Earthquake is one of the natural calamities. Its origin can be traced to the early days of earth formation. It is responsible for a lot of damage to living and non-living beings. For many centuries man didn’t know why earthquakes occur and how they occur and to what extent they would damage. He only felt that mother earth was angry with him and so caused the earthquake and he always feared it.
It was left to Aristotle, the great Greek philosopher, to relate the phenomenon of earthquake to physical factors. According to Aristotle, when the air compressed within the arch escapes, it shakes some part of the land. This emission is called volcanic activity. When the volcano bursts, lots of lava, gas etc come out of the earth and fail out. This causes pressure and 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. The volcanic activity results in faulting. To fill up 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 prime areas and under the feet of hills and mountains, no well settle Earthquakes frequently occur in China, Japan, Philippines, southern parts of the Himalayas, volcano prime 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 very sure of the underground movements of the earth and its pressure points. So one can only identify areas, where they are likely to occur.
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 earthquake. The first one was Mercall’s scale. It is qualitative scale and not a quantitative scale and so not useful to measure the intensity. The second one is Richter scale. Richter scale is released from within. It is measured with numbers. If the earthquake measures 7 points on Richter scale it causes severe damage as it is of severe intensity. Those measuring 5 and less points may not cause much damage.
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 wave’s 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 India most of the earthquakes occur in the Himalaya zone, the Ganga and the Brahmaputra valleys. Only a few earthquakes have occurred in the Deccan Plateau. The earthquake of 1967 at Icwyna and the earthquake of 1993 at Latur in Maharashtra are the recent ones in this area.
In the matter of natural calamities man cannot be a master unless he becomes a master over nature completely. That is not possible for man with the limited knowledge of nature he has at his command.