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Fine-scale heterogeneity in the Earth's inner core

Nature volume 404, pages 273–275 (2000)Cite this article

Abstract

The seismological properties of the Earth's inner core have become of particular interest as we understand more about its composition and thermal state1,2. Observations of anisotropy and velocity heterogeneity in the inner core are beginning to reveal how it has grown and whether it convects3,4. The attenuation of seismic waves in the inner core is strong, and studies of seismic body waves5,6 have found that this high attenuation is consistent with either scattering or intrinsic attenuation5. The outermost portion of the inner core has been inferred to possess layering and to be less anisotropic than at greater depths7,8,9,10. Here we present observations of seismic waves scattered in the inner core which follow the expected arrival time of the body-wave reflection from the inner-core boundary. The amplitude of these scattered waves can be explained by stiffness variations of 1.2% with a scale length of 2 kilometres across the outermost 300 km of the inner core. These variations might be caused by variations in composition, by pods of partial melt in a mostly solid matrix or by variations in the orientation or strength of seismic anisotropy.

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Figure 1: Average seismic-wave amplitude arriving between 970 and 1,280 s after all events.
Figure 2: Location map of explosions, earthquakes, LASA, and midpoints of ray-paths.
Figure 3: Comparison of ICS with PcP for the 27 September 1971 and 29 August 1974 nuclear tests.
Figure 4: Stacks of inner-core scattering and noise amplitude.

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Acknowledgements

We thank the Albuquerque Seismological Laboratory and specifically R. Woodward and H. Bolton for access to LASA data; we also thank P. Shearer, F. Xu, S. Persh and J. Green for comments on the manuscript. L. Knopoff generalized the formula for scattering to non-Poisson solids.

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Authors and Affiliations

  1. Earth and Space Science Department,

    John E. Vidale & Paul S. Earle

  2. Institute of Geophysics and Planetary Physics, University of California at Los Angeles, Los Angeles, 90095-1567, California, USA

    John E. Vidale

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  1. John E. Vidale
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  2. Paul S. Earle
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Correspondence to John E. Vidale.

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Vidale, J., Earle, P. Fine-scale heterogeneity in the Earth's inner core. Nature 404, 273–275 (2000). https://doi.org/10.1038/35005059

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