1. Practice with thrust faults and normal faults
Recognizing faults
Practice with
thrust faults and
normal faults

2. 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...
Good resource:

3. Some faults are easy to see…
We pointed out the curve at the bottom of the ‘normal’ fault - one kind of evidence for that type. We looked at the evidence of drag on the San Andreas… indicating that it slipped sideways (this class did not study slip faults very much)
A Normal fault
The San Andreas fault - a slip fault

4. Some are harder to see ……an extensional fault
Death Valley (photo by M. Miller)
The fault is here
<===(normal fault)
<========
The level land has dropped DOWN

5. Orientation of fault surfaces:
Strike and Dip
strike
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.

6. The Nature of Fault Shapes
Wytch Farm Oil Field, southern England (taken from Kttenhorn & Pollard, AAPG Bull, 2001)
Faults are not infinite
Faults can be irregularly shaped

7. Strike Slip Fault

9. Compression Oldest fault Newest fault
Pointed out youngest faults are new faults appearing at the ‘front edge’ as in the sandboxes.

10. Compression
A thrust fault showing how layers have moved. (black is a layer of coal)
Hanging wall
Used this to establish hanging wall, foot wall. Looked for same layer on both sides, talked about which way it has moved.
Foot wall

11. 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
Curved/bent layers are one evidence of movement along a thrust fault.
Foot wall
Fault

12. Extensional faults (Utah)

13. Extension An area of extension is called Basin and Range topography.
(the flat areas are basins, the mountains are ranges)

14. Extension The fault line is here This lower area has dropped down
Hanging wall
This lower area has dropped
down
<====
I’m not sure this is really extension… trying to show the larger feature (larger scale). Actually we said this photo did not provide enough evidence to be sure about which kind of fault it is.
Foot wall

15. Extension Normal faults Foot wall Hanging wall Foot wall
Following a layer provides evidence of movement up, or in this case, down.
Foot wall
Notice this broken layer has moved down.

16. Extension Can you see a normal fault in this picture? Hanging Wall
The black shale layer has dropped down compared to the other side.
Looking for layers as evidence of which way it moved
Foot Wall

17. #1 Is this a normal or thrust fault?
Hanging wall
Foot wall
First of six slides used to practice, or as a quiz. Normal fault as evidenced by layers

18. #2 Is this a normal or thrust fault?
Hanging wall
(Same layer)
Foot wall
Practice - a thrust fault as evidence by displaced layers

19. #3 Is this a normal or thrust fault?
Hanging wall
(older rock)
(younger rock)
Foot wall
Evidence is older rock over younger rock… a thrust fault

20. #4 Normal or Thrust fault?
Normal fault (layers are evidence)

21. #5 Normal or thrust fault?
Curved layers - evidence of drag in a thrust fault

22. #6 Thrust or Normal faults?
Normal faults (layers are evidence) I’m not sure what to make of the upper layers of rock. We just looked at the lower half of the picture (lighter colored area).