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

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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