Move Over, I'm Coming Through

Move Over, I'm Coming Through!

When you look closely at various rock formations, you often find that they seem to not always follow the order of oldest on the bottom and youngest on the top. This experiment is designed to help you see ways that Earth's changes can alter the order that rocks are found in. If you have some clay or want to make some salt dough, you can model these examples on your own.

There are three kinds of faults that can occur when an earthquake happens. Each of these is the result of Earth's movement along the fault line.

 A strike-slip fault occurs when the rocks on either side of the fault slip past each other sideways with little up-or- down motion.  A normal fault occurs at an angle, so one block of rock lies above the fault while the other block lies below the fault.  A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

A difference between the normal and reverse fault is that the force deforming the crust in a normal fault pulls apart while the force deforming the crust in a reverse fault pushes together. Another difference is that in a normal fault the half of the fault that lies above is called the hanging wall. The half of the fault that lies below is called the footwall. The rock forming the hanging wall of a reverse fault slides up and over the footwall.

A fault is a break in Earth’s crust where slabs of rock slip past each other. In this activity, you will make a model of the movements along faults.

Materials:

 Modeling clay or salt dough in two or more colors  Marking pen  Plastic knife

Procedure:

1. Roll some modeling clay into a sheet about 0.5 centimeter thick and about 6 centimeters square. o Then make another sheet of the same size and thickness, using a different color. o Make additional sheets if you have more colors. 2. Stack the sheets on top of each other, alternating colors (as shown to the right.) 3. Press the layers of modeling clay together to form a rectangular block that fits in the palm of your hand. 4. Use the knife to slice carefully through the block at an angle like this “/”. 5. Place the two blocks formed by the slice together, but don’t let them stick together. 6. Review the descriptions and diagrams of faults. o Decide which piece of your block is the hanging wall and which is the footwall. o Using the marking pen, label the side of each block. o What part of your model illustrates the fault itself?

Answer:

o What part of the model represents the land surface?

Answer:

7. Fill out the table below with the information learned from each type of fault (questions #8-10):

Type of Fault How the Sides of the Fault Move Changes in the Land Surface

8. Using your blocks, model the movement along a strike-slip fault. Record your motion and the results on the data table. 9. Repeat step 8 for a normal fault. 10. Repeat step 8 for a reverse fault.

Analysis:

1. Describe how this model helps you picture what is happening along a fault.

2. In what ways does the model not accurately reflect what happens along a fault?

3. How is this model helpful?

4. How does the model explain why rock layers may not be accurate in terms of the older rocks being underneath the younger rocks?

Extensions: Draw a river on the surface of your clay model. Modify your data chart to show the effects the three faults have on the river.

Enrichment: On Earth’s surface, individual faults do not exist all by themselves. With one or more of your classmates, combine your models to show how faults combine to form mountains.