Inner Core Anisotropy and the Inner-Most Inner Core

Miaki Ishii
UCSD


Abstract:      
Although the presence of anisotropy in the inner core is generally accepted, its strength 
and depth dependence vary considerably from model to model.  Our joint inversions of 
normal-mode splitting-function coefficients and absolute and differential body-wave travel 
times demonstrates that a significant part of the data can be explained by a simple model 
of anisotropy with the symmetry axis aligned with the Earth's rotation axis.

This model fits the PKIKP data trend well at all distance ranges except between 173 and 
180 degrees.  The distance range corresponds to the inner-most 300~km of the Earth, where 
mode constraints are weak, and where constraints from differential travel times are likely 
contaminated by mantle structure. When the PKIKP travel times are inverted for anisotropic 
parameters of the inner-most inner core, we obtain a model with a slow direction oriented 
~45 degrees from the equator, in contrast to the bulk inner core where the slowest wave 
propagation occurs when the rays are parallel to the equatorial plane.