Seismologists have discovered huge mountains 660 kilometers underground as a result of an earthquake in Bolivia.
Scientists have long debated the nature of the interior of the Earth, because of the difficulties encountered in creating an image of the different layers. Using shock waves caused by massive earthquakes and a global network of seismic instruments, a complex terrain of mountain ranges has been revealed.
This is known from research published by Wenbu Wu, Sidao Ni and Jessica Irving as part of a collaboration between the Chinese Academy of Sciences and the University of Science and Technology, both in China, and the University of Princeton, United States.
The results, published in the journal Science, show that it is possible that these mountain ranges are larger than the Himalayas or the Rockies.
Their depth is significant. The 660-kilometer boundary between the upper and lower layers of the planet also contains much smoother areas, such as mountain ranges and abyssal plains on the Earth's crust.
The challenge of determining a hitherto underground landscape was considerable. Only the deepest and most powerful earthquakes are able to generate seismic waves adapted to the task. The one that rocked Bolivia in 1994, the second deepest earthquake ever recorded, was a prime candidate.
"You want a powerful, deep earthquake that will shake the whole planet," says Irving.
Waves from really powerful earthquakes cross the Earth's interior and are reflected and diffused in a detectable way, allowing researchers to visualize the different layers of the Earth.
"Earthquakes of this magnitude do not happen very often," says Irving.
"We are lucky now to have a lot more seismometers than 20 years ago. Seismology is a different field from that of 20 years ago, between instruments and computer resources. "
The implications of the research help reveal the processes that occur at the boundary between the upper mantle and the lower mantle. The scientific debate has long focused on the competing evidence of a well-mixed mantle that allows heat transfer across the 660-kilometer limit and a poorly mixed mantle of distinct layers.
The work of Wu and his colleagues could be a boundary between the two processes, allowing for more mixing in the plains and less in the mountains.
In addition to determining what is happening at the border, Irving adds, "What's interesting with these results is that they give us new information to understand the fate of the ancient tectonic plates that have descended into the mantle and where old mantle materials could still reside. "
By imagining regions under tectonically active areas, such as Japan, as well as more benign areas at the seismic point, including Antarctica, research indicates that these slabs could eventually penetrate the mantle inferior.
"Seismology is very exciting when it allows us to better understand the inside of our planet in time and in space," says Irving.