So, why are we seeing earthquakes in unusual places?

“This event is rare, but not unheard of,” said University of Minnesota Geophysicist Val Chandler, who takes the long view of earthquake history.

“There was an earthquake nearBostonin 1755 that was around 6,” he said. “In fact there was a 5.8 quake inNew Yorkabout 65 years ago.”

But since 1900, there have been 50 quakes of magnitude 5.8 or greater in California alone.

Last year there were 80 earthquakes in the U.S. stronger than a 5.0.

“Most are in the ‘Ring of Fire’ of the Pacific, where seduction zones or shear-like movement of the San Andreas fault,” he said.

The California coast is right by where the two tectonic plates that make the earth’s crust come together.

“It’s kind of a noisy earth, it chatters around,” said Chandler.

Virginia and the east coast is in the middle of a plate, so there’s no consistent crashing together.

Still there are faults everywhere. Some of them are leftovers from 500 million years ago when the Earth crashed around to create the Appalachian Mountains.

“All those processes form lots and lots of faults. Those old faults: their primary activity is done. But they remain as weakness zones,” saidChandler.

In fact, Chandler said he believes we’re not seeing a trend of earthquakes in unusual spots.

“It’s just been an unusual year,” he said.

Last year we had no major earthquakes outside of the usual west coast spots. We had two the past two days. The Colorado quake hit at midnight, though, far from population centers, so it didn’t make quite the splash that the one on the east coast did.

“Is there anywhere in the U.S.where you can’t get an earthquake?” asked WCCO reporter Jason DeRusha.

“There’s no place that’s absolutely safe. Minnesota is way down in the low end of risk, but if you head south, it’s even a little less likely to have an earthquake,” he said.

Minnesota did see an earthquake in April near Alexandria, a 2.5.  But the Virginia quake on Tuesday was approximately 89,000 times stronger than that one, according to the calculator on the United States Geological Survey web site.

The magnitude scale compares the height of waves on a seismograph, not the energy of the quake.

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