Ashtyn Asay There may be more going on beneath the Garden State than previously thought. Researchers from Columbia University recently discovered a previously unmapped fault in the New Jersey Highlands that may have been responsible for the magnitude 4.8 earthquake that shook the region in April 2024. The newly named Mountainville Fault is located about 3.5 kilometers west of the earthquake’s epicenter, near the much larger Ramapo Fault. A study published earlier this month in the Journal of Geophysical Research: Solid Earth provides evidence that this lesser-known fault, not the Ramapo Fault, was the source of the earthquake. The finding could change how scientists think about earthquake hazards in New Jersey and along the East Coast at large. Read on to learn more about the unmapped fault in the New Jersey Highlands.
What Happened During the 2024 New Jersey Earthquake?
On April 5th, 2024, a magnitude 4.8 earthquake struck near Tewksbury, sending seismic waves across the tri-state area. According to the U.S. Geological Survey, the earthquake was the largest to occur in New Jersey since 1950.
The earthquake occurred close to the Ramapo Fault, one of the largest and best-known fault systems in the region. Stretching roughly 300 kilometers through the Northeast and Mid-Atlantic, the fault was the obvious suspect. There was just one problem: The Ramapo Fault isn’t oriented particularly well for movement under the current stress conditions in the region. So researchers began looking elsewhere.
“Studies of intraplate earthquake hazards commonly focus on mature, prominent faults,” the researchers wrote. “Yet, earthquake records document moderate-magnitude earthquakes on inconspicuous faults.”
Meet the Mountainville Fault
Researchers combined seismic data from the earthquake and its aftershocks with high-resolution LiDAR scans, which use laser measurements to create detailed maps of the Earth’s surface, geological fieldwork, and laboratory experiments. The aftershocks provided one of the biggest clues. When researchers mapped their locations and projected them toward the surface, they aligned with a series of subtle topographic features in the New Jersey Highlands.
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Researchers then followed the suspected fault zone in the field. At exposed bedrock locations, researchers they found clusters of fractures with smooth, slick surfaces, which is evidence that the rocks had moved against one another before. Together, all of this evidence taken together pointed toward a previously unmapped fault zone, which researchers dubbed the Mountainville Fault.
Could the Mountainville Fault Have Caused the New Jersey Earthquake?
Laboratory experiments on rock samples collected from the suspected fault zone suggest that the Mountainville Fault can become frictionally unstable, meaning it is capable of slipping under the stresses currently affecting the Earth’s crust. Researchers also analyzed the fault’s orientation and regional stress field and found that the fault is favorably oriented for movement.
Still, there may have been additional factors that triggered the earthquake. Laboratory results suggest that fluids interacting with the rocks underground may have affected the fault’s frictional properties. Changes in local stress could also have helped push the fault toward failure.
The discovery isn’t necessarily a reason for New Jersey residents to start worrying about earthquakes. Instead, it gives scientists a better understanding of how earthquakes can happen in a region where many faults aren’t obvious at the surface.
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