PUNE, February 20: While seismologists in general have time and again debated the suspicious role of the Koyna reservoir in the occurrence of frequent earthquakes in western Maharashtra, results of research being conducted by the Central Water and Power Research Station here since 1963 clearly establish strong relations between unusually high seismic activity in the region with the impoundment of the Koyna reservoir.The observations gain significance in the light of the spate of mild earthquakes last week that rocked the entire Koyna region, once again raising serious doubts about the disputed "non-seismic" character of the Koyna reservoir.
A scientific paper authored by the former joint director of the Station, Dr S K Guha, on the basis of research conducted by the CWPRS and published in the year 1992 clearly speaks of earthquakes observed in Koyna region as distinctive characteristics of reservoir-induced seismicity (RIS). In fact, the paper describes Koyna reservoir as a "classic case of RIS".
Thegeological term explains the phenomenon of initiation of seismic activity in an aseismic region or enhancement of activity in an area with very mild seismic activity due to impoundment of an artificial reservoir.
It may be noted that as a part of its massive project to study the RIS phenomenon, CWPRS had installed a network of local seismic stations in the Koyna reservoir area in 1963.
The Koyna dam and the Shivjisagar lake formed by it are located in the peninsular shield of India, which was considered to be the geologically stable Precambrian shield. "However," says Guha in his paper, "soon after the impounding of the Shivsagar lake in the monsoon of 1963, the reservoir area began to experience mild earth tremors, the frequency and intensity of which increased with time. The main earthquake of magnitude 7.0 occurred on December 10, 1967 after about four years of initial impounding of the reservoir". The seismic network installed around the Koyna reservoir has to date recorded more than one hundredthousand earthquakes above magnitude zero, he adds. While on one hand there has been practically no acknowledgement or sincere efforts on part of the government to initiate measures, those living in the vicinity of the dam and the nearby regions continue to do so under intense psychological trauma.
A couple of years ago, Dr S V Umarjikar, a renowned geologist from Karad, had predicted major intensity earthquakes in the region, defining the recurring seismic activity in western Maharashtra's Koyna region as a clear indicator to the reduced time-expectancy for reactivation of the under-crust fault zones.
Copyright © 1998 Indian Express Newspapers (Bombay) Ltd.
