# 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 (like you learned on the previous Sci-ber text page.) This page is designed to help you see ways that the Earth's changes can alter the order that rocks are found in.

Sometimes the layers in the Earth become rearranged through faulting and/or folding. This often results from an earthquake caused by the movement of the Earth’s tectonic plates. A fault is a fracture in the crust of the earth where one side moves in a different direction than the other. There are three kinds of faults that can occur when an earthquake happens.Each of these is the result of the 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. Image courtesy of USGS.

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.

Imagine yourself climbing into the crevice of a fault with nothing but your lantern; because of course it would be very dark in there!!! The wall that you could stand on is the footwall and the wall you could hang your lantern on is called the hanging wall.

Now that you are familiar with faulting, let’s discuss folding. Folding occurs when layers of rocks or sediment are pushed together causing them to bend or curve. This can result in a younger layer of rock being placed below an older rock layer. See the picture below - if you click on the image, you can view it full size (warning - large file size.).

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.

Modeling Earth's Faults modified from a USGS lab by Lucy Jones

Key Points:

• The outermost portion of the Earth is made up of layers of rocks.
• There are three main types of faults: normal, thrust, slip strike.
• We can see the evidence of an earthquake in the offset layers of the Earth.

Materials:

Safety concerns: Be sure to keep all chemical safety rules. As with all science lab activities, the most important safety rule is to follow all teacher directions. Attention- students with nut allergies should avoid using peanut butter in this activity. JUST USE JELLY!

Procedure:

1. Create or print a .pdf version of a table that includes the headings, “Type of Fault”, “How the Sides of the Fault Move”, and “Changes in the Land Surface.”
 Kind of Fault How the sides of the fault move Changes that happen on the land surface Sketch
1. Make peanut butter and jelly sandwich using three slices of bread with peanut butter and jelly in between twice.
2. Slice the sandwich at an angle and then model the movement along a strike-slip fault.
• Record your motion and the results on the data table. Be sure to include arrows on your sketch.
3. Repeat step 3 for a normal fault and record your data.
4. Repeat step 3 for a thrust or reverse fault and record your data.
5. Eat sandwich.
6. Got Cow Juice?

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

Extensions:

How could you change this lab to show why some sedimentary rock layers may not always appear with youngest rocks on top and the older rocks below.

Review Science safetey rules here.

Get the plug-ins: , and . (The QuickTime plug-in is needed to play sounds and movies correctly.)

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