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Mains Practice Questions

  • Q. What are seismic waves? Give a detailed account of different types of seismic waves.

    15 Jun, 2021 GS Paper 1 Geography


    • Start the answer by introducing the origin of seismic waves and their types.
    • Discuss the different types of seismic waves and their characteristics.
    • Conclude Suitably.


    During an earthquake seismic waves are generated which spread outwards in all directions from the focus. Seismic waves are of three types (i) P waves or Primary Waves, (ii) S Waves or Secondary Waves, and (iii) L Waves or Surface Waves.


    Types of Seismic Waves and their Characteristics

    • P-Waves:
      • These are compressional waves which cause the particles of rock to vibrate in the longitudinal direction.
      • The P waves travel fastest, therefore they reach a seismic station first
      • Their velocity is 1.7 times than that of S waves
      • They pass through solids as well as liquids.
    • S-Waves:
      • These are shear waves which are transverse in nature.
      • These can only pass through solids.
    • L-Waves or Surface Waves:
      • When P and S waves reach the earth's surface, they are converted into L waves.
      • The L waves travel along the surface and cause earthquakes.
      • They are transverse in nature and their velocity is much less than the P and S waves.


    Surface waves are responsible for causing earthquakes while the main significance of P and S waves is in the study of the earth's interior. P and S waves travel through the interior of the earth and are reflected and refracted as they enter a layer of different material.

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