The science fiction writer Jules Verne once imagined an underground landscape deep in the planet in his great work “Journey to the Center of the Earth.” Although we are not going to run into prehistoric creatures down there, a new study has revealed that mountains and plains exist 660 kilometers under the earth’s crust.
Precisely a team of geophysicists from Princeton University (USA) and the Chinese Academy of Sciences used the echoes of a massive earthquake that shook Bolivia two decades ago to reconstruct the topography deep below the surface.
On June 9, 1994, a magnitude 8.2 earthquake on the Richter scale shook a sparsely populated region of the Amazon in the South American nation. Nothing so powerful had been seen in decades, and its echo was felt even in Canada.
“Earthquakes that big don’t happen very often,” says geoscientist Jessica Irving.
This earthquake was not only large, but also deep, with an estimated focal point at a depth of just under 650 kilometers. Unlike earthquakes that move through the crust, the energy of these geological monsters can shake the entire mantle like a bowl of jelly.
The quake was one of the first to be measured in a modern seismic network, providing researchers with unprecedented recordings of the waves bouncing off our planet’s interior.
Just as sound waves from an ultrasound can reveal differences in the density of tissue within a body, the huge waves that pulse through the molten bowels of the Earth as its crust shudders and move against itself can be used. to draw a perfect picture of what may be down there.
Scientists took advantage of the intensity of the 1994 earthquake to detect the dispersion of waves as they passed between layers, revealing details of the boundaries.
“We know that almost all objects have surface roughness and therefore scatter light. That is why we can see these objects: scattered waves carry information about surface roughness,” says Wenbo Wu, Institute of California technology and leader of the work publishing the journal Science . “In this study, we investigated scattered seismic waves traveling within Earth to limit the roughness of Earth’s 660-kilometer boundary.”
At this depth, there is a division between the stiffer lower parts of the mantle and an upper area that is not under as much pressure, one that creates a discontinuity marked by the appearance of various minerals.
The deepest hole in the world that we have dug is barely 12 kilometers deep, so without a Jules Verne-scale tunnel to let us go down to that depth, we have no idea what this transition zone is like. Up to now. (Wow, it looks like there are no giant ants …).
Mountains and plains under the earth’s crust
Experts have concluded that the meeting point between the upper and lower parts of the mantle forms a zigzag mountain range that reveals something superficial.
” In other words, stronger topography than the Rocky Mountains or the Appalachians is present at the 660-kilometer boundary, ” says Wu.
This jagged line has significant implications for the formation of the Earth. Most of the mass of our planet consists of mantle, so knowing how it mixes and changes when transferring heat tells us how it evolves over time.
Knowing the details of this underground mountain could decide the fate of various models that describe the ever- changing geological history of our planet.
“What’s exciting about these results is that they provide us with new information to understand the fate of ancient tectonic plates that have descended into the mantle, and where ancient mantle material might still reside,” Irving clarifies.
Referencia: Wenbo Wu, Sidao Ni and Jessica Irving. Inferring Earth’s discontinuous chemical layering from the 660-kilometer boundary topography. Science, 2019 DOI: 10.1126/science.aav0822
