Origin of the depth-dependent anisotropy in the Earth’s inner core

The understanding of the origin of seismic anisotropy in the Earth’s inner core (IC) remains a subject of debate and requires examining the deformation behavior of potential core materials. In this research, we investigated the effect of silicon and carbon on the deformation of the hexagonal close-packed iron alloy employing radial X-ray diffraction at high-pressure, high-temperature conditions. We revealed the low anisotropy of the sound velocity (~2 %) of the Fe-Si-C alloy that is compatible with the anisotropy observed in the IC’s outer shells. This finding provides an explanation for the heterogeneous depth-dependent elastic anisotropy in the IC originating from the stratification of silicon and carbon within the inner core upon its crystallization.