Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Texturing of the Earth's inner core by Maxwell stresses

Nature volume 413, pages 60–63 (2001)Cite this article

Abstract

Elastic anisotropy in the Earth's inner core has been attributed to a preferred lattice orientation1, which may be acquired during solidification of the inner core2 or developed subsequent to solidification as a result of plastic deformation3,4,5. But solidification texturing alone cannot explain the observed depth dependence of anisotropy6,7,8, and previous suggestions for possible deformation processes have all relied on radial flow, which is inhibited by thermal9 and chemical stratification10. Here we investigate the development of anisotropy as the inner core deforms plastically under the influence of electromagnetic (Maxwell) shear stresses. We estimate the flow caused by a representative magnetic field using polycrystal plasticity simulations for ε-iron, where the imposed deformation is accommodated by basal and prismatic slip11. We find that individual grains in an initially random polycrystal become preferentially oriented with their c axes parallel to the equatorial plane. This pattern is accentuated if deformation is accompanied by recrystallization. Using the single-crystal elastic properties of ε-iron at core pressure and temperature12, we average over the simulated orientation distribution to obtain a pattern of elastic anisotropy which is similar to that observed seismologically13,14.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Schematic illustration of the inner core and the magnetic field B.
Figure 2: Simulated texture development in ε-iron.
Figure 3: Averaged aggregate P-wave velocity for ε-iron polycrystals.

Similar content being viewed by others

References

  1. Song, X. Anisotropy of the Earth's inner core. Rev. Geophys. 35, 297–313 (1997).

    Article  ADS  Google Scholar 

  2. Bergman, M. I. Measurements of elastic anisotropy due to solidification texturing and the implications for the Earth's inner core. Nature 389, 60–63 (1997).

    Article  ADS  CAS  Google Scholar 

  3. Wenk, H.-R., Baumgardner, J. R., Lebenshon, R. A. & Tomé, C. N. A convective model to explain anisotropy of the inner core. J. Geophys. Res. 105, 5663–5677 (2000).

    Article  ADS  Google Scholar 

  4. Yoshida, S., Sumita, I. & Kumazawa, M. Growth model of the inner core coupled with the outer core dynamics and the resulting elastic anisotropy. J. Geophys. Res. 101, 28085–28103 (1996).

    Article  ADS  CAS  Google Scholar 

  5. Karato, S. Seismic anisotropy of the Earth's inner core resulting from flow induced by Maxwell stresses. Nature 402, 871–873 (1999).

    Article  ADS  CAS  Google Scholar 

  6. Song, X. & Helmberger, D. V. Depth dependence of anisotropy in Earth's inner core. J. Geophys. Res. 100, 9805–9816 (1995).

    Article  ADS  Google Scholar 

  7. Creager, K. C. Large-scale variations in inner core anisotropy. J. Geophys. Res. 104, 23127–23139 (1999).

    Article  ADS  Google Scholar 

  8. Garcia, R. & Souriau, A. Inner core anisotropy and heterogeneity level. Geophys. Res. Lett. 27, 3121–3124 (2000).

    Article  ADS  Google Scholar 

  9. Yukutake, T. Implausibility of thermal convection in the Earth's solid inner core. Phys. Earth Planet. Inter. 101, 1–13 (1998).

    Article  ADS  Google Scholar 

  10. Stacey, F. D. Theory of thermal and elastic properties of the lower mantle and core. Phys. Earth Planet. Inter. 89, 219–245 (1995).

    Article  ADS  Google Scholar 

  11. Wenk, H.-R., Matthies, S., Hemley, R. J., Mao, H.-K. & Shu, J. The plastic deformation of iron at pressures of the Earth's inner core. Nature 405, 1044–1046 (2000).

    Article  ADS  CAS  PubMed Central  Google Scholar 

  12. Steinle-Neumann, G., Stixrude, L., Cohen, R. E. & Gülseren, O. Elasticity of iron at the temperature of the Earth's inner core. Nature 413, 57–60 (2001).

    Article  ADS  CAS  Google Scholar 

  13. Creager, K. C. Anisotropy of the inner core from differential travel times of the phases PKP and PKIKP. Nature 356, 309–314 (1992).

    Article  ADS  Google Scholar 

  14. Tromp, J. Support for anisotropy of the Earth's inner core from free oscillations. Nature 366, 678–681 (1993).

    Article  ADS  Google Scholar 

  15. Yoo, C. S., Akella, J., Campbell, A. J. & Mao, H.-K. Phase diagram of iron by in situ x-ray diffraction: Implications for Earth's core. Science 270, 1473–1475 (1995).

    Article  ADS  CAS  Google Scholar 

  16. Stixrude, L. & Cohen, R. E. High-pressure elasticity of iron and anisotropy of Earth's inner core. Science 267, 1972–1975 (1995).

    Article  ADS  CAS  Google Scholar 

  17. Mao, H. K. et al. Elasticity and rheology of iron above 220 GPa and the nature of the Earth's inner core. Nature 396, 741–743 (1998).

    Article  ADS  CAS  Google Scholar 

  18. Glatzmaier, G. A. & Roberts, P. H. Rotation and magnetism of Earth's inner core. Science 274, 1887–1891 (1996).

    Article  ADS  CAS  PubMed Central  Google Scholar 

  19. Buffett, B. A. & Bloxham, J. Deformation of Earth's inner core by electromagnetic forces. Geophys. Res. Lett. 27, 4001–4004 (2000).

    Article  ADS  Google Scholar 

  20. Buffett, B. A. Geodynamic estimates of the viscosity of the Earth's inner core. Nature 388, 571–573 (1997).

    Article  ADS  CAS  Google Scholar 

  21. Molinari, A., Canova, G. R. & Ahzi, S. A self-consistent approach of the large deformation polycrystal viscoplasticity. Acta Metall. 35, 2983–2994 (1987).

    Article  CAS  Google Scholar 

  22. Lebensohn, R. A., Wenk, H.-R. & Tomé, C. N. Modelling deformation and recrystallization textures in calcite. Acta Mater. 46, 2683–2693 (1998).

    Article  CAS  Google Scholar 

  23. Wenk, H.-R. & Tomé, C. N. Modeling dynamic recrystallization of olivine deformed in simple shear. J. Geophys. Res. 104, 25513–25527 (1999).

    Article  ADS  CAS  Google Scholar 

  24. Wenk, H.-R., Matthies, S., Donovan, J. & Chateigner, D. BEARTEX, a Windows-based program system for quantitative texture analysis. J. Appl.Crystallogr. 31, 262–269 (1998).

    Article  CAS  Google Scholar 

  25. Tanaka, S. & Hamaguchi, H. Degree one heterogeneity and hemispherical variation of anisotropy in the inner core from PKP(BC) - PKP(DF) times. J. Geophys. Res. 102, 2925–2938 (1997).

    Article  ADS  Google Scholar 

  26. Vidale, J. S. & Earle, P. S. Fine-scale heterogeneity in the Earth's inner core. Nature 404, 273–275 (2000).

    Article  ADS  CAS  PubMed Central  Google Scholar 

  27. Singh, S. C., Taylor, M. A. J. & Montagner, J. P. On the presence of liquid in Earth's inner core. Science 287, 2471–2474 (2000).

    Article  ADS  CAS  PubMed Central  Google Scholar 

Download references

Acknowledgements

We thank G. Steinle-Neumann for sending us a preprint of his work. B.A.B. was supported by NSERC, and H.R.W. acknowledges support from IGPP-LANL and NSF.

Author information

Authors and Affiliations

  1. Department of Earth & Ocean Sciences, University of British Columbia, Vancouver, V6T 1Z4, Canada

    B. A. Buffett

  2. Department of Earth & Planetary Science, University of California, Berkeley, 94720, California, USA

    H.-R. Wenk

Authors
  1. B. A. Buffett
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. H.-R. Wenk
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to B. A. Buffett.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Buffett, B., Wenk, HR. Texturing of the Earth's inner core by Maxwell stresses. Nature 413, 60–63 (2001). https://doi.org/10.1038/35092543

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/35092543

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing