Seismic activity at Idukki worries scientists

KOZHIKODE: Raising more questions over the safety of the Idukki reservoir and the Mullaperiyar dam, a group of scientists has pointed out that the increase in the frequency of earthquakes during 2011 in the vicinity of the Idduki reservoir is unusual and is a cause for concern.The concern was voiced by  the scientists of the Centre for Earth Sciences, Bangalore, and Peechi Seismic Observatory, Centre for Earth Science Studies, Thrissur, in an article published in the latest issue of the “Current Science Journal”.They said it is quite normal to observe slight tremors during the time of initial filling of reservoir, but the sudden increase in the frequency of earthquakes during 2011, including an earthquake of the magnitude of 3.9, raises several questions.“The renewed activity near this reservoir has raised questions about the sensitivity of the area and the most important question is why the reservoir continues to generate earthquakes and whether the low-level activity observed in the recent periods is the forerunner of a larger earthquake,” the article says.It also points out that the proximity of the Idukki Dam to the 116-year-old Mullaperiyar Dam upstream of the Periyar River makes these questions more compelling. The researchers further say that excluding the 1988, 2000 and 2001 earthquakes, which were 25-40 km away from the Idukki reservoir, the area had experienced only very low-level microseismic activity till last year.   “Starting July 2011, microtremors were felt in the area and the sequence included at least three earthquakes of the magnitude of more than 3.0 out of the total twenty tremors recorded until November 2011. It is also important that the recent activity is located close to the western limb of the reservoir, a region that has experienced low-level activity in the past,” the article points out.  Calling for more studies, one of the researchers Sreekumari Kesavan, scientist at CESS, Thrissur, said,“the area where the reservoir is situated has two or three faults and what we try to convey through this article is the importance of carrying out more studies. As of now, there is no need to panic and the reservoir is completely safe.”The other three scientists are Kusala Rajendran, C P Rajendran and R Naveen, all from the Centre for Earth Sciences, Indian Institute of Science, Bangalore.