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Earthquakes - Lesson Summary

An earthquake is a sudden tremor or movement of the earth's crust, originating at or below the surface. The outer layer of the earth is solid and is divided into many sections known as plates on which all the continents stand.

The plates float over the molten magma flowing beneath the earth’s crust, moving slowly. Sometimes, during the course of their movements, these plates move against each other. Earthquakes occur on the edges of these plates along fault lines where the plates collide or try to slide past each other.

Earthquakes are also caused by explosive volcanic eruptions. There are other man-made causes of earthquakes like vibrations caused by big rocks falling down hills because of erosion, hollow parts of mines falling down due to dissolution of minerals by water and due to nuclear explosions.

The point of origin of the earthquake within the crust or mantle is called the seismic focus. The location of the earthquake is referred to as the point on the surface of the earth, vertically above the seismic focus called the epicentre.

The extent of damage that an earthquake can cause depends on its magnitude. Earthquakes can be measured with a device called the seismometer; a device which also records is known as a seismograph.

The magnitude of the earthquake is measured through an instrument called ‘Richter Scale’.
The under-sea earthquakes, give rise to giant waves called the tsunami, which cause great deal of destruction along the coasts.

Two thirds of all the earthquakes occur in the ‘Ring of Fire’ in the Pacific Ocean. Kashmir, western Himalayas, middle Himalayas, northeast India, the plains of the Ganga and Indus, Rajasthan, Gujarat, Lakshadweep, Andaman and Nicobar Islands are the earthquake- prone regions in India.

Measures for preparing against earthquakes:
  • In absence of an early warning system, the information about earthquakes and their intensity should be shared with the public through radio, television and newspapers.
  • Buildings must be based on earthquake-resistant techniques and all under-construction houses should be made to follow the building guidelines.
  • Buildings to be constructed over concrete and iron pillars built deep in the ground.
  • In emergency, water, ration, first-aid kits, radios, flash lights, battery, blankets, jackets and fire extinguishers should be stored in safe places.

To do things when an earthquake strikes:
  • Remain calm
  • Take cover under a solid surface like a table, or stand in the doorway if inside building or house
  • Move to an open space away from trees, electric poles and buildings if outside
  • Switch off the gas and electric supply in the house during a quake and don not use elevators.
  • After the quake the affected people should be given immediate medical help and vaccinated to stop
  • epidemics from spreading.
  • Transport and communication facilities should be restored as soon as possible so that rescue teams can reach the earthquake-hit area.
  • Police and paramilitary forces should be deployed to protect properties which had to be abandoned from theft.


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