A Study on Deformation of the Chelungpu Fault Zone in Shihgang Area, Central Taiwan

The 1999 Chi-Chi earthquake caused surface ruptures and severe deformation in Shihgang area, Central Taiwan. Many studies related to the Chelungpu fault were conducted in recent years, especially focused on the surface ruptures, paleoseismology and seismology. In this paper we use the precise and dense cadastral surveying to identify the deformation characteristics of the Chelungpu fault zone in Shihgang area. The resulted displacement is characterized by a clear E-W oriented break that coincident with the surface trace of the Shihgang backthrust. Besides, the result of strain analysis shows that most of the study areas are under compression in N-S direction, and extension in E-W. The contours computed by derived compressional stress also show a sharp strain contrast on both sides of the Shihgang backthrust and gradually decreases eastward. Therefore, the coseismic uplift and surface deformation in the Shihgang area during the Chi-Chi earthquake can be reasonably explained by adding compensation from Shihgang backthrust.