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Faults and Faulting
Geol341-342
2016Many diagrams are from Earth Structure, van der Pluijm and Marshak, 2004
TopicsCh. 8
• 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
Terminology
Hanging wall
Foot wall
Faults, fault zones, shear zones
Fault Zone Shear Zone
Fault zone geometry depends on mechanical stratigraphy
(Richard et al., 2013)
Fault
Wide fault zone
Shear zone
Vertical Fault DiscontinuityRole of Mechanical Stratigraphy
Richard et al. 2013
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(Bazalgette 2009)
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3
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Fault damage zone definitions Fault Zone in Granitic Gneiss
Fault zone, Brooks Range,
AK
Fault zone in Quartzites-Brooks Range
Fault rocks with depth Fault Rocks
• Gauge: non-cohesive, fine grain• Breccia: coarse angular fragments• Cataclasite: cohesive fragments• Mylonite: ductile-brittle shear zone
Depth
• Fault Melt (pseudotachylite): due to friction
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Fault scarp after an earthquake- Nevada Fault zone breccia
in QuartziteBrooks Range,
AK
Hydrothermal Fault Breccia Fault Melt
Mylonites= metamorphic shear zone rocks
Undeformed granite Shear zone granite
Types of fault
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Oblique slip
Small Normal Faults
Photo: EL Miller
Low angle fault- Whipple Mts, CA Small Thrust Fault – Moss Beach, Ca
Photo: EL Miller
Plate Boundary-San Andreas Fault
Fault
Fence
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Fault Striations- Slikenlines
Faults Account for Regional Strain
e= (L1-L0)/L0
e= 0.16
e= -0.16
Orientation of Fautls to the Stress Field Types of Fault and the Principal Stresses
Normal Thrust Strike-slip
Faults are shear fracturesin an elastic solid Fault Propagation
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Trishear:Strain in front of the fault
tip.Fault Propagation and
associated folding
Which came first: the fault or the fold?
Stress concentration at the tips
• Right-lateral Coulomb stress change on planes parallel to the
main fault (Stein and Lisowski, 1983).
The longer a fault, the more displacement
it hasEvolution of
an ActiveMountain
Front
Young Mountains-Active Fault –Basin and Range Province
Slot Canyon, Faulted Alluvial Fan- Death Valley
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Faults Symbols in Map View
Normal Faults
Thrust Faults
Decorations are on the hanging wall
Strike-slip
Fault on a Geological Map
Cambrian
Silurian
What kind of fault is shown on this map?
North
Map View of FaultsSlip vs. Separation
Block Diagram
Separation : 2DIf layers are tilted, the map may be deceiving
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What kind of fault is this?
How is this possible?
Some faults are almost flatFaults in Seismic Reflection Data- Hope Basin, AK
Interpreted Seismic Data
3 km
0Map view of normal fault
(Fossen, 2010)
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Faulted structure contour map Normal faults from well data
Well Logging SP Log (Spontaneous Potential)
Electrical logsSpontaneous Potential
Electrical Resistivity
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Thrust Fault in a Well
(after Nelson, 2001)no scale
UNION OOLITE
DEPI #5639 (047-055-00226) Gamma Ray log
UNION OOLITE(Hanging wall)
UNION OOLITE(Foot wall)
100’
PILOT KNOB THRUST FAULT
228’ vertical displacement
Cross-section A - A’
A A’
0
-500
-1000
-1500
PILOT KNOB
ARISTA
NW SE
Scale:500’
500’
UNION
PICKAWAY
DENMAR
LITTLELIME
PRICE
Take Home Points• Relationship of type of fault to principal
stresses
• Types of fault rocks vs. depth
• Fault slip vs. separation
• Recognizing faults in outcrop and in wells– Normal faults omit section
– Thrust faults repeat section
• Faults don’t go on for ever they are elastic dislocations