Recently, it became possible to generate a high-resolution digital elevation model (DEM) with the airborne laser scanner (LiDAR). Because the airborne laser scanner can obtain the altitude under the vegetation, we can gather the geomorphologic information that is more detailed than the map through the use of aerial photogrammetry. This has made precise visualization of topographic features easy.
We made the slope angle map from an airborne laser scanner digital elevation model (ALSDEM), and examined the effectiveness of plural technique. By adding information of the altitude to the slope angle map, we were able to develop a new mapping technique, and named it the ELSAMAP (Elevation and Slope Angle Map). ELSAMAP is generated by superimposing the elevation and slope angle information, which are represented in graduated color phase and gray scale, respectively. It is considered to be an effective method of topographical visualization that will support geomorphologist, allowing intuitive and correct understanding of relative location and vertical interval of the topography. Furthermore, the adjustment of the altitude indication colors and the brightness of slopes ensure the visual highlighting of the landforms according to respective purposes.
We examined the Tokachi-Plain Fault Zone in Hokkaido, Japan as a case study of the topographic reading using ELSAMAP. We made several ELSAMAP which showed the microtopography of the area possibly displaced by an active fault. Using ELSAMAP, we were able to identify in detail the different topographic features such as erosional and depositional landforms on the terrace surface. As a result, in the northern part of the Tokachi-Plain Fault Zone, we recognized a low cliff, which had been recognized as the Inaho Fault by existing documents, was not an enough evidence of the displacement of the active fault. We also identified a fragmentary geomorphic surface in a hilly area of the Kochien Fault in the southern part of the Tokachi-Plain Fault Zone, and estimated the height of displacement with high accuracy. Topographic reading with ELSAMAP combined with the detailed terrain analysis with ALSDEM can give reliable information regarding fault displacements and improve the resolution of age estimates in an active fault study.
ELSAMAP is an effective tool in visualizing topographical features especially in interpreting slight changes ofaltitude on the ground, such as visualizing in detail the microtopography in low land or terrace and broad deformation of ground and volcanic topography.

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The slope failure and debris-flow occurred on the Rasho tunnel end of route 45 with the rain on 11 July 2002. The geological setting on this area is decomposed granite in the granites of the southern Kitakami mountains. The area of past slope failure and vegetation change was judged by the aerial photo interpreting. Then, it turned out that there is much past slope failure at the place of the same vegetation classification as the slope failure in 2002. The unstable range was specified by the investigation on the other side slope (S-2) by the portable dynamic cone penetration test. The characteristic by the vegetation of the other side slope and the thickness of the decomposed granite was similar with the slope failure in 2002.

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[in Japanese]

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