Abstract:

On May 12, 2008, a great earthquake of Ms 80 occurred in Wenchuan County, Sichuan Province. After this devastating earthquake, many scientists have done detailed field work on the surface rupture zone, especially aiming at the coseismic displacement. However, the nearfault horizontal shortening amount of Wenchuan Ms 80 earthquake, a crucial parameter of coseismic displacement of reverse fault, is relatively less studied. We concluded nearfault horizontal shortening from trenching at some locations along the BeichuanYingxiu Fault and GuanxianJiangyou Fault as: 28 m (Qingping), 32 m (Leigu), 13 m (Pingtong), 25 m (Bailu), 14 m (Jiulong) and 06 m (Hanwang). Based on these studies, we further excavated more trenches along the surface rupture to calculate horizontal shortening. Horizontal shortening from trenches on the BeichuanYingxiu Fault and Xiaoyudong Branch Fault are as: 26±01 m (Yingxiu), 26±02 m (Leigu), 18±01 m (Pingtong), 2±01 m (Xiaoyudong). There are two horizontal shortening peaks in Shenxigou and Leigu along the BeichuanYingxiu Fault, 34 m and 32 m, respectively. Horizontal shortening along the GuanxianJiangyou Fault ranges from 25 m to 06 m, with the highest value toward the southwest. Sums of horizontal shortening on the corupture segment along the GuanxianJiangyou Fault and BeichuanYingxiu Fault are larger than other parts. According to this study, maximum nearfault  horizontal shortening across the surface rupture of the Wenchuan earthquake is about 53 m or slightly larger, which means the shortening near the surface rupture is the main part of the crustal shortening.

Key words: Ms 80 Wenchuan earthquake, nearfault, trench, horizontal shortening amounts