Hypothetical analysis of ground deformation and its effects on archaeological sites of the Silk roads with SBAS-DInSAR: An exploratory application in Xi'an City, China

“Silk Roads: Routes Network of Chang'an-Tianshan Corridor” is a series of heritage sites inscribed in the World Heritage List. Heritage sites are vulnerable to local ground deformations, but corresponding measurements to the Silk Roads are lacking. Xi'an City is the eastern origin of the Silk Roads and boasts the most sites of all cities along the corridor. Moreover, differential ground deformation in Xi'an has been given more prominence. The Small BAseline Subset (SBAS) Differential Interferometric Synthetic Aperture Radar (DInSAR) is one of the time-series techniques analyzing a stack of multiple SAR image pairs to measure ground deformations, and has been well-assessed for heritage studies. Here we provide technical insights and references by investigating the ground's deformations through the use of SBAS-DInSAR, in some areas integrated with ground-based geodetic techniques to derive digital models of heritage entities. Specifically, we processed 97 Sentinel-1 SAR images from 2019 to 2022 through SBAS-DInSAR. The results revealed that the Great Wild Goose Pagoda (GWGP) and Small Wild Goose Pagoda (SWGP) were located at uplifting areas, while the Weiyang Palace (WP) of the Western Han Dynasty was located in a subsiding area. Along the Line-of-Sight direction, the uplifting rates at GWGP and SWGP exceeded 9 mm/year, and the time series showed positive correlations with groundwater recharging. Based on the fundamental assumption that injections into the aquifer resulted in uplifting, groundwater recharging nearby benefited the restoration of the GWGP, providing an insightful example for the treatment of leaning problems in other ancient buildings. The south palace wall of WP was subsiding less than 4 mm/year. The Daming Palace of the Tang Dynasty remained stable throughout the monitoring period. The Xingjiaosi Pagodas (XP) remained stable with ∼1 mm of accumulative deformation until May 2022 when a subsiding trend was observed. On-site observations and numerical modeling revealed the southwest-leaning status of Xuanzang Pagoda (XZP) at XP, which may be exacerbated by the local northwest leaning observed by InSAR. The findings were speculative and lacked quantitative validation or ground-truth support. Nevertheless, InSAR documents the past, while 3D laser scanning records the present. Analyzing the scientific data from the past and present is of great significance for future preservations of World Heritages.