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baltimoresun.com

East Coast earthquake, one year later

By Scott Dance

9:09 AM EDT, August 23, 2012

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A year ago, life paused for a minute in Baltimore and across a wide swath of the country as the ground shook beneath us. Buildings emptied, text messages flew and everyone asked each other, "Did you just feel that?"

The U.S. Geological Surveyconfirmed quickly it was a 5.8 magnitude earthquake 38 miles northwest of Richmond, Va. But there are still unkowns about the rare event, according to the USGS.

We have learned some significant things about the quake, though. It was among the largest on the East Coast and may have been felt by more people than any other earthquake in history, according to a USGS podcast looking back at the event.

This USGS map comparing the quake with one of a similar magnitude in California shows that while it may not have been as intense as some of the most severe West Coast earthquakes, it could be felt more widely. It helps explain why the quake may have been record setting for its reach -- it was felt in major cities including Chicago, Atlanta, Washington, Baltimore, New York Philadelphia, Pittsburgh and Boston.

Damage was significant across central Virginia near the epicenter, and in Washington, the National Cathedral and Washington Monument were damaged.

In Baltimore, signs of the quake remain. At the Basilica of the Assumption, the nation's oldest Catholic cathedral completed in 1821, crews began erecting scaffolding Monday. The restoration effort is expected to last until at least March, said Sean Caine, spokesman for the Archdiocese of Baltimore. Since the quake, about 60 significant cracks have been discovered in various parts of the basilica, he said.

The quake is the second strongest in Virginia history, and much stronger than Maryland's most severe. The record for Virginia is 5.9 magnitude, set in 1797, while Maryland's is a 3.4 magnitude from July 16, 2010.

Maryland is, of course, not a hotbed for seismic activity based on hazard maps and history, with only a handful of small quakes over the past 40 years. Nine earthquakes have been felt in the state since 2001, according to the Maryland Geological Survey.

Scientists are working to learn more about the forces involved in the quake, using data gathered a year ago and since then to build a model explaining the geologic structure that led to it. It's still unclear precisely what fault caused the quake.

"The trouble with eastern US earthquakes is they don't happen very often, and sometimes the faults on which they happen haven't had an earthquake for a very long time," Michael Blanpied, associate coordinator of the USGS's earthquake hazards program, said on the USGS podcast. "Our trick is to figure out which one of those faults -- one of those many, buried, not very well-understood faults -- had an earthquake on it, back in August."

Have a weather question? E-mail me at sdance@baltsun.com or tweet to @MdWeather.