Abstract
The difference between the travel times of com-pressional waves that turn in the Earth's liquid outer core (PKP-BC) and those that run in the solid inner core (PKIKP-DF) is primarily sensitive to structure near the inner-core boundary. Such differential travel times measured from short-period waveforms are consistent with small-amplitude deviations from radial symmetry except when ray paths are nearly parallel to the Earth's spin axis. These near-axial paths consistently produce large travel-time anomalies, providing compelling evidence for large-amplitude, axisymmetric aniso-tropy in the outermost portions of the inner core.
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Creager, K. Anisotropy of the inner core from differential travel times of the phases PKP and PKIKP. Nature 356, 309–314 (1992). https://doi.org/10.1038/356309a0
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DOI: https://doi.org/10.1038/356309a0
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