The earthquake that hit the Northeast on Friday morning rattled nerves but did not do much damage. Still, it left many New Yorkers wondering how afraid they should be of a bigger one hitting closer to the city.

The answer? It’s hard to say.

Some news reports suggest that a large earthquake is “due” in New York City because moderate ones — with a magnitude of 5 or more — typically occur every few hundred years. The last one took place in the 1700s. Friday’s earthquake, in comparison, was a magnitude 4.8.

In 2008, Columbia University’s Lamont-Doherty Earth Observatory found that the risk of earthquakes in the New York City area was greater than previously believed. That is because smaller earthquakes occur regularly in New York City, like a magnitude 1.7 earthquake that was recorded in Astoria, Queens, in January.

Experts caution that it is impossible to know when an earthquake will strike or how much damage it might cause. But if an earthquake much stronger than Friday’s were to hit closer to New York City, “it would be a different story,” said Kishor S. Jaiswal, a research structural engineer with the U.S. Geological Survey. Forecasts from the city suggest that such a quake could result in dozens of injuries and billions of dollars in damage.

There were few reports of damage or injuries after Friday’s earthquake. Still, city officials said they were inspecting bridges, train tracks and buildings, and that people should be prepared for aftershocks for at least several days.

Earthquakes with a similar magnitude to Friday’s are “rare, but they’re not unheard-of” close to New York City, said Leslie Sonder, an associate professor of earth sciences at Dartmouth College.

Earthquakes are often caused by the friction and movement of Earth’s tectonic plates underground. The energy that is released as a result travels in waves and causes the shaking that is felt above ground.

The effect of an earthquake will depend on the location of the epicenter, how deep the earthquake was and the quality of the construction of the buildings in the area, Ms. Sonder said.

“It’s really hard to predict whether a building will have damage at a magnitude 5, or if it will take a seven or an eight,” she said.

The waves from an earthquake on the East Coast might be felt hundreds of miles away because of the type of rocks underground. Because the Northeast is densely populated, many people end up feeling the effects and it becomes a topic of conversation, even if it does not cause much damage, she said.

There are reasons to believe New York City’s buildings might be vulnerable. But many new buildings are designed to withstand earthquakes, and some older buildings have been retrofitted, experts said.

“There’s a saying that ‘earthquakes don’t kill people, buildings do,’” said Jeffrey Schlegelmilch, director of the National Center for Disaster Preparedness at Columbia Climate School. “That’s why it’s so important to sort of have these things in place.”

The most significant tremors in New York City occurred in 1884, when a magnitude 5.2 earthquake with an epicenter off Coney Island shook the city. That earthquake was about four times as strong as Friday’s, and its epicenter was dozens of miles closer to the city. (Friday’s epicenter was in New Jersey, about 40 miles west of New York City.)

If an earthquake similar to that of 1884 hit the city today, officials estimate that it would “potentially cause $4.7 billion in damage to buildings, transportation, and utilities,” leave 100 buildings destroyed and 2,000 people without shelter.

Old brick buildings, buildings with storefronts on the ground level and buildings with “brittle” concrete frames are the most susceptible to cracking and damage, said Abi Aghayere, a forensic structural engineering professor at Drexel University.

Building codes for earthquake safety emerged around the 1930s, and many major cities have also strengthened their codes in recent years to help their infrastructure withstand strong shakes.

For example, the Port Authority of New York and New Jersey in Midtown spent more than $50 million over 15 years ago to retrofit the bus terminal to withstand damage from a seismic event.

In general, New York City has plans for every possible disaster scenario, said Sarah Kaufman, director at the N.Y.U. Rudin Center for Transportation.

“We have probably the best emergency management department in the country,” Ms. Kaufman said.

Once an earthquake occurs, officials’ attention quickly pivots to assessing the damage.

Consolidated Edison, the electricity, gas and steam utility that services 10 million people in New York City and Westchester County, has protocols for checking for damage with an emphasis on its gas distribution network. After Friday’s earthquake, no damage was found, said Matthew Ketschke, the president of the utility.

Still, Mr. Ketschke urged anybody who smelled gas to dial 911 or notify the company.


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