Skip to main content
Earth, Planets and Space
Download PDF
  • Letter
  • Published:

Existence of finite rigidity layer at the base of the Earth’s liquid outer core inferred from anomalous splitting of normal modes

Earth, Planets and Space volume 54, pages 167–171 (2002)Cite this article

Abstract

We calculate normal modes for the Earth model, which has a slight rigidity layer at the base of the liquid outer core. We show that such a layer with thickness about 40 km and the shear wave velocity of 0.017 km/sec can produce a normal mode, which has a close eigenfrequency to that of liquid core model, without affecting fundamental modes and most of the higher modes. Our results indicate that the thin finite rigidity layer at the base of the outer core might explain the anomalous splitting of the Earth’s normal modes, which has not been fully explained by the anisotropy in the inner core.

References

  • Buland, R., Variational Methods, in Seismological Algorithms: Computational Methods and Computer Programs, edited by D. J. Doornbos, pp. 371–400, Academic Press, New York, 1988.

    Google Scholar 

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

    Article  Google Scholar 

  • Dahlen, F. A. and J. Tromp, Theoretical Global Seismology, 619–624, Princeton Univ. Press, New Jersey, 1998.

    Google Scholar 

  • Dziewonski, A. M. and D. L. Anderson, Preliminary reference Earth model, Phys. Earth Planet. Int., 25, 297–356, 1981.

    Article  Google Scholar 

  • Dziewonski, A. M. and M. Ishii, A three parameter model of inner core anisotropy, IAGA-IASPEI Joint Scientific Assembly, Abstracts, 37, 2001.

  • Giardini, D., X.-D. Li, and J. H. Woodhouse, Three-dimensional structure of the Earth from splitting in free oscillation spectra, Nature, 325, 405–411, 1987.

    Article  Google Scholar 

  • Gilbert, F. and A. M. Dziewonski, An application of normal mode theory to the retrieval of structural parameters and source mechanisms from seismic spectra, Phil. Trans. Roy. Soc. Lond., Ser. A, 278, 187–269, 1975.

    Article  Google Scholar 

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

    Article  Google Scholar 

  • Poupinet, G. R., R. Pillet, and A. Souriau, Possible heterogeneity of the Earth’s core deduced from PKIKP travel times, Nature, 305, 204–206, 1983.

    Article  Google Scholar 

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

    Article  Google Scholar 

  • Romanowicz, B. A. and L. Breger, Anomalous splitting of core sensitive normal modes: is inner core anisotropy the cause?, EOS Trans. AGU, 80, F17, 1999.

    Google Scholar 

  • Romanowicz, B. A., L. Breger, and H. Tkalcic, Core sensitive mode and body wave data: possible alternatives to inner core anisotropy, EOS Trans. AGU, 81, S314, 2000.

    Google Scholar 

  • Saito, M., DISPER80: A subroutine package for the calculation of seismic normal mode solutions, in Seismological Algorithms: Computational Methods and Computer Programs, edited by D. J. Doornbos, pp. 293–319, Academic Press, New York, 1988.

    Google Scholar 

  • Sato, Y., Soft core spectrum splitting of the torsional oscillation of an elastic sphere and related problems, Bull. Earthq. Res. Inst., 42, 1–10, 1964.

    Google Scholar 

  • Takeuchi, H. and M. Saito, Seismic surface waves, in Seismology: Surface Waves and Free Oscillations, Methods in Computational Physics 11, edited by B. A. Bolt, pp. 217–295, Academic Press, New York, 1972.

    Chapter  Google Scholar 

  • Tromp, J., Support for anisotropy of the Earth’s inner core, Nature, 366, 678–681, 1993.

    Article  Google Scholar 

  • Tromp, J. and E. Zanzerkia, Toroidal splitting observations from the great 1994 Bolivia and Kuril Islands earthquakes, Geophys. Res. Lett., 22, 2297–2300, 1995.

    Article  Google Scholar 

  • Widmer, R., G. Masters, and F. Gilbert, Observably split multiplets—Data analysis and interpretation in terms of large-scale aspherical structure, Geophys. J. Int., 111, 559–576, 1992.

    Article  Google Scholar 

  • Wiggins, R. A., A fast, new computational algorithm for free oscillations and surface waves, Geophys. J. R. Astron. Soc., 47, 135–150, 1976.

    Article  Google Scholar 

  • Woodhouse, J. H., The calculation of the eigenfrequencies and eigenfunctions of the free oscillations of the Earth and Sun, in Seismological Algorithms: Computational Methods and Computer Programs, edited by D. J. Doornbos, pp. 321–370, Academic Press, New York, 1988.

    Google Scholar 

  • Woodhouse, J. H., D. Giardini, and X.-D. Li, Evidence for inner-core anisotropy from splitting in free oscillation data, Geophys. Res. Lett., 13, 1549–1552, 1986.

    Article  Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Graduate School of Integrated Science, Yokohama City University, Yokohama, 236-0027, Japan

    Seiji Tsuboi & Masanori Saito

  2. Institute for Frontier Research on Earth Evolution, Japan Marine Science Technology Center, Yokosuka, 237-0061, Japan

    Seiji Tsuboi

Authors
  1. Seiji Tsuboi
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Masanori Saito
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Seiji Tsuboi.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Tsuboi, S., Saito, M. Existence of finite rigidity layer at the base of the Earth’s liquid outer core inferred from anomalous splitting of normal modes. Earth Planet Sp 54, 167–171 (2002). https://doi.org/10.1186/BF03351717

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1186/BF03351717

Keywords