Transcript Faults And Folds

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.
Most Faults Have a Hanging Wall and a
Foot Wall
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.
Types of Faults
• 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.
Folds
• An anticline looks like
a “rainbow”; a
syncline looks like a
“smile”.
Examples of Folds