Abstract
VLF-EM method and radioactivity prospecting were carried out in Bandai-san Caldera. The distribution and characteristic of fault system in Bandai-san Caldera occurred in 1888 eruption were made clear.
The results of these prospecting show that the fault systems is divided into three directions; north-south direction, northeast direction and east-northeast direction. The most prominent fault identified by this study was the north-south fault located within the central portion of the caldera. The northern extension of this fault appeared to be connected to the eastern scarp of Avalanche valley and the southern extension appeared to be under the peak of Kobandai-san which was destroyed by a volcanic eruption in 1888. Northeast and east-northeast faults cut across the caldera.
Considering the results of this study and other geological informations, it may be inferred that the northsouth fault was formed by intrusion of north-south dike. The directions of northeast and east-northeast fault are concordant with the ridge direction of Kobandai-san. The feature suggests that the northeast and the east-northeast fault are gravity fault caused landslide plane.
