For the first time, scientists have properly observed an ultra-low speed zone. These enigmatic pockets of rock lie close to the Earth’s core, some 3,000 kilometers (1,864 miles) below the surface.
At that depth they’re obviously hard to study, but we know they’re there because of the way seismic waves flow through the Earth. These zones get their name from the way seismic waves slow down as they pass through them.
Up to this point, images of these areas have been grainy and difficult to analyze, but now released in a new study reveals an area below Hawaii in much more detail, providing new insight into the inner workings of our planet and its history.
“Of all the features of the Earth’s deep interior, these are the most fascinating and complex,” says geophysicist Zhi Li, from the University of Cambridge in the UK.
“Now we have the first hard evidence showing its internal structure: it’s a real milestone in deep-Earth seismology.”
The latest computational modeling techniques were used to produce the image, techniques applied to a high-frequency signal that was recorded as seismic waves through the ultra-low-velocity zone.
It gives experts a kilometer-scale look at the pocket of rock, an order of magnitude improvement in resolution when it comes to studying the boundary between Earth’s iron-nickel core and the mantle that envelops it.
The flow of hot mantle rock is what causes earthquakes, volcanoes, and other related activity, and scientists are interested in learning more about how ultralow-velocity zones might trigger or influence that activity.
It’s thought that the extra iron in these unusual zones could be creating the extra density that shows up in seismic wave patterns, and discovering one way or another could tell us more about how Earth formed and how its core works today.
“It is possible that this iron-rich material is a remnant of ancient rocks from early Earth history or even that iron is escaping from the core by an unknown means,” says seismologist Sanne Cottaar of the University of Cambridge.
Scientists have also detected a link between ultra-low velocity zones and volcanic hot spots, such as those in Hawaii and Iceland. One hypothesis is that these hot spots could be caused by material shooting from the core toward the surface.
Better images of these deep, mysterious zones should also help in that area of research, and scientists are also studying basalt rock on Hawaii’s surface for evidence of core leaks.
Study of ultra-low-velocity zones is limited in some ways by where earthquakes occur and where seismographs are set up, but the team wants to apply their high-resolution imaging enhancements to other places deep on Earth.
“We are really pushing the limits of modern high-performance computing for elastodynamic simulations, taking advantage of wave symmetries that have not been noticed or used before,” says data scientist Kuangdai Leng, from the University of Oxford. in the United Kingdom.
The research has been published in nature communications.