Modeling Movement Along Faults
ANSWER KEY
Type of
fault
Type of
Stress
How blocks of rock move
in relation to each other
Normal
Tension
Hanging wall slides
DOWN along footwall.
Reverse
Strike-Slip
Compression Hanging wall slides UP
along footwall.
Shearing
The two blocks move
sideways alongside each
other.
How the surface changes
One side of the fault will
have higher elevation than
the other. This could form
a cliff.
One side of the fault will
have higher elevation than
the other. This could form
a cliff.
Surface features would be
shifted sideways.
How the river changes
A waterfall is formed.
The river is dammed
up; a lake or pond
forms.
The river would change
course.
Analysis and Conclusions
Answer the following questions in your notebook in complete sentences that restate the question.
1. If a river is flowing toward the hanging wall, a normal fault could produce a waterfall because the
hanging wall slides down along the footwall, so it is lower than the footwall. The water would cascade
over the edge of the footwall and fall onto the hanging wall below.
2. When the hanging wall slides up along the footwall a reverse fault is formed. This occurs in response to
compression.
3. After a reverse fault forms, if the hanging wall continues to slide up along the footwall, the slab of rock
with the hanging wall could end up on top of the slab of rock with the footwall. This could happen if
compression was continually applied to the block of crust.
4. If one observed only the land surface around a fault and noticed that a lot of features seemed to be
shifted sideways across the fault line, one could assume it is a strike-slip fault. For example, there might
be a river that has changed its course or a rock formation that seems to be divided sideways. This would
indicate shearing had occurred. However, if there were a cliff running along the surface, the fault might
have been a normal fault, formed when the hanging wall slid downward. A strike-slip fault indicates
lateral movement , while a normal fault indicates upward and/or downward movement.
5. Even though this model is not completely realistic, it is still very useful to help illustrate what happens
along a fault. One of the realistic aspects of this model is the way it shows the different types of
movement along the fault line in response to stress. For example, when tension is applied to the model, a
normal fault forms, just as tension in the earth’s crust can cause normal faulting. Similarly, compression
causes a reverse fault, and shearing results in a strike-slip fault, exactly what occurs in actual crust.
Another aspect that was realistic was that the block was composed of different layers, which represent
rock strata. In addition, we made the fault line on a slant so that it would form a footwall and a hanging
wall. One very unrealistic aspect of our model was the fact that our fault blocks exist as a small piece of
crust in the middle of nowhere. In reality, they would be surrounded on all sides by more crust. Another
factor that is unlike the real world is the softness of the clay. The blocks of crust are hard, rigid, and
brittle. A final, unrealistic feature is the large gap that sometimes formed between the two fault blocks.
In reality there would be probably not be much space between them. Despite these unrealistic factors,
the model was helpful in demonstrating movement along fault lines.