Spatiotemporal Analysis of Persistent Surface-Deformation Anomalies at the Shurtan Gas Field, Uzbekistan, Using Sentinel-1 SBAS-InSAR

Introduction. Long-term monitoring of surface deformation is essential for assessing geodynamic processes and ground instability in hydrocarbon-producing regions. This study investigates the spatiotemporal persistence of deformation anomalies across the Shurtan gas field in southern Uzbekistan, a semi-arid region characterized by industrial development and hydrocarbon extraction.

Methods. Sentinel-1 ascending-orbit SAR observations acquired from 2017 to 2024 were processed using the LiCSBAS small-baseline time-series workflow. Mean line-of-sight (LOS) velocity and residual velocity fields were derived for seven consecutive two-year windows. To reduce topography-correlated atmospheric effects, a linear elevation-dependent component was estimated and removed from each residual field. Negative deformation anomalies were defined using the first-quartile threshold (q25), and their recurrence frequency was calculated for each pixel. Persistent clusters were delineated where anomalies occurred in at least four of the seven windows, whereas core zones represented recurrence in at least five windows.

Results. The correction reduced the mean absolute Pearson correlation between residual LOS velocity and elevation from approximately 0.34 to 0.26 and the corresponding Spearman correlation from 0.36 to 0.24. Three spatially coherent persistent deformation clusters were identified, covering approximately 43.6, 13.5, and 1.3 km². Their recurrence across multiple observation windows suggests that these patterns cannot be explained solely by isolated temporal fluctuations or a single anomalous period.

Conclusions. The proposed recurrence-based analysis improves the separation of persistent deformation zones from transient and topography-correlated signals. The results establish a spatial basis for targeted field investigations and continued integration of InSAR observations with GNSS measurements and production data at the Shurtan gas field.