Quake looms large over Koyna: NGRI

A greater than five magnitude earthquake will rock Koyna in Maharashtra "over the next few weeks," seismologists have warned.

They say they are monitoring the seismic activity in the region and shall be able to make an exact forecast, "one to two days before the event."

Forecasting earthquakes is a risky business and scientists rarely make predictions. Nowhere in the world has this been done with confidence.

But in what is perhaps the first time, seismologists at the National Geophysical Research Institute (NGRI) have given the exact place and likely date of an earthquake to take place in the country.

The prediction is published in the journal 'Current Science' by Harsh Gupta and ten others at NGRI. Gupta was former director of NGRI and recently retired as secretary for the department of ocean development.

"We have reasons to believe, based on the study of several factors, that a five magnitude earthquake may occur in the Koyna region over the next few weeks," scientists report.

"Should it not occur till the end of December 2005, this forecast should be considered as a false alarm," they say. Koyna region experienced its first earthquake (6.3 magnitude) in 1967. Gupta was one of those who theorised that the quake was the result of filling the Koyna reservoir six years earlier.

Ever since the impounding of water, Koyna had experienced several hundred small tremors, 19 of which were of magnitude 5. The last magnitude 5 earthquake occurred on March 14, 2005, after a lapse of four-and-a-half years.

According to Gupta and his colleagues, all the 19 m-5 events occurred following the start of loading or unloading of the reservoir.

They say their prediction for an impending quake is based on the fact that water levels in both Koyna dam and the nearby Warna reservoir have not only reached the peak but the loading had been "quite rapid."

Koyna dam attained its peak level on August 17, 2005, for the first time after several years. The water level rose from 627.685 to 657.784 m in just 55 days, which is "the fastest loading seen so far at the Koyna dam".

The loading of the Warna reservoir this year has also been quite rapid. "From a level of 594.06 m on June 23, 2005, it has risen to 626.9 m on August 15 2005, in just 53 days," the scientists said.

More significantly, for the first time, water level at Warna has exceeded the previous maximum of 627.88 m recorded on September 13, 2003, thus satisfying the conditions for the Kaiser effect to be operative. (According to the Kaiser effect, magnitude-5 earthquakes will occur when the previous maximum water level gets exceeded).

The NGRI team says it is closely monitoring seismic activity in the Koyna-Warna region, to be able to identify a phenomenon called "nucleation" in real time.

"If we succeed in identifying this nucleation when it is half-way through, we shall be able to make a short-term forecast, one to two days before the event," they said in their report.