Importance of Studying Earth’s Interior

Provides insights into the formation and characteristics of Earth’s physical features.

• Helps trace the evolution of life on the planet.
• Aids in the discovery and extraction of minerals and energy resources.
• Enables a better understanding of past climatic changes on Earth.
• Assists in studying other planets in the solar system and distant celestial bodies.
• Contributes to the understanding of Earth’s magnetic field.

Seismic Waves

During an earthquake, energy is released in the form of seismic waves, which originate from the earthquake’s focus.

• Instrument of Measurement: Seismometer
• Graph Produced: A seismogram, which records the seismic wave patterns.

Types of Seismic Waves

1. Body Waves:
   • Originate within the Earth’s interior.
   • Travel through various layers of the Earth.

Classification of Body Waves:

• Primary Waves (P-Waves):
  • First waves to reach the surface.
  • Travel at speeds of 5 to 14 km per second, making them the fastest seismic waves.
  • Similar to sound waves.
  • Can travel through solids, liquids, and gases, but their speed reduces in liquids and gases.
  • Also called compressional waves.
  • Cause particles to vibrate in the same direction as the wave’s propagation.
• Secondary Waves (S-Waves):
  • Reach the surface after a delay compared to P-waves.
  • Slower, with speeds of 3.5 to 7.2 km per second.
  • Travel only through solid materials.
  • Also known as transverse or shear waves.
  • Cause particles to vibrate at right angles to the wave’s direction of movement.

1. Surface Waves:
   • Travel along the Earth’s surface and are the last to arrive.
   • Cause oblique motion and affect only the Earth’s surface.
   • Known for their destructive impact.

Types of Surface Waves:

• Love Waves:
  • The fastest type of surface wave.
  • Move the ground in a side-to-side motion.
• Rayleigh Waves:
  • Roll over the surface like ocean waves, causing elliptical ground motion.

Previous Year Question (PYQ)

Question: Consider the following statements:

1. In a seismograph, P waves are recorded earlier than S waves.
2. In P waves, individual particles vibrate to and fro in the direction of wave propagation, whereas in S waves, particles vibrate up and down at right angles to the direction of propagation.

Which of the statements given above is/are correct?
(a) 1 Only
(b) 2 Only
(c) Both 1 and 2
(d) Neither 1 nor 2

Answer: (c) Both 1 and 2