Name Class Date
Lab: The Earthquake Machine
Background
Tectonic earthquakes are caused by a sudden slippage along the boundary between two plates. The type of motion that occurs between two plates is used to classify faults as strike-slip, thrust (reverse) and normal. Typical rates of plate motion are a few cm per year. Why then, might someone ask, do destructive earthquakes occur in which many meters of fault slip happen so quickly that the vibrations are recorded by seismographs all around the world and are sometimes strong enough to destroy nearby buildings and bridges? This is a result of friction and elasticity. Shallow portions of the plates are relatively cool; two plates act brittle and cannot flow past each other. The faults instead tend to stick or lock up for years or centuries at a time. Each year the portions of plates near locked faults deform elastically by a few more cm. The more the plates are bent and deformed, the greater the force is on the fault (shear stress). Eventually the force is sufficient to make the plates break free of one another and the elastic energy that has been stored up is released as frictional heating on the fault and ground vibrations. (seismic waves). This process of faulting is called stick-slip or elastic rebound.
Hypothesis
Read the entire procedure below and then write a hypothesis explaining what will happen as the block is pulled across the sandpaper.
PROCEDURE
1. In this lab, one student will be the puller, one will be the observer, and two or three will take notes.
2. The puller will put a pencil in the rubber band to more easily mark the distance on the meter stick and start with the rubber bands pulled out so that there is almost no tension on the block.
3. This initial position on the meter stick of the leading edge of the block and the leading end of the string of rubber bands needs to be recorded by the recorders. Then when everyone is ready, the puller will move the end of the rubber bands 1 cm and then count out loud, "one,” move the end of the rubber bands 1 more cm and then count out loud, "two," move 1 cm, count out loud, "three" and so forth.
4. The observer will read out loud the position of the block at its initial position and then after each movement that the puller makes.
5. The recorder(s) will write down the numbers from the puller and the observer.
6. Repeat steps 2 – 5, three more times on the sandpaper (total 4), and then 4 times on the smooth counter top (total 4).
7. Make a line graph of the position of the block versus the position of the end of the rubber bands that was being pulled. Use one color for the sandpaper and another for the smooth counter top (graph grid is on the last page).
LAB QUESTIONS
1. How is the movement of the block related to friction?
2. Where did the energy that made the block move come from? Where might this same energy come from in the Earth to create an earthquake?
3. After using the earthquake machine model, Write a definition of an earthquake based on the model.
4. What did this model allow you to see that you don’t think you would be able to see if you were looking at a real fault?
5. How is this model similar AND different from an actual fault and earthquake?
6. How would you modify the model so that it would no longer store energy? How do you think your modification would impact the model’s overall operation?
7. What trend did you see when you graphed your results?
8. How did this experiment prove or disprove your hypothesis?
Name Class Date
Create your graph below. Don’t forget to title your graph and label the X and Y axes!