Transcript Recognizing faults - Gallaudet University

Recognizing faults
Practice with
thrust faults and
normal faults
Why study faults?
Classification of faults:
- each type of fault forms under different geologic
conditions
- so, if we can characterize the nature of the fault, we
can conclude something about the geologic history...
Some faults are easy to see…
• A Normal fault
The San Andreas fault - a slip fault
Some are harder to see
……an extensional fault
• The fault is here
<===(normal fault)
<========
Death Valley (photo by M. Miller)
The level land has
dropped DOWN
Orientation of fault
surfaces:
Strike and Dip
Note: for mechanical reasons fault planes are seldom
planar over long distances…thus, we must take MANY
strike and dip measurements along a fault.
The Nature of Fault Shapes
• Faults are
not infinite
• Faults can be
irregularly
shaped
Wytch Farm Oil Field, southern England (taken from
Kttenhorn & Pollard, AAPG Bull, 2001)
Strike Slip Fault
•
http://earthobservatory.nasa.gov/Study/denali/
Oldest fault
Compression
Newest fault
Compression
Hanging wall
Foot wall
A thrust fault
showing
how layers
have
moved.
(black is a
layer of
coal)
Compression:
Distortion along a fault
• Movement drags on the rock next to this thrust fault.
• The layers
became bent
when the walls
moved.
Hanging wall
Foot wall
Fault
Extensional faults (Utah)
Extension
• An area of
extension is called
Basin and Range
topography.
(the flat areas are
basins, the
mountains are
ranges)
Extension
• The fault line is here
Hanging wall
Foot wall
This lower area has dropped
down
<====
Extension
• Normal faults
Foot wall
Hanging wall
Foot wall
Notice this
broken layer has
moved down.
Extension
• Can you see a normal fault in this picture?
Hanging Wall
The black shale
layer has
dropped down
compared to the
other side.
Foot Wall
http://raider.muc.edu/~mcnaugma/structur.htm
#1 Is this a
normal
or
thrust fault?
Hanging wall
Foot wall
http://virtual.yosemite.cc.ca.us/ghayes/Death_Valley_Friday.htm
#2 Is this a normal or thrust fault?
(Same layer)
Foot wall
http://raider.muc.edu/~mcnaugma/structur.htm
Hanging wall
#3 Is this a normal or thrust fault?
Hanging wall
(older rock)
(younger rock)
Foot wall
http://raider.muc.edu/~mcnaugma/structur.htm
#4 Normal or Thrust fault?
www.pitt.edu/.../7Structures/NormalFaults.html
#5
Normal
or
thrust
fault?
http://gpc.edu/~pgore/geology/geo101/faults.htm
#6 Thrust or Normal faults?