Formation Processes Based on GIS Analysis of Erosional Low-relief Surfaces and Active Faults in the Western Chugoku Mountains, Southwest Japan

A detailed analysis is conducted using digital elevation model (DEM) data and aerial photographs of low-relief surfaces and active faults distributed in the western Chugoku Mountains. In particular, geographic information systems (GIS) are used to identify low-relief surfaces and provide a clear, detailed image of their distribution. The analysis suggests that many parts of Surface I may have been flattened by periglacial action from the ridges of mountainous spines with a certain altitudinal difference. Surfaces II-1, II-2, and III-1 may have originated from valley floor plains formed by rivers that crossed the spine mountains in the past. Therefore, in this area, the hypothesis that the difference in height between high- and medium-level low-relief surfaces was caused by crustal deformation accompanied by fault activity can be rejected. Furthermore, preceding rivers probably flowed north to northwest toward the Sea of Japan. Many parts of Surfaces IV-1, IV-2, and IV-3 may have originated from floodplains formed by rivers in the current river system or in the relatively recent past. In this area, the water system has changed significantly due to the uplift of the mountainous spine and various low-relief surfaces have formed. Furthermore, the activity of main faults caused displacements of each low-relief surface, forming a topography of steep cliffs on the northwest sides of spine mountains, whereas a mountainous topography descending in a step-like manner formed on the southeast side.