Abstract: Field investigations on the 2008 surface rupture north to Shikan village show that the surface rupture is still significant in this section.The surface rupture changes its strike at the north of the town of Shikan and does not follow the previously mapped thrust which was initially considered the location the rupture traversed.Nevertheless,clear morphological expressions suggest repeated coseismic displacements along the fault trace the 2008 earthquake rupture followed.Contrast to the previous work,another 12-km-long rupture was found.It runs between Shikan town and Woqian village,trends 15°～45°,and shows thrusting with dextral slipping.The relatively large vertical and dextral strike-slip displacements of 2.1m and 3.0m respectively at Kuangpingzi do not suggest that co-seismic slip diminished gradually from a high value to a low one.The increased component of strike slip may suggest that the rupture ended as a strike-slip mode.Field observations suggest that the rupture terminates at the southwest of the Donghekou village about 20km north to Woqian village.

Key words: Wenchuan earthquake, surface rupture, coseismic displacement, length of rupture

摘要： 对汶川M_S8.0地震地表破裂石坎乡以北段的野外地质调查显示,这一段地表破裂仍然十分明显。地表破裂并未沿地质填图所标定的位置发育,而是在走向上稍有变化,但清楚的地貌显示它在此段并不是一条新生断裂。与前期工作相比,可观察到的地表破裂又往NE方向延长了约12km。该段破裂位于平武县石坎乡至青川县马公乡窝前村之间,走向为15°～45°,运动学性质主要为右旋走滑逆冲。地震地表破裂显示的同震垂直位移与石坎乡一带相近,为1～2m左右;右旋水平位移略有增加,为2.0～3.0m之间。地表调查的情况显示,地表破裂在北端可能消失在红光乡东河口一带。

关键词: 汶川地震, 地表破裂, 同震位移, 破裂长度