Study On Setback Distance From Surface Rupture For Post-Wenchuan Earthquake Reconstruction

The Wenchuan Earthquake caused an infrequent damage in history, especially along the surface rupture zone, a large number of collapsed structures and geological disasters can be seen everywhere caused by surface permanent displacement. With the process of post-disaster reconstruction advancing, near the surface rupture zone, farmer-house reconstruction, as well as large industrial facilities, which all need a more reasonable seismic design, especially to avoid permanent displacement caused by seismic faults. So, reasonable analysis of seismic hazard caused by surface permanent displacement is necessary.In addition, with economic growing in China, a number of large-scale infrastructure constructions is also built in recent years, especially as South-North water diversion, West-East gas pipeline project, road and rail bridges across the river or the canyon, and tunnels through the mountains, inevitably to cross a high active seismic region or seismic fault. It would cause severe disaster, which are caused by a permanent displacement induced by strong earthquakes. This makes the seismic risk analysis caused by surface permanent displacement and seismic risk analyses are equally important, both are input earthquake parameter to structures.This paper started from the field investigation of the Wenchuan earthquake surface rupture and the damage surrounding it, some characteristics of seismic damaged buildings nearby the earthquake surface rupture zone were described in detail. Investigating show that the impact of the earthquake surface rupture zone to the building damage is limited, there are some good buildings near the rupture zone, but the building across the fault was all collapsed. Moreover, seismic surface rupture induced many secondary geological disasters, such as large-scale landslides, rock-falls. The width of the Wenchuan earthquake surface rupture zone is slightly less than the width of the completely collapsed buildings, the width of the completely buildings collapsed on hanging wall is slightly larger than the width of that on footwall. It's obvious that the characteristics of the collapse structure on surface rupture zone of thrust fault, inclining and overturning of the building, were caused by permanent displacement.The characteristics of seismic damage near the surface rupture zone are recognized. In order to put forward the fault setback distance in post-disaster reconstruction after the Wenchuan earthquake, this dissertation try to establish a probability risk analysis model for permanent seismic displacement. Probability of seismic hazard analysis had been applied to estimates of ground motion, liquefaction and landslide, but has not been applied in permanent displacement analysis. In general, there are two reasons, the zone induced by seismic surface permanent displacement is relatively small, and the sites of some very important building have selected in lower seismic activity, or a'setback distance'was taken into account.Finally, the tectonic setting of the Longmenshan fault and seismic activity are analyzed, the model of probability analysis permanent displacement and the relationship of the width of surface rupture zone and the width of the completely buildings collapsed are adopted, the permanent displacement of the surface under the exceeding probability of 10 percent in the future 100 years is calculated, which corresponds the setback distance is about 10m, and a brief discussion on avoidance measures.