Inner core static tilt inferred from intradecadal oscillation in the Earth’s rotation

This paper investigates the presence of a static tilt between the Earth's inner core and mantle by analyzing an approximately 8.5-year signal in polar motion and length-of-day variations. The authors identify this signal as the inner core wobble (ICW) and, based on its amplitude and phase consistency in both datasets, infer a static tilt angle of about 0.17 ± 0.03°, likely towards -90°W relative to the mantle. This tilt is significantly smaller than previously assumed in some geodynamic research and is consistent with a higher average density in the northwestern hemisphere of the inner core. The observed ICW period also suggests a density jump at the inner core boundary of 0.52 ± 0.05 g/cm³.

Yachong An, Hao Ding, Zhifeng Chen, Wenbin Shen, Weiping Jiang