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Groundwater has been over-pumped and excessive use during the past decades due to the lack of sufficient surface water caused by rapid economic developments and growing population, especially in the central part of Taiwan. The alluvial fan of the Cho-Shui River in Western Taiwan suffers the most serious land subsidence hazard with a maximum subsidence rate in excess of 3 cm/yr which is affecting the transportation infrastructures across the land subsidence area. The long-term spatial land subsidence variation from 1995 to 2020 reveals that the center of land subsidence area changed significantly with time from the coastal area to inland area. The decreasing of land subsidence could obviously be detected by the velocity profile along the Taiwan High Speed Rail during different time periods from geodetic measurements. Not only the vertical displacement increases the risk on potential damage on transportation infrastructures across the land subsidence bowls but also the induced additional horizontal displacement owing to the vertical subsidence could result in the unexpected risk for the infrastructure. In this study, we used the technique of multi-temporal InSAR to calculate the vertical deformation and the east-west deformation combined with the velocity field of the ascending and descending orbits. Three large-scale subsidence bowls are detected and accompanied by maximum additional horizontal deformation of ~8 mm/yr than that predicted by tectonic movement outside of the subsidence bowl. This additional E-W displacement is the major risk concerns of the N-S trending Taiwan High Speed Rail.

Slow-moving landslides can transform into catastrophic landslides at certain conditions. In recent decades, catastrophic landslides around the world have caused widespread damage to buildings and threatened human lives. Thus, the detection of surface displacement variation and the definition of precursory motion for extensive slow-moving landslides become a primary goal of current researches. This study dedicates to detect and monitor surface displacement of multiple slow-moving landslide areas in Taiwan by the multitemporal interferometric SAR (MTInSAR) technique. A new package was established to generate interferograms of multiple slow-moving landslide areas at the same time. Thus, the surface displacement information in large spatial coverage and a long period of time can be obtained efficiently. The landslide characteristics in space and time domain of those slow-moving landslides were investigated and analyzed. Especially, the significant acceleration movements of certain slow-moving landslides were observed and agreed with the in situ monitoring data. The results of this study provide important information of landslide hazard assessment and show the opportunity of detecting the landslide precursory motions by the MTInSAR technique in the future.