Travel times ofP-waves in North-East India     

M. V. D. Sitaram  George John  P. G. Rao  M. M. Saikia 《Studia Geophysica et Geodaetica》1990,34(2):96-109

Summary Based on 90 accurately localized earthquakes in and around North-East India and the local crustal velocity model of Gupta et al. [4], the travel times of P-waves have been determined from the foci of these earthquakes at arbitrarily selected depths of 5, 13, 25, 41 and 50 km to the sites of the seismic stations operated by the Regional Research Laboratory, Jorhat and the National Geophysical Research Institute, Hyderabad, and also to the sites of the Shillong and Tura seismic stations run by the India Meteorological Department, New Delhi. The travel times of P-waves fit a straight line very well with velocities of 5·97 ± 0·31, 6·18 ± 0·01, 6·41 ± 0·03, 7·82 ± 0·07 and 7·95 ± 0·01 km/sec at each of the depths under study. Similar investigations of P* and Pg-waves of 16 earthquakes at a depth of 10 km have revealed velocities of 6·53 ± 0·31 and 5·64 ± 0·34 km/sec, respectively. A simplified two-layered crustal model consisting of an average crustal thickness of 41·5 km with 22·2 and 19·3 km thick layers has been obtained.  相似文献   

Experimental Studies and its Application using PLAXIS-2D for Lithomargic Clay Stabilized by GBFS and Lime     

Mahesh Bhat  K.  Nayak  Sitaram 《Geotechnical and Geological Engineering》2021,39(7):4901-4915

Geotechnical and Geological Engineering - Lithomargic clay is found along the Eastern and Western coasts of Southern India. Presence of weak soils like lithomargic clay below the foundations, cause...  相似文献   

Seasonal and inter-annual variability of atmosphere CO<Subscript>2</Subscript> based on NOAA Carbon Tracker analysis and satellite observations     

M. Krishnapriya  A. Bhuvana Chandra  Rabindra K. Nayak  N. R. Patel  P. V. N. Rao  V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2018,46(2):309-320

A study on seasonal and inter-annual variability of the atmospheric CO₂ is carried out based on National Oceanic and Atmospheric Administration Carbon Tracker (NOAACT) re-analysis and satellite measurements of mid-troposphere CO₂ by Atmosphere Infrared Sounder on board NASA’s Aqua and lower troposphere CO₂ by Greenhouse-gas Observing Satellite. Seasonal and non-seasonal components of each time series were extracted by means of least square based harmonic analysis procedure. The data of surface CO₂ fluxes used in the NOAACT are also analyzed to examine its relationship with the atmosphere CO₂ variability at different time scales. There exists good consistency between NOAACT analysis and satellite observations in their respective seasonal harmonics and climatology. Surface layer CO₂ exhibits large climatological mean over the regions of major anthropogenic sources together with strong seasonal cycle over the humid and cold climatic terrestrial regions especially over the northern hemisphere. Existence of high coherency with the different components of the surface fluxes shows that surface layer atmosphere CO₂ seasonality is primarily contributed from the terrestrial ecosystem exchanges and secondarily by anthropogenic and oceanic exchanges. The mid-troposphere CO₂ exhibits large values associated with climatology and amplitudes of semi-annual and annual cycles over the northern extra tropics and Polar Regions along with a gradual decreasing trend from northern to southern hemisphere. Inter-annual variability of atmospheric CO₂ in the NOAACT in some extent is consistent with the satellite observations. Large scale circulation patterns, its fluctuations associated with ENSO events and large scale ecosystem disturbances have significant influence on the inter-annual variability.  相似文献   

Impacts of ENSO and IOD on tropical cyclone activity in the Bay of Bengal     

Mahala  Biranchi Kumar  Nayak  Birendra Kumar  Mohanty  Pratap Kumar 《Natural Hazards》2015,75(2):1105-1125

Natural Hazards - The impacts of El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) on tropical cyclone (TC) activity (intensity, frequency, genesis location, track and average...  相似文献   

Book reviews     

M. R. Nayak  George Voulgaris 《Estuaries and Coasts》1999,22(3):728-730

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Evaluation of impact of industrial effluents on intertidal sediments of a creek   总被引：1，自引：0，他引：1  

S. P. Volvoikar  G. N. Nayak 《International Journal of Environmental Science and Technology》2013,10(5):941-954

A large amount of material in the form of industrial effluents and urban sewage containing metal contaminants directly enters Dudh creek. Metals on entering the creek tend to settle at the bottom and become part of the sediments. The distribution of metals with depth reflects changes in their supply as well as diagenetic modifications with time. In the present study, an attempt has been made to understand the impact of waste discharged from Tarapur Maharashtra Industrial Development Corporation on Dudh creek. Two cores were collected, one close to the creek mouth and the other in the inner part of the creek. Sediment component, organic carbon and metal (vanadium, copper, nickel, lead, zinc, manganese, iron and aluminium) analyses were carried out on the two cores. The variation in the distribution of sediment components with depth reflects changes in hydrodynamic condition of the creek over the years. Increase in concentration of most of the metals in the upper part of the cores indicates additional input in recent years. The core collected in the inner part of the creek showed higher metal and organic carbon concentration as compared to the downstream core. This was very well supported by distribution of points on an isocon plot. Enrichment factor and index of geoaccumulation were used to find the extent of pollution in sediments of the creek. Correlation and R-mode factor analysis have also been computed to understand the association and source of metal input in sediments of Dudh creek.  相似文献   

Experimental Studies on Behaviour of Stone Columns in Layered Soils     

R.?Shivashankar  M.?R.?Dheerendra BabuEmail author  Sitaram?Nayak  V.?Rajathkumar 《Geotechnical and Geological Engineering》2011,29(5):749-757

Stone columns are found to be effective and economical ground improvement technique in soft grounds. Understanding its behaviour when they are installed in stratified soils, in particular when the upper layer consists of weak soil, will be of great practical significance. This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the behaviour of stone columns in layered soils, consisting of weak soft clay overlying a relatively stronger silty soil, for various thicknesses of the top layer. Tests were carried out with two types of loading (1) the entire area in the unit cell tank loaded, to estimate the stiffness of improved ground and (2) only the stone column loaded, to estimate the limiting axial capacity. Laboratory tests were carried out on a column of 90 mm diameter surrounded by layered soil, for an area ratio of 15%. It is found that the depth of top weak layer thickness has a significant influence on the stiffness, load bearing capacity and bulging behavior of stone columns.  相似文献   

Arc–continent collision and orogenesis in western Tasmanides: Insights from reactivated basement structures and formation of an ocean–continent transform boundary off western Tasmania     

G.M. Gibson  M.P. Morse  T.R. Ireland  G.K. Nayak 《Gondwana Research》2011,19(3):608-627

Crustal architecture in formerly contiguous basement terranes in SE Australia, Tasmania and northern Victoria Land is a legacy of late Neoproterozoic–Cambrian subduction-related processes, culminating in formation of the Delamerian–Ross orogen. Structures of Delamerian–Ross age were subsequently reactivated during late Mesozoic–Cenozoic Gondwana breakup, strongly influencing the geometry of continental rifting and providing clues about the origins and configuration of the pre-existing basement structures. An ocean–continent transform boundary developed off western Tasmania follows the trace of an older Paleozoic strike-slip structure (Avoca–Sorell fault system) optimally oriented for reactivation during the final separation of Australia from Antarctica. This boundary cuts across rocks preserving an earlier record of arc–continent collision during the course of which continental crust was subducted to mantle depths and Cambrian mafic–ultramafic island arc rocks were thrust westwards over late Neoproterozoic–Cambrian passive margin sequences. Collision was accompanied by development of a foreland basin into which 520–600 Ma arc-derived detrital zircons were shed. Following a reversal in subduction polarity, and change to transcurrent motion along the Gondwana margin, Tasmania migrated northward along the proto-Avoca fault system before entering a subduction zone located along the Heathcote–Governor fault system, precipitating a second collision, south-vergent thrusting, and tectonic reworking of the already accreted Cambrian arc–forearc assemblages and underlying passive margin sequences.  相似文献   

Depositional environment of mudflats and mangroves and bioavailability of selected metals within mudflats in a tropical estuary   总被引：1，自引：1，他引：0  

M. C. Fernandes  G. N. Nayak  A. Pande  S. P. Volvoikar  D. R. G. Dessai 《Environmental Earth Sciences》2014,72(6):1861-1875

Four sediment cores representing adjacent mudflat and mangrove sub-environments of middle estuary (Shastri) were analyzed for sand, silt, clay, and organic carbon. Total metal concentration of iron (Fe), manganese (Mn), nickel (Ni), zinc (Zn), chromium (Cr), copper (Cu), cobalt (Co), and lead (Pb) and chemical speciation of Fe, Mn, and Co on selected samples was also carried out on mudflat cores. The sediments in the upper middle estuary were found to be deposited under highly varying hydrodynamic energy conditions; whereas lower middle estuary experienced relatively stable hydrodynamic energy conditions with time. The tributary joining the river near the upper middle estuary is found to be responsible for the addition of enhanced organic carbon and metal concentrations. Speciation study indicated Fe and Co are from natural lithogenic origin while Mn is derived from anthropogenic sources. Higher Mn and Co than apparent effects threshold can pose a high risk of toxicity to organisms associated with these sediments.  相似文献   

Characterizing spatial variability of soil properties in salt affected coastal India using geostatistics and kriging   总被引：2，自引：0，他引：2  

Rahul Tripathi  A. K. Nayak  Mohammad Shahid  R. Raja  B. B. Panda  S. Mohanty  Anjani Kumar  B. Lal  Priyanka Gautam  R. N. Sahoo 《Arabian Journal of Geosciences》2015,8(12):10693-10703

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