1999 Chi-chi Earthquake, Taiwan: Active Tectonics

Department of Geological Sciences Research

Charles M. Rubin, Department of Geology, Central Washington University, Ellensburg, Washington

Introduction

Taiwan's destructive Chi-Chi earthquake of September 21, 1999 was a dramatic expression of active tectonic processes at a complex collisional plate boundary, resulting in more than 2,400 deaths and tens of billions of dollars of property loss. During the earthquake, an 85-km stretch of the country's mountainous backbone moved upward and westward along the range-bounding Chelungpu thrust fault.

Charlie Rubin and Kerry Sieh (Caltech) are currently investigating the complex surface and sub-surface rupture and conducted paleoseismologic studies, together with Drs. Yue-Gau Chen of NTU, Jian-Cheng Lee of AS, and Chu Hao-Tsu of CGS. Armed with sub-surface geologic and paleoseismic techniques that characterize the timing and magnitude of past earthquakes, our group is characterizes the prehistoric seismic record of the Chelungpu and adjacent faults.


Trench wall exposure of the 1999 rupture at Wufeng. The red fence
was constructed after the earthquake.

Selected Images

Active tectonic setting of Taiwan

Map of 1999 rupture

Active fault map of Taiwan showing the historic surface rupture (red) and neighboring major faults. Historical surface ruptures from Bonilla [1975].

Map of trench wall exposure shows fluvial gravel, overbank and soil layers all broken by the fault. Line-length restoration shows that about 3 m of shortening occurred in the plane of the exposure. Close inspection of the stratigraphy suggests existence of pre-existing scarp.

Photograh of the 1999 surface rupture near Fengyuan City. View towards the south. Here, vertical offset was about 5 m. Structural damage was very heavy along the Chelungpu fault, in particular on the hanging-wall block. If construction along the Chelungpu fault had been developed under Alquist-Priolo regulations, the loss of life and property would have been greatly reduced.