MUMBAI, MAY 23: As the fate of the Sardar Sarovar Project hangs in balance in the wake of Jabalpur quake which rocked Madhya Pradesh recently, geological experts say that the quake has nothing to do with the safety of the dam and have given a clean chit to the dam authorities to go ahead with the construction works.

Besides, experts dismiss the very concept of reservoir-induced seismicity, an idea which the green activists have been heavily banking upon to stall the Narmada project, in the case of Narmada dam or for that matter any reservoir. According to them, earthquake mechanism is by and large a subject of plate tectonics and hydrostatic pressure (as contributed by the weight of the liquid column in the dam) is too infinitesimal to trigger off a quake.

``The only precaution one has to take in light of the Jabalpur episode is to insist aseismic design in all the constructions along the Narmada river basin,'' says Prof V Subramanyan, a noted geologist from Indian Institute of Technology (IIT).

``I don't know why there is so much fuss about Narmada, when a major dam like Bahkra Nangal across Beas-Sutlej link, which harbours a major fault just below the dam, can exist safely for nearly 40 years,'' he added. At the time of building the dam, the authorites went ahead only after getting the clearance from geological experts.

The geologist, who has been studying the Narmada and other major river basins for over 30 years said that the Narmada Tribunal gave the green signal to the dam authorities only after getting an expert opinion from many sides. At the same time, Subramanyan didn't try to conceal the possibility of an impending future shock. ``The government shouldn't stop any such developmental projects in response to Jabalpur incident. We have to learn to live with quakes as Japan and US have done and use available quake-resistant technology to minimise the impact,'' he said.

``When we analyse the quakes in recent years, there is a strong indication that there is no area which can be called as absolutely aseismic -- free from earthquakes,'' Subramanyan opined. Geologists have been forced to take this extreme standpoint since many of the recent quakes like Koyna and Latur occurred as a result of intra-plate dynamics. Previously, experts held the opinion that earthquakes occur only as a result of collision among tectonic plates but not within the plates.

As far as the Jabalpur quake is concerned, Subramanyan cites his paper published in the Journal of Geological Society of India in 1981, which gives a seismic interpretation to some rivers flowing along some older structures. The paper points out that Narmada and Son rivers have got superimposed along the resurrected older structures.

The Narmada originates at Amarkantak in black basalts, which are younger rock formations (around 65 million years), and flows on the same basalts curvilinearly till it reaches south of Jabalpur. Here it leaves the basalts and flows on the Precambrian metamorphics (older rock formations) and strikes between Tilwaragat and Bheraghat through the marble rock gorge.

Subramanyan opines that this stretch of Narmada is actually flowing through an ancient valley on the schists and marbles, the deep gorge and water falls (often exploited by Bollywood producers) being later additions in its geological history.

Subramanyan says with certainty that the recent quake is a result of the natural unloading of rocks and minerals towards east of Narmada due to rain and erosion. ``Since a substantial amount of land mass is displaced by this process, it can create new faults or activate older faults. In Jabalpur what might have happened is reactivation of an older fault,'' he explained. To put it more simply, the violent fault lines which have been kept under check by land mass suddenly release the built up stress as a result of rock displacement.

He also pointed that the recent quake has lot of implications for the country as a whole since over 500,000 sq kms of the peninsula is covered by the same rocks which are found near Jabalpur.

The quake also testifies to another fear, posited by The Indian Express shortly after the Kevadia tremor in December last year (which reported Jabalpur as the starting point of the trouble), that errantly flowing rivers could be indicators of impending quakes. Incidentally, the Narmada which keeps a north-western course for a long distance suddenly turns at Jabalpur and maintains a straight westerly course for over 200 kms.

Copyright © 1997 Indian Express Newspapers (Bombay) Ltd.