| 講演要旨(和文) | | 地震波内部減衰は地層の物性を解明するのに重要である一方で、亀裂性状解明のための散乱波の有効利用が進められている。これまでデータから得られる全減衰は内部減衰と散乱減衰との線形和が成り立つ仮定が設けられてきたが、この仮定は散乱現象が拡散現象に近似できほど十分散乱現象が進んだ場合にのみ成り立つものであり、通常は成立しないことを数値実験データで示した。本研究では、このような仮定を前提としない散乱減衰分離手法を提案し数値実験データならびにフィールドで取得されたゼロオフセットVSPデータに適用しその有効性を示す。なお、散乱減衰分離手法は、MMFS(modified median frequency shift)法を修正する方法であるが、そのコンセプトは周波数依存成分を散乱減衰とみなし、非周波数依存成分を内部減衰と関連付けるものである。 |
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| | 講演要旨(英文) | | The intrinsic component of attenuation is important in characterizing the physical properties of subsurface formations while positive utilization of seismic scattering to characterize fracture systems has been investigated. However, it is generally difficult to distinguish between intrinsic attenuation and scattering effects. Our numerical experiments demonstrate that the most popular method estimating scattering attenuation for field zero-offset VSP data by using synthetic data and isolating the intrinsic attenuation by subtracting the scattering attenuation from the total attenuation is not appropriate for separating intrinsic and scattering attenuation. Although most existing studies assume that the total attenuation is a summation of the intrinsic and scattering attenuation, the present study supports the existing knowledge that this assumption holds for the limit of extreme scattering in which the entire seismic energy propagation satisfies the diffusion equation. To overcome this limitation, we proposed a novel method for separating intrinsic and scattering attenuation for zero-offset VSP data by slightly modifying the MMFS (modified median frequency shift) method. We investigate the advantages of the proposed method by applying the proposed method to synthetic data. Finally, we preliminarily apply the proposed methods to field zero-offset VSP data and demonstrated the applicability of the proposed method. |
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