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

P. N. Vijayaraghavan ¹, R. K. Tiwari ¹

Affiliations
1 Hindustan Copper Limited, Bandalamottu, Guntur District, Andhra Pradesh, IN

Abstract

Mineralisation is essentially confined to dolomitic host rock. The strict lithological control of mineralisation with its width extremes and layering defined by the bedding planes in the dolomite and the folding of mineralised zones conforming in style to that of the host rock are strong field evidences to suggest syngenetic origin of the deposit.

Due to structural complexity of the deposit, basic information from 100 m spaced drill intersections does not give correct picture regarding the disposition of ore bodies. No fixed norms for mining could, therefore, be established in advance and every mineralised section will have to be negotiated depending upon the structural domain and allied features governing the mineralisation in that particular section.

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S. Sri Lakshmi ¹, R. K. Tiwari ¹

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

Abstract

The modern concept of fractal and chaos theory has invariably been applied to earthquake time series to understand the nature of earthquake dynamics and hence to characterize the model behaviour. However, prior to proposing an earthquake generating model and predictive behavior of earthquake data, it is essential to understand the possible influence of foreshocks and aftershocks on the earthquake dynamics.We study the impact of foreshocks and aftershocks on the nature of earthquake dynamics using the modern nonlinear forecasting approach. We used here monthly frequency earthquake data sets obtained from one of the most Seismo-Tectonically crucial regions of northeast India bounded by latitude 20-28°N and longitude 88-98°E, spanning over a time window of 1920-1988. For the present purpose, two sets of monthly earthquake time series are prepared: (i) original earthquake data and (ii) data after removing foreshocks and aftershocks, and then analyzed separately using the non-linear forecasting approaches. Comparative results indicate that earthquake data free from aftershocks and foreshocks show better predictive behaviour than the original data (i.e. combined with aftershocks and foreshocks), thus revealing a significant effect of foreshocks and aftershocks on the model characterization of earthquake dynamics.

Keywords

Fractals, High Dimensional Chaos, Foreshocks and Aftershocks, Nonlinear Forecasting Analyses, Northeast India Earthquakes.

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U. K. Singh ¹, R. K. Tiwari ², S. B. Singh ², S. Rajan ¹

Affiliations
1 National Centre for Antarctic & Ocean Research, Vasco Goa - 403 804, IN
2 National Geophysical Research Institute, Hyderabad 500 007, IN

Abstract

The artificial neural network (ANN) technique is at present most efficient and modern tool for parameter estimation and inversion of geophysical data. This paper deals with the application of ANN technique for the inversion of vertical electrical resistivity sounding(VES) data obtained from the NNW SSE part of Barmer district, Rajasthan. The efficiency of ANN technique is tested first on synthetic resistivity data generated from the numerical model and then trained on the actual VES field data. The analyses predict sediment thickness of the order of 172 m at Rawtra (S 15, and indicate that there is possibility of fresh aquifers at all sounding locations along the profile except at Sonadi (S 1). These results match with the depth-Resistivity structure obtained by the conventional method. However, the high accuracy and faster ANN imaging system seems to have highly correlated with that of conventional method for mapping the complex subsurface resistivity structures with less ambiguity. These finding also correlate remarkably well with known drilling results and geologic boundaries.

Keywords

Artificial Neural Network, Backpropagation Algorithm, VES Data, Resistivity Layer Parameters, Fresh Aquifer, Saline Aquifer, Barmer District, Rajasthan.

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R. K. Tiwari ¹, K. N. N. Rao ¹

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

Abstract

We examine here the latest available episodic and continuous records of long-term geo-hydro-bio-chemical processes using the non-parametric and modern spectral approaches. These analyses confirm the earlier findings of a 33 ± 3 million years (Myr) periodicity and reinforce that mega geo-bio-atmosphenc processes are cyclic in nature. Interestingly, six major extinction events coincide well with low phosphorous bunal rate (PBR) indicating that complex geochemical oscillations, probably caused by astronomically induced impact events, may have precipitated ocean productivity crisis leading to the biological upheaval in the earth's history. The present study combined with earlier evidence of a periodicity in the impact cratering record may provide a significant constraint on any theoretical framework attempting to unify terrestrial observations in widely different fields.

Keywords

Mega Geocycles, Phosphorus Burial Rate, Galactic Cycles, Spectral Analyses, Cychcity in Earth-Processes.

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R. K. Tiwari ¹, K. N. N. Rao ¹

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

Abstract

The Northeast Indian region (NEI) is characterised by frequent earthquakes associated with swarms and quiescence activities. To gain physical insight about its origin, inter-event time series of earthquakes M≥3 and 5 has been analysed using rank-order statistics and non-linear perspective. The rank-order statistics of inter-event time series intlicates "mixed response" with distinct breaks in slope suggesting unstable, quasi-deterministic and random recurrence time that is sensitive to earthquake dynamics. The break in "slope" possibly suggests that the long term (of recurrence time > 400 days) earthquake dynamics in this region is unstable. The middle segment representing the time range of approximately 30-400 days can be described by Power Law function indicating the possible element of determinism on this time scale. Lastly, the existence of "roll off" towards higher rank-order, however, seerns to indicate the transition in the nature of structure. In order to constrain these results, we further compute the second order Kolmogorov-Sinai entropy (K₂), which reveals a coherent time structure with predictive time limit of about 12 to 16 months, indicating a quasi-deterministic dynamics that apparently is also evident (Power Law) in rank-order statistics. This predictive time limit seems to be too short to be associated with major global tectonics. We therefore, propose an alternative possible physical mechanism, which may coexist with regional tectonics. In the light of present results, we suggest that surface/subsurface water infiltration into the main fractures and faults during a favourable season could increase the pore pressure thereby triggering frequent earthquakes, particularly in critically unstable tectonic regions.

Keywords

Earthquakes, Power Law, Random, Deterministic, Rank-Order, Entropy, Northeast India.

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