Faults, fault zones, shear zones...
Transcript of Faults, fault zones, shear zones...
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Faults and Faulting
Geol342
2008Many diagrams are from Earth Structure, van der Pluijm and Marshak, 2004
Topics
• Faults on outcrop, maps, and cross sections• Fault zones and fault rocks• Types of faults and terminology• Slip vs separation• Faults in wells• Fault propagation
Faults, fault zones, shear zones Terminology
Hanging wall
Foot wall
Fault Zone in Granitic Gneiss
Fault scarp after an earthquake- Nevada
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Plate Boundary-San Andreas Fault
Fault
Fence
Fault zone in Quartzites-Brooks Range
Small Normal Faults
Small Thrust Fault – Moss Beach, Ca
Types of fault
Oblique slip
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Fault Striations- Slikenlines
Regional Strain
Types of Fault and the Principal Stresses
Normal Thrust Strike-slip
Fault rocks with depth Fault Rocks
• Gauge: non-cohesive, fine grain• Breccia: coarse angular fragments• Cataclasite: cohesive fragments• Mylonite: ductile-brittle fault zone
Depth
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Fault zone breccia
in QuartziteBrooks Range,
AK
Hydrothermal Fault Breccia
Fault Melt
Mylonites
Undeformed granite Deformed
Young Mountains-Active Fault –Basin and Range Province
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Evolution of an ActiveMountain
Front
Triangular Facets on an active Mountain Front
Faults Symbols in Map View
Normal Faults
Thrust Faults
Decorations are on the hanging wall
Strike-slip
Fault on a Geological Map
What kind of fault is this?North
Map View of FaultsSlip vs. Separation
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Block Diagram
How is this possible?
Some Faults are Almost flatFaults in Seismic Reflection Data- Hope Basin, AK
Interpreted Seismic Data
3 km
0
Faulted structure contour map
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Faults from well dataFaults are shear fractures
in an elastic solid
Fault Propagation
• Right-lateral Coulomb stress change on planes parallel to the main fault (Stein and Lisowski, 1983).
The longer a fault, the more displacement
it has