” Even though the mantle makes up the largest part of Earth, theres still a lot we dont understand about it,” stated Sunyoung Park, a geophysicist with the University of Chicago and the lead author on the research study. “We believe theres a lot more we can find out by utilizing these deep earthquakes as a method to penetrate these questions.”
Mantle secrets
We still know remarkably little about the Earth underneath our feet. The outermost anyone has actually handled to dig down is about 7 and a half miles before the increasing heat actually melts the drill. Hence researchers have had to use ideas like how seismic waves move to infer the different layers that comprise the world, consisting of the mantle, core, and crust.
Something that has actually stymied scientists is an exact measurement of how thick the mantle layer is. The mantle is the layer below the crust. Its made of rock, however at the extreme temperature level and pressures at that depth, the rock really becomes viscous– streaming extremely slowly like honey or tar.
” We want to know precisely how fast the mantle streams, because that affects the advancement of the entire Earth– it affects how much heat the planet retains for how long, and how the Earths products are cycled gradually,” described Park. “But our present understanding is very minimal and includes a lot of assumptions.”
A new study led by University of Chicago geophysicist Sunyoung Park recommends there may be a layer of remarkably fluid rock located in the Earths mantle.
350-mile-deep earthquake utilized in clinical study to make elusive measurements of the Earths layers.
There may be a layer of remarkably fluid rock ringing the Earth, at the very bottom of the upper mantle, according to a new study from a University of Chicago researcher.
The finding was made by determining the sticking around movement registered by GPS sensing units on islands in the wake of a deep earthquake in the Pacific Ocean near Fiji. Released on February 22 in Nature, the study shows a brand-new approach to determine the fluidity of the Earths mantle.
Thus scientists have had to utilize clues like how seismic waves move to infer the various layers that make up the planet, including the crust, mantle, and core.
One thing that has actually stymied researchers is an exact measurement of how viscous the mantle layer is. The mantle is the layer listed below the crust. Occasionally, there are earthquakes that come from deep within the Earth– down to 450 miles listed below the surface. Due to the fact that they reach down into the mantle, Park believed they may use a way to comprehend the behavior of the mantle.
Park thought there may be a special way to get a measurement of the mantles properties by studying the after-effects of extremely deep earthquakes.
Most of the earthquakes we find out about on the news are relatively shallow, coming from in the top crust of the Earth. However periodically, there are earthquakes that originate deep within the Earth– down to 450 miles listed below the surface. These earthquakes are not as well-studied as shallower ones, because theyre not as harmful to human settlements. Due to the fact that they reach down into the mantle, Park believed they may offer a way to understand the behavior of the mantle.
Park and her associates looked at one specific such earthquake, which took place off the coast of Fiji in 2018. The quake was magnitude 8.2, however it was so deep– 350 miles down– that it did not cause any major damage or deaths.
When the scientists thoroughly examined the information from GPS sensing units on numerous nearby islands, they found the Earth kept moving– after the earthquake was over.
The data revealed that in the months following the quake, the Earth was still moving, settling in the wake of the disruption. Even years later, Tonga is still moving slowly down at a rate of about 1 centimeter each year.
” You can consider it like a jar of honey that slowly comes back to level after you dip a spoon in it– except this takes years instead of minutes,” said Park.
This is the first strong observation of the deformation following deep quakes; the phenomenon had actually been observed prior to for shallow earthquakes, however specialists believed the impact would be too little to be observable for deep earthquakes.
Park and her colleagues utilized this observation to infer the viscosity of the mantle.
” Even though the mantle comprises the biggest part of Earth, theres still a lot we dont learn about it.”
— Asst. Prof. Sunyoung Park
By taking a look at how the Earth deformed over time, they discovered evidence of a layer about 50 miles thick that is less thick (that is, “runnier”) than the remainder of the mantle, sitting at the bottom of the upper mantle layer. They think this layer may extend around the whole world.
This low-viscosity layer might describe some other observations by seismologists that suggested there are “stagnant” slabs of rock that do not move quite, situated around the very same depth at the bottom of the upper mantle. “It has been tough to reproduce those features with models, but the weak layer found in this research study makes it simpler to do so,” Park said.
It also has implications for how Earth transportations heat, cycles and blends products between the crust, core, and mantle with time.
” Were actually thrilled,” Park said. “Theres a lot more to discover with this technique.”
The other co-authors on the paper were Jean-Philippe Avouac and Zhongwen Zhan of California Institute of Technology and Adriano Gualandi of Italys National Institute of Geophysics and Volcanology.
Recommendation: “Weak upper-mantle base revealed by postseismic deformation of a deep earthquake” by Sunyoung Park, Jean-Philippe Avouac, Zhongwen Zhan and Adriano Gualandi, 22 February 2023, Nature.DOI: 10.1038/ s41586-022-05689-8.
Funding: The University of Chicago, California Institute of Technology, National Science Foundation.
