Search

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]

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 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]

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]

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]