[S-CG50] 島弧の構造・進化・変形とプレート沈み込み作用

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

*石山 達也¹、佐藤 比呂志²、加藤 直子³、越谷 信⁴ (1.東京大学地震研究所、2.静岡大学防災総合センター、3.日本大学文理学部、4.岩手大学理工学部システム創成工学科社会基盤・環境コース)

キーワード：再活動、リフト、活断層

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.