The air]borne magnetic surveys are reported to determine the distribution of susceptible layers to landslide in the southwestern Toyama, including the boundary between the Hida belt and the green tuff region. The results show the strong magnetic anomaly for the igneous rocks but the weak magnetic anomaly for the hydrothermal alternation zone or thick colluvial deposits that are susceptible to landslide, and therefore determine the landslide areas in the Funatsu granitic rocks and the colluvial deposits in the Neogene formations. Further, there is a strong positive correlation between the boundary of the anomalies and the group of faults that divide granitic rocks and Neogene formation in the area. The air]borne magnetic survey is not affected by small variation such as intrusive rocks due to its relatively low resolution of less than several meters, suggesting that this technique could be a powerful tool for the first screening survey for the susceptible layers to landslide, although the magnetic properties of the regional rocks have to be clarified in advance.

Key wordsFhelicopter magnetic prospecting, magnetic structure, magnetic anomaly, landslide