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Imanishi (this issue) commented that (1) the noise level at Matsushiro, Japan (MA) is much lower than at Syowa Station, Antarctica (SY), (2) oscillation signals are not observed at MA, and therefore (3) peaks below 3 mHz observed at SY are unlikely to be real signals of free oscillations. We point out that (1) he made a comparison between MA in the Japanese quiet month and SY in the Antarctic windy month, (2) the Matsushiro record does show up oscillation signals, and therefore (3) his assertion that peaks below 3 mHz observed at SY are unlikely to be real signals is not founded.


  • Agnew, D. C. and J. Berger, Vertical seismic noise at very low frequencies, J. Geophys. Res., 83, 5420–5424, 1978.

    Article  Google Scholar 

  • Imanishi, Y., Comment on “Incessant excitation of the Earth’s free oscillations” by Nawa et al., Earth Planets Space, 50, this issue, 883–885, 1998.

    Article  Google Scholar 

  • Kobayashi, N. and K. Nishida, Continuous excitation of planetary free oscillations by atmospheric disturbances, Nature, 395, 357–360, 1998.

    Article  Google Scholar 

  • Nagata, Y., M. Kawamiya, Y. Michida, and M. Odamaki, Seasonal variations of the sea level at Syowa Station, Antarctica, Proc. NIPR Symp. Polar Meteorol. Glaciol., 7, 60–72, 1993.

    Google Scholar 

  • 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, 1998a.

    Article  Google Scholar 

  • Nawa, K., N. Suda, Y. Fukao, T. Sato, Y. Tamura, K. Shibuya, H. McQueen, and H. Virtanen, Detection of Earth’s background free oscillations using the Australian and Finnish superconducting gravimeter records (abstract), Jpn. Earth Planet. Sci. Joint Meeting, Sn-p003, 1998b.

  • Percival, D. B. and A. T. Walden, Spectral Analysis for Physical Applications, 583 pp., Cambridge University Press, Cambridge, 1993.

    Book  Google Scholar 

  • Sato, T., H. McQueen, B. Murphy, K. Lambeck, Y. Hamano, K. Asari, Y. Tamura, and M. Ooe, On the observations of gravity tides and Earth’s free oscillations with superconducting gravimeter CT#031 at Mt. Stromlo, Australia, Proc. 13th Int. Symp. Earth Tides, Bruxelles, 1998 (in press).

  • 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 

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Correspondence to Kazunari Nawa.

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Nawa, K., Suda, N., Fukao, Y. et al. Reply. Earth Planet Sp 50, 887–892 (1998).

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  • Free Oscillation
  • Real Signal
  • Seismic Noise
  • Superconducting Gravimeter
  • Syowa Station