[S-CG62] 島弧の構造・進化・変形とプレート沈み込み作用

[SCG62-P06] 反射法地震探査データからみた富山トラフ周辺のoblique rift系の再活動

*石山 達也¹、佐藤 比呂志^1,2、加藤 直子³ (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)

キーワード：oblique rift、reactivation、active fault

We analyzed spatially varied structural characteristics of reactivated oblique failed rift system in Hokuriku region at the southwestern extension of the northern Honshu rift system (NHRS) (Sato et al., 2004), by use of onshore and offshore seismic reflection data including a new onshore deep seismic profile (Ishiyama et al., 2023; Ishiyama et al., in prep.). Combining geology and geomorphic limitations with rift-related structures seen in the seismic dataset, polyphase reactivation has occurred since the late Miocene, resulting in the formation of complex fault networks. Major map-scale structures within the rift system's E-W trending segment are separated into NNE, NS, and E-W trending faults. Among them, NE trending reverse faults, such as the Morimoto-Togashi fault zone (MTFZ), appear favorably oriented to the current stress field and commonly exhibit Quaternary activity, whereas NNE and E-W trending faults exhibit late Miocene activity before quiescent in the Quaternary, most likely as a result of their unfavorable orientations. A moderately east-dipping reverse fault plane that is overlain by a monocline of Miocene to Pleistocene sedimentary strata is revealed by our old and new seismic reflection profiles across the MTFZ. T rishear fault-propagation modeling of the deformed units suggests that the monocline formed above positively reactivated normal faults. Combined with the kinematic histories of nearby NNE and E-W trending faults in the E-W segment of the oblique rift, this finding suggests that the MTFZ and subparallel reverse faults originated from secondary structures within a major shear zone connected to the NE trending rift system extending from the Toyama trough.Re