New York Earthquake Background

24 August 2008 | 04:35 Code : 17935 Geoscience events
Existing U.S. Geological Survey seismic hazard maps show New York City as....

Existing U.S. Geological Survey seismic hazard maps show New York City as facing more hazard than many other eastern U.S. areas. Three areas are somewhat more active—northernmost New York State, New Hampshire and South Carolina—but they have much lower populations and fewer structures. The wider forces at work include pressure exerted from continuing expansion of the mid-Atlantic Ridge thousands of miles to the east; slow westward migration of the North American continent; and the area’s intricate labyrinth of old faults, sutures and zones of weakness caused by past collisions and rifting.Due to New York’s past history, population density and fragile, interdependent infrastructure, a 2001 analysis by the Federal Emergency Management Agency ranks it the 11th most at-risk U.S. city for earthquake damage. Among those ahead: Los Angeles, San Francisco, Seattle and Portland. Behind: Salt Lake City, Sacramento, Anchorage.New York’s first seismic station was set up at Fordham University in the 1920s. Lamont-Doherty Earth Observatory, in Palisades, N.Y., has operated stations since 1949, and now coordinates a network of about 40.Dozens of small quakes have been felt in the New York area. A Jan. 17, 2001 magnitude 2.4, centered in the Upper East Side—the first ever detected in Manhattan itself--may have originated on the 125th Street fault. Some people thought it was an explosion, but no one was harmed.The most recent felt quake, a magnitude 2.1 on July 28, 2008, was centered near Milford, N.J. Houses shook and a woman at St. Edward’s Church said she felt the building rise up under her feet—but no damage was done.Questions about the seismic safety of the Indian Point nuclear power plant, which lies amid a metropolitan area of more than 20 million people, were raised in previous scientific papers in 1978 and 1985.Because the hard rocks under much of New York can build up a lot strain before breaking, researchers believe that modest faults as short as 1 to 10 kilometers can cause magnitude 5 or 6 quakes.In general, magnitude 3 quakes occur about 10 times more often than magnitude fours; 100 times more than magnitude fives; and so on. This principle is called the Gutenberg-Richter relationship

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