Direct and indirect evidence of pre-seismic electromagnetic emissions associated with two large earthquakes in Japan

Electromagnetic emissions (EMEs) associated with earthquake (EQ) epicenters are found to be one of the most reliable phenomena for the short-term pre-seismic mechanism of earthquakes. The detection mechanism of such emissions can have both direct and indirect techniques. In this manuscript, we attempted to present the signature of such emissions before two strong EQs, one in Fukushima on November 21, 2016, and another in Kumamoto on April 15, 2016, in Japan. We use the lithospheric emission in the range of ultra-low frequency (ULF) waves as observed from the Kakioka observatory in Japan for direct measurement. For the indirect investigation, we use the concept of energetic particle precipitation in the inner radiation belt due to wave–particle interaction through the pitch angle scattering processes. We use the particle enhancement (electron and proton) observed from the space-based National Oceanic and Atmospheric Administration (NOAA) satellites. The ULF results found an abnormal increase in lithospheric radiation for Kumamoto and Fukushima EQs on three days and ten days before the EQs, respectively, and an ionospheric depression on six days before both the cases. The satellite observations related to the EMEs from these EQs exhibit electron particle bursts (PB) on the day of the Fukushima EQ. We observe particle bursts 4–5 and 10 days before the mainshock for the Kumamoto EQ. We are not found any proton precipitation for the Fukushima EQ where signatures of proton count number are observed for the Kumamoto EQ. This type of simultaneous observation from the ground and satellite-based instruments establishes that EMEs are observed before the EQs and can be a potential candidate for short-term precursory studies.