Abstract
Some faults run through the sliding areas in Nagano Pref. The faults affect the landslides occurring along them. I have investigated the landslides taking place along Nakayama, Otari and Mochigyo fault in which the fault structures are clearly seen and the effect of faults on the landslide occurrence. The crushing of basement rock due to faulting in most conspicuously found in the lutaceous rock but is not so remarkable in the sandstone and conglomerate. The lutaceous rocks are crushed in meshes by faulting and the crushed rocks are softened to induce the landslide.
The shape of the sliding area is dependent on the crossing of the direction of the fault and that of the landslide; when a landslide occurs parallel to the direction of the fault, a narrowly depressed landform is often produced. Even in places where the basement rock is crushed deeply by faulting, the depth of the sliding surface is shallow and less than 10 meters: since the repetition of the sliding activity is remarkable and the colluvial soilis deposited in the lower of the sliding area, the depth of the sliding plane is apt to become great. Groundwater is often interrupted by the fault and this stored groundwater, in many cases, promotes the landslide occurrence.
