17:15 〜 18:30
[SSS31-P22] チベット高原Altyn Tagh断層で発生した2014 Mw 6.9 Yutian地震による地震断層の共役Riedel構造
キーワード：Altyn Tagh断層、2014 Mw 6.9 Yutian 地震、共役地震断層、チベット高原
本講演では、2014年２月12日にチベット高原北部の Altyn Taghで発生したMw 6.9 Yutian地震に伴って現れた地表地震断層については報告する。
The Altyn Tagh Fault is located at the northwestern edge of the Tibetan Plateau, and is the largest active strike-slip fault in Asia with a total length of ~2000 km. The fault accommodates sinistral motion between the Tibetan Plateau and the Tarim Basin within the India–Eurasia collision zone. Although the Altyn Tagh Fault plays a key role in accommodating India–Eurasia convergence, little is known about its nature as a seismogenic strike-slip fault due to a lack of instrumentally recorded large earthquakes on the fault. The 12 February 2014 Mw 6.9 Yutian earthquake, which occurred in the Yutian region of the Tibetan Plateau, provides an opportunity to study the seismotectonic nature of the Altyn Tagh strike-slip fault system.
Field investigations reveal that the 2014 Mw 6.9 Yutian earthquake on the left-lateral strike-slip Altyn Tagh fault system, Tibetan Plateau, produced a ~25-km-long surface rupture zone that contains conjugate Riedel shear faults (Li et al., 2016). The co-seismic surface ruptures occurred mainly along two parallel ENE-trending active left-lateral strike-slip faults. Rupture also occurred in a conjugate, WNW-trending zone along an active right-lateral strike-slip fault. The ENE-trending ruptures are concentrated in a zone of <500 m wide and ~25 km long, and are characterized by Riedel shear structures including distinct shear faults (Y) with a maximum sinistral displacement of ~1 m, right-stepping en echelon cracks, and mole tracks. In contrast, the WNW-trending ruptures occur within a zone of up to 1.5 km wide and ~4 km long in the jog area between the two parallel ENE-trending faults, and this zone is characterized by discontinuous shear faults with dextral displacements of <0.5 m, left-stepping en echelon cracks, and mole tracks, all oriented oblique to the ENE-trending rupture zones at an angle of 30°–40°. The lengths and displacements of the co-seismic surface ruptures measured in the field are comparable with those obtained from the empirical relationships between magnitude and co-seismic surface rupture length and displacement. Our findings demonstrate that the co-seismic conjugate Riedel faulting was controlled mainly by pre-existing active faults of the Altyn Tagh fault system, reflecting the present-day tectonic stress field associated with the ongoing penetration of the Indian Plate into the Eurasian Plate.
References
Li, L., Pan, J., Lin, A. (*corresponding author), other 8, 2016. Co-seismic surface ruptures associated with the 2014 Mw 6.9 Yutian earthquake on the Altyn Tagh Fault, Tibetan Plateau. Bulletin of Seismological Society of America, in press.
The Altyn Tagh Fault is located at the northwestern edge of the Tibetan Plateau, and is the largest active strike-slip fault in Asia with a total length of ~2000 km. The fault accommodates sinistral motion between the Tibetan Plateau and the Tarim Basin within the India–Eurasia collision zone. Although the Altyn Tagh Fault plays a key role in accommodating India–Eurasia convergence, little is known about its nature as a seismogenic strike-slip fault due to a lack of instrumentally recorded large earthquakes on the fault. The 12 February 2014 Mw 6.9 Yutian earthquake, which occurred in the Yutian region of the Tibetan Plateau, provides an opportunity to study the seismotectonic nature of the Altyn Tagh strike-slip fault system.
Field investigations reveal that the 2014 Mw 6.9 Yutian earthquake on the left-lateral strike-slip Altyn Tagh fault system, Tibetan Plateau, produced a ~25-km-long surface rupture zone that contains conjugate Riedel shear faults (Li et al., 2016). The co-seismic surface ruptures occurred mainly along two parallel ENE-trending active left-lateral strike-slip faults. Rupture also occurred in a conjugate, WNW-trending zone along an active right-lateral strike-slip fault. The ENE-trending ruptures are concentrated in a zone of <500 m wide and ~25 km long, and are characterized by Riedel shear structures including distinct shear faults (Y) with a maximum sinistral displacement of ~1 m, right-stepping en echelon cracks, and mole tracks. In contrast, the WNW-trending ruptures occur within a zone of up to 1.5 km wide and ~4 km long in the jog area between the two parallel ENE-trending faults, and this zone is characterized by discontinuous shear faults with dextral displacements of <0.5 m, left-stepping en echelon cracks, and mole tracks, all oriented oblique to the ENE-trending rupture zones at an angle of 30°–40°. The lengths and displacements of the co-seismic surface ruptures measured in the field are comparable with those obtained from the empirical relationships between magnitude and co-seismic surface rupture length and displacement. Our findings demonstrate that the co-seismic conjugate Riedel faulting was controlled mainly by pre-existing active faults of the Altyn Tagh fault system, reflecting the present-day tectonic stress field associated with the ongoing penetration of the Indian Plate into the Eurasian Plate.
References
Li, L., Pan, J., Lin, A. (*corresponding author), other 8, 2016. Co-seismic surface ruptures associated with the 2014 Mw 6.9 Yutian earthquake on the Altyn Tagh Fault, Tibetan Plateau. Bulletin of Seismological Society of America, in press.