A 4.8 magnitude earthquake rattled NJ on April 5, 2024. What we've learned since

Yahoo

06-04-2025

One year ago, on April 5, 2024, a magnitude 4.8 earthquake struck near Tewksbury, rattling homes and nerves across New Jersey and beyond. The strongest quake to hit the state in more than a century, it was felt from Virginia to Maine but left little lasting damage.
The Hunterdon County earthquake was the most significant to hit North Jersey since Aug. 10, 1884. On that day, a magnitude 5.2 quake near Jamaica Bay in New York shook buildings as far inland as Rahway.
Only three other quakes in modern history have caused damage in the Garden State: one in 1737 near Weehawken, another in 1783 in the Rockaway Township area and a third in 1927 off the coast near Asbury Park. The damage in those cases was limited to collapsed chimneys and falling objects—similar to the minor incidents reported in 2024, according to the New Jersey Office of Emergency Management.
The state has no record of an earthquake-related fatality.
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The epicenter of last April's quake was located about two miles from Tewksbury, within the Ramapo Fault System. This fault network, running from Pennsylvania through northern New Jersey and into New York, is the region's most active seismic zone. Though earthquakes are more common in plate boundary regions, the Ramapo Fault is among the few locations in the eastern U.S. with recurring seismic activity.
The April 2024 earthquake's damage was wide-ranging and not limited to the area around the epicenter. That is unusual, as were the high number of aftershocks — more than 200 — according to findings by the Columbia Climate School's Lamont-Doherty Earth Observatory.
"Once it moved, it stressed the whole area," said Rutgers-Newark geology professor Alexander Gates, noting the aftershocks were scattered around the epicenter "like a shotgun blast."
Based on existing models, the epicenter of the earthquake should have sustained substantial damage. It did not. Meanwhile, New York City shook harder than expected, suffering some minor damage.
While a 4.8 magnitude earthquake is not major, it was felt by 42 million people, according to the U.S. Geological Survey. The response triggered by the quake was also unusual. The USGS online portal that crowdsources first-person reports of shaking received nearly 184,000 entries — the most from any U.S. earthquake.
Scientists at South Korea's Seoul National University analyzed the low-frequency waves of energy that bounced back and forth between the Earth's surface and the boundary between the Earth's crust and mantle, which in this area lies about 35 kilometers or 21 miles down.
Their analysis suggests that the quake took place on a previously unmapped fault that runs from south to north. The fault is not vertical but rather dips eastward into the Earth at about a 45-degree angle.
According to the analysis, the movement was rapid and complex. There was a circular combination of the two sides of the fault sliding horizontally against each other and one side also shoving itself up and over the other.
In 2025, things have been quiet deep underground. Some state residents felt the earth shake in the early morning of March 21, when a minor earthquake struck Somerset County, but no damage was reported, officials said.
The 1.8-magnitude earthquake originated about 4.3 miles from Gladstone, not all that far from Tewksbury, according to the U.S. Geological Survey. It struck at 8:23 a.m. about 5 miles deep.
Residents reported minimal shaking, according to Cartographer Mitch Adelson.
Some residents also reported feeling some shaking on Jan. 24, when, according to the U.S. Geological Survey's earthquake map, a magnitude 2.4 earthquake with a depth of more than 8 miles occurred near Paramus just after 1 p.m. No damage was reported, but residents reported loud booms, rattling and shaking.
Most years are relatively quiet, according to Gates. In the half-century before 2024, the state had about 350 earthquakes. Most are too small to cause major concern.
Before April 2024, the largest quake in the state this century was a 3.5 magnitude event north of Milford. Most others have been below 2.0, according to state records.
Earthquakes below magnitude 2.5 are generally too weak to be felt, according to an assessment from Michigan Tech University. Those between 2.5 and 5.4 are typically noticeable but cause little damage. Quakes ranging from 5.5 to 6.0 can result in minor structural damage.
Despite the rarity of strong earthquakes, vulnerabilities exist.
Earthquakes like last year's were intraplate quakes, occurring within a tectonic plate rather than along its boundaries.
"These are really difficult to predict," Gates said, comparing them to interplate quakes that happen where plates meet.
Interplate quakes, like those that occur along the famous San Andreas Fault in California, are more predictable than the ones that hit near New Madrid, Missouri, in the early 1800s, he added.
The first, estimated at a magnitude between 7.2 and 8.2, hit on Dec. 16, 1811. It was followed by a 7.4 aftershock the same day. Two more quakes of similar magnitude followed in January and February 1812.
"Those were monsters," Gates said. "That's three in less than two years, and then nothing."
New Jersey's major modern-era quakes have been in the magnitude 5.0 range and normally happen in 100-year cycles, Gates said.
"Does that mean we have to wait 100 years for another?" Gates said. "Most Likely. Can I say that another one will not happen in the foreseeable future with any certainty? No."
There also remains the possibility of a New Madrid-type catastrophe. Modelling shows the Metro New York area is due for a similar size earthquake, 7.0 or greater, every 3,500 years, he said.
If a major quake does hit, the state and federal departments of transportation's liquefaction maps indicate that bridges in Bergen, Essex, Hudson, Middlesex, Ocean and Union counties have a high risk of ground instability. Older buildings and infrastructure — built before modern seismic codes — are also more susceptible to damage.
A 2,500-year earthquake event could lead to economic losses of more than $24 billion, according to the 2024 New Jersey State Hazard Mitigation Plan. Hazard levels are highest in Bergen, Hudson and Passaic counties. Levels generally decrease to the west and south.
Historical records show that earthquake epicenters have been recorded in 20 of New Jersey's 21 counties. Most have occurred in the northern part of the state, but every county except Cape May includes earthquakes as a hazard in its mitigation plans.
Like other natural disasters, earthquakes can severely disrupt critical infrastructure, leading to power outages, fuel shortages and failures in water supply and energy distribution systems.
Earthquakes can trigger landslides and mudslides, particularly on steep slopes with clay-rich soils that lose cohesion during seismic activity. Unstable slopes can also release hazardous materials, posing risks to people and the environment. Earthen dams and levees are especially vulnerable, with failures considered a secondary risk of earthquakes, state records show.
Dam failures caused by earthquakes typically result from slumping or settlement in earth-fill dams that were not properly compacted, according to state reports. If a dam slumps while full, overtopping and rapid erosion can lead to structural failure. Concrete dams may also suffer heavy damage from strong ground motion, while earthquake-induced landslides into reservoirs have been known to cause dam collapses.
Tsunamis, though rare in the region, can also result from earthquakes. On Nov. 18, 1929, just as the Great Depression was beginning to take hold around the world, a 7.2 magnitude earthquake rocked the Western North Atlantic, according to the National Oceanic and Atmospheric Administration. It was felt as far away as New York and Montreal, but it was not clear at first that an underwater landslide had triggered a tsunami.
About two and a half hours after the earthquake, the tsunami hit the southern end of Newfoundland's Burin Peninsula in three main surges. Reports put wave heights as high as 13 meters (42.6 feet). The tsunami was recorded along the east coast of Canada and the U.S., in Bermuda and as far south as Martinique in the Caribbean.
This article originally appeared on NorthJersey.com: What we've learned since a 4.8 magnitude earthquake rattled NJ