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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