A local, crossing‐path study of attenuation and anisotropy of the inner core

We report results from studying a region under the north Pacific using 46 ray paths along east‐west and north‐south directions to study the nature of inner core anisotropy, and find an anisotropy signal in differential PKPBC–PKPDF at about the resolution of the data, with north‐south paths faster than east‐west, but no dependence of attenuation on wavespeed or depth in this part of the inner core. Inner core Q is 130−52+255 between 140–340 km depth. The observations also provide constraints on the degree of homogeneous meridional anisotropy possibly present in the core, to between 0.1 and 0.6% velocity differences in the fast and slow directions, significantly smaller than the 2–4% axi‐symmetric anisotropy in the inner core. The small meridional component to anisotropy argues against significant contributions to anisotropy from low‐order inner core convection or stresses imposed on the inner core by the outer core field.