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The current geodetic investigation is based on nearly a decade of continuous Global Positioning System (GPS) data towards the western part of the Indian Plate (2009–2019). This research focused on the Kachchh Rift Basin (KRB), the seismically most active intra‐plate region of the Indian Plate, which has seen three ≥ M 7.0 earthquakes in the last two centuries. The GPS stations on the northern and southern margins show SSW and NNE directed motion, indicating that the KRB is currently under the influence of regional compressive stress on both flanks and the same is reflected in the form of earthquake activity in the center portion. Furthermore, the existence of intra‐basin stress, in addition to regional stress, increases strain accumulation and results in the creation of a Principal Deformation Zone (PDZ) in the central part of the KRB. The average annual deformation in the middle of KRB remains 1.0 ± 0.5 mm/year, while sites near the South Wagad Fault (SWF) experience 1.2 mm/year of fault parallel motion. The dominant fault normal motion along the flanks with a maximum fault parallel motion in the middle intimates the existence of strike‐slip tectonics in the central Kachchh. The geometric relationship of strike‐slip faults in a compressive margin and strain accumulation in pre‐existing faults (PDZ) is responsible for current strike‐slip and thrust motion in the Kachchh, including the 2001 Bhuj earthquake (M 7.7). Our geodetic model is well‐corroborated with the geological observations of the wrench fault model of strike‐slip faults. PS‐InSAR results in the northern part of the region between Khadir and Bela Islands show ≤6.0 mm of annual LOS displacement. GPS results indicate ≈ 1.3 to 1.4 ± 0.5 mm/year of fault parallel motion along the transverse Ekal Amrapar Fault (EAF). The non‐significant variation in GRACE‐derived TWS values (from 2009 to 2018) rules out non‐tectonic deformation in the vicinity of EAF and thus points to tectonic activity as the cause of the derived deformation in the region. [ABSTRACT FROM AUTHOR]

Presently, ground subsidence in urban areas is becoming a peril to the infrastructure and society. In this study, we conducted a detailed analysis of the results, based on the Persistent Scatterer Interferometry (PSI), Global Navigation Satellite System (GNSS) and groundwater in the 'World Heritage City' of Ahmedabad, a major metro city in western India. The PSI technique is applied to measure the ground subsidence using the Sentinel 1 A dataset for the period 2017 to 2020. The results reveal a subsidence, maximum up to the level of 25mm/yr in the areas of the southeast and west parts of the city. Analysis derived from GNSS results indicates a significant amount of ground subsidence based on the 2009-2020 dataset. Groundwater data (1995-2019) were analyzed to identify factors likely to cause ground subsidence and the results are in close agreement with the PSI and GNSS results. [ABSTRACT FROM AUTHOR]

The Persistent Scatterer Interferometry (PSI) and Global Navigation Satellite System (GNSS) techniques were used to identify the deformation rates in the Saurashtra region, western India. A sizable number of mild to severe earthquakes (with up to M5.1) have been observed in this part of the Indian plate. In order to calculate the crustal deformation, 241 Sentinel 1A images of path 107 with frame numbers 518 and 523, acquired between 2017 and 2020, were used. Similarly, processing of the GNSS dataset was done for four sites between 2009 and 2020. The foremost geodetic results from Saurashtra indicate the existence of a significant amount of deformation. PSI results show movements towards the satellite line of sight (LOS) of up to 5.0 ± 2.0 mm/year at several places and GNSS results indicate horizontal movements of less than 1.0 ± 0.4 mm/year and vertical movements of up to 2.3 ± 0.5 mm/year in the Saurashtra region. The projected LOS displacement of the GNSS is closely comparable with the PSI derived displacement. The results highlight isolated deformation pockets in various parts of the study area. Further, two loci with significant linear displacement were observed in south and east Saurashtra. Considering the seismic activity of the region, the inferred deformation rates may pose increased seismic risk for the region. [ABSTRACT FROM AUTHOR]

We analyze the behavior of Total Electron Content (TEC) in the Ionosphere using the GPS data between 2009 and 2017 towards the western part of India. The GPS data used in the present study consists of 22 Continuously Operating Reference Sites (CORS), bounded between 200- 240 N Latitude and 680 - 740 E Longitude. All the GPS data used in the study are generated using the Leica 1200 receivers and AX1202GG antennas with a sampling interval of 0.03 Hz. The TEC value of this study is calculated using the L-band GPS frequencies L1 (1575.42 MHz) and L2 (1227.36 MHz). The results reveal maximum TEC values during the daytime (03.30–04.30 IST) for all the years and a maximum of 120 TECu (TEC unit) was observed during the year 2014. The reflection of seasonal variation was visible in the time-series of TEC in all the years, while E season (March, April, September and October) observed maximum TEC values in all the stations. The mean monthly TEC values of the present study illustrate the solar cycle-24 and the coefficient of correlation (r 2) of 0.74 indicates a close relationship between the sunspot number and TEC values. A fall of 35% TECu was observed on the annular solar eclipse day on 15 January 2010. [ABSTRACT FROM AUTHOR]

In this study, we present the first estimates of crustal deformation using the time series (2009–2015) from GPS Network of Gujarat (GNG), comprising 10 GPS continuous and 5 campaign mode stations in the seismically active Kachchh region. The GPS data were processed using GAMIT/GLOBK/GLORG software and results reveal very low amount of intra-plate deformation in this part of the Indian plate. International Terrestrial Reference Frame (ITRF) velocity of sites deduced in this study indicates 46–51 mm/yr of motion with one sigma uncertainty. A maximum of ≈3.0 ± 0.5 mm/yr of deformation has been estimated in the Kachchh region. However, estimated strain rate from the velocity field indicates a maximum strain of 5 nano-strain/yr. Our results indicate deformation of a weak zone, where earthquakes may trigger due to the combination of local as well as regional stress. The analysis of strain tensors near the major fault systems (KMF, KHF, SWF and GF) indicates strike normal compression in the area. The low rate of deformation, derived in the present study, is important to understand the seismic hazard level in this part of the Indian intra-Plate. [ABSTRACT FROM AUTHOR]

To understand the geodynamics in the vicinity of Dholavira, a Harappan Civilization Site (HCS), in Kachchh - western India, GPS data from 2009 to 2015 were processed and analyzed. Tectonically, this part of northern Kachchh is in the influence of Island Belt Fault (IBF) and Allah Bund Fault (ABF) and is seismically one of the most active intra-plate regions of India. The motion with respect to Indian plate is used for the estimation of deformation and strain rate while fault associated slip rate has been estimated by inverse modeling of observed site motions. The analysis reveals that the ABF deforms with an average rate of 1.8 mm/yr. However, the segmented IBF has a maximum deformation rate of 2.9 mm/yr towards the Pachham Island and minimum towards the Khadir Island. The computation discloses a maximum seismic moment (M 0) of 2.1 × 1024 dyne-cm in this part which corresponds to an earthquake of ≈Mw 6.0. The calculated maximum strain of 0.04 micro-strain/year is low but significant in the intra-plate region. The postseismic deformation, after the Mw 7.7, 2001 Bhuj earthquake is estimated to be low in this part. The reverse along with strike-slip motion of faults builds up stress in the area and accumulating more strain. [ABSTRACT FROM AUTHOR]

We present geodetically estimated crustal strain rates in Uttarakhand Himalaya, a region which has long been considered as a part of seismic gap. We processed and analyzed the GPS data, acquired from the sites enveloping all the litho-tectonic units from the Sub Himalaya in the south to the Tethys Himalaya in the north together with the major Himalayan thrust/fault systems. On the basis of the obtained dataset, we conclude that the maximum amount of crustal shortening takes place towards the hinterland in the vicinity of Main Central Thrust and Inner Lesser Himalaya which is also in agreement with high seismic activity in these sectors. The GPS velocities of the sites (Indian reference frame) show significant variation from the sub-Himalaya to the Tethys Himalaya. The Sub and Inner Lesser Himalayan parts exhibit low deformation rate in contrast to the maximum amount of deformation in the Inner Lesser and Higher Himalayan segments. The strain analysis reveals lateral variation with high strain zones (HSZ) and moderate strain zones (MSZ) within the compressional regime in the Uttarakhand Himalaya. The strain rate of 0.45 and 0.25 micro-strain/year is observed in the HSZ and MSZ respectively. By comparing the strain rate with the seismicity pattern for the past five decades, we suggest that the earthquakes in the HSZ are related with ramp structure of the MHT, whereas, part of accumulated strain in the MSZ is being released in form of the present day seismic activity. [ABSTRACT FROM AUTHOR]

The Gangotri glacier is retreating like other glaciers in the Himalaya and its volume and size are shrinking as well. Reoccupying the historical snout positions using Global Positioning System (GPS) in rapid static mode indicates the varying rates of retreat during different time-spans of the last century, with the total retreat of 1519.13 m in the last 69 years. Post 1971, the rate of retreat of the glacier has declined. Monitoring of glacier terminus using GPS survey in kinematic mode reveals that the glacier has retreated at much lower rate (12.10 ± 0.041 ma-1) between 2004 and 2005. The study further shows that the southern portion of the snout is retreating at significantly lower rate in comparison to the northern part. However, maximum recession (13.76 ± 0.048 m in 2004-05) took place along the centreline of the glacier. [ABSTRACT FROM AUTHOR]

The present study area represents one of the active segments of the frontal part of the Arunachal Himalaya. The major structural boundaries traversing the area are the Main Boundary Thrust (MBT) and the Himalayan Frontal Thrust (HFT) and other local faults are tectonically active, as evident from the landforms that evolved in the fault zones. Strath terraces and uplift fluvial terraces are observed in the hanging‐wall block of the HFT and MBT, and along the HFT straight to curvilinear mountain fronts are observed. Normal faults both transverse and parallel to the strike of HFT are observed in the hanging‐wall block of the HFT. West of Pasighat the sub‐Himalaya terrain resembles a duplex, where there is gradual rise in elevation from the Brahmaputra Plain to the low‐lying hills of the sub‐Himalayan and sudden rise in elevation across the MBT. Drainage aligning to the bedrock structures and stream migrations are observed in the fault zones. Along the MBT, the sub‐Himalayan rocks are thrusted over either by quartzite or black carbonaceous shales, in some sections the MBT is behaving as a back‐thrust that dips towards the south. The MBT has also been displaced by almost N–S‐trending transverse faults where highly sheared bedrocks are also observed. Tilting of Quaternary fluvial deposits are observed in the hanging‐wall blocks of intraformational thrusts at two locations. Signatures of paleoseismic activities in the form of various soft‐sediment deformational structures are observed in Quaternary deposits in the HFT zone and also in the hanging‐wall block of the MBT. To determine the deformation and strain rate accumulation, we have re‐analysed the available GNSS results of the area, which indicate a deformation rate of up to 16 mm/year in the vicinity of the Pasighat region. The GPS‐derived deformation rates are well corroborated with the existing results of peak ground acceleration (PGA) anomalies. The component–wise motion indicates higher fault perpendicular motion in this part, which reveals an accumulation of more strain along the major Himalayan faults. [ABSTRACT FROM AUTHOR]

Quaternary sediments are preserved in disconnected patches along the middle and lower reaches of major river valleys like Damanganga, Par, Ratakhadi and Dongarkhadi in the Dadra and Nagar Haveli region of Konkan coastal belt, Western India. These deposits mainly consist of stratified sand, silt, clay and gravel beds. The study area has been earlier affected by moderate earthquakes. The identified soft-sediment deformation structures (SSDS) are mainly developed in the sand silt, sand gravel and clay beds; and includes intrusive sedimentary bodies (dykes and sills), slump structures, suspended clast blocks and convolute structures. The nature, shape and dimension of SSDS suggest that the trigger mechanism and driving forces for the origin of these structures were seismic shock waves. Sediment loading and storm events as a trigger for the SSDS are less likely the reason and the proximity of these structures to the faults support the inference that it may be of seismic origin. Deformation in the Quaternary sediments of Dadra and Nagar Haveli imply the presence of neotectonic activity and points to an earthquake of magnitude >5.5 that struck the study area after sediment deposition. [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]

A response to a letter to the editor about the article regarding the position coordinates of snout in different years from 1935 and 1971 that was published in the previous issue is presented.

Paleoseismic and archaeological records of the Kachchh Rift Basin (KRB) of western India indicates that the region become tectonically active during the period of Middle to Late Holocene. To understand the relationship between strain accumulation, earthquake genesis, and landform development, we analyzed uplifted Late Quaternary terraces and archaeological evidence along the Kachchh Mainland Fault (KMF) zone. Dividing the elevation of the bedrock strath at each site by their ages, yields vertical uplift rates of 0.29–1.17 mm/y for the KMF zones. Archaeological data from the excavation of the Kotada Bhadli site suggest that the site was occupied during the Late mature Harappan (2300-2500 BCE) period and abandoned around 1900 BCE. The ruins of Harappan civilization at Kotada Bhadli location are resting over the Middle Holocene fluvial sediments. The oldest fluvial sediment is dated to 4 ka, whereas the youngest sediment yielded an age of 3 ka. The chronological constraints in geomorphic and archaeological records suggest that the area was hit by an earthquake around 2200 BC (∼3.5ka). The geomorphic and chronologically constrained uplift rates reveal that the KMF zone of the intraplate region of the Kachchh is geodynamically controlled by several fault segments, which are consistent with the ambient tectonic stress field owing to the northward movement of the Indian Plate concerning the Eurasian Plate. [ABSTRACT FROM AUTHOR]

In the present study, an attempt has been made to delineate anomalous morphotectonic elements in the lower valley of Ravi and Beas rivers of the NW Himalaya by utilising the digital elevation model (DEM) as well as GIS based approach. We selected the surrounding areas of both the rivers as these have developed tectonically formed lakes such as Khajjiar and Rewalsar in late Holocene and lie in the north and south of Kangra re-entrant structure. We generated topographic swath profiles, calculated normalized steepness index (ksn) and hypsometric integral (HI) and conducted lineament analysis and finally correlated the obtained data set with the contemporaneous seismicity to decode the tectonic activity in the region. Based on the calculated HI for both the areas as 0.45 and 0.47, we infer that there are anomalous changes in the steepness, pointing to the presence of active tectonics. By using lineament analysis, geological information and the quantitative analysis, we identified lineaments parallel and oblique to the regional strike of the NW Himalaya, indicating the area as tectonically active. The lower steepness values along the inferred lineaments suggest the presence of strike-slip features that absorb the oblique convergence of the Indian plate with Eurasia. The GPS based additional observations suggest significant amount of deformation, showing higher deformation rate in the vicinity of the Khajjiar as compared to the Rewalsar locality. Based on remote sensing and GIS based approaches, we conclude that the study area is tectonically very active, hence there is need of careful examination of identified structures and impact on the development of infrastructure and seismic hazard assessment of the western Himalaya. [Display omitted] • Pull apart Sundernagar basin and Rewalsar lake were studied. • KJR exhibits higher steepness than the RWL. • Lithology does not affect steepnessand HI distribution locally. • Lineaments with seismicity supports their tectonic nature. [ABSTRACT FROM AUTHOR]

An earthquake of 2006 Mw 5.7 occurred along east–west trending Gedi Fault (GF) to the north of the Kachchh rift basin in western India which had the epicenter in the Wagad upland, which is approximately 60 km northeast of the 2001 Mw 7.7 earthquake site (or epicenter). Development of an active fault scarp, shifting of a river channel, offsetting of streams and uplift of the ground indicate that the terrain is undergoing active deformation. Based on detailed field investigations, three major faults that control uplifts have been identified in the GF zone. These uplifts were developed in a step-over zone of the GF, and formed due to compressive force generated by left-lateral motion within the segmented blocks. In the present research, a terrace sequence along the north flowing Karaswali river in a tectonically active GF zone has been investigated. Reconstructions based on geomorphology and terrace stratigraphy supported by optical chronology suggest that the fluvial aggradation in the Wagad area was initiated during the strengthening (at ~ 8 ka) and declining (~ 4 ka) of the Indian Summer Monsoon (ISM). The presence of younger valley fill sediments which are dated ~ 1 ka is ascribed to a short lived phase of renewed strengthening of ISM before present day aridity. Based on terrace morphology two major phases of enhanced uplift have been estimated. The older uplift event dated to 8 ka is represented by the Tertiary bedrock surfaces which accommodated the onset of valley-fill aggradation. The younger event of enhanced uplift dated to 4 ka was responsible for the incision of the older valley fill sediments and the Tertiary bedrock. These ages suggest that the average rate of uplift ranges from 0.3 to 1.1 mm/yr during the last 9 ka implying active nature of the area. [ABSTRACT FROM AUTHOR]

In present study the results of integrated studies of landform development and geomorphic indices of drainage networks across the South Wagad Fault (SWF) zone have been presented. The SWF is a structure that is morphogenic in nature, creating a 40-m-high E–W trending escarpment that extends ~ 80 km at the southern end of the Wagad uplift. The SWF got reactivated during the Bhuj earthquake of 2001, continued aftershock activity of M ≥ 4 levels were recorded in the epicentral zone, north of the Kachchh Mainland Fault and west of the SWF. Strath terraces along the river valleys and the truncation of alluvial fans along the mountain front, incision, and offset of rivers suggests an active nature of the SWF. To assess the relative tectonic activity, morphometric indices such as stream-gradient ( SL ) index, hypsometric integral ( HI ), basin asymmetry ( AF ), mountain front sinuosity ( S mf ) index, sinuosity index ( SI ), and basin shape ( B S ) have been analyzed. The landform development along the river valley in the SWF zone suggests reactivation of the SWF between 12 and 3 ka. The southern front of Wagad is found to be uplifting at the rate of 2.8 mm/y during the last 12 ka as estimated through OSL dates. The relative index of active tectonics (RIAT) by the study of different geomorphic parameters and field checks indicates that most of the Wagad highland is active. The compressional strain of 0.05 μstrain/y inferred from the GPS study in the SWF area attests to the activeness. [ABSTRACT FROM AUTHOR]