Surface deformation in the Chengdu plain area produced by the Wenchuan MS8.0 earthquake of 12 May 2008, Sichuan, China
成都平原内汶川MS8.0级地震的地表变形

The 12 May 2008 Wenchuan MS8.0 earthquake occurred on the Longmen Shan (Mountains) thrust-nappe structure zone in the eastern margin of the Tibetan plateau. It has produced 240 km long and 72 km long rupture zones on the surface along the Yingxiu-Beichuan fault and Guanxian-Jiangyou fault, respectively, which are branches of the Longmen Shan fault system. Besides, our field investigation found that this shock has also caused a weak rupture zone on the ground nearby the Shigu town, Shifang city that lies in the western Chengdu plain east to the epicenter. This rupture zone and the other two ruptures in the Longmen Shan mountainous area aforementioned constitute a northwest-dipping imbricate structure. It is about 7.5 km long, trends in 30°, manifested by a series of directed deformation phenomenon such as damages of buildings, channel dislocations, ground folds, erupted sand and earth fissures on the surface. Observations in the exploratory trenches indicate that there is a fold uplift of 0.2 m in the youngest strata (including the surface) produced by the Wenchuan MS8.0 event, and a fold uplift of 0.4 m in the clay bottom in the trench, presumably resulted from a paleoearthquake of similar size to the Wenchuan shock in 2008. Seismic exploration to shallow subsurface demonstrates that in the place of the Chengdu plain with the found seismic rupture zone exists active faults of the late Pleistocene as well as active folds of the Quaternary.