Global 3D configuration of seismic velocity heterogeneities in the mantle as imaged by seismic tomography Global 3D configuration (extending from the mapped surface to the core-mantle boundary) of seismic velocity heterogeneities in the mantle as imaged by seismic tomography. Red regions have relatively low S-wave velocities, while blue regions have relatively fast S-wave velocities. The image is dominated by two enormous low-velocity regions, beneath Africa and the central Pacific plates, and by a ring of high velocities underlying subduction zones around the rim of the Pacific. (Image courtesy of A. Dziewonski).