Earth's inner core slowdown: A startling shift detected by the scientists from the University of Southern California

New analyses of seismic data from earthquakes and nuclear tests have provided evidence that Earth's inner core has begun to slow down relative to the planet's surface. According to scientists, this trend started around 2010.

In new research published in the journal "Nature" (DOI: 10.1038/s41586-024-07536-4), scientists from the University of Southern California (USC) determined that Earth's inner core is slowing relative to the planet's surface. They point out that this slowdown is influenced by the gravitational pull of Earth's mantle and the dynamics of the liquid outer core surrounding the inner core. This phenomenon may potentially have a slight impact on Earth's rotation.

It is commonly thought that Earth's core is a sphere with a radius of nearly 3,500 kilometres. It consists mainly of nickel and iron alloys but may have traces of sulphur, silicon, or potassium. Researchers differentiate three structures that make up Earth's core: the liquid outer core, the inner core, and the transition zone between them — the Lehmann discontinuity. Earth's inner core freely rotates, surrounded by a sea of molten iron, the outer core. It has a radius of about 1,250 kilometres and exhibits the characteristics of a solid body.

Convection currents in Earth's core create the geodynamo, which envelops and protects our planet with a magnetic field. Above the core is the Earth's mantle, and above that is the Earth's crust, where we live. The Earth's core is located at great depth and can only be studied through the analysis of seismic waves.

The movement of the inner core has been a subject of debate within the scientific community for decades. New research by specialists from USC provides unequivocal evidence that the inner core began slowing its velocity around 2010.

"When I first saw the seismograms that hinted at this change, I was stumped," said John Vidale of USC. "But when we found two dozen more observations signaling the same pattern, the result was inescapable. Other scientists have recently argued for similar and different models, but our latest study provides the most convincing resolution," he added.

Compared to its speed in previous decades, the inner core is slowing relative to the planet’s surface. Researchers point out this is happening for the first time in 40 years.

Vidale and Wei Wang from the Chinese Academy of Sciences, co-authors of the publication, used recurring earthquakes — seismic events that occur in the exact location, have similar strength and have the same source — for their research. The scientists gathered and analysed seismic data recorded during earthquakes around the South Sandwich Islands. Between 1991 and 2023, there were 121 tremors. The researchers also used data from Soviet nuclear tests conducted between 1971 and 1974, as well as similar tests carried out by the French and Americans.

Using data showing how these seismic waves accelerate, decelerate, and interact with each other, scientists can estimate the position and movement of the inner core.

According to the authors of the publication, the slowdown in the inner core’s speed is due to disturbances in the dynamics of the liquid outer core. It is also influenced by the gravitational pull of the dense regions of the Earth's mantle above it.

This phenomenon could potentially affect the Earth's surface. It is only possible to speculate what the consequences of the inner core's movement change might be. Vidale admitted that the inner core's slowdown may impact the entire planet's rotation and change the length of the day by fractions of a second.