Seismic waves

The shaking experiences during earthquake is caused by a release of built up elastic strain energy. You can hold a yardstick over the edge of a table and vibrate it by bending it and letting go. If we bend it too far, it will break.
  • What determines when the ruler will break?
  • In the Earth, what determines when the crust will break?
  • After the Earth breaks, what kind of structure is formed?

    (Review the 3 main types of faults, thrust, normal, strike-slip)

    When displacement occurs along a fault, the built up strain e energy is released in the form of seismic waves. There are two types of body waves, S-Waves and P-Waves.

    Our goal is to discover the difference between P- and S-waves using a slinky.

    A stretched out slinky can help show how each type of seismic wave can propagate. Have one person hold each end..

    P-waves Use a quick pulsing motion to initiate a wave down the spring. Try 2 different ways of doing this:

  • by pushing a wave
  • by pulling a wave

    Put a small piece of tape on the slinky and notice which direction the tape moves as the wave pass through.
    Describe and illustrate this motion, is the vibration direction parallel or perpendicular to the direction of the wave moves?




    S-waves Using a side to side motion generate another type of wave in the slinky.

    Describe and illustrate this motion, is the vibration direction parallel or perpendicular to the direction of that the wave moves?




    Summarize what you know about seismic body waves.