Detection of Electromagnetic Precursors of Earthquakes Mediated by the Terrestrial Ground Surface Plasma Wave

Abstract

Detection of precursors of earthquakes has long been a controversial issue in regard to its possibility and realizability. Here we present stable observation of distinct electromagnetic precursors of earthquakes in Japan using specifically designed narrowband filters to suppress noises for a radiowave at the very high frequency (VHF) range. Electromagnetic precursors are observed consistently with our high-sensitivity and low-noise equipment as sudden rises and/or falls of received radiowave power within the 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 substantially clear precursory signals at two distant locations a day before the Fukushima offshore M7.4 earthquake on the Pacific side of Japan on March 16, 2022. We identified the signals as precursors of the earthquake by comparing synchronously with the meteorological, ionospheric, and 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.