Investigating the Surprising Effects of the Tewksbury Earthquake on Seismic Perception

A magnitude 4.8 earthquake in Tewksbury, New Jersey, was felt across a wide region, including New York City, with minimal damage reported locally. Researchers found the direction of the earthquake’s rupture may explain the widespread shaking reports, indicating a need to reevaluate seismic risks and fault lines in the eastern United States.

On April 5, 2024, a magnitude 4.8 earthquake struck Tewksbury, New Jersey, marking the most powerful instrumentally recorded seismic event in the state since 1900. The earthquake was notably felt across a vast region of the U.S. East Coast, with millions reporting trembling sensations. However, an intriguing observation arose: residents in New York City, approximately 40 miles away, reported significantly strong shaking despite minimal damage being documented near the epicenter. In a study published in The Seismic Record, YoungHee Kim of Seoul National University and her colleagues investigated this peculiar pattern of seismic activity. After surveying the area just hours following the earthquake, the researchers were surprised to find little to no physical damage to structures, which contradicted expectations from a magnitude of this scale. “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,” the researchers noted in communications. By contrast, the `U.S. Geological Survey` (USGS) received over 180,000 reports of shaking through their “Did You Feel It?” app, indicating widespread felt sensations. This earthquake reportedly affected around 42 million people from Virginia through to Maine. Reports from areas southwest of the epicenter indicated only “weak” shaking, while those northeast reported “light to moderate” sensations. The researchers theorized that the direction in which the earthquake rupture occurred played a critical role in influencing the perceived intensity of shaking. Using a specific type of seismic wave, the Lg waves, Kim and her colleagues modeled how the rupture propagated. Their findings suggested that the earthquake ruptured east-northeast down an east-dipping fault plane, potentially channeling the seismic energy away from Tewksbury and towards the northeast. Notably, this earthquake in New Jersey is atypical as most earthquakes in the northeastern U.S. typically occur on north-south trending faults. The Tewksbury event seems to have resulted from a complex interaction of thrust and strike-slip faulting. Following the main shock, a series of aftershocks were recorded, reinforcing the presence of a previously hidden fault in the area. While a reconnaissance team documented some minor damages such as cracked drywall and items dislodged from shelves, broader impacts on infrastructure appeared limited. The researchers have yet to identify a specific fault responsible for the earthquake, suggesting that the well-known Ramapo fault system may not have contributed to this event. Kim and her colleagues emphasize the implications of this quake for understanding seismic risks in the eastern United States. “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,” they concluded, indicating that ongoing research could enhance preparedness for future seismic events.

Earthquakes in the northeastern United States, particularly those occurring in states like New Jersey, are infrequent compared to other regions, which raises interest when significant seismic events such as the Tewksbury earthquake occur. Historically, such earthquakes have been linked to established fault lines; however, new research indicates more complex interactions may be at play. This particular earthquake not only challenged existing models of earthquake intensity and damage expectations but also provided an opportunity for researchers to reassess the region’s seismic vulnerabilities and understanding of fault mechanics. The Tewksbury earthquake, being the largest in New Jersey’s recorded history since 1900, has become crucial in informing both scientific inquiries and community preparedness for future seismic activity.

The magnitude 4.8 earthquake that occurred in Tewksbury, New Jersey, offers crucial insights into rare seismic events in the eastern United States. The study highlights the unexpected intensity of shaking felt in remote locations such as New York City compared to minimal damage near the epicenter. Researchers concluded that the earthquake’s rupture direction likely influenced the distribution of felt reports. As investigations continue, the findings have promising implications for understanding previously overlooked seismic sources, enhancing future preparedness and response strategies.

Original Source: phys.org