The times and amplitudes of core phases for a variable core-mantle boundary layer

Abstract

SUMMARY Synthetic pulse forms of core phases have been computed in models of an undulating core-mantle boundary or an undulating boundary layer at the base of the mantle. A simple detector has been applied to the pulse forms of PcP, PKP (BC and AB) and PKKP (BC). The detections are influenced by amplitude and waveform changes due to focusing, defocusing and interference. Numerical results are given for the increased bias and the change of variance of the traveltime residuals. The results for traveltime bias follow the observed trend in real data of core phases, although the computed bias is less than observations suggest. Special attention is paid to the underlying assumptions of seismic tomography. It is shown that these assumptions are not tenable for several of the phases and models considered here. In those cases, seismic tomography will produce models that are in poor agreement with the true model. The synthetics were computed by introducing the concepts of 3-D dynamic ray tracing with a Kirchhoff type of integral over a spherical reference surface. Simple expressions are given for propagating the ray propagators of 3-D dynamic ray tracing through spherically symmetric parts of the model.