The center of the Earth has slowed down its rotation: what will happen on its surface?

“When I first saw the seismograms that indicated this change, I was taken aback”, recognizes John Vidale. This professor of earth sciences at the Dornsife College of Letters, Arts and Sciences at the University of Southern California has combed through seismic records over the past thirty years. Its objective was to put an end to a debate within the scientific community: does the heart of the Earth rotate more or less quickly than the planet?

To answer this question, he teamed up with Wei Wang of the Chinese Academy of Sciences. In a study, published in Nature, they detail their working method for studying an inaccessible thing. Unlike many scientific topics, the center of the Earth is almost 5,000 km below our feet. No one has ever really observed it.

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A study based on seismic activity records from the Sandwich Islands

However, the two researchers used a specific technique to define the rotation speed of the heart of our planet, indicates Phys.org. They were interested in repeated earthquakes. These events occur in the same place and generate identical seismograms. It is by identifying these repetitions that the movement of the Earth’s inner core can be recreated.

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John Vidale and Wei Wang focused on seismic activity in the South Sandwich Islands in the southern Atlantic Ocean. They are located more than 2,400 km east of the tip of South America.

Their study is based on seismic records of earthquakes recorded between 1991 and 2023. Over this period, 121 repeated earthquakes were identified.

“When we found two dozen additional observations reporting the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades. Other scientists have recently argued for similar and different models, but our latest study provides the most convincing solution”assures John Vidale.

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An extension of the Earth’s rotation of the order of a thousandth of a second

The center of the Earth takes the form of a sphere of solid iron and nickel. While all around, the outer core is composed of the same elements but liquid. For the professor at the University of Southern California, this slowdown would be due to the mixing of the outer core which surrounds it and which generates the Earth’s magnetic field, but also by the gravitational forces exerted by the density of the rocky mantle of the planet.

With decreased rotation, the center of the Earth influences the overall rotation of the Earth. Thus, a slower inner core implies that the planet rotates less quickly. A detail likely to extend the duration of a day. “It’s very difficult to notice, it’s on the order of a thousandth of a second”reassures John Vidale.

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But what now interests the two scientists are the exact reasons for the movement of the center of the Earth. They therefore wish to map this trajectory in an even finer manner. “The inner core dance could be even livelier than we know so far”concludes John Vidale.