Browsing by Author "Uma Shankar"

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3D and 2D topographic correction to estimated geothermal gradient from the base of gas hydrate stability zone in the Andaman Forearc Basin
(KeAi Communications Co., 2024) Uma Shankar
Methane gas hydrate related bottom-simulating reflectors (BSRs) are imaged based on the in-line and cross-line multi-channel seismic (MCS) data from the Andaman Forearc Basin. The depth of the BSR depends on pressure and temperature and pore water salinity. With these assumptions, the BSR depth can be used to estimate the geothermal gradient (GTG) based on the availability of in-situ temperature measurements. This calculation is done assuming a 1D conductive model based on available in-situ temperature measurement at site NGHP-01-17 in the study area. However, in the presence of seafloor topography, the conductive temperature field in the subsurface is affected by lateral refraction of heat, which focuses heat in topographic lows and away from topographic highs. The 1D estimate of GTG in the Andaman Forearc Basin has been validated by drilling results from the NGHP-01 expedition. 2D analytic modeling to estimate the effects of topography is performed earlier along selected seismic profiles in the study area. The study extended to estimate the effect of topography in 3D using a numerical model. The corrected GTG data allow us to determine GTG values free of topographic effect. The difference between the estimated GTG and values corrected for the 3D topographic effect varies up to ∼5 °C/km. These conclude that the topographic correction is relatively small compared to other uncertainties in the 1D model and that apparent GTG determined with the 1D model captures the major features, although the correction is needed prior to interpreting subtle features of the derived GTG maps. © 2023 Sinopec Petroleum Exploration and Production Research Institute
Assessing S-wave velocity in the shallow subsurface layers of Varanasi city through a combination of passive seismic and standard penetration test measurements
(Springer, 2024) Sangeeta Kumari; Uma Shankar
Abstract: The S-wave velocity (SWV) is a crucial parameter in seismic site characterization and seismic microzonation. In Varanasi city, we determined the shear wave velocity through a dual approach, employing joint inversion of microtremor array survey and the Horizontal to Vertical Spectral Ratio (HVSR) method. This combined analysis from two distinct methods enhances the reliability of our S-wave velocity model for the subsurface soil strata. To assess the S-wave velocity profile in shallow subsurface soil layers, we conducted forward and inverse modelling of geophysical data. This evaluation was cross-referenced with geotechnical borehole data to ensure accuracy. Microtremor measurements were conducted at 115 single stations and 12 array stations in the city. Joint modelling of HVSR and Rayleigh wave phase velocity dispersion provided insights into the site characteristics. Utilizing neighbourhood algorithms, we inverted dispersion curves from microtremor array measurements to obtain the S-wave velocity profile. The results were validated using geotechnical borehole data in the study area. The microtremor-derived S-wave velocity disclosed significant impedance contrasts in the topsoil layer, reaching a depth of approximately 12 m, with velocities ranging from 180 to 250 m/s. The second layer, extending to around 40–50 m, exhibited velocities between 300 and 400 m/s, while the bottom layer surpassed 600 m/s. Comparisons with SPT-derived S-wave velocity confirmed a well-correlated S-wave velocity profile for the top layer. The various methods converged to an average S-wave velocity of 360 m/s up to a depth of 50 m. Research Highlights: S-wave velocity determination through passive seismic measurements. 1D shear wave velocity derived from joint modelling. Estimation of shear wave velocity from SPT-N values using an empirical relation. Validation of observed results with existing SPT borehole data. © Indian Academy of Sciences 2024.
Assessment of gas hydrate accumulations using velocities derived from vertical seismic profiles and acoustic log data in Krishna-Godavari Basin, India
(Elsevier Ltd, 2019) U.S. Yadav; K.M. Shukla; Maheswar Ojha; Pushpendra Kumar; Uma Shankar
The second Indian National Gas Hydrate Program Expedition (NGHP-02) was executed in 2015 in four areas termed as Areas A, B, C and E. During this expedition, twenty five research sites were drilled and/or cored in Krishna-Godavari (KG) and Mahanadi Basins, eastern Indian offshore. During NGHP-02, zero offset vertical seismic profile (VSP) data were acquired at three sites: Sites NGHP-02-17, −19 and −22 in Area B of the KG Basin. In this study, we focus on the three sites in Area B of the KG Basin, where, zero-offset VSP and downhole acoustic log data are used to assess and characterize the gas hydrate deposits. Zero-offset VSP data are correlated with wireline log, surface seismic and synthetic seismic data to characterize and delineate gas hydrate accumulations in the KG Basin. Low velocities ranging from 1500 to 1650 m/s are observed in the unconsolidated shallow sedimentary section above gas hydrate-bearing units, whereas, very high velocities are observed in the acquired acoustic log and VSP data. In the gas hydrate-bearing sedimentary sections, the VSP derived interval velocities range from 2000 to 3000 m/s in the depth interval between 267 and 287 m below sea floor (mbsf) at Site NGHP-02-17, between 1650 and 1750 m/s in the depth interval between 306 and 366 mbsf at Site NGHP-02-19 and between 1700 and 1800 m/s in the depth interval between 198 and 290 mbsf at Site NGHP-02-22. Gas hydrates are distributed both as pore-filling and fracture-filling at all three sites, however, high concentrations are only observed as pore-filling morphology. We estimate the amount of gas hydrate considering both isotropic (pore-filling) and anisotropic (fracture-filling) acoustic reservoir models. Our estimations of gas hydrate saturation match well with the available pressure core data and suggest that high gas hydrate concentrations (to nearly 85% of pore space) are distributed in a load bearing morphology. © 2019 Elsevier Ltd
Assessment of gas hydrate reservoir from inverted seismic impedance and porosity in the northern Hikurangi margin, New Zealand
(Elsevier Ltd, 2021) Uma Shankar; Maheswar Ojha; Ranjana Ghosh
Hikurangi margin, New Zealand, the shallowest subduction zone on Earth is the unique place to study the slow slip creep-like deformation and seafloor failure, and their probable link to the presence of gas hydrate, cold seeps and fluid migration. International Ocean Discovery Program expedition 372 discovered gas hydrate within thin intervals (ranging from ~5 to 25 m) of the deformed sediments in the Tuaheni landslide complex area of the northern Hikurangi margin. Seismic profiles show typical BSRs (bottom simulating reflectors) cutting across the dipping strata throughout the sections. To characterize the reservoir, here, we invert both acoustic impedance (product of velocity and density) and porosity along two perpendicular seismic profiles crossing the well using a model-based post-stack seismic inversion technique. Results show the layer structure of alternate high-impedance with low-porosity and low-impedance with high-porosity sediments. Interestingly, each layer is consisting of thin and relatively low impedance intra-layers, which clearly indicates the possible pathways for fluid and gas migration, and one of the reasons for seafloor collapse in this region. Very low impedance observed below the BSR is due to the gas-charged sediments at the dipping strata, and is the probable source of free-gas migrating upward. Next, we apply rock physics theory to know the distribution of gas hydrate at Site U1517 as well as along two perpendicular seismic profiles. Rock physics modeling using sonic velocity at well location shows that gas hydrate is distributed mainly within the depth intervals of 5–50 m, 90–115 m and 130–155 m with an average saturation of about 10–15% and the maximum concentration of about 35% of the pore space at 100 m depth. Prediction of gas hydrate saturation from the resistivity method using neutron porosity and NMR (nuclear magnetic resonance) logs in Archie's empirical formula shows less saturation compared to that from the sonic log. Whereas, estimated gas hydrate saturation from the chloride concentrations ranges from 0 to 45% of the pore space. The spatial distributions of gas hydrate along seismic profiles are predicted by rock physics theory using the inverted impedance and porosity. Saturation of gas hydrate along the seismic profiles varies from 0 to 40% with an average of ~10% of the pore space. The correlation between inverted impedance and porosity indicates that the high impedance layers are due to low porosity consolidated sediment without significant gas hydrate concentration. Gas hydrate is distributed in relatively high porosity and low impedance layers along the seismic profiles. Our result shows that the amount of gas hydrate concentration is low in this region and sediments are highly deformed/disturbed in the presence of many fluid/gas migration pathways. © 2020 Elsevier Ltd
Estimation of gas hydrate saturation using isotropic and anisotropic modelling in the Mahanadi basin
(Springer, 2019) Uma Shankar; Ashok Kumar Pandey
A base of gas hydrate stability zone was established after coring and drilling under the National Gas Hydrate Program (NGHP) Expedition-01 in the Mahanadi basin. At two sites, logging-while-drilling log data, and, at one site, wireline log data, were acquired during the NGHP Expedition-01. Gas hydrate reservoirs modelling can be performed in two different ways. One way is isotropic (load bearing) and, on the other hand, anisotropic media (fracture filling with gas hydrate). Here, we have performed anisotropic modelling and estimated gas hydrate saturation using P-wave velocity, assuming an incidence angle of 75∘ represents the vertical fracture. The estimated gas hydrate saturation at sites NGHP-01-08 and NGHP-01-09, assuming anisotropic media, reduces the estimate by half compared to the saturation estimation by assuming isotropic media. The saturation at site NGHP-01-19 estimated from the isotropic and anisotropic P-wave velocity models are more or less similar except in the zone (175–210 m) just above the bottom simulating reflector depth, and this zone shows similar reduction in saturation as estimated at sites NGHP-01-08 and NGHP-01-09. Observations show that average gas hydrate saturations are relatively low (up to 5% of the pore space). The saturation of a gas hydrate estimated from an isotropic P-wave model varies from 5% to 20%. However, the saturation estimated from the anisotropic P-wave model shows a variation up to 10% of the pore spaces at three sites. © 2019, Indian Academy of Sciences.
Estimation of gas hydrates saturation and pore pressure prediction from offshore well log data
(European Association of Geoscientists and Engineers, EAGE, 2019) Shalini Singh; Uma Shankar
Estimation of pore pressure and in-situ vertical stress play a vital role in understanding the geomechanical behaviour of deep sedimentary formations especially those bearing gas-hydrates. Often such formations are not hydrostatic, instead the pore pressure is quite elevated. In order to carry out drilling with minimum risk, these abnormal pressures must be predicted precisely. This study has been carried out using conventional well-log data from the site 19 of the Mahanadi basin conducted under the Indian national gas hydrate programme (NGHP). The pore pressure and fracture pressures in the subsurface formation is derived by Bower’s method. The vertical stress has been computed using formation density log. The coefficients of best fit curve have been computed from velocity-effective stress plot for the well under study and applied on the seismic velocity to transform into the effective stress. By using resistivity log data and Archie’s empirical relation at concerned site, the saturation of gas hydrates is calculated.The Zhang’s porosity method of pore pressure prediction has also been used to validate the results obtained from Bower’s method. Since, gas hydrate bearing sediment has higher electrical resistivity than that of the host sediments, two gas hydrate zones have been found in the well in the depth interval between 174 m to 192 m and between 195 m to 213 m with saturations up to 26% and less than 20% respectively. Since LOT (Leak off test) data is not available, Bower’s method has been used to compute the formation fracture pressure. The probable mud weight window has been estimated from calculated pore pressure and fracture pressure. © 2019 1st Indian Near Surface Geophysics Conference and Exhibition. All rights reserved.
Estimation of reservoir properties using pre-stack seismic inversion and neural network in mature oil field, Upper Assam basin, India
(Elsevier B.V., 2024) Pawan Kumar Singh; Uma Shankar
The mature oil fields require comprehensive characterization for enhanced hydrocarbon production, and subsequently demands estimation of reservoir properties. The key properties viz. volume of clay, effective-porosity, hydrocarbon-saturation has been evaluated for an aging Oligocene reservoir of Upper Assam basin, located in northeastern India from seismic and well log data. Elastic properties (acoustic and shear impedance) and density are derived from pre-stack inversion of 3D seismic data. These elastic properties are analyzed for their sensitivity for discrimination of lithology and fluid-content, and many derived attributes are computed from elastic properties. These attributes are assessed for their predictability to predict the target reservoir properties using multi-attribute analysis. For each of the target property neural network is trained with the most predictable attributes, and multi-dimensional, non-linear neural network models are created using multilayered feed forward neural network (MLFN), followed by Probabilistic neural network (PNN). The specific neural network models for each target property are employed for quantitative estimate of volume of clay, effective-porosity, hydrocarbon-saturation in inter-well regions. The estimated properties leverage the identification of untapped oil reserves and provide promising opportunity for enhanced production through drilling of infill wells. © 2024 Elsevier B.V.
Evaluation of site-specific characteristics using microtremor measurements in the Gorakhpur city of Uttar Pradesh, India
(Springer, 2021) Uma Shankar; Pawan Kumar Yadav; A.P. Singh; Arun Kumar Gupta
The microtremor measurements are carried out in and around the Gorakhpur city (Uttar Pradesh), India, overlain by alluvium at about 150 sites to understand the local site conditions. Horizontal-to-vertical spectral ratio (HVSR) confirms that the majority of sites have a predominant frequency of ~0.45 Hz, which may suggest the prevalence of thick soft sediments in the area. Conspicuously, a number of multiple peaks in HVSR curves at few sites may reflect the presence of different interfaces with significant impedance contrasts. Maximum amplification is observed of 4.0–5.3 to the NW–SE of the city, whilst few sites in the city are found to be associated with different values of peak amplification factor that varied between 2.0 and 4.0. It is also observed that the ground vulnerability index (Kg) in Gorakhpur city has values higher than 10.0 at most of the sites. Assimilation of 1-D velocity model for the city clearly shows that low shear wave velocity (~300 m/s) down to the depth of ~35 m, suggesting thick piles of sediments that may correspond to fluvial river system in the area, whilst the peak frequency of about 0.45 Hz may correspond to the Quaternary–Tertiary sediment boundary that may exist at deeper layers (~1000 m). The inference of this study may be used as inputs for earthquake risk management by reducing the severity of earthquake shaking through design of earthquake risk resilient structures. © 2021, Indian Academy of Sciences.
Functional response of grub and adult of Coccinella septempunctata (L.) and Coccinella transversalis (Fabr.) on mustard aphid, Lipaphis erysimi (Kalt.)
(2010) Sanjeev Rai; N.N. Singh; Uma Shankar
Studies were conducted in the laboratory of Entomology, Institute of Agricultural Sciences, BHU, Varanasi to determine the effect of different prey (aphid) densities (functional response) of second, third, fourth instars of grub and adult of two important aphidophagous coccinellids, Coccinella septempunctata (L.) and Coccinella transversalis (Fabr.) i.e. 20, 40, 80, 100, 200, 400 and 800, during 2003 and 2004. The present study revealed that the prey density has significant influence on the preying capacity of the grub and adult of both species. Prey consumption by the second, third, fourth instars of grub and adult of Coccinella septempunctata (L.) and Coccinella transversalis (Fabr.) followed an increasing trend from lower prey density (20) to higher prey densities i.e. 40, 80, 100, 200, 400 and 800, while the percentage of prey consumption decreased with increasing prey (aphid) densities. It was also observed that functional response of fourth instar grub was found to be maximum (287.7 ± 2.87) (187.7 ± 2.56) followed by third instars, adult and second instar grub of C. septempunctata and C. transversalis on prey density of 800, respectively. The determination factor (R2) was found to be significant. © 2010 Taylor & Francis.
Gas hydrate saturation from NGHP 02 LWD data in the Mahanadi Basin
(KeAi Communications Co., 2024) Uma Shankar; Pradeep Kumar Yadav; Sneha Devi; Udham Singh Yadav
During the Indian National Gas Hydrate Program (NGHP) Expedition 02, Logging-while-drilling (LWD) logs were acquired at three sites (NGHP-02-11, NGHP-02-12, and NGHP-02-13) across the Mahanadi Basin in area A. We applied rock physics theory to available sonic velocity logs to know the distribution of gas hydrate at site NGHP-02-11 and NGHP-02-13. Rock physics modeling using sonic velocity at well location shows that gas hydrate is distributed mainly within the depth intervals of 150–265 m and 100–215 mbsf at site NGHP-02-11 and NGHP-02-13, respectively, with an average saturation of about 4% of the pore space and the maximum concentration of about 40% of the pore space at 250 m depth at site NGHP-02-11, and at site NGHP-02-13 an average saturation of about 2% of the pore space and the maximum concentration of about 20% of the pore space at 246 m depth, as gas hydrate is distributed mainly within 100–246 mbsf at this site. Saturation of gas hydrate estimated from the electrical resistivity method using density derived porosity and electrical resistivity logs from Archie's empirical formula shows high saturation compared to that from the sonic log. However, estimates of hydrate saturation based on sonic P-wave velocity may differ significantly from that based on resistivity, because gas and hydrate have higher resistivity than conductive pore fluid and sonic P-wave velocity shows strong effect on gas hydrate as a small amount of gas reduces the velocity significantly while increasing velocity due to the presence of hydrate. At site NGHP-02-11, gas hydrate saturation is in the range of 15%–30%, in two zones between 150-180 and 245–265 mbsf. Site NGHP-02-012 shows a gas hydrate saturation of 20%–30% in the zone between 100 and 207 mbsf. Site NGHP-02-13 shows a gas hydrate saturation up to 30% in the zone between 215 and 246 mbsf. Combined observations from rock physics modeling and Archie's approximation show the gas hydrate concentrations are relatively low (<4% of the pore space) at the sites of the Mahanadi Basin in the turbidite channel system. © 2023 Sinopec Petroleum Exploration and Production Research Institute
Gas Hydrates, Subsurface Structures and Tectonic Features of the Tuaheni Landslide Complex in the Northern Hikurangi Margin, New Zealand, Revealed by Seismic Attribute Analysis
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Maheswar Ojha; Uma Shankar; Ranjana Ghosh
The Tuaheni Landslide Complex, located on the upper slope of the northern Hikurangi Margin in New Zealand, is a unique place to research on slow slip creep-like deformation and seabed failure, as well as their possible relationship with the presence of gas hydrates, cold seeps, and fluid migration. Based on the visual interpretation of seismic data, it is sometimes very difficult to identify various subsurface structures and tectonic features. We study certain seismic attributes, namely the reflection strength, instantaneous frequency, instantaneous phase, and the Hilbert transform, in the Tuaheni Landslide Complex and observe that these attributes play a very important role in identifying and interpreting various subsurface geological features and bed boundaries that are not clearly visible in the seismic sections. In general, these seismic attributes are studied to identify hydrocarbons such as oil and gas. However, in this present study these seismic attributes nicely illustrate the fluid migration pathways, the decollement of the sediment slide, the base of the debris flow, the base of the deformed sediment and gas migration, etc., along two perpendicular seismic profiles crossing the Site U1517 of IODP Expedition 372. The instantaneous phase and Hilbert transform attribute depict the bed boundaries and discontinuities, whereas the reflection strength and instantaneous frequency attributes characterize the various strata in terms of whether they are associated with fluid at their bases. The possible role of tectonic activity and seafloor slope failure due to gas hydrate dissociation and vice versa is clearly visible through fluid-filled weak zones in the seismic attribute volumes. Gas hydrates are dissociating and BSRs are abruptly pinching out towards the seafloor due to the movement of hot fluid and free gas, enhancing seafloor sliding and local tectonic activities together. © 2023 by the authors.
Identification of significant subsurface geological structural feature using gravity and magnetic survey in parts of Kamrup district, Assam and West Khasi Hills district, Meghalaya
(Springer, 2023) Ashish Kumar; Rajesh Kumar; Chandrai Murmu; Uma Shankar; Nabendu Majumdar
Gravity and magnetic survey have been carried out in parts of the Kamrup district of Assam and the West Khasi Hills district of Meghalaya. The objective of the survey is to delineate the subsurface geological structure and identify the mineralization potential zone. Regional-residual separation, radially averaged power spectrum, Euler's depth solutions and 2D-depth model maps mainly have been analyzed for interpretation. High Bouguer anomalies were observed over exposed Assam–Meghalaya gneissic complex (AMGC) rocks whereas low anomalies were observed over quaternary sediments. The general trend of the gravity and magnetic contours are in the NE–SW direction which is also the trend of geological formations, i.e., AMGC and older metamorphic group rocks. Based on Bouguer contours several inferred contact/lineament/faults have been identified. These contact/lineament/faults are very well validated with Euler’s depth solutions and total horizontal gradient of gravity anomaly. Significant high magnetic anomalies have been observed over older metamorphic group rocks and the Assam–Meghalaya gneissic complex. After the correlation with the physical properties of rock samples, geology and interpretation of gravity and magnetic maps, a potential zone has been identified for detailed investigation from a mineralization point of view. © 2023, Indian Academy of Sciences.
International ocean discovery program expedition 372 preliminary report creeping gas hydrate slides and Hikurangi LWD
(2018) Ingo A. Pecher; Philip M. Barnes; Leah J. LeVay; Sylvain M. Bourlange; Morgane M.Y. Brunet; Sebastian Cardona; Michael B. Clennell; Ann E. Cook; Brandon Dugan; Judith Elger; Davide Gamboa; Aggeliki Georgiopoulou; Shuoshuo Han; Katja U. Heeschen; Gaowei Hu; Gil Young Kim; Hiroaki Koge; Karina S. Machado; David D. McNamara; Gregory F. Moore; Joshu J. Mountjoy; Michael A. Nole; Satoko Owari; Matteo Paganoni; Paula S. Rose; Elizabeth J. Screaton; Uma Shankar; Marta E. Torres; Xiujuan Wang; Hung-Yu Wu; Stephanie M. Sharuga; Erin K. Todd; Jacob C. Robinson; Mark Robinson; Robert Aduddell; Susan Boehm; Inva Braha; Ty Cobb; Lisa Crowder; Aaron De Loach; Lachlan Douglass; Keith Dupuis; David Fackler; Timothy Fulton; Clayton Furman; Randy Gjesvold; Kevin Grigar; Sandra Herrmann; Michael Hodge; Jon Howell; Minh Huynh; Rhonda Kappler; Nicolette Lawler; Aaron Mechler; Mike Meiring; William Mills; Beth Novak; David Pedulla; Garrick Van Rensburg; Liam Warda
International Ocean Discovery Program (IODP) Expedition 372 combined two research topics, slow slip events (SSEs) on subduction faults (IODP Proposal 781A-Full) and actively deforming gas hydrate-bearing landslides (IODP Proposal 841-APL). Our study area on the Hikurangi margin, east of the coast of New Zealand, provided unique locations for addressing both research topics.SSEs at subduction zones are an enigmatic form of creeping fault behavior. They typically occur on subduction zones at depths beyond the capabilities of ocean floor drilling. However, at the northern Hikurangi subduction margin they are among the best-documented and shallowest on Earth. Here, SSEs may extend close to the trench, where clastic and pelagic sediments about 1.0-1.5 km thick overlie the subducting, seamount-studded Hikurangi Plateau. Geodetic data show that these SSEs recur about every 2 years and are associated with measurable seafloor displacement. The northern Hikurangi subduction margin thus provides an excellent setting to use IODP capabilities to discern the mechanisms behind slow slip fault behaviour. © 2018 IODP-MI. All rights reserved.
Linear Model for Pore Pressure Predication in Gas Hydrate-bearing Sand Formation of Krishna-Godavari Basin (India) – A Case Study
(Geological Society of India, 2024) Pradeep Kumar Yadav; Uma Shankar
Pore pressure is a crucial geomechanical parameter, to decide the mud density while well drilling. The mud weight should be between formation pressure (pore pressure) and the fracture gradient of the reservoir rock, otherwise various kind of unwanted incidents like, kicks, blowout, breakout, well collapse, mud loss and lost circulation can happen; which can increase the cost of drilling and in worst case it may lead to a dangerous accident and consequently loss of life and assets at drilling site. In this study we are trying to find pore pressure within water bearing shale formations and gas hydrate (solid) bearing sand formation of four wells of Area B in the Krishna-Godavari Basin, namely, NGHP-02-17A, 19A, 22A, and 23A. Bower’s sonic, Eaton’s resistivity and Eaton’s sonic empirical equations have been used to estimate effective stress in the water-bearing shale formation. In gas hydrate-bearing sand formations these empirical equations cannot be useful for effective stress or pore pressure estimation and hence a linear model based on pressure-core data, relating effective stress and depth in meter below seafloor (mbsf) is generated. This model is applicable for the effective stress estimation in gas hydrate bearing sand formations of the Krishna-Godavari basin. The effective stress estimated from linear model and from core data are found in good agreement in all the wells. At site NGHP-02-23, in-situ pore-pressure was measured between depth of 270.38 to 271.38 mbsf with the help of modular dynamic formation tester (MDT) tool. The in-situ pore pressure (28.2 MPa) and estimated pore pressure (27.8 MPa) from the linear model are found in good agreement. Further, fracture pressures from Matthew-Kelly and Eaton’s method were estimated. The mud weight base on the reported mud density 1.3g/cc are found to higher than the pore pressures and lower than the fracture pressures and hence fulfil the criteria for safe drilling. © 2024 Geological Society of India, Bengaluru, India.
Microtremor measurements in the India's holy city, Varanasi for assessment of site characteristics
(Elsevier Ltd, 2021) Uma Shankar; Sangeeta Kumari; Pawan Kumar Yadav; A.P. Singh; Arun Kumar Gupta
Microtremor measurements are used for preliminary site effect of the Quaternary sediments of Varanasi in Indo-Gangatic plain, which is being planned as a Smart City of India. We evaluated site effects using single and arrays Microtremor measurements at various sites in the Varanasi City, Uttar Pradesh, India. At City, H/V spectral ratios using microtremor measurements indicate fundamental frequency range 0.37–0.63 Hz, corresponds amplification 5 to 14 times. This indicates that the deep thickness of the upper soft soil at about several hundreds of meters. Such huge amount of sediments deposition sources could be associated with fluvial rivers system in the area and sediment drain from Himalaya. The average peak frequency (~0.5) may reflect the Quaternary-Tertiary boundary. Microtremor array measurements at two sites were taken using circular arrays (30 and 60 m) which consists of three recording stations on the circumference of circle and one in the centre of circle. The Phase velocity dispersion of Rayleigh wave is calculated from array using SPAC method, and a 1-D shear wave velocity structure is determined by means of inversion processes. The top layers up to 50 m show shear velocities between 280 and 320 m/s and the velocities of underneath layer vary between 1500 and 1600 m/s till 100 m of depth. These results from the present study would be useful for future planning purposes as well as risk management and to reduce severity of earthquake effects in the study area. © 2021 Elsevier Ltd and INQUA
New vegetation type map of India prepared using satellite remote sensing: Comparison with global vegetation maps and utilities
(Elsevier B.V., 2015) P.S. Roy; M.D. Behera; M.S.R. Murthy; Arijit Roy; Sarnam Singh; S.P.S. Kushwaha; C.S. Jha; S. Sudhakar; P.K. Joshi; Ch. Sudhakar Reddy; Stutee Gupta; Girish Pujar; C.B.S. Dutt; V.K. Srivastava; M.C. Porwal; Poonam Tripathi; J.S. Singh; Vishwas Chitale; A.K. Skidmore; G. Rajshekhar; Deepak Kushwaha; Harish Karnatak; Sameer Saran; A. Giriraj; Hitendra Padalia; Manish Kale; Subrato Nandy; C. Jeganathan; C.P. Singh; C.M. Biradar; Chiranjibi Pattanaik; D.K. Singh; G.M. Devagiri; Gautam Talukdar; Rabindra K. Panigrahy; Harnam Singh; J.R. Sharma; K. Haridasan; Shivam Trivedi; K.P. Singh; L. Kannan; M. Daniel; M.K. Misra; Madhura Niphadkar; Nidhi Nagabhatla; Nupoor Prasad; O.P. Tripathi; P. Rama Chandra Prasad; Pushpa Dash; Qamer Qureshi; S.K. Tripathi; B.R. Ramesh; Balakrishnan Gowda; Sanjay Tomar; Shakil Romshoo; Shilpa Giriraj; Shirish A. Ravan; Soumit Kumar Behera; Subrato Paul; Ashesh Kumar Das; B.K. Ranganath; T.P. Singh; T.R. Sahu; Uma Shankar; A.R.R. Menon; Gaurav Srivastava; Neeti; Subrat Sharma; U.B. Mohapatra; Ashok Peddi; Humayun Rashid; Irfan Salroo; P. Hari Krishna; P.K. Hajra; A.O. Vergheese; Shafique Matin; Swapnil A. Chaudhary; Sonali Ghosh; Udaya Lakshmi; Deepshikha Rawat; Kalpana Ambastha; Akhtar H. Malik; B.S.S. Devi; K.C. Sharma; Prashant Mukharjee; Ajay Sharma; Priya Davidar; R.R. Venkata Raju; S.S. Katewa; Shashi Kant; Vatsavaya S. Raju; B.P. Uniyal; Bijan Debnath; D.K. Rout; Rajesh Thapa; Shijo Joseph; Pradeep Chhetri; Reshma M. Ramachandran
A seamless vegetation type map of India (scale 1: 50,000) prepared using medium-resolution IRS LISS-III images is presented. The map was created using an on-screen visual interpretation technique and has an accuracy of 90%, as assessed using 15,565 ground control points. India has hitherto been using potential vegetation/forest type map prepared by Champion and Seth in 1968. We characterized and mapped further the vegetation type distribution in the country in terms of occurrence and distribution, area occupancy, percentage of protected area (PA) covered by each vegetation type, range of elevation, mean annual temperature and precipitation over the past 100 years. A remote sensing-amenable hierarchical classification scheme that accommodates natural and semi-natural systems was conceptualized, and the natural vegetation was classified into forests, scrub/shrub lands and grasslands on the basis of extent of vegetation cover. We discuss the distribution and potential utility of the vegetation type map in a broad range of ecological, climatic and conservation applications from global, national and local perspectives. Weused 15,565 ground control points to assess the accuracy of products available globally (i.e., GlobCover, Holdridge's life zone map and potential natural vegetation (PNV) maps). Hence we recommend that the map prepared herein be used widely. This vegetation type map is the most comprehensive one developed for India so far. It was prepared using 23.5m seasonal satellite remote sensing data, field samples and information relating to the biogeography, climate and soil. The digital map is now available through a web portal (http://bis.iirs.gov.in). © 2015 Elsevier B.V.
Recent Advances in the Synthesis of 2-Hydroxy-1,4-naphthoquinone (Lawsone) Derivatives
(Georg Thieme Verlag, 2023) Ram Sagar; Uma Shankar; Ashish Khanna; Kavita Singh; Ghanshyam Tiwari
Lawsone, also known as 2-hydroxy-1,4-naphthoquinone, has been extensively studied and found to be a crucial precursor in the production of a diverse range of natural products such as molecular scaffolds, which are highly sought-after for biological research purposes. Due to its unique chemical composition, lawsone has been utilized for over a century as a starting material for the synthesis of numerous biologically active molecules and materials, and its intriguing properties have been showcased across a wide range of scientific and technological applications. Additionally, the various characteristics of lawsone have been widely used in organic synthesis processes. Recent advances in the synthesis of different scaffolds starting from lawsone, and their applications, are discussed in detail in the current review covering the period 2017 to 2023. 1 Introduction 2 Synthetic Developments on 2-hydroxy-1,4-naphthoquinone 3 Conclusions. © 2022. The Author(s).
Seismic anisotropy and mantle deformation beneath Eastern Ghats Mobile Belt using direct-S waves
(Elsevier B.V., 2021) Niptika Jana; Astha Singh; Ashwani Kant Tiwari; Tuna Eken; Arun Singh; Chandrani Singh; Uma Shankar
Seismic anisotropy observations provide a potential tool to constrain the signatures of various continental-scale deformations that have shaped the lithospheric structure of various mobile belts and ancient cratons across the world. They shed light on various aspects of evolutionary tectonics in any region. The current study primarily aims at examining the direct S-wave derived seismic anisotropy beneath the Eastern Ghats Mobile Belt (EGMB) and the adjacent Archean Singhbhum and Bastar Cratons. The granulite Terrane of EGMB represents the complex deformational history and is a crucial link in the reconstruction of Rodinia and Gondwana supercontinents. The Terrane underwent collision and rifting in Mesoproterozoic, followed by thermal overprint of the mid-Neoproterozoic to early Phanerozoic orogeny modifying its lithospheric structure. We have implemented the Reference Station Technique and obtained 854 well-constrained individual splitting measurements. The observations are based on 185 earthquake events (with Mw⩾5.5, and epicentral distance ranging 30° to 90°) recorded at 27 seismic stations deployed in the study area. The large splitting delay times (1.2–2.3 s) suggest that the lithospheric mantle is highly anisotropic. The NNE-SSW oriented Fast Polarization Directions (FPDs) observed at the Singhbhum Craton can be devoted to the evolutionary tectonic regime of the craton. The strained minerals at the deeper depths, result in FPD patterns sub-parallel to the Kerajung Fault Zone (~70°) in the Angul Domain. The FPDs are predominantly oriented along the Absolute Plate Motion (APM) direction of the Indian plate (~39°) for the Bastar Craton. However, the varying FPD patterns in the Eastern Ghats Boundary Shear Zone (Khariar Domain) signify the influence of the lithospheric deformation along with APM. The imprints of the continental building orogenies, that have modified the lithospheric structure of the study area over the Mesoproterozoic, mid-Neoproterozoic, and early Phanerozoic periods, are preserved as frozen anisotropic signatures. Our observations highlight these signatures. The study also investigates seismic anisotropic patterns in the hitherto uncharted regions close to Chilka Lake using the core-mantle refracted (SKS, SKKS, and PKS) and direct S phases. The markedly distinct E-W (average ~95°) oriented fast wave azimuths, against the ~47° average FPD of the adjacent western Phulbani Domain, distinguishes it as a separate block amongst the collage of domains forming the Eastern Ghats Province. © 2021 Elsevier B.V.
Seismic Source Characteristics and Scaling Relations in the Northwest Himalayan Region: Case Study of Himachal Pradesh & Uttarakhand
(Birkhauser, 2024) Shikha Vashisth; Ambikapathy Ammani; Himanshu Mittal; Uma Shankar; O.P. Mishra
The Himachal Pradesh and Uttarakhand areas are known for their high seismic activity in India. According to the Bureau of Indian Standards, the areas are situated in seismic zones IV and V, and have the potential to produce small to large earthquakes. These areas have also seen significant seismic events in the past. To accurately and reliably estimate the seismic hazard and simulate the characteristics of strong ground motion in the region, it is essential to evaluate the source characteristics of earthquakes and their scaling relationships. Our investigation involved the estimation of earthquake source parameters and high-frequency spectrum decay parameters using 1059 seismograms, corresponding to 247 earthquake events with magnitudes ranging from 3.0 to 5.5 that occurred in the Himachal Pradesh and Uttarakhand regions of the Northwest Himalaya between 2010 and 2020. The classic Brune’s model is used to estimate source parameters. The relationship can be expressed as M0=2×1015fc-2.316 for Himachal Pradesh and M0=2×1016fc-3.445 for Uttarakhand region, which agrees with previous studies given for the study region, providing vital insights into tectonics and structural heterogeneity beneath the respective regions of Northwest Himalaya. Our analysis revealed that for earthquakes in Himachal Pradesh, the source radius of circular fault ranges from 42 to 771 m, whereas, for events in the Uttarakhand region, it varies from 48 to 437 m. Additionally, the seismic moment ranged from 2 × 1011 N-m to 9.93 × 1015 N-m for Himachal Pradesh and 1.11 × 1011 N-m to 1.40 × 1016 N-m for Uttarakhand events. An increasing trend in stress drop is observed, varying from 0.0026 MPa to 8.66 MPa for Himachal Pradesh and 0.0014 MPa to 9.51 MPa for Uttarakhand, within the similar range of seismic moment. Moreover, the study highlighted that the estimation of κ and fmax is influenced by both source characteristics and propagation path, with the source exerting a significant impact. A detailed analysis of the data suggests that the differences in how earthquakes start and fade in Himachal Pradesh and Uttarakhand are due to the complex geological structures and the intricate earthquake processes in these regions. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.
Site Characterization for Seismic Hazard Analysis in Gorakhpur City Using Shear Wave Velocity (Vs) from Ambient Noise Measurements
(Springer, 2023) Pawan Kumar Yadav; Uma Shankar
The Gorakhpur city experienced several high-intensity tremors because of ongoing seismic activities in the Himalayan region. Therefore, the characterization of its subsurface is crucial for a better assessment of the seismic hazards. Ambient noise measurements at 360 sites single-station and four array sites show the predominant frequency peak varies between 0.434 to 1.02 Hz from horizontal-to-vertical spectral ratio (HVSR) analysis and amplitude increasing toward the north with maximum amplification is 4.81. The structure of the shallow soft soil has been observed by frequency wavenumber (F–K) analysis. Joint inversion of the HVSR and Rayleigh wave dispersion curves reveals three layers of soft, dense and stiff soil sediments of varying thickness. The shear wave velocity (Vs) of the sediment varies between 280 to 1200 m/s from top soil to 100 m subsurface depth. The observed Vs models correspond to soil classifications ranging from soft soil to very dense soil and rock. © 2023, The Author(s), under exclusive licence to Indian Geotechnical Society.