Magnitude 5.8 Quake Rattles East Coast

by |August 23, 2011
The magnitude 5.8 quake was felt from Boston to South Carolina. Credit: Won-Young Kim, Lamont-Doherty Earth Observatory.

The magnitude 5.8 quake was felt from Boston to South Carolina. Credit: Won-Young Kim, Lamont-Doherty Earth Observatory. (click to enlarge)

The magnitude 5.8 earthquake that shook central Virginia on Tuesday afternoon is one of the biggest earthquakes to hit the East Coast since 1897, and was comparable in strength to a quake on the New York-Canadian border in 1944, according to the U.S. Geological Survey. It was centered near Mineral, Va., about 38 miles northwest of Richmond, and in an area known for frequent though lesser quakes. Tremors were felt as far north as Ontario, Canada, and as far south as Alabama, but damage was minimal because the immediate area is not densely settled. The earthquake lasted only a few moments but vibrations were felt for up to 30 seconds. Meredith Nettles, a seismologist at Columbia’s Lamont-Doherty Earth Observatory, was in her second-floor office when the motion started. “I could see power cords in my office swaying,” she said. “That shaking is the waves from the earthquake passing through the ground right underneath you”

The earthquake was relatively shallow—3.7 miles below the surface—and occurred in the Piedmont plains, near ancient faults involved in creating the Appalachian Mountains some 250 million years ago. “It’s not a quiet area, but a 5.8 earthquake is unexpected,” said Lamont-Doherty seismologist Won-Young Kim, who analyzed earthquake sequences in this region in a 2005 study. Smaller earthquakes have been recorded in the so-called Central Virginia Seismic Zone but so far, none has formed a pattern suggesting that a single fault may be causing the tremors, says the U.S. Geological Survey. Seismologists, including Kim, are at the site now, positioning temporary seismometers that will record aftershocks and give them a clearer picture of the underlying rock.

The rigid rock that underlies the East Coast is able to transmit energy long distances, explaining why the tremors were felt so widely yet caused so  little damage. In Washington D.C., the White House, Capitol and national monuments on the Mall were evacuated; Amtrak stopped its trains and the highways filled with workers fleeing the city. Two towering landmarks–the Washington Monument and National Cathedral–were shut to the public after cracks were discovered at the top of the monument and in the main tower respectively.

A seismometer in Manhattan’s Central Park recorded the Virginia earthquake’s movement in three dimensions: the top trace (BHZ) shows vertical ground motion; the middle (BHN), north-south motion; the bottom (BHE), east-west motion. Time lapsed after the quake is measured in seconds. The first waves reached Central Park, 290 miles away, a minute after the quake while most shaking was felt two minutes later when the larger motions from the waves arrived.

A seismometer in Manhattan’s Central Park recorded the Virginia earthquake’s movement in three dimensions: the top trace (BHZ) shows vertical ground motion; the middle (BHN), north-south motion; the bottom (BHE), east-west motion. Time lapsed after the quake is measured in seconds. The first waves reached Central Park, 290 miles away, a minute after the quake while most shaking was felt two minutes later when the larger motions from the waves arrived. (click to enlarge)

The most recent large earthquake in New York City– a magnitude 5.3 in 1884–toppled chimneys and panicked swimmers at Coney Island. Starting in the 1970s, the Lamont seismic network has located hundreds of smaller earthquakes, including a magnitude 3 every few years. By locating the quakes, mapping their position and calculating the accumulation of stress, researchers estimate that quakes far more powerful than the 1884 New York City event are possible. Magnitude 6 quakes—10 times bigger–may take place about every 670 years. Those of magnitude 7—100 times greater—may strike every 3,400 years. A magnitude 7 earthquake could cost the New York region up to $197 billion, according to a 2003 analysis by The New York City Area Consortium for Earthquake Loss Mitigation.

“You could debate whether a magnitude 6 or 7 is possible, but we’ve already had three magnitude fives, so that is very realistic,” said Lamont-Doherty seismologist John Armbruster. “With only a partial 300-year history, we may not have seen everything we could see. There could be surprises—things bigger than we have ever seen.”

So, while a big earthquake in the New York area is relatively uncommon, it can happen and society should be prepared, seismologists say. “The location and timing of earthquakes in this region follow a pattern,” said Arthur Lerner-Lam, a seismologist and Lamont-Doherty’s Interim Director. “The Virginia event will teach us a lot about the potential damage from a New York metro-area quake, and we can use that knowledge to make our buildings and infrastructure more resilient. This is a wake-up call to take earthquake preparedness in the northeast more seriously. Let’s not turn over and go back to sleep.”

Update:

Lamont scientists have been talking to the media across the country about the Virginia earthquake. Here’s a listing of some of their appearances:

Expert explains what shook NYC — NY1 News – Aug. 23, 2011

Rare Earthquake Stuns East Coast — Wall Street Journal – Aug 23, 2011

East Coast quake prompts confusion, fear, humor — CBS TV – The Early Show – Aug. 24, 2011

More from CBS on the quake: CBS TV

A Rare Bustle in the Lab as Seismometers Quiver — New York Times – Aug. 25, 2011

Above all else, eastern quake rattles nerves — New York Times – Aug. 23, 2011

Earthquake 101 – WNYC’s Brian Lehrer Show — WNYC — Aug 24, 2011

For central Virginia’s seismic zone, quake is an event of rare magnitude — Washington Post – Aug. 23, 2011

Mark Levin syndicated radio show — WABC Radio – Aug. 23, 2011

East Coast Quake’s Shock Waves Felt Farther — Newsday – Aug. 23, 2011

New Yorkers Shake Off Quake — NY1 – Aug. 23-24, 2011

Fox News – Aug. 23, 2011

Christian Science Monitor – Aug. 25, 2011

East Coast Fault Lines: Virginia Earthquake highlights significant … — Slate Magazine – Aug 23, 2011

Pentagon Being Evacuated After Possible Earthquake Felt in DC Area — North Jersey – Aug 23, 2011

Yes, That was Just an Earthquake — NY Magazine – Aug 23, 2011

Earthquake Felt in New York City — DNAinfo – Aug 23, 2011

Pearl River Patch – Aug. 23, 2011

Lohud.com – Aug. 24, 2011

Albany Times-Union – Aug. 23, 2011


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