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Explain the causes for origination of earthquakes.

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Temporary imbalance in isostatic equilibrium of a particular place is the major cause of formation of earthquake. Following are the factors which create imbalance in the isostatic equilibrium due to which formation of earthquakes takes plac

1. Faulting: Due to stress and compression of the isostatic forces, cracks and fissures form in the rocks and faults appear. Earthquakes originate during these activities and earthquakes occur due to this reason on the edges of newly folded mountains and ridge valleys.

2. Vulcanism: Vulcanism is the major cause for formation of earthquake. At the time of volcanic eruption, when rapid and violent gases exert pressure to come out on the earth’s surface, sudden and violent turbulence takes place on the land. Destructive earthquakes occurred at the time of eruption of Etna, Krakatoa, Vesuvius, etc. volcanoes. 

3. Water Load: According to some scholars, due to the construction of massive dams, water gets deposited in the surface part in excessive amount, which leads to transformation in the rocks which are situated below the water deposit. Koyna Dam is regarded as one major cause of Koyna earthquake which occurred in Maharashtra in December 1967.

4. Contraction of the Earth: Some scholars have regarded contraction of the earth to be the cause for formation of earthquakes. According to them, temperature of the earth is on a continuous decline due to radioactive activity. Due to this, the earth’s surface contracts due to cooling down. When this activity takes place in a rapid and violent manner, earthquakes are caused. 

5. Isostatic Adjustments: Normally, balance is present between various land forms of the earth such as mountains, plateaus, plains and oceanic bottom. Whenever load becomes more in oceanic regions due to debris deposited by erosion process, temporary imbalance is created in this isostatic equilibrium. In Himalayan mountainous regions, earthquakes usually occur due to this cause.

6. Elastic Rebound Theory: According to Prof. F. S. Reid, rocks stretch up till some extent just like rubber. After this, they break down and the broken rock parts re – gain their place by re – stretching themselves, due to which, earthquakes are formed. 

7. Plate Tectonic: On their edges, plates diverge, converge or shift towards the right or left which create turbulence during these activities, which gives rise to earthquakes. 

8. Other Reasons: Apart from the above mentioned reasons, expansion of gases, breaking down of cliffs in oceanic regions, falling down of ceilings of caves, etc. result into earthquakes with small impact. Apart from this, man – made reasons, such as – nuclear explosion, explosion in mining regions, deep drilling, etc. also result in earthquakes which have local impact.

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