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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 4, issue 5/6
Nat. Hazards Earth Syst. Sci., 4, 647–653, 2004
https://doi.org/10.5194/nhess-4-647-2004
© Author(s) 2004. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

Special issue: Precursory phenomena, seismic hazard evaluation and seismo-tectonic...

Nat. Hazards Earth Syst. Sci., 4, 647–653, 2004
https://doi.org/10.5194/nhess-4-647-2004
© Author(s) 2004. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  19 Oct 2004

19 Oct 2004

Results of subionospheric radio LF monitoring prior to the Tokachi (M=8, Hokkaido, 25 September 2003) earthquake

A. V. Shvets2,1, M. Hayakawa2, and S. Maekawa2 A. V. Shvets et al.
  • 1Usikov Institute for Radiophysics and Electronics, Kharkov, Ukraine
  • 2The University of Electro-Communications, Tokyo, Japan

Abstract. Results of simultaneous LF subionospheric monitoring over two different propagation paths prior to the very strong Tokachi earthquake (near the east coast of Hokkaido Island, 25 September 2003) of magnitude 8.3 are presented firstly. Nighttime amplitude fluctuations of the Japanese Time Standard Transmitter (JG2AS, 40kHz) signal received at Moshiri (Japan, 142°E, 44°N) and at Petropavlovsk-Kamchatski (Russia, 158°E, 53°N) were analyzed. As a possible precursory signature we observed synchronous intensification of quasi periodical 16-day variations of the dispersion in the signals received at both observation stations before the earthquake. The strongest deviations observed as a rule were depletions of signal amplitude probably connected with increase of loss in the ionosphere by the enhancement of turbulence. This is due to dissipation of internal gravity waves (IGW) at the lower ionosphere heights. A scheme for seismo-IGW-planetary waves (PW) interconnection has been justified to explain the observed connection with strong earthquakes. It considers the seasonal variability in the signal.

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