Abstract
Three major N-S trending active structures, the Tobetsu fault and Nakagoya semi-dome, the Shunbetsu anticline, and the Kaigan anticline, from east to west, occur in the Ishikari Hills. Middle to Late Pleistocene terraces are widely distributed overlying these active structures and they are good reference for the late Quaternary tectonic movements. The mean vertical displacement rate of the Tobetsu fault and Nakagoya semi-dome, the Shunbetsu anticline, and the Kaigan anticline are over 0.6 to 0.7mm/year, over 0.4mm/year, and about 0.1mm/yr, respectively. The late Quaternary anticline axes of the Kaigan anticline and the Shunbetsu anticline occur on the eastern side of the Miocene to Lower Pleistocene anticline axes. On the Shunbetsu anticline, the shape of Pliocene to Lower Pleistocene is symmetrical, but their overlying terraces are deformed as asymmetrical folding. This change of deformation pattern occurred during the early Pleistocene to the later middle Pleistocene. Small faults and folds which locate near the axes of the Shunbetsu anticline and Kaigan anticline, and sink the anticline axis side have small displacement rate, and are interpreted to be subsidiary flexural slip faults.
