1. Department of Earth & Ocean Sciences, University of British Columbia, Vancouver, V6T 1Z4 Canada
2. Department of Earth & Planetary Science, University of California, Berkeley, California 94720, USA

Correspondence to: B. A. Buffett¹ Correspondence and requests for materials should be addressed to B.A.B (e-mail: Email: buffett@geop.ubc.ca).

Abstract

Elastic anisotropy in the Earth's inner core has been attributed to a preferred lattice orientation¹, which may be acquired during solidification of the inner core² or developed subsequent to solidification as a result of plastic deformation^{3, 4, 5}. But solidification texturing alone cannot explain the observed depth dependence of anisotropy^{6, 7, 8}, and previous suggestions for possible deformation processes have all relied on radial flow, which is inhibited by thermal⁹ and chemical stratification¹⁰. Here we investigate the development of anisotropy as the inner core deforms plastically under the influence of electromagnetic (Maxwell) shear stresses. We estimate the flow caused by a representative magnetic field using polycrystal plasticity simulations for -iron, where the imposed deformation is accommodated by basal and prismatic slip¹¹. We find that individual grains in an initially random polycrystal become preferentially oriented with their c axes parallel to the equatorial plane. This pattern is accentuated if deformation is accompanied by recrystallization. Using the single-crystal elastic properties of -iron at core pressure and temperature¹², we average over the simulated orientation distribution to obtain a pattern of elastic anisotropy which is similar to that observed seismologically^{13, 14}.

1. Department of Earth & Ocean Sciences, University of British Columbia, Vancouver, V6T 1Z4 Canada
2. Department of Earth & Planetary Science, University of California, Berkeley, California 94720, USA

Correspondence to: B. A. Buffett¹ Correspondence and requests for materials should be addressed to B.A.B (e-mail: Email: buffett@geop.ubc.ca).