Precursors toPKIKPand seismic wave scattering near the mantle-core boundary

Detailed distributions of slownesses, azimuths, and amplitudes along PKIKP precursor wave trains observed at NORSAR are shown to be fully consistent with theoretical results for scattering of PKP waves by small-scale random inhomogeneities in the lowermost mantle, where the PKP waves enter into and exit from the core. It is also shown that data recently interpreted as corroborating the existence of sharp reflecting discontinuities within the outer core are also consistent with the scattering interpretation. The NORSAR data discriminate sharply against previous interpretations which have required the presence of transition layers between inner and outer cores.