NYC earthquake: Where was the epicenter? How long did it last? Answering top questions

California may be used to powerful earthquakes, but NYC area residents were shocked, surprised and confused when a quake rocked the Tri-State Friday morning.

Some thought they felt an explosion, and one coffee shop patron was captured on video asking, "Am I gonna die?" 

Here's what you need to know about the earthquake felt by millions on the East Coast.

Where was the earthquake?

The U.S. Geological Survey reported a quake at 10:23 a.m. with a preliminary magnitude of 4.8, centered near Whitehouse Station, New Jersey, or about 45 miles (72 kilometers) west of New York City and 50 miles (80 kilometers) north of Philadelphia.

How long did the earthquake last?

The earthquake lasted for about 30 seconds,

How many people felt the earthquake?

The agency's figures indicated that over 42 million people might have felt the rumbling. People from Baltimore to the Massachusetts-New Hampshire border reported feeling the ground shake.

Were there aftershocks? Will there be more?

At least four aftershocks were reported near the epicenter of Friday's quake as of 2:30 p.m.

According to the USGS forecast, there is a 45% chance of at least one 3+-magnitude aftershock within the next week.

Earthquake map

Why did an earthquake hit the East Coast?

Earthquakes are less common on the eastern than western edges of the U.S. because the East Coast does not lie on a boundary of tectonic plates. The biggest Eastern quakes usually occur along the mid-Atlantic Ridge, which extends through Iceland and the Atlantic Ocean.

Quakes on the East Coast can still pack a punch, as its rocks are better than their western counterparts at spreading earthquake energy across long distances.

"If we had the same magnitude quake in California, it probably wouldn’t be felt nearly as far away," said USGS geophysicist Paul Caruso.

Robert Thorson, a University of Connecticut earth sciences professor, said the quake resulted from the constant compression of the earth's hard, brittle crust in New Jersey.

"It’s like having a big block of ice in a vise, and you are just slowly cranking up the vise," he said. Eventually, you’re going to get some crackling on it."

Earthquakes with magnitudes near or above 5 struck near New York City in 1737, 1783 and 1884, the USGS said. And Friday's stirred memories of the Aug. 23, 2011, earthquake that jolted tens of millions of people from Georgia to Canada. With an epicenter in Virginia, it left cracks in the Washington Monument and rattled New Yorkers ahead of the 10th anniversary of the Sept. 11 terror attacks.

A screen shows an emergency alert in New York City area, Friday, April. 5, 2024, in New York. An earthquake shook the densely populated New York City metropolitan area Friday morning, the U.S. Geological Survey said, with residents across the Northea

When was the last time NY had an earthquake?

In January. an earthquake was reported in New York City Tuesday morning and may have prompted reports of an explosion on the East River's Roosevelt Island.

The U.S. Geological Survey reported a 1.7 magnitude earthquake near Astoria, Queens.

The Associated Press contributed to this report.