Quake could hit Tehri dam any day: government scientists

Environmentalists have complained from its inception that the Tehri mega-dam in the Garhwal Himalayas is not only an ecological disaster but also extremely dangerous, as it lies astride a well-known sensitive seismological zone that has seen several earthquakes over recent years.

Now this viewpoint has been confirmed by scientists in the government-run National Geophysical Research Institute. They have found that there is an active fault beneath the Tehri dam that enhances the earthquake risk.

The dam was created by blocking the Ganges at its source in the Himalayas and submerging the entire town of Tehri as it originally existed. It has of course completely destroyed the ecology of the area – it is well known to ecologists that such large dams are major emitters of ethane gas, which is about 10 times more dangerous than carbon dioxide in terms of greenhouse effect.

But the more immediate threat is probably an earthquake disaster – the last major earthquake, measuring as much as 8.9 on the Richter scale, happened in the region just about four years ago. Luckily, its epicentre was a little away from Tehri.

"The tectonic loading on this active fault due to local seismicity, coupled with the reservoir loading and unloading, may generate earthquake(s) and cause additional seismic risk in this critically stressed region," Sandeep Gupta and co-workers in NGRI claim in their report in the latest issue of 'Current Science' published by the Indian Academy of Sciences.

They say their conclusion is based on evidence obtained by mapping of the seismicity pattern in the Kumaon-Garhwal Himalayas in general and around the Tehri dam in particular, using observations from a temporary seismological network they operated for over 39 months during 2005-2008. During this period, over 20 earthquakes of magnitude 1.6-2.8 on the Richter scale were recorded in a 20-km radius of the dam site.