Study on structure of fracture zone and landslide structure of fracture zone landslide in the Sambagawa metamorphic belt, Shikoku

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Fracture zone landslide defined by Koide(1955) is a collapse of slide type which has features that the landslide moving body breaks into debris, the mass of debris falls down on mountain slope, and it often dames up stream of river. Fracture zone defined by Koide(1955) is a zone of crushed rocks characterized by fractures with a polished and slicked surface. However Koide asserted fault gouge consisting of fault clay and fault breccia to posses no requirement necessary for fracture zone. Many of the fracture zones named after Koide run through in accretionary complex. Fractured rocks satisfying the criterion of recognition for fracture zone are fractured serpentinite, fractured greenstone and pelitic merlage fractured along a polished scaly cleavage.Among many geologists and geo-technicians it has been seemed that landslides in the Sambagawa metamorphic belt are typical of the fracture zone landslide, but they are not a collapse of slide type but a slow moving and repeating landslide. Fractured rocks occurred in the Yoshino river-Kino river fracture zone and the Mikabu fracture zone are not tectonic origin but non-tectonic origin due to gravitational creep tilting.This paper made clear that large-scaled collapse caused by heavy rainfall of the No. 10 typhoon in 2004 at Azue, Naka-cho, Tokushima Prefecture is atypical fracture zone landslide occurred in fractured greenstone.