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

Coulomb Failure Law

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

Envelope of Frictional Sliding

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

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

Anderson’s Theory of Faulting

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

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

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

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

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

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

Kink Folds cylindrical folds with angular hinges, assymetric

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

Continue Plotting Axial Traces (Steven Dutch)

Completed Beds (Steven Dutch)

Fill in the Lithologic Units (Steven Dutch)

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

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

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!

Chevron Fold

Kink bands