Episodic Change, Quiescence, and Recovery of Earth's Inner Core Surface

Abstract

While a consensus has emerged that the hypothesis of inner core differential rotation cannot provide a consistent explanation for the seismic data, it remains debated whether the seismic data indicate a concurrence of a temporal change of inner core surface with an inner core differential rotation or the temporal change of inner core surface alone sufficiently and consistently explains the seismic data. Accompanying the debate are another two important unresolved issues: what are the general characteristics and physical mechanisms of the inner core surface change? Here, we show that the data contradictions to the hypothesis of inner core differential rotation are extensive and temporal changes of the inner core surface provide a simple and consistent explanation for the seismic data without any inner core differential rotation. In a first detailed study of general characteristics of inner core surface change, we map the spatiotemporal evolution of the inner core surface beneath eastern South America between 2003 and 2024 using a repeating earthquake cluster. Seismic mapping reveals that inner core surface changes vary greatly with geographic locations and possess irregular episodes of change, quiescence and recovery. We propose two physical mechanisms for the inner core surface changes: localized viscous deformation induced by episodic small‐scale forces and localized alternate solidification/melting. Our results indicate that, on a time scale of years to days and in a way of large geographical variations, the inner core plays a significant role in influencing small‐scale driving forces of Earth's geodynamo and/or interacting with the small‐scale forces near its surface.