| 講演要旨(和文) | | 電磁式震源を用い採石地域において2014年７月と８月それぞれ１週間のタイムラプス観測を行った。毎日夕方の８時から朝の８時まで震源を稼働しそれを地中に埋設した地震計と70m、200mの深さの坑内地震計で観測した。この間震源を同じ状態に保って加振した結果、観測期間を通じ各時間毎の波形の再現性はきわめて良かった。P波分の差分波形を作りそれを受振点から逆伝搬した。その結果、北西、西南西方向に異常を起こした原因があるという結果を得た。この結果を採石場所における過去の変動域と比べたところ、良い一致があることがわかった。 |
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| | 講演要旨(英文) | | We carried out the seismic time-lapse experiment in an old quarry region. We used an electro-magnetic seismic source to maintain the same vibration condition at the same position in each one week in July and August, 2014, respectively. We used a number of buried geophones and two borehole seismometers at 70m and 200m depth. The area is approximately 3 km x 4 km. The sweep frequency was from 10 to 50Hz during 100 seconds. We obtained the transfer function by division of one hour stacked data by the source signature. The calculated transfer functions during two months show very subtle changes except later arrivals. The later arrivals could be surface waves travelling near surface sediment layer. The effect of rainfall in July are not so large in contrast to the case of Awaji Island in February 2011. We compute the residual P-waveforms and back-propagated those from the receivers. The obtained images suggest some good correlation with the imaged direction and past subsidence region. |
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