• An Earthquake refers to shaking or trembling of the earth’s surface caused by sudden movements in the earth’s crust due to the release of energy from the broken rocks.
  • The following terms are closely related to earthquake:
  1. Seismic waves
  2. Seismic focus and
  3. Epicenter
  • The energy stored in the strained rock when released as powerful vibrations, tremors or shock waves are known as seismic waves.
  • The place of origination of an earthquake just below the earth’s surface is known as seismic focus.
  • Epicenter is the point on the earth’s surface directly above the seismic focus, which experiences the maximum impact of an earthquake.
  • Earthquakes can lead to vertical or lateral displacement of crust, raising or lowering of parts of sea floor, raising or lowering of coastal regions, landslides, and tsunamis.
  • Earthquake is caused by the constant movement of the plates inside the earth. The main causes of earthquakes are development of faults in crust due to disturbances caused by erosion and deposition on ocean floors, movement of molten rocks below or within crust and lateral or vertical forces of tension and compression inside the crust.
  • Earthquake zones of the world are region surrounding the Pacific Ocean known as the ring of fire, and Mid-world Mountain belt stretching from Eastern Europe to China through Central Asia, Pakistan and India.
  • Earthquakes can be measured through two scales devised by the seismologists.
  • The two scales are Richter scale and Mercalli scale.
  • Three types of seismic waves are Primary waves (p), Secondary waves (s), and Long waves or surface waves (l).
  • Primary waves can pass through gases, liquids and solids.
  • Secondary waves can pass through solids only.
  • Long waves are also known as surface waves. They are of two types-Rayleigh waves and Love waves.
  • Movement of seismic waves is recorded by a vibrating pen on a travelling strip of paper of an instrument known as seismograph.
  • Effects of earthquake include loss of lives, collapse of building and bridges, rupturing of power lines causing fires, broken water supply lines, landslides in hilly areas, broken dams causing floods, and disruption of transport and communication lines.
  • There are various landforms produced by earth movements. Continental collision results in the formation of Fold Mountains.

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