SEISMIC ACTIVITIES
Wikki reports
The dam is situated in a seismically active zone. An earthquake measuring 4.5 on the Richter scale occurred on June 7, 1988 with maximum damage in Nedumkandam and Kallar (within 20 km of the dam). Consequently several earthquake tremors have occurred in the area in recent times. These could be reservoir-induced seismicity, requiring further studies according to experts. A report by IIT Roorkee states that the dam "was likely to face damage if an earthquake of the magnitude of 6.5 on the Richter scale struck its vicinity when the water level is at 136 feet".
After the 1979 Morvi Dam failure which killed up to 25,000 people, safety concerns of the aging Mullaperiyar dam's and alleged leaks and cracks in the structure were raised by the Kerala Government. A Kerala government institution, Centre for Earth Science Studies (CESS), Thiruvananthapuram, had reported that the structure would not withstand an earthquake above magnitude 6 on the Richter scale. The dam was also inspected by the Chairman, CWC (Central Water Commission). On the orders of the CWC, the Tamil Nadu government lowered the storage level from 142.2 feet to 136 feet, conducted safety repairs and strengthened the dam.
Strengthening measures adopted by Tamil Nadu PWD from 1979 onwards include cable anchoring of the dam's structure and RCC backing for the front slope. During a recent scanning of the Mullaperiyar dam using a remotely operated vehicle by the Central Soil and Materials Research Station on directions from the Empowered Committee of the Supreme Court, the Kerala Government observer opined that "mistakes in the strengthening works carried out by Tamil Nadu" in 1979 damaged the masonry of the dam.
Excerpts from a continued feature in Mathrubhumi daily by Sri.Jayachandran,P.K
M D was built when the earth science was in its infancy.-No authentic scientific tests were feasible then.The potential danger was understood in later studies.The dam stands at a place where there are a number of clefts on the earth and it lies in the seismic sensitive area.Mullapperiyar lies in the much daunted area in the seismic regions. The expert committee under Dr.M.Baba the ex-director of Trivandrum CESS has found that Mullapperyar situates on the rendezvous of Kambam,Udumbamchola seismic line.Again the Baby dam is situated in another seismic centre as reported by the Geological survey of India.Kerala lies in the 3rd zone where magnitude of 6.5 in Ricture scale is possible.Such tremors can destabilise the rocks in the bottom where leakage can increase through the vents created.However as per the latest study by BIS(Bureau of Indian Statistics),Kerala is sheduled in the 4th zone where themagneude of maximum intensity of 7.5 is predicted. Nedungandam in Idukki a quack of magnitude 4.5 was felt.John Mathaui a Senior scientist from CESS says that the seismic centre of the tremors felt at Uluppooni,valavukodu,Kannambadi were near to Mullapperiyar Dam.
In Kerala it has been pointd out that the seismic Zones are active.The seismic zone centering the Continental shelf in the Arabian sea is also active,.The tremor at a magnitude of 4.5 felt at Trivandrum was centered on this.The tremor felt in the south west of Kolambo in November also was centered in this zone which passes from Bombay High to Sreelanka.The possibility of a severe earth quake in kerala is rare since the frequently felt minor quakes exit the pressure in earth.But some scientists do believe that these shocks are the harbinger of a greater shock.
According to the strength of tremor the country is being divided in to 4 zones.Lathur in Maharashtra was in the 1st zone (expected magnitude 4.8 )where,contrary to expectations of scientific community ,an earth quake of magnitude 6.3 occurred in September 1993 killing 20,000 people in the process.Before the mishap there were 40 short and minor fore shocks which was neglected by the scientific community.The locales who marched to the taluk office , complaining of cracks to their houses ,were brutally caned and dispersed.
Dr C.P.Rajendran an Earth quack scientists from Indian Institute of Science ,Bangalore says that studies have not established that the dam has suffered due to the frequent earthquakes experienced recently.There is remote chances of earth quakes of appreciable magnitude.The existing dam has reduced strength which would mean that it has to be decommissioned which might take time.The water level should not be increased.
The Kerala government has sought reducing the storage level of the dam which has a gross capacity of 15.6 TMC by16 ft to 120 ft and reaffirmed its demand to build a new dam at the site proposed. Kerala has contended that the region has recorded 22 quakes /tremors this year. State irrigation minister P J Joseph claims that studies conducted by scientists from IIT-Roorkee and Thiruvananthapuram-based Centre for Earth Science Studies (CESS) have pointed out that the Mullaperiyar dam is in a seismic zone and the quake of six or more on the Richter Scale can not be ruled out. CESS scientist John Mathai is of the opinion that any quake of the magnitude of six on the Richter Scale could damage the dam located 4,000 ft above the sea level and put millions of people in the downstream area at a grave risk.
If the dam bursts, flood waters released in its wake could submerge small towns before reaching the Idukki dam, the biggest in the state. The force of the water could breach the Idukki dam also and it could be catastrophic as 3.5 million people would be affected.Above all, the rare flora and fauna in the Periyar National Park and adjoining Periyar Tiger Reserve would be completely destroyed.
Recent tremors (Collected from daily news,Mathrubhumi)
In the last century more than 100 tremors of varying intensity have been recorded in the region ,the majority of them in 2011.Although history witnessed two major quakes in 1342 at Neryamangalam and in 1875 at Palght Kerala is considered as a region where tremor susceptibility is minimal.But scientists say that dormant seismic zones have recently became active.Since 1976 when Idukki was first filled with water ,900 tremors per year ,mild and insignificant though ,have occurred in the vicinity of 2 Km from the dam.The tremors are expected to come down with in 25 years of Dam construction.But things remain negative.
1)Magnitude 4.5 in Dec2000 centered at Melukavu
2)Magnitude 5 centered at Erattuopetta
3)Magnitude 2.8 of 20 Km away from Dam on 18th Aug 2006
4)Magnitude 2.2 centered at Nedunkandam on 30th Jan 2008 -30Km from the Dam
5)Magnitude 3.2 epicenter at Malayatti on 26th June 2009-67 Km from the Dam
6)Epicenter at Peryar Wild Life Sanctuary -Ranni on 3rd November
7)Magnitude 2.9 epicenter at Vellakkayam near Cheruthoni-on 7th November 2010-37 Km from the Dam
There were 23 incidences of tremors of small and large in the last 9 months-the seismic center being in the Idukki project area starting from 5th March last year.
Major quakes reported in 2011.
1)Magnitude 3.8 centered at Kottamala on 26th July 2011.Continued to this there were 7 tremors shortly after-cracks developed in the dam.
2)Magnitude 2.0 centered at Upputhara on 23rd October 2011-30 Km from the Dam
3)Magnitude 2.1 centered at Parathott near Thoprankudi -16th september 2011-repeated trmors after 5 minutes. again and on 18th
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