National Geophysical Research Institute

Groundwater is a vital renewable natural resource that largely supports the agriculture sector, especially in semi-arid climate of hard rock. However, the over-exploitation and inadequate recharge of groundwater in crystalline granitic terrains have depleted the shallow aquifer systems constraining the groundwater to be sporadically distributed in deep fractures. Therefore, tracing bedrock fractures becomes important, but the overlying thick pile of unsaturated saprolite layer presents a challenge to map them due to geophysical ambiguity. Currently, most studies have been done at laboratory scale, while bedrock fractures at natural field conditions are rarely attended as evidenced by numerous failures of borehole drillings in semi-arid hard rock terrain. To trace saturated bedrock fractures at natural field sites, we performed a multi-disciplinary experiment comprising hydro-geological insights, social information, remote sensing, gradient resistivity profile (GRP), vertical electrical sounding (VES) and electrical resistivity tomography (ERT) followed by exploratory borehole drillings, and hydro-chemical source speciation in a semi-arid, crystalline granitic terrain in southern India. The results showed (1) GRP as a precursor records the signatures of saturated bedrock fractures qualitatively, (2) least square inversion models of ERT demarcate distinct litho-units and saturated bedrock fractures, (3) exploratory borehole drilling shows saturated bedrock fractures at 49–54 m and 63–67 m depth designated with high yield (Q = 3382 lph), which compare well with electrical imaging results, and (4) hydro-chemical source speciation with dominated alkali-feldspar (albite) weathering confirmed groundwater from bedrock fractures, which supplemented the geophysical anomalies. These observations led to a practical step-by-step field guide for tracing deep-seated bedrock fractures in geologically similar semi-arid regions.

This study examines hydraulic connectivity in Warna region of Maharashtra by analyzing rainfall, reservoir, and groundwater levels. Correlation analysis and entropy measures were employed to investigate this connectivity, which is notably influenced by rainfall and reservoir water level on groundwater. The findings reveal significant seasonal variability in rainfall, with peaks occurring during the monsoon season (June–September). The Warna Reservoir’s water levels respond significantly to monsoon rainfall, with notable increases of approximately 20 m during peak monsoon periods, indicating a strong interaction between rainfall and reservoir levels. Groundwater levels show variable correlations with both rainfall and reservoir water levels. The Marleswar well, for example, demonstrates a strong negative correlation with rainfall (− 0.82), indicating a rise in groundwater levels with increased rainfall, which persists during the monsoon, with a correlation of − 0.77. Correlations with reservoir water levels are more varied; the Ukalu well exhibits the strongest negative correlation, suggesting a significant relationship with reservoir water level fluctuations. Phase-segmented data analysis reveals strong cross-correlations between reservoir and groundwater levels in some wells, with the Ukalu well showing the highest connectivity during the peak monsoon period, which indicates effective reservoir recharge. Entropy and transinformation analysis for the Ukalu well indicate a substantial correlation between groundwater and reservoir levels, with transinformation averaging 54%, reflecting notable seasonal and phase variations. The variability in hydraulic connectivity appears to be influenced by geological conditions. The Ukalu well, located nearer to the Warna reservoir, shows better connectivity compared to wells situated in the Western Ghats. The basaltic terrain and associated fractures likely affect groundwater flow and connectivity, influencing well responses to variations in reservoir levels and rainfall. This study highlights the non-linear interactions and feedback mechanisms that traditional methods may not fully capture, presenting valuable insights for similar hydrogeological conditions.

The tectonic and depositional history of the Hanoi basin is intricately shaped by the India-Eurasia collision, resulting in a complex subsurface structure that remains of significant interest for geophysical studies. In this research, classical and recent edge enhancement filters are applied to map subsurface features in the sediment-covered southern Hanoi basin. Additionally, the tilt-depth technique is employed to estimate the depth of subsurface structures in the study area. The interpretation revealed several subsurface structures, most of which have depths ranging from 0.9 km to 4 km. The subsurface features revealed by the enhancement filters show that the region’s structural trend is generally NW-SE, aligning with significant faults within the Red River fault zone, including the Song Chay and Song Lo. According to the tilt-depth estimates, the faults are identified at intermediate to deeper depths, reflecting geological displacements during the Oligocene and early Miocene that caused the Indochina geoblock to move about 700 km southeast along the Red River fault zone. Our detailed analysis also showed the Hanoi basin forms the landward extension of the Song Hong basin. The findings not only align with established tectonic features but also underscore the effectiveness of advanced filtering techniques, particularly the improved edge detector, in refining subsurface mapping within complex geological settings.

Energy is essential for the survival of all living organisms. Energy is categorized into two types: renewable and non-renewable. The non-renewable energy sources include coal, petroleum oil, natural gas, biomass, and nuclear power. Coal and oil are the most widely utilized sources of energy, particularly in India. Oil and natural gas are highly accessible energy sources that are extensively utilized globally. The per capita energy demand is increasing steadily as a result of the growing significance of energy and fuels in all aspects of our everyday lives, and the parallel increase in the global population as well. A sharp increase in the demand for natural gas is due to its environmentally friendly nature and minimal chemical pollution compared to other fossil fuels. Moreover, the available conventional energy resources on Earth are limited. Natural gas resources are extracted from both conventional and unconventional geological formations.

Understanding pore characteristics is vital for assessing storage capacity and flow mechanisms in shale. These characteristics encompass pore size distribution, type, geometry, network, porosity, total pore volume, specific surface area, and other factors. The micro and mesopore geometry and associated pore networks in shale are extremely intricate and heterogeneous. The pore network consists of interconnected voids, pores, and natural fractures with complex and irregular shapes. At the nanoscale, the intricate network and geometry of pores in shale, combined with very low connected porosity and permeability, govern fluid storage and migration in the reservoir.

Evaluating the shale gas potential of sedimentary reservoirs requires thorough laboratory analysis. The growing significance of shale gas has redirected attention to these heterogeneous rock sequences in sedimentary basins, which were previously overlooked. Traditional laboratory techniques are inadequate for examining these highly variable, fine-grained shale rocks. Consequently, accurate characterization of shale necessitates carefully selecting a range of new and sophisticated laboratory tests.

Characterization of fine-grained clay-rich shale requires establishing a connection between its petrophysical and elastic properties. Such clay-rich sediments exhibit intrinsic anisotropy and have bi-connected matrix and fluid phases for a large range of porosity. This anisotropy must be properly accounted for to avoid misinterpreting seismic data. Therefore, it is challenging to accurately explain shale's transversely isotropic elastic property resulting from the preferred dispositional orientation of clay layers and the volumetric content, type, and dispersal of organic matter within the rock.

At the Dhala impact structure, the monomict breccia and the impact melt rock outcrops are present in proximity. Generally, these impactite lithologies are formed by different mechanisms and in different parts of the crater. The emplacement setting of impact melt rocks at Dhala has been well studied. Therefore, we studied the emplacement of monomict breccia using field, microscopic, and magnetic fabric investigations. Our results show that the intensities of the rock magnetic parameters in monomict breccia are comparable with the unshocked target granitoid at Dhala. Thus, the magnetic fabrics developed during pre-impact processes and were not altered due to impact. The absence of the reorientation of magnetic fabrics indicates that the peak shock pressures were below 0.5 GPa. Such shock pressures typically exist near the crater wall/floor or outside the crater. Moreover, there is no local variation in the orientations of magnetic fabrics at different locations in the same outcrop. Thus, the monomict breccia was not displaced from their pre-impact position. Based on the shock barometry and absence of displacement, we propose that the present-day annular outcrops of monomict breccia are located just outside the final crater. Furthermore, the monomict breccia annular outcrop ring has an internal diameter of 4.5 km and is juxtaposed with impact melt rocks, which formed within the crater (previous studies). We, thus, suggest that the present-day crater diameter is~4.5 km.

The environment combines all external factors that affect an individual’s life or a population of living organisms (Liu et al. 2021). Man is exploiting the environment by destroying natural resources. Natural ecosystems were balanced and remained unaffected since the dawn of civilization. The uncontrolled human population has disturbed everything and created a negative impact on the environment through environmental pollution, causing a diagnostic change in the characteristics of air, land and water, which affect all living species on the planet (Sherbinin et al. 2007).

Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleoweathering, paleoclimate, provenance, and tectonic setting of the basin. Records for Permo–Triassic mass extinction and climatic fluctuations are commonly traced from the sediments in the Gondwana basins. Nevertheless, our understanding on sedimentation, provenance, and regional tectonics of the Raniganj Basin, a Gondwana basin in the eastern India is poor. Minerals including clay particles and major and trace element concentrations of the siliciclastic sediments from different formations of the Raniganj Basin have been studied to establish the paleo-weathering, paleoclimate, provenance, and tectonic settings of the basin. This study suggests that the Talchir Formation experienced cold and dry climatic conditions at the sediment source area, while the Barakar, Raniganj, and Panchet formations had prevailing semiarid climates. The sources of the siliciclastic sediments are from the felsic rocks of the Chotanagpur Granite Gneissic Complex (CGGC). Further, the geochemical results suggest a rift-like (passive) tectonic setting for the Raniganj Basin, while few samples represent the collision tectonic setting of the basement CGGC, formed due to collision of major Indian blocks during the Paleo-Neoproterozoic time.

Eastern Himalayan Syntaxis (EHS) holds the unique significance and one of the least studied regions in the eastern Himalaya. In this study, Moho topographic undulation map of the study region and the vertical tectonic stress caused by isostatic adjustment are obtained by using the Bouguer gravity anomaly (BGA), topographic and isostatic anomaly data from the WGM2012 model. The source depth and cutoff wavenumber estimated from spectral analysis are found to be ≈ 46 km and 0.012 km−1, respectively. The BGA is then filtered using a low-pass filter with 83 km wavelength to obtain the regional anomaly corresponding to Moho topography. The resulting regional anomaly map is inverted using the Parker–Oldenberg method to obtain a gravity Moho. The gravity Moho is found to be varied from 36 to 56 km. The isostatic Moho depth is computed using the Airy model. The resulting gravity Moho is in good agreement with previous seismological studies in the region. Using the resulting gravity and isostatic Moho, an isostatic compensation map is derived, which shows all three states of isostatic compensation in the region. The state of isostatic compensation obtained in our study corroborates well with the isostatic anomaly map. In addition, we estimated the vertical tectonic stress caused by lithospheric load in the study region. In the Southern Tibet detachment, Namcha Barwa Antiform (NBA), and Lohit plutonic complex (LPC), the vertical stress is negative and reaches the maximum value of 80 MPa. The central zone of the study region (EHS) features tensional and compressional stresses that vary from − 20 to 20 MPa. In the southern EHS, the Assam valley shows a significant increase in vertical compressional stress. In the Assam valley, the compressional vertical stress varies up to 60 MPa. Due to under-compensation, the mountains in the NBA and LPC subside downward, causing tensional negative stress, while the Assam valley has the highest compressional stress due to topographic uplift, which accounts for the surface mass lost during fluvial erosion.

The source features and their scaling relationships in the Andaman Nicobar Islands (ANI) have been estimated using the local earthquakes with local magnitude (ML) varying from 2 to 4.5. Brune’s spectral model has been applied to a number of 66 local earthquakes to compute source properties from both primary (P-) and secondary (S-) waves. Brune’s stress drop of earthquakes is obtained from both P- and S-waves by assuming a circular fault at the hypocentral depth of earthquakes and a uniform velocity of P- and S-waves. The estimate of stress drop varies between 0.02 and 23.4 bar obtained from P-waves and between 0.02 and 18.4 bar from S-waves. The seismic moment, determined by analyzing P-waves, lies between 2.0 × 1011 and 3.6 × 1024 N-m, whereas S-wave analysis gives an estimated range of 5.0 × 1010–4.9 × 1013 N-m. Seismic moment computed from P- to S-waves show a strong correlation (96%) with each other. As per the analysis, stress drop varies with the seismic moment, and a breakdown in the law of self-similarity for the range of earthquakes analyzed in the present study is reported. The source properties and their scaling relationships that have been computed here correlate with the research conducted in other seismically active regions worldwide. The determined source properties and their scaling relationships can be applied to assess seismic hazards and explain mechanisms involved in the occurrence of earthquakes in ANI.

The elemental records of the sediments from two IODP cores, U1501C (Oligocene and Late Miocene-Pliocene) and U1499A (Pliocene to Pleistocene) in the Northern South China Sea have been studied here to understand the variability in the sedimentary provenance and depositional environment, which are impacted by the tectonic and East Asian monsoon evolution through time. The major oxides and REE abundances indicate the sources of sediment influx to be significantly from the South China, North and North eastern parts of SCS since ~ 33 Ma, and prominent contributions from Pearl River, Hainan Island and Taiwanese rivers since ~8.3 Ma. The depositional redox is corroborated by the Ce anomaly and trace element proxies such as U/Th, V/Cr, V/(V + Ni), and Ni/Co. The chemical weathering intensity, evidenced by the Chemical Index of Alteration and major elements (Ca/Ti, Na/Ti, Al/K, Al/Ti, AL/Na), and La/Sm ratios, was observed to be low. Early Oligocene witnessed the deposition of littoral sediments, caused by the initial rifting and spreading in SCS. During the late Miocene (~ 8.3 Ma), sedimentation was influenced by the prevailing arid climate and intensification of East Asian Winter monsoon (EAWM). Since Pliocene–Pleistocene (~ 5.3 Ma−0.01 Ma), the sediment deposition remained unaffected by tectonism, but was majorly influenced by the intensification of EAWM and the glacial-interglacial cycles.

To evaluate seismic anisotropy beneath ten broadband seismic stations in the Western margin of Eastern Dharwar Craton (EDC) (near Hyderabad region of India), we perform the shear wave splitting analysis using core refracted phases (such as SKS, SKKS) of teleseismic events. Seismic anisotropy is quantified by measuring the shear wave splitting parameters: the direction of the fast-polarized wave (Φ) and the delay time (δt) between the two components. These parameters indicate the orientation in which seismic waves travel fastest due to the material’s anisotropic properties and the strength of the anisotropy, respectively. We estimate the Φ and δt using the Rotational Correlation and Minimum Energy methods. In the upper mantle, minerals like olivine tend to align along the direction of maximum shear, as reflected in the orientation of Φ. Our results across all stations show that in a NNR NUVEL-1A, no-net- rotation reference frame, the estimated Φ and δt range from (54)° to (82)° and 0.42 to 0.90 s, respectively. The average (Φ) orientation is N(68 ± 4)⁰E, which is sub-parallel N(25 ± 4)⁰E to the absolute plate motion (APM) and the average (δt) is (0.53 ± 0.002)s. Our analysis shows discrepancy of shear wave splitting of SKS/SKKS phases which makes us believe that the source of seismic anisotropy beneath this region possibly lies in the lower mantle, as also observed in other similar studies. The observation of small (δt) lead to an interpretation of the weak anisotropy, however, due to lack of sufficient SWS data to support two—or more layers, we are not able to give a depth constraint, but the anisotropy layer may be located n the lower mantle. This observed lower mantle anisotropy may be driven by paleo-lithospheric plastic deformation in the deeper mantle (with anomalous D” structure). While under favourable temperature–pressure conditions, another possibility also exists for the phase transformation from lower mantle minerals like perovskite (Pv) to post-perovskite phase (pPv), resulting in the lattice preferred orientation (LPO) of these minerals. This observation of well detected seismic anisotropy is in contrast to many earlier researchers that had characterized this region as having either null or insignificant upper mantle seismic anisotropy. Due to sparsity of our splitting data, we are unable to constrain the depth of lower mantle anisotropy, however, this study provides valuable inputs for the studies on geodynamic evolution along the western margin of EDC.

Between 2022 and 2024, a 330-km-long NE-SW trending profile of ten three-component broadband seismographs has been deployed by the CSIR-NGRI, Hyderabad, in Rajasthan (India), to estimate Moho depths and crustal Vp/Vs ratios using H–K stacking of radial P-receiver functions. The modelled Moho depths range from (34.3 ± 2.50) km at SPRA [24.87°N, 74.21°E] to (43.1 ± 2.54) km at DBKR [25.60°N, 74.96°E]. Additionally, the typical values of crustal Vp/Vs range from (1.61 ± 0.04) at DNGT [26.37°N, 75.78°E] to (1.81 ± 0.05) at SPRA. The region’s average crustal thickness is (39.8 ± 2.5) km, similar to the global average for the early and middle Archean crust. Additionally, the region’s average crustal Vp/Vs ratio is 1.73 ± 0.07, indicating a felsic to intermediate composition. The Moho depths obtained from the analysis, depth migration, H–K, and Common Conversion Point (CCP) stacking of radial PRFs show a high level of agreement. Based on the results of our modelling, we can conclude that the crust beneath the northern Alluvium part of our broadband seismic network is mostly felsic, as evidenced by modelled crustal Vp/Vs ratios ranging from 1.61 to 1.77 with a mean of (1.67 ± 0.07). This contrasts with the southern portion of the profile, which has modelled crustal Vp/Vs ratios ranging from 1.74 to 1.81 with a mean of (1.78 ± 0.03). Our modelling shows a major crustal up-warping in the NE-SW direction, with a depth of 4–9 km below the region over a length of about 200–300 km. The observed crustal undulation could be linked to the Indian plate’s buckling or folding at the crustal level, which most likely occurred as a result of the Indian-Eurasian plate collision roughly 50 million years ago.

Kimberlites are one of the most unique terrestrial rocks because they, along with rocks such as lamproites and ultramafic lamprophyres, provide direct clues to mantle conditions and are hosts for diamonds in the world. In India, the Eastern Dharwar Craton is host to several kimberlite fields that have been mapped in detail. The present study examines the petrophysical attributes of kimberlites from the Eastern Dharwar Craton (EDC) in India, analyzing magnetic susceptibility and density alongside their petrology and geochemistry on 17 drill core samples from the Wajrakarur Kimberlite Field (WKF) (including Chigicherla Kimberlite Cluster (CC)) and Raichur Kimberlite Field (SK). In this study, the kimberlite samples have a density in the range of 2.6–3.1 g/cm3, grain density (GD) values between 2.5 and 2.9 g/cm3 , bulk density (BD) values between 2.4 and 2.76 g/cm3 and porosity \6%. The magnetic susceptibility lies in the range of 12–1550 (910–6 C.G.S.). The degree of serpentinization for six kimberlite pipes has been calculated and correlated with the observations of serpentinization both in the field and under the petrological microscope. Examinations combining petrophysical, petrological, and geochemical information indicate a connection between magnetic susceptibility and the ratio of ferromagnetic minerals, whereas density is predominantly affected by iron or titanium oxide minerals, carbonate and olivine. The clear linear correlation between density and magnetic susceptibility underscores the importance of ferromagnetic minerals in shaping the petrophysical properties of kimberlites. Magnetic susceptibility is found to be the most important factor controlling the petrophysical properties of the majority of EDC kimberlites. The present study finds that the magnetic susceptibility of kimberlites found in India belonging to Proterozoic age closely resembles that of kimberlites from Canada and southern Africa of Cretaceous age, while density values indicate global uniformity with Indian kimberlites. The documented petrophysical dataset is expected to aid ongoing exploration efforts for kimberlite occurrences in India, as well as contribute to geophysical mapping endeavors using magnetic and gravity methods.

The Tonga‐Hunga volcanic eruption on 15 January 2022 at 04:14:54 UTC produced large perturbations in the lower atmosphere and ionosphere globally. We report that the long period (0.28–16.67 mHz) ionospheric disturbances followed the surface pressure perturbations, which traveled globally. Here, we analyzed the Global Positioning System (GPS) data to understand the propagation of long period ionospheric disturbances together with the pressure waves in the regions along a great circle passing through Tonga, and also in the polar sectors. We also infer the strong westward propagation of ionospheric anomalies from GPS sites in Australia. This response of the ionosphere to the surface pressure fluctuations could be a possible reason for the observed ionospheric perturbations in polar regions. Our results demonstrate that (a) the pressure wave irregularities propagated all over the globe with an average velocity of ∼320 m/s and stimulated the non‐dispersive ionospheric perturbations with the same velocity, (b) the volcano ionospheric disturbances due to multiple eruptions lasted for more than 3 hr and are even noticed in the northern and southern polar regions, (c) the variation of amplitude of the ionospheric perturbations with distance from Tonga follows an exponential decay with some irregularities near the equator, and (d) a low‐frequency surface pressure irregularity of 12 hr duration is observed nearly 36 hr before the main eruption.

This study presents a gravity-based structural map of the southern Benue Trough in Nigeria, employing various edge enhancement techniques. The spectrum analysis is used to isolate anomalies of interest from Bouguer gravity data. The filtered anomaly map is then interpreted using derivative-based techniques, specifically the total horizontal gradient, theta map, normalized horizontal gradient, tilt angle of the total horizontal gradient, total horizontal gradient-based edge detector, and the Euler deconvolution to delineate tectonic and geological structural features and their depths. The analysis reveals that the region is characterized by N-S and NE-SW trending lineaments. The NE-SW trending features align with the tectonic framework of the Benue Trough and are likely to have been rejuvenated during the Cretaceous period, while the N-S structures in the western part may be influenced by underlying faults. These structural features show a good correlation with the Euler deconvolution map demonstrating the variation of the source depths (from 1 to 6.4 km). This study provides an updated structural map, elucidating the interconnection between the gravity-based structural map and the tectonic setting of the southern Benue Trough.

Opencast coal mining produces trash of soil and rock containing various minerals, that are usually dumped nearby the abandoned sites which causes severe environmental concern including the production of acid mine drainage (AMD) through oxidation pyrite minerals. The current study entailed assessing the potential production of AMD from an opencast coal mining region in Northeast part of India. In order to have a comprehensive overview of the AMD problem in Makum coalfield, the physico-chemical, geochemical, and petrological characteristics of the coal and overburden (OB) samples collected from the Makum coalfield (Northeast India) were thoroughly investigated. The maceral compositions reveal that coal features all three groups of macerals (liptinite, vitrinite, and inertinite), with a high concentration of liptinite indicating the coal of perhydrous, thereby rendering it more reactive. Pyrite (FeS2) oxidation kinetics were studied by conducting the aqueous leaching experiments of coal and (OB) samples to interpret the chemical weathering under controlled laboratory conditions of various temperature and time periods, and to replicate the actual mine site leaching. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) was operated to detect the disposal of some precarious elements from coal and OB samples to the leachates during our controlled leaching experiment. The Rare earth element (REE) enrichment in the samples shows the anthropogenic incorporation of the REE in the coal and OB. These experiments reveal the change in conductivity, acid producing tendency, total dissolved solid(TDS), total Iron(Fe) and dissolved Sulfate(SO42−) ions on progress of the leaching experiments. Moreover, the discharge of FeS2 via atmospheric oxidation in laboratory condition undergoes a significant growth with the rise of temperature of the reaction systems in the environment and follows pseudo first order kinetics. A bio-remediative strategies is also reported in this paper to mitigate AMD water by employing size-segregated powdered limestone and water hyacinth plant in an indigenously developed site-specific prototype station. Apart from neutralisation of AMD water, this eco-friendly AMD remediation strategy demonstrates a reduction in PHEs concentrations in the treated AMD water.