Inner core's seismic anisotropy is related to its rotation

The inner core has a differential rotation relative to the crust and mantle , the relative linear velocity between the solid inner core and the molten outer core is the biggest at the equator and zero at pole area, As a result , the inner core grows faster at the equator than at the pole area. The gra vitational force drives the material flow from the equator to the pole area and makes the inner core remain quasi-orbicular. The corresponding axial s ymmetric stress field makes c-axes of hexagonal close packed (hcp) iron ali gn with inner core's rotation axis, resulting in observed seismic anisotrop y.