A new study is reshaping how scientists understand the earthquake that rattled New Jersey and much of the surrounding region in 2024, pointing to a newly discovered fault rather than the one that had long been suspected as the cause.
The magnitude 4.8 earthquake was centered in Tewksbury, in Hunterdon County, back in April of 2024. It was strong enough to be felt by many people across New Jersey and beyond, making it one of the more notable seismic events the area has experienced in recent memory.
For some time, geologists believed the quake had been caused by the Ramapo fault line, the region's largest and best-known fault. The new study instead identifies a newly discovered Mountainville fault zone as the true source of the shaking.
Researchers say the earlier explanation never quite fit the evidence. As one put it, it didn't really match what they were expecting from the seismic data. The identification of the previously unmapped fault helped resolve that mismatch and gave scientists a clearer picture of what actually happened underground.
According to the study, the newly discovered fault dips into the earth at an angle, and that geometry helped send the quake's effects rippling well beyond New Jersey. The shaking was felt as far north as Maine and as far south as Virginia, a reach that reflects how the energy travelled along the fault.
The finding may also help explain why Tewksbury itself avoided any significant damage, even though it sat at the epicenter. The way the fault and its released energy were oriented appears to have spared the immediate area from the kind of destruction that its magnitude might otherwise suggest.
Experts are quick to stress that New Jersey is not a high earthquake-hazard region in the way places like California, Chile, Japan or the Philippines are. Even so, the discovery of a previously unrecognized fault is a reminder that hidden fault lines can act as earthquake sources and merit closer study along the US east coast.