Permalink : http://hdl.handle.net/2115/38145

JaLCDOI : 10.14943/gbhu.72.51

The Sarobetsu marshland, it is one of the vast marsh in Hokkaido, is constructed by the Teshio River and the Saribetsu River. Because of the maximum scale high moor of Japan, various vegetation and waterfowls breeding at the Penke and the Panke swamps, Sarobetsu marshland is registered in Ramsar Convention in 2005. But recently, drawing up the underground water by farmers, drain work at surrounding area to make farmland and invasion of Sasa (a kind of bamboo) make the marshland dry. Therefore, it is an urgent problem for the preservation of marshland environments. Geological Survey of Hokkaido (GSH) and Horonobe Research Institute for the Subsurface Environment (Horonobe-RISE) had started electrical and geological surveys to clarify the underground water structure in this area to maintain a balance of marshland and farmland. In the results, resistivity layer in this area is divided into five layers and the third layer is further subdivided into two layers. And also we can make four lines of two-dimensional resistivity model. Comparing with the resistivity model and geological data, we conclude that the layers I, II and III, are correspond to the alluvium, the layer IV corresponds to the basement, and the layer V corresponds to the Koetoi layer. From the depth contour map of the base of the layer III (or the top of the layer IV), the alluvium layer get sharply thinner as closer to the eastern hills. This area is meandering zone of Sarobetsu River and mostly corresponds to the Sarobetsu fault zone.