Multiscale model of global inner-core anisotropy induced by hcp-alloy plasticity

TL;DR

This paper presents a multiscale model explaining Earth's inner-core seismic anisotropy through hcp alloy deformation, combining plasticity, formation models, and seismic simulations to match observed anisotropy levels.

Contribution

It introduces a novel multiscale approach integrating plasticity and formation models to reproduce Earth's inner-core anisotropy from first principles.

Findings

Seismic anisotropy of 1-3% can be explained by hcp alloy deformation.

Single-crystal elastic anisotropy ranges from 5 to 20%.

Pyramidal slip and low-degree formation models are key to the anisotropy.

Abstract

$\bullet$ Multiscale model of inner-core anisotropy produced by hcp alloy deformation$\bullet$ 5 to 20% single-crystal elastic anisotropy and plastic deformation by pyramidal slip $\bullet$ Low-degree inner-core formation model with faster crystallization at the equatorThe Earth's solid inner-core exhibits a global seismic anisotropy of several percents. It results from a coherent alignment of anisotropic Fe-alloy crystals through the inner-core history that can be sampled by present-day seismic observations. By combining self-consistent polycrystal plasticity, inner-core formation models, Monte-Carlo search for elastic moduli, and simulations of seismic measurements, we introduce a multiscale model that can reproduce a global seismic anisotropy of several percents aligned with the Earth's rotation axis. Conditions for a successful model are an hexagonal-close-packed structure for the inner-core Fe-alloy, plastic deformation by pyramidal \textless{}c+a\textgreater{} slip, and large-scale flow induced by a low-degree inner-core formation model. For global anisotropies ranging between 1 and 3%, the elastic anisotropy in the single crystal ranges from 5 to 20% with larger velocities along the c-axis.