Outer core density heterogeneity and the discrepancy between PKP and PcP travel time observations

Abstract

We derive 3-D maps of the Earth’s mantle, CMB and outer core by means of least squares tomographic inversions. The data set includes compressional wave travel time measurements associated with the phases P, PcP, PKPbc, PKPdf, all based on the bulletins of the International Seismological Centre (1964-1995), after source relocation by Antolik et al. [2001]. Maps of the CMB derived independently from only core-reflected (PcP) or only core-refracted (PKP) phases are not well correlated. We study the radial coherence of whole-Earth tomographic images, to investigate potential trade-offs between CMB undulations and velocity anomalies in the mantle and/or outer core. We find that imaged lateral heterogeneities in the outer core are correlated with the topography of the CMB. This, together with the studies of Wahr and De Vries [1989] and Piersanti et al. [2001], suggests that the core anomalies might not be entirely fictitious