報告書番号

N05047

タイトル（和文）

日本列島沿岸海域における海底活断層調査の現状と課題－海底活断層評価の信頼度向上にむけて－

タイトル（英文）

The existing states and problems of submarine active fault investigation in the coastal region of the Japanese Islands.-Improvement in reliability of submarine active fault evaluation-

概要 （図表や脚注は「報告書全文」に掲載しております）

海底活断層調査の信頼度を向上させるために必要な課題の克服に取り組み，以下の成果を得た．１）日本列島周辺の海底地質情報の整備状況は，深度1000 メートル程度までの地質構造を網羅的に概観できるレベルにある．２）現状の海底活断層調査結果に基づく活動性評価は，断層により地層が切断され明確に上下変位が確認される場合については，被覆する地層の形成年代が把握されれば，陸域と同等レベルで可能である．３）海底において地形的には一連となる褶曲構造も，震源断層が活動した場合に変形が顕著に累積する区間として，セグメンテーションが可能である． ４）複数の平行，もしくは雁行する横ずれ断層については，地下深部における収斂を念頭に置いたフラワーストラクチャー全体を評価対象とし，この地下構造形態を捉えることが重要である． 海底活断層調査に基づく各断層セグメントの連動性評価が今後の課題となる．

概要 （英文）

Since the Great Hanshin Earthquake of 1995, earthquake-related research grants have been awarded to local governing bodies to conduct surveys on fault activities. Numerous unofficial investigations into active faults and predicting the magnitude of earthquakes have also been undertaken. Based on such a existing state, in this research, we examined four subjects described below to improve the reliability of submarine active fault evaluation.(1) Generalization and database construction of submarine geological information in the Japanese-Islands coast seabed.(2) Verification of the technical level of submarine active fault investigation, and the check of the reliability of the activity evaluation technique of a submarine active fault.(3) Examination of the activity evaluation technique to submarine fault related fold.(4) Examination of the activity evaluation technique to submarine strike-slip fault. Consequently, we obtained the result described below.(1) We can grasp the geological structure around the Japanese Islands comprehensively to 1000m under the seabed using the existing submarine geological information. However, the detailed age information about marine sediment is insufficient.(2) When the age of the deposition layer which covers fault has been grasped, the level of fault activity evaluation based on the present submarine active fault investigation is the same level as the case of land.(3) Long fold in topography as well as an active fault can be divided morphologically to a short segment. However, the segmentation of fold shows the section which deformation of the stratum accompanying the displacement of earthquake source fault accumulates notably. The activity section of earthquake source fault itself is not shown.(4) When many submarine strike-slip faults which go side by side are distributed over the seabed, it is the most important subjects for activity evaluation of them to grasp the subsurface structural forms like the flower structure typical of them. The social request to active fault investigation is earthquake magnitudes evaluation. For that purpose, the fault evaluation based on submarine active fault investigation must improve from the activity evaluation for an individual fault to interlocking evaluation of each fault segment.

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