Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

C. Ramachandran ¹, C. V. L. Narasimham ²

Affiliations
1 Geological Survey of India, AMSE Wing, Prestige Complex, 2nd Church Street. Bangalore 560001, IN
2 Geological Survey of India, Training Institute, 2.11.252/11, Jabbar Building, Begumpett Hyderabad 500016, IN

Abstract

The compressional wave velocity, compressive strength, tensile strength, permeability and density are measured for some coal-bearing rocks of Eastern India. The ranges of compressional wave velocities for the different rock types are presented. It is observed that the compressional wave velocity in sandstones increases linearly with increase of density, compressive strength, tensile strength and Young's modulus. The absorption coefficient of compressional waves in sandstones decreased linearly with increase of Young's modulus. The permeability, determined in a few sandstone samples, increased with porosity.

Empirical relations obtained by least squares technique are also presented, relating to the variation of compressional wave velocity with density, Young's modulus and the strength of sandstones. The results would find application in coal exploration and extraction.

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C. Ramachandran ¹, M. Ramachandran Nair ¹, S. Datta ²

Affiliations
1 Geological Survey of India, 29/6. 38th Cross, 8th Block, Jayanagar, Bangalore 560 082, IN
2 Department of Applied Geophysics, Indian School of Mines, Dhanbad 826 004, IN

Abstract

The P-wave velocities and their relation to depth of burial, density, porosity and electrical resistivity are studied for the coal measure rocks of Ranigunj and Jharia coalfields. From studies on the P-wave velocities in the dry and fluid saturated states, it is observed that the effect of fluid saturation is significantly more in a direction perpendicular to the bedding plane, than in the direction parallel to the bedding plane. The effect of fluid saturation is maximum in coarse-grained sandstones with low P-wave velocities. The anisotropy factor (Vp/⊥ Vp), decreased after fluid saturation. The absorption-anisotropy relation for sandstones is found to depend on grain-size distribution as well as fluid saturation conditions. The results show that saturating conditions, direction of measurement and anisotropy assume importance in the interpretation of velocity data.

Keywords

Coal, Eastern India Coalfields, Geophysics, Seismology.

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C. Ramachandran ¹, Lili Rani Bosu ²

Affiliations
1 Geological Survey of India, 323, C.M.H. Road, Indiranagar, Bangalore 560038, IN
2 Geological Survey of India, P-49, C.I.T. Road, Beliaghata, Calcutta 700010, IN

Abstract

2.67 gm/cc is the normally assumed density value for the upper crystalline crust, in gravity data reductions. The densities measured in 210 metamorphic rocks, spread over a traverse distance of 2500 km from the granulite terrain of South India, gave a mean density of 2.77 gm/cc. The results show that 2.67 gm/cc is too Iow a value and 2.76 ± 0.01 gm/cc would be an appropriate choice for the mean density of the upper crystalline crust in South Indian granulite terrain.

Though in some of the charnockites the magnetic susceptibility is considerably reduced due to retrograde metamorphism, the effect is not perceptible on the density. The areas with high paleopressures have the maximum mean densities.

Keywords

Granulite Terrain, High Grade Rocks, South India, Geophysics

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C. Ramachandran ¹

Affiliations
1 Geological Survey of India, 29/6, 38th Cross, 8th Block, Jayanagar, Bangalore 560082, IN

Abstract

The magnetic susceptibilities measured in 220 metamorphic rocks collected over a traverse distance of about 2500 km, from South Indian granulite terrain, varied over a wide range. The wide variation in the susceptibilities, 6-4420×10^-6 emu/cc is explained in terms of changes in magnetic mineralogy during prograde and retrograde metamorphic processes.

Keywords

Geophysics, Magnetics, Metamorphism, Granulite, South India.

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C. Ramachandran ¹, M. Kesavamani ¹

Affiliations
1 Training Institute, Geological Survey of India, Bandlaguda, Hyderabad-500068., IN

Abstract

Detailed structural interpretation of the regional gravity map over the Deccan traps has brought out a number of major structural discontinuities (fault/fractures), particularly the E-W features whlch were not delineated by earlier investigators. The most significant among them is the major E-W fault from west coast to east coast along Bombay-Latur-Hyderabad-Bhadrachalam-Visakhapatnam (BLHV fault). Several features of the BLHV fault suggest it to be a major reactivated strike slip fault. The structural scenario presented in this paper will have great implications in earthquake studies in Deccan trap area. Based on some aspects of fault segmentation technique for earthquake hazard and from the structural interpretation of the regional gravity map over Deccan traps, several zones are identified which could be termed as earthquake hazard zones. These hazard zones are typically located at: (1) the segment boundaries or fault steps of BLHV and other major E-W faults, (2) in many cases are associated with gravity low nosings which possibly reflect buried granite intrusions (regarded as asperities or barriers in the context of seismicity), and (3) intersection of major E-W faults with other transverse structural trends (fault/fractures). The areas where the major E-W faults terminated against the west coast fault system can also be important in terms of future seismicity. The recent seismicity in the Deccan trap, area is inferred to be due to the reactivation of the major E-W faults due to the still continuing convergence of India with Asia.

The present work, for the first time, demonstrates the importance and application of fault segmentation technique in earthquake hazard studies in Deccan trap area, and also the full potential of gravity interpretation in such studies.

Keywords

Gravity Studies, Seismo-Tectonics, Deccan Traps.

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M. Kesavamani ¹, C. Ramachandran ¹, M. V. R. Krishna Rao ¹, R. M. C. Prasad ¹, M. Venkateswarlu ¹

Affiliations
1 Geological Survey of India, Bandlaguda, Hyderabad-500 068, IN

Abstract

No Abstract.

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M. Kesavamani ¹, C. Ramachandran ¹, R. M. C. Prasad ¹, M. V. R. Krishna Rao ¹

Affiliations
1 Geological Survey of India Bandlaguda, Hyderabad - 500 068, IN

Abstract

No Abstract.

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