Abstract
Several faults which cut Pleistocene sediments have recently been discovered in Aimi Town to the south of Yonago, Tottori Prefecture, southeast Japan. They are developed along the western margin of a plateau of Pleistocene alkaline basalt (Tsuruta basalt), which rests unconformably upon Paleogene granite. Trenching investigations show that one of these faults (Asakane Fault) has been reactivated seven times, with four of the events in the period 130,000yrs B. P. to 2500yrs B. P. Although the fault has secondary fractures which indicate lateral displacement, it cannot be determinded if the displacement is dextral or sinistral.
The surface of the unconformity between the Tsuruta basalt and granite is partially inclined at a high angle, links with a fracture in granite, and is accompanied by breccia at its foot, and so thought to have been a small cliff caused by faulting. The Asakane fault is inferred to have become active just before the effusion of the Turuta basalt, because it has the same geological characteristics with steeply inclining unconformity. Moreover, it is probable that the Asakane fault is a reactivated fracture, which formed initially as a concentric fracture around a collapsed basin of early Miocene age.
