New Jersey Earthquake Source Found: Hidden Mountainville Fault Identified

Researchers have finally pinpointed the source of the magnitude 4.8 earthquake that surprised millions along the U.S. East Coast on April 5, 2024. The tremor, which originated near Tewksbury, New Jersey, and was felt from Virginia to Maine, was not caused by the region's largest known fault, the Ramapo Fault, as initially suspected. Instead, a study published this month in JGR Solid Earth reveals the quake stemmed from a previously unrecognized fault zone in the New Jersey Highlands, now officially designated the "Mountainville Fault." This discovery highlights the potential for significant seismic activity from subtle, unmapped fault systems in densely populated areas.

Lead author Folarin Kolawole, a structural geologist at Columbia University's Lamont-Doherty Earth Observatory, stated, "This study shows that some of the region’s greatest earthquake hazards may come from faults that are difficult to recognize at the surface." He further emphasized the importance of identifying such systems for improving seismic hazard assessments in populated regions. Unlike the West Coast, where earthquakes are primarily associated with the boundaries of tectonic plates, East Coast seismic events occur within the North American plate itself. These typically involve thrust faulting along north-south trending faults, where blocks of rock move against each other, releasing built-up stress.

Unraveling the Mystery of the East Coast Quake

Previous analyses of the April 2024 earthquake by scientists at Columbia University suggested it was unusual, exhibiting a fault plane with both thrust and strike-slip mechanisms. This pointed toward the existence of an unknown fault. To investigate further, Kolawole and his team employed a multidisciplinary approach, combining aftershock data, field mapping, laboratory friction experiments, stress analyses, and LiDAR technology. LiDAR, a remote sensing technique, allowed them to examine the Earth's surface in detail.

The researchers observed that the upward projection of aftershock locations precisely matched a lineament identified through LiDAR imagery. This lineament corresponded to an unmapped fault zone located approximately 2 miles (3.5 kilometers) west of the earthquake's epicenter. Upon examining the exposed bedrock along this lineament, they found evidence of an "immature" fault. Such faults lack the extensive internal structure and prominent surface features of larger, more established faults but are nonetheless capable of generating seismic events.

By tracing the 2024 Tewksbury earthquake to the newly identified Mountainville Fault, the study underscores that the East Coast's most significant seismic events may originate from systems beyond its large, well-documented fault networks. While the April earthquake did not cause widespread destruction, it registered as the most powerful earthquake in New Jersey since 1900. Its reach extended to tens of millions of people, prompting a re-evaluation of seismic risk assessment for the region, particularly in areas close to major urban centers like New York City.