Researchers have created the first global map showing how Earth's deepest mantle is deformed, primarily in regions where ancient subducted tectonic slabs reside. Using over 16 million seismograms, the team confirmed patterns predicted by geodynamic models. The findings, published in The Seismic Record, offer new insights into mantle flow near the core-mantle boundary.
Jonathan Wolf of the University of California, Berkeley, and colleagues analyzed seismic waves from earthquakes to map deformation in the lowermost mantle, about 2,900 kilometers beneath the surface. They covered nearly 75% of this layer, detecting seismic anisotropy—variations in wave speeds by direction—in roughly two-thirds of the studied areas. Most deformation aligns with locations of deeply buried slabs from past subduction, as expected from simulations but now shown globally using seismic data. Wolf noted, “We don't have any of this kind of large-scale understanding for flow in the lowermost mantle. And that's really what we want to get at.” The study drew from more than 16 million seismograms across 24 worldwide data centers, including waves that travel through the core and back. This massive dataset revealed how slabs may retain 'fossil' anisotropy or develop new patterns from intense interactions at extreme depths. Wolf described the data as a “treasure trove” for future research, cautioning that absent signals do not mean no deformation. He hopes for expanded analysis to map global flow directions in the deep mantle.