| 講演要旨(和文) | | 既設砂防堰堤の地下埋没部分の形状を調査するために、極浅層反射法地震探査を行った。堰堤の天端部分で起振・受振を行い、基礎部底面からの反射波を用いて底面のイメージングを試みた。CMP重合処理の他、一定速度を仮定した重合前深度マイグレーション（PSDM）による処理を行い、地下埋没部分の底面からの反射を抽出した。今回は堤体地上部における弾性波トモグラフィも行ったので、それにより得られたP波速度を参考に重合速度を決定した。コンクリートのように速度がある程度一様で平均速度が分かっている場合、底面形状の推定に定速度PSDM処理が有効であることが分かった。 |
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| | 講演要旨(英文) | | Very shallow seismic reflection was adopted to investigate the shape of buried base of an existing check dam. The receivers and shot points were placed on the crown of dam. Reflection imaging of the base of dam was attempted by CMP stacking and pre-stack depth migration (PSDM) with constant velocity. Though PSDM has an advantage in dealing with irregular surface topography, it needs the correct velocity model to provide the correct image. In the case of a concrete structure whose elastic property is expected not to differ from the typical one, PSDM processing is effective. We confirm the availability of this method through the simulation using 2D synthetic waveform records. Even though the wavelength of the P wave propagating through concrete is long compared to required precision, the reflection surface can be determined with certain accuracy. |
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