| 講演要旨(和文) | | 岩石試料の内部構造や特性の推定には，透過波を用いたモニタリングが有効である．しかし，試料は一辺が数cm程度と小さく，端面で反射・変換された波が複雑な後続相を作り出すため，波形全体を活用する解析は難しかった．本研究では後続相の活用に向けて，まず各位相の成因を把握することを目的として，3次元差分法による波動伝播シミュレーションを行った．円柱形試料における波の伝播過程を，計算から得た波動場や実測した透過波形との比較から評価したところ，震源から出た直達波が試料の周境界で反射波や変換波を生みながら伝播し，震源と反対側の面で反射した後，再び反射・変換波を生じながら逆方向に伝播するという過程が何度も繰り返される様子が明らかになり，こうした波群が後続波を形成していることがわかった．また，ゆっくりと試料表面を伝播するS波群の存在や，時間が十分経過するとP波よりもS波成分を持つ波群が卓越する様子も確認できた． |
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| | 講演要旨(英文) | | Wave transmission test is an effective way to estimate the inner structure and characteristic of a rock sample. Since later phases of transmitted waves in a small finite sample were contaminated by reflected and converted waves, it was difficult to analyze entire waveform. For the purpose to clarify the propagation process of reflected and converted waveforms generated in a rock sample, we performed 3D finite difference method simulation. Using the snapshots of the wavefield and waveform obtained at laboratory, we tried to identify the generation process of each characteristic phase appeared on the waveforms. The result show the direct waves propagate through the sample with generating the reflected and converted waves at the curve boundary of the sample side surface, and a group of S wave which slowly propagate along the curved boundary. Then, these waves reflected at the opposite surface and propagate through the sample with generating reflected and converted wave again which form complex shape of seismic trace as we saw in the transmitted wave obtained by laboratory experiments. This propagation process was repeated many times, and when a time enough elapsed S wave component in the rock sample became much dominate than P wave. |
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