The effect of D″ on PKP(AB−DF) travel time residuals and possible implications for inner core structure

The hypothesis that the deep inner core is anisotropic is based on PKP travel time observations at large distances and relies on a small number of very anomalous measurements for paths quasi-parallel to the Earth’s rotation axis. Here, we analyze a global dataset of PKP(AB−DF) travel times residuals, and discuss their significant dispersion (±2 s), and coherent large scale patterns. We show that the trends observed for quasi-equatorial paths are consistent with predictions from recent tomographic mantle models, when the latter are modified to account for strong heterogeneity at the base of the mantle under the Pacific Ocean and Africa, as documented in several recent studies. Likewise, for polar paths, we show that a large part of the signal could be explained by deep mantle structure. The effects of complex structure in the deep mantle on PKP(AB−DF) travel times should be carefully considered in order to reliably estimate the anisotropic structure of the central part of the inner core.