SURFING ROCK WAVES
Earthquakes happen all over the world. On the surface we do not always feel them. The movement we do feel can be described in two motions: P waves and S waves. Students will use slinkies to imitate and better understand the two types of waves.
Instructional Method: Experiment
Goal: Explain wave motions associated with earthquakes.
Objectives: Students will be able to:
- Describe earthquake movements.
- List the names of the two waves.
Activity time: 30 minutes
Discussion: 15 minutes
- Large sheet of paper
- Crayons or marker
When movement occurs between two pieces of crust, called fault blocks, we feel an earthquake. To create a mini-earthquake, slide two blocks of rock against each other. Can you feel the roughness of the two rocks as they pass by each other? The friction between the two rocks is what creates the vibrations in an earthquake except on a much greater scale. These vibrations in nature are called seismic waves.
Most earthquakes are too small to be felt by people. Larger earthquakes are not only felt by people, but can severely damage structures. The motion from an earthquake travels through rock in the form of waves. There are two types of waves associated with earthquakes: P waves and S waves.
The fastest of the waves is a primary wave, or P wave. These waves feel like a push-and-pull movement on the crust as it is stretched and compressed. P waves are also called compressional waves. The slower of the two waves is called a secondary wave, or S wave. These waves travel in a side to side motion and produce more shaking than P waves. The side-to-side motion of S-waves causes the most damage to structures during an earthquake.
In large earthquakes it is possible to feel the difference between P and S waves. P waves feel like someone has run a semi-truck into your house and S waves feel more like you are riding waves at a lake or ocean. The following schematic shows how these waves travel through rock.