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Low-Noise High-Sensitivity Observation of Electromagnetic Precursors of Large Earthquakes in Japan
  • Masafumi Fujii
Masafumi Fujii
University of Toyama

Corresponding Author:mfujii@eng.u-toyama.ac.jp

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Detection of precursors of earthquakes has long been a controversial issue in regard to its possibility and realizability. Here we present successful and stable observation of the electromagnetic precursors of earthquakes in Japan using a specifically designed narrowband filter to suppress noises for a radiowave at the very high frequency (VHF) range. Electromagnetic precursors are observed consistently with our high-sensitivity low-noise equipment as sudden rises and/or falls of received radiowave power in a time scale of a few hours. The signals are distinctive from other electromagnetic noises and observed typically some hours to some days before large earthquakes. We have observed numerous precursory signals of earthquakes for several years. Recently, we obtained surprisingly clear precursory signals at two different locations more than 200 km apart a day before the Fukushima offshore, the Pacific side of Japan, M7.4 earthquake on March 16, 2022. We identified carefully the signals as precursors of the earthquake by comparing the signals in time with the meteorological, ionospheric, geomagnetic field data. Observation of such radiowave precursors contributes to the prediction of earthquakes as well as monitoring the lithospheric stress and pre-seismic activity over a broad area of a few hundred kilometers.