Seismology

• What is Seismology


  Study of Earthquakes
• What causes Earthquakes?

  Elastic Rebound Theory
• Rocks along a fault want to slide past each other but can’t, they are held together by friction. They start to deform
• Plate tectonics apply stress to the rock, this builds up strain energy
• What is the Energy built up in Elastic Rebound Theory?

  Strain Energy
• Eventually Strain energy is greater than the strength of friction and the rocks suddenly slide pass each other- The Earthquake
• The energy is transmitted as seismic waves
• Earthquakes can happen without a fault, a section of rock could be under stress, change shape and then break
• What is the Focus


  Point where the rupture happens, waves spread out from this point
• What is the Epicentre


  Point in the earths surface directly above the focus
• What is Elasticity


  A property of materials that results in wave propagation and earthquakes
• What are the two Body Waves

  1. P-Waves - Longitudinal
  2. S-Waves - Transverse
• What are the two surface waves?

  1. Rayleigh Waves
  2. love Waves
• P-Waves 


  Longitudinal waves, particle movement is parallel to the direction of propagation
• What is Wave Propagation


  The direction of wave movement
• S-Waves


  Transverse Waves, particle motion is perpendicular to the direction of propagation
• Rayleigh Wave


  Particle movement consists of elliptical motions parallel to the direction of propagation. Amplitude decreases with depth
• Love Wave


  Particle movement is perpendicular to the direction of propagation.

  Amplitude decreased with depth
• P-waves arrive roughly 1.7 times faster than S-Waves
• What are the 3 Factors affecting wave speeds?

  1. Incompressibility
  2. Density
  3. Rigidity
• Incompressibility


  Is the ability of a rock to resist a change in volume without changing shape
• P-waves cause compression, a rock with a high incompressibility will quickly return to its original shape - the P-wave will travel quickly
• Density


  The denser a material, the harder it is for a wave to pass through- it’s slows down
• • the Lower down the rocks, the higher the confining pressure
  • as you go deeper the density of the rocks increases- P-waves should slow down
• Incompressibility increased faster so P-Waves speed up as they get deeper
• Rigidity


  How much a material resists a bending force
• • As waves pass through they try and change the shape of the rock
  • liquids have no rigidity
  • The more rigid the faster the wave