Why Earthquake Aftershocks Continue Rattling NJ After Historic April Tremor

Nearly one month after New Jersey experienced a historic 4.8-magnitude earthquake, parts of the state are still experiencing aftershocks and residents are wondering if it's a cause for concern.

The April 5 earthquake originated in Hunterdon County near Tewksbury and could be felt throughout New Jersey, New York and Pennsylvania. While the tremor spurred waves of jokes and memes, the last time an earthquake of that magnitude or higher was recorded in the area was 1973.

The U.S. Geological Survey (USGS) told Newsweek it has recorded 161 earthquakes connected to the Tewksbury quake. The most recent aftershock occurred on Wednesday just after 7 a.m. near Gladstone, measuring at a magnitude of 2.6. The area also experienced a 2.9-magnitude earthquake last Saturday.

James Bourke, a post-doctoral fellow at the Rutgers University Department of Earth and Planetary Sciences, told Newsweek the aftershocks are especially affecting those near the epicenter.

"For the people living directly above the earthquakes, they are feeling most or all of these," Bourke said. "I have spent the last few weeks driving around North-Central New Jersey installing sensors and there is a real concern by many people I have spoken to that live around the epicenter."

Despite residents' fears, Bourke explained the aftershocks will likely decrease in magnitude over time and it is unlikely for the area to experience another large quake.

"There is absolutely no reason to be concerned, what is most likely is we have experienced the larger aftershocks already, and they will decrease in size as time goes on," Bourke said. "There is a very small probability of another sizeable earthquake to occur, but again, there is little to no chance that it would be dangerous or destructive."

While seismic activity will likely decline over time, USGS said people in the affected area may experience earthquakes for the next year or longer.

Bourke said while there has been a "decent" amount of aftershocks, it can possibly be attributed to the rarity of the earthquake.

"They do seem to be rather consistent, this is likely due to the nature of the rocks, we do not experience earthquakes here in [New Jersey], so when they occur it may take the rocks a bit of extra time to settle into a new equilibrium," Bourke said. "Again, it is important to note that we do not expect this to produce any strong or dangerous earthquakes.