How earthquake-proof are NYC’s high-rises and new buildings?

The city's building code was amended in 1995 to ensure that new buildings and upgrades to older ones included earthquake-resistant measures.

Although the earthquake that shook New York City and the surrounding region on Friday didn’t cause systemic damage, it left many residents wondering how the city’s buildings would fare under stronger seismic waves.

Engineering experts say New York City’s glass towers and luxury steel skyscrapers, which can be over 1,000 feet tall, are actually at much lower risk of sustaining damage or collapsing during an earthquake than the city’s older buildings.

“I have total confidence in high-rise buildings in New York,” said Eric Cowley, president of Cowley Engineering.

The city’s building codes were amended in 1995 to ensure that new construction or any significant upgrades are designed to make buildings earthquake-resistant and minimize the probability of collapse, which is the biggest cause of death during temblors.

“The more modern seismic codes in this country came after the Northridge and Loma Prieta earthquakes in California,” said Chris Cerino, president of the National Council of Structural Engineers Association and senior structural engineer at STV, a structural engineering firm. Those earthquakes happened in 1994 and 1989, respectively.

The city isn’t located on an active fault line and strong earthquakes are uncommon. And even though Friday’s 4.8 magnitude earthquake was rare in its intensity, it was still considered “light,” according to the city’s hazard mitigation plan. But even a moderate earthquake could cause damage, and New York City’s dense population puts it at particular risk.

Cowley said newer buildings are much lighter and must adhere to building design codes requiring them to have a “seismic gap,” or a certain amount of distance from other neighboring buildings.

“So the building can wiggle and not bang the building next door,” Cowley said. He added that the gap is determined by many factors, such as a building’s height, the type of soil it’s built on, and its foundation’s capacity to remain intact.

Cerino said newer buildings are meant to sway, and that’s a good thing: The design that makes them wind-resistant also makes them earthquake-resistant, he said.

“Like a tree, you want your tree to sway and not hit another tree to impart force on each other. You want it to just sway in the wind and dissipate the energy naturally,” he said. “You should be more concerned if your building is not swaying because then you're not dissipating the force, especially when you're in a high-rise, it has to sway to relieve the forces and perform as designed. Nothing can be rigid and that tall.”

He said residents of newer buildings who want to know how their buildings are protected from earthquakes can simply go to their emergency staircases.

“If you are in your stairwell and you knock on your walls that are concrete, that’s your seismic and wind resistance system there,” he said.

But most of New York City’s nearly 1 million buildings were built between the mid-1800s and 1930s, before design codes were amended to account for seismic activity.

More than 200,000 multi-family, unreinforced brick buildings are particularly vulnerable to earthquakes, according to the city’s hazard plan. Brooklyn has the largest share of these buildings, followed by Queens and the Bronx. The plan said these buildings aren’t designed to bend, flex or absorb forces and are more at risk of damage or collapse.

“Prewar buildings typically have structural steel frames that are encased in concrete. Those are heavy, but short,” Cowley said. But he said damage remains of minimal concern for 4.8 magnitude earthquakes or others within that range.

“Your biggest worry would be maybe some step cracks in the facade of a building, maybe some broken or ornate things,” he said. “The brittle sections on a prewar building would be the things that are brittle to begin with: terracotta, cornices, that kind of stuff.”

Cerino said brownstones can be another concern because many of them have wood flooring that is pocketed into the wall. But he added that the types of strong earthquakes that could potentially damage them are atypical for the area.

“So if the building sways and moves in a little bit, and the floor can actually pull out of the wall pocket, then it would fall,” he said. “Even though [these buildings are] very susceptible, we haven't had a seismic event that's ever been a problem for them.”

Residents who are concerned about structural damage or want to know the risks their buildings face during seismic activities should contact a structural engineer to conduct an inspection.