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