1. GSC 1530 Chapter 10
Crustal Deformation

2. Crustal Deformation
Crustal deformation processes have produced some of the world’s most beautiful scenery (e.g., the Himalaya Mountains) but also some of its most deadly events (e.g., the earthquake which induced the massive 2004 Indian Ocean tsunami)

3. Terminology Stress – amount of force applied to a given area of a body
Three main types of non-uniform (differential) stress: compressive ( ), tensional ( ) and shear ( )
Strain – change in shape of a body resulting from the applied stress
Three main types: brittle, elastic and plastic (ductile); see classroom examples and slides

4. Figure 10.8

5. Joints and Faults Joints and faults result from brittle rock behavior
Joints – rock fractures along which no appreciable displacement has occurred

6. Earthquake Origin?
Fault – a crack in rock along which rock shifting (displacement) has occurred
Earthquakes result from brittle rock behavior which produces faults
Elastic Rebound Theory: earthquakes result from the rapid release of elastic strain energy that produces rock rupture and displacement (shifting)
See classroom examples, including slide illustrating the elastic rebound theory

7. Elastic Rebound
Phenomenon
and Earthquake
Production

8. Elastic Rebound
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

10. Earthquakes and Faults
An initial earthquake produces the fault and subsequent movement can occur along the fault if sufficient strain energy accumulates to cause brittle behavior

11. More Earthquake Terminology
Focus – subsurface origin point of earthquake; earthquake (seismic) energy radiates outward in all directions from the focus
Epicenter – point on the Earth’s surface directly above the focus; seismic surface waves radiate outward from this point
Fault scarp – relatively steep landform produced from fault motion with a substantial vertical component
Seismic waves – the vibrational energy produced during an earthquake

13. Fault Types
Faults can be broadly classified as dip-slip (rock displacement is primarily vertical) and strike-slip (rock displacement is primarily horizontal)
Dip-slip faults can be further subclassified as reverse or normal faults
To correctly subclassify a dip-slip fault, you need to know the relative motion of the hanging wall and footwall blocks (see slide)

15. Hanging Wall
Reverse fault – hanging
wall block moves upward
relative to the footwall
block
Footwall
Normal fault – hanging
wall block moves
downward relative
to the footwall
block
Footwall
Hanging Wall

17. SF 10.22b

19. Type of dip-slip fault?

20. Type of dip-slip fault?

21. Major landforms produced by normal faulting
Horst – uplifted block of crust bounded by normal faults that diverge
with depth
Graben – a basin (valley) formed by a subsided block of crust
bounded by normal faults that converge with depth

22. Figure 10.23

26. Strike-slip fault

29. Lateral displacement (~8
Lateral displacement (~8.5 feet) of fence during the 1906 San Francisco Earthquake

30. Major Fold Types
Rocks, under certain conditions, may fold (ductile deformation) instead of faulting
What are the four major factors that determine whether a rock will fold or fault?
Rock temperature
Amount of stress exerted upon rock
Rate stress is exerted upon the rock
Rock composition

31. Major Fold Types
There are three major folds you should be able to describe: anticlines, synclines and monoclines
Anticline – an arch-like package of folded rocks
Syncline – a trough-like package of folded rock

34. SF 10.11

36. Major Fold Types
Monoclines – strata exhibiting a single inclination direction (see slide)

37. Monocline

38. Related Fold Types Domes - large-scale upwarping of sedimentary rocks
Basins - large-scale downwarping of sedimentary rocks (see slides)

39. SF 10.14

40. Michigan’s
Lower
Peninsula is
often described
by geologists
as the Michigan
Basin

41. Folds and Faults
Folded and faulted rock often coexists; the rocks fold until their brittle strain threshold is exceeded and then fault (see slide)

42. Folded and Faulted
Sedimentary Rock