Examining the Tewksbury Earthquake: Insights into Seismic Anomalies in New Jersey

The magnitude 4.8 Tewksbury earthquake on April 5, 2024, surprised many due to strong shaking reports from distant areas like New York City, while reported damage near the epicenter was negligible. Researchers examined the earthquake’s unusual rupture direction, which may explain this discrepancy and suggest possible new fault activity in the region.

The recent magnitude 4.8 earthquake in Tewksbury, New Jersey, has drawn significant attention due to its unusual circumstances and widespread effects on the East Coast. Despite being the largest instrumentally recorded earthquake in New Jersey since 1900, observers and researchers alike were surprised to see minimal damage near the epicenter while reports of strong shaking came from as far as 40 miles away in New York City. Researchers YoungHee Kim from Seoul National University and Won-Young Kim from Columbia University undertook an investigation into the earthquake’s rupture direction, as discussed in their paper published in The Seismic Record. Upon visiting the epicenter a mere eight hours post-mainshock, the researchers expected to find signs of structural damage typical of a magnitude 4.8 earthquake. To their astonishment, they reported, “We expected some property damage—chimneys knocked down, walls cracked or plaster fallen to the ground—but there were no obvious signs of property damage.” This observation starkly contrasted with the overwhelmingly high number of felt reports from the New York City area, where residents experienced what they described as strong shaking, despite being over 65 kilometers away from the epicenter. The earthquake amassed more than 180,000 felt reports, the highest ever recorded for a single earthquake via the U.S. Geological Survey’s (USGS) “Did You Feel It?” platform. An estimated 42 million people across the eastern U.S., from Virginia to Maine, reported feeling the tremor. Notably, while reports from areas southwest of the epicenter indicated weak shaking, those northeast reported light to moderate shaking—contradicting standard models that predict strong shaking within roughly six miles of the epicenter. To further understand these dynamics, Kim and her team utilized seismic wave data, particularly Lg waves, which are seismic waves that propagate within the Earth’s crust. Their analysis revealed the earthquake rupture traveled east-northeast down a fault plane dipping towards the east, potentially directing the shaking away from the epicenter and towards the northeast, thus explaining the uneven distribution of reported shaking. Unlike typical northeastern U.S. earthquakes that occur along north-south trending thrust faults, Tewksbury’s earthquake exhibited characteristics of both thrust and strike-slip mechanisms along a possible north-northeast trending fault. Despite this insight, the researchers have yet to pinpoint a specific fault responsible for the quake, although evidence suggests that the well-known Ramapo fault system was inactive during the event. Observations made by response teams uncovered instances of structural damage, including cracks and the partial collapse of historical structures such as Taylor’s Mill near Lebanon, New Jersey. Oliver Boyd of the USGS emphasized that these findings could reshape our understanding of seismic activity in the eastern United States. He noted, “Good station coverage can also allow us to observe how earthquake ground motions vary across the region as a function of magnitude, epicentral distance, and Earth structure, each of which can help us better appreciate potential seismic hazards.”

The Tewksbury earthquake serves as a significant case study in understanding seismic activity on the U.S. East Coast, which is not typically associated with earthquakes of notable magnitude. The 4.8 magnitude event occurred on April 5, 2024, catching the attention of researchers due to a discrepancy between the level of shaking reported in distant cities like New York and the apparent lack of damage at its epicenter. This prompted scientists to investigate the factors contributing to this phenomenon, including the orientation of the earthquake’s rupture and the geological characteristics of the area.

The Tewksbury, New Jersey earthquake illustrates a complex interaction of geological factors that resulted in widespread felt reports and minimal local damage. The findings, notably regarding the earthquake’s rupture direction, enhance our understanding of seismic behavior in the northeastern United States and may help identify new sources of earthquakes in the region. Continued study and monitoring will provide essential insights into how the crust behaves during such events and what potential hazards may arise in the future.

Original Source: phys.org