USC researchers identified a six-year cycle of super and sub-rotation in the Earth’s inner core, contradicting previously accepted models that suggested it was constantly spinning at a faster rate than the planet’s surface. Credit: Edward Sotelo / USC
USC scientists have found evidence that the Earth’s inner core oscillates, contradicting previously accepted models that suggest it is constantly rotating at a faster rate than the planet’s surface.
His study, published today in Advances in Science, shows that the inner core changed direction during the six-year period from 1969 to 1974, according to seismic data analysis. Scientists say its pattern of movement of the inner core also explains the variation in the length of the day, which has been shown to fluctuate persistently over the past few decades.
“From our findings, we can see the displacements of the Earth’s surface compared to its inner core, as people have been saying for 20 years,” said John E. Vidale, co-author of the study and professor. from the Dean of Earth Sciences at USC Dornsife College of Arts, Arts and Sciences. “However, our latest observations show that the inner core rotated slightly slower between 1969 and 1971 and then moved in the other direction between 1971 and 1974. We also observe that the length of the day grew and grew. reduce as might be predicted.
“The coincidence of these two observations makes the oscillation the probable interpretation.”
Atomic test analysis determines the speed and direction of rotation
Our understanding of the inner core has expanded dramatically over the last 30 years. The inner core, a hot, dense ball of solid iron the size of Pluto, has been shown to move and / or change over decades. It is also impossible to observe directly, that is, researchers struggle through indirect measures to explain the pattern, speed, and cause of movement and change.
Research 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, about 1 degree per year. Vidale’s later findings reinforced the idea that the inner core rotates super, albeit at a slower pace.
Using data from Large Aperture Seismic Array (LASA), a U.S. Air Force facility in Montana, researcher Wei Wang and Vidale found that the inner core rotated more slowly than previously anticipated, approximately 0.1 degrees per year. The study analyzed the waves generated by Soviet underground nuclear bomb tests between 1971 and 1974 in the Arctic archipelago Novaia Zemlya using a new beam-forming technique developed by Vidale.
The new findings emerged when Wang and Vidale applied the same methodology to a couple of previous atomic tests under Amchitka Island at the tip of the Alaska Archipelago: Milrow in 1969 and Cannikin in 1971. Measuring Compression Waves derived from nuclear explosions, they discovered. the inner core had reversed direction, subtracting at least a tenth of a degree per year.
This last study was the first time that the well-known six-year oscillation had been indicated by direct seismological observation.
“The idea that the inner core oscillates was a model that existed, but the community has been divided on whether it was viable,” Vidale says. “We went into this hoping to see the same direction and speed of rotation in the previous pair of atomic tests, but instead we saw the opposite. We were quite surprised to find that it was moving in the other direction.”
Future research to delve into why the inner core was formed
Vidale and Wang noted that future research would depend on finding sufficiently accurate observations to compare them with these results. By using seismological data from atomic tests in previous studies, they have been able to identify the exact location and time of the very simple seismic event, Wang says. However, Montana LASA closed in 1978 and the era of U.S. underground atomic testing is over, meaning researchers should rely on comparatively inaccurate earthquake data, even with recent advances in instrumentation. .
The study supports the speculation that the inner core oscillates depending on variations in the length of the day (about 0.2 seconds over six years) and geomagnetic fields, both agree with the theory both in amplitude as in phase. Vidale says the findings provide a compelling theory for many of the questions raised by the research community.
“The inner core isn’t fixed, it moves under our feet and it seems to go back and forth a couple of miles every six years,” Vidale said. “One of the questions we’ve tried to answer is whether the inner core is moving progressively or is mostly blocked compared to everything else in the long run? We’re trying to understand how the inner core was formed and how it moves over time. It’s an important step in understanding this process. ”
Earth’s inner core: a mixture of solid Fe and light, liquid-like elements More information: Wei Wang et al, Seismological observation of the Earth’s oscillating inner core, Advances in Science (2022). DOI: 10.1126 / sciadv.abm9916. www.science.org/doi/10.1126/sciadv.abm9916 Provided by the University of Southern California
Citation: The Earth moves far below our feet: a new study shows that the inner core oscillates (2022, June 10) recovered on June 10, 2022
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