Japan is an island chain located off the north-western rim of the Pacific Ocean. Generally, in Japan, precipitation occurs mostly during typhoon seasons on the Pacific Ocean side, and in winter (heavy snow) on the Japan Sea side. This paper deals with synoptic descriptions of failures that occurred in various areas, along with rainfall and failure relationships during the typhoons of 2004 in Shikoku. In this paper, the effective amount of rainfall that triggered landslides in the Shikoku Island during these typhoons was identified along with information of occurrence time and landslide-triggering thresholds for Shikoku Island were interpreted.
Experience shows that landslide occurrences on hill slopes have very close relationship with availability of water. As a result, many types of landslides occur after heavy rainfall in tropical and temperate climatic zones (Jakob and Weatherly, 2003). Landslides triggered by rainfall occur in most mountainous landscape of the world. They pose a significant natural hazard and they have a high damage potential. Many statistically meaningful analyses have been published to demonstrate threshold values of rainfall and landslide triggering (e.g., Caine, 1980; Wilson and Wieczorek, 1995; Crozier, 1999; Aleotti, 2004; Guzzetti et al., 2007). Within the last few years, many studies focusing on rainfall thresholds for triggering landslides with hydroclimatic condition, antecedent rainfall (Crozier, 1999; Glade et al., 2000), and hydraulic conductivity (Terlien, 1998) were conducted. In this context, this paper describes some scenarios of rainfall-triggered landslides that occurred in Shikoku Island, Japan (north western Pacific Ocean side) during various typhoon events in 2004. It is 225 km long and 50-150 km wide, with more than 80% of land consisting of steep mountain slopes. It is a heavily forested mountainous region of Japan. It has a few plain areas along the coastal lines and elevated peaks in the central part.
