Scientists analyzing over two million earthquake records using an advanced machine learning algorithm have discovered six previously undocumented structures near the boundary where Earth’s solid mantle meets its liquid outer core. The findings provide new targets for understanding how deep interior dynamics influence surface events like earthquakes and volcanoes.
Using Artificial Intelligence to Map the Deep Mantle Boundary
Studying the interior of our planet has long presented monumental challenges. While the deepest hole ever drilled, the Kola Superdeep Borehole created by the Soviet Union during the Cold War, reached 12,263 meters down, that extraordinary feat barely scratched the surface, remaining only a fraction of the way through Earth’s crust. To probe thousands of kilometers deeper to the core-mantle boundary located roughly 1,800 miles beneath the surface, researchers instead turn to seismic waves generated by earthquakes.
A recent study published in the journal JGR Solid Earth details how scientists in China applied machine learning to analyze over two million earthquake recordings spanning a 35-year period. Manual identification of these seismic signals has historically been slow, laborious, and subjective. By deploying an AI model trained on human-identified data, the research team identified approximately 175,000 high-quality PKP precursors
—weak seismic waves that arrive at detectors before the main earthquake wave.
That automated approach yielded roughly ten times more PKP signals than all previous studies combined. Because these specialized waves scatter and deflect when encountering small inconsistencies or heterogeneities just above the core-mantle boundary, they serve as invaluable probes for mapping hidden deep-Earth features that would otherwise remain invisible.
Six Never-Before-Seen Mystery Structures Revealed in Continuous Bands
With a comprehensive global map generated from the newly filtered seismic data, the researchers uncovered a clearer picture of the planet’s deepest layers than was previously possible. Whereas older studies could only identify sparse, isolated patches sampled by precursors, the researchers concluded that these potential heterogeneities extend across broad regions in the form of continuous bands.
Most notably, the analysis pinpointed six major areas hosting significant heterogeneities that had never been documented before. The researchers write in their published paper: 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.
While scientists cannot yet say precisely what these six deep-seated scatterers are composed of, they occupy a volatile zone where extreme conditions prevail. The boundary experiences an enormous temperature jump with a difference of about 1,000°C from the lower mantle to the liquid outer core.
Theories on Thermochemical Piles and Ancient Planetary Remains
The extreme temperatures and vast pressures at the base of the mantle suggest that these structures may act as thermochemical piles of material distinct from the surrounding rock. Material dragged down from outer layers into subduction zones can undergo radical chemical alterations under such extreme environments, taking on vastly different physical properties.
Some scientists suggest these mysterious accumulations could incorporate pieces of sunken continental crust or even remnants of Theia, a Mars-sized protoplanet theorized to have collided with early Earth and formed the moon 4.5 billion years ago. Whatever their exact origin, these massive hot rock formations and their surrounding material play a fundamental role in heat transfer and material cycling.
Massive heat escaping from the liquid iron outer core drives convection currents in the mantle known as mantle plumes. These plumes dictate areas of surface volcanic activity, while density differences at the boundary cause seismic waves to slow down significantly, giving geologists an indirect window into subterranean mechanics.
Connecting Deep Interior Dynamics to Earth’s Magnetic Field
Parallel research emphasizes how deeply these base-mantle structures affect planetary scale behavior. In a study published in Nature Geoscience, a research team led by the University of Liverpool combined palaeomagnetic data with advanced supercomputer models of the geodynamo—the movement of liquid iron in the outer core that generates Earth’s magnetic field—to investigate how massive rock formations beneath Africa and the Pacific Ocean influence core activity over millions of years.
The Liverpool team’s numerical models demonstrate that these deep features have shaped planetary magnetism for ages. By linking ancient magnetic records with modern seismic mapping, scientists are steadily closing the massive knowledge gap concerning the violent, dynamic realm operating silently miles beneath our feet.
