Far below the Earth’s surface, where the solid mantle touches the molten outer core, scientists have found almost 175,000 seismic signals that had never been recorded before. This is over ten times as much as earlier studies found.
Researchers at the Institute of Geology and Geophysics, Chinese Academy of Sciences, created a new deep learning tool to spot PKP precursors—faint seismic waves that appear just before stronger ones as they bounce off irregularities near the core-mantle boundary.
The team, whose findings will appear in the Journal of Geophysical Research: Solid Earth in 2026, trained their algorithm using over 2 million seismic waveforms from around 5,000 earthquakes recorded between 1990 and 2024.
By repeatedly correcting its mistakes, they enabled the system to analyze data on a scale that would be impossible for humans to process by hand.
Previous maps of the deepest part of the mantle showed these anomalies scattered at random. With the much larger dataset, scientists now see that most of these once-isolated patches are actually linked together, forming broad bands along the core-mantle boundary.
These bands might include fragments of oceanic crust and sediment that have sunk deep into the Earth over millions of years. Some could be associated with extended low shear-velocity zones, often called ‘blobs,’ or with debris from the ancient collision that led to the formation of the Moon.
Under the immense pressure at these depths, this material can melt or transform into minerals that differ markedly from the surrounding rock.
The researchers have found six regions that have not been studied extensively before, such as high-latitude Eurasia, Central Asia, and the South Atlantic. They see these as top priorities for future research using different seismic wave methods.
The study flags six previously under-sampled regions, including zones beneath high-latitude Eurasia, Central Asia, and the South Atlantic, as priorities for future research using several types of seismic waves.
