亀の瀬地すべり (その 1)

亀の瀬地すべりの地質学的背景

抄録

At the Kamenose Landslide Region, nine wells and tunnels were excavated from 1979 to 1979, in accord with the outcrop observation of the wells, landslide surface, geological stracture and characteristic of sliding zone were clarified. Therfore we can make suggestion of geological background for the process of the landslide development in detail.
On the whole, the process of the landslide development is controlled by following conditions.
1. Geology of this area consists of Ryoke granitic rocks and the Miocene Nijo Croup and the Plio-Pleistcene Osaka Group. Landslide took place in the Nijo Croup distribute enclosed by granite The Nijo Group that is consists mainly of andestic lava flow, pyroclatic rocks some intercalated tuffaceous sand stone and conglomerate, are divided into two formations disconformably. The lower formation is called Harakawa formation with Myojin lava, the upper formation called Jyogashiro formation with Dolokolo lava.
In the Shimizudani block, the western part of the Kamenose Landslide area, the slip surface is along disconformity between Harakawa formation and Jyogashiro formation.
In the Toge block, the eastern part of the Kamenose Landslide area, the slip surface is formed in the tuffceous sand and conglomerate called the Kamenose conglomerates which are intercalated with lava. By observing the sample from the slip surface original minerals of tuffceous rocks were altered and disturbed.
Therefore tuffceous rocks alter easily to clayey soil with bearing of ground water. The Upper lava has many open cracks and a good permeability. Then the groundwater is gathered at the bottom of, lava and tuffceous part between the lavas seemed to be formed easily to shear zone
2. The dip of Nijo Group is south-west. By the effect of gravity the upper lava slips along the tuffceous rocks. The tilted block that the north-west side of Yamatogawa fault dips south west, controlled by Neotectonic movement and it seems to continue now.
3. Divergence of landslide mass controlled by the faults and reliefe of the basement rock. The direction of slide and the activity is more or less different from each other.