Lecture on Seismic Waves

Introduction to Seismic Waves

• Seismic waves are crucial for understanding Earth's composition.
• They are associated with earthquakes and any event that sends energy through Earth.
• Two main types of seismic waves:
  • Surface Waves
  • Body Waves

Surface Waves

• Travel across the surface of the ground.
• Analogous to water waves.
• Two types of surface waves:
  • Rally Waves: Ground moves up and down.
  • Love Waves: Ground shifts left and right.
• Movement is perpendicular to the direction of the wave (transverse waves).

Body Waves

• Travel through the body of the Earth.
• Fastest moving waves.
• Used to determine Earth's structure.
• Two varieties of body waves:
  • P-Waves (Primary Waves)
  • S-Waves (Secondary Waves)

P-Waves (Primary Waves)

• Characteristics:
  • Compression waves.
  • Molecules bump into adjacent molecules, transferring energy.
  • Movement is in the same direction as the wave.
• Medium of Travel:
  • Can travel through air, liquid, and solid.
  • Speed varies by medium:
    • Air: ~330 m/s (speed of sound)
    • Liquid: ~1500 m/s
    • Granite (solid): ~5000 m/s

S-Waves (Secondary Waves)

• Characteristics:
  • Movement is perpendicular to the direction of wave travel (transverse waves).
• Medium of Travel:
  • Can only travel through solids.
  • Cannot transmit through liquids (unlike surface waves on water).
• Speed:
  • Travel slower than P-waves (60% of P-wave speed).

Importance of Seismic Waves

• Determining Earth’s Composition:
  • P-waves travel through all states of matter.
  • S-waves only travel through solids, indicating the presence or absence of liquid layers.
• Understanding these waves helps in mapping the internal structure of the Earth.