汶川M_s 8.0级地震地表破裂带近断层水平缩短量研究

The study of near-fault horizontal shortening of the surface rupture in Wenchuan M_s 8.0 earthquake.

2008年5月12日四川汶川发生Ms8.0特大地震后,地表同震位移量已有了大量的详细调查和研究,然而对于近断层同震水平缩短量的研究却相对较少。笔者在中央断裂、前山断裂以及北西向分支断裂上选择合适地点进行大量探槽开挖,获得了近断层同震水平缩短量的分布情况为:中央断裂清平镇(2.8 m)、擂鼓镇(3.2 m)、平通镇(1.3 m),前山断裂白鹿镇(2.5 m)、九龙镇(1.4 m)、汉旺镇(0.6 m)。文中进一步在中央断裂和小鱼洞分支断裂地表破裂带上开挖数个探槽研究其近断层水平缩短量的问题,得到结果如下:龙门山中央断裂带映秀镇、擂鼓镇、平通镇探槽近断层水平缩短量分别约为(2.6±0.1)m、(2.6±0.2)m、(1.8±0.1)m;小鱼洞分支断层近断层水平缩短量约为(2±0.1)m。汶川5.12地震中央断裂地表破裂近断层较大水平缩短量出现在深溪沟和擂鼓一带,分别约为3.4 m、3.2 m;前山断裂地表破裂带近断层水平缩短量最大值出现在白鹿一带,约为2.5 m,白鹿以北,近断层水平缩短量逐渐减小。中央断裂和前山断裂联合破裂段水平缩短量值之和大于中央断裂带其两侧段落,最大水平缩短量总和可能约为5.3 m,地表破裂带近断层水平缩短量为整个地壳缩短量的主体部分。

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.