Research on Geologic Control of Slope Movements --- Analysis of Lithology and Geologic Structure of Basement Rocks

点击翻译按钮获取中文摘要

We have mainly investigated slope movements of Cretaceous to Neogene formations in Kinki and Shikoku areas, for example the Kobe Group and the Hokutan Group of Neogene age, and the Shimanto Belt of Cretaceous to Paleogene age. By means of image analysis of aerophotos, we have measured and analyzed many geomorphological and geological data of slope movements in the specific areas mentioned above. Particularly, we made clear the relationship between slope movements and lithology and/or geologic structure of basement rocks. The term "slope movement" means all kinds of moving phenomena of materials found on slopes, including landslides.The following geologic and geomorphologic factors are commonly pointed out as the generating factors of slope movements. (1) Many large-scale slope movements usually occur in fine clastic sediments, such as mudstone or fine tuff. This is called the lithological control. (2) The masses are mainly composed of debris and soil derived from basement rocks, and sh … More ow the secondary movement. On the other hand, new slope movements occur by artificial cutting of Slopes in order to construction of roads. (3) Generally, a sliding surface includes abundant clay minerals, such as montmorillonite, illite and chlorite, and its formation is closely connected with action of groundwater. It is difficult to analyze flow conditions of groundwater in hilly and mountain areas. (4) Many sliding masses move along the dip direction side of bedding plains of basement rocks. This is called the "Nagareban' structure type, and show the typical structural control. On the other hand, a small number of slope movements, which belong-the "Ukeban type, slide along the opposite side of the bedding plains. (5) The development of slope movements is not always concerned with faults. However, remarkable tectonic movements widely brought about weathering and fracture of rocks. This gave great influence to generation of slope movements. (6) A large number of slope movements occur on slopes with specific slope angle, namely 10ﾟ-15ﾟ in the Neogene formations and 25ﾟ-30ﾟ in precretaceous formations. These angles are small compared with slopes without slope movements, and then it is pointed out that their occurrences form gradient slopes. (7) The slope movement areas are often used as rice field or farms, because of abundant water. Less