Cross section through the mantle showing how ray paths for diverse seismic phases from various source regions constrain the extent of the large, low-shear velocity province beneath Africa, which is bounded by the green outline. S-wave velocities within the province are about 3% lower than in the surrounding lower mantle. The structure extends upward more than 1000 km above the core-mantle boundary. (Image from Y. Wang and L. Wen, 2007. Geometry and P and S velocity structure of the “African Anomaly,” Journal of Geophysical Research, 112, B05313, doi:10.1029/2006JB004483.)