1. Faults, Folds, and Landscapes

2. Objectives
Introduce basic terminology used in describing rock structure
Distinguish between types of fault movements and the landforms they produce
Discuss the folding of rocks and relate it to the landforms produced
Call attention to occurrence of regional deformation of the crust, in addition to more local faults and folds

3. Terminology of Structure
Strike
Line representing the intersection of a planar feature with a horizontal plane
Dip
Angle of a tilted bed relative to a horizontal plane

4. Fault Terminology Fault Joint
Fracture in crustal rock involving displacement of one side of the facture with respect to the other
Joint
Fracture in the earth’s crust, but with no displacement of rock bodies
An aerial view of the San Andreas fault in the Carrizo Plain, Central California. © USGS

5. Fault Terminology Hanging Wall Footwall
Block of rocks above the fault line
Footwall
Block of rocks below the fault line
Figure. Image of hanging wall and footwall. © USGS NPS

6. Compressional Faults Reverse fault
Hanging wall moves up relative to the footwall
Fault plane angle >45°

7. Compressional Faults Thrust fault
Hanging wall moves up relative to footwall
Fault plane angle <45°

8. Tensional Fault Normal fault
Hanging wall moves down relative to footwall
Produced by extensional forces

9. Tensional Fault

10. Tensional Fault Landscapes
Basin and Range
A series of mountains (horsts) and valleys (grabens)
Rift Valleys
Long, narrow band of downdropped block caused by plates being pulled apart (tension) and

11. Transverse Fault Strike-slip fault
Blocks of rock slide past one another
Horizontal displacement

12. Fold Formation Folding Compressional force is applied to rocks
Rocks respond by bending before fracturing

13. Fold Structures Anticlines Archlike fold with limbs dipping away
[Insert anticline]

14. Fold Structures Synclines
Troughlike fold with limbs dipping toward the axes

15. Anticlines Erosion removes upper portion of anticline
Limbs dip toward the center of fold
Older rocks are near center and becomes progressively younger with distance

16. Synclines Erosion removes upper portion of anticline
Limbs dip toward the center of fold
Older rocks are near center and becomes progressively younger with distance

17. Plunging Folds and Associated Landscapes
Anticlines and synclines often plunge; axes dip