| 講演要旨(和文) | | 河川堤防においてランドストリーマー表面波探査を実施した際に，表面波相の後に明瞭なS波反射波比定相が捉えられることがある．そこで高密度で測定したあるサイトの表面波探査データに対してS波反射法探査データ処理を施し，S波反射断面を作成した．その結果，急傾斜する浅部基盤構造をイメージングすることができた．その深度断面を橋台設置工事に伴う地盤改良杭の施工実績と比較したところ，きわめて調和的であった．さらにコーン貫入試験，サイスミックコーン貫入試験を追加したところ，処理対象とした波群はSV波であることがわかった．このことは，ランドストリーマー表面波探査によって表層15m程度までのS波速度構造だけでなく，深さ50m程度までの堆積構造をも復元可能であることを意味している．なおこの調査研究の一部は河川整備基金研究助成金を受けて実施した． |
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| | 講演要旨(英文) | | Distinct P- and SV-wave reflections are frequently recognized in the high-resolution surface wave survey records. Because the settings of data acquisition for the surface wave survey are fundamentally the same as those for seismic reflection survey when using Land Streamer, it is possible to apply S-wave reflection processing steps to the dataset. We conducted a small size levee survey at a site where a bridge foundation was to be constructed. A migrated depth section, obtained through the reflection seismic processing to the surface wave data, clearly reconstructed the near-surface structure down to 40 m.The estimated depths to the unconformity were well concordant with array piling works for the bridge foundation. In addition, CPT and SCPT measurements were carried out to clarify the S-wave and geotechnical properties in the near surface. CPT profiles and VSP processing results were consistent with the depth section. Moreover, it was confirmed that the dominant phases were the direct SV waves which were generated at the surface and reflected from the near-surface boundaries. In conclusion, when conducting surface wave survey densely compatible to the conventional seismic reflection surveying, seismic reflection processing is effective to the near-surface imaging and characterization, especially for levee systems. |
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