Year after 4.8 magnitude earthquake rattled Long Island, recent microquake recorded near epicenter

One year after a rare earthquake rattled Long Island, scientists have discovered continued seismic activity near the New Jersey epicenter of that temblor — with the most recent microquake recorded by the United States Geological Survey last week.

On March 25, about five miles from the epicenter of last year’s quake, geologists recorded a 0.7 magnitude earthquake in Califon, New Jersey, according to USGS geophysicist Dara Goldberg, who is based in Colorado.

Quakes lower than a 3.0 magnitude are unlikely to be felt by people, according to scientists.

Since the 4.8 magnitude earthquake on April 5, 2024, which was felt on the Eastern Seaboard from Maine to parts of Virginia, scientists have been investigating the reasons behind it, while assessing future risks.

In the past year, USGS has dispatched five seismic instruments near the epicenter of last year’s quake in Tewksbury, New Jersey, learning the area is rife with seismic activity. Goldberg said it’s unclear whether the activity is linked to aftershocks, which could continue for years.

Meanwhile, geologists at Columbia University are readying to set up a "special geophysical imaging instrument across the exposure of the fault" in Tewksbury next week, according to Folarin Kolawole, a structural geologist at Columbia University's Lamont-Doherty Earth Observatory. 

"The goal is to see the fine-scale structure of the damages along the fault which were created by multiple cycles of earthquake events along the fault," Kolawole told Newsday.

Active faults

Earthquakes occur on fault lines, scientists said. Faults are fractures "between two blocks of rock" and during an earthquake the rock on one side of the fault "suddenly slips with respect to the other," according to the USGS.

Kolawole, who was at the university’s lab in Palisades in Rockland County when he felt the temblor last April, drove an hour to the epicenter to begin mapping out the fault that same day. He was measuring fractures when he felt an aftershock that evening.

"I was like 500 meters from the epicenter, and we felt it. It was big. It was like a landslide running towards us. It was amazing," he said.

Kolawole and his colleagues have since identified the fault that caused the 4.8 magnitude quake. Named the "Mountainville Fault," it connects to the larger Ramapo Fault system, which runs from Pennsylvania to southeastern New York, he said. 

Their work has revealed "the faults showed precursory activity before and that provides us a means to investigate other faults in the region that can potentially rupture earthquakes in the future," he said. The scientist added that there is evidence other faults in the region also are setting off small magnitude earthquakes.

To pinpoint which faults are more dangerous, Kolawole said he is continuing to study other faults that are active.

There are several larger fault lines in New York City, with the top four identified as the 125th Street Fault and the Dyckman Street Fault, both in Manhattan, the Van Cortlandt Park Fault in the Bronx, and the East River Fault, according to Charles Merguerian, a geologist who is principal of Duke Geological Laboratory, a geotechnical firm based in Stone Ridge.

Merguerian, professor emeritus of geology, environment, and sustainability at Hofstra University, said there are also hundreds of other minor faults throughout New York City. He has mapped 300 faults within the five miles of the Queens-Midtown Tunnel.

The 125th Street Fault in Harlem, Kolawole said, "keeps popping off small earthquakes every now and then, like every 8-10 years."

He said he and his team are readying to deploy a novel seismic instrument called DAS, or distributed acoustic sensing, to "record strain" at that location. The technology, part of continual research, plugs into fiber optic cables to detect vibrations and will be set up for testing in about two weeks.

Chances of another quake

Felt by millions of people, last year’s 4.8 magnitude quake caused no reported property damage or deaths. While New York does not sit on active plates like the West Coast, earthquakes are still possible on the East Coast for different reasons, scientists said. 

Kolawole said that in the New York area, fault lines formed millions of years ago when Africa was splitting from North America. Continents move apart through the development of fault lines that slip, he said. When the continents tore apart, the Atlantic Ocean was formed and the faults died, he said.

But the Mid-Atlantic Ridge, a chain of underwater volcanic mountains that runs down the center of the Atlantic Ocean, is forming a rift valley, according to scientists. 

"That process creates stresses on the crust, on the margins of the oceans, and New York area is on the margin. So we know that those faults are prestressed," Kolawole said.

Stony Brook University geophysicist William Holt said that while we don’t live on a plate boundary like California, the rare earthquake may occur in New York in response to what he called "amazing global processes," like mantle convection and the movement of the plates.

The chances of another earthquake remain small but not zero, scientists said.

"Our aftershock forecast indicates there is a 7% chance of a magnitude 3 or greater in the next year," Goldberg said, adding that there is less than a 1% chance of an earthquake stronger than last year’s occurring.

The last biggest earthquake to strike New York City was the 5.2 magnitude earthquake in 1884 in Coney Island, causing some chimneys to crumble, scientists said. 

For one Long Island resident, the chance of another temblor doesn't keep her awake at night. Debbie Napp, 69, of Huntington, felt the shaking during last year’s big event and dashed outside.

"I thought something happened to my boiler. I just didn't know what to think," Napp said in a recent interview. "I have so many other things to worry about." 

The anomaly of such an event in New York means some people might not know what to do but scientists said fleeing outside has been shown to put people at risk of injury.

"I think what's important is just to know that earthquakes can and do happen on the East Coast, and if you do feel shaking, to drop, cover and hold on to protect your body from anything falling," Goldberg said.