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

P. R. Reddy ¹, P. Koteswara Rao ¹, N. Venkateswarlu ¹, A. S. S. S. R. S. Prasad ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500 007, IN

Abstract

A systematic analysis of refraction data obtained in West BengaI basin, has been carried out to bring into focus the utility of the seismic refraction data in delineating fault zones. The study clearly points out the different conspicuous signatures present in the refraction travel time data, associated with the shallower fault zones affecting the top sedirnentry column and the crystalline basement.

Keywords

Seismology, Geophysics, Structure, West Bengal.

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P. R. Reddy ¹, P. Koteswara Rao ¹, A. S. S. S. R. S. Prasad ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Skips/shadow zones in the first arrival travel seismic time data (refraction) help in delineating hidden low velocity formations sandwiched between two high velocity zones. Efficacy of this processing methodology has been successfully tested utilising analog refraction data acquired along a profile located in the Deccan Trap country. The 2D velocity depth details also suggest probable presence of hidden Sub-Trappean Gondwana formations.

Keywords

Seismic Refraction, Skips/Shadow Zones, Low Velocity, Gondwana.

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T. Seshunarayana ¹, B. Rajendra Prasad ¹, A. S. S. S. R. S. Prasad ¹, D. Mysaiah ¹

Affiliations
1 National Geophysical Research Institute (CSIR), Uppal Road, Hyderabad - 500 007, IN

Abstract

A detailed, integrated gravity and magnetic study across the Main Central Thrust (MCT) along the Pala-Maneri traverse in Uttaranchal, NW Himalaya was carried out. The gravity data was acquired using a CG-3 gravity meter with an accuracy of 0.005 mGal, while magnetic data was acquired using a proton precession magnetometer with a station interval of 20 m. Data was collected along a 11.7 km, NE-SW traverse from Pala to Maneri along the proposed route of a hydroelectric headrace tunnel. The measured variation in the gravity field was approximately 70 mGal, with two prominent highs recorded at distances of 0.5 km, 7.5 km and lows at 3.0 km, 10.5 km from Maneri. The gravity highs can be attributed to presence of high-density rocks along the thrust planes. The sharp gravity low recorded at 10.5 km distance possibly indicates a sympathetic fault of the MCT that is highly saturated with fluids (water). The broad gravity low between 2.5 km and 4.0 km distance is likely to represent the gravity signature of the MCT itself. The measured variation in the magnetic field was approximately 285 nT. The associated gravity and magnetic signatures located several faults along the traverse including presence of the MCT at Kumaltigad.

Keywords

Gravity and Magnetic, Thrust Planes, MCT, Modeling, High-Density Rocks.

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