The East Coast earthquake was caused by a fault that had been dormant for hundreds of millions of years but suddenly reactivated.

• The 4.8 magnitude earthquake that occurred on the East Coast on Friday was caused by old faults.

• The faults were formed when two continents collided about 500 million years ago, creating the Appalachians and the Atlantic Ocean.

• Stress from the retreat of Ice Age glaciers may have reactivated the sleep 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 said Friday.

Millions of New Yorkers and other East Coast residents may have been shocked to hear the shaking of the 4.8 magnitude earthquake Friday morning. The region is not actually known for its seismic activity.

However, the earthquake did not come suddenly. Scientists knew that a potential danger existed deep below the Earth’s surface; The old faults were sleeping silently.

“This is an area of ​​older, generally inactive faults, but they could become active again at any time,” Jessica Jobe, a geologist with the U.S. Geological Survey, said at Friday’s briefing.

Ancient faults resulting from the formation of the Appalachian mountains

According to USGS preliminary data, the epicenter of the earthquake appears to be in New Jersey.

This means it comes from a fault zone called the Appalachian fold and thrust belt, which is much older and quieter than the fault lines on the West Coast.

“A lot of these faults, we don’t know where they are until the earthquake happens,” Lingsen Meng, an associate professor of geophysics at UCLA, told Business Insider.

These faults result from the collision of two continents between 500 and 300 million years ago. Continental plates crashed into each other, closing the existing ocean and opening the Atlantic Ocean, while the plates crashed into each other, forming the Appalachian Mountains.

This extreme event also opened fault lines in the Earth’s crust throughout the region.

“There were dozens of faults that were active millions of years ago, and these faults are still present in the Earth’s crust,” Jobe said. said. “As tectonic plates move and experience some form of movement stress in the Earth’s crust, occasionally one of these faults will become active infrequently or intermittently in a single earthquake or a series of small earthquakes.”

The story continues

As far as scientists know, these faults have not been active since they formed “a few 100 million years ago,” Jobe said.

It is not yet known whether this will be a single earthquake or a series. The USGS warned that aftershocks were possible in the coming weeks. Most likely aftershocks will be smaller earthquakes, but the likelihood of a follow-up earthquake being of similar or larger magnitude is also low.

Because there are dozens of faults in the Appalachian fold-and-thrust belt, the USGS cannot yet attribute Friday’s earthquake to any specific fault line, but initial data suggests the culprit is about 3 miles deep.

The next question is what caused the fault to reactivate on Friday.

This earthquake may be a remnant of the retreat of Ice Age glaciers

On the West Coast, earthquakes are often caused by movements along the boundaries of tectonic plates. However, the East Coast is located in the middle of a plate and does not experience much of this movement.

Instead, East Coast earthquakes are caused by accumulated stress along these old fault lines.

“When that stress is removed, earthquakes occur. And that seems to be what happened in New Jersey this morning,” Ben Fernando, a postdoctoral researcher studying seismology at Johns Hopkins, told BI.

One possible source of this stress, Meng said, is the rebound of the Earth’s crust due to the weight of glaciers (yes, the glaciers that covered North America during the last Ice Age, about 20,000 years ago).

“This was a huge weight that deformed the rock beneath the crust,” Fernando said.

Glaciers heavily weighed and compressed the northern part of the East Coast. Although this weight has been lifted for over 10,000 years, the earth’s crust is still returning to its original shape.

“It’s constantly recovering,” Meng said. “In this process, weak structures will be stressed no matter what.” [are] in the shell.”

This gradually creates a slight stress on the fault lines, he said, but “given enough time, you can still build up enough stress to cause earthquakes.”

As scientists continue to analyze the data, they should be able to discern whether glacier rebound contributed to Friday’s tremor.

Read the original article on Business Insider