Decades worth of seismic data confirms the rotation of Earth’s inner core is moving slower than the planet’s surface.
Key takeaways
- Seismic data from the past decades confirms that Earth’s inner core has been rotating more slowly than the planet’s surface.
- Researchers at the University of Southern California (USC) utilized seismic data from earthquakes and nuclear explosions to visualize the inner core’s movement, revealing changes in the speed and interaction of seismic waves within Earth’s layers.
- This slowing of the inner core affects the duration of our days by fractions of a second, though the impact is considered insignificant.
- The study, led by USC, attributes the slowing to convection within the liquid iron outer core, which supports Earth’s magnetic field, and gravitational forces in the mantle.
- Analysis included seismic data from 121 repeated earthquakes near the South Sandwich Islands (1991-2023) and global nuclear tests, highlighting subtle differences in seismic wave travel times indicating the core’s rotational changes.
More than a decade ago, the rotation of Earth’s inner core began to slow, affecting the duration of our days by fractions of a second.
Researchers at the University of Southern California (USC) developed visualizations of the inner core’s movement using seismic data from numerous earthquakes and nuclear explosions, both of which cause vibrations across the planet. The position and mobility of the inner core can be estimated by analyzing the speed and interaction of seismic waves inside the Earth’s layers.
According to a USC statement, the study reveals that since roughly 2010, the Earth’s inner core has been slowing down, or retracing, in comparison to earlier decades; it is also traveling slower than the Earth’s surface.
“The inner core had slowed down for the first time in many decades,” said John Vidale, co-author of the study and a USC Earth Sciences professor, in a statement. “Other scientists have recently argued for similar and different models, but our latest study provides the most convincing resolution.”
The Earth’s inner core is a hot, compact, and solid ball consisting of iron and nickel that sits 3,200 miles (5,150 kilometers) beneath our feet. It is encircled by a liquid iron-nickel outer core and enclosed in a solid rocky mantle. According to the current study, the slowing of the inner core is caused by convection inside the liquid iron outer core, which supports the Earth’s magnetic field, as well as the pull of gravitational forces in the mantle above it.
To reach their results, the researchers reviewed seismic data acquired from 121 repeated earthquakes that occurred around the South Sandwich Islands in the South Atlantic between 1991 and 2023, as well as data from various nuclear tests conducted worldwide.
Repeating earthquakes should give identical seismograms since they occur in the same area. That is why comparing seismic data from various times in time can show changes under the Earth’s surface. Subtle differences in the time it took seismic waves to travel through the Earth at various points in its history indicated the inner core’s slowing. While this alteration may affect the duration of a day by fractions of a second, the researchers believe it will be insignificant.
Their findings were published in the journal Nature.
