Abstract
The 2-D electrical resistivity prospecting (1, 000m in survey depth) was conducted in order to investigate the subsurface structure of the volcanic body and the large-scale collapse site at the Shirataka volcano, Yamagata Prefecture, northeast Japan. As a result of the prospecting, the resistivity structure around the Shirataka volcano shows two layer systems. According to a surrounding geological structure and the geology of borehole cores, the upper layer of high resistivity corresponds to the volcanic product and debris avalanche deposit, and the lower layer of low resistivity corresponds to the Tertiary which is the basement of the Shirataka volcano. The hydrothermal alteration part, recognized as a low resistivity part which is distributed widely from surface to deep in the Bandai volcano, is not found in the Shirataka volcano. This result supports the opinion that an immediate cause to collapse the volcanic body is not volcanic activity but landslides.
