The Earth moves far under our feet: A new study shows that the inner core oscillates

[Jim__]

From phys.org

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 consistently rotates at a faster rate than the planet’s surface. Credit: Edward Sotelo/USC
_________________________________________________________________________________________________

Their study, published today in Science Advances, shows that the inner core changed direction in the six-year period from 1969–74, according to the analysis of seismic data. The scientists say their model of inner core movement also explains the variation in the length of day, which has been shown to oscillate persistently for the past several decades.

"From our findings, we can see the Earth's surface shifts compared to its inner core, as people have asserted for 20 years," said John E. Vidale, co-author of the study and Dean's Professor of Earth Sciences at USC Dornsife College of Letters, Arts and Sciences. "However, our latest observations show that the inner core spun slightly slower from 1969–71 and then moved the other direction from 1971–74. We also note that the length of day grew and shrank as would be predicted.

"The coincidence of those two observations makes oscillation the likely interpretation."

...

Our understanding of the inner core has expanded dramatically in the past 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's also impossible to observe directly, meaning researchers struggle through indirect measurements to explain the pattern, speed and cause of the movement and changes.

more ...