On seismic-wave scattering by a rough core?mantle boundary

Abstract

Summary. A formulation is given for the seismic-wave scattering by a rough solid-liquid interface, in analogy to results derived for a solid-solid interface and a heterogeneous volume. Using Kennett’s approach and the reciprocity theorem, the scattering is formulated as the excitation by an equivalent dislocation. Using interface parameters relevant to the core-mantle boundary (CMB), computational results for several types of body-wave scattering are given and compared to scattering by a heterogeneous volume. In an application to the generation of PKP precursors it is concluded that, whereas some data groups point to heterogeneity (which may not be small) in the lower mantle above CMB, in other cases a rough CMB may be considered equally feasible. Scattering at the source or receiver side of the core by both a slightly rough CMB (radial variations up to a few hundred metres) and a slightly heterogeneous lower mantle (relative variations in physical parameters up to a few per cent) produces the energy level that is observed in most of the PKP precursors; also the relevant scale lengths of variation are about the same ie both mechanisms (10-20 km with possibly somewhat higher values at relatively long epicentral distances).