The Current State of Research on Deformation, Strain, and Velocity across the Alpine-Himalayan Belt Using Transcontinental Sentinel-1 InSAR and GNSS

MOHIT SHEODE 

Research on present-day deformation across the Alpine-Himalayan belt has crossed a methodological threshold. Regional Sentinel-1 studies in Anatolia, Iran, and Tibet have now been joined by the first transcontinental three-dimensional velocity and horizontal strain-rate field, derived from more than 222,000 radar images acquired during 2016-2024 and a belt-wide GNSS compilation. The result provides approximately 1 km sampling over more than 20 million km² and 11,000 km of active continental deformation. This review assesses what that advance changes scientifically, and what it does not. The emerging belt-wide picture is neither a rigid-block system nor a uniformly deforming continuum. Strain is sharply localized on the North Anatolian, Haiyuan, Kunlun, and related faults, along the Himalayan and Pamir convergence fronts, and within Tibetan rifts; elsewhere, shortening, shear, and extension are distributed across broad interiors. Horizontal velocities are mainly tectonic, whereas much of the short-wavelength vertical field records aquifer depletion, sediment compaction, permafrost change, landsliding, or other shallow processes. The main limitations now arise from how observations are combined: line-of-sight geometry, uneven GNSS density, reference-frame and epoch differences, correlated atmospheric errors, phase unwrapping, regularization, and the treatment of fault creep and postseismic motion. Consequently, kilometre-scale pixels do not imply kilometre-scale independent resolution, and a strain anomaly cannot be equated directly with locked-fault hazard. The next phase should move from static average velocities toward uncertainty-aware four-dimensional models that combine C- and L-band radar, denser GNSS, explicit fault discontinuities, and process-based separation of tectonic and non-tectonic deformation.