The ULF/ELF electromagnetic radiation before the 11 March 2011 Japanese earthquake

Abstract

The ULF/ELF short‐term electromagnetic precursor is discovered for the disastrous Japan earthquake (EQ) occurred on 11 March 2011. This analysis is based on the records measured by search coil magnetometers located at Nakatsugawa (geographic coordinates; 35.42°N, 137.55°E), Shinojima (34.67°N, 137.01°E), and Izu (34.64°N, 137.01°E) of the Chubu University network. The data of these magnetometers are extensively used to analyze the ULF/ELF seismo‐atmospheric radiation. It is then found that the ULF/ELF atmospheric radio emission is reliably detected on 6 March before the main shock on 11 March, probably as a precursory signature of the EQ. Further confirmation on its seismic origin was provided by the observational fact that the azimuths of the radiation source from all observation sites coincide approximately with the region of the forthcoming EQ.