Observations of co-seismic broadband electromagnetic waves in the VHF band

Abstract

Many observations have been conducted to clarify the relation between electromagnetic phenomena and seismic activities. We have been observing seismic electromagnetic waves in FM broadcasting frequency band from 76 MHz to 90 MHz using PLL type synthesized digital FM tuners since 1998. We are operating thirteen observatories in Japan. From observations at Ibaraki by the dual frequency method using two different frequencies, nine events of co-seismic electromagnetic waves were observed for seven years from January 1, 2002 to December 31, 2008. Received electromagnetic levels rose up at the same moment of arrival of seismic waves. Further, we examined the relation between the co-seismic broadband electromagnetic waves and the seismic parameters. It was confirmed that the detected peak electromagnetic levels were well correlated with the peak ground accelerations of the earthquakes.