Depth dependence of anisotropy of Earth's inner core

Both body wave (PKP) travel times and fits to the splitting of core modes show general agreement that the top 300 km of inner core is very anisotropic. The anisotropy displays axial symmetry around the Earth's spin axis, with the polar direction 3% faster than the equatorial direction. One key problem now is the depth dependence of the inner core anisotropy. Here, polar path studies are extended to include both long-period and short-period modeling for the PKP phases at ranges 120° to 173°. The results suggest that the top 150 km of the inner core is only weakly anisotropic (less than 1%), with strong evidence indicating that the top 60 km is not anisotropic at all. -from Authors