Friday's earthquake ranks among largest ever in NJ and NYC, scientists say

Friday's 4.8-magnitude earthquake flustered and unnerved New Yorkers for good reason: It was one of the largest in the region's recorded history.

Geologists say it’s very uncommon for earthquakes of that magnitude to originate in the area, but it has happened before. At least three stronger earthquakes struck the region in the 1700s and 1800s, U.S. Geological Survey officials said.

Such earthquakes are unsettling and can cause damage, as in Newark on Friday, where dozens of people were evacuated from their homes. But experts said they are generally not deadly. Putting Friday's event into context, Rutgers geology professor Alexander Gates said that “killer earthquakes are something above a 7.”

Technology used to measure earthquake strength wasn’t widely standardized until the 1950s. That means measurements prior to that were less reliable than those conducted with more modern technology, said John Mutter, a professor of earth and environmental sciences at Columbia University.

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A partial history of earthquakes in our region

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1737: An estimated 5.1 magnitude quake hit the greater New York City area, according to the USGS. The New Jersey Department of Environmental Protection said the quake was felt from Boston to Philadelphia, and some chimneys fell down in New York City.

1783: An earthquake west of New York City was estimated to be 5.1 in magnitude, according to the USGS. People felt it from New Hampshire to Pennsylvania, the New Jersey Department of Environmental Protection said.

1884: An estimated 5.3 magnitude quake toppled chimneys in New York City and New Jersey, according to the New Jersey Department of Environmental Protection. People reported feeling it from Maine all the way to Virginia.

1927: An earthquake struck off the New Jersey coast, according to the New Jersey Department of Environmental Protection. The magnitude is unknown, but there were reports of chimneys damaged from Asbury Park to Long Branch.

Today's scientists use a global network of machines to ensure accurate readings.

“There's a network of seismometers throughout the world that are identical. So the readings you get from one are directly comparable with the readings you get from another,” Mutter said.

There have been several magnitude 4.0 earthquakes recorded in the region in recent decades, according to USGS.

Friday's quake had an epicenter about 50 miles west of New York City where no active fault lines exist. However, long dormant fault lines can become briefly reactivated. Mutter said Friday’s quake might have occurred along the Ramapo Fault, a fissure that was tectonically active about 200 million years ago and once caused much larger earthquakes.

Paul Earle, a seismologist with the USGS’s National Earthquake Information Center, said earthquakes on the East Coast often are felt more widely than those on the West Coast because the rock is harder and the seismic waves travel further.

“In the past hundred years, there have been a handful of earthquakes in the broader area of similar magnitudes,” Earle said. “You’re going to have a lot more people feeling this earthquake than you would a similar size earthquake in California.”

USGS had reported several small aftershocks near the original epicenter as of Friday afternoon followed by a larger 3.8 magnitude quake that hit just before 6 p.m. On Friday evening the federal agency estimated there is a 78% chance of another 3.0-or-greater aftershock within the next week and a 16% chance of a 4.0-or-greater aftershock.

This story is based on preliminary data from the USGS and is subject to change.