Elasticity and rheology of iron above 220 GPa and the nature of the Earth's inner core

Recent numerical-modelling and seismological results have raised new questions about the dynamics` - ' and magnetism of the Earth's core. Knowledge of the elasticity and texture of irons' ' at core pressures is crucial for understanding the seismological ; observations, such as the low attenuation of seismic waves, the low shear-wave velocity and the anisotropy of compressional-wave velocity - quot;. The density and bulk modulus of hexagonal-close-packed iron have been previously measured to 1 core pressures by staticquot; and dynamicquot;,quot; methods. Here we study, using radial X-ray diffraction 1 5 and ultrasonic techniques', I the shear modulus, single-crystal elasticity tensor, aggregate compressional- and shear-wave velocities, and orientation dependents of these velocities in iron. The inner core shear-wave velocity is lower than the aggregate shear-wave velocity of iron, suggesting the presence of low-velocity components or anelastic effects in the core. Observation of a strong lattice strain anisotropy in iron samples indicates a large (--24% compressional wave anisotropy under the isostress assumption, and therefore a perfect alignment of crystals, would not be needed to explain the seismic observations. Alternatively the strain anisotropy may indicate stress variation due to preferred slip systems