[S-CG49] 島弧の構造・進化・変形とプレート沈み込み作用

[SCG49-P04] 日本海のfailed rift systemの再活動による北陸地域のアクティブ・テクトニクス

*石山 達也¹、佐藤 比呂志¹、加藤 直子¹ (1.東京大学地震研究所)

By compiling regional geology, geomorphology and new and pre-exiting seismic reflection data, we define tectonic backgrounds of Quaternary strain accommodation in the southwestern Sea of Japan failed rift system (Hokurku region), where both active thrusts and strike-slip faults are predominant. We first recognized that the 1948 Fukui (M7.1), a devastating blind strike-slip earthquake, occurred within a Miocene rift-related transfer fault system that offset hangingwall basement blocks and overlying pre-rift units. New seismic reflection profiling collected to precisely locate the shallower extension of the 1948 seismic source fault successfully imaged strike-slip fault-related structures of Miocene and younger sediments just above it, suggesting its repeated fault activities, despite lack of both coseismic surface ruptures and geomorphic fault signatures. Considering the aforementioned regional structural framework, the blind active strike-slip faults generated the 1948 earthquake are interpreted as comprising Quaternary reactivated transfer fault system, which bound segments of active crustal wedges formed during the Miocene rifting (Ishiyama et al., 2017). This finding shows that both normal faults and transfer faults within reactivated failed rift systems simultaneously play important roles in accommodating permanent strains, fault activities and modern seismicity.