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

A. G. B. Reddi ¹

Affiliations
1 A.M.S.E. Wing, Geological Survey of India Bangalore, IN

Abstract

No Abstract.

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A. G. B. Reddi ¹, M. P. Mathew ¹, Baldau Singh ¹, P. S. Naidu ²

Affiliations
1 Geological Survey of India, AMSE Wing, Bangalore 560001, IN
2 Indian Institute of Science, Bangalore 560 012, IN

Abstract

As conventional mapping of near-surface geology has been completed already on a certain scale for most part of the country, the primary objective of the on-going National Aeromagnetic Survey seems to lie in uncovering the structural configurations at depth by producing relief maps at one or more levels within the crustal column, although such maps cannot but be tentative and open to revision in the light of new data.

This exercise has been attempted for the peninsular segment south of 12°N latitude resulting in the production of a map of a relatively shallow magnetic basement. A filtered (low-pass) anomaly map is also presented that apparently reflects a deeper simatic layer and, therefore, the Moho, by implication. The area seems to be composed of a mosaic of independent crustal blocks involved in relative vertical movements. A graben is indicated sub-parallel to the west coast extending into the Gulf of Mannar and possibly beyond into Sri Lanka. The Palghat-TiruchirapalJi region is also downfaulted suggesting a junction of profound structural dislocation between the granulite terrane and the Karnataka craton. An overall increase in crustal thickness towards north and east is also inferred. The gravity rise towards the Tamil Nadu coast (in striking contrast with the uneventful fatI in magnetic values) may have to be explained in terms of lateral changes in crustal and subcrustal parameters rather than in terms of a simile rise of the Moho.

These results should hopefully encourage the generation of subsurface maps of structure even for the rest of the country based on aeromagnetic and other ground geophysical data, thus, ushering in a new chapter of Indian geology in three dimensions.

Full Text

     

A. G. B. Reddi ¹

Affiliations
1 Geological Survey of India, AMSE Wing Bangalore 560001, IN

Abstract

No Abstract.

Full Text

   

A. G. B. Reddi ¹

Affiliations
1 Geological Survey of India, AMSE Wing, Bangalore, IN

Abstract

No Abstract.

Full Text

   

A. G. B. Reddi ¹

Affiliations
1 516, 1st J Cross, 6th Block, IIPhase, B.S.K. 111 Stage, Bangalore - 560 085, IN

Abstract

An earthquake is but a culmination of stress build-ups that go on over a period of time at various brittle-ductile transitions located mainly within the crust. Mapping such transitions must therefore form an integral part of any effort at understanding the seismicity of a region. However, this aspect has been grossly neglected, most of our concerns so far revolving round faults and allied structures that only provide a mechanism for stress dissipation as distinguished from stress accumlation.

As a matter of fact, any holistic approach to the problem must invariably include within its ambit an investigation of the thickness and composition of the crust on the one hand and surface heat flow on the other, since these are known to have a direct bearing on the seismic propensity of a region. For instance, a thicker than average crust or a higher than normal heat flow (with consequent thinning of the lighter upper crust) could signify a potential seismogenic area. The same thing could be said of areas where strong rheological stratification is suggested at depth by the presence of say, low velocity layers, seismic reflectors or electrical conductors.

There is a distinct possibility of many of these situations finding expression in gravity maps which could consequently provide a very reasonable basis for effctive selection of areas for detailed follow-up, by more complex methods. Adopting this principle, a broad geophysical strategy has been mooted for the active consideration of geoscientists in the country. While it may be debated and improved upon in regard to detail, its overall implementation as a national project is an imperative dictated by the ominous prospect of a more and more common recurrence of earthquakes in the peninsula in the years ahead.

Keywords

Geophysics, Seismicity, Indian Shield.

Full Text

     

A. G. B. Reddi ¹

Affiliations
1 516, 1st J Cross, 6th Block, II Phase, B. S. K. III Stage, Bangalore-560085, IN

Abstract

No Abstract.

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A. G. B. Reddi ¹

Affiliations
1 Bangalore, IN

Abstract

No Abstract.

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A. G. B. Reddi ¹

Affiliations
1 516, 1st 3 Cross, 6th Block, II Phase, Banashankari III Stage, Bartgalore - 560 085, IN

Abstract

No Abstract.

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