Seismic waves

• Whenever large-scale events like volcanoes, earthquakes & explosions happen, they produce seismic waves that spread out in every direction & travel through the different layers of the earth.

  
• The two types of seismic waves:

  • P-waves
  • S-waves

  
• P-waves:


  A type of seismic wave.

  • Longitudinal waves
  • Can travel through solids & liquids
  • Faster than s-waves
  • can pass through the liquid outer core

  
• S-waves:


  • A type of seismic wave
  • Transverse waves
  • Can only travel through solids
  • Theoretically can pass through the solid inner core
  • but can’t reach it as it’s surrounded by the liquid outer core

  
• • By studying how the waves travel through the earth, scientists are able to figure out its internal structure to understand what the earth is made of.

  
• Seismologist can detect the waves using devices called seismometers.

  • By comparing those result with other seismologists all around the world.
  • They can work out how long it took the waves to travel from the earthquake site to different parts of the earth.
  • This gives them clues about the structure of the earth

  
• When seismic waves reach a boundary between two different mediums of different densities, they can be:

  • reflected
  • absorbed
  • transmitted
  • refracted

  
• Between the mantle & the liquid outer core, there’s a sudden change in density.

  • so when seismic waves reach the boundary, there's a sudden change in the direction of the wave.
  • Since the liquid outer core itself isn’t all the same density either, as waves pass through it, they’re constantly being refracted slightly.
  • It seems to curve as they slowly change direction.
  • The same thing happens in the mantle, which isn’t all the same density, so the waves are refracted & seem to curve.

  
• Scientists were able to discover the internal structure of the earth by:

  • Measuring which types of waves could be detected at different places around the earth.
  • P-waves can travel through solids & liquids while s-waves can only travel through solids.

  
• S-waves produced at one region of the earth can’t be detected on the opposite side of the earth.

  
• P-waves produced at one region of the earth can be detected almost everywhere of the earth.