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Ground deformation on a regional to local scale is the consequence of a wide range of natural processes such as tectonic and anthropogenic activities. Globally, the over-extraction of groundwater and hydrocarbon exploitation are the primary causes of ground subsidence. The current study demonstrates regional scale ground subsidence analysis of the Dibrugarh and Digboi regions of Brahmaputra alluvial plain, Assam, Northeast India. To understand the ongoing surface deformation satellite base, the RADAR technique has been applied using SENTINEL-1A data, which were acquired between 15 October 2015 to 25 January 2022. The assessment carried out via the time series analysis of the radar data suggests that the Dibrugarh area is subsiding at a rate of ~5 mm/yr, whereas the Digboi is deforming at a much faster rate (±22 mm/yr) than Dibrugarh. The presence of active faults in the subsurface and associated deformation is another reason for active ground subsidence. The outcomes of the current study validate that the study area is currently undergoing active subsurface deformation caused by both endogenic as well as exogenic processes. Furthermore, our Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) and satellite-based analysis suggest that the over-exploitation of the natural resources is enhancing the rate of deformation in the Brahmaputra alluvial plain in the northeast of India. [ABSTRACT FROM AUTHOR]

The key objective of the present study is to estimate the surface displacement and to understand/monitor the active deformation pattern in the Kachchh region post the 2001 Bhuj Earthquake by implementing the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSI) and Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques. We employed the ENVISAT ASAR (15 images), ALOS PALSAR (6 pairs) and SENTINEL-1A (117 images) data sets acquired during the periods 2003–2005, 2007–2009, and 2016–2020 respectively. The PSI results of the Envisat dataset reveals that the Kachchh mainland region has undergone an average surface deformation of ± 22 mm/yr during 2003–2005. The maximum displacement observed from the ALOS PALSAR data sets (Window-1 to 6) during the period 2007–2009 is ∼ ± 1.2 cm. Further, the ground displacement observed from the Sentinel-1A dataset during the period 2016–2020 is ±16 mm/yr for the west-central region and 6 mm/yr uplift and 8 mm/yr subsidence in the eastern Kachchh mainland region. Surprisingly, high rate of deformation is detected towards the Pachham Island, Banni, Rann and the eastern region of the Kachchh after the 2001 Bhuj event. Correlating the results of different data sets, it is concluded that the deformation is high near the vicinity of the fault zones indicating the tectonically active nature of the faults. From the obtained results, we infer that, post the 2001 Bhuj earthquake, the surface displacement in the Kachchh mainland region is escalated till 2009 which is due to continuous aftershock activity and then started declining because of the ongoing seismic settlement. The acquired deformation rates are correlating well with the GPS derived displacement rates. Further, our results will assist in accurately demarcating the extent of the fault zones and also helps in precisely marking the areas undergoing active deformation, which will aid in micro zonation studies, mitigation planning and also for the preparation of an active tectonic map for the region. [ABSTRACT FROM AUTHOR]

Active surface deformation, displacement pattern, and erosional variability is estimated using the geomorphologically sensitive morphometry along with the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) technique using the Sentinel-1Adata (119 images) acquired between 07- 02-2017 and 10-02-2021. The average velocities for this dataset are estimated to be between ±11 mm/y. The Raunthi River catchment from where the flood was triggered is undergoing ~8 mm/y subsidence and ~10 mm/y uplift. Compared to this the basin wide deformation (Rishi Ganga basin) is estimated to be around ±10 mm/y with commulative ground displacement of around ±45 mm. The times series analysis suggests an increase in the ground displacement by around 5 mm/y and seems to be responsible for the expansion of pre-existing cracks in the vicinity of the Vaikrita Thrust (VT) and subsequent failure of the northern face of Nandi Peak on 7th February 2021. The Global Positioning System (GPS) derived strain distribution pattern indicate a relatively higher accumulation of strain (>0.35µ strain/y). The normalized steepness index (k sn) variation along the longitudinal section of Rishi Ganga and Raunthi River sub-basin in Central Himalayan region shows anomalous increase at the glacio-fluvial transitional processes. Moreover, the χ profiles as well as planform plots shows anomalously lower values within the Raunthi River sub-basin when compared with the Rishi Ganga basin. Based on the lower values of χ it is observed that Raunthi River sub-basin is undergoing high erosion which can be caused by the presence of sheared lithology and incision of the relict glacial and paraglacial sediments. We negate the suggestion that abrupt rise in the temperature was the major triggering mechanism for the recent disaster, instead it is the sheared lithology and pre-existing fissure developed because of differential uplift and subsidence in Raunthi River that led to the wedge failure and subsequent flash flood. Had the climate was the major driver of the recent tragedy ?, it should have impacted multiple hanging glaciers in the Rishi Ganga valley. Therefore, the study calls for detailed geomorphological, structural and glaciological investigation in regions dominated by glacial and paraglacial processes in the strategic regions of the Himalaya. Towards this, the state of art PSInSAR technique seems to provide fast and reliable detection of terrain instability/stability along with identification of potential areas of slope failures in near future in the glacial and preglacial zones. [ABSTRACT FROM AUTHOR]

The consequence of strain accumulation along various Himalayan thrusts is manifested in shaping the topography and present day lanscape features of the Himalaya. Consequently, the strain accomodation is attributed to the occurrence of various devastating earthquakes in the Himalayan domain including 1905 Kangra earthquake (Mw 7.8) which occurred along the Kangra valley fault. In the present study, we analyzed and estimatedsss fault related parameters, gradient-length anomaly (GLA) analysis together with Interferometric Synthetic Aperture Radar (In-SAR) measurements to understand the landscape evolution and deformation pattern within the Soan dun (piggy back basin) in the northwest Himalayan front. We combined the results of geodetic, geological, geomorphology and InSAR to constrain the uplift and subsidence between Himalayan Frontal Thrust (HFT) and Main Boundary Thrust (MBT) zones. The estimated results of fault parameters reveal that the horizontal shortening of northwest Himalaya is higher than the vertical uplift. The computed values of GLA magnitude analysis for the uplifted region vary from −9.21 to −0.77, whereas these range from 5.48 to 26.60 for the subsided region. The depicted range of vertical deformation observed from the InSAR measurements ranges from −3.13 to +3.14 mm/y, where the positive and negative value of phases are correlated with the ground uplift and subsidence. The rate of deformation observed from Persistent Scatterer Interferometry (PSI) phase velocity and GLA magnitude is positively supported by the chronologically constrained uplift rates as 3.4 ± 0.3 mm/y. The geomorphic evidences such as folded, tilted and truncated alluvial fan surfaces, offsetting of channels, fault scarps and displaced sedimentary sequences indicate active nature of the Soan dun. The study would be eventually useful for seismic hazard assessment and future infrastructure development in the seismotectonically active regions like Soan dun of NW Himalayan front. [ABSTRACT FROM AUTHOR]

In the present study, the rate of deformation of the Kashmir basin has been determined using the Sentinel-1A based Persistent Scatterer Interferometry Synthetic Aperture Radar (PSInSAR). The study reveals highest rate of uplift in the Pir-Panjal range (8–13 mm/y) whereas, in the Saribal range the rate of upliftment is 5–6 mm/y. The line of sight displacement in the Kashmir basin was recorded in the range of −20 to +30 mm/y over the period of 2015 to 2021. However, the temporal displacement variation in the Kashmir valley varies in different years during the observation period and was found maximum in the year 2021. The Persistent Scatterer Interferometry (PSI) clearly show dominant uplift in the valley and surrounding hill ranges. The PSInSAR results were further validated with the GPS based deformation rates, which indicates a maximum of 10 mm/yr of deformation in the study area. The high / lows of gravity and magnetic based surveys are well corroborated with the observed positive and negative anomalies of present PSInSAR velocity results. Further, the Global Positioning System (GPS) based crustal strain results are also collectively substantiating our PSInSAR based crustal behaviour of the Kashmir basin. • Sentinel-1a based crustal deformation of the Kashmir basin. • The Persistent Scatterer Interferometry results shows show dominant uplift in the valley and surrounding hill ranges. • The seismic based high (uplift) and lows (subsidence) of gravity and magnetic are well corroborated with PSInSAR results. • GPS derived strain analysis shows average compression of −7.22 × 10−8 nano strain/year. [ABSTRACT FROM AUTHOR]

The co-seismic deformation of the 28th April 2021 Assam earthquake with a magnitude of 6.4 has been investigated using the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR). The results obtained from the PSInSAR are validated with the results of the Global Positioning System (GPS). It is observed that the co-seismic deformation of the earthquake is not visible because of the atmospheric noise. Therefore, we used the Sentinel-1 time-series data of the area to minimize the atmospheric noise effect the data using the Atmospheric Phase Screening (APS) processing of Sentinel-1 time series data. The time-series analysis shows minor changes that occurred during the earthquake. Firstly, the detection of coherence-based changes was carried out to identify the most affected areas, caused by the earthquake. The results of time series analysis suggest that the region located to the north of the Brahmaputra River is subsiding at a much faster rate (−25 to -75 mm/y) than its southern counterpart, where the southern part is subsiding with an average velocity of −0.1 to −15 mm/y. The subsided locations identified using the PSInSAR are further confirmed by the presence of liquefaction features, ground cracks, and tilted buildings related to post-liquefaction ground settlement. To see the deformation along the Bomdila Fault (BF), re-analysis of the available GPS results has been carried out and the derived results reveal a significant amount of deformation (∼4 mm/y) associated with BF and Jorhat Fault (JF); whereas the deformation associated with Kopili Fault (KF) is 3.14 mm/y. Further, our results suggest the presence of compressional strain in the BF zone, while extensional strain in the KF zone. The earthquake focal mechanism analysis suggests that the event of the April 2021 was primarily associated with the BF rather than the KF. • We investigated co-seismic deformation caused by 28th April 2021 Assam earthquake. • Time-series analysis reveals significant amount of ground subsidence in the area. • We identified higher subsidence rates towards the north of Brahmaputra River • GPS result suggests that the Bomdila fault (BF) is deforming much faster than KF. • The identified co-seismic deformation of BF is ∼4 mm/y and 3.14 mm/y along the KF. [ABSTRACT FROM AUTHOR]

The focus of the present study is to estimate the active surface deformation/displacement affecting the landscape of the eastern Kachchh basin with a particular emphasis on the Wagad, Khadir Island, Bela Island, Chorar Island, and adjoining regions by implementing Differential Interferometry Synthetic Aperture Radar (DInSAR) technique using ENVISAT and SENTINEL-1A radar imagery. To evaluate the deformation pattern using DInSAR, we used ENVISAT-ASAR 2003 to 2005 and 2006 to 2009 data products and SENTINEL-1A data set of 2018–2020. The cumulative displacement of 0.2–0.3 cm for the period of 2003–2005 and 0.19–0.22 cm for the period of 2006–2009 has been observed for the South Wagad Fault region. Similarly, the results acquired from SENTINEL-1A data set revealed a cumulative displacement of 0.16–0.18 cm for the period of 2018–2020. The Island Belt Fault zone shows 0.27 cm displacement, while it is 0.10–0.17 cm for the Gedi Fault zone. The rate of deformation estimated from the present study is well corroborated with the existing results of GPS driven uplift rates. The combined results of DInSAR and GPS indicate that the northern part of the Wagad region is deforming much faster than the south Wagad region. The displacement detected to the east of the epicentral zone of the 2001 Bhuj earthquake indicates the presence of a zone of weaker structures, which may trigger a large magnitude earthquake in the future. Our estimated results of the short-term ground displacement are well corroborated with the existing geological information. This ground displacement is attributed to the tectonic subsidence towards the eastern part of the South Wagad Fault region and within the wide zone of the Island Belt Fault and Gedi Fault zones. The areas with a high amount of displacement have experienced continuous seismicity during the last two decades in the Eastern Kachchh region and might encounter moderate to high seismicity in the near future. The results also provide a better understanding of the active surface deformation pattern taking place in the seismically sensitive eastern Kachchh region. [ABSTRACT FROM AUTHOR]