Is inner core seismic anisotropy a marker of plastic flow of cubic iron?

TL;DR

This study examines if seismic anisotropy in the Earth's inner core can be explained by a cubic iron structure, concluding that observed anisotropy is incompatible with cubic Fe alloys undergoing plastic deformation.

Contribution

It demonstrates that cubic Fe alloys cannot produce the observed seismic anisotropy through plastic deformation, challenging previous assumptions about inner core structure.

Findings

Seismic anisotropy is below 0.4% for cubic Fe alloys.

Cubic Fe alloys are incompatible with observed global anisotropy.

Large-scale anisotropic structures must exist if the inner core is cubic.

Abstract

This paper investigates whether observations of seismic anisotropy are compatible with a cubic structure of the inner core Fe alloy. We assume that anisotropy is the result of plastic deformation within a large scale flow induced by preferred growth at the inner core equator. Based on elastic moduli from the literature, bcc- or fcc-Fe produce seismic anisotropy well below seismic observations ($\textless{}0.4\%$). A Monte-Carlo approach allows us to generalize this result to any form of elastic anisotropy in a cubic system. Within our model, inner core global anisotropy is not compatible with a cubic structure of Fe alloy. Hence, if the inner core material is indeed cubic, large scale coherent anisotropic structures, incompatible with plastic deformation induced by large scale flow, must be present.