Generation of inner core anisotropy by anisotropic thermal conductivity of iron crystals

Abstract Seismic anisotropy in the Earth’s inner core refers to the observation that seismic waves travel faster along the Earth’s rotation axis than in the equatorial plane, a feature inferred from decades of global seismological observations. This directional dependence of wave speeds provides important clues about the structure, composition and dynamics of the inner core. Here we explore a coupled thermo-mechanical mechanism for the generation of inner core anisotropy, focusing on the effects of anisotropic thermal conductivity in iron crystals as the inner core cools. We propose that the higher thermal conductivity of iron along the crystallographic c -axis compared with the a -axis leads to differential heat flow, generating temperature anomalies within the inner core. These anomalies drive flow and contribute to the development of elastic anisotropy. Our model suggests that this thermally induced flow mechanism can account for the observed seismic anisotropy without requiring extrinsic contributions. These findings provide insights into the internal dynamics of the inner core, providing a more comprehensive understanding of its thermal evolution and anisotropic properties.