USC researchers demonstrate that Earth’s core is losing momentum

A new study provides clear evidence that Earth’s inner core began to slow down in 2010.

USC Scientists have discovered that Earth’s inner core is slowing down relative to the planet’s surface, which began in 2010 after decades of the opposite trend. This significant shift was detected through extensive seismic data analysis from earthquakes and nuclear tests. The inertia is influenced by the dynamics of the surrounding liquid outer core and the gravitational force from the Earth’s mantle, which slightly affects the Earth’s rotation.

Inner core dynamics

USC scientists have demonstrated that Earth’s inner core is receding relative to the planet’s surface—slowly—as shown in new research published June 12 in the journal Nature. Nature.

The scientific community has long debated the motion of the inner core, with some studies suggesting that it rotates faster than the Earth’s surface. However, USC’s latest research, starting in 2010, shows that the inner core has slowed and is now moving more slowly than the planet’s surface.

„When I first saw the seismic maps showing this change, I was stunned,” said John Vidal, dean’s professor of geosciences in the USC Thornsife College of Letters, Arts and Sciences. „But when we found more than two dozen observations indicating the same pattern, the conclusion was inescapable. The inner core has decreased for the first time in decades. Other scientists have recently argued for similar and different patterns, but our latest study provides the most definitive resolution.”

Relativity of recoil and deceleration

For the first time in approximately 40 years, the inner core is thought to be inverting and receding relative to the planet’s surface, moving slightly slower than the Earth’s mantle instead of faster. Compared to its speed in previous decades, the inner core is slow.

The inner core is a solid iron-nickel sphere surrounded by a liquid iron-nickel outer core. Roughly the size of the moon, the inner core sits more than 3,000 miles below our feet and poses a challenge for researchers: it can’t be visited or seen. Scientists must use seismic waves from earthquakes to create the movement of the inner core.

A new approach of iterative approach

Vidale and Wei Wang of the Chinese Academy of Sciences used waveforms and repeated earthquakes in contrast to other research. Seismic events that occur at the same location to produce similar seismograms are repeated earthquakes.

In this study, researchers compiled and analyzed seismic data recorded around the South Sandwich Islands from 121 consecutive earthquakes that occurred between 1991 and 2023. Nuclear tests from other studies of the inner core.

Vidal said that the deceleration of the inner core was caused by the turbulence of the liquid iron outer core around it, creating the Earth’s magnetic field.

Impact on Earth’s surface

The implications of this change in the movement of the inner core to the Earth’s surface can only be speculated. The recession of the inner core can change the length of a day by fractions of a second, Videl said: “On the order of thousandths of a second, it’s very difficult to observe something almost lost in the noise of the oceans and atmosphere. „

Future research by the USC scientists wants to chart the path of the inner core in more detail, revealing exactly why it changes.

„The dance of the inner core may be more lively than we’ve known so far,” Videl said.

Reference: Wei Wang, John E. Vidal, Guanying Bong, Keith D. Cooper and Ruoyan Wang, 12 June 2024, “Inversion of Seismic Waveform Changes by Inner Core Backtracking” Nature.
DOI: 10.1038/s41586-024-07536-4

In addition to Vidal, other study authors include Ruoyan Wang of USC Dornsife, Wei Wang of the Chinese Academy of Sciences, Guanning Pang of Cornell University and Keith Koper of the University of Utah.

This research was supported by the National Science Foundation (EAR-2041892) and the Institute of Geography and Geophysics of the Chinese Academy of Sciences (IGGCAS-201904 and IGGCAS-202204).