Skip to main content
Earth, Planets and Space
Download PDF

Comment on “Incessant excitation of the Earth’s free oscillations” by Nawa et al.

Earth, Planets and Space volume 50, pages 883–885 (1998)Cite this article

Abstract

The report of Nawa et al. (1998) that incessant excitation of the Earth’s free oscillations was discovered in the low frequency spectra of the superconducting gravimeter at the Syowa station in Antarctica is reexamined. The mean spectra for Syowa are compared with those for Matsushiro, another superconducting gravimeter station in an extremely calm circumstance, hence showing a much lower noise level than Syowa. Although the spectra for Syowa have many peaks below 3 mHz corresponding to those present in the time-frequency diagram of Nawa et al., no similar peaks are found in the spectra for Matsushiro. This result suggests that the peaks below 3 mHz in the Syowa spectra are not real signals of the Earth’s free oscillations.

References

  • Crossley, D. and J. Hinderer, Global Geodynamics Project-GGP: Status report 1994, in Proc. Second IAG Workshop on “Non-Tidal Gravity Changes: Intercomparison between Absolute and Superconducting Gravimeters”, Cahiers du Centre Européen de Géodynamique et de Séismologie, Luxemburg, 11, 244–274, 1995.

    Google Scholar 

  • Crossley, D., O. Jensen, and J. Hinderer, Effective barometric admittance and gravity residuals, Phys. Earth Planet. Inter., 90, 221–241, 1995.

    Article  Google Scholar 

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

    Article  Google Scholar 

  • GWR Instruments, Superconducting gravity meter operating manual, 1989.

  • Imanishi, Y., J. Segawa, I. Furuya, S. Kashiwabara, H. Takayama, and Y. Nishimae, Gravity observation by means of a superconducting gravimeter at Matsushiro, Japan, in IAG Proceedings “Gravity, Geoid and Marine Geodesy”, 115–122, 1997.

  • Kobayashi, N. and K. Nishida. Continuous excitation of planetary free oscillations by atmospheric disturbances, Nature, 1998 (in press).

  • Nawa, K., N. Suda, Y. Fukao, T. Sato, Y. Aoyama, and K. Shibuya, Incessant excitation of the Earth’s free oscillations, Earth Planets Space, 50, 3–8, 1998.

    Article  Google Scholar 

  • Sato, T. and Y. Imanishi, A superconducting gravimeter network-GGP-Japan network, poster presented at the International Symposium on “New images of the Earth’s interior through long-term oceanfloor observations”, 1997.

  • Suda, N., K. Nawa, and Y. Fukao, Earth’s background free oscillations, Science, 279, 2089–2091, 1998.

    Article  Google Scholar 

  • Tanimoto, T., J. Um, K. Nishida, and N. Kobayashi, Earth’s continuous oscillations observed on seismically quiet days, Geophys. Res. Lett., 25, 1553–1556, 1998.

    Article  Google Scholar 

Download references

Author information

Authors and Affiliations

  1. Ocean Research Institute, University of Tokyo, 1-15-1, Minamidai, Nakano, Tokyo, 164-8639, Japan

    Yuichi Imanishi

Authors
  1. Yuichi Imanishi
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Yuichi Imanishi.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Imanishi, Y. Comment on “Incessant excitation of the Earth’s free oscillations” by Nawa et al.. Earth Planet Sp 50, 883–885 (1998). https://doi.org/10.1186/BF03352182

Download citation

  • Received:

  • Revised:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1186/BF03352182

Keywords

  • Gravity Data
  • Free Oscillation
  • Lower Noise Level
  • Superconducting Gravimeter
  • Syowa Station