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

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 from16 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=10.11H+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．