NYC area hit with aftershock after rare 4.8-magnitude quake. There could still be more.

• The East Coast was rocked by a rare 4.8 magnitude earthquake on Friday morning.
• The US Geological Survey warned that the region will be hit with aftershocks.

New York City experienced an aftershock just hours after it was hit with a rare 4.8 magnitude earthquake on Friday morning.

The NYC Emergency Management Agency said on X around 6 p.m. local time that it was experiencing "shaking" at the facility.

The US Geological Survey confirmed the aftershock and reported that initial data showed the new quake had a 4.0 magnitude with its epicenter near Gladstone, New Jersey.

"Aftershocks will continue for days and weeks ahead. When shaking starts, remember to Drop, Cover, and Hold On," USGS posted with its announcement.

More specifically, official guidance is to drop where you are, cover your head and neck (ideally by crawling under a sturdy table or other low-lying furniture that can protect you), and hold on until the shaking stops.

Running for doorways or trying to leave a building during shaking is not safe.

Experts further advised Business Insider that East Coasters should prepare for aftershocks by moving or securing loose objects that could fall on you, especially anything above you while you sleep.

Aftershocks were expected, and there could still be more

Following the morning 4.8 magnitude earthquake, USGS seismologists warned that the East Coast could experience aftershocks in the coming weeks to months, most likely in the "two or three range."

There is a small chance of an aftershock of similar or greater magnitude than the initial quake.

"No one can predict the exact time or place of any earthquake, including the aftershocks," Jessica Jobe, a geologist at the US Geological Survey, said in a briefing following the morning quake.

However, aftershocks "tend to get progressively smaller over time, and they tend to get progressively rarer over time," Ben Fernando, a post-doctoral fellow studying seismology at Johns Hopkins, told BI after the 4.8 quake in the morning. "People should just stay alert, monitor alerts that are put out, et cetera."

The Friday morning earthquake was a rare seismological event that was felt by the entire tristate area, from Norfolk, Virginia, and Philadelphia to Boston and Maine, according to the USGS.

It came from a system of dozens of fault lines which have been dormant for millions of years, USGS seismologists reported.

"As we have tectonic plates move, and stresses kind of moving around in the Earth's crust, every now and then one of those faults will become infrequently or intermittently active, just in a single earthquake, or a series of small earthquakes," Jobe said.

According to a 2019 report on earthquake mitigation, it may have been the largest earthquake felt by the state of New Jersey in about 250 years.