Scientists just discovered a hidden fault lying under New Jersey’s surface. With it, an answer to the mystery that had bewildered them for over two years.
On April 5, 2024, a 4.8 magnitude earthquake hit near Tewksbury Township, New Jersey. The quake wasn’t just strong for Jersey, it was felt across the East Coast—an estimated 42 million people felt the earthquake, marking one of the most widely spread earthquakes in USGS history.
A UN Security Council meeting was interrupted, airlines halted flights, tunnels were closed, residents forced to evacuate. Millions in NYC felt the shock—within hours, Manhattan souvenir shops were selling “I survived the NYC earthquake” t-shirts.
Despite the wide reports, scientists were still stumped: what fault actually caused the earthquake?
The Obvious Suspect
In the wake of the geological event, the obvious suspect was the Ramapo Fault—the region’s largest at 300 km long.
As with many things in life, the easiest answer isn’t always the correct one. There was one glaring issue: the orientation of the Ramapo Fault didn’t match the path of the 2024 earthquake. This led scientists studying the event down a rabbit hole. The Flemington Fault was also briefly looked at, but ultimately deemed not the cause.
As first reported by ScienceAlert, this led researchers from Columbia’s Lamont-Doherty Earth Observatory broadening their scope in search of another explanation. How was an earthquake felt by 42 million shrouded in so much mystery?
How They Discovered the Mountainville Fault
The answer to the mystery was hiding in plain sight. Literally.
A study published in the Journal of Geophysical Research outlines the discovery of the Mountainville Fault—an unmapped fault zone hiding underneath the earth’s surface. The researchers used aftershock data combined with Light Detection and Ranging (LiDAR) and physical field mapping, which led them to unveil the previously unmapped fault line, located just 3.5 km west of the earthquake’s epicenter.
The Mountainville Fault is classified as an “immature” basement-hosted fault, according to the report. While typical faults appear as one, large crack, this one was a series of fractures that haven’t yet merged. Picture a single crack in a sidewalk versus a spiderweb of cracks.
To test their theory, they took rock samples from the area—along with ones from the Ramapo Fault—and recreated slip conditions to see how the rocks would react to pressure mimicking that of the underground. The sample from the newly discovered region was a closer match to the behavior of the 2024 earthquake.
Still, it wasn’t a perfect match. This left researchers again searching for answers—suspecting that something else underground helped trigger the earthquake.
Their best guess: a small, local change close to the surface, maybe underground water pressure shifting, or some rock nearby being removed or worn away. It is entirely plausible that any of these factors could have nudged an already-stressed fault into slipping.
Underneath the Earth is a World of Mystery
More than 200 aftershocks were reported following the 2024 earthquake, with a 3.7 magnitude one hitting just seven hours after the initial quake.
Scientists warn that there could be others hiding underneath the surface, stating “We propose that in the highly populated US east coast, seismically unstable, immature, structurally complex faults similar to the Mountainville Fault may constitute important earthquake sources… and thus, pose previously unrecognized but critical earthquake hazards.”
Because most earthquake-risk planning focuses on big, well-known faults, these smaller hidden ones might be getting overlooked entirely.
In other words: we might not know until another quake like 2024 hits.
Moving Forward
Scientists aren’t stopping at discovery—they plan on continuing to study the Mountainville Fault. Additionally, they believe there might be other un-discovered faults tucked beneath the surface that require a closer look.
Even with the newfound information, earthquake research is a never-ending game. The earth is constantly shifting, and multiple smaller earthquakes—including two August 2025 quakes near Hasbrouck Heights and Hillsdale—have hit since the 4.8 magnitude event that originally sent researchers down the rabbit hole.
It took scientists two years to find their culprit for an earthquake that shook millions. It poses some frightening questions: What else is lying beneath us? And will we know before we’re made to?
Peter Candia is the Food + Drink Editor at New Jersey Digest. A graduate of The Culinary Institute of America, Peter found a passion for writing midway through school and never looked back. He is a former line cook, server and bartender at top-rated restaurants in the tri-state area. In addition to food, Peter enjoys politics, music, sports and anything New Jersey.
