Taipei has experienced significant urban development in recent years with the expansion of the Taipei Mass Rapid Transit (MRT) system. One major extension is the Tamsui–Xinyi Line (Red Line), which includes the new Guangci Fengtian Temple Station. This station extends the line eastward from Xiangshan Station into the Xinyi district. The project has been considered one of the most challenging MRT developments because of the complex geological conditions, where very soft sediments transition to hard rock over short distances. In this study, Sentinel-1 SAR images were used to measure tunnel excavation-induced settlement through ascending and descending tracks, enabling the estimation of vertical and horizontal deformation time series. In the vertical component, local subsidence zones were identified along Fude Street and Xinyi Road Section 6, with maximum subsidence rates reaching 42 mm/yr between January 2021 and August 2025. In the horizontal component, most monitoring points showed westward velocities, whereas points located directly above the excavation line exhibited eastward motion. This bidirectional displacement pattern suggests that the deformation behavior is strongly controlled by the excavation geometry. Additional subsidence signals were detected near the buffer stop construction area at the eastern end of the extension. Gaussian trough models fitted to the settlement profiles produced high R² values between 0.92 and 0.96, indicating strong agreement with observations. The estimated settlement trough widths were approximately 100 m along Fude Street and 70 m along Xinyi Road Section 6.