抄録
Building damage resulting from unequal settling caused by earthquakes occurs often on embankments and along cut-and-fill boundaries in hilly areas. To predict and prevent damage, determining the location of cut-and-fill boundaries is crucial. Boundaries can be determined by comparing digital elevation models (DEMs) of present-day and old terrain. The accuracy of the boundary is dictated by the accuracy of the old terrain data, because present-day 5-m DEMs created from airborne lidar are highly accurate. The Geospatial Information Authority of Japan (GSI) has published procedures formeasuring old terrain, but accuracy is not addressed directly. We create 5-m DEMs from a 1:3000-scale old topographic map published in 1956 and from aerial photographs taken by the GSI in 1965, by a private corporation in 1956, and by the US military in the late 1940s, and validate their accuracy by comparing unchanged areas. There are fourmain outcomes. (1) The highest accuracy (SD = 0.6 m) is achieved using the aerial photograph taken in 1965. The lowest accuracy (SD = 1.14 m) is obtained using the 1:3000-scale topographic map. (2) The accuracy of photogrammetry depends not only on the scale of a photograph but also on the base-to-height ratio. (3) Allmeasures of accuracy are within the range specified in the GSI manual, but better accuracy might be achieved using 1:20000-scale photographs. (4) The accuracy provided when using the 1:3000-scale map is not satisfactory for predicting and preventing damage. Photogrammetry should be carried out where possible to determine the locations of cut-and fill boundaries.
