Forces deep underground seem to be deforming Earth's inner core

Earth’s solid inner core appears to have changed shape in the past 20 years or so, according to seismic wave measurements – but the behaviour of these waves could also be explained by other shifts at the centre of the planet.

Since the 1990s, models and seismic measurements have indicated that Earth’s iron-nickel inner core moves at its own pace. Over decades, the rotation of the inner core speeds up and slows down relative to the rest of the planet, affecting things such as the length of a day.

Those changes in rotation are mainly due to magnetic forces generated by convection in Earth’s liquid outer core, says John Vidale at the University of Southern California. “That flow is continually torquing the inner core.”

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