OBJECTIVES:

• Discovering why an earthquake causes damage.
• Observing different energy experiments.

VOCABULARY:

• earthquake
• energy wave
• tsunami

MATERIALS:

• tape of 1964 Alaskan Earthquake (if available)
• margarine tubs
• teaspoons
• oil
• water
• aluminum foil

Students observe how waves move through different substances.

San Fernando, California 1971

BACKGROUND:

Earthquakes are caused by the sudden movement and fracturing of rock masses along preexisting faults. A fault is a broken surface within the Earth’s crust. The point on the fault at which the displacement begins is called the focus of the earthquake. The point on the surface of the Earth directly above the focus is the epicenter. Your students need to understand that an earthquake happens in rocks that have been stressed. This stress is stored until the strength of the rock is exceeded. The actual break (the earthquake) then releases the energy. As described in the Pre Lab, this energy travels in the form of waves.

The seismic waves generated by an earthquake can be recorded and measured on a seismograph. The record produced by a seismograph is called a seismogram. The interpretation of the waves provides seismologists with a way of "seeing" into the inside of the Earth. The waves produced by earthquakes travel through the Earth and bounce off different features of the Earth's interior. The patterns they form after bouncing off these features can be used to create images of the interior.

Earthquakes generate many different types of seismic waves. Two major types are P (push/pull; compressional, or primary) and S (shear or secondary). P-waves are faster than S-waves and are recorded on the seismogram first. Secondary waves are recorded second, and is shown as a sharp increase on the seismogram. Other waves like Raleigh waves, Love waves, and over 200 different types of waves are recorded afterwards.

PROCEDURE:

1. Ask the students to predict what causes damage during an earthquake before showing the beginning of the 1964 Alaskan Earthquake video. Write their comments on the board or on the screen if you are using a projector. Use a chart similar to the one below.

2. After you show the video, ask the students the same question, and again record their responses. (You may want to selectively reshow portions of the tape). See if their responses have changed.
     
3. You may want to demonstrate the lab before the students begin their investigation, so that the students have an idea of what "gently" means. The goal of the lab is for the students to observe how the waves that they generate change as more energy is applied. Explain that the water waves they are creating are a type of energy wave, and are analogous to a real type of earthquake wave.
     
4. After the students finish the lab, ask them again what causes damage during an earthquake. Record their answers on the diagram. Hopefully they will now see that energy transmitted by waves during an earthquake is what causes damage to buildings and structures. The shaking of the ground can also cause disasters such as landslides, tsunamis (due to crustal movement under the ocean), and building collapse. You might want to remind the students that the release of stress inside the earth is what causes earthquakes.
     
5. Discuss with the class any earthquake-caused damage that they have seen in the newspaper or on television. Ask them if they have ever seen damage in person or if they know of anybody that was affected by damage during an earthquake.

ANSWERS:

1. Tap the sides of the tub gently. What are you creating in the tub?
   SMALL WAVES (BE SURE TO ILLUSTRATE WHAT SMALL WAVES ARE)
2. Tap the sides a little harder. Does the pattern change? How?
   THE WAVES GET HIGHER AND FORM MORE CLOSELY TOGETHER
3. Float a flattened piece of foil in the tub. Tap gently. What happens?
   IT GOES UP AND DOWN AS THE ENERGY AFFECTS THE FOIL
4. Tap a little harder on the outside. Does it still float?
   YES (MAKE SURE STUDENTS DON'T TAP THE TUB TOO HARD)
5. With the teaspoon, tap the water directly. Can you cause the foil to sink without touching the foil and without spilling any water?
   LET STUDENTS EXPERIMENT BY HITTING THE SIDES; IT CAN BE DONE.
6. Take the foil out. Put 1 teaspoon of oil on the water. Tap the sides gently.
   What happens?
   THE OIL GOES UP AND DOWN
7. Tap the sides a little harder. What happens?
   THE OIL WILL BREAK UP

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