The Eastern United States experienced its biggest earthquake in decades Tuesday — a magnitude 5.8. The epicenter of the quake was about 40 miles northwest of Richmond, Va. What caused the quake is still a mystery.
RENEE MONTAGNE, Host: It's MORNING EDITION, from NPR News. I'm Renee Montagne.</s>DAVID GREENE, Host: And I'm David Greene, in for Steve Inskeep.</s>DAVID GREENE, Host: The eastern United States shook yesterday with a magnitude 5.8 earthquake. It rattled both buildings and nerves from North Carolina to Boston and beyond. We definitely felt the jolt here at NPR's headquarters in Washington, D.C.</s>RENEE MONTAGNE, Host: Well, here in California, where I am, we are used to earthquakes. But the East Coast is not. And thousands took to the Web to react to what was for many their first big quake.</s>RENEE MONTAGNE, Host: People shared photos of the aftermath, ranging from bricks that had fallen off buildings, to books displaced from shelves.</s>DAVID GREENE, Host: Large or small, some well-known D.C. landmarks are closed today after sustaining damage in the quake. There are cracks near the top of the Washington Monument. And on the other side of town, spires cracked and fell from the central tower of the National Cathedral. That's the highest point in the city.</s>DAVID GREENE, Host: The epicenter of the earthquake was about 40 miles northwest of Richmond, Virginia. And as NPR's Christopher Joyce tells us, it's not a region known for seismic shaking.</s>CHRISTOPHER JOYCE: There have been pretty big earthquakes in the East before. In South Carolina, there was a magnitude seven quake, many times bigger than yesterday's event. But that was in 1886.</s>CHRISTOPHER JOYCE: So when the geology building at Virginia's College of William and Mary started to shake yesterday, seven geology professors - they were having a meeting - were momentarily perplexed. Professor Christopher Bailey was there.</s>CHRISTOPHER BAILEY: There was a little bit of disbelief. I was actually watching a projector on the ceiling. And after about 10 seconds, you know, we're like this is a big earthquake.</s>CHRISTOPHER JOYCE: It took geologists 10 seconds to figure that out?</s>CHRISTOPHER BAILEY: Oh, yeah. We're slow in some ways.</s>CHRISTOPHER JOYCE: Turns out, 10 seconds was only about half the duration of the quake - clearly a serious event.</s>CHRISTOPHER BAILEY: And then we, of course, ran for our electronic devices to see what the web of seismometers has to tell us.</s>CHRISTOPHER JOYCE: What's it told you so far?</s>CHRISTOPHER BAILEY: Well, what we know right now is that this was really the largest earthquake that has been instrumented in Virginia and really much of the East Coast, really, in 50 years.</s>CHRISTOPHER JOYCE: The quake disrupted flight schedules at some airports and altered some train travel. The federal government evacuated some of its buildings in Washington, D.C.</s>CHRISTOPHER JOYCE: Among the more worrisome developments was at the North Anna nuclear power plant in Virginia, not far from the quake's epicenter. The two reactors there lost power from the electricity grid, but they shut down automatically. Diesel- powered generators kept cooling water flowing to the reactors as designed. The federal Nuclear Regulatory Commission reports no damage or release of radioactivity.</s>CHRISTOPHER JOYCE: What caused the quake is still a mystery. Bailey says he suspects the section of rock that moved may be the Spotsylvania Fault. It's not on the edge of our North American plate, where big quakes often happen. It's well inside the plate. But Bailey says it came to life in 2003, when there were two small quakes there.</s>CHRISTOPHER JOYCE: Whether it was that fault or another, Bailey thinks the area could be stressed, as the big tectonic plate that sits under the Atlantic Ocean pushes westward against our North American plate.</s>CHRISTOPHER BAILEY: So, in essence, we're re-breaking old faults, and we're doing it under, you know, stresses that do exist and are transmitted into the interior of plates.</s>CHRISTOPHER JOYCE: Another curious thing about this moderate earthquake was how far its effects extended, as far as New York and Boston, hundreds of miles away. John Vidale, a seismologist at the University of Washington, says that's because the rock underneath the East Coast is different from the seismically active West Coast.</s>JOHN VIDALE: The East Coast carries seismic waves better than the West Coast. You can think of the West Coast as sort of broken up by all the faults constantly moving, but the East Coast is actually relatively solid, and the waves don't get damped out as they travel.</s>CHRISTOPHER JOYCE: As one geologist put it, East Coast rock is old and cold - less active, but when it does move, you really feel it. Vidale says the chances of another quake from the same fault are unlikely.</s>JOHN VIDALE: Well, the rule of thumb is there's about a one in 10 chance of having a bigger earthquake after any earthquake. But there'll certainly be a lot of aftershocks. Almost every earthquake has hundreds of tiny aftershocks.</s>CHRISTOPHER JOYCE: In fact, there have been reports of some aftershocks, but they're very small, and as time passes, those are likely to diminish.</s>CHRISTOPHER JOYCE: Christopher Joyce, NPR News.