Earthquakes are like the electrocardiograms of the pulsating Earth. The recent devastating earthquake of Japan has become one of the best recorded earthquake events which has given tremendous information to the seismologists. The ultimate objective of the seismologists is to develop a way to predict the earthquakes. The scientists of Woods Hole Oceanographic Institution, Kyoto University and United States Geological Survey have identified several areas of Japan at risk. The predictions at this point of time cannot be called as foolproof but yes the scientists are confident that they are a wee bit closer to forecasting a quake.
An earthquake generates stress, which is passed on further to cause aftershocks or an earthquake. This can be better explained with the examples of cycles parked closely at a cycle stand. If one cycle trips at one end the ripple effect makes all of them to topple like a pack of cards. The plates underneath us also topple almost in a similar way - it is just a matter of time that the seismologists will find out the date and time when a set of plates or a major fault will move to cause a major earthquake.
India, a country on fast track of development is prone to earthquakes, though the frequency may be much less than Japan. The mishap at Japan has compelled the geologist fraternity of India to ponder over the possibility of a similar event here. The emerging scenario is scary. Though the tectonic picture of Japan is more chaotic, the calm and stable looking Indian land mass is no less vulnerable. An earthquake in India can bring colossal devastation in terms of loss of life and economy.
K.S. Valdiya, a noted earth scientist and teacher, currently at National Institute of Science, Bangalore, in a recent paper in Current Science has dwelt upon the tectonic scenario of India vis-à-vis probability of earthquakes and tsunamis in India. Compared to Japan the scientific data on past earthquakes is much less, yet the information available does not paint a cheerful picture.
The Indian subcontinent has not been there since times immemorial. Twenty million years ago it travelled a long distance after breaking off from a super continent which included South Africa, Antarctica and Australia. The landmass came floating on the ocean like a giant Noah’s Arc carrying its fauna and flora and collided with the Asian continent. The collision is not yet over even now the northwestern, eastern and northeastern borders of the sub-continent are constantly pressing against the Asian continent.
The recent technological developments have made it possible to work out the rate at which the Indian continent (plate) is going under the Asian plate in different sectors. The Indian Peninsula is moving at the rate of 58 ± 4 mm per year says Valdiya. With the advent of the Geographical Positioning System (GPS) it is now possible to measure the precise rate of movement. And Valdiya says that the Indian crust is slipping under the Himalaya at a rate of 10-20 mm/year in the Sikkim sector, 10-18 mm/year in the Uttarakhand sector and 14-20 mm/year in the western sector. Due to this constant movement the Indian crust is under great stress. The subsurface stress needs an outlet. The movement of Indian crust under the Asian continent is strongly resisted by the huge continental block; consequently only about 5 cm/year of the Indian crust is adjusted by the tectonic movements in the Himalaya and one third under the Tibetan landmass.The remaining one third of the continental convergence must be affecting the Indian Peninsular mass itself says Valdiya. The stress passed on to the peninsular mass finds a release through old fault planes and often leads to earthquakes. Amongst these the active and locked faults are the ones that are most risky as far as earthquakes are concerned. These apart there are blind faults which have proved to be dangerous and not much is known about them.
Active faults are described in sporadic papers says Valdiya and there is no published largescale map of active and locked faults. India is on a construction spree. The builders claim their construction is earthquake resistant. Only time will tell about the validity of their claim, it is a risky gamble though. Earthquakes come unannounced and do not bother to check the local body’s approved plans. Builders on the other hand rarely engage a structural engineer to ensure the safety of the behemoth.
The stresses are not restricted to the Himalayan front. The Bay of Bengal part of the Indian Ocean floor is moving eastwards at the rate of 30 mm per year, plunges deepdown to the depth of 200 km under the Andaman-Nicobar Island claims Valdiya. This part sinks along a deep oceanic trench called the Java Trench. The catch lies at this point. There is no space left in the Java Trench to absorb the stress, as it is completely filled with the material brought by the Himalayan Rivers draining India and neighboring countries in the region. It is common knowledge that sinking of Java Trench in Sumatra caused an earthquake leading to disastrous tsunami. But this was not the first time that a tsunami struck our coasts. Earthquakes in the Andaman Islands in 1881 and 1941 generated tsunamis. There is no record of damage caused by 1941 tsunami in the war torn sub-continent says Valdiya.
Like the Java Trench on the east, there is Oman Trench on the west. The Arabian Sea floor is moving towards this trench. It is well known that the River Indus drains the northwest India and meets the Arabian Sea on the west. The Oman Trench is packed with the material transported by the Indus. Thus the two trenches in the sea floor are of no use as a shock absorber or a place where the stresses could be released without affecting the landmass. Like the east coast, in November 1945 there was an earthquake of magnitude 8 on the west, which generated a tsunami that reached up to Mumbai coast.
The western part of the country is presumed to be safe from tremblers by the planners. Prestigious nuclear plants, off shore drilling units etc. are situated there, apart from innumerable industries. We must know that the serene looking Konkan-Kanara-Malabar belt of Sahyadris has multiple faults. Many of them are deep seated as evidenced by the presence of hot springs. It is known that the core of the earth is a molten mass. Water at depth gets heated up and the faults and fissures in the abyss of the earth are the vents of this hot water under pressure to come out to the surface in the form of hot springs. Thus despite their medicinal and tourism value the areas pock marked by hot springs are potential areas for an earthquake in case the faults are activated due to the release of stresses at depths.
Mumbai the film city, bustling with people has all the industrial houses, high rise buildings, petrochemical plants, nuclear facilities etc. The find of 40000 year old forest (lignite) off the dockyard at Mumbai at a depth of 6-12 m is an indicator that a massive earthquake not very far in time (in terms of a geologist) had struck the coast. Thus in recent past (may be around 10-15000 years!) landward fault blocks moved up to bury the forest, which is now a mass of lignite. We must remember that the nature can always repeat the history.
It is thus evident that the moving Indian landmass is stressed and there is hardly any area remaining for the release of stress. Consequently it is the landmass, either at the mountain front or on the coasts which will get more affected in the event of an earthquake. The coastal belts are doubly prone because in case of an earthquake in the sea floor a tsunami may be triggered which could affect a large chunk of population.
Redlener, Director of the National Center for Disaster Preparedness at Columbia University’s Mailmen School of Public Health says Americans are grossly unprepared for next disaster. The horrific 9/11 and Katrina events have not even acted as wake up calls, people are back to their slumber! Well if this is the situation there one can jolly well visualize what is happening in India. We are erecting behemoth after behemoth without bothering about the fall out in case of a disaster. We are heading full steam for nuclear power development, unmindful of the consequences, because whether we survive a holocaust or not is not the issue. The issue is how to generate power for developing the country. It is agreed that development must go on, but we have to think at what cost? We are at the crossroads of development and disasters. Personally I support the development in harmony with nature. But do you or does the Government support this ideology? Only time will tell.
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