A lot of landslides distribute around the area of intrusive rocks, caprocks and so forth. In this paper relationship among slope angle, geology and landslide occurrence in this area is discussed. It becomes clear quantitively that relative frequency of landslide occurrence is heigh around areas of intrusive rocks and caprocks. With this results, a landslide hazard zonation method using slope angle and geology is proposed.

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Recent field surveying technique composed of electro-optical distance-meter and theodolite has enabled rapid and precise measurement of distant objects. To apply this technique to landslide monitoring, i. e., displacement observation of marked objects in landslide area, surveying station is constructed on safe and stable ground apart from the landslide realm. At this station, main terrain of the landslide should be observed, and surveying of the marked objects is carried on with an interval of several days or weeks corresponding to velocity of the landslide movement.
Change of three dimensional coordinates of the marked objects is furnished by succeeding surveyed data, so that behaviour of the landslide is detected by trajectory of marked objects on a horizontal or several vertical planes. Observing trace of each marked point on the horizontal projection plane, areal extent and main moving direction of landslide is distinguished. On a vertical projection plane parallel to the main moving direction, entire traces of marked points are examined.
When the traces show a tendency of concentric circles, we can treat the landslide as rotational movement. To find rotational center of concentric circles on the vertical projection plane, two analytic approaches, geometrical method and least square method are considered. In numerical analysis, least square method shows better convergence than geometrical method, but the latter has simplicity in computation.
In general, on vertical projection plane parallel to main moving direction of rotational landslide, shape of sliding surface analogizes with circle. Then using the above mentioned center of concentric circles and an obvious position of failure on main sliding surface, head scarp, toe buldge, sheared position in borehole etc., a circle is drawn on the vertical projection plane, which shows projected shape of main sliding surface of the landslide.
As an applicative example, landslide occurred at Komoro in Nagano prefecture in August, 1981 is analyzed, and remarkable notes are stated.

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Recently, design of public works in a landslide area trends to demand evaluation for landslide susceptibility from the viewpoint of prevention against disasters. A conventional method for this evaluation is carried out in the following manner. The first step is collection of data which characterize the feature of a landslide area with the aid of field survey, and secondly each area is empirically ranked for landslide susceptibility. However, this method requires such experience for landslide that of ten givse a different result of ranking in correspondence to the degree of experience. On the other hand, this paper proposes a new method applying the quantification theory to categorical data which are collected from field survey. A region of Shikoku district in Japan was dealt with, an evaluation map was obtained showing land slide susceptibility, and comparison was made between the present method and the conventional method. The result convictsus the reliability of the present method for evaluation of landslide susceptibility.

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