Focus on Arts and Ecology

The magnitude 4.8 quake struck in northern New Jersey and was felt across the tri-state area.

ByIsaac Schultz, April 5, 2024

Whoa! Did you feel that? It was an earthquake with an epicenter in northern New Jersey, and it set off a flurry on social media Friday morning. The quake was centered about 20 miles west of North Plainfield and occurred at about 10:23 a.m. ET according to a European seismological center.

The U.S. Geological Survey reported the quake had a magnitude of 4.8 and occurred at a depth of about 3.11 miles (5 kilometers). Phone alerts sent to some in New York at 11:02 am ET stated the quake’s magnitude as 4.7 and warned residents to stay indoors and call 911 if injured.

The phone alert also linked to a USGS Frequently Asked Questions page about how to stay safe during an earthquake. A follow-up alert sent to New York City residents at 11:46am stated that aftershocks may be felt, but New Yorkers can continue their usual activities. An apparent aftershock was felt across the city just before 6:00 p.m. ET, and NYC Emergency Management posted on X stating that they were confirming the aftershock with USGS. USGS’s website states the second tremor had a magnitude of 4.0 and occurred at a depth of 5.84 miles (9.4km).

“Different parts of the planet feel earthquakes with different severities and different frequencies depending on the geological setting and how close they are to other features like subduction zones,” said Benjamin Fernando, a seismologist at Johns Hopkins University, in a phone call with Gizmodo. “The northeast of the US tends to be pretty quiet, so events like this are quite rare. Certainly not something you see every year, or maybe even necessarily every ten years.”

The Holland Tunnel posted on X, formerly Twitter, stating that the transit corridor between New York and New Jersey would be temporarily held for inspection in both directions.

In a post on X, the Federal Aviation Administration wrote that “a 4.8 magnitude earthquake in New Jersey may impact some air traffic facilities in New York, New Jersey, Philadelphia and Baltimore. Air traffic operations are resuming as quickly as possible.”

According to a USGS Community Internet Intensity Map, shaking was felt as far south as Maryland and as far northeast as central Connecticut. Parts of central Pennsylvania and central New York also reported light shaking.

The exact time of the quake was 10:23:20 Eastern Time, according to the USGS. Its epicenter was 40.683°N 74.753°W—about 4.35 miles (7km) north of Whitehouse Station, New Jersey.

The quake received a green alert from the USGS, meaning there is a very low likelihood of casualties or substantial damage. The USGS reported that there is a 46% chance of an aftershock of Magnitude 3 or more in the next week; however, the likelihood of a Magnitude 4+ aftershock was much lower, at 16%. The 5:59 p.m. quake confirmed the USGS’ calculations were sound. A detailed breakdown of the USGS’ aftershock forecast can be found here.

Fernando noted that the moment magnitude scale is not always the best indicator of an earthquake’s severity, because magnitudes can feel very different in different parts of the world. “New York is actually built on really solid bedrock, so it won’t shake that much,” he said. “But if you go somewhere like the San Francisco Bay area where you’ve got lots of soft sediments, the same earthquake will produce quite a lot more shaking.”

That’s why the USGS also detailed the quake’s severity on the Modified Mercalli Intensity (MMI) scale, a near-century-old system for measuring an earthquake’s intensity based on its observed effects.

In New York City the quake had an MMI of 3.5, equating to weak-to-light shaking. In The Severity of an Earthquake, the USGS defines such a quake as: “Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck.” Indeed, many in New York City described the quake on social media as feeling like a subway train passing beneath them.

The quake’s MMI measured closer to 4.5 in a 5-mile radius of its epicenter, and about 5.5 closest to its epicenter. An MMI of 5 is “Felt by nearly everyone; many awakened,” and dishes and windows would likely be broken.

“That’s pretty substantial, but people shouldn’t be overly worried,” Fernando said. “5.5 is between moderate and strong. People notice [the quake], are perhaps a little bit worried—but we’re not expecting significant damage to buildings.”

(Sources: Gizmodo)