National Geophysical Research Institute NGRI

Hyderabad andhra Pradesh, India

National Geophysical Research Institute NGRI

Hyderabad andhra Pradesh, India
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Mikhailov V.O.,Russian Academy of Sciences | Arora K.,National Geophysical Research Institute NGRI | Ponomarev A.V.,Russian Academy of Sciences | Srinagesh D.,National Geophysical Research Institute NGRI | And 2 more authors.
Izvestiya, Physics of the Solid Earth | Year: 2017

The state of the art in the geological and geophysical study of the region of Koyna and Warna water reservoirs is reviewed. The probable geodynamical factors of induced seismicity are discussed. The detailed geophysical surveys, satellite geodetic data, and time history of the seismicity in the region reveal a complicated pattern of the structure and recent geodynamics of the region. The existing data suggest that the induced seismicity is here most likely to be caused by the regional (intraplate) stresses driving the displacements along the orthogonal network of the faults whose strength has dropped and continues decreasing due to the reservoir impoundment and operation processes. The evolution of the seismicity which started immediately after the rapid filling of the Koyna reservoir in the region of the dam, then rapidly expanded southwards and eventually became concentrated in the region of the subsequently constructed Warna reservoir shows that seismic events can be initiated by a number of factors whose contributions may vary with time. The key ones among them include reservoir loading and its seasonal variations; water saturation of the faults which guide the propagation of the front of fracture, increased permeability, and, probably, mineral transformations (hydrolysis) under the water level fluctuations in the reservoirs; and displacement of the front of the high pore pressure down to the main source zone of the earthquakes at a depth of 6–8 km. Based on the analysis presented in the paper, we outline the directions of the future research aimed at studying the nature and dynamics of induced seismicity in the region of large water reservoirs. © 2017, Pleiades Publishing, Ltd.

Jaiswal R.K.,National Geophysical Research Institute NGRI | Singh A.P.,Institute of Seismological Research | Rastogi B.K.,Institute of Seismological Research | Murty T.S.,University of Ottawa
Natural Hazards | Year: 2011

We present the seismic energy, strain energy, frequency-magnitude relation (b-value) and decay rate of aftershocks (p-value) for the aftershock sequences of the Andaman-Sumatra earthquakes of December 26, 2004 (Mw 9.3) and March 28, 2005 (Mw 8.7). The energy released in aftershocks of 2004 and 2005 earthquake was 0.135 and 0.365% of the energy of the respective mainshocks, while the strain release in aftershocks was 39 and 71% for the two earthquakes, respectively. The b-value and p-value indicate normal value of about 1. All these parameters are in normal range and indicate normal stress patterns and mechanical properties of the medium. Only the strain release in aftershocks was considerable. The fourth largest earthquake in this region since 2004 occurred in September 2007 off the southern coast of Island of Sumatra, generating a relatively minor tsunami as indicated by sea level gauges. The maximum wave amplitude as registered by the Padang, tide gauge, north of the earthquake epicenter was about 60 cm. TUNAMI-N2 model was used to investigate ability of the model to capture the minor tsunami and its effect on the eastern Indian Coast. A close comparison of the observed and simulated tsunami generation, propagation and wave height at tide gauge locations showed that the model was able to capture the minor tsunami phases. The directivity map shows that the maximum tsunami energy was in the southwest direction from the strike of the fault. Since the path of the tsunami for Indian coastlines is oblique, there were no impacts along the Indian coastlines except near the coast of epicentral region. © 2010 Springer Science+Business Media B.V.

Naganjaneyulu K.,National Geophysical Research Institute NGRI | Santosh M.,Kochi University
Journal of Asian Earth Sciences | Year: 2011

The Madurai Block in southern India is considered to represent the eroded roots of an arc-accretionary complex that developed during the subduction-collision tectonics associated with the closure of the Mozambique Ocean and final suturing of the crustal fragments within the Gondwana supercontinent in the Late Neoproterozoic-Cambrian. Here we present a magnetotelluric (MT) model covering the main collisional suture (Palghat-Cauvery Suture Zone) in the north into the central part of the Madurai Block in the south comprising data from 11 stations. Together with a synthesis of the available seismic reflection data along a N-S transect further south within the Madurai Block, we evaluate the crustal architecture and its implications on the tectonic development of this region. According to our model, the predominantly south dipping seismic reflectors beneath the Madurai Block define a prominent south-dipping lithological layering with northward vergence resembling a thrust sequence. We interpret these stacked layers as imbricate structures or mega duplexes developed during subduction-accretion tectonics. The layered nature and stacking of contrasting velocity domains as imaged from the seismic profile, and the presence of thick (>20. km) low resistivity layers 'floating' within high resistivity domains as seen from MT model, suggest the subduction of a moderately thick oceanic crust. We identify several low resistivity domains beneath the Madurai Block from the MT model which probably represent eclogitised remnants of oceanic lithosphere. Their metamorphosed and exhumed equivalents in association with ultrahigh-temperature metamorphic orogens have been identified from surface geological studies. Both seismic reflections and MT model confirm a southward subduction polarity with a progressive accretion history during the northward migration of the trench prior to the final collisional assembly of the crustal blocks along the Palghat-Cauvery Suture Zone, the trace of the Gondwana suture in southern India. © 2010 Elsevier Ltd.

Murugesan V.,Annamalai University | Krishnaraj S.,Annamalai University | Kannusamy V.,Annamalai University | Selvaraj G.,Annamalai University | Subramanya S.,National Geophysical Research Institute NGRI
Geo-Spatial Information Science | Year: 2011

The main objective of the study is to identify groundwater potential zones in Thirumanimuttar basin with an integrated approach using Remote Sensing and geographical information system (GIS). FCC Image of Landsat TM 30 m resolution data and topographic maps has been used to generate thematic maps like geology, geomorphology, lineament and lineament density, drainage, drainage density, and slope map of the study area. A number of geomorphic units such as Denudational hills, structural hills, Bajadas, Colluvial plain, Pediplain, Deep Pediment and Alluvial plains have been observed. A composite groundwater potential map has been generated as very high, high, medium, low and very low based on the groundwater availability area. The upper, middle and downstream of the basins have been identified as potential zones for groundwater exploration. The regions of lineaments and intersecting lineaments proved for groundwater potential zones. The data generated was validated with field checks and observed to be in conformity with the same. © 2011 Wuhan University and Springer-Verlag Berlin Heidelberg.

Naganjaneyulu K.,National Geophysical Research Institute NGRI | Naidu G.D.,National Geophysical Research Institute NGRI | Rao M.S.,National Geophysical Research Institute NGRI | Shankar K.R.,National Geophysical Research Institute NGRI | And 4 more authors.
Physics of the Earth and Planetary Interiors | Year: 2010

Magnetotelluric data at 45 locations along the Mahan-Khajuria Kalan profile in the central India tectonic zone are analysed. This 290. km long profile yields data in the period range 0.001-1000. s across the tectonic elements of the study region bounded by Purna fault, Gavligarh fault, Tapti fault, Narmada South fault and Narmada North fault. Multi-site, multi-frequency analysis suggests N70°E as the geo-electric strike direction. Data rotated into the N70°E strike direction are modelled using a non-linear conjugate gradient scheme with error floors of 10% for both apparent resistivity and phase components. Two-dimensional magnetotelluric model yields conductors that correlate with known faults in the study region and regional seismicity. Presence of a -30 mgal gravity high together with the observed conductive bodies (less than 20. ohm. m) in the deep crust beneath the Purna graben and Tapti valley is explained by the process of magmatic underplating. The conductive bodies beneath the Mahakoshal rift belt and Vindhyans accompanied by regional gravity lows of the order -70. mgal are attributed to the presence of deep crustal fluids. Following the re-activation model proposed for the entire region, the conductors (20. ohm. m) at various depth levels correspond to mafic magmatic and/or fluid intrusions controlled by deep-seated faults that seem to tap reservoirs beyond the crust-mantle boundary. The shallow depth localized faults also seem to have facilitated further upward movement of these underplated material and fluids release during this process. © 2010 Elsevier B.V.

Naganjaneyulu K.,National Geophysical Research Institute NGRI | Santosh M.,Kochi University
Journal of Geodynamics | Year: 2010

The southern Indian crustal fragment occupied a central position within the Late-Neoproterozoic-Cambrian Gondwana supercontinent assembly. Here we synthesize the available geophysical data that includes gravity, seismic tomography, deep seismic sounding (DSS) and magnetotellurics (MT) from the Palghat-Cauvery Suture Zone (PCSZ), which is considered as a trace of the Gondwana-forming suture in southern India, as well as the surrounding regions to delineate the crustal architecture and tectonic history of the region. An increased crustal thickness immediately north of the PCSZ is correlated to crustal thickening associated with the subduction-collision processes during continental amalgamation. A prominent gravity low of about -45m gal beneath Kodaikanal in the central Madurai Block, south of the PCSZ might suggest the deep root of a thick magmatic arc. Deep seismic studies in and around Chennimalai at the central domain of the PCSZ indicate the presence of ca. 10km thick low velocity (6.0km/s) layer at mid-crustal depths. The gravity model indicates a high density (2.80gm/cm3) layer corresponding to these depths. Two-dimensional MT model shows highly resistive (>20,000Ω-m) felsic upper crust down to 15-16km all along the profile. The resistivity of the mid-crust is more than 10,000Ω-m and the resistivity of the lower crustal domains is in the range of 500-3000Ω-m. The MT model and revised gravity model, constrained by MT, show a southward dipping low resistive zone (<100Ω-m) and a high density region at a depth range of 15-45km beneath the Chennimalai dome within the PCSZ. The interpretation of magnetotelluric and revised gravity model confirm the PCSZ to be the trace of a major suture zone, and correlate with a plate tectonic model of subduction-collision-accretion tectonics along this zone related to the final amalgamation of the Gondwana supercontinent. © 2009 Elsevier Ltd.

Murty A.S.N.,National Geophysical Research Institute NGRI | Prasad B.R.,National Geophysical Research Institute NGRI | Rao P.K.,National Geophysical Research Institute NGRI | Raju S.,National Geophysical Research Institute NGRI | Sateesh T.,National Geophysical Research Institute NGRI
Pure and Applied Geophysics | Year: 2010

2-D shallow velocity structure is derived by traveltime inversion of the first arrival seismic refraction and wide-angle reflection data along the E-W trending Narayanpur-Nandurbar and N-S Kothar-Sakri profiles, located in the Narmada-Tapti region of the Deccan syneclise. Deccan volcanic (Trap) rocks are exposed along the two profiles. Inversion of seismic data reveals two layered velocity structures above the basement along the two profiles. The first layer with a P-wave velocity of 5.15-5.25 km s-1 and thickness varying from 0.7-1.5 km represents the Deccan Trap formation along the Narayanpur-Nandurbar profile. The Trap layer velocity ranges from 4.5 to 5.20 km s-1 and the thickness varies from 0.95 to 1.5 km along the Kothar-Sakri profile. The second layer represents the low velocity Mesozoic sediments with a P-wave velocity of 3.5 km s-1 and thickness ranging from about 0.70 to 1.6 km and 0.55 to 1.1 km along the E-W and N-S profiles, respectively. Presence of a low-velocity zone (LVZ) below the volcanic rocks in the study area is inferred from the travel-time 'skip' and amplitude decay of the first arrival refraction data together with the prominent wide-angle reflection phase immediately after the first arrivals from the Deccan Trap formation. The basement with a P-wave velocity of 5.8-6.05 km s-1 lies at a depth ranging from 1.5 to 2.45 km along the profiles. The velocity models of the profiles are similar to each other at the intersection point. The results indicate the existence of a Mesozoic basin in the Narmada-Tapti region of the Deccan syneclise. © 2010 Birkhäuser Verlag, Basel/Switzerland.

Naganjaneyulu K.,National Geophysical Research Institute NGRI | Santosh M.,Kochi University
Gondwana Research | Year: 2010

The Central India Tectonic Zone (CITZ) is a prominent divide and a major suture zone between the North Indian and South Indian crustal blocks. The resistive upper crust as modeled in the magnetotelluric data from CITZ suggests a dominant tonalite-trdondhjemite-granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components. The highly conductive bodies in this zone might represent mafic/ultramafic-layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the Cretaceous Deccan flood basalts. The uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of Archaean and Paleoproterozoic subducted slabs. We redefine the nature of deep faults traversing the CITZ, which were described as steep and penetrating the Moho by previous workers, and classify them as listric faults with gentle dips at depth. Seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the Bhandara Craton. Reflection data from the central part of the CITZ show northerly dip in the southern part suggesting northward subduction of the Dharwar Craton. However, an opposite trend is observed in the northern part of the suture with a southward dip of the Bundelkhand craton. Based on these features, and in conjunction with existing magnetotelluric models, we propose a double-sided subduction history along the CITZ. This would be similar to the ongoing subduction-accretion process in the western Pacific region, which possibly led to the development of paired collision-type and Pacific-type orogens. One important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust. The high resistivity felsic domain suggests underplated sediments/felsic crust that would have caused the doming. Our model also accounts for the extrusion of regional metamorphic belts at the orogenic core, and the occurrence of high pressure-ultrahigh-temperature paired metamorphic belts within the suture. © 2010 International Association for Gondwana Research.

Naganjaneyulu K.,National Geophysical Research Institute NGRI
Earth, Planets and Space | Year: 2010

Magnetotelluric (MT) data at 24 locations in the Son Narmada region, Central India,were collected across the Tapti North Fault and Son Narmada Fault along the Chinchpada-Godhra profile (220 km). MT impedance tensors were then estimated in the period range 0.001-1,000 s using robust processing codes. The N70 E geo-electric strike direction was obtained by multi-site, multi-frequency analysis. The data were modeled using non-linear conjugate gradient scheme taking both apparent resistivity and phase into account. The two-dimensional MT model obtained (after static shift correction) represents resistive bodies (1,000-3,000 ohm-m) and conductive bodies (<20 ohm-m) in the deep crust. The resistive bodies in the lower crust are interpreted to be granitic intrusive complexes. The conductor on the south of Son Narmada Fault is attributed to the presence of magmatic bodies due to underplating, and the conductor on the north as due to the presence of fluids. The highly resistive (>2,000 ohm-m) upper crust is interpreted to comprise felsic rocks of granitic composition, and the low-resistive (<100 ohm-m) deep crust as being composed of dense mafic granulites. The Domal upwarp structure near Son Narmada Fault, with a thick felsic crust sandwiched between the mafic and intermediate crust, can be explained by underplated sediments/felsic crust which jacked-up the lithounits above. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

PubMed | National Geophysical Research Institute NGRI and University of Burdwan
Type: | Journal: Chemosphere | Year: 2016

This research work primarily deals with the geochemistry and genesis of fluoride (F

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