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

Manish K. Purohit ¹, K. K. Prajapati ¹

Affiliations
1 Department of Applied Geology, Dr. H.S. Gour University, Sagar - 470 003, IN

Abstract

The Bhuj earthquake (26 January 2001) in India and the Ghori earthquake (8 October 2005) in Pakistan, both occurred close to the Indian-Iranian plate boundary related to the activity along the intracontinental Chaman transform fault. It is suggested that the seismic activity along NNW to NNE trending weak zones or faults is more intense in the sub-continent than along the WNW trending zones, since the stress along the former is less compressive but more of the shear or translational type. The devastative Koyna (1967) and Latur (1993) earthquakes both occurred along faults or weak zones that were close to the meridional rather than the equatorial trend. The Indian plate is moving to the north or NNE or NNW, along a rotational trajectory and hence the force tends to be more compressive along the equatorial weak zones. In contrast, it tends to be less compressive and more of the shear or translational along the weak zones that are close to meridional trend. The seismic activity is therefore more intense along the weak zones with NNW to NNE trend than along the ENE to EW trending zones.

Keywords

Earthquakes, Seismicity, Meridional Trend, Equatorial Trend, Regmatic Fracture Pattern, Bhuj Earthquake, Ghori Earthquake.

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Prakash P. Roday ¹, Manish K. Purohit ², K. K. Prajapati ²

Affiliations
1 7, Vastu Vihar, Khajuri Kalan Road, Piplani, Bhopal - 462 022, IN
2 Department of Applied Geology, Dr. H. S. Gour University, Sagar - 470 003, IN

Abstract

Fry method enables rapid estimate of finite strain from deformed aggregates such as clastic grains, fossil colonies, oolitic or pisolitic aggregates, prophyroblastic minerals or phenocrysts. It has an advantage over the other methods of finite strain analysis in its very quality of enabling rapid estimation with a reasonable degree of accuracy. Details of the software to prepare a plot using Fry method are outlined. This program has an advantage over other computer based programs on the world wide web in its aesthetic getup, small size, user friendliness and a help file.

The program is a freeware and can be downloaded by following the links on a software website http://www.alstructural-geology-software.com.FryPlotSetup.zip or http://www.al-structural-geology-software.com/FryProg/ FryPlotProgSetup.exe.

Keywords

Fry Method, Centre-To-Centre Technique, Finite Strain, Computer Program, Visual Basic, Deformed Aggregates.

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Manish K. Purohit ¹, K. K. Prajapati ¹, R. K. Trivedi ¹

Affiliations
1 Department of Applied Geology, Dr. H. S. Gour University, Sagar - 470 003, IN

Abstract

Re-examination of the outcrop of conjugate of strike-slip faults mapped by Roday et al. (1989) near forest rest house at Hirapur reveals that the main dextral strike-slip fault that strikes N35°E and is a manifestation of the earliest NE-SW trending subhorizontal σ₁ that produced extensional reef system in the Bundelkhand massif. Although the change in the stress system though 90° rotation of the principal compressive stress σ₁ and σ₃ (with σ₂ maintaining near vertically) is correct, another point of interest is that the σ₁ for the system of faults bisects the obtuse angle between the two sets and not an acute one as required by the brittle failure criterion. The sinistral strike-slip faults were probably formed by rejuvenation of the initial dextral strike-slip faults that were generated when the maximum principal compressive stress was oriented NS. The reversal of fault displacement is seen on all scales in the Bundelkhand massif. The dextral strike-slip fault related to the late stress system was preferentially produced along pre-existing tensile fractures that were generated under NE-SW directed subhorizontal σ₁. Some of these fractures were converted into sinistral strike-slip faults under NS directed maximum principal compression acting subhorizontally.

Keywords

Dextral and Sinistral Strike-Slip Faults, Rejuvenation, Pre-Existing Fractures, Stress Field, Obtuse Wedge, Central India.

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