Magnitude 5.8 Quake Rattles East Coast

August 24, 2011
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 after-shocks and give them a clearer picture of the underlying rock.

 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 may be rare, it can happen and society needs to be prepared. "The location and timing of earthquakes in this region follow a pattern," said seismologist  Arthur Lerner-Lam , interim director of Lamont-Doherty. "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.”



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