Earthquake Zone Intersection Threatens Indian Point Nuclear Plant

The Indian Point nuclear power plant, with its two nuclear generating units, is situated 24 miles north of New York City, on the Hudson River at Buchanan, New York.

Researchers from Columbia University's Lamont-Doherty Earth Observatory have located a previously unknown active seismic zone running from Stamford, Connecticut, to the Hudson Valley town of Peekskill, New York, where it passes less than a mile north of the Indian Point nuclear power plant.

The Stamford-Peekskill line intersects with the known Ramapo seismic zone, which runs from eastern Pennsylvania to the mid-Hudson Valley, passing within two miles northwest of Indian Point.

The Stamford-Peekskill line stands out sharply on the researchers' earthquake map, with small events clustered along its length, and to its immediate southwest. Just to the north, there are no quakes, indicating that it represents some kind of underground boundary.

The pattern emerged when the Earth Observatory scientists compiled a catalog of all 383 known earthquakes from 1677 to 2007 in a 15,000 square mile area around New York City. The observatory runs the network of instruments that monitors most of the northeastern United States for earthquake activity.

Their paper appears in the current issue of the "Bulletin of the Seismological Society of America."

Indian Point nuclear power plant at Buchanan, New York (Photo by Daniel Case)

"Indian Point is situated at the intersection of the two most striking linear features marking the seismicity and also in the midst of a large population that is at risk in case of an accident," says the paper. "This is clearly one of the least favorable sites in our study area from an earthquake hazard and risk perspective."

Lead author Lynn Sykes says the data show that large quakes are infrequent around New York compared to more active areas like California and Japan, but that the risk is high, because of the overwhelming concentration of people and infrastructure.

"The research raises the perception both of how common these events are, and, specifically, where they may occur," he said. "It's an extremely populated area with very large assets."

Nearly 10 million people live within 25 miles of the Indian Point nuclear plant, including the 8.2 million in the New York metropolitan area.

Sykes, who has studied the region for 40 years, is known for his early role in establishing the global theory of plate tectonics.

Sykes and his team say the insight comes from sophisticated analysis of past quakes, plus 34 years of new data on tremors, most of them perceptible only by modern seismic instruments.

It is parallel to other faults beginning at 125th Street in New York City, so the researchers believe it is a fault in the same family. They say it is probably capable of producing at least a magnitude 6 quake, strong enough to damage structures.

Sykes said the existence of the Stamford-Peekskill line had been suggested before, because the Hudson River takes a sudden unexplained bend just to the north of Indian Point, and definite traces of an old fault can be along the north side of the bend.

"The seismic evidence confirms it," he said.

Dr. Lynn Sykes with the Lamont-Doherty Earth Observatory, Columbia University (Photo courtesy LDEO)

The findings come at a time when Entergy, the owner and operator of Indian Point, is trying to relicense the two operating plants for an additional 20 years - a move being fought by surrounding communities and the New York State Attorney General. Licenses for Indian Point's two reactors expire in 2013 and 2015.

Last fall New York Attorney General Andrew Cuomo, alerted to the then-unpublished Lamont data, told a Nuclear Regulatory Commission panel in a filing, "New data developed in the last 20 years disclose a substantially higher likelihood of significant earthquake activity in the vicinity of [Indian Point] that could exceed the earthquake design for the facility."

The state alleges that Entergy has not presented new data on earthquakes past 1979. However, in a little-noticed decision July 31, the panel rejected the argument on procedural grounds. A source at the attorney general's office said the state is considering its options.

The Earth Observatory research shows a pattern of subtle but active earthquake faults that makes the risk of earthquakes to the entire New York City area greater than scientsts had previously believed.

The evidence charts unseen but potentially powerful structures whose layout and dynamics are only now emerging, say the scientists.

Starting in the early 1970s Lamont began collecting data on quakes from dozens of newly deployed seismometers; these have revealed distinct zones where earthquakes concentrate, and where larger ones could come.

For data on the earlier quakes, coauthor John Armbruster estimated sizes and locations of dozens of events before 1930 by combing newspaper accounts and other records.

His research shows that magnitude 5 quakes - strong enough to cause damage - occurred in 1737, 1783 and 1884.

There was little human settlement in the area to be hurt by the first two quakes, whose locations are vague due to a lack of good accounts; but the 1884 quake, thought to be centered under the seabed somewhere between Brooklyn and Sandy Hook, toppled chimneys across the city and New Jersey, and panicked bathers at Coney Island.

Based on this analysis, the researchers say such quakes should be routinely expected, on average, about every 100 years.

"Today, with so many more buildings and people, a magnitude 5 centered below the city would be extremely attention-getting," said Armbruster. "We'd see billions in damage, with some brick buildings falling. People would probably be killed."

Based on the lengths of the faults, the detected tremors, and calculations of how stresses build in the Earth's crust, the Earth Observatory researchers say that magnitude 6 quakes, or even magnitude 7, are possible.

Copyright Environment News Service (ENS) 2008. All rights reserved.