For the past two decades, seismological studies have identified anomalous low-velocity zones above the CMB, such as the large low-shear-velocity provinces (LLSVPs) beneath Africa and the Pacific.

Scientists have known that seismic waves slow down when passing through ultra-low velocity zones, or ULVZs, but only knew they existed around hotspots that create volcanic island chains.

The bottom of each field is the core-mantle boundary. Ultra-low velocity zones can be seen in the top and middle fields, forming at the toes of the light blue zones. Credit must be given to the ...