Scientists identify a six-year cycle of hyper- and sub-rotation that affected the length of a day based on their analysis of seismic data. The structure of the Earth is divided into layers, with the inner core in the center followed by the outer core, the lower mantle, the upper mantle, the crust and the atmosphere. The inner core is the hottest part of the planet at about 10,000 ° F (5400 ° C), which is similar to the temperature of the sun’s surface! It is believed to consist mainly of iron-nickel alloy, the inner core is mainly a solid sphere with a radius of about 760 miles (1,220 km). It spins a little faster than the planet, which is called super-rotation. Scientists at the University of Southern California (USC) have found evidence that the Earth’s inner core is oscillating, in contrast to previously accepted models that have suggested that it rotates steadily at a faster rate than the planet’s surface. Their study, published today (June 10, 2022) in the journal Science Advances, shows that the inner core changed direction in the six years 1969-74, according to seismic data analysis. Scientists say their model for moving the inner core also explains the fluctuation during a day, which has been shown to fluctuate steadily in recent decades. “From our findings, we can see the displacements of the Earth’s surface relative to its inner core, as people have been claiming for 20 years,” said John E. Vidale, co-author of the study and Professor of Science. Land at USC Dornsife College of Letters, Arts and Sciences. “However, our latest observations show that the inner core rotated slightly more slowly from 1969-71 and then moved in the other direction from 1971-74. We also note that the duration of one day increased and decreased as expected. “The coincidence of these two observations makes oscillation the possible interpretation.” USC researchers have identified a six-year cycle of hyper- and sub-rotation in the Earth’s inner core, in contrast to previously accepted models that suggested it is constantly rotating at a faster rate than the planet’s surface. Credit: Edward Sotelo / USC
Individual test analysis accurately detects rhythm and direction of rotation
Our understanding of the inner core has expanded dramatically over the last 30 years. The inner core – a hot, dense sphere the size of Pluto – has been shown to move and / or change over the decades. It is also impossible to observe directly, which means that researchers struggle through indirect measurements to explain the pattern, speed and cause of movement and change. A study published in 1996 was the first to suggest that the inner core rotates faster than the rest of the planet – also known as super-rotation – by about 1 degree per year. Subsequent findings by Vidale reinforced the idea that the inner core was super-rotating, albeit at a slower rate. The layers and structure of the earth. Using data from the Large Aperture Seismic Array (LASA), a U.S. Air Force facility in Montana, researchers Wei Wang and Vidale found that the inner core rotates more slowly than expected, about 0.1 degrees per year. The study analyzed waves generated by Soviet underground nuclear bomb tests from 1971-74 in the Arctic archipelago of Novaya Zemlya using a new beam-forming technique developed by Vidale. The new findings came as Wang and Vidale applied the same methodology to a pair of previous atomic tests under the island of Amchitka at the top of the Alaskan archipelago – Milrow in 1969 and Cannikin in 1971. Measuring compressive waves from nuclear emissions. , they discovered the inner core was reversed, subtracting at least a tenth of a degree a year. This latest study marked the first time that known six-year oscillations had been indicated by direct seismic observation. “The idea that the inner core oscillates was a model that was out there, but the community is divided over whether it was viable,” says Vidale. “We did this expecting to see the same direction and pace of rotation in the previous pair of individual tests, but instead we saw the opposite. “We were surprised to find that it was moving in the other direction.”
Future research to explore more deeply why the inner core was formed
Vidale and Wang both noted that future research would depend on finding sufficiently accurate observations to compare these results. Using seismic data from atomic tests in previous studies, they were able to pinpoint the exact location and time of the very simple seismic event, Wang said. However, the Montana LASA closed in 1978 and the era of US underground atomic tests is over, which means that researchers will have to rely on relatively inaccurate earthquake data, even with recent instrumental developments. The study supports the assumption that the inner core oscillates based on fluctuations in day length – plus or minus 0.2 seconds in six years – and geomagnetic fields, which fit the theory in both amplitude and phase. Vidale says the findings provide a compelling theory for the many questions posed by the research community. “The inner core is not stable – it moves under our feet and seems to go a few miles every six years,” Vidale said. “One of the questions we tried to answer is, is the inner core moving progressively or is it mostly locked compared to anything else in the long run? “We are trying to understand how the inner core was formed and how it moves over time – this is an important step in better understanding this process.” Reference: “Seismological observation of the oscillating inner core of the Earth” by Wei Wang and John E. Vidale, June 10, 2022, Science Advances.DOI: 10.1126 / sciadv.abm9916
