Observations of CD-seismic Electromagnetic Phenomena in VHF Band

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1)Observation systemIn our investigation, the observation of seismic electromagnetic phenomena have been conducted to solve these following subjects. 1.Does electromagnetic phenomena associated with EQ occur? 2.Does the EQ make the ionospheric layer reflect the FM broadcasting waves? To realize our observation, we have constructed the VHF band observation systems. The feature of our observation system is as followings.- Observation in FM broadcasting band : This band is hardly influenced by artificial or urban noises.- Dual Frequency Observation : To distinguish the seismic broadband phenomena from FM broadcasting waves, we have developed a novel dual frequency observation method in which the observation is made attwo different frequencies- Observation using digital FM tuner : This tuner has high frequency selectivity and stability, and thequantitative observation can be realized.(2)Observation results1.Observation of seismic electromagnetic phenomenaWe could observe the seismic phenom … More ena in Geiyo EQ (2001), Ibaraki-ken-oki EQ (2002), and Niigata-kenChuetsu EQ (2004). In these EQ, the broadband electromagnetic waves were observed. And it is found that these observed electromagnetic waves are generated from the seismic swing of the land near the observation site. Moreover, the other EM phenomenon detected in VHF band disappeared at the time of earthquake. Amplitude fluctuations of about 2 dB were observed since one day before the Geiyo EQ, then, the fluctuations disappeared at the occurrence of EQ.2.Observation of long-distance FM broadcasting propagationThe 77.1 MHz FM broadcasting wave from Sendai has been observed in Ibaraki observation site. From this observation, it is found that the FM broadcasting wave propagates in the tropospheric duct or on the geosphere. Our observation results show that the EQ hardly influence the ionospheric layer to reflect the FM broadcasting waves at the occurrence of EQ.(3)Improvement of observation system.Especially in the high electric field strength, the BPF should be inserted to reduce the intermodulation distortion. Less