CHARACTERIZATION OF SURFACE RUPTURE AND STRUCTURAL DAMAGE IN HONGKOU TOWN DURING WENCHUAN EARTHQUAKE

Abstract

Hongkou Town is located north of Dujiangyan City, around 27 km away to the northeast of the epicenter of Wenchuan Earthquake on May 12, 2008. The middle segment of the central fault, that is the Yingxiu-Beichuan Fault of the Longmenshan Fault belt, passes through the town, along which almost every form of surface ruptures is developed. The quake also resulted in 73 of the town's residents dead or missing and 95% of its buildings or infrastructures damaged, including the collapse of Gaoyuan Bridge. Its estimated intensity was around XI. On the other hand, in Shenxigou Village and Gaoyuan Village, many houses successfully withstood the quake. In this paper, the authors examine why the latter houses withstood the earthquake well. Based on field investigation and local geology, especially fault configuration in the area, a detailed description is given on the characteristics of surface rupture and structural damage in the two villages and an attempt is made to correlate fault movement with structural damage. The results show that: (1) Fault movement or surface rupture may be affected by local geological configuration and topography. Compression can lead to local strike-slip movement. (2) Structural damage is associated with fault movement. Strike-slip movement causes less damage to structures, while in the adjacent area of fault with thrust movement, the structures in the hanging-wall can be more easily damaged than the ones on the footwall, i.e. hanging-wall effects. An area located on the footwalls of two nearly parallel faults may result in a "safer island," where structural damage is much lighter that those outside the island. (3) Apart from shaking effect, site effects should also be considered in structural design.