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Newly discovered fault line explains why NYC shook so hard after earthquake
By
Rosemary Misdary
Published Oct 23, 2024
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David Dee Delgado/Getty Images
By
Rosemary Misdary
Published Oct 23, 2024
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A newly discovered fault line in the Northeast may explain why April’s 4.8 magnitude earthquake had very little impact near its epicenter in New Jersey, but shook millions of people 40 miles away in New York City.
A new study announced by Columbia University’s Lamont-Doherty Earth Observatory on Monday identified unusual movements along the fault line on April 5, the day of the quake. Researchers wrote that the fault line runs south to north and dips down into the Earth at a 45-degree angle. When the earthquake occurred, the sides of the previously unmapped fault slid against each other horizontally, with one of the sides thrusting over the other, researchers wrote.
Seismic waves typically move toward the surface during such a rupture, causing the most damage near the epicenter. But in April’s quake, the force of the event traveled downward until it hit a thick layer of rock 20 miles below the Earth’s surface. The seismic waves then bounced up toward New York City and elsewhere along the fault’s path. The tremors were strengthened by the region's rocks, which are hard and dense, making them ideal conductors of energy, according to the study.
“Near the epicenter, there was much less damage or shaking than expected from a magnitude 4.8 earthquake, and that was one thing which was peculiar with that earthquake,” said Columbia professor Won-Young Kim, one of the study's authors. “In New York City, it was felt as an intensity 4, so you were shaking so everyone will feel the earthquake.”
Researchers identified the new fault line by analyzing seismic activity between the surface and the Moho, which is the layer between the planet’s crust and mantle.
The earthquake rattled New York City doors, walls and windows. More than 150 buildings had minor damage, such as superficial cracks to masonry, according to the study. A school in Brooklyn had to close its gym for repairs. Gas and water pipes leaked in the Hudson Valley.
In Newark, officials temporarily evacuated more than two dozen people from their homes to inspect possible damage from the quake.
But nothing much happened in Tewksbury, the small town at the epicenter.
More than 500 known quakes have hit the region since the 1600s, with most going unnoticed in the moment. Researchers suggested that seismic activity along the fault line could represent a greater threat than previously known.
“The realistic scenario will be that this kind of magnitude 5 earthquake will happen again,” Kim said. “Usually it happens once in 100 years, but it can happen tomorrow. That is the unpredictable nature of earthquake occurrence in this area.”
Research released by Columbia University in 2008 suggested that more destructive quakes could occur in the region, with a magnitude 6 every 700 years. That would be more than 10 times as powerful as the Tewksbury quake. Although skyscrapers built on Manhattan’s solid bedrock could withstand an earthquake of that magnitude, it could be destructive in neighborhoods like Astoria and Long Island City, which are built on clay, sediment and fill.
Every estimated 3,400 years, the region could experience a magnitude 7 earthquake, which is 100 times more powerful than the Tewksbury quake, according to research. The most powerful earthquake recorded by humans in the New York City region was magnitude 5.2 in 1884, five years before the first skyscraper was built.
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Health and Science
Rosemary Misdary
Rosemary is health & science reporter. Got a tip? Email [email protected] or Signal 646-544-9524.
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