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AN UNDERESTIMATED DANGER: INTRAPLATE EARTHQUAKES IN THENORTHEASTERN US

This article discusses the causes of earthquakes in the Northeastern US and why they

have the potential to be so destructive, as well as how to mitigate their harm.


By Charlotte Laetsch

Introduction


On April 5, 2024, a magnitude 4.8 earthquake struck the Northeastern Coast of the United States in Whitehouse Station, New Jersey. It was the strongest earthquake in the region in over 241 years, rupturing gas lines, forming sinkholes, and damaging buildings throughout the Northeast. Although the earthquake itself had a relatively low magnitude on a global scale, it was felt across the eastern half of the continent, with an estimated 42 million people from Canada to Florida experiencing at least some degree of shaking. Despite not being located near a plate boundary, the Northeastern US experiences intraplate earthquakes like this relatively frequently – a magnitude 3 or greater earthquake happens in the area every couple of years.7 This article aims to explain the commonality and characteristics of earthquakes in the Northeastern US to better prepare for their effects.


A map showing Northeastern US, the region of interest, as well as the epicenter of the April 2024 earthquake (shown via a red star) and the observed intensity of shaking (Boyd et al.)
A map showing Northeastern US, the region of interest, as well as the epicenter of the April 2024 earthquake (shown via a red star) and the observed intensity of shaking (Boyd et al.)

Geologic History


To understand why these intraplate earthquakes occur today, you first have to look back into the past. About 300 million years ago, modern-day North America and Africa collided in the last mountain-building event that formed the Appalachian Mountains. The stress from these two landmasses pushing against each other broke the crust in several locations, creating numerous fractures and faults along the margins of the continents. Once the collision ceased and compressional stresses waned, these faults and fractures largely became inactive.


But this was not the end of these faults; the breaks in the crust left large zones of weakness throughout the region where the continents had first joined together. When Pangaea began to split apart 200 million years ago, the rifting naturally concentrated in

these preexisting zones of weakness, reactivating the faults that had first formed during collision. This activation and the reactivation created the unique fault geometry still found in the Northeastern US. Instead of being found individually, faults in the Northeast

usually occur in irregular systems of many faults that branch out from each other and then rejoin later along the system. Another effect of their unique formation is that despite frequently being shallow in the crust, most of these faults lack fault scarps or visible surficial evidence of their existence.


Stress Buildup


The Northeastern US has plenty of faults, but stress is also needed to create earthquakes. Rocks’ friction and resistance to bending mean that when stress is placed on them, they don’t move immediately, but instead slowly accumulate stress. Once this stress overcomes the rocks’ strength, the rocks slip past each other quickly and the stress is all released at once, causing an earthquake. Luckily for the earthquakes and unluckily for the people who live here, the stress conditions in the Northeastern US are constantly in flux. This is because the settling of rocks from rifting and convergence is still occurring, erosion of the Appalachian mountains decreases the overburden pressure on the faults, and the constant expansion of the Atlantic Ocean places compressional stress on the region. In addition, as ice sheets quickly advanced and then retreated in the area during the last ice age, a lot of weight was placed on the area and then removed. This pressure fluctuation created a rebound effect that stressed faults even more.1 When you combine all these factors in one area, it’s no wonder that stress sufficient to generate earthquakes frequently builds up in the Northeastern US. The region’s old, rigid bedrock helps too: it can store large amounts of stress without much deformation, meaning it abruptly fractures and creates powerful earthquakes with significant energy.


Earthquake Mechanisms


If you take a typical earthquake and map out the degree of shaking it caused in the surrounding areas, the pattern will reveal a circular bullseye with the highest values at the center. Models predicted that the epicenter of the April 2024 earthquake should have experienced high magnitude shaking, damaging and partially collapsing some buildings. However, the maximum damage seen in the epicenter was much less: just some cracking in drywall and objects falling off shelves. The shaking was actually strongest 110 km towards the northeast of the epicenter, near New York City.



As the map of intensity values on the left shows, the April 2024 earthquake had a distorted, non-circular pattern in which shaking could be felt farther away from the epicenter than expected. Part of this can again be explained by the local bedrock– the rigid, poorly fractured bedrock transmits seismic waves through it for longer distances than the younger, heavily faulted bedrock found in tectonically active regions. In fact, an earthquake on the East Coast travels on average 10 times farther than an earthquake on the West Coast due to these bedrock differences. However, this explanation doesn’t

account for the distribution of shaking intensity. For that, analyses of the fault that caused the earthquake had to be done by looking at the location of the aftershocks. Seismic data revealed a previously unmapped oblique-slip fault dipping at about 45 degrees towards the northeast, with rupture likely occurring down-dip in that direction.


In a typical earthquake, most of the energy released goes towards the surface, while in the April 2024 earthquake, most of the energy was channeled downwards into the crust. It travelled down until it hit the discontinuity between the crust and the mantle, where it bounced up and headed towards the surface, then hitting New York City. Once it reached the surface, it bounced back down, and it repeated this cycle until it slowly lost all its energy. This type of seismic wave is known as an Lg wave, and its unique properties allow Northeastern earthquakes to do more damage at greater distances from the epicenter.


Conclusion


The existence and size of Northeastern earthquakes has the possibility of posing a real threat to the lives and livelihoods of those in the area. A history of mountain building and rifting in the region has left a fault-rich area in one of the most populated places in the United States, with large cities like New York, Philadelphia, and Washington D.C. within the possible zone of destruction.10 The region’s rigid bedrock not only can store and release a large amount of the geologic stress common to the area, but it also efficiently transmits seismic waves, meaning even small earthquakes in the Northeastern US have the potential to cause widespread damage. Intraplate earthquakes are even more hazardous due to the lack of common knowledge about their risk. Neither the infrastructure nor the people of the region are prepared for the very real possibility of a large earthquake. The fault systems are not well mapped or understood, and there is no large-scale network of seismometers in the area to monitor the faults or alert the public in the case of an earthquake.


In addition, residential buildings, nuclear power plants, dams, and critical infrastructure like pipes or wires are severely underfortified.9 But more deadly than any of the infrastructure issues, the people in the region do not expect an earthquake to the extent that someone living in a tectonically active zone does. Public awareness remains limited, which can lead to panic during even small earthquakes. Updates in building codes and public education programs to take into account intraplate earthquakes are the clear solution to avert the harms to public safety and security that would otherwise arise. It is time to stop ignoring the seismic hazards of the Northeastern US just because it is not on a plate boundary, and fix.


References


1. Bassi, Margherita. (2024). “Geologists Finally Explain New Jersey’s Strange


2. Boyd, Oliver S. et al. (2024). “Preliminary Observations of the 5 April 2024 Mw


3. Crone and Wheeler. (2000). “Data for Quaternary faults, liquefaction features,

and possible tectonic features in the Central and Eastern United States, east of the

Rocky Mountain front”. https://pubs.usgs.gov/of/2000/ofr-00-0260/ofr-00-0260.pdf.


4. Earthquake Track. (2025). “4.8 magnitude earthquake 7 km from Whitehouse

Station, New Jersey, United States”. https://earthquaketrack.com/quakes/2024-04-05-14

-23-20-utc-4-8-4.


5. Fuller, Thomas. (2025). “Earthquake Rattles New York and New Jersey, but


6. Han, Sangwoo et al. (2024). “Rupture Model of the 5 April 2024 Tewksbury,

New Jersey, Earthquake Based on Regional Lg-Wave Data”. https://pubs.geosciencewo


7. Johnson, Carolyn Y. (2024). “Why the New Jersey earthquake was felt severalhundred miles away”. https://www.washingtonpost.com/science/2024/04/05/earthquake-new-jersey-new-york-why/.


8. Kennett, B.L.N. (1986). “Lg waves and structural boundaries”. https://pubs.geo


9. Nash, Margo. (2001). “ON THE MAP; Exploring the Fault Where the Next Big


10. NESEC. (2025). “Earthquakes Hazards”. https://nesec.org/earthquakes-hazards/.


11. NJDEP. (2024). “April 5 2024, the largest earthquake in over 241 years”.

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