The U.S. Geological Survey said the quake registered magnitude 5.8. By West Coast standards, that is mild. But the East Coast is not accustomed to earthquakes at all, and this one unsettled some of the nation's biggest population centers.
In New York and Washington, people said their thoughts were of an explosion or terrorist attack. In some cases, workers in Washington mentioned the tremors in phone calls to colleagues in New York, and seconds later, the shaking reached there, too.
"We thought it was a bomb at first because everyone has 9/11 on the brain and that it's so close to September and the 10th anniversary," said Cathy McDonald, who works in an IRS office in downtown Washington.
Hundreds of people spilled out of the federal courthouse blocks from ground zero after the quake struck just before 2 p.m. EDT. Workers in the Empire State Building rushed into the streets, some having descended dozens of flights of stairs.
"I thought we'd been hit by an airplane," said one worker, Marty Wiesner.
Adrian Ollivierre, an accountant who was in his office on the 60th floor when the shaking began, said: "I thought I was having maybe a heart attack, and I saw everybody running. I think what it is, is the paranoia that happens from 9/11, and that's why I'm still out here -- because, I'm sorry, I'm not playing with my life."
The quake was felt as far north as Toronto, as far west as Indiana and Kentucky and as far south as Atlanta and Savannah, Ga. It was also felt on Martha's Vineyard off Massachusetts, where President Barack Obama, who is vacationing there, was getting ready to tee off in a round of golf.
The White House said there were no reports of major damage to the nation's infrastructure, including airports and nuclear facilities. Two nuclear reactors at the North Anna Power Station in Virginia were automatically taken off line by safety systems, said Roger Hannah, a spokesman for the U.S. Nuclear Regulatory Commission. The plant is in the same county as the quake's epicenter, about 80 miles southwest of Washington and 40 miles northwest of Richmond, Va.
The Park Service closed all monuments and memorials on the National Mall, and ceiling tiles fell at Reagan National Airport outside Washington. Many nonessential workers in Washington were sent home for the day. The Capitol was reopened by late afternoon for people to retrieve their things.
At the Pentagon, a low rumbling built until the building itself was shaking, and people ran into the corridors of the complex. The shaking continued, to shouts of "Evacuate! Evacuate!" The main damage to the building, the largest single workspace for the federal government, came from a broken water pipe.
The National Cathedral said it had sustained "significant damage," with three capstones, each shaped like a fleur-de-lis, breaking off the main tower. Cracks appeared in the flying buttresses around the apse at the cathedral's east end, the oldest part of the building.
"Everyone here is safe," the cathedral said on its official Twitter feed. "Please pray for the Cathedral as there has been some damage."
Around Mineral, Va., a small town close to the epicenter, people milled around in their lawns, on sidewalks and parking lots, still rattled and leery of re-entering buildings. All over town, masonry was crumpled, and there were stores with shelf contents strewn on the floor. Several display windows at businesses in the tiny heart of downtown were broken and lay in jagged shards.
Carmen Bonano, who has a 1-year-old granddaughter, sat on the porch of her family's white-frame house, its twin brick chimneys destroyed. Her voice still quavered with fear.
"The fridge came down off the wall and things started falling. I just pushed the refrigerator out of the way, grabbed the baby and ran," she said.
By the standards of the West Coast, where earthquakes are much more common, the Virginia quake was not strong. Since 1900, there have been 50 quakes of magnitude 5.8 or greater in California alone. Quakes in the East tend to be felt across a much broader area.
"The waves are able to reverberate and travel pretty happily out for miles," said USGS seismologist Susan Hough.
The Geological Survey put the quake in its yellow alert category, meaning there was potential for local damage but relatively little economic damage.
The agency said the quake was 3.7 miles beneath the surface, but scientists said they may never be able to map the exact fault. Aftershocks may help to outline it, said Rowena Lohman, a seismologist at Cornell University. There have been a few aftershocks. Two were magnitudes 2.2 and 2.8 but a later one measured 4.8.
The last quake of equal power to strike the East Coast was in New York in 1944. The largest East Coast quake on record was a 7.3 that hit South Carolina in 1886. In 1897, a magnitude-5.9 quake was recorded at Giles County, Va., the largest on record in that state.
A 5.8-magnitude quake releases as much energy as almost eight kilotons of TNT, about half the power of the atomic bomb dropped on Hiroshima, Japan. The earthquake that devastated Japan earlier this year released more than 60,000 times as much energy as Tuesday's.
The Virginia quake came a day after an earthquake in Colorado toppled groceries off shelves and caused minor damage to homes in the southern part of the state and in northern New Mexico. No injuries were reported as aftershocks continued Tuesday.
For the most part, the East Coast quake was a curiosity, at least after the initial fear faded away. It disrupted what was, for millions of people, an ordinary workday.
In New York, the police commissioner, Raymond Kelly, was in a meeting with top deputies planning security for the upcoming anniversary when the shaking started. The district attorney, Cyrus R. Vance, was starting a news conference about the dismissal of the sexual assault case against Dominique Strauss-Kahn, the former head of the International Monetary Fund. Reporters and aides began rushing out the door until it became clear it was subsiding.
On Wall Street, the floor of the New York Stock Exchange did not shake, officials said, but the Dow Jones industrial average sank 60 points soon after the quake struck. The Dow began rising again a half-hour later and finished the day up 322 points.
Amtrak said its trains along the Northeast Corridor between Baltimore and Washington were at reduced speeds and crews were inspecting stations and railroad infrastructure before returning to normal.
In Charleston, W.Va., hundreds of workers left the state Capitol building and employees at other downtown office buildings were asked to leave temporarily.
"The whole building shook," said Jennifer Bundy, a spokeswoman for the state Supreme Court. "You could feel two different shakes. Everybody just kind of came out on their own."
In Ohio, office buildings swayed in Columbus and Cincinnati. The press box at Progressive Field, home of the Cleveland Indians, shook, as did the stadium at the consolation game of the Little League World Series in South Williamsport, Pa.
John Gurlach, air traffic controller at the Morgantown Municipal Airport in West Virginia, was in a 40-foot-tall tower when the earth trembled.
"There were two of us looking at each other saying, `What's that?"' he said, even as a commuter plane was landing. "It was noticeably shaking. It felt like a B-52 unloading."
Immediately, the phone rang from the nearest airport in Clarksburg, and a computer began spitting out green strips of paper -- alerts from other airports in New York and Washington issuing ground stops "due to earthquake."
The earthquake caused a stir online, where people posted to Facebook and Twitter within seconds and described what they had felt. The keywords in posts, or hashtags, included "DCquake," "VAquake" and "Columbusquake," an indication of how broadly the quake was experienced.
Quake photos and videos also made the rounds. A handful were authentic. Many more were not -- they were favorite earthquake scenes from Hollywood blockbusters or footage of people shaking their glasses and plates at an Olive Garden.
On the West Coast, where the last major quake to strike a metro area was a magnitude-6.7 event that ravaged greater Los Angeles in 1994, what happened back East was cause for outright mockery.
"Californians yawn, shrug and go back to their iced lattes," Marcus Beer, who reviews video games for a local news broadcaster, said in a Twitter post.