For the first time, scientists have examined an ultra-low velocity zone in detail. These mysterious rock pockets are around 3,000 kilometers (1,864 miles) below the surface, close to the Earth's core.
They're obviously impossible to analyze at that level, but we know they're there because of how seismic waves travel through the Earth. The way seismic waves slow down when they pass through these zones gives them their name.
Images of these zones had previously been blurry and difficult to decipher, but a new study has published one that reveals a zone beneath Hawaii in considerably greater detail, revealing new insight into the inner workings of our planet and its history.
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| Conceptual drawing of the ultra-low velocity zone. |
"Of all Earth's deep interior features, these are the most fascinating and complex," says geophysicist Zhi Li of the University of Cambridge in the United Kingdom.
"We've now got the first solid evidence to show their internal structure – it's a real milestone in deep Earth seismology."
The image was created using cutting-edge computer modeling techniques applied to a high-frequency signal acquired as seismic waves flowed across the ultra-low velocity zone.
When it comes to examining the boundary between Earth's iron-nickel core and the mantle wrapped around it, it gives specialists a kilometer-scale view of the rock pocket, a resolution improvement of orders of magnitude.
Earthquakes, volcanoes, and other associated activity are caused by the flow of hot mantle rock, and scientists are interested in understanding more about how ultra-low velocity zones may be causing or affecting that action.
Extra iron in these atypical zones is considered to be causing the extra density seen in seismic wave patterns, and finding out whether this is true or not could reveal more about how Earth formed and how its core functions now.
"It's possible that this iron-rich material is a remnant of ancient rocks from Earth's early history or even that iron might be leaking from the core by an unknown means," explains University of Cambridge seismologist Sanne Cottaar.
Scientists have discovered a relationship between ultra-low velocity zones and volcanic hotspots like Hawaii and Iceland. These hotspots could be generated by material shooting up from the core to the surface, according to one theory.
Better photography of these deep and mysterious zones should help in that sector as well, and scientists are looking for signs of core leakage in basalt rock on the surface in Hawaii.
The team hopes to apply their high resolution picture upgrades to additional deep pockets of Earth in the future.
"We are really pushing the limits of modern high-performance computing for elastodynamic simulations, taking advantage of wave symmetries unnoticed or unused before," says data scientist Kuangdai Leng of the University of Oxford in the United Kingdom.
