20 Minutes
Mini
LAB
Modeling a Fault
Materials
• Two fist-sized pieces of
different-colored clay
• wire
Procedure
1
Flatten each piece of clay
until it is about 1 cm thick.
Cut each piece into two
congruent rectangles.
2
Stack all four rectangles,
forming a block with layers of
alternating colors.
3 Using the wire, cut through the
block diagonally, as shown.
4
Move one side of the block
up and the other down. Move
the sides in the opposite
directions.
Analysis
Faults
As you learned in Chapter 10, a fault is a break in the lithosphere along
which movement has occurred. Not only are movements along fault planes
the primary cause of earthquakes, they are also an important part of the
process of mountain formation.
The illustration at the right shows
Fault
a fault plane, which is the surface
plane
between the two pieces of moving
crust at a fault. The part of the fault
above the fault plane is called the
hanging wall. The part of the fault
Footwall
below the fault plane is the footwall.
Hanging wall
Geologists classify faults by the
way in which the rocks on either side
of the fault plane move with respect
to each other. In each of the fault
illustrations below, the large arrows
indicate stress being applied to the
rocks. The small black arrows show movement along the fault plane.
A normal fault occurs when the hanging wall moves down with
respect to the footwall. Normal faults occur in areas where tension is
pulling the crust apart.
A reverse fault occurs when the hanging wall moves up with respect
to the foot wall. Reverse faults are caused by compression. Such
compression may occur, for example, when two plates collide. The
compression at a reverse fault thickens and shortens rocks.
What types of faults have you
modeled? For each fault, what
type of stress did you exert?
What would you change to model
other types of faults?
Hanging wall
Footwall
Hanging wall
NORMAL FAULT
A thrust fault is a reverse fault in
which the fault plane dips 45° or less
from the horizontal. Thrust faults are
common in many mountain belts,
including the Appalachians. From
studies of thrust faults, geologists
have seen that compressive stresses
can move sheets of rock over
great distances.
240
Unit 3 Dynamic Earth
Footwall
REVERSE FAULT
Hanging wall
Footwall
THRUST FAULT