Deepest Earthquake Ever? Scientists Confirming Temblor 467 Miles Underground

by Quentin Blount

A record-breaking temblor is in the process of being confirmed by scientists. If it is indeed confirmed, it would change the way geologists look at earthquakes.

Most temblors take place within just a few dozen miles of the Earth’s surface. But six years ago, scientists were baffled when our planet was struck by quakes deep at its core. We aren’t talking about the normal few-dozen-mile range. We’re talking hundreds of miles inside Earth — depths where it was previously thought that due to the intense temperature and pressure, a normal earthquake wouldn’t be possible.

The unlikely earthquake struck 467 miles beneath the planet’s surface in a layer called the lower mantle. There have been some hints here and there of lower mantle quakes, but scientists were never able to pinpoint them.

Douglas Wiens is one researcher who believes this is evidence enough. He’s a seismologist who specializes in deep quakes at Washington University in St. Louis. He wasn’t a part of the study team, but he still has his own thoughts about the event.

“This is by far the best evidence for an earthquake in the lower mantle,” Wiens explained to National Geographic.

Similarly, Heidi Houston shared her thoughts with the outlet. Houston is a geophysicist and deep quake expert at the University of Southern California. Like Wiens, she was also not a part of the study team.

“It can’t be ruled out,” she said. “That’s one of the things that makes this interesting and exciting and important to look into.

How Often do Deep Earthquakes Happen?

The short answer? Not often.

Actually, the majority of earthquakes are rather shallow. To illustrate this point let’s take a deep dive into the numbers. There were 56,832 moderate to large quakes recorded during a 44-year period between 1976 and 2020. Of those, only about 18 percent were deeper than 43 miles. Moving on, only about four percent struck below 186 miles. That is the cut-off depth that is commonly used to categorize a “deep earthquake.” So, as you can imagine, a 7.9 earthquake happening at 467 miles underground is completely bizarre.

Scientists and researchers all over the world are still trying to figure out how these quakes can happen at all. When it comes to temblors at the surface, it’s pretty straightforward — tectonic plates build up stress until the ground fractures and shifts. That’s when we see and feel the shudders of a quake.

Deep inside the planet though, this is not the case. The insanely high pressure prevents those shudders.

“Everything is just very strongly compressed in all directions,” Houston said.

Magali Billen, a geodynamicist at the University of California, Davis, said that rocks tend to act more like putty than solid chunks inside Earth’s core. So, what is it that can cause a quake to happen? Researchers are still exploring that very question.