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EARTH SCIENCE
Earthquakes Unit
Day 3
Name_______________________________________________
Day 3:
Objective 6.1.3
Modeling Faults
Geology Activity Kit
Introduction
Explore the three main types of geological faults and how they form using this hands-on modeling activity.
Concepts
• Normal faults
• Reverse faults
• Strike-slip faults
• Earthquakes
Background
As molten rock material moves through the Earth a great deal of pressure is created. The pressure builds up in the rocks until the rocks reach
a breaking point and can no longer bend or stretch. As the rocks break, they move along surfaces or cracks called faults. When a fault is created,
the rocks slide past or rub against each other in different directions. The energy created and released by this phenomenon creates vibrations in the
Earth called earthquakes. Most earthquakes occur along tectonic plate boundaries.
At divergent plate boundaries, or areas where plates are spreading apart, rocks are subjected to stretching forces known as tension. Tension can
pull apart rocks and create normal faults. A normal fault occurs when a portion of rock drops downward relative to another portion of rock (see
Figure 1)- Normal faults are the result of the expansion of the Earth's crust.
Rock portion drops
downward
Figure 1. Normal Fault
Reverse faults occur when one portion of rock is pressed upwards relative to another portion of rock (see Figure 2). Compression forces at
convergent plates (areas where plates are being pushed together) are responsible for reverse faults. The compression pushes on rocks causing them
to bend and break and move along a reverse fault surface.
Rock portion
moves upward
Figure 2. Reverse Fault
A transform or strike-slip fault occurs where two portions of rock slide past one another without much upward or downward movement (see
Figure 3 on the next page). Rocks exposed to strike-slip faults are subject to shearing. Shearing forces push on rocks from different directions. As
the rocks move past each other, their surfaces rub upon each other and cause a large amount of strain or twisting. Irregular surfaces of rock are
created that hinder the movement of the plates. In these areas a large amount of stress is created and as the rocks reach their elastic limit, they
break and earthquakes result. If an object such as a road or riverbed has been moved to the left of its original position due to a strike-slip fault, the
fault is known as a left-lateral strike-slip fault. Conversely, if an object has been move to the right, the fault is known as a right-lateral strike-slip fault.
EARTH SCIENCE
Earthquakes Unit
Day 3
Rock portions
move/slide
past each other
Experiment Overview
Figure 3. Strike-Slip Fault
A model landform section consisting of multiple layers will be created to compare and contrast the three main types of faults-normal,
reverse, and strike-slip faults. The movements of each type of fault will be simulated, sketched, and their impact
will be explored.
Materials
Foam strips, 13/a" x 8'/z", 6 (2 strips each of 3 different colors)
Rubber bands, 3
Marker
Scissors
Ruler
Safety Precautions
Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.
Procedure
1. Obtain six strips of foam (two strips each of three different colors). Each strip is 13/a" wide by 8'/2" long.
2. Stack the foam strips on top of one another. The two strips of each color should be next to each other (see Figure 4). The stacked strips
represent a layered cross section of land, with each color representing a different rock layer
Figure 4. Side View
3. Using a marker, draw two lines down the center of the top strip as shown in Figure 5. These lines represent a river.
River is flowing this direction.
Figure 5. View from Top
4. Using a ruler, measure 2'/2" inches from one side of the top of the stacked strips. Use a marker to place a small mark on the top foam
strip at this location. See Figure 6.
EARTH SCIENCE
Earthquakes Unit
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5. Repeat step 4 on the other side of the strip.
6. Using scissors, make a diagonal cut starting at the 21/2" mark on one side as shown in Figure 7. For best results, cut each strip
individually.
Figure 7. View from top.
7. Repeat step 6 on the other side of the strips as shown in Figure 7.
8. The cuts that were made in steps 6 and 7 represent faults in the land. Sketch the cross section of land and the faults on the Modeling
Faults Worksheet.
9.
Rubber band each of the three land sections as shown in Figure 8.
Rubber bands
Figure 8. View from top.
10. Hold on to two of the land sections that are touching one another. Simulate a normal fault. Observe the locations of different layers of
rock relative to one another. Sketch and record all observations, including the overall movement of rock land masses, on the Modeling
Faults Worksheet. Label the foam layer colors as well.
11. Using the same two land sections, simulate a reverse fault. Observe the locations of different layers of rock relative to one another. Sketch
and record all observations on the Modeling Faults Worksheet. Label the foam layer colors as well.
12.
Return all three land sections to their original positions.
13.
Simulate two strike-slip faults using all three of the pieces.
14. Sketch and record all observations on the Modeling Faults Worksheet. Be sure to pay close attention to the river drawn on the top foam
layer.
15.
Answer the Post-Lab Questions.
EARTH SCIENCE
Earthquakes Unit
Day 3
Modeling Faults Worksheet
Cross Section of Land
Normal Fault Sketch
Normal Fault Observations
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Earthquakes Unit
Day 3
Reverse Fault Sketch
Reverse Fault Observations
Strike-Slip Fault Sketch
Strike-Slip Fault Observations
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Earthquakes Unit
Day 3
Post-Lab Questions
1. Define the following terms and explain the conditions under which they normally occur.
a. Fault
b. Tension
c. Compression
d. Shearing
2. Complete the following table.
Fault
Normal
Reverse
Strike-Slip
Type of Force
Overall Movement
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Earthquakes Unit
Day 3
3.What happened to the river as the land sections underwent strike-slip faults? How would this affect the course of the river?
4.What event may occur when a fault forms? Describe this process.
5.Why is it easier to predict where an earthquake will occur rather than when it will occur?
EARTH SCIENCE
Earthquakes Unit
Day 3