| 講演要旨(和文) | | 我々は有限差分法と境界積分方程式法を用いて、波動伝播を数値的に表現し、その地震波動より得られたcoda-Q値より地盤中の応力が取得可能かどうかを検討した。尚、数値計算モデル中にクラックを配置し、そのクラックからの散乱波によりコーダ波を形成した。有限差分法で得られた結果より、coda-Q値は応力の大きさに比例し、さらに応力方向の違いによって、coda-Q値が異なった挙動を示すことが分かった。また、境界積分方程式法の結果からもQ値が応力の大きさと関係を持つことが分かっている。以上のことより、地震波形から得られたcoda-Q値より、地震波伝播の場の応力変化を捉えられる可能性があると言える。 |
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| | 講演要旨(英文) | | We employ a finite different method (FDM) and a boundary integral equation method (BIEM). Using them, we simulate the scattering of these 2-D models to see if we can obtain the information of the stress loaded to the underground from variation of coda-Q. In both cases, we assumed that the scattering of seismic waves takes place due to existing cracks in the medium. We revealed that the coda-Q has relationship with the loaded stress. From the results from FDM, it turned out that the magnitude of the stress could be estimated from the coda-Q. Since the stress-dependent coda-Q shows different behavior according to the direction of the loaded stress, we think it possible to know the stress orientation, too. This tendency is derived from the occurrence of the anisotropy in the phase velocity of elastic waves, which is induced by the stress. Also from the result of BIEM, it is observed that the coda-Q varies according to the loaded stress but not depending on the orientation of cracks that might reflects stress history of the medium. We would like to conclude that the possibility of stress to be loaded to subsurface medium could be estimated using the variation of coda-Q. |
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