New York City might not be waiting for "The Big One" as Los Angeles or San Francisco are, but that doesn't mean the city is free from earthquake hazards. A new survey of the area's seismic history going back to the late 17th century reveals that events strong enough to cause damage and injury have popped up every now and then--and that the next such quake seems to be overdue.
As far as seismologists are concerned, there's no such thing as solid ground. Earth's rocky, eggshell-thin crust is cracked into massive plates that float atop the semimolten mantle. Those plates move constantly though usually imperceptibly. Over geological time, as they bump into, slide past, or slip under one another--or, in the case of the U.S. East Coast, buckle in the middle--they can build up enormous amounts of energy that is released through earthquakes. Usually, such activity takes place along the fault zones between the plates, such as the San Andreas near San Francisco and the Northridge under Los Angeles. Both have been the source of major quakes in those cities within the past century or so.
Other parts of the country face tectonic hazards too, including New York. Researchers at the Lamont-Doherty Earth Observatory in Palisades, New York, gathered data on 383 quakes that have struck near the city since 1677 as part of an evaluation of hazards for two projects: relicensing of the Indian Point Energy Center in Buchanan and prospective repairs to or replacement of the half-century-old Tappan Zee Bridge over the Hudson River. Taking seismometer data since 1974, and secondary sources--such as eyewitness and newspaper accounts--before then, the team determined that three temblors around magnitude 5 had occurred during that period, in 1737, in 1783, and in 1884.
All three of those quakes, if centered near the city today, would be enough to damage or destroy older buildings in disrepair, says seismologist and co-author John Armbruster. More such quakes are not out of the question, he adds. One reason, Armbruster and colleagues report in this month's Bulletin of the Seismological Society of America, is their discovery of an active fault zone running from Peekskill, New York, to Stamford, Connecticut. It lies parallel to other faults in the region, Armbruster says, and it's a potential source of future quakes in the magnitude-5 range, which seem to occur around every 100 years. The quakes are the indirect result of seafloor spreading along the mid-Atlantic Ridge.
Jennifer Post, a spokesperson for the New York State Department of Transportation in Albany says the agency is aware of potential earthquake risks. "We are in the midst of a comprehensive review and planning process, and from the onset we have taken seismic activity into consideration for the future of the Tappan Zee Bridge and the I-287 corridor."