Representative Styles of Deformation along the Chelungpu Fault from the 1999 Chi-Chi (Taiwan) Earthquake: Geomorphic Characteristics and Responses of Man-Made Structures

Abstract

The Chi-Chi earthquake provides dramatic evidence of the damaging effects of surface ground deformation to buildings, lifelines, and other facilities. Much of the building damage is associated with surface faulting and folding along the Chelungpu thrust fault. Our detailed surveying at representative sites along the fault shows that the rupture commonly is a relatively simple 1-to 4-m-high scarp with minor hanging-wall deformation and localized (but severe) uplift, folding, and graben formation along the scarp crest. For individual scarps, the width of deformation is about 10 to 20 times the net vertical displacement. Distributed secondary faulting and folding on the hanging wall occurred as much as 350 m from the primary fault. Near the northern end of the rupture, growth of a pre-existing 1-km-wide late Quaternary anticline produced severe ground rupture along multiple thrusts and backthrusts but only minor tilting between fault strands.The pattern of building damage coincides with the pattern of geologic deformation, with severe damage along large fault scarps and lesser but still significant damage attributable to distributed secondary surface deformation on the hanging wall. Rupture-related building damage on the footwall occurred next to the prerupture fault trace, where the hanging wall bulldozed onto the footwall. The width of this damage zone is related to the local horizontal shortening along the fault and generally is less than 10 m. Building zonation along reverse faults should account for this pattern of surface deformation. In addition, buildings with massive foundations locally influenced the style and location of near-surface deformation, producing variations in fault strike or accentuated secondary deformation on the hanging wall.

Fault rupture–foundation interaction: selected case histories

“…The Chelungpu fault, responsible for this extreme seismic event and oriented N-S, gave rise to N T a iw a n S tr a it s P a c if ic O c e a n a practically continuous surface fault rupture, extending for a distance of more than 100 km (Angelier et al 2003). Its orientation reveals its association with over-thrust of Miocene over Meso-Pleistocene formations (Kelson et al 2001). The dip of these formations ranges from 20 to 30 • , reaching 40 • close to the fault.…”

Foundation–structure systems over a rupturing normal fault: Part I. Observations after the Kocaeli 1999 earthquake

“…(d) Finally, the presence of a structure on top of the soil deposit may further modify the path of the rupture, as the latter propagates from the base rock to the ground surface. Depending on the rigidity of the foundation and the weight of the structure, even complete diversion of the fault path before it outcrops may take place (Niccum et al 1976;Youd 1989;Kelson et al 2001;Bray and Kelson 2006). Obviously, the damage that a given structure will suffer depends not only on its location with respect to the fault outcrop in the "free-field" but also on whether and by how much such a diversion may occur.…”

Reply to "Comment on `A Vertical Exposure of the 1999 Surface Rupture of the Chelungpu Fault at Wufeng, Western Taiwan: Structural and Paleoseismic Implications for an Active Thrust Fault,' by Jian-Cheng Lee, Yue-Gau Chen, Kerry Sieh, Karl Mueller, Wen-Shan Chen, Hao-Tsu Chu, Yu-Chang Chan, Charles Rubin, and Robert Yeats," by Yuan-Hsi Lee, Shih-Ting Lu, Tung-Sheng Shih, and Wei-Yu Wu

“…This brings up the issue of decoupling along the boundary of different deformed materials and their response to deformation with various rheology during earthquake faulting. These phenomena have also been described at several places along the 1999 surface ruptures (Kelson et al, 2001). It would be interesting to discuss the difference between the deformation on the surface level and that on the subsurface level; however, it is beyond the scope of the present study.…”