5.8-magnitude earthquake rattles East Coast

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Updated: August 23, 2011, 9:31 PM

 
photoA U.S. Geological Survey shake map based on reports filed over the Internet shows the level of intensity from Tuesday's 5.8-magnitude earthquake. (Click image for a larger view.)

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photoA worker with Baltimore Gas and Electric walks past a square where workers wait for word to re-enter their office buildings after an earthquake was felt in Baltimore on Tuesday. Downtown office buildings were cleared and workers were waiting for clearance to re-enter.

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photoA maintenance worker looks for additional cracked windows in a building on Market Street in Philadelphia after an earthquake was felt Tuesday.

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How's it compare?

The largest earthquake in Washington's recent history was the Nisqually quake, which struck on Feb. 28, 2001, and had a reported magnitude of 6.8. The largest recent quake to hit Oregon were two 6.0-magnitude earthquakes that struck Sept. 21, 1993, near Klamath Falls, Ore.

USGS on geology of quake area

Most bedrock beneath central Virginia was assembled as continents collided to form a supercontinent about 500-300 million years ago, raising the Appalachian Mountains. Most of the rest of the bedrock formed when the supercontinent rifted apart about 200 million years ago to form what are now the northeastern U.S., the Atlantic Ocean, and Europe.

At well-studied plate boundaries like the San Andreas fault system in California, often scientists can determine the name of the specific fault that is responsible for an earthquake. In contrast, east of the Rocky Mountains this is rarely the case.

The Central Virginia seismic zone is far from the nearest plate boundaries, which are in the center of the Atlantic Ocean and in the Caribbean Sea. The seismic zone is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths.

Accordingly, few, if any, earthquakes in the seismic zone can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake. As in most other areas east of the Rockies, the best guide to earthquake hazards in the seismic zone is the earthquakes themselves.

-U.S. Geological Survey

MINERAL, Va. — Tens of millions of people from Georgia to Canada were jolted Tuesday by the strongest earthquake to strike the East Coast since World War II. Three weeks before the 10th anniversary of Sept. 11, office workers poured out of New York skyscrapers and the Pentagon, relieved it was nothing more sinister than an act of nature.

There were no known deaths or serious injuries, but cracks appeared in the Washington Monument and the National Cathedral, which had three capstones break off its tower. Windows shattered and grocery stores were wrecked in Virginia, where the quake was centered. The White House and Capitol were evacuated.

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.

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.