Proposed relation between anomalous geomagnetic variations and the tectonic history of South India     

N. Nityananda  D. Jayakumar 《Physics of the Earth and Planetary Interiors》1981,27(3):223-228

Anomalous geomagnetic variations have been observed at all geomagnetic stations in South India and they have earlier been attributed to ocean and crustal conductors. The spectral character of induced variations indicate that, in addition to coastal effects and channelling of currents through the Palk Straits, there is a concentration of currents in a conducting body at deeper levels in the crust or mantle.Current thinking on crustal evolution and the influence of Precambrian lineaments on tectonism and mineralisation up to recent times, provides support for the conjecture that zones of high electrical conductivity exist in the crust, which are related to tectonic and mineral influences. The Eastern Ghats and granulite terrain of South India and Sri Lanka are probably associated with such a zone of fundamental weakness in the crust. Extended graphite mineralisation along the Eastern Ghats, occurrence of economic graphite deposits near Trivandrum and in Sri Lanka and the association of alkaline and ultrabasic metallic minerals with deep faults in South India are indications of the possible chemical causes of high electrical conductivity in some regions of the crust.Similar relations between induced anomalous variations and tectonism and mineralisation in the Precambrian crystalline crust have been found in North America and Scotland. However, the regions of high electrical conductivity have not yet been mapped in detail in South India to confirm such a relationship.  相似文献   

Rapid assessment on the impact of tsunami on mangrove vegetation of The Great Nicobar Island     

R. Sridhar  T. Thangaradjou  L. Kannan  A. Ramachandran  S. Jayakumar 《Journal of the Indian Society of Remote Sensing》2006,34(1):89-93

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Multidimensional scaling technique for analysis of magnetic storms at Indian observatories     

M. Sridharan  A. M. S. Ramasamy 《Journal of Earth System Science》2002,111(4):459-465

Multidimensional scaling is a powerful technique for analysis of data. The latitudinal dependence of geomagnetic field variation in horizontal component (H) during magnetic storms is analysed in this paper by employing this technique.  相似文献   

Remote sensing and GIS for artificial recharge study, runoff estimation and planning in Ayyar basin, Tamil Nadu, India   总被引：4，自引：0，他引：4  

S. Anbazhagan  S. M. Ramasamy  S. Das Gupta 《Environmental Geology》2005,48(2):158-170

This paper focuses on artificial groundwater recharge study in Ayyar basin, Tamil Nadu, India. The basin is covered by hard crystalline rock and overall has poor groundwater conditions. Hence, an artificial recharge study was carried out in this region through a project sponsored by Tamil Nadu State Council for Science and Technology. The Indian Remote Sensing satellite 1A Linear Imaging Self Scanning Sensor II (IRS 1A LISS II) satellite imagery, aerial photographs and geophysical resistivity data were used to prioritize suitable sites for artificial recharge and to estimate the volume of aquifer dimension available to recharge. The runoff water available for artificial recharge in the basin is estimated through Soil Conservation Service curve number method. The land use/land cover, hydrological soil group and storm rainfall data in different watershed areas were used to calculate the runoff in the watersheds. The weighted curve number for each watershed is obtained through spatial intersection of land use/land cover and hydrological soil group through GeoMedia 3.0 Professional GIS software. Artificial recharge planning was derived on the basis of availability of runoff, aquifer dimension, priority areas and water table conditions in different watersheds in the basin.  相似文献   

Assessing the copula selection for bivariate frequency analysis based on the tail dependence test     

D D Nguyen  K V Jayakumar 《Journal of Earth System Science》2018,127(7):92

The flood characteristics, namely, peak, duration and volume provide important information for the design of hydraulic structures, water resources planning, reservoir management and flood hazard mapping. Flood is a complex phenomenon defined by strongly correlated characteristics such as peak, duration and volume. Therefore, it is necessary to study the simultaneous, multivariate, probabilistic behaviour of flood characteristics. Traditional multivariate parametric distributions have widely been applied for hydrological applications. However, this approach has some drawbacks such as the dependence structure between the variables, which depends on the marginal distributions or the flood variables that have the same type of marginal distributions. Copulas are applied to overcome the restriction of traditional bivariate frequency analysis by choosing the marginals from different families of the probability distribution for flood variables. The most important step in the modelling process using copula is the selection of copula function which is the best fit for the data sample. The choice of copula may significantly impact the bivariate quantiles. Indeed, this study indicates that there is a huge difference in the joint return period estimation using the families of extreme value copulas and no upper tail copulas (Frank, Clayton and Gaussian) if there exists asymptotic dependence in the flood characteristics. This study suggests that the copula function should be selected based on the dependence structure of the variables. From the results, it is observed that the result from tail dependence test is very useful in selecting the appropriate copula for modelling the joint dependence structure of flood variables. The extreme value copulas with upper tail dependence have proved that they are appropriate models for the dependence structure of the flood characteristics and Frank, Clayton and Gaussian copulas are the appropriate copula models in case of variables which are diagnosed as asymptotic independence.  相似文献   

Widespread earth tremors in parts of Central Tamil Nadu on 12th August 2011 and its significance     

S. M. Ramasamy  J. Saravanavel  C. J. Kumanan  M. Muthukumar  S. Karthick 《Journal of the Geological Society of India》2013,81(6):821-826

The southern part of the Indian Peninsular has started witnessing fast recurring seismicities and earth tremors with the magnitude of 3–5 in the recent years. In this context, the earthquake occurred, with a magnitude of 3.5, east of Ariyalur, Central Tamil Nadu, on 12^th August, 2011 is significant. It is because, followed by the earthquake, tremors were felt in over 35–40 villages in an area of 8000 sq km along with the development of cracks and dislocations in buildings in several places. The remote sensing observations showed that while the Ariyalur epicenter is in the eastern Tertiary formations, the tremor felt villages lie in the western crystalline formations. Again the correlation of remote sensing based lineaments with Ariyalur earthquake, the related tremors and also a few past seismic events of the area showed that these epicenters mostly lie along NE-SW lineaments. The tremors related to Ariyalur event were also felt mostly in villages located again in the vicinity of NE-SW lineaments. The lineaments appear to be post collision tectonic grains related to the still on going northerly compressive force due to which only the Indian plate is buckling and fracturing now. Hence the 12^th August, 2011 seismic event of Ariyalur cannot be taken as an isolated phenomenon and appears to be related to the Indian plate deformation as a whole. So it calls for in depth studies in the context of fast relapsing seismicities in peninsular India.  相似文献   

Sedimentation assessment in a multipurpose reservoir in Central Kerala,India     

Girish Gopinath  M. K. Ashitha  K. V. Jayakumar 《Environmental Earth Sciences》2014,72(11):4441-4449

Dams and their reservoirs, constructed to manage the water scarcity problems of a region, sometimes lose whole or part of their functionality due to sedimentation. This issue, seen as a negative impact as far as reservoir life and its purpose is concerned, can be a boon to the construction industry, by providing a highly demanding construction material in the form of sand dredged from the reservoirs. Malampuzha reservoir, a multipurpose reservoir in the South Indian state of Kerala, is also losing considerable part of its storage due to siltation. This paper assesses the rate of sedimentation in Malampuzha reservoir, through bathymetric survey and suggests measures for utilization of the removable sediment. Our analysis has shown that the reservoir capacity is reduced from 226 to 205.19 Mm³; a reduction in capacity of 20.81 Mm³ in 55 years. The rate of sedimentation of the reservoir is estimated as 16.95 mm/year. The dead storage capacity of the reservoir has reduced to 47.5 % from the original at present. The composition of deposited sediments is also identified, based on which its productive use is recommended.  相似文献   

Revealing effect of bathymetry over tsunami run-up through factor analysis     

R. Selvakumar  S. M. Ramasamy 《Arabian Journal of Geosciences》2013,6(12):4701-4708

The east coast of Tamil Nadu, particularly Chennai–Nagapattinam was worstly affected by the 2004 tsunami. Run-up shows remarkable variation of 2–8 m with maximum at Cuddalore port and minimum at Marina beach. Factors like width of dislocation, source distance, orientation of the coastline, and bathymetry guide tsunami surge. While most of the parameters are similar in characteristics for the entire coast, it is presumed that variation in bathymetry have played an imperative role in guiding run-up. Based on gradient bathymetry, up to 50 km off the coast was classified into five classes, viz shallow, moderate, and steep continental slope and continental shelf. Statistical analysis was performed between offshore bathymetry and run-up. The results clearly indicate that moderate slopes have guided tsunami to attain maximum height. While steeper slope have acted as barriers and gentle slopes have shoaled tsunami surge resulting in reduced run-up height. The study offers early but potentially meaningful guidance on the role of bathymetry on run-up.  相似文献   

Asian Transboundary Aquifers Inventory and Mapping          下载免费PDF全文

Zai-sheng Han  Jayakunar Ramasamy  Yao Li  Jing He  Hao Wang  Yan-pei Cheng  Hua Dong  Zeng-shi Ni 《地下水科学与工程》2013,1(3):1-9

Transboundary aquifer (TBA) is an aquifer system that exists in more than one state. As an important component of the groundwater system, proper management and rational utilization in trans-boundary aquifers are significantly important for promoting sustainable development and good-neighbor relationships. The Transboundary Aquifers will not implicate by the country’s political boundary as it follows the natural boundary lines. Within the frame work of the UNESCO''s International Hydrological Programme (IHP-VI & VII) activities for the International Shared Aquifer Resource Management (ISARM), the inventory on TBA in Asia both preliminary and detail has accomplished. Those TBAs are classified in to two types: regional and local grade. A of Asian Transboundary Aquifers Map has advanced. The updated map provides the situation of the regional TBAs identify as the actual shape. Countries with the TBAs should strengthen cooperation for coordination and joint management of groundwater resources in order to achieve sustainable use  相似文献   

Study the Mechanism of Surface Chlorophyll–a Variability in the Southern Tropical Indian Ocean Using an OGCM     

Aravindakshan Jayakumar  Chellappan Gnanaseelan 《Marine Geodesy》2013,36(3):246-256

Eleven years (1997–2007) of SeaWiFS observations and Ocean General Circulation Model sensitivity experiments are used to understand chlorophyll–a variability in the southern tropical Indian Ocean. The strong offshore Ekman transport forced by anomalous southeasterly winds are responsible for inducing higher chlorophyll-a in the eastern equatorial Indian Ocean. In the case of the southwest tropical Indian Ocean, Rossby waves and local upwelling are responsible for lifting the phytoplankton from deep chlorophyll maxima to the surface. Both intraseasonal dynamical response and interannual forcing are responsible for the phytoplankton blooming in the western basin, whereas the interannual forcing is mainly responsible in the east.  相似文献