The Itoigawa-Shizuoka Tectonic Line (ISTL) lies along western margin of the northern Fossa Magna and forms an active fault system (Matsumoto Basin Eastern Margin Fault) that displays large vertical slip rates (ca.2- 3 mrn/yr). In this paper, we estimated surface deformation pattern in the Saigawa Hills, which locates to the east of the ISTL, using height of fluvial terraces along the R. Sai-gawa, R. Omi-gawa, and R. Aida-gawa. Next, based on obtained surface deformation pattern and estimated subsurface fault geometry of the active fault system using seismic reflection survey and geologic structures, we discussed a relationship between subsurface activity of faults and surface deformation. As a result, we concluded that deformation pattern of ground surface in the Saigawa Hills is regulated by subsurface fault geometry of the active fault system (flat-ramp structure), and that relative uplift has occurred above a subsurface ramp of the active fault system. By this research, we show the possibility that the activity of an active fault system with complex subsurface geometry can be evaluated based on deformation of ground surface in geomorphologic time scale.
