Unusual seismic wave changes deep within the planet may indicate unexpected activity in Earth's core.

The Earth's core naturally changes its rotation rate and shape over time, though not at the same time. However, new research suggests something unexpected is occurring beneath the surface.

For years, scientists have debated the cause of unusual seismic wave variations—triggered by earthquakes—as they pass through the core. One theory attributes these changes to shifts in the core’s rotation rate, while another suggests that deformations in the inner core’s shape alter the waves. A new study, published in Nature Geoscience by researchers from China and the US, indicates that both factors may be at play.

In 2010, Earth's inner core transitioned from rotating faster than the rest of the planet to moving more slowly. This shift, along with surface-level changes in the inner core, likely disrupted seismic waves. These waves function like X-rays, allowing scientists to "see" inside the planet. Researchers believe this discovery could provide deeper insights into the core’s properties and structure.

Figure 1.Earth's core may be shifting its shape.

“For now, these findings simply provide an observable change that might lead us to get a clearer picture of how the inner core is flexing on a timescale of years. Further surprises may await,” said Prof. John Emilio Vidale, the study's lead author, in an interview with BBC Science Focus. Figue 1 shows Earth's core may be shifting its shape.

The Earth's core is nearly as hot as the Sun's surface, buried about 6,500 km (4,000 miles) beneath us, and experiences pressures greater than those in the ocean's deepest trenches. As a result, direct study of the core is impossible.

Instead, scientists rely on seismic waves generated by earthquakes. By analyzing how these waves travel through different layers of the planet—particularly the core—they can gain valuable insights into its structure, movement, and behavior.

In this latest study, researchers examined seismic waves from 121 pairs of repeating earthquakes—twin quakes occurring in the same location with nearly identical wave patterns—recorded in the South Sandwich Islands between 1991 and 2023. These events were detected at two separate seismic arrays: Eielson (ILAR) in Alaska and Yellowknife (YKA) in Canada.

By studying the arrival times and waveform variations of these signals over multiple decades, the team was able to track subtle shifts in the core’s movement. If the inner core rotated at a steady rate, the seismic wave arrival times would have changed consistently over time.

Instead, the analysis revealed distinct trends in the inner core’s motion. It rotated faster than the Earth's mantle and crust for several decades but began slowing down around 2010 [1]. Interestingly, some earthquakes showed no significant time shifts, suggesting that the inner core's rotation may have temporarily paused or even reversed at times.

The study also uncovered a secondary finding: differences in the signals from the two seismic arrays suggested that something beyond just rotation was influencing the inner core.

Researchers believe the culprit may be viscous deformation near the inner-core boundary. Although the inner core is composed of solid metal, changes in the outer core’s shape or variations in the mantle’s density could alter its structure.

While this behavior appears unpredictable, there isn’t enough data to determine whether it is a normal process, making it difficult to fully understand how the Earth’s core is behaving.

According to Vidale, the simplest explanation is that movements in the outer core drive the inner core’s rotation, gradually realigning it over decades—though the exact mechanism remains unclear.

“If this was the case, the rotation of the cores would be mostly harmonic (predictable)," he explained[2]. Alternatively, "the inner core motion could be mostly chaotic, just going in the direction the outer core goes.”

For now, this research offers intriguing insights into the Earth's core, with the potential for further discoveries. Vidale suggests that additional studies could help identify when and where outer core convection is strongest or where the inner core is more or less rigid.

He also speculates that this research might uncover a link between inner-core changes and sudden shifts in Earth’s magnetic field. While these fluctuations don’t impact daily life, they can affect satellites and compasses.

Reference:

1. https://www.sciencefocus.com/news/earths-core-rotation-speed-changing
2. https://www.bbc.com/news/articles/c4gx37ky3gyo

Cite this article:

Keerthana S (2025),Scientists are puzzled as Earth's core may be shifting its shape, AnaTechMaz, pp. 204