Departmental Bulletin Paper 〈Research Reports〉Topographic characteristics of rainfall-induced shallow landslides on granitic hillslopes: A case study in Hofu City, Yamaguchi Prefecture, Japan

YAMASHITA, Kumiko  ,  HATTANJI, Tsuyoshi  ,  TANAKA, Yasushi  ,  DOSHIDA, Shoji  ,  MATSUSHIMA, Takashi

13pp.23 - 29 , 2017-12-22 , University of Tsukuba, Doctoral Program in Geoenvironmental Sciences, Graduate School of Life and Environmental Sciences
Heavy rainfall on July 21, 2009 caused many shallow landslides in Hofu City, western Japan. This paper reports topographic characteristics of shallow landslides in two areas: Yahazugadake area underlain by granodiorite (Gd area) and Tsurugi-kawa area underlain by granite (Gr area). Landslide density (numbers/area) of Gr area was much higher than that of Gd area. For both areas, the landslides had local slopes of 17–46 degrees and specific contributing areas (i.e. drainage area divided by landslide width) of 11–560 m, and there was a weak inverse correlation between local slope and specific catchment area. The landslides in Gd area have steeper local slope and larger specific contributing area than those in Gr area. Field and laboratory measurements of soil properties revealed that the Gr area has thinner soil and higher shear strength for slip plane. Differences in shear strength as well as the hydrological characteristics due to contrasting soil depths are the possible causes of contrasting landslide densities between Gr and Gd areas.

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