Slichter modes

In 1961, L. Slichter pointed out that some of the Earth's seismic modes might consist of translational oscillations of the solid inner core about its equilibrium position at the centre of the Earth. This motion, the "Slichter mode", is principally controlled by the density jump between the inner and outer core, and the Archimedean force of the fluid core. Its period is thought to lie within 4-8 hours and is split into 3 components by the Earth's rotation.