Abstract
The geology of the Sattomonai-Qkushunbetsu slide area consists primarily of andesitic or dacitic lavas and volcaniclastic rocks from the Middle Miocene, Upper Miocene, and Pliocene Series, as well as Pliocene andesite and rhyolite dikes. The Hydrothermal alteration zones that formed in this slide area during the Pliocene Age consist of smectite, zeolite, chlorite, interstratified illite/smectite, and illite zones. Three ancient slides are known to have occurred in this area. One is distributed on the fine tuff of the Upper Miocene Hanakushibe Formation, which is a smectite zone, and the other two are primarily distributed on the lapilli tuff of the Lower Pliocene Ikurushibeyama Lava, which is an interstratified illite/smectite zone. The ancient slides in these hydrothermal alteration zones are believed to have been caused by a swelling of clay minerals such as smectite or interstratified illite/smectite.
An understanding of geophysical stresses in hydrothermal alteration zones is useful when evaluating contemporary slide hazards and constructing hazard maps of ancient hydrothermal fields.
