Slope Evolution of a deep-seated landlide is investigated by using the data of borehole survey, groundwater tracing and seismic prospecting at the Taninouchi Landslide, southwestern Japan. Explanation of geological structure and movement of the present landslide which is located at the lower part of the whole landslide slope are also tried through consideration of slope evolution processes.
Double ridges at the head of landslide slope were formed by an ancient large-scale rock slide which formed the whole landslide slope. Because there are thin oxidized detritus or fragmental rock layers just under the slip plane at the toe part of landslide slope, the rock slide mass covered the ancient ground surface, bulldozing clayey schalstein layer along the slip plane. Displacement by the rock slide amounts around 150 m. Longitudinally S-shaped slip plane behind the rock slide-covered ground is considered to have been formed by passive rupture of the toe part of landslide at the beginning. River channels were also shifted and thrust up to the present locations.
Discontinuity of the schalstein layer between the toe part of landslide mass and the surrounding slopes is explained by the displacement of softened schalstein toward downslope along slip plane.
Geological structure and feature of slip plane (Figs. 2, 8) along which the present landslide occurs can be understood through consideration of the slope evolution processes described above. Surfacial distribution of the present landslide movement namely tension and compression is correspondent to the feature of the slip surface. Present landslide phenomena should be understood in relation to landslide slope evolution processes.

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A basic model of the slide to slope failure is derived from three assumptions . The basic slide equation in tertiary creep is given as following: υ=a υ+bυ². Here, υ is the velocity of displacement, υ the time differential of υ, a and b the constants. This equation expresses the acceleration mechanism of soil mass to slope failure and is available as a model of slope failure prediction. For friction coefficient (μ) theμ-υ relationship obtained shows the same tendency as the result of Dieterich, that is, μ decreases exponentially if υ increases. Lastly, the mutual relation of μ, υ and displacement (l) become clear by use of coefficients a, b and other physical parameters.

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This paper follows paper (I) with the same title and discusses the mechanical properties identified by the in-situ rock tests, then gives a conclusion based on both papers.
The conclusion is as follows:
(1) Strength and ductility of the landslide-mother-rocks do not necessarily increase or decrease in the sequence of geologic formation, and such transition of mechanical properties corresponds to the regional difference in the types of landslide movement.
(2) Mechanical properties of landslide-mother-rocks have a strong influence on the type of movement. On the other hand, since their qualitative properties are succeeded to the secondary or tertiary landslide debris, the type of secondary or tertiary landslide movement is also regionally different.

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This paper concerns an estimation of reach distance of debris flow by slope failures due to rainfall. The analyze is conducted by a quantification theory which bases on the inspection procedure of difference between the categorized adjacent average values. The main items governing reach distance of debris are shown as failure height, longitudinal slope profile and accumulative rainf all amount. The multiple correlation coefficient is 0.8470, and 70 % of the reach distance variation for all slope failures can be explained by the used items in this study.

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In the Abashiri-Kitami-Tsubetsu area, totally 1, 765 landslide landforms were identified through aerial photographs of which 290 (16.4 %) were found in the Mesozoic area, 1, 388 (78.6 %) in the Tertiary area, 37 (2.1 %) in the Quaternary pyroclastic area, and 50 (2.8 %) in the volcanic area.
In the Mesozoic area, most landslide landsforms are found sporadically in the area consisting of Jurassic to Cretaceous “green rocks, ” and most of them are small-scale debris-slumps (A type), debris-slides (F type) or debris-flows (G type).
In the Tertiary area, most landslide landforms are found concentrically in the area underlain by Oligocene to Miocene strata. They consist mainly of alternating beds of shale and soft siltstone, and contain intercalated tuff beds, and are featured by prevalence of folding structures associated with faults. Most of them are small-scale debris-slumps or debris-slides. Moreover, also recognized are large-scale rock-slumps (B type) and rock-slides (E type), both of which are found along faults and/or axes of folds. More than 60 percent of landslide landforms is dip slope slide type.
In the pyroclastic area, small-scale debris-slides are found sporadically on the steep slopes which are composed of sand and gravel, and the overlying pyroclastic flow deposits.
In the volcanic area, some large-scale rock-slump is found at the margins of Quaternary subaerial lavas, forming a cap rock structure.
In the Abashiri-Kitami-Tsubetsu area, the distribution, sizes and shapes of landslide landforms, and directions of landslide mass movement reflect landforms and geological conditions, such as lithology, lithofacies and geologic structures of bedrock geology.
Some recent landslide disaster was caused by partial or entire removal of older loose landslide mass, triggered by natural factors, such as thaw, heavy rain and earthquake, and artifical factors. Therefore, much attention should be paid to presence of landslide landforms from the viewpoint of landslide damage prevention.

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Land use are one of the remarkable indicator of the ground water condition and landslide activity. For example, rice field and cryptomeria grove are often assumed to be a sign for wet soil condition i. e. high ground water level, and it makes soil strength lower. Therefore, this kind of muggy area is apt to provide landslides, and vice-versa. On this point of view, land use has been studied as one of important factor to distinguish landslide prone area from other safer one in the remote sensing methods.
In this study, land use characteristics in eastern Chugoku district including northern Hyogo, Tottori, and northern Okayama prefecture are studied in terms of relative frequency “S” to each land use type. Here, S=NiL/Ni and NiL: land use frequency on landslides, Ni: land use frequency in the area investigated. The results of this study imply orchard or dry field as well as residential area is prominent in land use on landslides.
Rice field is only third in it, and oak wood which appears rather dry land than cryptomeria is remarkable.
Hence, it is not insisted that all land use feature on landslide in the area studied is related to the wet soil condition. It is important to consider about this results when landslide assessment is carried out in this area with a kind of remote sensing method.

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[in Japanese]

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