Abstract
In this study, we have reinvestigated the spatial distribution of shallow landslides in Izumozaki area, Niigata, caused by the heavy-rainfall in August 1961 and July 2004, by analyses using high resolution ortho images and a 2-m DEM. The results are as follows. The landslides occurred in 1961 are more than twice that in 2004. Among the 2004 landslides, the ratio of the landslides along roads is very high (1961: 4. 2%; 2004: 16. 4%) . More than half of landslides in 2004 (about 70 percent as the number ratio, 54 percent as the area ratio) were primary landslides in a valley side slope not including the 1961 landslides. Primary landslides occurred randomly on outfacing slopes and infacing slopes, if lithological and topographic conditions were the same. Most of the1961 landslides expanded due to the 2004 rainstorm developed on the upper part of slopes. These enlarged landslides tend to occur on slopes with daylighting beds except for the Nishiyama Formations.
