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对北川-青川间汶川MS8.0地震地表破裂的野外地质调查表明,在这一段内主要存在一条地震地表破裂带,总体沿北川-青川断裂带分布。沿黄家坝、陈家坝、桂溪、平通、南坝、石坎等地的观察显示,该段地表破裂沿走向连续分布,结构单一,破裂长度为60~90km,地表破裂没有到达青川县关庄镇。可观察到的破裂长度在北川北至石坎之间,长62km,走向总体为20°~55°,运动学性质主要为右旋走滑逆冲。地震形成的地表破裂主要表现为垂向上的地表拱曲,指示了深部断层的逆冲性质;在水平运动方向上则主要表现为右旋走滑,不存在左旋走滑分量。地震地表破裂显示的同震垂直位移从西南段黄家坝的3m左右,向东北逐渐降低至南坝、石坎的1.5m左右;右旋水平位移没有明显变化或者略有增加,一般在1.5~2.0m之间。地表破裂特征表明,引起本次汶川MS8.0地震的发震构造是映秀-北川-青川断裂带,该断裂以逆冲运动为主,兼具右旋走滑分量,逆冲方向由NW向SE。
The field geological survey of the surface rupture of the Beichuan-Qingchuan Ms 8.0 Wenchuan earthquake shows that there is mainly one seismic surface rupture zone in this segment, which is generally distributed along the Beichuan-Qingchuan fault zone. The observation along the Huangjiaba, Chenjiaba, Guixi, Pingtong, Nanba and Shikan shows that the surface rupture is continuously distributed along the strike direction and has a single structure with a rupture length of 60 ~ 90km. The surface rupture did not reach Qingchuan County Guan Zhuang town. The observed rupture length ranges from north Beichuan to heath, 62 km in length and 20 ° to 55 ° in general, and the kinematic properties are mainly dextral strike-slip thrust. The surface rupture caused by earthquakes mainly shows vertical surface arching, which indicates the thrusting property of deep faults. In horizontal direction, it is mainly dextral strike-slip and there is no left-slip strike-slip component. The vertical coseismic displacements of the earthquakes showed that the vertical displacements of coseismicity were about 3 m from Huangjiaba in the southwest section and gradually decreased to 1.5 m in the south dam and the stone ridge in the northeast. The horizontal displacement of dextrorotatory did not change obviously or slightly increased, m between. The characteristics of surface rupture indicate that the seismogenic structure that caused the MS8.0 Wenchuan earthquake is the Yingxiu-Beichuan-Qingchuan fault zone, which is dominated by the thrust movement and has the right-lateral strike-slip component. The thrust direction is NW to SE .