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:

Evidence for partial melt at the core–mantle boundary north of Tonga from the strong scattering of seismic waves

Nature volume 391, pages 682–685 (1998)Cite this article

Abstract

Scattered waves that precede the seismic phase PKP (which traverses the Earth's core) have been used to identify and locate small-scale heterogeneity in the Earth's mantle1,2,3,4,5,6. A recent study has demonstrated that the global data set of these precursors is consistent with weak heterogeneity (about 1 per cent r.m.s. velocity variation) distributed throughout the mantle7. Here we show, however, that anomalously large PKP precursors from earthquakes in northern Tonga require much stronger heterogeneity (10–15 per cent r.m.s. velocity variation) in a layer about 60 km thick near the core–mantle boundary below Tonga. This region of the core–mantle boundary is also marked by low shear-wave velocities in the lower mantle8 and is near an area of very low compressional-wave velocity in the lowermost tens of kilometres of the mantle9, which has been interpreted as evidence for the presence of partial melt10. The strength of thescattering that we observe provides strong support for the presence of partial melt in this area, and also suggests that vigorous small-scale convection is taking place at the core–mantle boundary.

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: Ray-paths and travel times of PKP phases.
Figure 2: Map of anomalous region of the CMB and the 22 earthquakes used in this study.
Figure 3: PKP precursor observations.
Figure 4: Data and synthetic curves.

Similar content being viewed by others

References

  1. Haddon, R. A. W. Corrugations on the CMB or transition layers between inner and outer cores? Eos 53, 600 (1972).

    Google Scholar 

  2. Cleary, J. R. & Haddon, R. A. W. Seismic wave scattering near the core-mantle boundary: a new interpretation of precursors to PKP. Nature 240, 549–551 (1972).

    Article  ADS  Google Scholar 

  3. Doornbos, D. J. & Husebye, E. S. Array analysis of PKP phases and their precursors. Phys. Earth Planet. Inter. 5, 387–399 (1972).

    Article  ADS  Google Scholar 

  4. Haddon, R. A. & Cleary, R. J. Evidence for scattering of seismic PKP waves near the core-mantle boundary. Phys. Earth Planet. Inter. 8, 211–234 (1974).

    Article  ADS  Google Scholar 

  5. King, D. W., Haddon, R. A. W. & Cleary, J. R. Array analysis of precursors to PKIKP in the distance range 129° to 142°. Geophys. J. R. Astron. Soc. 37, 157–173 (1974).

    Article  ADS  Google Scholar 

  6. Husebye, E. S., King, D. W. & Haddon, R. A. W. Precursors to PKIKP and seismic wave scattering near core-mantle boundary. J. Geophys. Res. 81, 1870–1882 (1976).

    Article  ADS  Google Scholar 

  7. Hedlin, M. A. H., Shearer, P. M. & Earle, P. S. Seismic evidence for small-scale heterogeneity throughout the Earth's mantle. Nature 387, 145–150 (1997).

    Article  ADS  CAS  Google Scholar 

  8. Su, W. J., Woodward, R. L. & Dziewonski, A. M. Degree-12 model of shear velocity heterogeneity in the mantle. J. Geophys. Res. 99, 6945–6980 (1994).

    Article  ADS  Google Scholar 

  9. Garnero, E. J. & Helmberger, D. V. Seismic detection of a thin laterally varying boundary layer at the base of the mantle beneath the central-Pacific. Geophys. Res. Lett. 23, 977–980 (1996).

    Article  ADS  Google Scholar 

  10. Williams, Q. & Garnero, E. J. Seismic evidence for partial melt at the base of the Earth's mantle. Science 273, 1528–1530 (1996).

    Article  ADS  CAS  Google Scholar 

  11. Jeanloz, R. & Richter, F. M. Convection, composition, and the thermal state of the lower mantle. J.Geophys. Res. 84, 5497–5504 (1979).

    Article  ADS  Google Scholar 

  12. Manga, M. & Jeanloz, R. Implications of metal-bearing chemical boundary layer in D″ for mantle dynamics. Geophys. Res. Lett. 23, 3091–3094 (1996).

    Article  ADS  CAS  Google Scholar 

  13. Lay, T. Structure of the core-mantle transition zone; a chemical and thermal boundary layer. Eos 70, 49–49 (1989).

    Article  ADS  Google Scholar 

  14. Loper, D. E. & Lay, T. The core-mantle boundary region. J. Geophys. Res. 100, 6397–6421 (1995).

    Article  ADS  Google Scholar 

  15. Mori, J. & Helmberger, D. V. Localized boundary layer below the mid-Pacific velocity anomaly identified from a PcP precursor. J. Geophys. Res. 100, 20359–20365 (1995).

    Article  ADS  Google Scholar 

  16. Bataille, K. & Flatté, S. M. Inhomogeneities near the core-mantle boundary inferred from short-period scattered PKP waves recorded at the global digital seismograph network. J. Geophys. Res. 93, 15057–15064 (1988).

    Article  ADS  Google Scholar 

  17. Vidale, J. E. & Houston, H. The depth dependence of earthquake duration and implications for rupture mechanisms. Nature 365, 45–47 (1993).

    Article  ADS  Google Scholar 

  18. Doornbos, D. J. & Vlaar, N. J. Regions of seismic wave scattering in the Earth's mantle and precursors to PKP. Nature 243, 58–61 (1973).

    ADS  Google Scholar 

  19. Chernov, L. A. Wave Propagation in a Random Medium(trans. Silverman, R. A.) (McGraw-Hill, New York, (1960)).

    Book  Google Scholar 

  20. Grand, S. P. Mantle shear structure beneath the Americas and surrounding oceans. J. Geophys. Res. 99, 11591–11622 (1994).

    Article  ADS  Google Scholar 

  21. van der Hilst, R., Widiyantoro, S. & Engdahl, E. R. Evidence for deep mantle circulation from global tomography. Nature 386, 578–584 (1997).

    Article  ADS  CAS  Google Scholar 

  22. Zerr, A., Serghiou, G. & Boehler, R. Melting of CaSiO2perovskite to 430 kbar and first in situ measurements of lower mantle eutectic temperatures. Geophys. Res. Lett. 24, 909–912 (1997).

    Article  ADS  CAS  Google Scholar 

  23. Vidale, J. E. & Benz, H. M. Asharp and flat section of the core-mantle boundary. Nature 359, 627–629 (1992).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

We thank H.-C. Nataf for a review; Q. Williams, S. Grand, E. Garnero, P. Shearer and D. Helmberger for discussions; J. Fyen and J. Torstveit for supplying the NORSAR data; and J. Ritsema for evaluating the PKP precursors from Tanzanian stations. This work was supported by the US NSF.

Author information

Authors and Affiliations

  1. Department of Earth and Space Sciences, University of California, Los Angeles, Los Angeles, 90095-1567, California, USA

    John E. Vidale

  2. Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, University of California, San Diego, La Jolla, 92093-0225, California, USA

    Michael A. H. Hedlin

Authors
  1. John E. Vidale
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Michael A. H. Hedlin
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to John E. Vidale.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Vidale, J., Hedlin, M. Evidence for partial melt at the core–mantle boundary north of Tonga from the strong scattering of seismic waves. Nature 391, 682–685 (1998). https://doi.org/10.1038/35601

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/35601

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