Characteristics of the FM radio waves propagated over the epicenters

We have gotten the first opportunity to observe characteristics of the FM radio wave propagated over the epicenter. In our observation system installed at Nobeyama, fluctuations of the FM radio wave of 82.3MHz had been observed on the two Niigata Prefecture earthquakes on October 23 in 2004 and on July 16 in 2007. In this paper, the propagation characteristics of FM radio wave are carefully checked for six years. Some EM anomalies of the FM radio waves had been detected before the earthquakes. However, the similar EM anomalies were detected not only before the earthquakes but also the following years. They have good correlated with the refractive index gradient of the atmosphere. Then, these EM anomalies are concluded not due to seismic but meteorological phenomena.