Models of the anisotropy of the Earth's inner core

Recent seismological studies have revealed that the Earth's inner core has acoustic anisotropy. Several models of the generation of the anisotropy have been proposed. Most of them attribute the anisotropy to preferred orientation of iron crystals, while the proposed mechanisms that give rise to the crystal alignment are diverse, including deformation, magnetic force and crystal growth. We review these models critically in order to suggest future directions for further development.