Chapter 1 Characteristics of Waves

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Chapter 1Characteristics of Waves

• Section 4
• Seismic Waves

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Types of Seismic Waves

• P Waves (Primary Waves) Longitudinal seismic
  waves. The fastest seismic waves. This is why
  they are called primary. Compress and expand
  the ground.
• S Waves (Secondary Waves) Transverse seismic
  waves, or shear waves.

S waves cannot travel through liquids, including
the Earths outer molten core. S waves move the
ground up and down and side to side.
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Types of Seismic Waves Continued

• Surface Waves A combination of a longitudinal
  and transverse waves that combine to travel along
  the Earths surface. They move more slowly than
  S and P waves. They combine up and down and side
  to side motions to make the Earths surface roll
  like ocean waves.
• Tsunamis Are ocean waves produced by
  displacement from an underwater earthquake. They
  are usually only 1 meter high in the deep ocean,
  but reach heights of 20 meters in shallow water.
  This is because the waves in the back catch up to
  the slower moving shallow waves.

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Detecting Seismic Waves

• Seismographs are used to record ground movements
  caused by seismic wave as they move through the
  Earth.

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Detecting Seismic Waves Continued

• Data from several seismographs shows the time
  differences in the arrival of P and S waves.
• The farther away the earthquake, the longer it
  takes the waves to reach the seismograph.

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Detecting Seismic Waves Continued

• Using a seismiograph in three locations, the
  focus (the source locations of the earthquake)
  and the epicentre (the location on the surface
  above the focus) can be found.

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Detecting Seismic Waves Continued

• Exploration Seismic waves are produced for the
  purposes of exploration of oil, gas, and other
  changes in density in the ground.