Earthquake's Major Tremors Felt 65 Kms Away in New York From Epicenter in New Jersey Baffle Scientists

The Tewksbury earthquake's strange impact on April 5 this year raised the eyebrows of seismologists worldwide. The event did not cause any major damage, but was 'experienced' by millions across cities far away from the epicenter, SciTech Daily reported. The phenomenon originated in New Jersey and made its impact felt in faraway New York.

After analysis, researchers in a study published in GeoScience World concluded, that the waves traveled such a massive distance, because of a combination of various unique factors.

They pointed out the rupture direction and funneling shaking from New Jersey towards New York City as major reasons behind the Tewksbury earthquake's widespread reach.

The Tewksbury Earthquake

The Tewksbury earthquake was first noted on April 5 in a northern New Jersey township, State of the Planet reported. It was recorded to have a magnitude of 4.8, which caused concern among the city's authorities. The region is no stranger to occasional small tremors, but such a high-magnitude earthquake had not occurred here since 1884.

The existing models of the region, available to seismologists indicate that an earthquake of such power should cause severe damage at the epicenter, but this is not what happened. More impact was experienced in New York City, with shaking extending to Virginia and Maine.

Peculiar Behavior of Earthquake

Researchers gathered all the available data and testimonies about incidents that occurred on the day of the earthquake, SciTech Daily reported. The testimonies revealed that the earthquake did not follow experts' assumptions.

"We expected some property damages—chimneys knocked down, walls cracked or plasters fallen to the ground—but there were no obvious signs of property damages," the researchers said in an email. "Police officers within a couple of kilometers from the reported epicenter calmly talked about the shaking from the mainshock. It was a surprising response by the people and houses for a magnitude 4.8 earthquake in the region."

In comparison, Residents in and around New York City located 65 kilometers away from the epicenter experienced more impact, as per their testimonies.

Analysis of the Earthquake

The previous model available to experts implied that an earthquake with a magnitude of 4.8 should cause strong shaking within about 10 kilometers or about six miles from its epicenter, SciTech Daily reported. Keeping this pattern in mind, the research team examined the directivity of the earthquake’s rupture.

Earthquake rupture is defined as the spatial and temporal distribution of displacement discontinuity that occurs in fault planes during the disaster, Science Direct reported. The rupture model showcases, the direction undertaken by the cracks in the fault during the disaster.

To create the rupture model, the researchers had to focus on Lg waves, since they had very little data regarding the seismic behavior, that took place in the area, during the earthquake. Lg waves are the kind of seismic waves that bounce back and forth from the crust between the Earth’s surface and the boundary between the crust and mantle. The model showcased that the earthquake rupture moved toward the east-northeast and then took a downturn on an east-dipping fault plane. 

Results

Researchers concluded that the direction undertaken by the rupture funneled the earthquake waves away from the epicenter, and directed them toward the northeast, SciTech Daily reported. The experts further noted that the Tewksbury Earthquake originated differently, compared to other similar phenomena in the area.

"Earthquakes in eastern North America usually occur along the pre-existing zone of weakness—that is, existing faults," the researchers explained.

"In the Tewksbury area, a hidden fault plane trending north-northeast and dipping moderately can be mapped from the numerous small aftershocks detected and located" after the Tewksbury mainshock. The researchers now want to find the particular fault, that caused the Tewksbury event. They believe this will help authorities in reexamining the assumptions in place about regional surface mechanisms.

"This can help us study, for example, mechanisms related to how the crust responds to the stress of a mainshock in the region, and how productive aftershock sequences can be in the eastern United States," USGS seismologist, Oliver Boyd, who was involved in the study explained.