It was centered in the Central Virginia Seismic Zone. "The Applachians were once bigger than the Rocky Mountains, and they've worn down over time, and we do still see seismic activity going up into Canada," said Grant. But the last quake of this size in that zone was most likely in 1875. In December 2003, a magnitude 4.5 earthquake in that zone produced minor damage.
According to convertalot.com, a web site that compiles measurements and calculators for a variety of statistics, the magnitude 5.8 earthquake released energy equivalent to the explosion of 10,676 tons of TNT.
Amanda Reidelbach, office manager and spokeswoman for the Louisa County Department of Emergency Services in Mineral, Va., said that the town has felt "at least a half dozen or so" aftershocks since the initial quake struck.
"There were pretty serious aftershocks," she said. "We walked out onto the street and felt the ground just rumbling."
There have been reports of structural damage to some residences in town, Reidelbach says, but no reports of significant injuries. Mandatory evacuations were put in place shortly after the quake with all non-essential government and county personnel were sent home for the day. Schools were also closed.
The epicenter of the quake is very close to two Dominion Power nuclear power plants, North Anna 1 and 2.
Elizabeth Stuckle, spokesperson for the Nuclear Regulatory Commission, said that the reactors were "automatically and safely shut down." The plant declared an "unusual event" which is the lowest category of four emergency classifications. Back-up generators automatically kicked in to keep the reactors cool, the NRC said.
Nine other nuclear plants on the East Coast declared an "unusual event," but were none shut down.
The tremblor affected travel in the region.
Amtrak said it was running at reduced speed and was checking tracks and terminals for damage. The Washington Metropolitan Area Transit Authority said the Metro is moving at 15 mph as inspectors check all tracks.
Flights at Dulles International Airport in Virginia, JFK International in New York and in Philadelphia were temporarily halted. Control towers at JFK and Newark International airports were temporarily evacuated. The delay will cause slow air traffic throughout the region, the Federal Aviation Administration warned. In addition, about a dozen flights were diverted from JFK to Boston.
A woman who works at Mineral Barber Shop in Mineral, Va. said that the inside of her shop is a mess but there doesn't appear to be any major damage outside the town square.
In Richmond, Va., a woman who works on the 18th floor of a 20 story building said she and her co-workers left the building when the shaking first began.
"At first I thought it was someone jumping on floor above me, but then it was really loud and shaky," she said.
People in The New York Times building on 42nd street in Manhattan said they felt the entire building shift, and watched office furniture move. As the tall buildings in New York swayed, people ran out into the street.
The New York City Criminal Court in lower Manhattan was also evacuated.
In Baltimore, artist Lisa Lewenz was working in her basement studio when she began to feel movement under her feet.