A team of geophysicists at ETH Zurich in Switzerland has made a baffling discovery while analyzing earthquake waves to investigate the internal structures of the Earth.
Specifically, they found areas in our planet’s interior that appear to be the leftovers of submerged tectonic plates deep below large oceans.
The finding also presents scientists with a new puzzle: the pieces are far away from plate boundaries — nowhere near where they expected to find them.
It’s an intriguing finding that suggests a “lost world” could be lurking deep below the Pacific Ocean, highlighting how much there still is to learn about what’s going on deep below our planet’s crust.
As detailed in a paper published in the journal Scientific Reports, the team used a supercomputer to analyze the earthquake data, gathered from seismographic stations around the world, and create a new high-resolution model of the Earth’s interior.
The signs of submerged plates were found in areas not previously known for geological activity, such as plate subduction, which occurs when an oceanic plate slides beneath a continental plate.
By analyzing how earthquake waves propagate from an epicenter, scientists can deduce the density and elasticity of the rocky material the waves travel through. Armed with this data, geophysicists can then start building a map of what the composition of the Earth’s mantle might look like.
It’s a necessary workaround to make up for the fact that we have yet to dig deep enough to directly probe and return samples from the mantle itself.
The leftover pieces found under the Pacific Ocean surprised scientists as existing models have determined that there shouldn’t be any such material in the area due to the lack of plate subduction.
“Apparently, such zones in the Earth’s mantle are much more widespread than previously thought,” said first author and ETH Zurich doctoral student Thomas Schouten in a statement.
The jury is still out on what kind of material these remnants are made of, and how they could influence the Earth’s internal dynamics.
“That’s our dilemma,” Schouten said. “With the new high-resolution model, we can see such anomalies everywhere in the Earth’s mantle. But we don’t know exactly what they are or what material is creating the patterns we have uncovered.”
The geophysicist suggests that the “anomalies in the lower mantle have a variety of origins.”
“It could be either ancient, silica-rich material that has been there since the formation of the mantle about 4 billion years ago and has survived despite the convective movements in the mantle, or zones where iron-rich rocks accumulate as a consequence of these mantle movements over billions of years,” Schouten explained.
The waves we use for the model essentially only represent one property, namely the speed at which they travel through the Earth’s interior,” he added.
But to get a more accurate picture, “we have to calculate the different material parameters that could generate the observed speeds of the different wave types,” Schouten said. “Essentially, we have to dive deeper into the material properties behind the wave speed.”
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