Ongoing depletion of Iran’s groundwater, driven by human extraction, has contributed to 108 incidences of basin-scale land-surface subsidence covering 29,600 km² (>10 mm/yr, 1.8 %) of the country, 75 % of which correlates with agriculture. We find Karaj city, neighbouring Iran’s capital Tehran, is exposed to the steepest surface velocity gradients (angular distortion, β) caused by differential subsidence rates, with 23,000 people exposed to ‘high’ subsidence induced hazard. We further use these velocity gradients to aid identification of structural and geological controls on surface velocities of seven of Iran’s most populated cities, identifying potentially unmapped tectonic faults. We demonstrate that most of Iran’s subsidence is permanent (inelastic), with the spatial pattern of the proportion of inelastic deformation potentially depending on geology. During a recent, severe regional drought (2020–2023) we demonstrate the control of precipitation on the elastic, recoverable subsidence deformation magnitude with the elastic to inelastic deformation ratio falling from 41–44 % pre-drought to 31–36 % post-drought. We use automatically processed short baseline networks of Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) data, 2014–2022, to generate and estimate these ground displacements through time. We correct for atmospheric noise using weather model data and perform time series analysis in the satellite line-of-sight direction, serving this data through an open-access online portal. For each subsidence region, we decompose line-of-sight velocities into 100 m resolution vertical and horizontal (east-west) surface velocity fields. We use temporal Independent Component Analysis to constrain automatically and manually the inelastic and elastic components of subsidence, respectively.

Quantifying interseismic deformation of fault networks which are predominantly deforming in a north-south direction is challenging, because GNSS networks are usually not dense enough to resolve deformation at the level of individual faults. The alternative, synthetic aperture radar interferometry (InSAR), provides high spatial resolution but is limited by a low sensitivity to N-S motion. We study the active normal fault network of Western Anatolia, which is undergoing rapid N-S extension, using InSAR. In the first part of this study, we develop a workflow to assess the potential of decomposing InSAR line-of-sight (LOS) velocities to determine the N-S component. We use synthetic tests to quantify the impact of noise and other velocity components and outline the requirements to detect N-S deformation in future studies. In its current state, the N-S deformation field is too noisy to allow robust interpretations, hence in the second part we complement the study by including vertical deformation. Since most faults in the study region are normal faults, the high-resolution vertical velocity field provides new insights into regional active faulting. We show that tectonic deformation in the large graben systems is not restricted to the main faults, and seemingly less active or inactive faults could be accommodating strain. We also observe a potential correlation between recent seismicity and active surface deformation. Furthermore, we find that active fault splays causing significant surface deformation can form several kilometres away from the mapped fault trace, and provide an estimate of current activity for many faults in the region.

Embedded between the Tian Shan, Pamir, and Hindu Kush, the Tajik depression is a remnant of the Mesozoic-Miocene Tajik-Tarim basin system. Since ~12 Ma, westward collapse of the north-advancing Pamir-Plateau crust inverted the Tajik basin into a thin-skinned fold-thrust belt with ~150 km of ~E-W shortening distributed between foreland- and hinterland-vergent structures. Geodetically-derived shortening rates decay westward from ~15 to 2 mm/yr. Seismicity outlines the ~east-striking dextral Ilyak fault, bounding the fold-thrust belt in the north, and distributed shortening in the central and eastern Tajik depression. We derived E-W and vertical deformation-rate maps from radar interferometric time-series, consisting of 900+ radar scenes acquired over 2.0-4.5 years, and available accurate positioning data. We confirm the westward collapse of the Pamir and the drastic shortening-rate decline across the Main Pamir Thrust at the Pamir front. In the Tajik depression, the maps unveil a combination of basin-scale tectonics, local halokinesis, and seasonal/weather-driven soil or near-surface effects. Although the Tajik-basin strata move westward with rates decreasing away from the Pamir, the most external Babatag backthrust currently absorbs the highest shortening (~6 mm/yr) as it has done in the past (>20 km). The Ilyak fault accommodates ~5-8 mm/yr, eastward-increasing slip; rates decay sharply across the fault, suggesting a locking depth of <1 km - possibly creep. At least 10 mm/yr uplift and westward motion occur across the Tajik-depression-Pamir transition, including the sinistral Darvaz fault zone, likely outlining a crustal-scale ramp. The Hoja Mumin salt fountain is spreading laterally at >300 mm/yr.

Interferometric Synthetic Aperture Radar (InSAR) is used to measure deformation rates over whole continents to constrain tectonic processes. The resulting velocity measurements are only relative, due to unknown integer ambiguities introduced during propagation of the signal through the atmosphere. However, these ambiguities mostly cancel when using spectral diversity to estimate along-track motion, allowing measurements to be made with respect to a global reference frame. Here, we calculate along-track velocities for a partial global dataset of Sentinel-1 acquisitions and find good agreement with ITRF2014 model values. We include corrections for solid-earth tides and gradients of ionospheric total electron content. By combining data from ascending and descending orbits we are able to estimate north and east velocities with average precision of 4 and 20 mm/year, respectively. Although we have calculated these over large 250x250 km areas, such measurements can also be made at much higher resolution, albeit with lower accuracy. These “absolute” measurements can be particularly useful for global velocity and strain rate estimation, where GNSS measurements are sparse.

The launches of the Sentinel-1 synthetic aperture radar satellites in 2014 and 2016 started a new era of high-resolution velocity and strain rate mapping for the continents. However, multiple challenges exist in tying independently processed velocity data sets to a common reference frame and producing high-resolution strain rate fields. We analyse Sentinel-1 data acquired between 2014 and 2019 over the northeast Tibetan Plateau, and develop new methods to derive east and vertical velocities with ~100 m resolution and ~1 mm/yr accuracy across an area of 440,000 km^2. By implementing a new method of combining horizontal gradients of filtered east and interpolated north velocities, we derive the first ~1 km resolution strain rate field for this tectonically active region. The strain rate fields show concentrated shear strain along the Haiyuan and East Kunlun Faults, and local contractional strain on fault junctions, within the Qilianshan thrusts, and around the Longyangxia Reservoir. The Laohushan-Jingtai creeping section of the Haiyuan Fault is highlighted in our data set by extremely rapid strain rates. Strain across unknown portions of the Haiyuan Fault system, including shear on the eastern extension of the Dabanshan Fault and contraction at the western flank of the Quwushan, highlight unmapped tectonic structures. In addition to the uplift across most of the lowlands, the vertical velocities also contain climatic, hydrological or anthropogenic-related deformation signals. We demonstrate the enhanced view of large-scale active tectonic processes provided by high-resolution velocities and strain rates derived from Sentinel-1 data and highlight associated wide-ranging research applications.

InSAR measurements of ground displacement are relative, due to unknown integer ambiguities introduced during propagation of the signal through the atmosphere. However, these ambiguities mostly cancel when using spectral diversity to estimate along-track (azimuth) velocities allowing measurements to be made with respect to a terrestrial reference frame. Here, we calculate along-track velocities for a partial global dataset of Sentinel-1 acquisitions as processed by the COMET LiCSAR system, and find good agreement with model values from ITRF2014 plate motion model. We include corrections for solid-Earth tides and gradients of ionospheric total electron content based on a moderate resolution model IRI2016. Application of tidal corrections improves the average velocity precision from 23 to 11 mm/yr. Ionospheric corrections, however, have significant effect only in near-equatorial regions. The median difference between along-track velocities and values predicted by ITRF2014 is 3 mm/yr. A preliminary study using reprocessed precise orbit determination products in a limited dataset shows significant improvement in both precision and accuracy. By combining data from ascending and descending orbits we are able to estimate north-south (N-S) and east-west (E-W) velocities with an average precision of 3 and 16 mm/yr, respectively. Although we have calculated these estimates over large 250 x 250 km areas, such measurements can also be made at much higher resolution, albeit with lower precision. These “absolute” measurements can be particularly useful for global velocity and strain rate estimation, where GNSS measurements are sparse. We will also investigate large-scale averages of across-track (range) pixel offsets, which are most sensitive to E-W and vertical displacements, and perform a comparison to a GNSS network in selected areas.