Magnetic studies in the northern Bay of Bengal     

M. V. Ramana  V. Subrahmanyam  K. S. Krishna  A. K. Chaubey  K. V. L. N. S. Sarma  G. P. S. Murty  G. S. Mittal  R. K. Drolia 《Marine Geophysical Researches》1994,16(3):237-242

Total magnetic intensity and bathymetric surveys were carried out in the northern Bay of Bengal between 6° to 11° 45 N latitudes and east of 84° to 93° 30 E longitudes. The hitherto known 85° E Ridge is characterised as a subsurface feature by a large amplitude, positive magnetic anomaly surrounded by Mesozoic crust. A newly identified NE to NNESSW trending magnetic anomaly between 7° N, 87° 30 E and 10° 30 N, 89–90° E may be one of the unidentified Mesozoic lineations in the northern Bay of Bengal. The Ninetyeast Ridge is not associated with any recognizable magnetic anomaly. The Sunda Trough to the east of the Ninetyeast Ridge is characterised by a positive magnetic anomaly. A combined interpretation, using Werner deconvolution and analytical signal methods, yields basement depths ~ 10 km below sea level. These depths are in agreement with the seismic results of Curray (1991).Deceased 24 December 1991  相似文献   

Gravity field, structure and tectonics of the Eastern Ghats     

C. Subrahmanyam  R.K. Verma 《Tectonophysics》1986,126(2-4)

The Eastern Ghats are a prominent topographic feature on the Indian Peninsula, stretching from the southern tip of the peninsula to near Bhubaneswar (20°N, 86°E) along the east coast. The belt is characterised by occurrences of high grade metamorphic rocks such as pyroxene granulites, sillimanite gneisses, charnockites and gabbro-anorthosite masses. The gravity field over the Eastern Ghats is appreciably positive as compared to the surrounding low grade gneissic terrain.Analysis of the gravity field along the coastal and southern granulite terrain comprising the Eastern Ghats shows that a large number of gravity highs are associated with charnockites of basic and intermediate nature as well as gabbro-anorthosite masses. The lows appear to be associated with acid charnockites, syenite masses or granitic intrusives.The boundary between the Eastern Ghats terrain and the adjoining Dharwar/Bastar cratons appears to be a faulted one. The crust underneath the Eastern Ghats is inferred to be of a higher density than that of the Dharwar/Bastar cratons to its west. The gravity field over the Eastern Ghats is compared to that of similar terrains in other parts of the world. It is inferred that the Eastern Ghats are characterised by a crust of higher than normal density.  相似文献   

Hydrogeochemistry of the Sarada river basin,Visakhapatnam district,Andhra Pradesh,India     

D. John Devadas  N. Subba Rao  B. Thirupathi Rao  K. V. Srinivasa Rao  A. Subrahmanyam 《Environmental Geology》2007,52(7):1331-1342

Systematic hydrogeochemical survey has been carried out for understanding the sources of dissolved ions in the groundwaters of the area occupied by Sarada river basin, Visakhapatnam district, Andhra Pradesh, India. Khondalites, charnockites and granite gneisses and calc-granulites of Precambrians and alluvial deposits of Quaternaries underlie the study area. Groundwaters are both fresh and brackish; the latter waters being a dominant. Most groundwaters are characterized by Na⁺:HCO₃⁻ facies due to chemical weathering of the rocks. Enrichment of Na⁺, K⁺, Cl⁻, SO₄²⁻, NO₃⁻ and F⁻ in some groundwater samples is caused by seawater intrusion, locally accompanied by ion-exchange, and anthropogenic activities, resulting in an increase of brackish in the groundwaters. Based on the results of this hydrogeochemical study, suitable management measures are recommended to solve the water quality problems.  相似文献   

Crossover analysis of geophysical data in Bay of Bengal     

N. K. Thakur  T. Gangadhara Rao  C. Subrahmanyam  Ramesh Khanna 《Geo-Marine Letters》1999,19(4):262-269

Geophysical data (magnetic, gravity, and bathymetric) collected by international and national agencies along intersecting track lines in the Bay of Bengal show discrepancies that are analyzed and adjusted by crossover techniques. The original magnetic anomaly map over this region exhibits high gradients over the entire region, which do not fit with the known geological framework. The corrected map is devoid of artifacts, and the contours became smooth, which can be utilized for meaningful geological interpretation. The corrected free-air gravity map indicates improvements from the original in resolution with clear isolated anomalies in high track density areas. Corrected bathymetry does not show much improvement. Received: 29 May 1998 / Revision received: 23 February 1999  相似文献   

Interpretation of Magnetic Phase Anomalies over 2D Tabular Bodies     

M. Subrahmanyam 《Pure and Applied Geophysics》2016,173(5):1733-1749

  相似文献   

IMPACT OF LATENT HEAT FLUX ON INDIAN SUMMER MONSOON DURING EL NI?O/LA NI?A YEARS     

苏伯拉曼雅姆  王东晓 《热带气象学报(英文版)》2011,17(4):430-440

El Nio or La Nia manifest in December over the Pacific and will serve as an index for the forecasting of subsequent Indian summer monsoon,which occurs from June to mid-September.In the present article,an attempt is made to study the variation of latent heat flux (LHF) over the north Indian Ocean during strong El Nio and strong La Nia and relate it with Indian monsoon rainfall.During strong El Nio the LHF intensity is higher and associated with higher wind speed and lower cloud amount.During El Nio all India rainfall is having an inverse relation with LHF.Seasonal rainfall is higher in YY+1 (subsequent year) than YY (year of occurrence).However there is a lag in rainfall during El Nio YY+1 from June to July when compared with the monthly rainfall.  相似文献   

Assessment of the impact of industrial effluents on water quality in Patancheru and environs, Medak district, Andhra Pradesh, India     

K. Subrahmanyam  P. Yadaiah 《Hydrogeology Journal》2001,9(3):297-312

The effects of multiple industrial-pollutant sources on the groundwater system were evaluated in the Industrial Development Areas (IDAs) of Medak district, Andhra Pradesh (AP), India. The quality of groundwater in the region has been affected negatively due to the discharge of effluents on open land and into ponds, tanks, and streams. Water samples from surface-water bodies, dug wells,and bore wells were analyzed for their major ion concentrations. The high values of electrical conductivity (EC) and concentrations of Na⁺, Ca²⁺, Cl^–, and HCO₃ ^– indicate the impact of industrial effluents. Based on the hydrochemistry, the groundwater is classified into various types, such as sodium-chloride, sodium-bicarbonate, calcium-chloride, and magnesium-chloride, and its suitability for drinking and irrigation has been assessed. The present studies made it possible to demarcate areas of contaminated groundwater and those prone to contamination in the near future. Water in the area has deteriorated all along Nakka Vagu up to a maximum distance of 500–700 m from the eastern bank. The groundwater quality in and around Patancheru (to a depth of 30 m) has become hazardous. Some possible remedial measures are suggested. Electronic Publication  相似文献   

Origin and compensation of Chagos-Laccadive ridge, Indian ocean, from admittance analysis of gravity and bathymetry data     

B. Ashalatha  C. Subrahmanyam  R.N. Singh 《Earth and Planetary Science Letters》1991,105(1-3)

The Chagos-Laccadive ridge (CLR) is a prominent aseismic, volcanic ridge in the northern Indian ocean. The ridge, together with the Southern Mascarene plateau (SMP), to which it is genetically related, is considered as a volcanic trace of the Reunion hotspot. We have examined the isostatic compensation of the CLR through transfer function analysis of gravity and bathymetry data along seven profiles. The analysis suggests that the CLR is compensated locally, with an Airy crustal thickness (T_c) of 20 km. The rather low elastic plate thickness (T_e) of about 4 km implies that the volcanism of the ridge took place very near a spreading centre. The proximity of the Chagos fracture zone indicates that the emplacement was probably near a spreading centre-transform junction.  相似文献   

Fine particles processing: shear-flocculation and carrier flotation — a review     

T. V. Subrahmanyam  K. S. Eric Forssberg 《International Journal of Mineral Processing》1990,30(3-4)

Shear-flocculation/flotation and carrier flotation are methods by which fine mineral values are aggregated and then recovered by flotation. The aggregates formed have better floatabilities. Without prior treatment ahead of flotation, significant quantities of fines are lost in tailings. An overview of the problems associated with fine particles is presented. Like froth flotation, the mechanisms of shear-flocculation and carrier flotation are governed by physical, chemical and geometrical variables. The present paper deals with the effects of these variables on shear-flocculation and carrier flotation, based on a detailed literature review.  相似文献   

Characteristic curves for the inversion of magnetic anomalies of spherical ore bodies     

T. K. S. Prakasa Rao  M. Subrahmanyam 《Pure and Applied Geophysics》1988,126(1):69-83

Characteristic curves are presented for interpreting vertical and total components of the anomalous magnetic field caused by spherical ore bodies. The curves use characteristic distances which are easy to measure on an anomaly profile. The method is fast, and does not require prior knowledge of the base level or the origin. Inversion with the characteristic curves is demonstrated on two field examples and the curves computed for the estimated parameters match well the field curves.  相似文献