The surface rupture of the 1999 Chi-Chi earthquake (Mw 7.6) trends more than 100 km in a north–south direction. Surface deformation at the northern end stops abruptly at an area between the Tachia River and the Taan River where a broad pop-up structure with east to northeast strike can be found that has a trend different from the north–south-striking main thrust. We combine the absolute elevation data before and after the Chi-Chi earthquake to obtain the regional vertical displacement and the magnitude of the pop-up structure. The greatest uplift could reach as high as 15–16 m. Using deformation magnitude and the area-balancing method, we measure the depth of the detachment to show the subsurface geometry of the Chelungpu fault at its northern end. This shows that the geometry of the Chelungpu fault controls termination of the surface rupture and the depth of the detachment controls the amount of deformation.