Seismic hemispheric asymmetry induced by Earth's inner core decentering

TL;DR

This paper proposes that the observed seismic hemispheric asymmetry at the Earth's inner core boundary can be explained by a slight eastward displacement of the inner core, challenging the traditional view of spherical symmetry.

Contribution

It introduces a novel hypothesis that inner core decentering accounts for hemispheric asymmetries, supported by numerical seismic ray simulations.

Findings

Seismic asymmetry can be explained without altering inner core material properties.

Displaced inner core hypothesis aligns with multiple hemispheric asymmetries.

Implications for Earth's thermal, mechanical, and magnetic processes.

Abstract

In a first approximation the Earth's interior has an isotropic structure with a spherical symmetry. Over the last decades the geophysical observations have revealed, at different spatial scales, the existence of several perturbations from this basic structure. Some of them are situated in the neighborhood of the inner core boundary (ICB). One of the best documented perturbations is the asymmetry at the top of the inner core (ATIC) characterized by faster seismic wave velocity in the eastern hemisphere than in the western hemisphere. All existing explanations are based on a hemispheric variation of the material properties near ICB inside the inner core. Using numerical simulations of the seismic ray propagation, we show that the ATIC can be explained as well by the displacement of the inner core towards east in the equatorial plane tens of kilometers from the Earth's center, without modifying the spherical symmetry in the upper inner core. The hypothesis of a displaced inner core is also sustained by other observed hemispheric asymmetries at the top of the inner core and at the bottom of the outer core. A displaced inner core would have major implications for many mechanical, thermal, and magnetic phenomena in the Earth's interior.