According to research published in the Journal of Geophysical Research: Solid Earth, a deep-learning system developed by researchers at the Chinese Academy of Sciences identified 174,929 faint seismic signals known as PKP precursors across nearly 35 years of seismic data. By analyzing over two million waveforms from roughly 5,000 magnitude-6-plus earthquakes recorded between 1990 and 2024, the artificial intelligence discovered six previously undocumented zones at the Earth’s core-mantle boundary.
Deep Learning Uncovers Hidden Seismic Signals
Over the course of many years, human review of seismic archives failed to catch essential faint reflections bouncing off irregularities situated roughly 2,900 km down, where solid mantle rock meets the liquid iron-nickel outer core, roughly 2,900 km down. As reported in the study, these PKP precursors arrive just before the main seismic wave, making them weak enough to drown in noise. Reviewing these records manually was a slow, subjective, and geographically patchy process. Researchers trained a deep-learning classifier on human-labeled precursor examples, ran it across decades of archived recordings, and used iterative human-in-the-loop validation to sharpen accuracy.
Did you know? PKP precursors act as a kind of indirect tool for studying hidden features of the Earth’s interior because they scatter when they encounter small heterogeneities near the core-mantle boundary.
Six New Zones Mapped at the Core-Mantle Boundary
The system mapped six strong-scattering regions, labeled B1 through B6, located beneath high-latitude Eurasia, Central Asia, the South Atlantic, and other undersampled zones. Earlier studies had only documented isolated, seemingly random anomalies. In contrast, the new dataset reveals larger, belt-like zones extending across parts of the globe, connecting areas that previously appeared separate.
What Lies Beneath: Remnants and Ultra-Low Velocity Zones
The transition zone between the malleable mantle rock and the liquid iron-nickel experiences a temperature jump of around 1,000°C, operating at approximately 5,500°C across the interface. According to the research, several of the identified areas correspond to what is known in geophysics as ultra-low velocity zones, where seismic waves travel more slowly due to different physical or chemical properties. Researchers point out that these structures could relate to thermochemical accumulations formed by ancient subducted tectonic plate remnants, localized partial melting, and interactions with large low shear rate provinces, known as LLVPs.
Frequently Asked Questions
What are PKP precursors?
Following a planetary tremor, faint seismic impulses known as PKP precursors emerge prior to the arrival of stronger, more dominant waves. They scatter when they encounter small heterogeneities near the core-mantle boundary.
Where are the newly discovered zones located?
The six new zones, designated B1 through B6, are located near the boundary between Earth’s solid mantle and liquid outer core, approximately 2,900 kilometres under the surface.
How did artificial intelligence help find these structures?
A deep-learning classifier trained on human-labeled precursor examples processed over two million seismic waveforms recorded between 1990 and 2024, identifying patterns and signals that manual analysis missed over decades.
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