Spatial comparison of two high-resolution landslide inventory maps using GIS-A case study of the August 1961 and July 2004 landslides caused by heavy rainfalls in the Izumozaki area, Niigata Prefecture, Japan

Abstract

The spatial distribution of shallow landslides in the Izumozaki area, Niigata, caused by the heavy rainfalls in August 1961 and July 2004 was investigated using high-resolution ortho-photoimagery and a 2-m DEM. We found that the number of the August 1961 landslides is more than twice the July 2004 landslides. More than half of the July 2004 landslides (about 70% as the number ratio and 54% as the area ratio) were primary landslides. These primary landslides seem to occur randomly regardless of the geological structure of the stratum. The large landslides which occurred in July 2004 were often expanded landslides immediately higher than the August 1961 landslides. These expanded landslides often occurred on daylighting dip slopes. Among the July 2004 landslides, the ratio of landslides along roads is very high compared to 1961 (1961: 4.2%; 2004: 16.4%).