Reflection point residuals of PP and SS waves obtained from the residuals of PP-P and SS-S with respect to the J–B tables are shown to be in need of corrections. Recent velocity models of the Earth's mantle predict residuals that differ considerably amongst themselves and from the J–B tables. Before useful reflection point residuals can be determined by this method a reference model has to approximate closely the actual velocity distribution of the Earth between the source and receiver. Lateral variations, layering in velocity, and scattering in the vicinity of the reflection point of short-period PP also contribute large uncertainties in defining the reflection points of PP and its precursors. All of the foregoing problems suggest that interpretations of PP and SS wave residuals in terms of structure near the symmetric reflections points, as far as they have been determined up to now, are subject to serious errors.

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