|
|
 |
|
|
Ann. Geophys., 24, 2219-2225, 2006
www.ann-geophys.net/24/2219/2006/
© European Geosciences Union 2006
A statistical study on the effect of earthquakes on the ionosphere, based on the subionospheric LF propagation data in Japan
S. Maekawa1, T. Horie1, T. Yamauchi1, T. Sawaya1,*, M. Ishikawa1,**, M. Hayakawa1, and H. Sasaki2
1The University of Electro-Communications, Department of Electronic Engineering, 1-5-1 Chofugaoka, Chofu Tokyo 182-8585, Japan
2Kochi University, Department of Physics, Akebono-cho Kochi, Japan
*now at: Murata Manufacturing Co., Ltd., Yokohama, Japan
**now at: Antenna Giken Co., Ltd., Saitama, Japan
Abstract. A superimposed epoch analysis has been undertaken, in order to find the
correlation of the ionospheric perturbations with seismic activity. We take
the wave path from the Japanese LF transmitter (frequency=40 kHz) and an
observing station of Kochi (wave path length of 770 km), and a much longer
period (of five years) than before, is considered. This subionospheric LF
propagation can be called "an integrated measurement" in the sense that any
earthquakes in the LF sensitive area just around the great-circle path can
influence the observed LF signals, so that we define the "effective
magnitude" (Meff) by integrating the total energy from different
earthquakes in the sensitive area on a current day and by converting it back
into magnitude. A superimposed epoch analysis for the effective magnitude
greater than 6.0 has yielded that the ionosphere is definitely disturbed in
terms of both amplitude and dispersion, and that these perturbations tend to
take place prior to an earthquake. The statistical z-test has also been
performed, which has indicated that the amplitude is definitely depleted 2–6
days before the earthquake day and also that the dispersion is very much
enhanced during the same period. This statistical study has given strong
support to the existence of seismo-ionospheric perturbations for high
seismic activity.
Full Article in PDF (766 KB) |
|
|
