An earthquake is one of the worst natural calamities. As the name itself suggests, earthquakes is the quivering or shaking of the surface of the earth, at some point on the earth. Its origin can be traced to the early days of earth formation. The cause of an earthquake is the movement or dislocation of lava and hot gases under the depths of the earth’s crust. When an earthquake is about to occur, there is first a mild movement of the mass of the earth as if it is moving as a cradle, such slight movements are usually quite a few in number and they serve as warning signals, that, more and fast movements can be expected in its wake. This slight quiver may or may not be followed by stronger tremors, but, if they do, people on earth in that particular area are in for big trouble.
For many centuries man did not know why earthquakes occur and how they occur and to what extent they would cause damage. He only felt that mother earth was angry with him and so caused the earthquakes and he always feared it. It was Aristotle, the great Greek philosopher who related the phenomenon of earthquake to physical factors. According to Aristotle when the air compressed within the earth escapes, it shakes some part of the land. This emission is called volcanic activity. When the volcano bursts, lots of lava, gas etc comes out of the earth and fallout. This causes pressure imbalance and results in producing earthquake waves in the surrounding areas. It was thus identified that volcanic activity is one of the reasons for earthquakes. This volcanic activity results in faulting. To fill in the new faults the movement of earth takes place. This causes tremor.
The second reason is Isostatic adjustment. The surface of the earth has certain raised up blocks and certain depressed blocks. They keep the balance of the earth, when it moves revolving on units of axis. These raised up blocks are washed down due to various reasons and cause imbalance. Then also the earthquakes occur to regain and maintain that balance.
We could therefore see that earthquakes commonly occur in volcano prone areas and under the feet of hills and mountains, not well settled in Earth. Earthquakes frequently occur in China, Japan, Philippines, southern parts of the Himalayas, volcano prone parts of Europe and western parts of North and South America. They are also likely to occur in Rajasthan in India and Arabian countries. One cannot say that earthquakes do not occur in other places. They may occur in any part of the world at any time. We are not sure of the underground movements of the earth and its pressure points, so one can only identify areas, where they are likely to occur.
Results of these quakes: All earthquakes did not cause severe damage. Those which are of severe intensity are really dangerous. In residential areas the earthquakes cause real damage. Earthquakes may cause changes in the natural environment. It may cause rift in the earth’s surface which further results in water fountains which emit a lot of sand. It may change the course of the river which may cause floods. In the hilly areas it results in landslides. It also results in the destruction of man-made buildings, roads, railway tracks, bridges and telephone connections. The earthquakes cause maximum damages in the sky scrapers and densely populated areas.
How to lessen the effects of earthquakes: The best way to lessen the consequences of the earthquakes is to keep a vigil on the earthquake frequented areas and to keep the public well informed about its possibilities. The people should be evacuated from th earthquake prone areas well in time. The scientists are now able to study and define the secondary waves and tertiary waves also in earthquakes. Scientists are able to study the underground movements of waves with the help of a machine called seismograph. With its help one can also predict the likely possibility of earthquakes occurrence as to where and when they are likely to occur. In the areas that are more prone to earthquakes, houses are made of lighter material like thatch, bamboo and wood which even when rocked and broken do not injure life.
How to measure the intensity of earthquake: All earthquakes do not cause severe damage. Those which are of severe intensity are really dangerous. There are scales to measure the intensity of the earthquakes. The first one is Mercall’s scale. It is a qualitative scale and not a quantitative scale and so not useful to measure the intensity. The second one is Richter scale. Richter scale is measured with the help of a graph which measures the energy that is released from within. It is measured with numbers. If the earthquakes measures 7 points on Richter scale, it causes severe damage as it is of severe intensity. Those measuring 5 and less points do not cause much damage.
Earthquakes in India: Looking at near about 1200 earthquakes that occurred in India at various intervals the Meteorological Department has divided the country into five zones.
Zone 1: Dangerous; Zone 2: Less dangerous; Zone 3: Medium danger; Zone 4: Much danger prone zone; and Zone 5: Too much i.e. excessive danger prone.
Near about 55% of the land area in India remains in the grip of earthquakes. But the intensity of the earthquakes is not the same in all the areas. The recent experiences reveal that not even a single area of India is earthquake free. The earthquake prone areas of India are the Himalayan Region, North-eastern India, Kuchh, the Western Coastal Area near Ratnagiri and the Andaman and Nicobar Islands. The more dangerous areas are- The Gangetic plains, the Brahmaputra valley and Western Rajasthan.
Only a few earthquakes have occurred in the Deccan Plateau. The earthquake of 1967 aat Icwyna, the earthquake of 1993 at Latur in Maharashtra and the one in Gujarat in 2000 are the latest ones in this area.
In the matter of natural calamities man cannot be a master unless he masters nature completely. That is not possible for man with the limited knowledge of nature he has at his command.