Earthquake risks in the greater New York City area are reassessed in a major study released today by a team of seismologists based at Columbia University's Lamont-Doherty Earth Observatory, Palisades, N.Y. Though the report reaffirms that large earthquakes are relatively rare in New York, it finds that fault patterns are more complex than previously appreciated. In particular, two fault systems are found to converge very close to the controversial Indian Point nuclear power plant, 24 miles north of the city.
The authors of the study catalogued 383 earthquakes from 1677 to 2007, and, in those three-plus centuries, identified three magnitude 5 quakes capable of causing serious damage. They estimate that a potentially catastrophic category 6 quake might occur every 370 years, and a category 7 every 3,400 years. Though those probabilities are relatively low, the damage risk from a New York City earthquake is still very high because of the city's concentration of people and physical infrastructure, observes Lynn Sykes, the very eminent seismologist who led the study.
A previously known geologic feature, the Ramapo Seismic Zone, runs from eastern Pennsylvania to the Hudson Valley, passing within a couple of miles of Indian Point, with roughly parallel fault lines to the south, as far down as Harlem. Now, in addition, the study has identified a second fault line that originates to the east near Stamford, Connecticut, and intersects with the Ramapo zone, passing within a mile of Indian Point. Thus, "Indian Point is situated at the intersection of the two most striking linear features marking seismicity," says the paper. "This is clearly one of the least favorable sites in our study area from an earthquake hazard and risk perspective."
In hindsight, even without the new discovery, it's scarcely imaginable that a nuclear power plant would be sited today at Indian Point, if the decision were to be made again. It's bad enough that the reactor is at the edge of a metropolitan area with 25 million people, and directly upriver of the city, so that if there were a reactor meltdown, the whole harbor estuary would be permanently contaminated. But the issue of whether to keep recommissioning Indian Point will nonetheless be a difficult one to resolve. The plant supplies a large fraction of the city's energy, and in terms of climate, it's a big green fraction.
And that's not the only issue the city will have to consider and reconsider. "We need to step backward from the simple old model, where you worry about one large, obvious fault, like they do in California," observes study co-author Leonardo Seeber, reflecting on the webby fault systems they found. "The problem here comes from many subtle faultsâ''Ã'Â¶ Each one is small, but when you add them up, they are probably more dangerous than we thought."