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

• Published in: Geophysical research letters 2016-02, Vol.43 (3), p.1084-1091
• Main Authors: Lincot, A., Cardin, Ph, Deguen, R., Merkel, S.
• Format: Article
• Language: English
• Subjects: Alignment; Alloys; Anisotropy; Computer simulation; Crystals; Deformation; Earth axis; Earth core; Earth rotation; Earth Sciences; Elastic anisotropy; Fe alloy; Ferrous alloys; Formations; Geophysics; hcp; inner‐core anisotropy; inner‐core formation; Iron; Modulus of elasticity; Plastic deformation; Plastic properties; Plasticity; polycrystal plasticity; Polycrystals; Sciences of the Universe; Seismic activity; Single crystals; Slip
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2015GL067019

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 〈c + a〉 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. Key Points 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