The airborne magnetic survey results are compared
to the geological structures of the major landslide
areas and other regions:
1. Oshiba: The landslide area clearly appears as
a low magnetic anomaly area by RTP transformation.
The Funatsu granitic rocks are obviously altered by
hot water from deep underground to the surface, and
especially significant alteration by hot water as well
as extremely low magnetic anomaly was found at the
middle of the slope. A hydrothermal alteration zone in
the bedrock is found after RTP transformation. Moreover,
two Igw locations show very different magnetic
strengths. Based on geological reconnaissance as well
as boring survey results, the layer thickness of Igw
reached a maximum of 100 m near the bottom, whereas
the Igw thickness was thinner in the upper part, reflecting
the influence of the high magnetic anomaly
of the Funatsu granite.