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:

Limits on differential rotation of the inner core from an analysis of the Earth's free oscillations

Nature volume 402, pages 66–69 (1999)Cite this article

Abstract

Differential rotation of the Earth's inner core has been inferred by several seismic ‘body-wave’ studies1,2,3,4,5,6 which indicate that the inner core is rotating at a rate between 0.2° and 3° per year faster than the Earth's crust and mantle. The wide range in inferred rotation rate is thought to be caused by the sensitivity of body-wave studies to local complexities in inner-core structure3,7. Free-oscillation ‘splitting functions’, on the other hand, are insensitive to local structure and therefore have the potential to estimate differential rotation more accurately. A previous free-oscillation study8, however, was equivocal in its conclusions because of the relatively poor quality and coverage of the long-period digital data available 20 years ago. Here we use a method for analysing free oscillations9 which is insensitive to earthquake source, location and mechanism to constrain this differential rotation. We find that inner-core differential rotation is essentially zero over the past 20 years (to within ±0.2° per year), implying that the inner core is probably gravitationally locked to the Earth's mantle10.

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: Splitting functions for the two modes 10S2 and 13S2.
Figure 2: Splitting functions for mode 13S2.
Figure 3: Time-dependent inner-core rotation angles.
Figure 4: Inner-core rotation rates obtained for nine core-sensitive modes.

Similar content being viewed by others

References

  1. Song,X. & Richards,P. G. Seismological evidence for differential rotation of the Earth's inner core. Nature 382, 221–224 (1996).

    Article  ADS  CAS  Google Scholar 

  2. Su,W., Dziewonski,A. M. & Jeanloz, R. Planet within a planet: rotation of the inner core of the Earth. 274, 1883–1887 (1996).

  3. Creager,K. C. Inner core rotation rate from small-scale heterogeneity and time-varying travel times. Science 278, 1248– 1288 (1997).

    Article  Google Scholar 

  4. Souriau,A. Earth's inner core—is the rotation real? Science 281, 55–56 (1998).

    Article  ADS  CAS  Google Scholar 

  5. Souriau,A. New seismological constraints on differential rotation rates of the inner core from Novaya Zemlya events recorded at DRV, Antarctica. Geophys. J. Int. 134, F1–F5 ( 1998).

    Article  Google Scholar 

  6. Souriau,A., Roudil,P. & Moynot,B. Inner core differential rotation: facts and artefacts. Geophys. Res. Lett. 24, 2103– 2106 (1997).

    Article  ADS  Google Scholar 

  7. Creager,K. C. Large-scale variations in inner core anisotropy. J. Geophys. Res. (in the press).

  8. Sharrock,D. S. & Woodhouse,J. H. Investigation of time dependent inner core structure by the analysis of free oscillation spectra. Earth Planets Space 50, 1013–1018 (1998).

    Article  ADS  Google Scholar 

  9. Masters,G., Laske,G. & Gilbert,F. Autoregressive estimation of the splitting matrix of free-oscillation multiplets. J. Geophys. Res. (submitted).

  10. Buffet,B. A. A mechanism for decade fluctuations in the length of day. Geophys. Res. Lett. 23, 3803–3806 (1996).

    Article  ADS  Google Scholar 

  11. Masters,G. & Gilbert,F. Structure of the inner core inferred from observations of its spheroidal shear modes. Geophys. Res. Lett. 8, 569–571 ( 1981).

    Article  ADS  Google Scholar 

  12. Woodhouse,J. H., Giardini,D. & Li, X.-D. Evidence for inner core anisotropy from free oscillations. Geophys. Res. Lett. 13, 1549–1552 (1986).

    Article  ADS  Google Scholar 

  13. Morelli,A., Dziewonski,A. M. & Woodhouse, J. H. Anisotropy of the inner core inferred from PKIKP travel times. Geophys. Res. Lett. 13, 1545–1548 (1986).

    Article  ADS  Google Scholar 

  14. Poupinet,G., Pillet,R. & Souriau,A. Possible heterogeneity of the earth's core deduced from PKIKP travel times. Nature 305, 204– 206 (1983).

    Article  ADS  Google Scholar 

  15. Jeanloz,R. & Wenk, H.-R. Convection and anisotropy of the inner core. Geophys. Res. Lett. 15, 72– 75 (1988).

    Article  ADS  Google Scholar 

  16. Karato,S. Inner core anisotropy due to magnetic field-induced preferred orientation of iron. Science 262, 1708– 1711 (1993).

    Article  ADS  CAS  Google Scholar 

  17. Yoshida,S., Sumita,I. & Kumazagawa, M. Growth model of the inner core coupled with the outer core dynamics and the resulting elastic anisotropy. J. Geophys. Res. 101, 28085–28103 ( 1997).

    Article  ADS  Google Scholar 

  18. 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 

  19. Su, W-J. & Dziewonski,A. M. Inner core anisotropy in three dimensions. J. Geophys. Res. 100, 9831– 9852 (1995).

    Article  ADS  Google Scholar 

  20. Shearer,P. M. & Toy,K. M. PKP(BC) versus PKP (DF) differential travel times and aspherical structure in Earth's inner core. J. Geophys. Res. 96, 2233– 2247 (1991).

    Article  ADS  Google Scholar 

  21. McSweeney,T. J., Creager,K. C. & Merrill, R. T. Depth extent of inner core seismic anisotropy and implications for geomagnetism. Phys. Earth. Planet. Inter. 101, 131–156 (1997).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  23. Woodhouse,J. H. The coupling and attenuation of nearly resonant multiplets in the earth's free oscillation spectrum. Geophys. J. R. Astron. Soc. 61, 261–283 (1980).

    Article  ADS  Google Scholar 

  24. Woodhouse,J. H. & Dahlen,F. A. The effect of a general aspherical perturbation on the free oscillations of the earth. Geophys. J. R. Astron. Soc. 53, 335– 354 (1978).

    Article  ADS  Google Scholar 

  25. Woodhouse,J. H. & Giardini,D. Inversion for the splitting function of isolated low order normal mode multiplets. Eos 66, 300 (1985).

    Google Scholar 

  26. Ritzwoller,M., Masters,G. & Gilbert, F. Observations of anomalous splitting and their interpretation in terms of aspherical structure. J. Geophys. Res. 91, 10203–10228 (1986).

    Article  ADS  Google Scholar 

  27. Giardini,D., Li, X.-D. & Woodhouse,J. H. Splitting functions of long period normal modes of the earth. J. Geophys. Res. 93, 13716–13742 (1988).

    Article  ADS  Google Scholar 

  28. Li, X.-D., Giardini,D. & Woodhouse,J. H. Large-scale three-dimensional even-degree structure of the Earth from splitting of long-period normal modes. J. Geophys. Res. 96, 551–577 ( 1991).

    Article  ADS  Google Scholar 

  29. Masters,G., Johnson,S., Laske,G. & Bolton,H. A shear velocity model of the mantle. Phil. Trans. R. Soc. Lond. A 354 1385–1411 (1996).

    Article  ADS  Google Scholar 

  30. Masters,G., Bolton,H. & Laske,G. Joint seismic tomography for P and S velocities: how pervasive are chemical anomalies in the mantle? Eos 80

Download references

Acknowledgements

The data used in this study were collected at a variety of global seismic networks and obtained from the IRIS-DMC, GEOSCOPE and BFO. This research was supported by the US NSF.

Author information

Authors and Affiliations

  1. Institute of Geophysics and Planetary Physics, University of California San Diego, 9500 Gilman Dr, La Jolla, 92093-0225, California, USA

    Gabi Laske & Guy Masters

Authors
  1. Gabi Laske
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Guy Masters
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Gabi Laske.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Laske, G., Masters, G. Limits on differential rotation of the inner core from an analysis of the Earth's free oscillations. Nature 402, 66–69 (1999). https://doi.org/10.1038/47011

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/47011

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