Landslide Periodicity and Prediction of Potential Landslide Sites

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Shallow landslide repeatedly occurs at a same slope site as a principal factor of slope development in forested drainage basins under warm and humic climate. in this type of landslide, recurrence of the landslide at the same slope site requires formation of the topsoil as sliding materials.The subjects of the study are to make clear the mechanism of landslide periodicity and to predict the potential sites for the shallow landslide based on the landslide periodicity.The results are summarized as follows;1. Many newer and older landslide scars have formed on steep slopes of two research areas, kagoshima-shi and shibisan, kagoshima prefecture, japan, composed of pyroclastic flow deposits and decomposed granite, respectively. The recurrence intervals of landslide at the same slope site are more than 80-100 years at the kagoshima-shi research area and more than 200 years in the shibisan research area, respectively.2. The topsoil has reformed on the landslide scars with lapse of time associated with invasion of plants. The formation of topsoil is mainly due to physical and mechanical processes during a period of less than 100 years after landsliding at the pyroclastic flow deposits area. While the formatiom of topsoil is due to chemical processes as well as the physical and mechanical processes at the decomposed granite area. The potential landslide sites which are old landslide scars with deep topsoil are predicted based on the landslide periodicity. The topsoil is closely related the vegetation on the scars, therefore the potential landslide sites can be predicted by using of the vegetation as an index.