1. Deformation of Rocks How Rocks Deform Brittle-Ductile Behavior
Faulting and Folding

2. Stress and Strain
The keys to understanding any deformation are stress (the cause) and strain (the effect)

3. Compression
Rocks are squeezed or compressed by forces directed toward one another.
Rocks are shortened by folding or faulting

4. Plate Boundary: Convergence Zones

5. Tension
Rocks are lengthened or pulled apart by forces acting in opposite directions
Rocks are stretched and thinned

6. Plate Boundary: Divergence Zones

7. Shear Forces act parallel to one another but in opposite directions
Results in displacement of adjacent layers along closely spaced planes

8. Plate Boundary: Transform Faults

9. Relationship between stress and strain
Elastic behavior
Fracture, breaks X
Strain 
Stress
Rock
Ductile behavior
Rubber band
Permanent strain

10. Relationship between stress and strain
Brittle behavior:
Very little ductile deformation before fracturing X
Strain 
Stress X
Fracture
Ductile behavior:
Extensive ductile deformation before fracturing

11. Ductile
Brittle

12. Ductile Behavior
Folding of Rocks
Brittle Behavior
Faulting of Rocks

13. What controls brittle vs. ductile?
Rate of deformation (fast = brittle)
Rock strength (strong = brittle)
Temperature (cold = brittle)
Confining pressure (shallow = brittle)
Just remember deeper = ductile
Near surface= rocks are brittle
At depth= rocks are ductile

14. What controls brittle vs. ductile?
Rate of deformation (strain rate)
Low strain rates Ductile (Mantle Convection)
High strain rates  Brittle (Earthquake waves)

15. Yield stress
Elastic limit
Effects of Temperature and Strain Rate

16. Brittle-Ductile Transition
Limits the depths of
earthquakes
surface
Brittle
Low Temperature
Low Pressure
15-20 km
Higher Temperature
Higher Pressure
Ductile
Crust
Mantle

17. Lithosphere-Asthenosphere
schematic
strength
profile through
continental
lithosphere
Strain
Stress
Yield
strength=0
T=1300 C
Lithosphere-Asthenosphere

18. Deformation in Progress

19. Abrupt Movement along Faults

20. Uplifted sea floor at Cape Cleare, Montague Island, Prince William Sound, in the area of greatest recorded tectonic uplift on land (33 feet). The very gently slopping flat rocky surface with the white coating which lies between the cliffs and the water is about a quarter of a mile wide. It is a wave cut surface that was below sea level before the earthquake. The white coating consists of the remains of calcareous marine organisms that were killed by desiccation when the wave cut surface was lifted above the high tide during the earthquake.
Uplifted sea floor at Cape Cleare, Montague Island, Prince William Sound. Uplift about 33 ft

21. LA SA uplift subsidence
FIGURE 4.15 Perspective view of the Los Angeles region with superimposed
InSAR measurements of ground motions between May and September 1999,
indicating seasonal and secular variations due to groundwater withdrawal and
recharge. Large regions of metropolitan Los Angeles are rising and falling by up to
11 centimeters annually, and a large portion of the city of Santa Ana is sinking at a
rate of 12 millimeters per year. The repeated color banding with the large oval
shows approximately 5 centimeters of subsidence. The straight line located just
inside the coastline is the Newport-Inglewood fault, which controls the extent of
subsidence. The small isolated bull’s-eye feature north of Palos Verdes and east of
downtown Los Angeles is from pumping activity in the Inglewood oil field. The
motion caused by the withdrawal of water, oil, and gas from the basin contaminates
GPS measurements of the deformation field. After corrections for these
effects using the InSAR data, the contraction across the Los Angeles Basin is estimated
to be approximately 4.5 millimeters per year. This deformation is thought to
be accommodated primarily on blind thrust faults, such as those that ruptured in
the 1987 Whittier Narrows and 1994 Northridge earthquakes. SOURCE: G.W.
Bawden, W. Thatcher, R.S. Stein, K.W. Hudnut, and G. Peltzer, Tectonic contraction
across Los Angeles after removal of groundwater pumping effects, Nature, 412,
, Reprinted by permission from Nature copyright 2001 Macmillan
Publishers Ltd.
Gradual Movement: Perspective view of the Los Angeles region with superimposed InSAR( Interferometric Synthetic Aperture Radar) measurements of ground motions between May and September Large regions of metropolitan Los Angeles are rising and falling by up to 11 cm annually, and a large portion of the city of Santa Ana is sinking at a rate of 12 mm per year.

22. Past Deformation: Folding
Large scale and small scale folds

23. Folding: large and small scale

24. Past Deformation: Faulting
Large scale and small scale

25. Strike and Dip

26. Measuring Deformation in the Rocks Strike & Dip

27. Faults
Fractures along which there is relative motion parallel to the fracture
The fracture is called the fault plane
Vertical motion (dip-slip)
horizontal (strike-slip).
Most faults have a combination of both types of motion (oblique).

28. Types of Faults
Classified according to:
Dip of fault
Direction of relative movement

29. Normal Fault (dip-slip)

30. Normal Faulting
Foot wall
Hanging wall

31. Tetons – fault range scale

32. Basin and Range Normal Faulting Horst-Graben Structures
Death Valley, CA
Classic basin-and-range topography: Death Valley, California. View from Dante's View across Badwater, the lowest point in the western hemisphere at 282 feet below sea level, to the Panamint Mountains and Telescope Peak (11,049'). Mt. Whitney, the highest point in the lower 48 states, is about 100 miles beyond Telescope Peak. Note the perfectly formed alluvial fans in the foreground at the base of the Black Mountains. Both mountain ranges are bordered by large normal faults.
Normal Faulting
Horst-Graben Structures

34. Reverse Fault (dip slip)

35. Reverse Faults

36. Thrust Fault (dip-slip)

37. Thrust Fault
Older rocks
Younger rocks

38. Thrust Faults. Snake Range, Wy

39. Strike-Slip Fault (horizontal motion, no vertical motion)

40. Strike-Slip Fault

41. San Andreas Fault Transform plate boundary (Pac / N.A.)
System of right lateral faults

42. Offset Streams (San Andreas Fault)
A pair of streams that has been offset by right-lateral slip on the San Andreas fault (lineament extending from left to right edge of photograph). View northeastward across fault toward the Temblor Range. Photograph by Sandra Schultz Burford, U.S. Geological Survey.

43. Strike-slip fault Off-set stream Right-lateral Strike-slip
Stress: shear

44. Types of Folds
During mountain building or compressional stress, rocks undergo ductile deformation to produce folds
anticline
syncline

45. Types of Folds

46. Anticline: Warped upwards. Limbs dip outward
Anticline: Warped upwards. Limbs dip outward. When eroded, oldest rocks crop out in the center (assuming everything is right-side-up).

47. Syncline: Warped downwards. Limbs dip inward
Syncline: Warped downwards. Limbs dip inward. When eroded, youngest rocks crop out in the center (assuming everything is right-side-up).

50. Basins and Domes resemble anticlines & synclines
 vertical motions instead of lateral motions

52. Stress, Strain & Plate Tectonics
Plate collisions (convergent margins)
Compressive strsses
Folds & reverse faults

53. Stress, Strain & Plate Tectonics
Divergent plate boundaries
Tensional stresses
Normal faults

54. Stress, Strain & Plate Tectonics
Transform plate boundaries
Shear stress
Transform faults