The 5.8 magnitude earthquake that hit Virginia Tuesday afternoon, sent city buildings swaying, but thanks to strict building codes — the ductility of newer buildings were not cause for concern. But structural engineers and architects said some of the city’s older buildings are not reinforced, and a stronger quake could have caused major damage.
“The current New York City building code design criteria is the same as you would have in San Francisco or Los Angeles for seismic events,” said Frederic Schwartz, FAIA, who designed the Staten Island Ferry Terminal, which, like every city building, reported no damage.
Schwartz said he wouldn’t be concerned about the Empire State building, but other buildings did give him pause for concern.
“I would be anxious about early modern buildings, that’s when they were pushing the envelop of building glass and thinness in relationship to seismic events,” Schwartz said. Speaking generally, he said buildings with heavy masonry, from the 1920s and 1930s, would be fine, but the skyscrapers of the 1940s and 1950s might need to be re-examined and reinforced to withstand a stronger quake.
Mayor Michael Bloomberg said the city was investigating two reports of minor damage, but said no buildings had been declared unfit for occupancy. “Property owners should do due diligence and visually inspect buildings for cracks, and contact building management if they feel the situation warrants it,” Bloomberg said.
The largest recorded earthquake in the city was in 1884 and measured at a magnitude of 5.5.
In 1995, one year after a 4.7 magnitude quake struck near Reading, Pennsylvania, the city passed an ordinance requiring all buildings taller than three stories be designed to withstand a 5.5 magnitude earthquake.
“Every time there’s a flood, tornado, hurricane, or something like that happens, that’s how building codes change,” architect Michael Lehrer, FAIA said.” He said because this was a “benign” quake, with no reported damage, it is a great time to examine the current building codes. “Reality has just changed. It’s like something that isn’t supposed to happen, happened.”
Robert Otani, a structural engineer for Thorton Tomasetti, said the building codes in New York are already have some of the highest standards in the world. The current building code is based on the “maximum considered earthquake” or calculated to withstand the worst earthquake in 2,500 years.
“I think the biggest challenge is what to do with the existing buildings. Because there’s a substantial number of buildings in New York City that have no designed earthquake resistance,” Otani said. “As the buildings get older and older, and as the materials deteriorate over time, the problem doesn’t get any better, it gets worse.”
Otani is part of a committee that is trying to find ways to make older buildings earthquake-safe, but he said often the best possible solution is to tear down structurally unsound buildings, but “that’s pretty much impossible.” So, he’s still searching for minimally evasive solutions.