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SRL: 2016年12月8日新疆呼图壁M6.2级地震发震构造探讨

2017/12/25 9:54:34

On December 8, 2016, an earthquake of moment magnitude 6.2 struckHutubi County in Xinjiang Province, northwestern China(Fig 1). This earthquake did not lead to surface ruptures or deaths but caused the destruction of surface structures as well as serious economic and property losses. There was, however, another large M7.7 Manas earthquake that occurred near this Hutubi earthquake, which led to thousands of casualties. By examining the location of the hypocenter, focal mechanism, regional geology, and artificial seismic reflection profiles, we are able to reveal the structural and sedimentary framework of a section of the northern Tian Shan through seismic interpretation.

Figure 1. Tectonic setting of the northern Tien Shan, northwestern China. The white lines represent major faults in the northern Tien Shan area. The blue circles indicate historic earthquakes (magnitude ≥ 5.0), and the red circles indicate earthquakes (magnitude ≥ 6.0) recorded since 1970. ①: Dushanzi–Anjihai anticline belt; ②: Huoerguosi–Manas–Tugulu anticline belt; ③: Qigu anticline belt; F1: Yamate fault; F2: Junggar southern margin fault; F3: Huoerguosi–Manas–Tugulu fault.

The strike, dip, and rake of the focal mechanismwere 49°/27°/50°, and the auxiliary nodal plane solution was 273°/70°/108° (Institute of Geophysics, China Earthquake Administration [IGCEA], 2016). USGS data state that the strike, dip, and rake of the focal mechanism were 80°/19°/81°, and the auxiliary nodal plane solution was 269°/71°/93°. Seismic interpretation shows that the fault has a ramp–flat–ramp geometry and is connected to the active Huoerguosi–Manas–Tugulu fault (F3) at the surface (Fig 1). Accumulated total stratigraphic offset at fault F3 is ~5.8 km with a fault shortening of ~5.4 km. This gives a shortening rate of ~0.9 mm/yr between the Qigu and Tugulu anticlines during the Late Cenozoic. Based on regional study of the fault plane, fault F3 is capable of producing earthquakes of Mw ≥ 8.0. This study suggests that fault F3 was the seismogenic fault responsible for the 2016 Hutubi M 6.2 earthquake and the 1906 Manas M 7.7 historical earthquake. This conclusion, however, is based on the location of the Hutubi M 6.2mainshock. If the mainshock is shallower in depth, the Hutubi earthquake may have occurred on a minor spaly fault in the duplex of the structural wedge. The cluster of aftershocks suggests that the north-dipping coseismic fault may be a black thrust fault, which cut the previous-existing faults. Moreover, we suggest that the seismogenic fault of Hutubi earthquake should have an irregular geometry responsible for the black thrust and folds. The active fault system in the northern Tian Shan mountain belt was involved in fault-related folding during the Late Cenozoic and therefore poses a potential seismic hazard in the study area.

Figure 2. Seismotectonic model of the 2016 Hutubi M 6.2 earthquake and the 1906 Manas M 7.7 earthquake.

The above results were published on the international journal of Seismological Research Letters “Seismotectonics of the 2016 M 6.2 Hutubi Earthquake: Implications for the 1906 M 7.7 Manas Earthquake in the Northern Tian Shan Belt, China”by Renqi Lu, Dengfa He, Xiwei Xu, Xiaoshan Wang, Xibin Tan, and Xiyan Wu.

Full text link: https://pubs.geoscienceworld.org/ssa/srl/article/523096/seismotectonics-of-the-2016-m-6-2-hutubi