Seismic Waves

• Body waves


  Waves that travel through the Earth
• Surface waves


  Waves that travel along the Earth's surface
• Earthquakes and explosions cause seismic waves
• Seismic waves from an earthquake

  1. Produced

  2. Travel out through the Earth

  3. Detected by seismometers on the surface

  4. Seismologists work out time taken to reach each seismometer

  5. Note parts of Earth that don't receive the shock waves
• Seismic waves reaching a boundary between different layers

  1. Some waves absorbed

  2. Some waves refracted

  3. If refracted, change speed gradually resulting in curved path

  4. If properties change suddenly, wave speed changes abruptly and path has a kink
• Seismic waves


  • Provide evidence for the Earth's structure
  • By observing how they are absorbed and refracted, scientists have worked out where properties of Earth change dramatically
  • Current understanding of internal structure and size of Earth's core is based on these observations
• Types of seismic waves

  • P-waves
  • S-waves
• 1. waves


  • Longitudinal
  • Travel through solids and liquids
  • Travel faster than S-waves
• 1. waves reaching the Earth's core


  Refract as density changes
• 1. waves


  Can pass through the core and be detected on the other side
• 1. waves


  • Transverse
  • Can't travel through liquids (or gases)
  • Slower than P-waves
• 1. waves reaching the liquid outer core


  Can't pass through it