Articles | Volume 8, issue 4
Nat. Hazards Earth Syst. Sci., 8, 653–656, 2008

Special issue: Earthquakes precursors and seismic hazard

Nat. Hazards Earth Syst. Sci., 8, 653–656, 2008

  09 Jul 2008

09 Jul 2008

On the statistical correlation between the ionospheric perturbations as detected by subionospheric VLF/LF propagation anomalies and earthquakes

Y. Kasahara1, F. Muto1, T. Horie1, M. Yoshida1, M. Hayakawa1, K. Ohta2, A. Rozhnoi3, M. Solovieva3, and O. A. Molchanov3 Y. Kasahara et al.
  • 1Department of Electronic Engineering and Research Station on Seismo Electromagnetics, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu Tokyo, 182-8585, Japan
  • 2Department of Electronics Engineering, Chubu University, Kasugai Aichi, Japan
  • 3Institute of Physics of the Earth, Russian Academy of Sciences, 10 Gruzinskaya Str., Moscow 123999, Russia

Abstract. Relatively long-period (4 years) data on different propagation paths by means of Japanese-Pacific VLF/LF network observation, are used to obtain further statistical significance on the correlation of ionospheric perturbations as revealed by VLF/LF propagation anomalies with earthquakes. Earthquakes with magnitude greater than 6.0, taken place only within the fifth Fresnel zone of each great-circle path are selected for the correlation study. It is finally found based on the superimposed epoch analysis that the nighttime trend (average amplitude) exhibits a significant decrease exceeding 2σ (σ: standard deviation) several days before the earthquake and the nighttime fluctuation exceeds the corresponding 2σ again several days before the earthquake when the earthquake depth is smaller than 30 km (shallow earthquakes). However, when we treat all earthquakes including deep earthquakes, the trend shows a significant decrease (just approaching 2σ line), and the nighttime fluctuation shows a less significant broad enhancement before the EQ.