抄録
This study is a statistical analysis of morphological characteristics. The characteristics are mainly derived by a standard GIS application on vector polygons representing the outlines of landslides (hereafter “landslide polygons”) delineated on a best available Digital Elevation Model (DEM) with 0.5 m resolution. The focus of the study is to gain new insights into the description of morphological features calculated by a simple GIS based on LiDAR data, which have improved dramatically in recent years. The study area is the area where more than 7,000 landslides were triggered by the 2018 Hokkaido Iburi Eastern Earthquake. The methods are as follows: (1) building materials in vector and raster format suitable for GIS calculation, (2) deriving statistics of each geomorphological feature, and (3) analysing statistical relationships between morphological features. As a result, some distinctive features were obtained. For example, (1) the average ratio of length to specific height was larger than that of previous landslides, and (2) the ordinal direction of the landslides was most frequent in the south-east direction, where crustal deformation was observed, and distributed in the east-west direction, where the amplitude of the velocity waveform of earthquake motion was larger. Other practical observations confirmed in this study are: (1) the applicability of valley openness estimated from contours for the evaluation of slope concavity instead of plan curvature calculated by GIS, and (2) the applicability of the ratio of soil surface thickness to the width of landslide blocks for preliminary risk assessment in the light of morphological characteristics. On the other hand, some important aspects were not clear enough to obtain conclusive results and remain for further study, such as (1) the subdivision of landslide polygons into collapse areas, run-out areas and accumulation areas, and (2) the study of hydrological processes in slopes and soil structures. The latter two have been removed from the current scope.
