UNIVERSITY OF SOUTH ALABAMA
GY 111: Physical Geology
Lecture 23: Faults
Instructor: Dr. Douglas W. Haywick
Last Time
A) Types of folds
B) Anatomy of a fold (terminology)
Web notes 22
Lab Manual Chapter 6
Folds
http://www.parstimes.com/spaceimages/zagros_anticlines.jpg
Folds
Anticlines: Open downwards
Synclines: Open upwards
Folds
Folds
Folds are simply bent planes and as such, can
be described using strike and dip connotation
Folds
A simple geological map of
an anticline
Folds
Folds can be horizontal or plunging
Asymmetrical Folds
Today’s Agenda
Faults (Brittle Deformation)
A) Types of Brittle Deformation
B) Types of faults/terminology
C) Faults on maps
Web notes 23:
Lab Manual Chapter 7
Stress vs. Strain Diagrams
• Brittle: rocks near the surface of the Earth behave as brittle
materials
Brittle Deformation
Rupture
Stress
Distortion below the elastic limit is
100% recoverable
Strain %
Mechanical Behavior of Rocks
Near-surface rocks that are under low T-P conditions behave as
brittle material:
– Fault fracture (slippage)
– Joint fracture (no slippage)
Deep rocks under elevated T-P conditions behave as ductile
material:
– Folding
Brittle Deformation
When rocks break, one of 3 things can occur:
1) cracking/fracturing
2) jointing
3) faulting
Brittle Deformation
Fractures are
irregularly spaced
cracks that cut
across rocks
http://roamingretirees.wordpress.com/category/state-parksrecreation-areas/
Brittle Deformation
Joints are regularly
spaced and parallel
fractures that result
from tension.
Rectangular
jointing is caused
by “unloading”
Brittle Deformation
Joints are regularly
spaced and parallel
fractures that result
from tension.
Columnar jointing
is caused by
cooling
Chalk Board
Brittle Deformation
Faults are fractures
that involve
movement.
Brittle Deformation
Faults are fractures
that involve
movement.
Brittle Deformation
Faults come in two main
flavors:
Dip Slip: movement is in the
direction of the dip of the fault
plane.
Brittle Deformation
Faults come in two main
flavors:
Dip Slip: movement is in the
direction of the dip of the fault
plane.
Strike Slip: movement is in the
direction of the strike of the
fault plane.
Brittle Deformation
A third type of fault involves a
combination of both strike and
dip movement.
Oblique Slip
Fault Terminology
All faults share some
features.
All active faults are
subject to earthquakes
Chalk Board
Fault Terminology
Dip Slip Faults are subdivided
into two types based upon the
sense of motion along the fault
plane and the type of stress
involved
Tension = Normal Fault
Compression = Reverse Fault
Fault Terminology
Then there is the Hanging
Wall and Foot Wall
components of faults
Chalk Board
Fault Terminology
Strike Slip Faults are also
subdivided into two types based
upon the sense of motion along
the fault plane.
Shear = Strike Slip Fault
Left Lateral Strike Slip Fault
Right Lateral Strike Slip Fault
Fault Terminology
The most famous strike slip
fault in this country is the San
Andreas Fault in California
Fault Terminology
Even more impressive is the
Alpine Fault in New Zealand
Fault Terminology
Even more impressive is the
Alpine Fault in New Zealand
Faults on Maps
Strike Slip Faults
(Right Lateral)
Faults on Maps
Normal Faults
Faults on Maps
Reverse Faults
Faults on Maps
There is a special class of
reverse fault that is common in
mountain belts
Thrust Faults
Faults on Maps
There is a special class of reverse fault that is common in mountain
belts
Thrust Faults
Faults on Maps
The Canadian Rockies
are one of the best places
to see thrust faults
Faults on Maps
Trust faults usually
occur in multiples (like
in the Rockies) leading
to complex geological
maps
Today’s Homework
Photograph assignment
Next Time
1) Earthquakes
2) Assignment 4 issued
3) Quiz (Short Answer)
GY 111: Physical Geology
Lecture 23: Faults
Instructor: Dr. Doug Haywick
dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposes.
For personal use only.