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NOTES
FAULTS and FOLDS
What is a fault?
 A fault is a fracture or series of fractures in
Earth’s crust that occurs when stress is applied too
quickly or stress is too great.
 Many faults occur along plate boundaries.
 Faults can also occur anywhere in the crust where
rocks are bent (folded) until they break.
 Faults occur as a result of various types of stress.
Stress vs. Strain
Stress is the force that acts on a material.
 Strain is the deformation (change of shape)
of a material in response to stress.
Most Faults Have a Hanging Wall and a
Foot Wall
 The Hanging Wall is the one with the slope on
which you could hang. The Foot Wall is the one
with the slope on which you could walk.
 The type of fault is determined by the motion of
the Hanging Wall.
The fault line would also be
called the fault plane. The
area around it would be
called the fault zone.
Is this the Hanging Wall or Foot Wall?
Is this the Hanging Wall or Foot Wall?
The FOOT WALL is the one with the slope
you would put your feet on.
Is this the Hanging Wall or Foot Wall?
The HANGING WALL is the one with the
slope you would hang from.
Types of Faults
 There are several different kinds of faults. These
faults are named according to the type of stress
that acts on the rock and by the nature of the
movement of the rock blocks either side of the
fault plane.
 Stresses can be compressional (push), tensional
(pull) or shear (slide past each other).
 The type of stress determines how the Hanging
Wall moves and therefore the type of fault.
3 Types of Faults Caused by 3 Different
Types of Stress
Normal Fault
(Caused by Tension)
Reverse Fault
(Caused by Compression)
Transform Fault
(Caused by Shear Stress)
Normal Fault
Occurs when tensional stress pulls the
fault apart and the Hanging Wall drops.
The fault is an example of tensional strain.
Reverse Fault
Occurs when compressional stress
pushes the two parts of the fault together
and the Hanging Wall moves up.
The fault is an example of compressional strain.
Transform Fault
AKA “strike-slip” fault
Shear stress causes the parts of the fault
to slide past one another.
This fault is an example of shear strain.
Examples of Faults
Folds
Occur when stress is applied to both ends of
a section of rock or rock layers. Some rocks
would break, but a fold occurs when rocks
bend. An anticline looks like a “rainbow”; a
syncline looks like a “smile”.
Examples of Folds
Your Assignment…
Do the “Lab: Constructing Fault Models”.
Color, fold and cut to create the model.
Then use it to answer the questions on the
other worksheet. Turn in both parts (be
sure your name is on them) today before
you leave.
Your test is next class and will include:
Layers of Earth, Continental Drift,
Seafloor Spreading, Plate Tectonics,
Faults and Folds.