Velocity Structure of the West-Bengal Sedimentary Basin, India along the Palashi-Kandi Profile Using a Travel-time Inversion of Wide-angle Seismic data and Gravity Modeling – An Update     

A. S. N. Murty  Kalachand Sain  B. Rajendra Prasad 《Pure and Applied Geophysics》2008,165(9-10):1733-1750

The 2-D shallow velocity structure along the north-south Palashi-Kandi profile in the West Bengal sedimentary basin has been updated by travel-time inversion of seismic refraction, wide-angle reflection and gravity data. A six-layer shallow model up to a depth of about 7 km has been derived. The first layer, which has an average velocity of 2.0 kms^?1, represents the alluvium deposit, which rests over the shale formation with average velocity of 3.0 kms^?1. The thin (200 m) Sylhet limestone, observed at a nearby Palashi well, remains hidden in the present data set. Hence a 200-m thin layer with a velocity of 3.7 kms^?1, corresponding to the Sylhet limestone, has been assumed to be present throughout the profile. The fourth layer with a velocity of 4.5–4.7 kms^?1 at a depth of 1.7–2.4 km represents the Rajmahal traps. The ‘skip’ phenomenon and rapid amplitude decay of first arrivals indicate a low-velocity zone (LVZ) in the study area. Using the ‘skip’ phenomena and wide-angle reflection data, identified on seismograms, the LVZ with a velocity of 4.0 kms^?1, indicating the Gondwana sediments, has been delineated below the Rajmahal traps. The next layer with a velocity 5.4–5.6 kms^?1 overlying the crystalline basement (5.8–6.25 kms^?1) may be associated with the Singhbhum group of meta volcanic rock that has been exposed in the western part of the basin. The basement lies at a variable depth of 4.9 to 6.8 km. The overall uncertainties of various velocity and boundary nodes are ± 0.15 kms^?1 and ± 0.5 km, respectively. The elevated basement feature in the north might have acted as a structural barrier for the deposition of Sylhet limestone during the Eocene epoch. The seismically derived shallow structure correctly explains the observed Bouguer gravity anomaly along the profile. The addition of reflections in the present analysis provides a stronger control on the depths and velocities of basement and overlying sedimentary formations, compared to the earlier model derived mainly by the first arrival seismic data.  相似文献   

Estimation of sedimentary layer shear wave velocity using micro-tremor H/V ratio measurements for Bangalore city     

B.V. Dinesh  G.J. Nair  A.G.V. Prasad  P.V. Nakkeeran  M.C. Radhakrishna 《Soil Dynamics and Earthquake Engineering》2010

For assessing earthquake hazard of metro cities, knowledge of soil amplification, thickness and properties of sedimentary layer are essential. In order to map the soil thickness using microtremor survey method, in Bangalore city, it is required to calibrate the relation between fundamental resonance frequency of the soil layer and its thickness for the region. For this purpose microtremor survey was carried out at 34 locations in the city where borehole log was available. The resonance frequency of the soil is evaluated from the microtremor recordings using the H/V ratio technique. A nonlinear regression relation between the thickness of sedimentary layer h (m), from the borehole logs, and the resonance frequency f_r (Hz), was derived as h=(58.3±8.8)f_r^{−(0.95)±0.1}. Using the model of shear wave velocity increasing with depth at these locations, the derived average shear wave velocity and the corresponding soil thickness were used, to get an empirical relation between V_S (m/s) and depth z(m), as V_s=(174±28)(1+z)^0.16±0.07. This relation also compares reasonably with the fit obtained between simulated V_S and depth from borehole logs for Bangalore city. The calibrated relations can be used at locations in Bangalore city where borehole logs are not available, for finding the thicknesses and shear wave velocities of the local soil layers at the survey locations.  相似文献   

Microfacies and Depositional Environments of Miocene Isolated Carbonate Platforms from Central Luconia, Offshore Sarawak, Malaysia     

Hammad Tariq JANJUHAH  José Antonio GáMEZ VINTANED  Ahmed Mohamed AhmedSALIM  Ibrahima FAYE  Mumtaz Muhammad SHAH  Deva Prasad GHOSH 《《地质学报》英文版》2017,91(5):1778-1796

The Luconia Province – offshore Sarawak – is a key geological unit for understanding the distribution of hydrocarbon resources in Malaysia. Nevertheless, little effort has been made to address the palaeoenvironmental characteristics of the Tertiary carbonates in the key sector of Central Luconia. We study the sedimentology and petrography of core samples from a well in Central Luconia, for which thirteen microfacies have been identified reflecting different depositional settings. This is the first microfacies scheme elaborated for Luconian carbonates. Lithofacies and microfacies distribution are compatible with deposition in a reef complex, originating around a framework reef, within the euphotic zone. Sediments were deposited in environments of backreef, reef crest, and forereef. The fair weather wave base is marked by the presence of coralline red algae, foraminifera, decreasing degree of bioclast fragmentation and other microfacies features. As a result, a depositional-environmental model is constructed, depicting a reef complex built around a framework reef developed on the margin of an isolated platform. In addition, an innovative, preliminary time series analysis of facies, microfacies and depositional environment data reveal the existence of seasonal cycles in the stacking patterns of facies and microfacies.  相似文献   

Biodegradation of ortho-dimethyl phthalate by a binary culture of <Emphasis Type="Italic">Variovorax</Emphasis> sp. BS1 and <Emphasis Type="Italic">Achromobacter denitrificans</Emphasis>     

B. Prasad 《International Journal of Environmental Science and Technology》2017,14(12):2575-2582

Binary mixture of Variovorax sp. BS1 and Achromobacter denitrificans degraded >99 % of 300 mg l^?1 of ortho-dimethyl phthalate (DMP) within 24 h of incubation at 30 °C. Rate of degradation of DMP followed the order: A. denitrificans > binary mixture > Variovorax sp. BS1. Transient intermediate metabolites were not detected using HPLC analyses at any time points using Variovorax sp. BS1 and binary mixture. However, using pure culture of A. denitrificans, monomethyl phthalate was accumulated during the course of DMP biodegradation which disappeared with time of incubation. Binary mixture of Variovorax sp. BS1 and A. denitrificans exhibited better efficiency in terms of biodegradation of DMP as compared to either individual bacterial strain. In addition, fluorescence in situ hybridization technique was used to estimate the population dynamics of Variovorax sp. BS1 in binary mixture. A. denitrificans in mixed culture were estimated by subtracting total number of cells of Variovorax sp. BS1 from the total counts of microbial cells using an epifluorescence microscope after staining with 4′,6-diamidino-2-phenylindole. Results obtained at mid-exponential growth phase suggested the abundance of both bacterial strains as primary degraders.  相似文献   

Sugarcane crop identification from LISS IV data using ISODATA,MLC, and indices based decision tree approach     

Amit Kumar Verma  Pradeep Kumar Garg  K.S. Hari Prasad 《Arabian Journal of Geosciences》2017,10(1):16

Image classification is one of the crucial techniques in detecting the crops from remotely sensed data. Crop identification and discrimination provide an important basis for many agricultural applications with various purposes, such as cropping pattern analysis, acreage estimation, and yield estimation. Accurate and faster estimation of crop area is very essential for projecting yearly agriculture production for deciding agriculture policies. Remote sensing is a technique that allows mapping of large areas in a fast and economical way. In many applications of remote sensing, a user is often interested in identifying the specific crop only while other classes may be of no interest. Indian Remote Sensing Satellite (IRS-P6) LISS IV sensor image of spatial resolution 5.8 m has been used to identify the sugarcane crop for the Chhapar village of Muzaffarnagar District, India. Classification of satellite data is one of the primary steps for information extraction for crop land identification. In recent years, decision tree approach to image analysis has been developed for the assessment and improvement of traditional statistically based image classification. In this study, ISODATA, MLC, and vegetation indices based decision tree approaches are used for classifying LISS IV imagery. The 11 vegetation index images have been generated for decision tree classification. All the three methods are compared and it is found that the best performance is given by the decision tree method. Vegetation indices based decision tree method for sugarcane classification, the user’s accuracy, producer’s accuracy, overall accuracy, and kappa coefficient were found 88.17, 86.59, and 87.93% and 0.86 respectively.  相似文献   

Phosphate pollution in the groundwater of lower Vamsadhara river basin, India     

N. S. Rao  P. Rajendra Prasad 《Environmental Geology》1997,31(1-2):117-122

 The lower Vamsadhara river basin, spreading over an area of 817 sq.km in northern Andhra Pradesh, represents a typical rural setting. The occurrence of phosphorus-bearing minerals reported in literature, and the increasing application of phosphatic fertilizers in the area have prompted these studies. Water samples from 113 wells were analysed for Ca, Mg, Na, K, Cl, SO₄, HCO₃, F, NO₃ and PO₄. The results indicate the presence of phosphate in the groundwater ranged from 0.72 to 7.07 mg/l, which is beyond the limits recommended for domestic and water treatment purposes. Samples of soils and weathered rocks were analyzed for their water-soluble phosphate and other chemical parameters. The water-soluble phosphate in the widely used fertilizers of the area was determined. The spatial variation of phosphate in the aquifer and the soil leachate characteristics supplemented by the chemical equilibrium calculations clearly indicate the dominance of geological sources over the fertilizer sources in contributing PO₄ to the groundwaters. Received: 4 March 1996 / Accepted: 29 July 1996  相似文献   

Temperature distribution of viscous incompressible flow along an infinite flat plate with variable suction     

A. Raptis  J. P. Mani  S. Prasad 《Astrophysics and Space Science》1990,172(2):185-210

Unsteady two-dimensional flow of an incompressible viscous fluid along an infinite flat plate is considered. The free-stream velocity follows the exponentially increasing small perturbation law. The suction of the plate is variable.  相似文献   

Diurnal and seasonal variations of radioactivity and electrical conductivity near the surface for a continental location Mysore, India   总被引：3，自引：0，他引：3  

B.S.N. Prasad  K. Nagaraja  M.S. Chandrashekara  L. Paramesh  M.S. Madhava 《Atmospheric Research》2005,76(1-4):65

Simultaneous measurements of the activity concentrations of radon and its progeny, and conductivity of both polarities i.e., positive and negative conductivities, were made at a height of 1 m above the ground at Mysore (12°N, 76°E, 767 m above mean sea level), India. Diurnal and seasonal variations of activities of radon and its progeny show their peak values in the early morning hours throughout the year. Observations show an increase in the concentration of radon and its progeny during nighttime compared to the daytime values, and are higher in winter than in other seasons. The electrical conductivity of the atmosphere that depends on the ionization rate also exhibits similar trends. These results are discussed in terms of ionization rate due to radioactivity and the influence of meteorological parameters on radioactivity. The results also show that the concentrations of radon, its progeny, and the electrical conductivity of both polarities exhibit a positive correlation with the relative humidity and are negatively correlated with the temperature of the atmosphere.  相似文献   

Structure and evolution of the Cauvery Shear Zone system, Southern Granulite Terrain, India: Evidence from deep seismic and other geophysical studies     

V. Vijaya Rao  B. Rajendra Prasad   《Gondwana Research》2006,10(1-2):29

The Southern Granulite Terrain with exposed Archean lower crustal rocks is studied using various geophysical tools. The crustal structure derived from seismic reflection and refraction/wide-angle reflection studies is used to understand the tectonic evolution of the region. Deep seismic reflection section along the Kolattur–Palani segment shows an oppositely dipping reflection fabric near the Moyar–Bhavani shear zone, which is interpreted as a signature of collision between the Dharwar craton and another crustal block in the south. The thickened crust due to collision was delaminated during the orogenic collapse and modified the central part, covering the Cauvery Shear Zone system, located between the Moyar–Bhavani and Karur–Oddanchatram shear zones. The delaminated lower crust is altered by magmatic underplating as evidenced by the high velocity layer just above the Moho. The velocity model of the region indicates crustal thickening at the boundary of the Dharwar craton and Moyar–Bhavani shear zone and thinning further south. Back-scattered seismic wave field with negative moveout and the Moho-offset indicate the spatial location and strike-slip nature of the shear zones. Present study suggests that the late Archean collision and suturing of the Dharwar craton with the southern crustal block at the Moyar–Bhavani shear zone may be responsible for the evolution of late Archean granulites. Late Neoproterozoic rifting is observed along the paleo-fault zones. The seismic studies constrained by gravity, magnetic and magnetotelluric data suggest that the Moyar–Bhavani and Karur–Oddanchatram shear zones of the Cauvery Shear Zone system mark terrane boundaries/suture zones.  相似文献   

Bianchi type V universe with bulk viscous matter and time varying gravitational and cosmological constants     

Prashant Singh Baghel  Jagdish Prasad Singh 《天文和天体物理学研究(英文版)》2012,(11):1457-1466

We consider spatially homogeneous and anisotropic Bianchi type V space- time with a bulk viscous fluid source, and time varying gravitational constant G and cosmological term Λ. The coefficient of bulk viscosity ζ is assumed to be a simple linear function of the Hubble parameter H (i.e. ζ = ζ 0 + ζ 1 H , where ζ 0 and ζ 1 are constants). The Einstein field equations are solved explicitly by using a law of variation for the Hubble parameter, which yields a constant value of the deceleration parameter. Physical and kinematical parameters of the models are discussed. The models are found to be compatible with the results of astronomical observations.  相似文献