INTERACTIONS BETWEEN SURFACE FAULT RUPTURE AND BUILDINGS DURING THE 1999 CHI-CHI (TAIWAN) EARTHQUAKE

We document the pattern of ground deformation along the Chelungpu fault at many sites that experienced surface fault rupture during the M7.6 Chi-Chi earthquake. The rupture traversed densely populated areas and provides an unprecedented opportunity to understand how surface fault rupture may affect buildings. While building damage at some sites was severe, other sites along the fault, surprisingly, experienced relatively little building damage. These results help explain why some locales and some buildings are more (or less) susceptible to severe damage from surface fault rupture. At KuangFu Middle School, a single well-defined fault rupture splays into three distinct west-stepping en echelon strands that go around or through several severely damaged buildings. The locations of and displacements on the strands vary relative to the locations, types, and orientations of the buildings. Borehole data suggest that the pre-1999 fault location differs slightly from the 1999 surface rupture, which also suggests that the building locations and orientations may have influenced the pattern of shallow rupture. In WuFeng, the thrust front wrapped around the undamaged Suncue Factory building, and had greater hanging-wall folding where it impinged upon the factory. Lesser buildings on the hanging wall collapsed as a result of the amplified folding. Similarly, near Tsaotun, a single fault scarp projects directly toward a 12-m-wide, 26-m-high concrete water tower. At the tower, the scarp wraps around the eastern side of the tower, where anticlinal deformation of the hanging wall is greater. North of the tower, deformation splays into a zone of distributed folding and faulting with much less hanging-wall damage. The presence of the tower apparently affected the distribution and style of surface deformation. Data from these and other sites show that the location, orientation, and type of buildings may influence patterns of shallow deformation (and damage to adjacent buildings).