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

Abstract

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±25552 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.