Additional horizontal displacement across the transportation infrastructures induced by land subsidence revealed by SAR interferometry

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.