One of the hot, dense drops deep within the Earth has been revealed thanks to new imagery


For the first time, scientists have looked at an ultra-low speed zone. These enigmatic rock pockets lie near the Earth’s core, about 3,000 kilometers (1,864 miles) below the surface.

At this depth they are obviously difficult to study, but we know they are there because of the way seismic waves pass through the Earth. These zones get their name from the way seismic waves slow down as they pass through them.

Until now, images of these areas have been grainy and difficult to analyze – but the one now published in a new study reveals an area beneath Hawaii in much greater detail, offering new insight into the inner workings of our planet and its history. .

Concept drawing of the ultra-low speed zone. (Li et al., Nature Communications, 2022)

“Of all the Earth’s deep interior features, these are the most fascinating and complex,” says geophysicist Zhi Li, from the University of Cambridge in the UK.

“We now have the first solid evidence to show their internal structure – this is a real milestone in deep Earth seismology.”

The latest computer modeling techniques were used to produce the image, techniques applied to a high frequency signal which was recorded as rippled seismic waves through the ultra-low velocity zone.

It gives experts a kilometer view of the rocky pocket, an order of magnitude improvement in resolution when studying the boundary between the Earth’s iron-nickel core and the mantle that surrounds it. .

The flow of hot mantle rock drives earthquakes, volcanoes and other related activity, and scientists are keen to learn more about how very low-velocity areas might trigger or influence this activity. .

It’s thought that the extra iron in these unusual areas could create the extra density that shows up in seismic wave patterns – and finding out one way or another could tell us more about how the Earth formed and how it worked. of its core today.

“It is possible that this iron-rich material is a remnant of ancient rocks from Earth’s early history or even that iron is leaking out of the core by some unknown means,” says seismologist Sanne Cottaar, from the Cambridge University.

Scientists have also spotted a link between very low-velocity zones and volcanic hotspots, such as those in Hawaii and Iceland. One hypothesis is that these hot spots could be caused by material rising from the core to the surface.

Better imaging of these deep, mysterious areas should also help in this area of ​​research, and scientists are also studying surface basalt rock in Hawaii for evidence of core leakage.

Studying ultra-low-velocity zones is limited in some ways by where earthquakes occur and where seismographs are installed, but the team is keen to apply their high-speed imaging improvements. resolution to other deep pockets of the Earth.

“We are really pushing the boundaries of modern high-performance computing for elastodynamic simulations, taking advantage of previously unnoticed or unused wave symmetries,” says data scientist Kuangdai Leng, from the University of Oxford in the UK.

The research has been published in Nature Communication.


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