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

A Lincot (1) , Ph Cardin (1) , R Deguen (2) , Sébastien Merkel (3)

1 ISTerre - Institut des Sciences de la Terre
2 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement
3 UMET - Unité Matériaux et Transformations - UMR 8207

• Multiscale model of inner-core anisotropy produced by hcp alloy deformation • 5 to 20% single-crystal elastic anisotropy and plastic deformation by pyramidal slip • Low-degree inner-core formation model with faster crystallization at the equator The 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 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.

Mots clés: convection; anisotropy; iron; Earth's Core; inner core; stratification

Domaines: Géophysique [physics.geo-ph]; Minéralogie

A Lincot, Ph Cardin, R Deguen, Sébastien Merkel. Multiscale model of global inner-core anisotropy induced by hcp-alloy plasticity. 2016. ⟨hal-01259186v2⟩