1. Stress, Strain and Faulting
Types of Faults
Stress, Strain and Faulting

2. Faults and strain
Faults form when stress causes the two opposing sides of a rock formation (called fault blocks) to break apart and move in different directions. Stress falls into 3 categories:
Tension
Compression
Shear

3. 3 Types of Stress
1. Tension – caused by tectonic forces pulling the fault blocks apart
Examples: # 1, 5, 6, 7 and 9a
2. Compression – caused by tectonic forces pushing the fault blocks together Examples: # 2, 8 and 9b
Shear – caused by tectonic forces
which cause the fault blocks to slide
past each other sideways –
Examples: # 3, 4, 9a & 9b

4. 3 Types of Stress
I. Rock Deformation A. Stress is the force that tries to change the shape of a rock. There are 3 types of stress: 1) Tension ( ) - forces are pulling the rock apart 2) Compression ( ) - forces are pushing (compressing) the rock 3) Shear ( ) forces are trying to slide or snap off the rock

5. 3 Types of strain Strain is the effect that stress has on the rock.
There are 3 types of strain:
1) Elastic Deformation - when stress is removed, the strain goes back to zero (rock or object returns to its original shape);
Ex: rubber band, ruler

6. 3 Types of strain Strain is the effect that stress has on the rock.
There are 3 types of strain :
2) Plastic Deformation - when stress is removed, the rock remains deformed;
Ex: Silly Putty.
Rocks deep in the crust are subject to the high confining pressures required for plastic deformation.

7. 3 Types of strain Strain is the effect that stress has on the rock.
There are 3 types of strain :
3) Brittle Deformation - stresses are so great that the rock breaks or ruptures.
Example: Pencil, twig, window glass
C. Rocks that undergo plastic deformation deep in the crust become folded.
Rocks that undergo rupture and move form faults:

8. Vertical Faults Normal Fault – due to Tension and Gravity1
Vertical Faults
Reverse Fault – due to Compression 2

9. Vertical Faulting - more damaging
Normal Fault
Reverse Fault 1 2

10. Vertical Faults Normal Fault – due to Tension and Gravity1
Vertical Faults 2
Reverse Fault – due to Compression

11. Lateral Faults Called Transform Faults or Strike-Slip Faults3
Right Lateral Transform Fault – due to Shear
Left Lateral Transform Fault – also due to Shear 4

12. Lateral Faults Left Lateral Transform Fault
Right Lateral Transform Fault 3 4

13. Lateral Faults Left Lateral Transform Fault –due to Shear4 3
Left Lateral Transform Fault –due to Shear
Right Lateral Transform Fault – also due to Shear

14. Normal Faults – due to Tension and Gravity
Horsts and Grabens 6 5
Normal Faults – due to Tension and Gravity

15. Horst and graben
Owens Valley, Eastern California

16. Block Faults – due to Tension and Gravity
Block Fault Mountains
Block Faults – due to Tension and Gravity 7

17. The Grand Tetons A Classic Block Fault Mountain Range Front View
Side View

18. Thrust Faults and Overthrust Faults8
Thrust Faults Low Angle Reverse faults - occur due to Compression
Blind Thrust – buried under new rock layers

19. Los Angeles Area Faults 8
Strike-Slip San Andreas Fault (caused by shear) is 90 miles east.
Blind Thrust Faults (caused by compression) are under Los Angeles

20. Faulting Ground offset by faulting can be minor…
…or it can cause major disruptions of the ground surface

21. vertical fault damage Alaskan Earthquake, 1964
Buildings and streets heavily damaged by vertical surface waves (Rayleigh Waves) and vertical faulting

22. Lateral fault damage
Railroad Tracks distorted by horizontal surface waves
(Love Waves)

23. Body Seismic Waves Surface Waves: ( L) E Body Waves: ( P & S ) F
Seismic Waves are shock waves given off by earthquakes.
There are 2 types:
1. Body Waves:
Originate from the focus (F)
Travel through the body of the earth.
Used to locate epicenters (E.)
Surface Waves:
( L)
Surface Waves E
Body Waves:
( P & S ) F

24. 2 Types of Body Waves E F Body Waves: ( P & S ) Primary (P) Waves:
compression waves
travel fastest through solids
first waves to arrive
Secondary (S)
Waves
shear waves
cannot travel through liquids
second to arrive
only half as fast as P waves
Surface Waves E F
Body Waves:
( P & S )

25. 2 Types of Body Waves P Waves – S Waves –
Compressional (or Longitudinal) Waves
S Waves –
Shear
(Transverse)
Waves

26. Surface Seismic Waves Surface Waves: ( L) E Body Waves: ( P & S ) F
Seismic Waves are shock waves given off by earthquakes.
There are 2 types:
2. Surface Waves:
Originate from the epicenter (E)
Travel slowly on the surface.
Cause a lot of damage
Surface Waves: ( L)
Surface Waves E
Body Waves:
( P & S ) F

27. 2 Types of Surface Waves Love Waves – Horizontal Shear Waves
Rayleigh Waves –
Vertical Shear Waves

28. 1. Epicenter could be ANYWHERE on the blue circle!!
Locating Earthquakes
S wave
arrives
P wave
arrives
1. Epicenter could be ANYWHERE on the blue circle!!

29. Locating Earthquakes S wave arrives P wave arrives Epicenter has to
be at one of the two intersections of blue and green circles.
P wave arrives

30. Locating Earthquakes by Triangulation
S wave arrives
1. Epicenter can only be at the point where all 3 circles intersect!
P wave arrives

31. Seismic Gaps – Strain Builds Up
7. Seismic Gaps are regions along an active faultline that are overdue to have a quake. (Short-term prediction is not possible yet.)