Massive 1994 Bolivian earthquake reveals mountains 660 kilometers below our feet

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https://www.princeton.edu/news/2019/02/1...w-our-feet

EXCERPT: In a study published this week in Science, Princeton geophysicists [...] used data from an enormous earthquake in Bolivia to find mountains and other topography on the base of the transition zone, a layer 660 kilometers (410 miles) straight down that separates the upper and lower mantle. (Lacking a formal name for this layer, the researchers simply call it “the 660-km boundary.”) To peer deep into the Earth, scientists use the most powerful waves on the planet, which are generated by massive earthquakes [1994 Bolivia Earthquake]. “You want a big, deep earthquake to get the whole planet to shake,” said Irving, an assistant professor of geosciences.

[...] The researchers were surprised by just how rough that boundary is — rougher than the surface layer that we all live on. “In other words, stronger topography than the Rocky Mountains or the Appalachians is present at the 660-km boundary,” said Wu. Their statistical model didn’t allow for precise height determinations, but there’s a chance that these mountains are bigger than anything on the surface of the Earth. [...]

“They find that Earth’s deep layers are just as complicated as what we observe at the surface,” said seismologist Christine Houser, an assistant professor at the Tokyo Institute of Technology who was not involved in this research. “To find 2-mile (1-3 km) elevation changes on a boundary that is over 400 miles (660 km) deep using waves that travel through the entire Earth and back is an inspiring feat. … Their findings suggest that as earthquakes occur and seismic instruments become more sophisticated and expand into new areas, we will continue to detect new small-scale signals which reveal new properties of Earth’s layers.”

The presence of roughness on the 660-km boundary has significant implications for understanding how our planet formed and continues to function....

https://www.princeton.edu/news/2019/02/1...w-our-feet
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