See rest of story at link https://interestingengineering.com/m...eters-below-us

Excerpt:

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.

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.


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.

Here is another link to a story on the same info https://sputniknews.com/science/2019...tle-mountains/