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

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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   

Surface of zero relative velocity in the gravitational field of a pair of interacting galaxies     

P. V. Subrahmanyam 《Astrophysics and Space Science》1980,67(2):503-510

Zero relative velocity surfaces in the orbital plane are computed for close pairs of spherical and disk galaxies.  相似文献   

Magnetic expression of some major lineaments and Cretaceous quiet zone in the Bay of Bengal     

A. S. Subrahmanyam  K. S. R. Murthy  S. Lakshminarayana  M. M. Malleswara Rao  K. Venkateswarlu  T. C. S. Rao 《Geo-Marine Letters》1997,17(3):202-206

 Magnetic data over the eastern continental margin of India and adjacent Bengal fan demarcate two major lineaments. A high amplitude N–S-trending lineation of the Cauvery offshore Basin corresponds to the offshore fragment of the 80°E lineament recorded onland. A N–S lineation of very high amplitude anomaly off Chilka lake considered as the possible northward extension of the 85°E ridge delineated, hitherto in Bengal Fan. A subdued magnetic anomaly zone is demarcated seaward of the continent–ocean boundary (COB) in the Bengal Fan. Over the northern Bengal Fan this zone is delineated east of 85°E lineation. This quiet zone might have evolved during the Early Cretaceous period of normal magnetic polarity between M0 and 34 (120–84 Ma) anomalies. Received: 6 April 1995 / Revision received: 3 September 1996  相似文献   

Analysis of multi-channel seismic reflection and magnetic data along 13° N latitude across the Bay of Bengal     

D. Gopala Rao  G. C. Bhattacharya  M. V. Ramana  V. Subrahmanyam  T. Ramprasad  K. S. Krishna  A. K. Chaubey  G. P. S. Murty  K. Srinivas  Maria Desa  S. I. Reddy  B. Ashalata  C. Subrahmanyam  G. S. Mital  R. K. Drolia  S. N. Rai  S. K. Ghosh  R. N. Singh  R. Majumdar 《Marine Geophysical Researches》1994,16(3):225-236

Analysis of the multi-channel seismic reflection, magnetic and bathymetric data collected along a transect, 1110 km long parallel to 13° N latitude across the Bay of Bengal was made. The transect is from the continental shelf off Madras to the continental slope off Andaman Island in water depths of 525 m to 3350 m and across the Western Basin (bounded by foot of the continental slope of Madras and 85° E Ridge), the 85° E Ridge, the Central Basin (between the 85° E Ridge and the Ninetyeast Ridge), the Ninetyeast Ridge and the Sunda Arc. The study revealed eight seismic sequences, H1 to H8 of parallel continuous to discontinuous reflectors. Considering especially depth to the horizons, nature of reflection and on comparison with the published seismic reflection results of Currayet al. (1982), the early Eocene (P) and Miocene (M) unconformities and the base of the Quaternary sediments (Q) are identified on the seismic section. Marked changes in velocities also occur at their boundaries.In the Western Basin the acoustic basement deepening landward is inferred as a crystalline basement overlain by about 6.7 km of sediment. In the Central Basin possibly thicker sediments than in the Western Basin are estimated. The sediments in the Sunda Arc area are relatively thick and appears to have no distinct horizons. But the entire sedimentary section appears to be consisting of folded and possibly faulted layers.The comparatively broader wavelength magnetic anomalies of the Central Basin also indicate deeper depth of their origin. Very prominent double humped feature of the 85° E Ridge and broad basement swell of the Ninetyeast Ridge are buried under about 2.8 km thick sediments except over the prominent basement high near 92° E longitude. The positive structural relief of the buried 85° E Ridge in the area is reflected in magnetic signature of about 450 nT amplitude. Flexural bulge of the 85° E Ridge and subsidence of the Ninetyeast Ridge about 24 cm my^–1 rate since early Eocene period have been inferred from the seismic sequence analysis.  相似文献   

Seasonal Variability of Cyclone Heat Potential in the Bay of Bengal     

Sadhuram  Y.  Rao  B. P.  Rao  D. P.  Shastri  P. N. M.  Subrahmanyam  M. V. 《Natural Hazards》2004,32(2):191-209

Monthly maps of cyclone heat potential (CHP) in the Bay of Bengalhave been prepared by using Levitus climatological data set. Seasonal variability ofCHP in the Bay of Bengal has been studied using the CTD data sets collected duringfive cruises during the period, 1993–1996. High value (>30 kcal/cm²) of CHP coincided with anticyclonic gyre (ACG) and the low value of CHP (16 kcal/cm²) coincided with thecyclonic gyre (CG). This emphasizes the importance of gyres in the distribution ofCHP, which play an important role in the intensification of cyclones/depressions.CHP is >14 kcal/cm² over Andaman Sea, southern and Central Bay of Bengal where the generation and movement of cyclones take place during post south west monsoon season (October–November). A depression formed on 07.11.95 at 11°N; 91°E and intensified into a cyclonic storm by 8th November evening and crossed Orissa Coast on 9th November 1995. A few days before its formation, the value of CHP at the origin of thiscyclone was about 20 kcal/cm². To understand the exact role of CHP in theformation and intensification of cyclones/depressions over Bay of Bengal, more intense and systematic data sets are essential.  相似文献