The Government of India is forging ahead with Jaitapur nuclear plant. At present it is a non-descript locality in Madban village of Ratnagiri district, Maharashtra. Once the nuclear plant comes up it would be the largest nuclear power generation plant in the world in terms of net electrical power rating, says the Wikipedia.
The recent much publicized mishap of Japan has certainly created a fear in the minds of the public. The anti-nuclear power lobby says building such a huge power-generation plant at a place not very safe from earthquakes amounts to playing with the lives of the people.
|Problem with India is that it is a mobile sub-continent, creeping northward at a rate of five cm per year. This constant movement makes the landmass vulnerable for earthquakes anytime, anywhere.
Is Jaitapur really unsafe from the earthquakes? This is what this story is all about.
Roger Bilham of Department of Geological Sciences, University of Colorado, Boulder, USA and Vinod K. Gaur of Centre for Mathematical Modeling and Computer Simulation, Bangalore, India have recently aired their views on the topic in the Current Science. It need not be emphasized that both of these scientists are renowned in the field of seismology.
It may also be mentioned that severest earthquakes often return in 1000 years. In other words while erecting a nuclear power station of the might of Jaitapur one needs to be assured that a catastrophic earthquake can be ruled out.
In order to ascertain how safe or unsafe a particular site is from the point of view of earthquakes and detailed record of past shaking spanning a few centuries is vital. In the history earthquakes older than 188AD have been depicted, but the data available is not enough to a precise record of past shaking. The structural engineers of the country are capable to design a nuclear power station to withstand the highest possible shaking. But the expenditure involved is directly proportional to the shaking. That is why an estimation of past shaking is necessary to design a plant that would have a higher cost benefit ratio and safety factor as well.
Bilham and Gaurin their recent communication say that ‘Jaitapur, however, has no record of local seismicity in the past century; although several approximate M3 (Magnitude) events cluster towards Koyna seismogenic area 100 km to north northwest.’ As of today, the records show that since the year 1900 no earthquakes of magnitude (M) 4.5 have occurred in this area. From 1985 onwards state of art earthquake recording stations have been established and it is confirmed that no shaking worth being scared of has taken place in the area.
Problem with earthquakes is that they are unpredictable. Koyna in Maharashtra was supposed to be situated on a ‘stable mass’ till 1967, when the myth was broken by M 6.4 earthquake, killing 177 people, injuring more than 2000 persons and rendering 50,000homeless. Such earthquakes and larger ones between less than 30 km to more than100 km from Jaitapur can cause appreciable damage. Bilham and Gaur state that Jaitapur has frequently experienced intensity VII shaking from such earthquakes.
An earthquake of intensity VII does little harm to properly designed and well- built structures and slight to moderate damage to well-built ordinary structures and considerable damage to poorly built or designed structures. While constructing structures like a nuclear plant it is expected that the authorities will give due attention to the parameters of design and monitor the quality of construction strictly. The only glitch here is that Jaitapur is close to Koyna and on the same tectonic set up. The intensity of Koyna earthquake had an intensity of VIII that is destructive.
The unpredictability of an earthquake is such that a destructive earthquake may not occur for thousands of years but may occur within the life time of a nuclear plant.
Indian shield is considered a stable landmass by the geologists. It is indeed so, but cannot be categorically kept in a no earthquake zone. Bilham and Gaur say that earthquakes can occur in special circumstances. They are:
- ancient rift zones that may ‘focus’ regional stresses;
- coastal regions that may have been stressed by rising sea level since the last Ice Age;
- regions where friction has been reduced artificially on existing highly stressed faults by reservoir impediment and
- continental regions experiencing flexural stress.
The nearest continental rift which has experienced considerable seismicity in the past(1819 and 2001) is Bhuj in Kachch. It is 800 km north of Jaitapur. Shaking from an earthquake from this source is anticipated to be less than or equal to MSK(Medvedev-Sponheuer-Karnik intensity scale) IV. This is considered to be a low intensity earthquake risk.
Compared to many coast lines, Indian coast line is supposed to be tectonically stable. Jaitapur lies in the coast line. Problem with large magnitude earthquakes or tsunamis is that they occur with a span of sometimes 1000 years or more. Thus if we take the risks in terms of past few hundred years then this area was engulfed by a tsunami which rocked Vasco De Gama’s fleet in 1524 near Daibuli, say Bilham andGaur.
Koyna was rocked in 1967 by a Reservoir Induced Earthquake of intensity 6.4. The main shock of this earthquake was powerful enough to destroy thousands of houses. Such shocks cannot be ruled out in future as well.
Problem with India is that it is a mobile sub-continent, creeping northward at a rate of five cm per year. This constant movement makes the landmass vulnerable for earthquakes anytime, anywhere. The constant 16-18 mm/year pushing of the Indian Plate in to Asian Plate has bent the northern edge of the Indian Plate downward by about 4-6 km, say Bilham and Gaur. Compared to northern part the central part of Indian plate is raised by about 400m. No other continental plate has this kind of stress regime and it has caused the southern part of the plate to buckle downward by about 60-60m.
Koyna, Latur and Jaitapur lie in this stressed part of the Indian plate. This kind of stress can cause moderate earthquakes of intensity 6.3 to 6.4. The plant design therefore must take in to account all kinds of possibilities of future earthquakes.
Before designing a structure of the like of Jaitapur nuclear power plant it is important to know the earthquake record in the history. This helps in working out the possibilities of intensities of future earthquakes. Unfortunately in India the historical record of earthquakes is not enough to develop a possible scenario. While erecting strategic structures like a nuclear power plant we try to mimic the designs or techniques of designing developed by other countries. Here it is pertinent to mention that Japan, China, parts of Europe and the Middle East has a detailed record of moderate intensity earthquakes of more than past 2000years. Unfortunately in India such record is sparse.
The written history of India regarding earthquakes is unreliable and incomplete before the arrival of the Portuguese in 1492, say Bilham and Gaur. Records of earthquakes during 1500 to 1770 were lost in Lisbon Earthquake and the duplicates were burned down by the ignorant Captain given charge of transshipping them to Lisbon in 1775. If we peep farther into history and try to build a picture it appears that quantitative and qualitative records of at least 5000 earthquakes of the subcontinent are not available. Whereas, for planning sensitive structure like a nuclear power station that too the intended World’s largest station of its type needs meticulous planning, collection and collation of data and a design that will take in to account the worst possible scenarios, as far as earthquakes are concerned.
Jaitapur has been quiet for some decades. Should we take this quiescence as an indicator of Jaitapur being on an aseismic zone! Or should we take it as a period of lull before the storm and that the accumulated stresses may be released some day without any warning! Here it is pertinent to quote Bilham and Gaur again, ‘….Unhappily, however, the apparent quietness of Jaitapur does not mean that a severe earthquake cannot occur there.’ However, in the same context they say that the area may be prone to an earthquake of M 6 or more but the probabilities are low.
Compare Jaitapur to a stressed human adult. The chances of a cardiac arrest for such a person are always there, but when it will happen, no one knows. Likewise Jaitapur could remain safe and firm for a few generations or it could go like the Fukushima way. Any guesses!