- Article
- Published:
Comment on “Incessant excitation of the Earth’s free oscillations” by Nawa et al.
Earth, Planets and Space volume 50, pages 883–885 (1998)
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.
Crossley, D., O. Jensen, and J. Hinderer, Effective barometric admittance and gravity residuals, Phys. Earth Planet. Inter., 90, 221–241, 1995.
Dziewonski, A. M. and D. L. Anderson, Preliminary reference Earth model, Phys. Earth Planet. Inter., 25, 297–356, 1981.
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.
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.
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.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
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
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1186/BF03352182