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Seismology

Inner core takes another turn

Nature volume 405, pages 411–412 (2000)Cite this article

Biologists have developed amazing tools to image blood flow in the human body. Is it possible to map motions in the deepest parts of the Earth using similar techniques? This is more or less what Vidale et al.1 (page 445 of this issue) have done. By measuring minute changes in seismic waves that are back-scattered by small heterogeneities in the inner core, the authors find that it rotates some 0.15° per year faster than the mantle. This is the latest, and most refined, estimate of relative core rotation.

The inner core is a ball of solid iron, 1,200 km in radius, at the centre of the Earth. It is surrounded by the outer core, an ocean of liquid iron 2,300 km thick. Convective motions in this electrically conducting ocean produce Earth's magnetic field through the so-called dynamo mechanism. Large-scale eddies at the surface of the outer core have been identified from the analysis of the slow drift of patches of magnetic field, with typical flow velocities of the order of 0.1° per year. These motions could be the surface expression of cylindrical structures extending across the bulk of the outer core because, in a rapidly rotating system, structures tend to be aligned with the axis of rotation.

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Figure 1: Three ways of detecting differential rotation of the inner core (yellow) with respect to the mantle (brown).

References

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  1. Observatoire des Sciences de l'Univers de Grenoble, CNRS, Université Joseph Fourier, BP 53, Grenoble, 38041, France

    Henri-Claude Nataf

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  1. Henri-Claude Nataf
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Correspondence to Henri-Claude Nataf.

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Nataf, HC. Inner core takes another turn. Nature 405, 411–412 (2000). https://doi.org/10.1038/35013184

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