Researchers at the Chinese Academy of Sciences used a machine learning program to sift through more than two million earthquake recordings, uncovering nearly 175,000 faint seismic signals near the boundary between Earth’s mantle and core, revealing six previously unknown deep structures and larger continuous belts than previously understood.
Uncovering Hidden Mantle Signals With Machine Learning
Roughly 2,900 kilometers (1,800 miles) beneath your feet, Earth’s solid-but-viscous mantle gives way to the planet’s liquid outer core. As those layers slowly smoosh about, driven by heat, their movement slides, pushes, and deforms Earth’s crust, the thin layer we live on above. While this movement drives tectonic activity and natural disasters, geologists use data on Earth’s inner rumblings to map our planet’s insides far deeper than drills could ever go.
A study published in the Journal of Geophysical Research: Solid Earth details how researchers at the Chinese Academy of Sciences trained a deep-learning system to analyze seismic data from nearly 5,000 earthquakes collected between 1990 and 2024. Traditionally, inspecting millions of earthquake recordings for faint seismic signatures required slow, painstaking manual work, and researchers might not always agree on whether a signal is a genuine precursor. The new algorithm first sorted recordings by quality, then determined whether they contained PKP precursors, with researchers manually checking and correcting the AI model’s mistakes and feeding the corrected examples back into the algorithm during the training process.
Mapping PKP Precursors and Six New Mystery Zones
The analysis focused on PKP precursors, which are faint waves that arrive shortly before much stronger seismic waves (PKIKP). When an earthquake occurs, both the stronger and weaker waves travel through Earth, and if some of those waves encounter small variations in the material near the core-mantle boundary, they can scatter and take slightly different paths. The scattered PKP waves, which pass through the outer liquid core but not the solid inner core, can then arrive ahead of the main PKIKP signal.
By analyzing wave times, these PKP precursors can ‘show’ unusual structures deep inside the planet. The automated screening sifted through more than 2 million earthquake recordings collected over three and a half decades, uncovering nearly 175,000 faint seismic signals that reveal unexpected, small-scale structures near the boundary between Earth’s mantle and core. We also discovered six areas that likely host significant heterogeneities that had never been documented before, providing clear priority targets for future exploration of Earth's deep interior,
the researchers write in their paper. The result is a comprehensive global map of these deep structures – which reveals that some of the strange features scientists have detected at the bottom of the mantle may be much more extensive than previously thought.
Reinterpreting Deep Earth Features and Magma Ocean Origins
Separate recent research published in Nature Geoscience offers fresh context for these deep structures. Led by Yoshinori Miyazaki with a team of collaborators, a recent study examines large low-shear-velocity provinces and ultra-low-velocity zones resting near the boundary between the mantle and the core nearly 1,800 miles below the surface. Large low-shear-velocity provinces are enormous masses of extremely hot, dense rock, with one positioned beneath Africa and the other under the Pacific Ocean, while ultra-low-velocity zones resemble thin, partly molten layers that cling to the core in puddle-like patches. Both strongly slow seismic waves, suggesting they contain materials or conditions unlike the surrounding mantle.
While scientists once expected ancient magma oceans to form distinct chemical layers as they cooled—similar to how frozen juice separates into sugary concentrate and watery ice—seismic observations reveal no such clear layering. Instead, large low-shear-velocity provinces and ultra-low velocity zones appear to form complex, uneven piles at the bottom of the mantle. The research team suggested that the missing factor is the core itself, with their model indicating that over billions of years, elements such as silicon and magnesium gradually escaped from the core into the mantle, disrupting the formation of strong chemical layers and accounting for the unusual composition of these provinces and zones, which the scientists interpret as the cooled remains of a basal magma ocean
altered by core-derived material.
“These are not random oddities. They are fingerprints of Earth’s earliest history. If we can understand why they exist, we can understand how our planet formed and why it became habitable.”
Yoshinori Miyazaki, Rutgers University, via sciencedaily.com
Connecting Deep Interior Processes to Surface Habitability
These discoveries suggest that deep mantle dynamics stretch far beyond mineral chemistry. Interactions between the mantle and core may have influenced how Earth released heat, how volcanic activity developed, and even how the atmosphere changed over time. Researchers point out that this perspective may help clarify why Earth ended up with oceans and life while Venus became extremely hot and Mars turned cold and barren, noting that what happens inside a planet—how it cools and how its layers evolve—could be a big part of the answer.
Furthermore, these deep anomalies may help fuel volcanic hotspots such as Hawaii and Iceland. By bringing together seismic observations, mineral physics, and geodynamic simulations, the team reframed large low-shear-velocity provinces and ultra-low-velocity zones as essential records of how Earth formed and how its deep interior processes shape planetary habitability.
