Abstract

Lateral variations in the velocity, attenuation, anisotropy, and scattering of seismic waves interacting with the inner core are more complex than a simple hemispherical pattern, exhibiting spatial correlation with the non-dipole magnetic field and with large-scale velocity structure in the lowermost outer core. In several regions of the uppermost inner core, it is possible to observe and model the effects of small-scale (< 10km) heterogeneity on both back-scattered PKiKP coda and forward scattered waves that broaden the PKIKP waveform. At antipodal ranges (175 to 180), sparse global observations of diffraction from the PKP -C cusp and PKIIKP , in addition to other focused and multipathed phases, observed or hypothesized, can provide tests on the existence of large-scale lateral heterogeneity and strong vertical gradients. Lateral variations in the process of compositional convection in the outer core may possibly explain some correlations of inner core structure with spatially persistent features of the non-dipole field.