1. Fractures, Faults, & Friction
Lab # 5 Review
Fractures, Faults, & Friction

2. Coulomb Failure Law

3. Byerlee’s Law
0.85 for low confining pressure, 0.6 for high confining pressure (>200 MPa)

4. Envelope of Frictional Sliding

5. Importance of Differential Sress
As differential stress increases, the range of fractures with favorable orientations for reactivation increases

6. Sandbox Experiment
normal faults on the left form at 60°, thrust faults on the right form at 30°

7. Anderson’s Theory of Faulting

8. Principal Stresses and Faulting
Coulomb Failure criteria predicts that most rocks will fail at ~30° to sigma1

10. Balancing & Restoring Cross Sections
Lab #7
Balancing & Restoring Cross Sections

11. Structure of the Lab Go through terminology and example
Build a simple cross section (Problem 1)
Restore a simple cross section (Problem 2)
Start working on assignment, Problem 3

12. Cross Sections Deformed Cross Section: subsurface geology as it is now
Restored Cross Section: what subsurface looked like before deformation
Balanced Cross Section: deformed cross section capable of being restored

13. Fold and Thrust Belt result of crustal shortening    Older Younger
Foreland
Hinterland  
• the area in front of the thrusts toward which the thrust sheet moved is the foreland
• the region behind the thrusts is the hinterland
• ramp is a fault that cuts across bedding, usually connecting two flats
blind thrust 
ramp
flat

14. Assumptions Conservation of Area Consistency of Bed Length
Plane Strain
Break-Forward Sequencing
Forward Ramping Faults
Kink-Style Folds

15. Kink Folds
cylindrical folds with angular hinges, assymetric

16. Kink Method Example
• We first find the line L12 that bisects the angle between dips 1 and 2
• Extend the dips out to L12. When you cross the line, continue with the dip on the opposite side

17. Continue Plotting Axial Traces
(Steven Dutch)

18. Completed Beds
(Steven Dutch)

19. Fill in the Lithologic Units
(Steven Dutch)

20. Restoring a Cross Section
Identify the foreland & hinterland
Identify the transport direction
Choose a pin line
Label each point where the trace of the axial plane of a fold crosses a contact - these will be your line segment end-points
restore youngest fault first
restore line segments
evaluate your loose line

21. Bed Length Conservation
• If you encounter a folded layer in the deformed cross section that does not intersect a fault, simply reproduce it as a horizontal line in the restored section.
Bed Length Conservation

22. Restoring a Cross Section - Faults
• Follow the fault in the direction opposite the Transport Direction until you hit the ramp. Draw a horizontal line segment at the top of the ramp with the same length as you measured above for the line segment.
• follow the fault in the direction opposite the Transport Direction until you hit the ramp. Draw a horizontal line segment at the top of the ramp with the same length as you measured above for the line segment.
• Faults should be reproduced as they are (without making lines horizontal) unless they show signs of being folded by younger stage faulting. This is part of why we restore youngest faults first!

23. Chevron Fold

24. Kink bands