[S-CG50] Structure, evolution and deformation of island arcs associated with subduction processes

[SCG50-10] Active tectonics of reactivated of rift-related structural elements: southwestern northern Honshu rift system

*Tatsuya Ishiyama¹, Hiroshi Sato², Naoko Kato³, Shin Koshiya⁴ (1.Earthquake Research Institute, the University of Tokyo, 2.Center for Integrated Research and Education of Natural Hazards, Shizuoka University, 3. College of Humanities and Sciences, Nihon University, 4.Department of Civil and Environmental Engineering, Faculty of Science and Engineering, Iwate University)

Keywords:Reactivation, Rift, Active fault

We provide an overview of structural characteristics of actively reactivated failed rift system at southwestern extension of the northern Honshu rift system (NHRS) (Sato et al., 2004), based on collected onshore and offshore seismic reflection data in the Hokuriku basin in recent years (Ishiyama et al., 2017ab; Ishiyama et al., in prep.). Based on these seismic reflection profiles, velocity structures from refraction tomography, and coupled geologic and geomorphic constraints on structures, stratigraphy and active deformation, we clarified that active tectonics in this region is a manifestation of reactivation of crustal wedges, normal faults, transfer faults and secondary structures within them originally formed during the Sea of Japan opening. These rift-related structures have experienced polyphase reactivation since late Miocene and subsequently formed networks of complex, NE to NNE and EW trending structures. Among them, structures which exhibit recent fault activities and modern seismicity including M~7 earthquakes such as 1948 Fukui (M7.1) earthquake, generally trend NE to NNE direction; they appear less favorably oriented to present stress field, suggesting high fluid pressures, low friction, and/or temporal fluctuation of regional stress field may play important roles in their reactivation. In this presentation, we elaborate examples of reactivated rift-related structures from the Hokuriku basin using both our and preexisting dataset, their geomorphic and structural characteristics, and implications from comparison with presently reactivated structures in other areas.