Overview
This is not an all-period activity, but a short introduction to seismic waves to prepare the students for the Epicenter program.
The shaking experienced during earthquake is caused by a release of built up elastic strain energy. 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.

Goals:
To discover the differences between P- and S-waves using a slinky.

Central Question:
What are the properties of seismic ground waves, how to they work, and what do they tell us about the Earth and earthquakes?

Materials for each team:
Slinky
Other resources:
Activity sheets

Setting the stage:
This is a very short activity, but quite important since it helps the students see the differences between P and S waves.
Review the three main types of faults, thrust, normal, and strike-slip.

Exploration/Investigation
Allow students to briefly experiment with P and S waves. For P waves, have two students hold either end of a slinky so that the slinky is stretched out almost horizontally. This can be done on the surface of a desk. Have one of the students push a wave toward the other. You could also have one of the students pull a wave. For S waves, again, have two students hold either end of a slinky so that the slinky is stretched out almost horizontally. Shake one end of the slinky or rope while holding the other end taut.
P waves are compressional waves and are faster than S waves. They arrive at the seismic station first. S waves are shear waves and they are slower than P waves. They arrive at the seismic station after the P wave. S waves do not travel through liquid or gas, while P waves can (but they are refracted{bent}). This is because gas and liquids can be compressed, but not sheared. This becomes very important when explaining the "quiet zone" or the "shadow zone of the Earth's core" on the opposite side of the Earth (more than 11,000 km away) as the earthquake's epicenter. Seismographs on the opposite side of the Earth can't pick up S waves and therefore it is impossible to determine the distance from the site with the seismogram. Also, the P waves they receive have been refracted. This is due to the liquid outer core of the Earth.

Bringing it together:
Class discussion
Summarize what we have learned about seismic body waves. What are the differences between P and S waves?

Assessment:
Class discussion
Students' summarize what they have learned about seismic body waves. What are the differences between P and S waves? This is an important introduction to the Epicenter program.

Background:
Seismograms, obtained from seismographs housed at seismic stations, provide a great deal of information about the behavior of seismic waves. Seismic waves are waves of elastic energy that radiate out in all directions from the site where an earthquake occurs (the focus.) We will be concentrating on body waves, but there are many other types of waves produced by an earthquake. P and S waves are the two main types of body waves.

P or Primary waves (A in figure below) are waves of compression. They push and pull rocks in the direction the wave is traveling. They are the faster of the two types of waves we will study today, and they arrive at the seismic station before the S wave. Have two students hold either end of a slinky so that the slinky is stretched out almost horizontally. This can be done on the surface of a desk. Have one of the students push a wave toward the other. You could also have one of the students pull a wave. P waves travel through liquid, solid, and gas (all of which are compressible.)

S or secondary waves (B in figure below) are shearing waves. The S wave moves the material at right angles to the direction that the wave is traveling. This can be illustrated by the slinky or by a piece of rope. Again, have two students hold either end of a slinky so that the slinky is stretched out almost horizontally. Shake one end of the slinky or rope while holding the other end taut. S waves do not travel through liquids or gasses as liquids and gasses do not resist changes in shape.

The difference in arrival times of the first P and S waves is used with a travel time graph (travel time versus distance to epicenter) to determine how far the waves have traveled from the earthquake's epicenter. When this distance is determined, a circle with a certain radius (that determined distance) is drawn around the seismic station. Remember that on a globe it will appear circular, but on a map projection (we are using a Mercator projection) it will not appear as a circle unless the seismic station is located toward the center of the map and very near to the earthquake's epicenter. You will need to use at least three seismic stations to determine the location (where the three radii intersect) of the earthquake through triangulation.

Activity Sheets:
Student Activity sheet can be downloaded and printed from HERE.