ALBANY COUNTY — Tremors from an earthquake centered in New Jersey were felt in Albany County on Friday morning.

At 10:23 a.m. Eastern Standard Time, a quake centered in Whitehouse Station, New Jersey was felt from Philadelphia to New York City and beyond.

The United States Geologic Survey reports the magnitude of the earthquake at 4.8 and the depth at 4.7 kilometers, nearly 3 miles, reaching a minimum distance of 72.1 kilometers, nearly 45 miles.

A series of smaller aftershocks followed.

Governor Kathy Hochul held a press conference Friday morning, saying the earthquake was felt in Albany and across New York state.

“At this point, heading into an hour and a half after the effects,” Hochul said, “we’ve not identified any life-threatening situations, but we are certainly asking our local law enforcement and emergency services teams to be on guard for that as well.”

She said that “all potentially vulnerable infrastructure sites throughout the state” would be reviewed.

At noon, New York City Mayor Eric Adams held a press conference with a slew of city commissioners, all stating that no injuries or infrastructure damage had been reported.

“All of us felt in some way or another the earthquake that hit our city,” said Adams, noting New York was 50 miles from the epicenter.

“New Yorkers should go about their normal day,” he said, stressing the safest place for children was in their school — a message echoed by the city’s education commissioner, Chancellor David Banks.

USGS mapped the reach of the earthquake and colored the epicenter green, for V, which indicates “moderate” shaking and “very light damage.”

All other areas where tremors were felt are colored blue, labeled IV, indicating “light” shaking and no damage.

The shaking scale runs from I for “not felt” to X for "extreme."

The USGS also charted shaking-related fatalities and economic loss from Friday morning’s earthquake. While noting the data was the “most preferred available” but not reviewed by a scientist, USGS concluded, “There is a low likelihood of casualties and damage.”

Finally, on X, formerly Twitter, USGS has a portal where “citizen scientists” — anyone who felt Friday morning’s tremor — can report their experiences.

Scientists have developed two ways to measure the size of earthquakes — through magnitude and through maximum intensity. Magnitude is the most familiar measure, often expressed on the Richter scale.

Scientists measure the zig-zags on a seismograph and compare that with a standard reference for earthquakes. The resulting number expresses the strength of an earthquake at the place where it started. Each whole number expresses a 10-fold increase in ground motion.

Up to a magnitude of 2 is usually detected only by instruments; a magnitude of 3 can be felt indoors; M4 can be felt by most people and cause light damage; M5 can be felt by everyone and the damage is mild to moderate; M6 causes moderate to major damage; M7 causes major damage; and, with an M8 earthquake or greater, there is major destruction.

The San Francisco earthquake of 1906, probably the most vivid in American consciousness, had a magnitude of 8.3.

Aftershocks

USGS also charts the chance of aftershocks.

The mainshock is the largest earthquake in a sequence, a series of earthquakes related to each other, the USGS explains. The aftershocks follow the mainshock.

“No one can predict the exact time or place of any earthquake, including aftershocks,” says USGS.

An hour after the April 5 mainshock, a 2.0 aftershock hit near Bedminster, New Jersey, followed by an 1.8 magnitude aftershock at 12:30 p.m., a 2.0 magnitude aftershock at 1:14 p.m., another 2.0 aftershock just before 3 p.m., and then a 3.8 magnitude aftershock near Gladstone, New Jersey, at around 6 p.m., striking 9.7 kilometers deep.

However, the USGS charts the chance of aftershocks in an interactive graph within various periods of time. Within one day, there is a 34 percent chance of a magnitude 3 aftershock and a 9 percent chance of a magnitude 4 aftershock. The chances of aftershocks of greater magnitude are 1 percent or less.

Within one month, there is a 54 percent chance of a magnitude 3 aftershock, a 21 percent chance of a magnitude 4 aftershock, a 4 percent chance of a magnitude 5 aftershock. The chances of aftershocks of greater magnitude are less than 1 percent.

Within one year, there is a 62 percent chance of a magnitude 3 aftershock, a 24 percent chance of a magnitude 4 aftershock, a 4 percent chance of a magnitude 5 aftershock. The chances of aftershocks of greater magnitude are less than 1 percent.

Mayor Adams encouraged New Yorkers to check on their loved ones, stating, “This can be extremely traumatic.”

Both Adams and Hochul warned of aftershocks and gave advice similar to that from USGS: Drop, cover, and hold on.

USGS elaborates on this advice:

— Drop where you are, onto your hands and knees. This position protects you from being knocked down and reduces your chances of being hit by falling or flying objects;

— Cover your head and neck with one arm and hand. If a sturdy table or desk is nearby, crawl underneath for shelter. If no shelter is nearby, crawl next to an interior wall. Stay on your knees; bend over to protect vital organs;

— Hold on until the shaking stops. Under shelter: hold on to it with one hand; be ready to move with your shelter if it shifts. No shelter: hold on to your head and neck with both arms and hands.

The USGS advice comes with this warning: “Your past experience in earthquakes may give you a false sense of safety; you didn't do anything, or you ran outside, yet you survived with no injuries. Or perhaps you got under your desk and others thought you overreacted.

“However, you likely have never experienced the kind of strong earthquake shaking that is possible in much larger earthquakes: sudden and intense back and forth motions of several feet per second will cause the floor or the ground to jerk sideways out from under you, and every unsecured object around you could topple, fall, or become airborne, potentially causing serious injury.

“This is why you must learn to immediately protect yourself after the first jolt — don't wait to see if the earthquake shaking will be strong!

East Coast quakes

Earlier this year, USGS warned that nearly 75 percent of the United States could experience damaging earthquake shaking in the next century, including the possibility of damaging earthquakes along the northeastern United States. 

The report noted that on Aug. 10, 1884, a magnitude 5.2 quake struck near Coney Island in New York city, shaking homes, crumbling chimneys, and leaving many confused by what had happened. 

In February, it asked the prescient question, “Would people be any less baffled if a large earthquake struck the city today?”

At that time, the USGS released a multilingual earthquake preparedness flier aimed at showing New York City dwellers what to do if they feel the ground shake: drop, cover, and hold on.

The USGS also provides a tectonic summary of earthquakes in the New York - Philadelphia - Wilmington Urban Corridor.

Since colonial times, it says, residents of that corridor have felt small earthquakes and suffered damage from infrequent larger ones. New York City was damaged in 1737 and 1884. Moderately damaging earthquakes strike somewhere in the urban corridor roughly twice a century, and smaller earthquakes are felt roughly every two to three years.

Although less frequent than earthquakes in the western United States, earthquakes in the central and eastern part of the country are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ao times larger than a similar magnitude earthquake on the west coast.

A magnitude 4.0 eastern U.S. earthquake, similar to the one on Friday, typically can be felt at many places as far as 60 miles or 100 kilometers from where it occurred, and it infrequently causes damage near its source.

A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 300 miles or 500 kilometers from where it occurred, and sometimes causes damage as far away as 25 miles or 40 kilometers.

Earthquakes everywhere occur on faults within bedrock, USGS explains, usually miles deep. Most bedrock beneath the urban corridor was assembled as continents collided to form a supercontinent about 500 to 300 million years ago, raising the Appalachian Mountains.

Most of the rest of the bedrock formed when the supercontinent rifted apart about 200 million years ago to form what are now the northeastern United States, the Atlantic Ocean, and Europe.

At well-studied plate boundaries like the San Andreas fault system in California, scientists can often determine the name of the specific fault that is responsible for an earthquake.

However, east of the Rocky Mountains this is rarely the case. New York City, Philadelphia, and Wilmington are far from the nearest plate boundaries, which are in the center of the Atlantic Ocean and in the Caribbean Sea.

The urban corridor is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths. So few, if any, earthquakes in the urban corridor can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake.

“As in most other areas east of the Rockies, the best guide to earthquake hazards in the New York - Philadelphia - Wilmington urban corridor is the earthquakes themselves,” the USGS concludes.

Local quakes

More than 50 small earthquakes have happened in and around Altamont since Jan. 1, 2000, according to a search on the USGS website, with the latest in March 2021.

Three decades ago, a seismograph machine was placed in the Helderbergs by the New York State Geological Survey to track tremors there — part of a network recording seismic activity in the northeastern United States and Canada.

Since the 1980s, there have been small earthquakes in the Helderbergs

“We feel the potential is there for an earthquake as large as [magnitude] 6,” Gary Nottis, a research assistant in seismology, told The Enterprise in 1991, when the seismograph was installed.

Nottis said the Thompsons Lake area had a series of small earthquakes and one, on Feb. 8, 1982, with a magnitude of 2.8, was not felt by anyone. It was preceded by several small earthquakes, called foreshocks, which typically occur days or hours before a larger quake. Aftershocks can occur for years after an earthquake.

Most earthquakes occur along edges of the Earth’s tectonic plates. Due to forces in the Earth’s molten interior, the tectonic plates move at a rate of up to four inches a year, traveling on a layer of softer rock called asthenosphere.

The plates separate or collide along their borders as they move, causing earthquakes and tremors. Even earthquakes many miles from a plate border can often be explained by the ripple effect of backup pressure caused by the collision.

A fault line runs from the Helderbergs to Lake George in the Adirondacks. An earthquake with a magnitude of 5.3 caused damage in Ausable Forks in 2002. On Oct. 7, 1983, an earthquake with a magnitude of 5.1 shook Newcomb in Essex County.

Both of those Adirondack earthquakes were in rural areas where no one was injured.

On June 17, 1991, Schoharie County had an earthquake with a magnitude of 4. In the 1870s and 1880s, there were two earthquakes in Schoharie County strong enough for people to feel.

The largest recorded earthquake in New York State was in Massena in St. Lawrence County on Sept. 5, 1944 with a magnitude of 6.

Roughly every 20 years, there is a damaging earthquake in New York State.