Close observations have shown that the Earth’s inner core (IC) moves and changes over the decades. The pattern, speed and driving force of the transition, on the other hand, are still being discussed.
Previously accepted models suggested that The inner core of the earth rotates consistently faster than the surface of the planet. A new study contradicts the previously accepted models and provides evidence that the earth’s inner core oscillates.
By analyzing seismic data, researchers from University of Southern California have shown that the inner core changed direction during the six years from 1969 to 74. They also proposed a new model for the movement of the inner core, which explains the variation in the length of the day, which has been shown to oscillate persistently over the past several decades.
The first study, published in 1996, suggested that the Earth’s inner core rotates about 1 degree per year faster than the rest of the world, a phenomenon known as superrotation. The new findings confirmed that the inner core is super-rotating at a slower rate.
John Vidale, co-author of the study and Dean’s Professor of Earth Sciences at USC Dornsife College of Letters, Arts and Sciences said, “From our findings we can see the earth’s surface changes compared to its inner core, as people have been claiming for 20 years. However, our latest observations show that the inner core rotated slightly more slowly from 1969 to 71 and then moved in the other direction from 1971 to 74. We also note that the length of the day grew and shrank as predicted. “
“The coincidence of these two observations makes oscillation the probable interpretation.”
After analyzing data from the Large Aperture Seismic Array, a US Air Force facility in Montana, the researchers found that the inner core rotated more slowly than previously predicted, about 0.1 degrees per year. The analyzed waves generated from Soviet underground nuclear bomb tests from 1971 to 74 in Arctic archipelago Novaya Zemlya using a new beamforming technology developed by Vidale.
Vidale said, “This latest study marked the first time the well-known six-year oscillation was indicated by direct seismological observation.”
“The idea that the inner core oscillates was a model out there, but society has been divided on whether it was profitable. We went into this and expected the same direction of rotation and speed in the previous pair of atomic tests, but instead we saw the opposite. We were quite surprised that it went the other way. “
Wei Wang, Department of Earth Sciences, University of Southern California, said: “Using seismological data from nuclear tests in previous studies, they have been able to determine the exact location and time of the very simple seismic event. But the Montana Large Aperture Seismic Array closed in 1978, and the era of the U.S. underground nuclear test is over; therefore we must rely on comparatively imprecise earthquake dataeven with the latest advances in instrumentation. “
The study supports speculation that the inner core oscillates based on variations in the length of the day – plus or minus 0.2 seconds over six years – and geomagnetic fields, both of which match the theory in both amplitude and phase.
Vidale sa, “The findings provide a compelling theory for many questions posed by the research community.”
“The inner core is not fixed – it moves under our feet, and it seems to go back and forth a couple of kilometers every six years. One of the questions we tried to answer is, does the inner core move gradually, or is it mostly locked? compared to everything else in the long run? We try to understand how the inner core is shaped and moves over time – this is an important step in better understanding this process. “
- Wei Wang and John E. Vidale. Seismological observation of the earth’s oscillating inner core. DOI: 10.1126 / sciadv.abm9916
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