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‘Extraordinary’ East Coast Quake a Reminder of Seismic Threat in Most States

August 23, 2011 at 12:00 AM EDT
A 5.8-magnitude earthquake shook much of the East Coast Tuesday afternoon, including Washington, D.C., and New York City. Hari Sreenivasan discusses the temblor and the seismic threat across much of the country with David Applegate of the U.S. Geological Survey.
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JEFFREY BROWN: The Eastern Seaboard was jarred today by one of the strongest earthquakes ever recorded in the region. The U.S. Geological Survey estimated more than 12 million people felt the quake, but there were no serious injuries.

Hari Sreenivasan has our report.

HARI SREENIVASAN: The quake hit just before 2:00 p.m. with a magnitude of 5.8. Stationary cameras caught scenes of shaking from the White House to Martha’s Vineyard, Mass., where the president was vacationing.

The epicenter was in Mineral, Va., about 40 miles northwest of Richmond. The half-mile-deep quake was felt from Washington, D.C., through Baltimore, Philadelphia, north into New York City, west through Toronto, Canada, and Detroit, and in the South down through North Carolina and into Georgia.

In Washington, the Pentagon was evacuated for a time, as was the State Department. Office workers flooded downtown streets.

MAN: The floor started to shake. Now, everybody told me what they experienced on the top floor. They seen the chandeliers move. But when the floor started shaking, I couldn’t really stand. My friend, he kind of turns around, he says, wait a minute, I haven’t been drinking.

(LAUGHTER)

MAN: So, yes, I could barely stand. And I tried to just run to the top.

HARI SREENIVASAN: And in this age of terrorism, many initially thought the hand of man, not Mother Nature, was at work.

MAN: It started shaking a little bit more violently. And everyone stood up, walked into the hallway. We were trying to figure out what to do.

QUESTION: What did you think it was?

MAN: At first, I thought it was construction above me. And then I thought about the Metro below me. I thought maybe some sort of terrorist thing.

WOMAN: I didn’t make the connection between 9/11 being just a few weeks away and today. But I — my first thought was that it was potentially a terror attack. My building just shook too violently for it to be anything normal.

MAN: I was in my office. And I thought it was like a terrorist attack or something. And so I was pretty scared.

HARI SREENIVASAN: And even with Congress on recess, thousands of staffers still at work fled buildings on Capitol Hill.

BRUCE GOODMAN, felt earthquake: First, you heard the shaking and the stuff moving, and then you felt the ground shake a little bit. But then it just — everything just shifted all of a sudden, and just — you heard people just like screaming, get out, get out, get out the building.

GAIL LINES, felt earthquake: It isn’t a huge deal, except that my keys and my purse and my car are in there, and I’m out here.

HARI SREENIVASAN: Mobile communications networks were quickly overloaded, as millions called, texted, tweeted and overtaxed the airwaves.

There were some reports and pictures of isolated damage, including this collapsed wall on a building in Baltimore. Washington’s National Cathedral was cordoned off, and there was some damage apparent high atop its main tower. Structural engineers will evaluate the building this week.

Sam Lloyd is the dean of the cathedral.

SAMUEL LLOYD, Washington National Cathedral: Because this place is so important place to so many people, we need to look after it.

HARI SREENIVASAN: Nearing the end of Washington’s summer tourist season, many monuments up and down the Mall were closed.

Phoebe Saad was visiting from Egypt.

PHOEBE SAAD, visiting From Egypt: I thought at first it was because of the subway. Then it get in mind this was an earthquake. Yes, sometimes in Egypt, subway sometimes do something like that. So, it’s OK. It’s some shaking. It’s some small shaking. But it’s earthquake, an earthquake in America? Come on.

HARI SREENIVASAN: And on Capitol Hill, Jeff Jones was visiting with his family.

JEFF JONES, visiting Washington, D.C.: We were just sightseeing. We were on a tour bus and coming down to Capitol Hill here, and the whole bus just started shaking and vibrating as we were coming up to — we didn’t realize what it was until we got up to Capitol Hill. Everybody said there was an earthquake in Virginia and they are evacuating everything.

HARI SREENIVASAN: Nearer the epicenter, in central Virginia, the North Anna nuclear power station automatically shut down during the tremor. The 1,800-megawatt plant reported no damage.

And in Tysons Corner, Va., part of an apartment building fell and crushed adjacent cars. Elsewhere, two of the New York metro area’s three main airports were closed, but quickly reopened.

Mayor Michael Bloomberg of New York:

MICHAEL BLOOMBERG, (I) mayor of New York: Certainly, the phones weren’t, as you would say, ringing off the hooks. I think people realized what it was and went back into buildings after a period of time and word spread pretty quickly. The fact that there was no damage was comforting to a lot of people.

HARI SREENIVASAN: And it was the second significant earthquake in the last 24 hours in the U.S. A 5.3 temblor shook Colorado overnight, the strongest there in a century.

Back in Washington, even if it wasn’t the big one, it was one to remember and the strongest quake on the East Coast since 1886.

For more on the quake, we’re joined by David Applegate, associate director for natural hazards at the U.S. Geological Survey.

Thanks for being with us.

DR. DAVID APPLEGATE, U.S. Geological Survey: Sure thing.

HARI SREENIVASAN: First, tell us, what kind of quake was it?

DR. DAVID APPLEGATE: Well, this was — the shallow earthquake was what we call a reverse motion. So think of it like one part of a fault pushing up or thrusting over another part. So, we refer to that as a reverse or a thrusting motion.

HARI SREENIVASAN: Is that something that’s common in the Northeast? I’m used to some of these in Northern California, but I haven’t heard of this.

DR. DAVID APPLEGATE: Right.

It is in — this general region, this Central Virginia Seismic Zone, which is the area of this particular quake, we have seen a number of different types of motion. And that reflects the fact that what you’re looking at are very, very ancient faults for the most part.

You know, this is in many ways a reminder that the Eastern U.S., which currently is far from any plate boundary, where about 90 percent of earthquakes occur, on the plate boundaries, but in a much earlier era, this was the show. The Appalachians were built. The Atlantic Ocean opened up. And so there are quite a number of different fault structures that underlie us.

HARI SREENIVASAN: So help explain how is it that people so far and wide felt this. It seems that other types of quakes are almost contained in a smaller area. This was felt all the way into Canada and down into South Carolina?

DR. DAVID APPLEGATE: Yes, it’s quite extraordinary. And that’s a very typical feature of earthquakes in the Central and Eastern U.S.

For example, we had an earthquake a couple of years ago right on the Illinois/Indiana border. It was about a 5.2 earthquake. That was felt over 16 states and well into Canada, over a much brooder area than we would see for a similar-sized earthquake in California.

Out in California or in Alaska or where the — the Earth’s plates are grinding against each other, the rock is much more broken up. Here, we have very stable continental crust. It’s old crust. It’s cold. It transmits the energy very well over long distances. So that’s one key factor.

The other one is that I mentioned that at one time the Appalachians were the show, but it’s been a long time. So its — they have been eroding for millions and millions of years. That’s built up thick piles of sediments. And the sediments amplify it is shaking. So you have all these cities and the large population that’s on areas of amplified shaking. So that’s why you feel what is a moderate-sized earthquake over a very broad area.

HARI SREENIVASAN: I think the question that’s coming across Twitter and comment boards is, is this the main attraction or have we — are we kind of building up to something bigger?

DR. DAVID APPLEGATE: Well, if we look at it from a historical perspective, you know, this is a reminder that you can have earthquakes pretty much anywhere in the U.S. This is a national hazard. We have had — we have a moderate to high seismic risk in 39 out of the 50 states.

And in this case — but if we look back at, for example, Charleston, S.C., in 1886 had a magnitude-7 earthquake. These events can happen, but they do appear to be fairly isolated. So it’s not that we — we would expect aftershocks. We always get these after an earthquake, smaller earthquakes that will decay with time in terms of their frequency.

So we wouldn’t be surprised to see additional quakes, magnitude-4, magnitude-3. There’s even a small probability that we could have an earthquake that’s the same size or bigger. But there’s nothing historically that would lead us to say that it is likely that this is leading to something bigger in this area.

HARI SREENIVASAN: What kind of — what has to happen geologically for that to occur?

DR. DAVID APPLEGATE: Well, in these areas that are far from where we have active plate deformation, in other words, where we can see the plates moving against one another — when a fault breaks, it’s essentially accommodating that slip — here, we’re looking at very distant stresses that build up over long periods of time.

So they’re going to get released, but it’s not going to be occurring on a rapid time scale. To a human time scale, I mean, the last earthquake we had had of this — roughly this size in Virginia was back in, I believe, 1897 out in Giles County in western Virginia.

And in this particular zone, the biggest quake had been a 4.8. So in our — in our human time frame, we’re not seeing a rapid release or sequence of events. That’s very different than on plate boundaries. For example, in Turkey, we have seen the North Anatolian Fault Zone, which is very similar to the San Andreas, where you get large earthquakes. They’re building up the stress in the next area. You see a sequence of earthquakes occurring.

HARI SREENIVASAN: So I have got to ask. You felt this in Virginia. As a geologist or a seismologist, what goes through your mind?

DR. DAVID APPLEGATE: Well, I was up on seventh floor of the USGS headquarters building out near Dulles Airport, just outside of Washington, D.C.

And on the first rumble, you’re thinking about different causes. But as it keeps going and you’re feeling that rolling motion, you pretty quickly know what it is. And I dutifully dropped, covered and held on. I got under a solid desk, since I wasn’t too concerned that the building was going to be coming down, but it’s really the non-structural damage. It’s the fact that light fixture could fall. You can have books, bookcases, that sort of thing.

HARI SREENIVASAN: And, finally, help put this in perspective for folks in just a few seconds that we have remaining here. For people who might not have been there to feel a Japan or a Haiti, how much more powerful were those?

DR. DAVID APPLEGATE: The Haiti earthquake was a magnitude 7, so it’s roughly sort of 10 to 15 times larger in terms of the magnitude.

But what’s really key here is the amount of energy released. So, for each order of magnitude, you’re looking at 33 times greater energy. The Japan earthquake was 1,000 times more energy than that Haiti earthquake, but it’s about 33,000 to 50,000 times more energy released than this one.

And so that’s what makes it truly amazing to have it felt over such a broad area, and a reminder that there is a potential for large earthquakes. We have had them in the Eastern U.S. We certainly have had them in the Central U.S. And they can have a big impact.

HARI SREENIVASAN: All right, David Applegate from the USGS, thanks so much for joining us.

DR. DAVID APPLEGATE: Sure thing.