NYC Quakes and not just on Wall Street

I once had the dubious pleasure of insisting on earthquake insurance on a property in Tennessee and being told by the borrower and my own insurance agent that I was nuts because earthquakes are West Coast phenomena. But I remembered a high school history text reference to an earthquake in the 18th century on the New Madrid fault in Tennessee that “rang the bells in Boston”. Now earthquake design requirements and insurance are the norm along one of the largest faults in the U.S. – but in NYC ???

Study: Large Earthquake Could Strike New York City – LiveScience – Robert Roy Britt -21 August 2008

The New York City area is at “substantially greater” risk of earthquakes than previously thought, scientists said Thursday.

Damage could range from minor to major, with a rare but potentially powerful event killing people and costing billions of dollars in damage.

A pattern of subtle but active faults is known to exist in the region, and now new faults have been found. The scientists say that among other things, the Indian Point nuclear power plants, 24 miles north of the city, sit astride the previously unidentified intersection of two active seismic zones.

The findings are detailed in the Bulletin of the Seismological Society of America.

Shaky history

While earthquakes are typically thought of as a West Coast phenomenon in the nation, strong quakes do occur in the Eastern United States, just much less frequently. Importantly, the geology of the East – lots of hard rock leftover from glacial times – makes any rumbling travel a lot farther and with greater intensity from the epicenter.

A 5.0 temblor in 1737, for example, knocked down chimneys in New York City and was felt from Boston to Philadelphia. A magnitude-5.5 quake in 1884 did similar damage in a wider region around New York. Another quake in this range struck in 1783.

The new study involved an analysis of past quakes, plus 34 years of new data on temblors, most of them perceptible only by modern seismic instruments. The scientists looked at 383 earthquakes from 1677 to 2007 in a 15,000-square-mile area around New York City, using newspaper records in some cases to estimate temblor magnitudes.

“The evidence charts unseen but potentially powerful structures whose layout and dynamics are only now coming clearer,” the scientists said. And even though eastern quakes are infrequent, the risk is high, because of the overwhelming concentration of people and infrastructure, said lead researcher Lynn R. Sykes of Columbia University’s Lamont-Doherty Earth Observatory.

“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.”

Based on history, the researchers say quakes at least 5.0 in magnitude should be expected, on average, about every 100 years.