Enhancements of electromagnetic broadband noise in 50MHz band which possibly associate with earthquakes

Abstract

Electromagnetic noises in 50 MHz band have been observed at Tateyama observatory in Chiba prefecture in order to find any precursory electromagnetic phenomena associated with seismic activity. Electromagnetic waves were received by a Yagi antenna in the horizontal west direction with the horizontal polarization. Wideband characteristics of received signal were obtained with a spectrum analyzer. The data obtained during a half year from Feb. 10, 2000 to Sep. 17, 2000 were evaluated in terms of natural noise level. Enhancements of the broadband noise with duration of a few days were observed six times during the period. Relation between these enhancements and occurrences of earthquakes greater than or equal to M4.5 has been investigated. Most of the enhancements of the natural noise started a few days before the occurrences of earthquakes that are located in the west direction from the observatory. This fact may suggest that electromagnetic noises were generated and/or anomalous propagations of electromagnetic waves occurred just before and during the earthquakes.