Precursory signature of several major earthquakes studied using 40Â kHz low frequency signal

To investigate the precursory signature of earthquakes on low frequency (LF) signal propagation, six earthquakes, having magnitude greater than equal to 6.5 and depth less than equal to 30 km, are being studied. The base line level of 40 kHz signal, transmitted from JJY station, Japan, is analysed with respect to Vd statistical parameter. Results show that the Vd parameter values starts fluctuating from its ambient levels before and during the days of the earthquakes, with significant variation starting 1-3 days prior to the earthquake concerned. This present study is an approach for identifying the precursory signatures of earthquakes on LF signal propagation using a new methodology with Vd parameter.