- 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)
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.
Creager, K. C., Anisotropy of the inner core from differential travel times of the phases PKP and PKIKP, Nature, 356, 309–314, 1992.
Dahlen, F. A. and J. Tromp, Theoretical Global Seismology, 619–624, Princeton Univ. Press, New Jersey, 1998.
Dziewonski, A. M. and D. L. Anderson, Preliminary reference Earth model, Phys. Earth Planet. Int., 25, 297–356, 1981.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Tromp, J., Support for anisotropy of the Earth’s inner core, Nature, 366, 678–681, 1993.
Tromp, J. and E. Zanzerkia, Toroidal splitting observations from the great 1994 Bolivia and Kuril Islands earthquakes, Geophys. Res. Lett., 22, 2297–2300, 1995.
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.
Wiggins, R. A., A fast, new computational algorithm for free oscillations and surface waves, Geophys. J. R. Astron. Soc., 47, 135–150, 1976.
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.
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.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
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
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1186/BF03351717