In 1886 a major earthquake in Charleston, South Carolina killed 60 people. Image: USGS.
NEW YORK CITY — The magnitude 5.8 quake that struck central Virginia today was unusual for the area. But parts of the eastern seaboard still face a high risk of earthquake damage and casualties, in some cases higher than that of cities on the west coast.
Though the rest of the country experiences far fewer moderate or large quakes than the Pacific Coast, which sits directly on an active tectonic plate boundary, when things like population density, building codes and preparedness are taken into account, the potential for disaster in the eastern U.S. is high. In some cases higher than cities like San Francisco.
“It’s important to think about how many people are in buildings, what kind of buildings they are, and what kind of soil they sit on,” said civil engineer Rachel Davidson of the University of Delaware’s Disaster Research Center. “These can all have a big effect from one block to the next.”
To better assess earthquake risk, Davidson helped create a simple and understandable gauge for major cities, called the Earthquake Disaster Risk Index in 1997. The basic idea is to illustrate how some regions with a lower chance of earthquake activity can face a greater overall risk of earthquake damage and casualties.
The results can be surprising. Despite Boston’s relatively low chance of a major earthquake occurring, for example, that city has a greater risk of disaster from quakes than San Francisco. Boston scored a 39, while San Francisco scored a 37 (the higher the number, the greater the risk).
While Davidson’s index isn’t used officially, she said the core idea has gained traction. One doesn’t need to look deep into the past to understand why.
In January 2010, a 7.0-magnitude earthquake led to the loss of 230,000 lives in Haiti, a region with poor urban planning and building codes. By comparison, the 9.0-magnitude earthquake that struck off the east coast of Japan was 100 times more powerful but claimed 16,000 lives — 14 times less than Haiti, thanks to stricter building codes and better emergency preparedness.
In the United States, where 90 percent of residential buildings have wood frames, Davidson said just a few bolts into the foundation can mean the difference between an intact home and one that needs major repairs after a quake.
“It doesn’t have to be expensive to make a building earthquake-resistant,” she said. “A small earthquake can move a home 6 inches or a foot off its foundation. That can be incredibly expensive to fix.”
An intensity map of the Aug. 23, 2011 earthquake that struck Virginia. (USGS)
Today’s quake, which struck near Mineral, Virginia and originated a little more than a half mile down into the Earth, was not uncommon planet-wide. About 1,300 such earthquakes between magnitude 5.0 and 5.9 occur each year. The event wasn’t big enough to cause any major damage, but people felt it in an area ranging from South Carolina to Massachusetts to Ohio, and even into few Canadian territories. (Here at Condé Nast headquarters in Times Square, we felt side-to-side swaying for nearly 20 seconds.)
“We definitely felt it here in Delaware, and that’s really unusual. We’re not at a tectonic plate boundary, like in California,” Davidson said. “This is a reminder that big earthquakes can happen on the east coast and in the central U.S. It might be today, or tomorrow, or 100 years from now. But they will happen, so it makes sense to prepare.”
Major earthquakes have hit the eastern part of the country in the past. In 1811 and 1812, at least three massive earthquakes struck near New Madrid, Missouri. The largest is estimated to have been greater than magnitude 8 and caused violent, damaging shaking in an area 10 times larger than did the 1906 San Francisco earthquake. And in 1886, a magnitude 7.3 quake killed 60 people making it one of the 10 deadliest earthquakes in U.S. history.
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