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

TL;DR

This study infers a small static tilt of the Earth's inner core using intradecadal oscillations in Earth's rotation, providing new insights into inner core dynamics and density distribution.

Contribution

It presents the first evidence of a small static tilt of the inner core based on Earth's rotation data, challenging previous assumptions of larger tilt angles.

Findings

Inner core tilt is approximately 0.17°, much smaller than previously assumed.

The 8.5-year oscillation period indicates a density jump of 0.52 g/cm³ at the inner core boundary.

The tilt suggests a denser northwestern hemisphere of the inner core.

Abstract

The geodynamic state of the inner core remains an enigma, encompassing the presence of a static tilt between the inner core and mantle. Following the experimental confirmation of an ~8.5yr signal in polar motion as the inner core wobble (ICW), a normal mode of the inner core, we report that the ~8.5yr oscillation contained in the length-of-day variations in the Earth's rotation has good phase consistency with it. Our analysis demonstrated a 0.17{\deg} static tilt of the inner core (more likely towards ~90{\deg}W) relative to the mantle, which is two orders of magnitude lower than the 10{\deg} assumed in certain geodynamic researches. This tilt is consistent with the assumption that the average density in the northwestern hemisphere of the inner core should be greater than that in the other regions. Besides, the observed ICW period (8.5yr) suggests a 0.52g/cm3 density jump at the inner core boundary.