Seismic data reveals Earth’s inner core is changing shape

New research led by John Vidale, a seismologist at the University of Southern California, suggests that Earth’s inner core is not just rotating but also undergoing notable shape changes, with regions potentially rising and falling by up to 1 km (0.62 miles) over short geological timeframes

The study utilized data from sensors at the Eielson Air Force Base in Alaska and the Yellowknife Seismological Array in Canada’s Northwest Territories. Researchers identified unexpected variations in wave behavior between 2004 and 2008 by comparing 168 earthquake pairs that originated in the same location but at different times.

The variations suggested that the inner core is not a perfectly uniform sphere but a structure with shifting regions, altering its topography over time.

“Spotting a process that was previously undocumented is a thrill,” Vidale stated.

Seismic wave analysis and core deformations

Seismic waves provide critical insights into the inner core, which lies approximately 5 000 km (3 100 miles) beneath the Earth’s surface. Waves passing through the core reveal information about its composition and any ongoing changes.

Key observations from the study showed that while deeper seismic waves remained consistent, those traveling along the outer layers of the inner core exhibited anomalies. This suggested localized deformations indicating that the inner core’s surface is in constant flux.

The variations in seismic waves point to regions of the inner core rising and sinking because of the redistribution of material or differences in solidification rates. This challenges the conventional view of a perfectly uniform inner core, suggesting a far more complex structure.

Potential causes of core surface changes

The shifting topography of the inner core may result from multiple factors related to extreme temperature and pressure conditions deep within the planet.

One possibility is that temperature fluctuations at the boundary between the inner and outer core cause continuous melting and solidification of iron, reshaping the core’s surface over time. Another theory suggests that iron may be bubbling out of the inner core in localized bursts, similar to magma upwelling in Earth’s mantle, albeit under extreme pressures.

Gravitational interactions between the inner core, outer core, and mantle could apply uneven pressure on different regions, leading to long-term, uneven changes observed in seismic wave data. The rapid changes detected between 2004 and 2008 suggest that these deformations occur faster than previously believed, raising questions about their broader implications for Earth’s geodynamic system.

Implications for Earth’s magnetic field and geodynamics

The inner core plays a crucial role in maintaining Earth’s magnetic field through its interaction with the outer core. Changes in its shape and movement could impact heat transfer between core layers, potentially altering the intensity and stability of Earth’s magnetic field over long timescales.

A key concern is whether these deformations influence the convective currents of molten iron in the outer core, which drive the geodynamo effect. Any disruptions in these currents could contribute to magnetic field fluctuations, including the gradual weakening of Earth’s magnetic field and periodic geomagnetic reversals.

Researchers are also investigating whether inner core deformations are linked to rotational variations. Asymmetric shifts in the core may cause minor fluctuations in Earth’s rotation, affecting planetary processes such as day length and angular momentum variations. Vidale noted that refining models will be important for understanding these complex interactions.

Future research and seismic monitoring

Long-term seismic data collection is essential for tracking inner core changes. Since these transformations occur over years to decades, continuous monitoring will improve model accuracy and predictions of core activity’s impact on geophysical processes.

Future research will focus on gathering more seismic data, enhancing computational simulations, and refining theoretical models of core-mantle interactions. Scientists aim to examine how these structural changes influence broader geodynamic processes, including mantle convection and plate tectonics.

Advancements in seismological technology will allow for even more precise measurements of inner core activity. Deploying additional seismic arrays and improving data analysis techniques will help develop a comprehensive understanding of how the inner core evolves over time.

These ongoing efforts reinforce the view that Earth’s deep interior is dynamic rather than static, playing a significant role in shaping the planet’s geophysical and magnetic behaviors.

References:

¹ Annual-scale variability in both the rotation rate and near surface of Earth’s inner core, John E. Vidale, Wei Wang, Ruoyan Wang, Guanning Pang & Keith Koper, nature – February 10, 2025 – https://doi.org/10.1038/s41561-025-01642-2

² Earth’s inner core might harbor volcanoes and landslides – Science – February 10, 2025

Rishika Yadav

Rishika holds a Master’s in International Studies from Stella Maris College, Chennai, India, where she earned a gold medal, and an MCA from the University of Mysore, Karnataka, India. Previously, she served as a Research Assistant at the National Institute of Advanced Studies, Indian Institute of Science, Bengaluru, India. During her tenure, she contributed as a Junior Writer for Europe Monitor on the Global Politics website and as an Assistant Editor for The World This Week. Her work has also been published in The Hindu newspaper, showing her expertise in global affairs. Rishika is also a recipient of the Women Empowerment Award at the district level in Haryana, India, in 2022.

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