Some considerations concerning the mass movements and geological conditions in Japan.

Abstract

The present paper discusses the substantial difference between the kinematic picture of the landslides in Japan and that of the mass movements in Czechoslovakia, from the viewpoints of geotectonics and engineering geology. A representative kinematic picture of the landslides in Japan which is typical of arcuate islands, is largely different from the one in a platform or a stable land like Czechoslovakia. The difference can be ascribed partly to the climatic condition and partly to the quantity of strain picture of the rock mass itself. Especially the latter factor would be reflected clearly in the real aspect of the mass movements. On the other hand, it should be noted that the physical and chemical properties of the basement rocks are intimately related to the maintenance and continuance of a mass movement in that place, such as the gliding of huge blocks. In other words, whether or not the clay of the slip surface acts as a lubricant to help sliding of the overlying blocks will largely influence the form of the kinematic picture. The writers would like to propose, therefore, that a mass movement of this type is a result of the interaction of the distribution of discrete surfaces in the blocks breaking away from the natural ground and the lithology of the mudstone that constitutes the basement. As an additional remark the writers suggest that in view of the geological conditions, particularly the geotectonic history, of the Japanese island arc, a mass movement of the Czechoslovakia-type can develop in Japan according to the geologic structure and the rock factors, and the cause of the movement can be explained geologically and geotechnically.