Articles | Volume 8, issue 1
Nat. Hazards Earth Syst. Sci., 8, 135–141, 2008
https://doi.org/10.5194/nhess-8-135-2008
Nat. Hazards Earth Syst. Sci., 8, 135–141, 2008
https://doi.org/10.5194/nhess-8-135-2008

  26 Feb 2008

26 Feb 2008

Detection of ionospheric perturbations associated with Japanese earthquakes on the basis of reception of LF transmitter signals on the satellite DEMETER

F. Muto1, M. Yoshida1, T. Horie1, M. Hayakawa1, M. Parrot2, and O. A. Molchanov3 F. Muto et al.
  • 1Department of Electronic Engineering and Research Station on Seismo Electromagnetics, University of Electro-Communications, Chofu Tokyo, Japan
  • 2LPCE/CNRS, Orleans, France
  • 3Institute of Physics of the Earth, Moscow, Russia

Abstract. There have been recently reported a lot of electromagnetic phenomena associated with earthquakes (EQs). Among these, the ground-based reception of subionospheric waves from VLF/LF transmitters, is recognized as a promising tool to investigate the ionospheric perturbations associated with EQs. This paper deals with the corresponding whistler-mode signals in the upper ionosphere from those VLF/LF transmitters, which is the counterpart of subionospheric signals. The whistler-mode VLF/LF transmitter signals are detected on board the French satellite, DEMETER launched on 29 June 2004. We have chosen several large Japanese EQs including the Miyagi-oki EQ (16 August 2005; M=7.2, depth=36 km), and the target transmitter is a Japanese LF transmitter (JJY) whose transmitter frequency is 40 kHz. Due to large longitudinal separation of each satellite orbit (2500 km), we have to adopt a statistical analysis over a rather long period (such as 3 weeks or one month) to have reliable data set. By analyzing the spatial distribution of JJY signal intensity (in the form of signal to noise ratio SNR) during a period of 4 months including the Miyagi-oki EQ, we have found significant changes in the intensity; generally the SNR is significantly depleted before the EQ, which is considered to be a precursory ionospheric signature of the EQ. This abnormal effect is reasonably explained in terms of either (1) enhanced absorption of whistler-mode LF signals in the lower ionosphere due to the lowering of the lower ionosphere, or (2) nonlinear wave-wave scattering. Finally, this analysis suggests an important role of satellite observation in the study of lithosphere-atmosphere-ionosphere coupling.

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