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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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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