Land subsidence characteristics in Tianjin based on multi-source data

Land subsidence is a widespread geological hazard, and Tianjin is one of the cities in China severely affected by it. Studying the characteristics of surface deformation helps in understanding the distribution of land subsidence and supports rational urban planning. Based on Sentinel-1 ascending and descending orbit data covering the Tianjin area, an improved small baseline subset time-series interferometry method was used to obtain the satellite line-of-sight (LOS) deformation velocity field. The derived deformation velocity field in Tianjin reveals significant uneven subsidence, with relatively minor deformation in the urban core of Tianjin. The Wuqing and Beichen Districts exhibit the most pronounced deformation, characterized by a large-scale deformation funnel in both extent and magnitude. The center of this deformation funnel is located in Wangqingtuo Town, Wuqing District, where the maximum LOS deformation rate reaches approximately 100 mm/a. By integrating GNSS deformation data and applying the Helmert variance component estimation method, the three-dimensional deformation results for the Tianjin area were derived. The maximum vertical subsidence rate obtained from the three-dimensional solution is about 90 mm/a. A spatiotemporal evolution analysis of Wuqing and Beichen Districts was conducted using the equal-fan analysis method, revealing that the subsidence funnel in this area is primarily concentrated in the S, SW, and SSW directions. Additionally, the time-series deformation characteristics of some urban infrastructures in Tianjin were analyzed. The results indicate that subway lines and Tianjin Airport are located in relatively stable deformation areas. Bridge deformation shows a certain correlation with temperature. The Tianjin Port area exhibits significant uneven subsidence, necessitating long-term time-series deformation monitoring. Analysis of the time-series deformation characteristics of infrastructures shows that the deformation trend has mostly eased after 2020, which is closely related to subsidence control measures implemented by relevant authorities.