Precursors of earthquakes in the line-of-sight propagation on VHF band

This paper was intended to find out any relation between anomalous line-of-sight propagations on VHF band and occurrences of earthquakes near the VHF propagation path. The TV broadcasting waves on the VHF band were measured continuously for 504 days, in which we assembled an automatic measurement system. The waves propagated on the line-of-sight from Tokyo Tower to Gunma Univ. in Kiryu were measured on VHF band. In order to distinguish anomalous propagation data from normal data, a statistical process is adopted in such a way that six times deviation from the mean value was adopted as a criterion for distinguishing between the anomalous or normal propagation data. In a time interval between the appearance of anomalous propagation and the occurrence of earthquake was shorter than 48 hours (2 days), the anomalous propagation was additionally recognized as being associated with the earthquake. During the observation period of 504 days, only four anomalous propagations happened and we observed three earthquakes associated with these anomalous propagations. As a result, it is found that anomalous line-of-sight propagations on VHF band might be associated with the earthquakes near the VHF propagation path.