報告書番号

N07017

タイトル（和文）

数値標高モデルを用いた段丘面形状の定量化と段丘対比への応用

タイトル（英文）

Quantification of morphological properties of terrace surface using digital elevation model and its application to stratigraphic correlation of terraces

概要 （図表や脚注は「報告書全文」に掲載しております）

数値標高モデル（DEM）から求めた地形量により段丘面の侵食の程度を定量化する手法を提案した．地形量は段丘の年代が古くなるにしたがって変化し，その傾向は侵食による段丘の地形発達過程と対応することから，段丘面の侵食の程度を定量的に表現できることが示された．さらに，地形量に基づいて推定した段丘の層位関係は空中写真判読による地形調査結果と整合し，対比指標として10万年程度の分解能を有することを示した．また，品質の異なるDEMから算出した地形量を比較検証することにより，段丘対比に適した標高データの精度とDEMの解像度を提案した．

概要 （英文）

Uplift estimation during late Quaternary is required for site selection of geological disposal facility of high level radioactive waste(NUMO, 2004). The terrace level and/or the difference in elevation of terraces is a good indicator of uplift. Therefore, a reliable method of terrace correlation and chronology is a key issues. Air-photograph interpretation is generally carried out in the early stage of a terrace investigation. However, a terrace classification often depends on the observer's qualitative interpretation. In order to improve objectivity of geomorphic investigation with air-photograph interpretation, we examine to quantify the morphological properties of terrace surface by some morphometric variables that are computed from Digital Elevation Model (DEM) . In this study, four morphometric variables (average slope, average laplacian, remaining ratio of the terrace surface and average depth of the erosion) were calculated using data sets of terraces of which chronological data are clearly described. The relationship between these variables and terrace ages shows constant tendencies respond to the geomorphological process caused by the erosion. To examine capability of morphometric variables as an index of terrace correlation, regression analysis were carried out. Regression age estimated from morphometric variables allows to classify terraces in correct sequence, and the error with observed age falls up to 100,000 years. In addition, to discuss appropriate qualities of DEM for terrace correlation, we used three different elevation data to create DEM : 1) aerial photogrammetry data; 2) airborne laser scanner data; 3) 1:25000-scale contour map. By comparing analysis results of each DEMs, we show suitable qualities of elevation data and DEM grid size to represent the degree of erosion correctly.

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