Open Access

An attempt to delineate very low frequency electromagnetic signals associated with earthquakes

  • Toshi Asada1,
  • Hisatoshi Baba1,
  • Mamoru Kawazoe2 and
  • Masahisa Sugiura3
Earth, Planets and Space201453:BF03352362

Received: 13 April 2000

Accepted: 29 September 2000

Published: 6 June 2014


We report on our observation of pulse-like electromagnetic signals in the frequency range 110 kHz that we associate with earthquakes. The severest difficulty in separating earthquake-associated VLF signals from those originating in lightning discharges stems from the circumstance that the latter signals are overwhelming in number compared with the former. While claims have often been made of observation of electromagnetic signals in association with earthquakes, most of the claims, excepting a few, heavily rely on temporal correlation. By means of simple instrumentation and data processing software, our method by and large enables us to isolate VLF signals whose direction of arrival is well focussed at the epicenter direction. In this preliminary report we present several examples that positively demonstrate the existence of a class of VLF signals having a peak frequency of occurrence 14 days prior to earthquakes of Magnitude 46. With an accumulation of experience the technique described in this paper would seem to offer a promising approach towards earthquake prediction.