[H-DS12] Seismic hazards on subduction earthquakes and active faults in the Central Japan

[HDS12-P03] Slip direction of the the Enasan and Sanageyama-North Faut system

*Norio Shigematsu¹, Takashi Azuma¹, Rei Nakashima², Ken-ichi Yasue³, Ryo Tateishi³, Kosuke Nakamura⁵, Daisuke Hirouchi⁴ (1.Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 2.Research Institute of Geology and Geoinformation, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 3.School of Sustainable Design, the University of Toyama, 4.Faculty of Education, Shishu University, 5.Graduate School of Science and Engineering for Education, University of Toyama)

Keywords:the Enasan and Sanageyama-North Faut system, Slip direction, 3D virtual outcrop model

The Enasan and Sanageyama-North Fault system is an active fault with the strike of NE–SW and the dip of SE extending from Nakatsugawa City in Gifu Prefecture to the northwestern part of Toyota City in Aichi Prefecture. The slip directions of the fault have not previously been revealed, although a reverse fault component or a dextral sense of shear has been reported based on the topographic features. The slip directions of faults are an important factor to predict the earthquake damages due to the directivity effect of rupture propagation. The purpose of this study is to clarify the slip direction of the Enasan and Sanageyama-Norht Fault system based on the measurements of slickenlines on the fault plane.
The Enasan and Sanageyama-North Fault sysmem is exposed for more than 100 meters in the Maruhara Quarry located in Hara Yamaoka-town Ena City, Gifu Prefecture, and form a boundary between silt stones belonging to the Toyama Formation of the Iwamura Group and the gravel layer belonging to the Mashizume Formation of the Seto Group. In this study, we first constructed a 3D virtual outcrop model to figure out the features of the exposure of the fault for 80 meters, and then excavate 4 pits with width of 4 to 8 meters that cross the fault. We further construct 3D virtual outcrop models of the pits and the exposure of the fault for 80 meters again after the excavation using the technique of photogrammetry. These models enable us to make it easy to figure out the features of fault zone numerically. Then we are planning to measure the slip direction according to the fault zone structures.
We will make a presentation about the results of the study. This study is a part of MEXT Project of “Focused active fault survey on the Byobuyama, Enasan and Sanageyama fault zone (Enasan-Sanageyamakita fault zone).