Massive Earthquake Reveals Mountains 660 Kilometers Below Us

It turns out Earth's inner core may be just as diverse as its surface.

Earthquakes, and in particular massive ones, bring fear into our hearts and sympathy for those exposed to them. In this case, though a massive earthquake brought forth a new discovery about our planet. 

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Some Princeton geophysicists in collaboration with Sidao from the Institute of Geodesy and Geophysics in China, explored data from a magnitude 8.2 earthquake, the second-largest deep earthquake ever recorded, that shook Bolivia in 1994 to find mountains and other topography on a layer located 660 kilometers (410 miles) below us.

If this seems like a good example of making lemonade out of lemons, it is. Scientists who study the Earth's core do so by using the most powerful waves which happen to be earthquakes.

The 660-km boundary

Now, the layer discovered through data from this old earthquake has been nicknamed by the researchers as "the 660-km boundary." And according to them, the boundary is incredibly rough. 

"In other words, stronger topography than the Rocky Mountains or the Appalachians is present at the 660-km boundary," said Princeton geophysicists Wenbo Wu.

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The researchers also believe these underground mountains may be bigger than anything on the surface. In addition, just like on Earth, they found that the roughness wasn't equally distributed. Instead, it had a variety of rough and smooth areas. 

Before you dismiss this as fun but useless knowledge it's important to note that the new discovery has crucial implications for understanding how our planet formed and even how it functions today. That newly-uncovered layer divides the mantle, a section which consists of about 84 percent of the Earth's volume.

Mixing thermally or physically

For years, geoscientists have debated just how important that boundary is. Some research has stipulated that the upper and lower mantle are chemically different while others have deduced that they are not. This difference is notable because the first would assume that the layers do not mix thermally or physically while the other would assume they do.

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"Our findings provide insight into this question," said Wu.

Luckily for everyone, the new data would suggest that both opinions might be right. The smoother areas of the 660-km boundary could have come from mixing, while the mountainous areas may indicate sections where the two mantles did not and still do not mix as well. 

"It's easy to assume, given we can only detect seismic waves traveling through the Earth in its current state, that seismologists can't help understand how Earth's interior has changed over the past 4.5 billion years," said Princeton geophysicists Jessica Irving. "What's exciting about these results is that they give us new information to understand the fate of ancient tectonic plates which have descended into the mantle, and where ancient mantle material might still reside."

The study is published this week in Science.

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