Understanding Joshimath landslide using PS interferometry and PSDS InSAR

The recent subsidence at Joshimath in the Indian State of Uttarakhand led to the displacement of thousands of residents. Large cracks developed in the buildings and on the ground. No extensive and comprehensive deformation measurement of this event has been made. In this study, we use both PS and PSDS InSAR time series to investigate the magnitude, spatiotemporal as well as kinematic evolution of this slow-moving landslide. Eighty-seven ascending Sentinel-1 scenes with a temporal baseline of 1056 days from 2020 to 2023 were stacked for interferometric analysis. StaMPS is employed to identify PS points by their amplitude and phase information. TomoSAR is utilized to stipulate a coherence matrix to form a dense PSDS network of interferograms to surge point density for suitable phase unwrapping. PS and DS points are coupled to develop slope velocity maps revealing mean displacement rates of –84 mm for PS and –107 mm for PSDS, respectively. Cross-section profiles drawn on the slopes of subsidence show target scatterers on CS1, CS2 and CS4, yield a cumulative displacement of 400 mm in the last 3 years. CS3 and CS5 show a total displacement of about 350 mm. This study applies PSDS time-series InSAR to decipher ground movement in traditionally decohered environments. It also seeks to establish the boundaries and intensity of subsidence to aid in the mitigation of failure progression.