With 50 Aftershocks Recorded Since Quake; Team Sets Out To Study Data

LONG ISLAND, NY — Six days after Friday's earthquake, which registered at a 4.8 magnitude and was deemed one of the largest in the last century in the area — a series of now-50 aftershocks have rattled New Jersey, with some felt across Long Island and the tri-state region.

To that end, a U.S. Geological Survey team has begun a seismic sensor deployment in an effort to capture aftershock data.

The team is deploying eight "aftershock kits" this week, which will gather information such as where aftershocks originate in the area, how long they last, and their magnitude, said Greg Tanner, a USGS electronics technician assigned to the USGS’s Albuquerque Seismological Laboratory, who is on the team installing kits in New Jersey.

This effort is being performed in cooperation with partners at the Lamont Doherty Earth Observatory at Columbia University, the Texas Seismological Network at the University of Texas at Austin, Rutgers University, and Yale University, that are also deploying seismic sensors, the USGS said.

Aftershocks are smaller earthquakes that occur in the same general area during the days to years following a larger event or "mainshock," the USGS said.

So far, the USGS has recorded 50 aftershocks ranging from magnitude 1.3 to 3.8 following the April 5 earthquake. In the coming week, the USGS forecasts that there is a 12 percent chance of a magnitude 3 or greater aftershock, and a one percent chance of a magnitude 4 or greater, the USGS said.

While earthquakes in the region are not frequent, they are not unexpected, explained USGS Research Geologist Jessica Thompson Jobe in a press conference held following the mainshock event Friday. She explained that while there are no active faults in that area, there are dozens of older, inactive faults that formed millions of years ago.

"Under the current stresses of tectonic plates moving, those faults can be intermittently reactivated," Jobe said.

Earthquakes are felt more intensely and farther from their epicenter in the eastern United States than in the West, which explains why there were wide reports of shaking along the East Coast, the USGS said.

More than 183,000 people self-reported feeling shaking using the USGS’s “Did you feel it?” tool online.

Eastern North America tends to have older rocks, some of which formed hundreds of millions of years before those in the West; these generally older formations have been exposed to extreme pressures and temperatures, making them often harder and denser, said USGS Research Geophysicist Oliver Boyd.

Faults in the older rocks have also had more time to heal, which allows seismic waves to cross them more effectively when an earthquake occurs.

"It’s like ringing a bell that’s in good condition verses ringing one with many cracks in it," Boyd explained. "The sound from the good bell will have a louder, stronger, and more lasting tone."

The aftershock kits deployed will include sensors that record strong motion and high frequency, a device that sends digital information through the cellular network, and solar panels. The sensors will send data in real time back to the USGS’s National Earthquake Information Center in Golden, Colorado for analysis. Some of the kits will stand alone and others will be co-located with already-existing stream gages monitored by USGS’s New Jersey Water Science Center, the USGS said.

"No one can predict the exact time, location, or place of any earthquake," said Sarah McBride with the USGS Earthquake Hazards Program.

However, studying aftershocks may provide researchers with vital information about the nature of earthquakes in order to best prepare for future events.

According to the United States Geological Survey, USGS, an earthquake registering as 4.8 took place 7 km northeast of Whitehouse Station, NJ Friday just after 10:20 a.m. The earthquake was felt across the tri-state area and upstate.

The New York State Office of Emergency Management sent out an alert just after noon. "An earthquake occurred in New Jersey. The earthquake has been felt throughout NY State. Aftershocks may occur. Call 911 only if you or others are injured or have an emergency."

The USGS said magnitude is expressed in whole numbers and decimal fractions, adding that "a magnitude 5.3 is a moderate earthquake, and a 6.3 is a strong earthquake." Michigan Tech reported that a magnitude of 2.5 to 5.4 is "often felt, but only causes minor damage", without about 500,000 reported yearly.

"A 4.8 magnitude earthquake hit west of Manhattan and has been felt throughout New York," Governor Kathy Hochul said. "My team is assessing impacts and any damage that may have occurred, and we will update the public throughout the day."

Hochul added: "This is one of the largest earthquakes on the East Coast to occur in the last century."

Across Long Island, residents turned to social media to share the experience: "My house shook," they echoed, one after another.