There is a long history of devastating earthquakes in our country and all over the world and they have been taking place with monotonous regularity.
The crust of over planet is built up of several solid rock faces which are not static. They are moving slowly even by millimeters, with thickness of plates and depths ranging from 30 to 80 kilometers below the surface. These huge moving plates have diversions separating them from other plates and are termed boundaries.
Earthquakes take place when these slowly moving plates clash with each other and are forced to rise or even when the individual fault lines in plates are in assertions causing interpolate quakes.
The quakes are caused by the release of elastic energy during these fault assertions or plate movements and are released in the form of seismic waves or shock waves travelling outwards in all directions. The epicenter is the point above the quake centre and is the place where maximum destruction occurs.
The earth’s crust is built up of such innumerable plates called tectonic plates and the effect of the quake, as mentioned earlier, is for some assertive fault in one plate or the effect of impact of two separate plates. This does not mean that there is any succession of related impacts continuously due to the impact on the previous one.
The massiveness of the 1819 Kutch Earthquake which had registered 8 on the Richeter Scale can be imagined from the fact that about 5000 square kilometers of area had become depressed by nearly 15 feet and 1500 square kilometers had been raised by nearly 50 feet in what is named as Allabund.
Unfortunately, even after so much progress has been made in understanding geological configuration, we still cannot predict reliably the intensity, place or occurrence of an earthquake. However studies are being made based on the speed at which shock waves travel through the ground, changes in levels of surface of the ground which rises when the pressure below the ground increases emission of an inert radioactive gas ‘Radon’ and changes in electro-magnetic behavior of rocks.
This intensity is measured on the Richeter scale devised by a seismologist Charles Richeter of California. He devised a logarithmic scale which measures on a scale of one to ten, the intensity or the magnitude depending on the amount of energy released at the focus.
As mentioned earlier, we cannot yet sto an earthquake from taking place but with the study of the warning signal, the levels of destruction can definitely be scaled down. As any prediction cannot be made with surety we can at least follow the example of another earthquake prone country Japan and construct our buildings in a manner to resist seismic forces.
The entire Himalayan Region, Deccan Plateau including Gujarat and Maharashtra, Delhi Region including Hardwar, Rohtak, Sonepat and Gurgaon are seismically active and we are just keeping our fingers crossed while awaiting disaster. The effect of a moderate earthquake, leave aside intense, in a congested city like Delhi with its high-rise buildings and ancient structures can be very well imagined from the effects of the recent quakes and the last one affecting Kutch in Gujarat on 26thJanuary 2001.
Professor Banerjee of the Indian Institute of Technology Mumbai calculated the intensity of the Gujarat earthquake as equivalent to the detonation of a 60 megaton Hydrogen Bomb. He also calculated this intensity as equivalent to the eruption of St. Helen Volcano in 1980 in USA.
Professor M. Nagi Toksoz of the Earth Resources Lab in Cambridge says, “Indian landmass is moving faster than the plate boundary on its western part and no one can say, when another earthquake will hit other high seismic zone in the near future.”
The scientists at the National Geophysical Institute in Hyderabad have stated that “the sea floor is pushing the land inwards in north easterly direction at the rate of 5 centimeters every years. At the same time Saurashtra region is rotating in an anti-clockwise direction. The advancement of the sea floor against the Indian Plate measures 125 to 150 centimeters in two to three decades, thus causing earthquakes at the edge of the plate in Saurashtra region. It hits the other end of the Himalayas too.”
India is also pushing against the Himalayas, moving at the rate of 3 to 5 inches every year. The enormous stress produced in the Indian tectonic plate colliding with the Himalayas may also result in severe earthquakes.
The earthquake which killed over 10000 people in Latur and Osmanabad districts of Maharashtra on the morning of September 30, 1993 was a devastating one. It was 3-57 a.m. when the tremors started and houses caved in on the sleeping inhabitants. This was one of the major surprises to geologists as according to them it does not fall in a high risk earthquake zone. They pointed out that there is a ‘Kuruwadi’ fault or thinning of the earth’s crust in the area. But the underground pressure building up to an earthquake of is intensity had not been predicted although some cognizance should have been taken of the earlier tremors experienced between August and October 1992. These could have served as pointers to the larger earthquake. However the inherent case of so much damage was mainly because it was so much shallow and closer to the earth’s surface.
What is more unfortunate and in fact repulsive was that lakhs of people had pured in from outside to stand and gape, hindering relief operations. Not only that a considerable number of these indulged in rampant loot of property left behind by the people who had run away or in houses where all the inmates had been killed. Nearly 70000 people had become homeless and nearly 2 lakh houses had developed cracks making them unsafe for habitation. Twenty-seven villages in Latur and twenty in Osmanabad district were completely destroyed together with innumerable hamlets.
The lessons learnt from this has resulted in buildings which are earthquake resitant and can withstand quakes of upto 7 on the Richeter Scale.
One of the major earthquakes in the early part of the last century was the one which struck Bihar. Residents of Patna ran helter skelter and roads cracked up creating chasms. Most of the houses in the city developed cracks although composed to the modern houses they had the advantage of better construction and mostly single storied. The occurrence was also in the morning when people were up and about, resulting in comparably reduced casualty figures. The rural side was in total shambles with most of the mud houses razed to the ground.
It is matter of dedicated research which only can save the world from such calamities besides the cyclones and tornadoes regularly leaving destruction of gigantic magnitude in their wake.