| 講演要旨(和文) | | 電磁式震源を用いて2014年７月と８月それぞれ１週間のタイムラプスフィールド観測を行った。一ヶ月間における伝達関数波形の変化を調べた。震源位置を一定位置に固定し、できるだけ状態を変化しないようにした。震源は10〜50Hzをまで100秒間でスイープし5秒間の休止時間をおき、これを１時間に32回繰り返した。受振スペクトルを震源特性で割り伝達関数を求めた。2km以内の地震計から求めた伝達関数のP波部分は1ヶ月の時間経過にも関わらずきわめて良い一致を示したが、表面波と思われる後続波は比較的大きな時間変化を示した。これにより震源の状態を変えない場合、移動型震源であっても震源特性の再現性は良く、短期間なら地下のタイムラプス観測に使えることがわかった。震源位置を多少変えた場合震源波形の再現性は良くなく、タイムラプス研究に使うのはやや難しい。 |
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| | 講演要旨(英文) | | Using a conventional seismic source, we carried out a time-lapse experiment in quarry during two weeks in total in July and August, 2014. The transfer function between source and receiver is defined by the division of observed seismic record by source signatures, it is necessary to minimize temporal changes of the source signature during one month. We used a fix location for the source and kept to minimize the change of source operational condition. The source was swept from 10 to 50 Hz during 100 seconds with 5 second rest. We repeated 32 sweeps during an hour and computed an hour-long stacked waveforms. The source signature is calculated by the force to the reaction mass and base plate. The calculated transfer functions within 2 km showed very similar wave forms on P arrivals. The comparison of these transfer functions of this observation to the past observations shows large discrepancies on the waveforms due to the difference of coupling condition of source and ground, and it may suggest the difficulty of direct comparison among those observations. |
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