Representative styles of deformation along the Chelungpu fault from the 1999 Chi-Chi (Taiwan) earthquake: Geomorphic characteristics and responses ofman-made structures

The Chi-Chi earthquake provides dramatic evidence of the damaging effects o f surface ground deformation to buildings, lifelines, and other facilities. Much of the building damage is associated with surface faulting and foldin g along the Chelungpu thrust fault. Our detailed surveying at representativ e sites along the fault shows that the rupture commonly is a relatively sim ple 1- to 4-m-high scarp with minor hanging-wall deformation and localized (but severe) uplift, folding, and graben formation along the scarp crest. F or individual scarps, the width of deformation is about 10 to 20 times the net vertical displacement. Distributed secondary faulting and folding on th e hanging wall occurred as much as 350 m from the primary fault. Near the n orthern end of the rupture, growth of a pre-existing 1-km-wide late Quatern ary anticline produced severe ground rupture along multiple thrusts and bac kthrusts but only minor tilting between fault strands. The pattern of building damage coincides with the pattern of geologic defor mation, with severe damage along large fault scarps and lesser but still si gnificant damage attributable to distributed secondary surface deformation on the hanging wall. Rupture-related building damage on the footwall occurr ed next to the prerupture fault trace, where the hanging wall bulldozed ont o the footwall. The width of this damage zone is related to the local horiz ontal shortening along the fault and generally is less than 10 m. Building zonation along reverse faults should account for this pattern of surface de formation. In addition, buildings with massive foundations locally influenc ed the style and location of near-surface deformation, producing variations in fault strike or accentuated secondary deformation on the hanging wall.