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Seismic waves help researchers analyze the interior of the Earth. A new study now shows what is happening to the Earth’s inner core.
Los Angeles – The Earth’s inner core is slowing down in relation to the Earth’s surface, and has been doing so since 2010. This is the result of a study carried out by a research team from the University of Southern California (USC). It is important to know that the Earth consists of different layers: The Earth’s inner core consists of solid iron and nickel and is about the size of the moon. It is surrounded by the Earth’s outer core, which consists of a liquid nickel-iron melt.
Because the Earth’s inner core only begins at a depth of more than 5,000 kilometers, it is not possible for researchers to study it directly. Therefore, indirect methods are used, usually seismic waves from earthquakes are examined to find out more about the interior of the Earth. In the case of the current study, the research team led by John Vidale (USC) used, among other things, recurring earthquakes to carry out their analyses. The work was in the journal Nature published.
The Earth’s core can only be examined by seismic waves
The team analyzed 121 repeating earthquakes recorded in the South Sandwich Islands between 1991 and 2023. The study also included data from Soviet nuclear tests from 1971 to 1974, as well as repeated French and American nuclear tests.
The result of the research surprised even the team: Since about 2010, the inner core of the Earth has been slowing down compared to the Earth’s surface. “When I saw the seismograms that indicated this change, I was amazed,” Vidale recalls in a Message from his university“But when we found two dozen more observations showing the same pattern, the conclusion was inescapable. The inner core has slowed down for the first time in many decades.”
The Earth’s inner core apparently oscillates and changes its direction of movement
After decades of studying the Earth’s interior, researchers assume that the Earth’s inner core oscillates – sometimes it rotates in one direction, then the other. Just last year, a study was published that assumed that the movement of the Earth’s inner core relative to the Earth’s surface had stopped completely.
According to Vidale, the slowing down of the Earth’s inner core is influenced by, among other things, the movement of the outer core made of liquid iron. The dense regions of the Earth’s overlying rocky mantle also play a role, according to the researcher. It is still unclear what effect the slower movement of the Earth’s inner core has on the planet’s surface. However, the USC researcher can imagine that the slowing down of the core can shorten the length of a day by fractions of a second. “It’s very difficult to notice, on the order of a thousandth of a second, almost lost in the noise of the churning oceans and atmosphere,” says Vidale.
In the future, the research team would like to analyze the movement of the Earth’s inner core in more detail and find out why it changes. “The dance of the inner core could be even more lively than we currently know,” explains Vidale. (tab)