Amounts and styles of coseismic deformation along the northern segment of surface rupture, of the 2008 Wenchuan Mw 7.9 earthquake, China

The May 12, 2008, Mw 7.9 Wenchuan earthquake occurred along the Longmen Shan fault zone, a thrust fault zone on the eastern margin of Tibet Plateau, and ruptured the ground surface for more than 200 km. A field investigation suggests that the earthquake also ruptured the northern segment (from Beichuan to Qingchuan), along which active evidence had been less identified before, 75–95 km long. This rupture commonly presents a relatively simple 1- to 6-m-high scarp with folding and tension cracks along the crest and with minor deformation on both the hanging wall and the footwall. The maximum measured vertical and dextral displacements along this segment are 9.0 m and 3.0 m, respectively. The amounts of the vertical coseismic displacements decrease from southwest to northeast, but the amounts of the dextral displacements increase toward the northeastern end of the rupture. The surface rupture apparently terminates as mainly strike-slip faulting at the northeastern end. The observable rupture zone is about 75 km long, between Beichuan and Shuiguan, showing mainly thrust slip, with a component of dextral strike-slip, dipping NW at an angle of 54–84°. The surface deformation along this segment is classified into five characteristic styles that range from pure thrusting, a mixture of thrust and dextral slip, to pure dextral slip. The amount of shortening is estimated to be minor, 0.2–1.0 m.