The highest quality images of the Earth’s interior have just been captured

A joint research project from the UK recently published a study of one of the least known or understood parts of the Earth’s interior – the core-mantle boundary. Concentrating their work on a large mantle plume under the Hawaiian Archipelagothey made some interesting observations about the most enigmatic parts of Earth’s geological system.

The study was first published in the journal Nature Communication.

Using new imaging techniques, the team was able to gain valuable insight into this very low-velocity zone that lies about 1,864 miles (3,000 km) below the Earth’s surface.

Until now, we knew that this zone exists thanks to the analysis of the seismic waves which cross the planet. The name of the area(s) comes from how seismic waves slow down as they pass through them.

So far, it’s been hard to make much sense of them beyond a few grainy, hard-to-parse images. However, this new study of the mantle beneath Hawaii produced much clearer, higher definition images.

“Of all the deep interior features of the Earth, these are the most fascinating and complex,” says geophysicist Zhi Lifrom the University of Cambridge in the UK and contributor to the study.

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

To create the images, the team developed new computer models that take high-frequency signals from the study area to generate an understandable image. Using this technique, he was able to produce a mile-scale view of the rock pocket, at better magnitude resolutions than using conventional techniques.

It is now hoped that this technique can be used to study the boundary between the Earth’s iron-nickel core and surrounding mantle to better understand one of the main drivers of plate tectonics, the formation of volcanoes and other related processes such as earthquakes.

Currently, it is thought that the extra iron in these unusual areas could create the extra density that shows up in seismic wave patterns. Whether this is correct or not, studying this region is a top priority for some geologists.

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

A possible link between ultra-low-velocity zones and volcanic hotspots

Other scientists also believe there is a link between very low-velocity zones and volcanic hotspots, such as those in Hawaii and Iceland. A hypothesis is that these hot spots could be caused by materials gushing from the core to the surface called “Mantle hotspots.

This new technique could also help revolutionize this field of study. Yet others can now better focus on the lava outpourings that sit above these hotspots to look for evidence of so-called “core leaks.”

Although the use of ultra-low-velocity area seismic data is limited in some respects by where earthquakes occur and where seismographs are installed, the team is very keen to apply their high-resolution imagery improvements to other deep pockets on 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 Lengfrom the University of Oxford in the UK.

The lowest mantle just above the core-mantle boundary is very heterogeneous and contains multiple poorly understood seismic features. The smallest but most extreme heterogeneities observed to date are “ultra-low-velocity zones” (ULVZs). We exploit seismic shear waves that diffract along the core-mantle boundary to provide new insight into these enigmatic structures. We measure a rare nucleus diffracted signal refracted by a ULVZ at the base of the Hawaiian mantle plume at unprecedented frequencies. This signal shows remarkably longer delays at higher frequencies than at lower frequencies, indicating pronounced internal variability within the ULVZ. Using the latest computational advances in 3D waveform modeling, we show here that we are able to model this high-frequency signal and constrain the high-resolution ULVZ structure at the kilometer scale, for the first time. This new observation suggests a chemically distinct ULVZ with increasing iron content towards the core-mantle boundary, which has implications for Earth’s early evolutionary history and core-mantle interaction.

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