PALISADES, NY — The discovery of a new fault line may explain the unusually strong and displaced shaking from April’s 4.8 magnitude quake that struck the heart of New Jerseybut felt strongest miles away from the epicenter, shows a new research study.

The earthquake occurred on April 5 late in the morning, in the middle of New Jersey‘s Tewksbury Township. But the quake sent shock waves through New York City 40-50 miles away and caused some damage in Brooklyn and NewarkNew Jersey.

It was the strongest quake in the region since 1884 and shook about 42 million people, according to US Geological Survey estimates. The The USGS said 184,000 people reported feeling the quake — A record number to populate the report.

STRONGEST NEW JERSEY QUAKE IN 240 YEARS OVER NEW YORK CITY, NORTHEAST

But researchers who went to the epicenter were puzzled to find that there was very little shaking and no noticeable damage was reported.

“We expected some property damage—chimneys knocked down, walls cracked or plaster falling, but there were no obvious signs,” study co-author Wong-Young Kim by Columbia Climate School’s Lamont-Doherty Earth Observatory said in a press release announcing the study results. “We talked to the police, but they weren’t very excited about it. Like nothing happened. It was a surprising response for a magnitude 4.8 earthquake.”

A USGS shaking intensity map from a magnitude 4.8 earthquake that struck New Jersey on April 5, 2024.

(FOX Weather)

Kim’s study said that based on existing models, the earthquake should have caused significant damage at the epicenter. Surface movement generated by earthquakes is measured at the 10 point Modified Mercalli Intensity Scale, and this quake should have brought level 7 or “very strong” shaking within 6 miles of the epicenter, Kim said.

However, no one at or around the epicenter reported tremors of intensity 7 or anything close to it, according to the release. The damage was limited to minor cracks in some plasterboard and some items were knocked off the shelves.

But instead, three townhouses were damaged in Newark, about 20 miles away, and New York City residents reported shaking at a level 4 on the Mercali scale, and about 150 buildings reported minor damage. Also New Hampshire reported a level 3 tremor about 280 miles away, the release said.

“So, very puzzling why a lot of people felt it in the Northeast, (but) a lot less people felt it south to Philadelphia and further south to Virginia — a lot less than people in the Northeast,” Kim told FOX Weather on Friday. “Like very small damage around the epicenter area.”

The seismic waves went in a different direction

Kim says a typical earthquake would send much of its energy straight up to the surface, usually making the epicenter the most dangerous place to be.

But in this case, the energy was sent downward until it reached the boundary between the crust and the mantle about 20 miles underground. There the energy wave bounced back up and appeared under the New York City area for the big jolt there.

Three homes were evacuated in Newark, New Jersey after a 4.8 earthquake shook the region on April 5, 2024.

(FOX 5 NEW)

After another downward cycle, the wave re-emerged slightly weaker New Englandrepeat the cycle until the energy is gone.

Kim’s team’s analysis suggests that the quake took place on a previously reorientated fault that runs south to north. But unlike traditional faults that run vertically, this one dips eastward into the Earth at about a 45-degree angle, sending the energy in unusual directions.

“In this case, on the 45-degree dip of the fault, the energy went northeast and into depth,” Kim told FOX Weather.

Northeast quakes are different from California tremors

Unlike the tremors that rattle California and West Coast with relative frequency and are caused by moving tectonic plates, Northeast quakes are left over from ancient fault zones stretching back 200 million years, researchers said.

That’s when what is now Europe broke away from North America, the study said. Some areas are still settling and adjusting all these years later, triggering occasional earthquakes.

Kim’s colleagues have calculated that a quake of April’s magnitude occurs about once every 100 years, but suggest the region could see quakes as large as a magnitude 6 every 700 years and up to a magnitude 7 every 3,400 years .

“No one knows if such quakes have occurred in human time or could,” wrote Kevin Krajick, the author of the press release. “But if one did, it would be disastrous.”

In the wake of the earthquake, researchers placed a temporary network of dozens of seismometers near the epicenter to measure the dozens of subsequent aftershocks, hoping to better map the region’s faults.

Earthquakes and aftershocks in New Jersey from the largest 4.8 quake on April 5, 2024.

(FOX Weather)

The data may trigger the need to reassess how future earthquakes would affect the populous northeast area.

“Some (quakes) that aren’t even that big might focus energy toward population centers,” Kim said. “If the (April) earthquake was just a little stronger, or a little closer to New York City, the impact would be much greater. We need to understand this phenomenon and its implications for ground motion prediction.”