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| | Abstract | | In order to prove the temporal change of seismic waves due to the injection of air into the ground, we carried out a field test near the Nojima Earthquake Fault in Awaji Island using a very accurate seismic source and a seismic array. The newly built seismic ACROSS was installed horizontally, and the rotational axis of weight-mass was horizontal. Although the instrument has been designed as 10 to 50Hz, we used 10-35Hz only. We injected air into the Okasa formation at 100 m depth. We used 32 3-component geophones and one 3-component borehole geophones at 800m depth. Appling source signature compensation to the filed records, we obtained the transfer functions between the source and receivers. The almost all differential transfer function between before the injection and each record showed very large changes of waveforms immediately after the beginning of injection of air at some sites. The station #7 at 100m from the injection well showed extremely large change at 1 day after the injection. The delay times for appearance of change vary place to place and the differential waveform characteristics for each station are quite different one by one. |
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