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

A. R. Sridhar ¹, H. C. Tewari ¹, V. Vijaya Rao ¹, N. Satyavani ¹, N. K. Thakur ¹

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

Abstract

A five-layered crustal model with 5.9-6.2, 6.0, 6.3, 6.6 and 7.0 kms^-1velocities is derived with seismic refraction/wide-angle reflection data along the Thuadara-Sendhwa-Sindad profile in central India. The profile traverses across the western part of the Narmada-Son lineament in the N-S direction. The data are subjected to 2-D forward modelling using both travel times and amplitudes. Refracted waves (P_n from the Moho observed as first arrivals at a distance of about 200 km are used to derive the upper mantle velocity of 8.1 kms-'. The Moho is well constrained both from the P_n and wide-angle reflections from four shot points. The main features of the velocity structure is the delineation of a low velocity layer (6.0 kms^-1) in the upper crust and a 12-16 km thick high velocity (7.0 kms^-1) layer at the base of the crust. The high velocity lower crustal layer, representing the magmatic underplating in the region, may be related to the formation of the Narmada Basin and the Deccan volcanic episode. The Deccan volcanism may be a consequence of the Reunion mantle plume activity. The crustal thickness varies between 37 and 43 km along the profile and the thickest crust is found between the Narmada and Tapti rivers. The gravity mode1 constrained from the seismic velocity structure corroborates the crustal structure. Deep-seated faults responsible for the evolution of Narmada Basin are inferred from the present study.

Keywords

Underplating, Deccan volcanism, Wide-Angle reflection, Low velocity layers, Moho, Narmada-Son lineament, Central India.

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A. R. Sridhar ¹, H. C. Tewari ¹, V. Vijay Rao ¹

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

Abstract

Trace normalized record sections of single fold seismic data, in Central India showed several reflections of large amplitude at upper crustal depth. Synthetic seismogram modeling of these reflections, reveal that they have originated from a combination of several alternating high-tow velocity layers. On a comparison of this model with other models available worldwide, it is felt that while some of these layers may be associated with the presence of fluids, the majority should be due to lateral variations in the near surface structures. However, the first arrival refraction and wide-angle reflection data do not show a similar structure even though, a prominent upper crustal low velocity laycr could be identified.

Keywords

Refraction Seismology, upper Crust, Near Vertical Reflection, Wide Angle Reflection, Low Velocity Layer, Central India.

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D. N. Avasthi ¹, A. R. Sridhar ²

Affiliations
1 C-190, Sarita Vihar, New Delhi - 110 076, IN
2 NGRI, Hyderabad - 500 007, IN

Abstract

No Abstract.

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P. R. Reddy ¹, K. Chandrakala ¹, A. R. Sridhar ¹

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, IN

Abstract

Re-examination of analog seismic data acquired across Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC) (western and middle parts of Kavali-Udipi DSS profile) indicate significant velocity variations in WDC and EDC. The synthesis of velocity details with the available geological signatures suggests that the two segments of the Dhanvar Craton have varying structure and evolution.

Keywords

Geophysics, Seismic Refraction, Velocity, Crustal Structure, Dharwar Craton, South India.

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