汶川地震地表破裂影响带调查与建筑场地避让宽度探讨

INVESTIGATION OF RUPTURE INFLUENCED ZONES AND THEIR CORRESPONDING SAFE DISTANCES FOR RECONSTRUTION AFTER 5.12 WENCHUAN EARTHQUAKE

5.12汶川Ms8.0级地震沿龙门山中央断裂带形成长度约270km的地表破裂带,破裂带垂直和水平位移一般为1.0～5.0m,最大可达9.8m。在地表破裂带附近,建筑物破坏严重。笔者系统调查了龙门山中央断裂带地表破裂的垂直和水平位移以及地震地表破裂影响带宽度,并采用物探测试方法对部分影响带宽度进行了验证。统计结果表明,汶川地震地表破裂影响带宽度主要集中在16～60m,影响带宽度(D)与垂直位移(H)具有较好的线性关系,即D=10.11H+16.0。对于逆冲性质为主的地震地表破裂而言,上盘影响带宽度与下盘的比值一般为3:1～2:1,据此可确定地表破裂带上、下盘的避让带宽度。笔者根据现场调查并借鉴国外经验提出,上盘避让宽度下限一般不应低于15m,下盘避让宽度下限不应低于10m。本项研究对于汶川地震灾后重建场地选址具有重要的实际意义。

The Wenchuan earthquake occurred along the Longmenshan thrust fault belt. The Longmenshan central fault is the earthquake causing fault. The total rupture length along the Longmenshan central fault caused by the Wenchuan earthquake is about 270 km and the average vertical and horizontal displacement range from 1.0 m to 5.0 m, up to about 9. 8 m in local parts. A lot of buildings were broken in the area where the ruptures passed through. In this paper, the authors report the investigation results of the vertical and horizontal displacements, as well as the width of rupture influenced zones which were confirmed by the geophysical survey methods, in different locations along the Longmenshan central fault. It is indicated that the influenced scopes of the earthquake ruptures mainly range from 16 m to 60 m, and the relationship between the influenced scopes （D）and the vertical displacement （H）is obvious linearity, which can be expressed as： D = 10. 11 H＋ 16.0. Due to the Longmenshan central fault being a mainly thrusting fault, the influenced zone ratio between the hanging wall side and the foot wall side is generally from 3 ： 1 to 2 ： 1, which can help to determinate the safe distance for building site. On the basis of field investigation and using overseas experience for reference, the limit of the safe distance on the hanging wall side should be not less than 15 m,and that on the foot wall side should be not less than 10 m. This research work has important significance for safe site selection in Longmenshan region during reconstruction after the earthquake.