- Friday’s magnitude 4.8 earthquake on the East Coast originated from ancient dormant faults.
- The faults formed when two continents collided about 500 million years ago, creating the Appalachian Mountains and the Atlantic Ocean.
- Residual stress from retreating Ice Age glaciers may have reactivated a dormant fault.
The earthquake that just shook the East Coast was caused by one of dozens of ancient fault lines that have remained dormant for hundreds of millions of years, leading scientists announced Friday.
Millions of New Yorkers and others on the East Coast may have been shocked to feel the impact of the 4.8 magnitude earthquake Friday morning. The area is not really known for its seismic activity.
But the earthquake didn’t come out of nowhere. Scientists knew of a potential danger deep beneath the Earth’s surface: ancient faults lying quietly dormant.
“This is an area of older faults, generally inactive, but they can be reactivated at any time,” Jessica Jobe, a geologist with the U.S. Geological Survey, said during a press briefing Friday.
Ancient faults from the formation of the Appalachians
The earthquake’s epicenter appears to have been in New Jersey, preliminary USGS data suggests.
Cones block fallen debris from the historic Taylor’s Mill in Lebanon, New Jersey, after Friday morning’s earthquake. Matt Rourke/AP Photo
This means it comes from a fault region called the Appalachian Fold and Thrust Belt, which is much older and quieter than the West Coast fault lines.
“A lot of these faults, we don’t know where they are until there’s an earthquake,” Lingsen Meng, an associate professor of geophysics at UCLA, told Business Insider.
These faults come from the collision of two continents 500 to 300 million years ago. When the continental plates crashed, closing an existing ocean and opening the Atlantic Ocean, the plates crushed against each other to give rise to the Appalachian Mountains.
The Appalachian Trail near Hot Springs, North Carolina. George Rose/Getty Images
This extreme event also opened fault lines in the Earth’s crust throughout the region.
“There were several dozen active faults millions of years ago, and these faults are still present in the Earth’s crust,” Jobe said. “As tectonic plates shift and stresses shift in the Earth’s crust, from time to time one of these faults will become active infrequently or intermittently, during a single earthquake or earthquake. a series of small earthquakes.”
As far as scientists know, these faults have not been active since they formed “some 100 million years ago,” Jobe said.
It remains to be seen whether it is simply one earthquake or a series. Aftershocks are possible in the coming weeks, the USGS warned. It is very likely that the aftershocks will be smaller earthquakes, but there is a small chance that an ensuing earthquake will be of a similar or larger magnitude.
Because there are dozens of faults in the Appalachian fold and thrust belt, the USGS is not yet able to attribute Friday’s earthquake to a specific fault line, although early data suggests that the cause was about 3 miles deep.
The next question is what caused the fault to reactivate on Friday.
This earthquake could be a remnant of the retreat of glaciers from the Ice Age
On the West Coast, earthquakes often originate from movements along tectonic plate boundaries. The East Coast, however, is located in the middle of a plate and does not experience much of this movement.
A map shows the boundaries between current tectonic plates in the middle of the Atlantic Ocean. NOAA
Instead, East Coast earthquakes come from stress building up on these ancient fault lines.
“When that tension is released, it causes earthquakes. And that seems to be what happened this morning in New Jersey,” Ben Fernando, a postdoctoral researcher studying seismology at Johns Hopkins, told BI.
A likely source of this stress, Meng says, is the Earth’s crust bouncing under the weight of glaciers — yes, the glaciers that covered North America during the last ice age, about 20,000 years ago.
“It was a huge weight that distorted the underlying rock in the crust,” Fernando said.
Glaciers have heavily weighed down and compressed the northern part of the East Coast. Although this weight has been lifted for more than 10,000 years, the Earth’s crust continues to return to its previous shape.
“It’s constantly bouncing around,” Meng said. “During this process, it will put pressure on weak structures inside the crust.”
That slowly put slight pressure on the fault lines, he said, but “given enough time you can still build up enough strain to cause the earthquakes.”
Scientists should be able to determine whether glacial rebound contributed to Friday’s shaking as they continue to analyze the data.
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