Study identifies previously unmapped ‘Mountainville Fault’ tied to 2024 New Jersey earthquake
NEW JERSEY — Researchers investigating the magnitude 4.8 earthquake that shook New Jersey in 2024 have identified a previously unmapped fault zone in the New Jersey Highlands that they say was responsible for the earthquake.
The findings were detailed in a study published Monday, Aug. 11, in the Journal of Geophysical Research: Solid Earth. Researchers designated the newly mapped structure the “Mountainville Fault.”
In April 2024, a magnitude 4.8 earthquake struck northern New Jersey, rattling buildings across the region. The quake occurred at about 10:23 a.m. and was centered roughly 4 miles north of Whitehouse Station at a depth of 4.7 kilometers, according to the U.S. Geological Survey.
The earthquake occurred near the approximately 300-kilometer-long Ramapo Fault. However, researchers found that the upward projection of relocated aftershocks aligned with topographic traces of a previously unmapped fault zone about 3.5 kilometers west of the earthquake’s epicenter.
Researchers combined seismicity-guided geological field mapping with laboratory friction experiments and an analysis of the tendency of faults to slip under the regional stress field.
Using LiDAR data, researchers identified north-northeast-striking topographic traces of fault scarps. Field examinations of exposed bedrock along those features revealed clusters of fractures showing evidence of past movement.
The researchers concluded that the structures represent portions of a deeper fault system that does not have a principal slip surface breaking through to the ground.
They characterized the Mountainville Fault as an “immature” fault zone, meaning its fractures are poorly connected and it lacks a well-developed principal slip zone at the surface.
Laboratory friction experiments using rock samples from the fault area also indicated conditions capable of producing earthquakes, particularly at depths where aftershocks occurred. Researchers said their results suggest concealed fluid-rock alterations could have played a role at the depth of the main earthquake.
The findings could have broader implications for understanding earthquake hazards in New Jersey and other areas located away from tectonic plate boundaries.
Researchers noted that earthquake hazard studies in such regions often focus on large, well-established faults. However, the New Jersey earthquake and other regional events demonstrate that moderate earthquakes can occur on less prominent faults.
The researchers said the characteristics of the Mountainville Fault are consistent with other structurally investigated earthquake sources in the region and suggest that difficult-to-detect, immature faults in basement rock may represent an important seismic hazard in intraplate areas.
