Differentiate between primary and secondary earthquake waves. Also explain how earthquake wave help in study of interior of earth.

Differentiate between primary and secondary earthquake waves. Also explain how earthquake wave help in study of interior of earth.
  • Introduction with earthquake and various types of waves
  • Differentiate between Primary and Secondary earthquake wave.
  • Explain how earthquake waves help in the study of interior of the earth
  • Conclude appropriately
Model Answer :
An earthquake is the shaking and vibration of the Earth’s crust due to movement of the Earth’s plates. The vibrations travel outwards from the epicentre as waves. Earthquake waves are basically of two types — body waves and surface waves. Body waves can travel through the earth’s inner layers, but surface waves can only move along the surface. There are two types of body waves: P-waves (Primary waves)  and S-waves (Secondary waves).
There are generally four differences between primary and secondary earthquake waves:
  • Form of Wave: Primary waves are made up of compression waves (also known as push-pull waves), while S waves are transverse waves.
  • Speed: P waves travel faster than S waves, and are the first to be detected by the seismographs. P waves travel at speeds between 1 and 14 km per second, while S waves travel significantly slower, between 1 and 8 km per second.
  • Travel Capability: P waves can travel through any kind of material, whether it is a solid, liquid or gas. S waves can only move through solids and are stopped by liquids and gases.
  • Size: S waves are generally larger than P waves and they move the earth around them with greater force. P waves are significantly smaller and do not cause as much damage because they compress particles in only one direction.
Interior of the earth:
Earth quake waves help in study of interior of the earth, and the following characteristics of earth’s interior are revealed by studying earthquake waves:
  • Earth’s interior has varying material density: The study of the speed and direction of these waves reveals that earth’s interior has layers of varying densities.
  • Earth has a layered structure : The seismic waves travel in curved paths, and get reflected and refracted when travelling through the earth. Analysis of the variation in the properties of various waves shows a three layered structure in the interior of earth.
  • Core is liquid: As stated earlier S waves cannot pass through liquid. S wave disappears at the angular distance of 105 deg from the epicentre and P wave weakens. It is evident from the diagram that S wave is totally absent in the core of earth. This shows that core is a liquid which is located at a depth of 2900 km from surface.
While earthquakes are considered natural disasters due to the devastation they cause, measuring and calculating the behaviour of earthquake wave on seismograph has also helped us study the interior structure of earth.

Subjects : Geography