Types Of Seismic Waves

• • Earthquakes occur when build-up of stress in Earth suddenly released - release of energy in form of seismic waves (these carry out a lot of energy and very destructive).
• • Point at which earthquakes begin is below Earth’s surface = focus
• • The epicentre = point on the surface directly above the focus
• • Happens when rocks suddenly fracture and move, fracturing process makes ground vibrate and citations travel away from focus if quake.
• If earthquake occurs, all three types of waves are created at the same time.
• • P waves - first waves (primary waves) to arrive at a point away from epicentre.
• • S waves - secondary waves arrive after as are slower.
• • Surface waves - slowest so last to arrive but most damaging.
• P WAVES:

  • Longitudinal
  • Fastest - primary waves
  • Can travel through solids and liquids.
• S WAVES:

  • Transverse
  • Slower than P waves, faster than surface waves - secondary waves
  • Can travel through solids only.
• SURFACE WAVES:

  • Longitudinal and transverse
  • Slowest waves
  • Can travel along the surface only.
• Earthquake or seismic vibrations are picked up by seismometers, measure strength of waves.
• Difference between arrival time of P and S waves = lag time
• Lag time can be used to calculate distance from three recording stations to the epicentre - draw circles with radius equivalent to that distance to find the point where all circles meet.