Large-scale structure at the core-mantle boundary from diffracted waves

A differential technique compares the arrival times of waves refracted across and diffracted around the core-mantle boundary to map the large-scale compressional-wave velocity variations within the D' thermal and chemical boundary layer. This map depicts the continent-sized variations at the core-mantle boundary that complements the shear-wave data. The diffracted waves provide an image of the D' layer, and the differential technique negates the effect of ray paths that are outside of D'. The results support a strong coupling between surface plate tectonics and the mantle base.