Although New York’s modern skyscrapers are less likely to be damaged in an earthquake than shorter structures, a new study suggests the East Coast is more vulnerable than previously thought. The new findings will help alter building codes.
By Mark Fahey
July 18, 2014 10:03 a.m.
New York Earthquake Hazard
The U.S. Geological Survey had good and bad news for New Yorkers on Thursday. In releasing its latest set of seismic maps the agency said earthquakes are a slightly lower hazard for New York City’s skyscrapers than previously thought, but on the other hand noted that the East Coast may be able to produce larger, more dangerous earthquakes than previous assessments have indicated.
The 2014 maps were created with input from hundreds of experts from across the country and are based on much stronger data than the 2008 maps, said Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project. The bottom line for the nation’s largest city is that the area is at a slightly lower risk for the types of slow-shaking earthquakes that are especially damaging to tall spires of which New York has more than most places, but the city is still at high risk due to its population density and aging structures, said Mr. Petersen.
“Many of the overall patterns are the same in this map as in previous maps,” said Mr. Petersen. “There are large uncertainties in seismic hazards in the eastern United States. [New York City] has a lot of exposure and some vulnerability, but people forget about earthquakes because you don’t see damage from ground shaking happening very often.”
Oddly enough, it’s not the modern tall towers that are most at risk. Those buildings become like inverted pendulums in the high frequency shakes that are more common on the East Coast than in the West. But the city’s old eight- and 10-story masonry structures could suffer in a large quake, said Mr. Lerner-Lam. Engineers use maps like those released on Thursday to evaluate the minimum structural requirements at building sites, he said. The risk of an earthquake has to be determined over the building’s life span, not year-to-year.
“If a structure is going to exist for 100 years, frankly, it’s more than likely it’s going to see an earthquake over that time,” said Mr. Lerner-Lam. “You have to design for that event.”
The new USGS maps will feed into the city’s building-code review process, said a spokesman for the New York City Department of Buildings. Design provisions based on the maps are incorporated into a standard by the American Society of Civil Engineers, which is then adopted by the International Building Code and local jurisdictions like New York City. New York’s current provisions are based on the 2010 standards, but a new edition based on the just-released 2014 maps is due around 2016, he said.
“The standards for seismic safety in building codes are directly based upon USGS assessments of potential ground shaking from earthquakes, and have been for years,” said Jim Harris, a member and former chair of the Provisions Update Committee of the Building Seismic Safety Council, in a statement.
The seismic hazard model also feeds into risk assessment and insurance policies, according to Nilesh Shome, senior director of Risk Management Solutions, the largest insurance modeler in the industry. The new maps will help the insurance industry as a whole price earthquake insurance and manage catastrophic risk, said Mr. Shome. The industry collects more than $2.5 billion in premiums for earthquake insurance each year and underwrites more than $10 trillion in building risk, he said.