Basement tectonics and flexural subsidence along western continental margin of India     

D.K. Pandey  Nisha Nair  Anju Pandey  G. Sriram 《地学前缘(英文版)》2017,8(5):1009-1024

The Paleocene-recent post-rift subsidence history recorded in the Mumbai Offshore Basin off western continental margin of India is examined. Results obtained through 2-D flexural backstripping modelling of new seismic data reveal considerable thermo-tectonic subsidence over last ca. 56 Myr. Reverse postrift subsidence modelling with variable β stretching factor predicts residual topography of ca. 2000 m to the west of Shelf Margin Basin and fails to restore late Paleocene horizon and the underlying igneous basement to the sea level. This potentially implies that:(1) either the igneous basement formed during the late Cretaceous was emplaced under open marine environs; or(2) a laterally varying cumulative subsidence occurred within Mumbai Offshore Basin(MOB) during ca. 68 to ca. 56 Ma. Pre-depositional topographic variations at ca. 56 Ma across the basin could be attributed to the extensional processes such as varied lower crustal underplating along Western Continental Margin of India(WCMI). Investigations about basement tectonics after unroofing of sediments since late Paleocene from this region support a transitional and heavily stretched nature of crust with high to very high β factors. Computations of past sediment accumulation rates show that the basin sedimentation peaked during late Miocene concurrently with uplift of Himalayan-Tibetan Plateau and intensification of Indian monsoon system. Results from basin subsidence modelling presented here may have significant implications for further studies attempting to explore tectono-climatic interactions in Asia.  相似文献   

Optimal Thresholding of Predictors in Mineral Prospectivity Analysis     

Baddeley  Adrian  Brown  Warick  Milne  Robin K.  Nair  Gopalan  Rakshit  Suman  Lawrence  Tom  Phatak  Aloke  Fu  Shih Ching 《Natural Resources Research》2021,30(2):923-969

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Influence of allochthonous input on autotrophic–heterotrophic switch-over in shallow waters of a tropical estuary (Cochin Estuary), India     

Shoji D. Thottathil  K.K. Balachandran  G.V.M. Gupta  N.V. Madhu  Shanta Nair 《Estuarine, Coastal and Shelf Science》2008

Bacterial productivity (BP) and respiration (BR) were examined in relation to primary productivity (PP) for the first time in a shallow tropical ecosystem (Cochin Estuary), India. The degree of dependence of BP (6.3–199.7 μg C L⁻¹ d⁻¹) and BR (6.6–430.4 μg C L⁻¹ d⁻¹) on PP (2.1–608.0 μg C L⁻¹ d⁻¹) was found to be extremely weak. The BP/PP (0.05–8.5) and PP/BR (0.02–7.9) ratios widely varied in the estuary depending on the season and location. There was a seasonal shift in net pelagic production from autotrophy to heterotrophy due to terrestrial organic matter input through rivers which enhanced the bacterial heterotrophic activity and very high pCO₂ (106–6001 μatm) levels. The heterotrophic zones were characterized by low PP but high bacterial production and respiration leading to oxygen undersaturation and exceptionally high pCO₂. We propose that the CO₂ supersaturation caused by increased bacterial respiration (in excess of PP) was a result of bacterial degradation of allochthonous organic matter. This indicates that sources other than planktonic compartment need to be explored to understand the C-cycling in this estuary. These results are of particular relevance to tropical ecosystems in general, where the bulk of world's river discharges occur.  相似文献   

Talkoot: software tool to create collaboratories for earth science     

Rahul Ramachandran  Manil Maskey  Ajinkya Kulkarni  Helen Conover  U. S. Nair  Sunil Movva 《Earth Science Informatics》2012,5(1):33-41

“Open science,” where researchers share and publish every element of their research process in addition to the final results, can foster novel ways of collaboration among researchers and has the potential to spontaneously create new virtual research collaborations. Based on scientific interest, these new virtual research collaborations can cut across traditional boundaries such as institutions and organizations. Advances in technology allow for software tools that can be used by different research groups and institutions to build and support virtual collaborations and infuse open science. This paper describes Talkoot, a software toolkit designed and developed by the authors to provide Earth Science researchers a ready-to-use knowledge management environment and an online platform for collaboration. Talkoot allows Earth Science researchers a means to systematically gather, tag and share their data, analysis workflows and research notes. These Talkoot features are designed to foster rapid knowledge sharing within a virtual community. Talkoot can be utilized by small to medium sized groups and research centers, as well as large enterprises such a national laboratories and federal agencies.  相似文献   

Estimation of radioactive leakages into the Pacific Ocean due to Fukushima nuclear accident     

R. N. Nair  Faby Sunny  Manish Chopra  L. K. Sharma  V. D. Puranik  A. K. Ghosh 《Environmental Earth Sciences》2014,71(3):1007-1019

High concentrations of several radionuclides were reported in the sea near the Fukushima Daiichi Nuclear Power Station (FDNPS) in Japan due to the nuclear accident that occurred on 11 March 2011. The main source of these concentrations was leakage of highly radioactive liquid effluent from a pit in the turbine building near the intake canal of Unit-2 of FDNPS through a crack in the concrete wall. In the immediate vicinity of the plant, seawater concentrations reached 68 MBq m^?3 for ¹³⁴Cs and ¹³⁷Cs, and exceeded 100 MBq m^?3 for ¹³¹I in early April 2011. These concentrations began to fall as of 11 April 2011 and, at the end of April, had reached a value close to 0.1 MBq m^?3 for ¹³⁷Cs. Following the nuclear accident, the Tokyo Electric Power Company (TEPCO) had initiated intense monitoring of the environment including the Pacific Ocean. Seawater samples were collected and the concentrations of few radionuclides were measured on a wide spatial and temporal scale. In this study, the measured concentrations of different radionuclides near the south discharge canal of the FDNPS were used to estimate their leakages into the Pacific Ocean. The method is based on estimating the release rates that reproduce the concentration of radionuclides in seawater at a chosen location using a two-dimensional advection–dispersion model in an iterative manner. The radioactive leakages were estimated as 5.68 PBq for ¹³¹I, 2.24 PBq for ¹³⁴Cs and 2.25 PBq for ¹³⁷Cs. Leakages were also estimated for ^99mTc, ¹³⁶Cs, ¹⁴⁰Ba and ¹⁴⁰La and they range between 0.02 PBq (^99mTc) and 0.53 PBq (¹⁴⁰Ba). It was estimated that about 11.28 PBq of radioactivity in total was leaked into the Pacific Ocean from the damaged FDNPS. Out of this, ¹³¹I constitutes 50.3 %; ¹³⁴Cs 20 %; ¹³⁷Cs 20 %; ¹⁴⁰Ba 4.6 %; ¹³⁶Cs 2.6 %; ¹⁴⁰La 2.3 % and ^99mTc 0.2 % of the total radioactive leakage. Such quantitative estimates of radioactive leakages are essential prerequisites for short-term and local-scale as well as long-term and large-scale radiological impact assessment of the nuclear accident.  相似文献   

Effect of co-operative fuzzy c-means clustering on estimates of three parameters AVA inversion     

Rajesh R. Nair  Suresh Ch Kandpal 《Journal of Earth System Science》2010,119(2):137-145

We determine the degree of variation of model fitness, to a true model based on amplitude variation with angle (AVA) methodology for a synthetic gas hydrate model, using co-operative fuzzy c-means clustering, constrained to a rock physics model. When a homogeneous starting model is used, with only traditional least squares optimization scheme for inversion, the variance of the parameters is found to be comparatively high. In this co-operative methodology, the output from the least squares inversion is fed as an input to the fuzzy scheme. Tests with co-operative inversion using fuzzy c-means with damped least squares technique and constraints derived from empirical relationship based on rock properties model show improved stability, model fitness and variance for all the three parameters in comparison with the standard inversion alone.  相似文献   

Seasonal variations in the sediment biogenic properties of a tropical mangrove environment,southwest coast of India     

M. Nair  J. Jacob  P. A. Nisha  G. D. Martin  K. Srinivas  P. Sheeba  C. M. Laluraj  T. Joseph  K. K. Balachandran 《Environmental Earth Sciences》2010,61(1):27-35

Temporal and spatial changes in the sediment properties of a mangrove ecosystem (Cochin, southwest coast India) are presented. The region was freshwater dominated during monsoon (June–September) and seawater dominated during other two seasons. The system remained eutrophic due to the high inputs of organic matter (OM) during most part of the year. The organic-rich sediments accumulated high amount of carbohydrates (22% of OM) and proteins (11% of OM) during non-monsoon months as compared to coastal environments. Principal component analysis showed that the biochemical properties are uniformly influenced by seasonal and spatial variations. Higher concentrations of sediment protein over carbohydrate indicate an efficient mineralization leading to the non-availability of aged OM in the system. The dominance of these labile components is generally indicative of the eutrophic condition of the system.  相似文献   

A finite element porothermoelastic model for dual-porosity media     

R. Nair  Y. Abousleiman  M. Zaman 《国际地质力学数值与分析法杂志》2004,28(9):875-898

An existing dual-porosity finite element model has been extended to include thermo-hydro-mechanical coupling in both media. The model relies on overlapping distinct continua for the fluid and solid domains. In addition, conductive and convective heat transfers are incorporated using a single representative thermodynamics continuum. The model is applied to the problem of an inclined borehole drilled in a fractured formation subjected to a three-dimensional state of stress and, a temperature gradient between the drilling fluid and the formation. A sensitivity analysis has been carried out to study the impact of thermal loading, effect of heat transport by pore fluid flow and, the effect of parameters of the secondary medium used to represent the fractures. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Changes in the measured image separation of the gravitational lens system PKS 1830-211     

C. Jin  M. A. Garrett  S. Nair  R. W. Porcas  A. R. Patnaik  R. Nan 《Monthly notices of the Royal Astronomical Society》2003,340(4):1309-1316

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Tropical cyclone activity in global warming scenario     

A. A. Deo  D. W. Ganer  G. Nair 《Natural Hazards》2011,59(2):771-786

Research efforts focused on assessing the potential for changes in tropical cyclone activity in the greenhouse-warmed climate have progressed since the IPCC assessment in 1996. Vulnerability to tropical cyclones becoming more pronounced due to the fastest population growth in tropical coastal regions makes it practically important to explore possible changes in tropical cyclone activity due to global warming. This paper investigates the tropical cyclone activity over whole globe and also individually over six different ocean basins. The parameters like storm frequency, storm duration, maximum intensity attained and location of formation of storm have been examined over the past 30-year period from 1977 to 2006. Of all, the north Atlantic Ocean shows a significant increasing trend in storm frequency and storm days, especially for intense cyclones. Lifetime of intense tropical cyclones over south Indian Ocean has been increased. The intense cyclonic activity over north Atlantic, south-west Pacific, north and south Indian Ocean has been increased in recent 15 years as compared to previous 15 years, whereas in the east and west-north Pacific it is decreased, instead weak cyclone activity has been increased there. Examination of maximum intensity shows that cyclones are becoming more and more intense over the south Indian Ocean with the highest rate. The study of the change in the cyclogenesis events in the recent 15 years shows more increase in the north Atlantic. The Arabian Sea experiences increase in the cyclogenesis in general, whereas Bay of Bengal witnesses decrease in these events. Shrinking of cyclogenesis region occurs in the east-north Pacific and south-west Pacific, whereas expansion occurs in west-north Pacific. The change in cyclogenesis events and their spatial distribution in association with the meteorological parameters like sea surface temperature (SST), vertical wind shear has been studied for Indian Ocean. The increase in SST and decrease in wind shear correspond to increase in the cyclogenesis events and vice versa for north Indian Ocean; however, for south Indian Ocean, it is not one to one.  相似文献