Geology 360 - Geology 360 - Introduction to Strike-Slip FaultsIntroduction to Strike-Slip Faults

Levant Strike-Slip FaultsLevant Strike-Slip Faults

Left-lateral strike-slip Levant fault, plate

boundary between Arabia and Africa

San Andreas San Andreas from Spacefrom Space

San Francisco Bay, California.

Two northwest-southeast-trending faults are visible.

The Hayward Fault, bordering the urban area east of San Francisco Bay

The San Andreas Fault, crossing the mid-San Francisco Peninsula before dipping beneath the Pacific Ocean and surfacing again northwest of Golden Gate Bridge

San Andreas fault, San Andreas fault,

western North Americawestern North America

OutlineOutline

• Stick-Slip and Creep

• Andersonian Theory

• Kinematics

• Strike-Slip Faults on Continental Margins

• Strike-Slip Faults on Mid-Ocean Ridges

Stick-Slip: Elastic Rebound TheoryStick-Slip: Elastic Rebound Theory

Elastic Rebound TheoryElastic Rebound Theory

• Imagine a fence across an active Imagine a fence across an active

faultfault

Elastic Rebound TheoryElastic Rebound Theory

• Imagine a fence across an active Imagine a fence across an active

faultfault

• Regional deformation occurs but Regional deformation occurs but

the fault does not break. The the fault does not break. The

fence becomes curved.fence becomes curved.

Elastic Rebound TheoryElastic Rebound Theory

• Imagine a fence across an active Imagine a fence across an active

faultfault

• Regional deformation occurs but Regional deformation occurs but

the fault does not break (locked the fault does not break (locked

fault) fault)

•Once the fault breaks, the fence Once the fault breaks, the fence

is sheared in half and marks offsetis sheared in half and marks offset

•The far-field strain may limit The far-field strain may limit

whether the fault accommodates whether the fault accommodates

all the plate motion at its traceall the plate motion at its trace

Elastic Rebound TheoryElastic Rebound Theory

Elastic Rebound TheoryElastic Rebound Theory

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Creep (Aseismic Slip)Creep (Aseismic Slip)

• Imagine a fence across an active Imagine a fence across an active

faultfault

• Slip occurs slowly on the fault Slip occurs slowly on the fault

continually over time (fault is not continually over time (fault is not

locked)locked)

• Creeping faults do not store Creeping faults do not store

elastic energy that might be elastic energy that might be

released by a stick-slip event (an released by a stick-slip event (an

earthquake)earthquake)

Andersonian TheoryAndersonian Theory

Conjugate Strike-Slip Conjugate Strike-Slip

FaultsFaults

Determining Sense of SlipDetermining Sense of Slip

Right-Lateral (Dextral)Right-Lateral (Dextral)

Left-Lateral (Sinistral)Left-Lateral (Sinistral)

Arrow Heads ( ) and Tails ( )Arrow Heads ( ) and Tails ( )

Block moving toward you like an arrowhead Block moving toward you like an arrowhead

heading towards youheading towards you

Block moving away from you like seeing the Block moving away from you like seeing the

feathers of an arrow feathers of an arrow

Arrow Heads ( ) and Tails ( )Arrow Heads ( ) and Tails ( )

Right-lateral or left-lateral?Right-lateral or left-lateral?

Arrow Heads ( ) and Tails ( )Arrow Heads ( ) and Tails ( )

Left-lateralLeft-lateral

Arrow Heads ( ) and Tails ( )Arrow Heads ( ) and Tails ( )

Sinistral or Dextral?Sinistral or Dextral?

Arrow Heads ( ) and Tails ( )Arrow Heads ( ) and Tails ( )

DextralDextral

Strike-Slip Faulting: Shallow Brittle vs Deep Strike-Slip Faulting: Shallow Brittle vs Deep

ShearShear

Strike-Slip Faulting: EQ’s = dislocationsStrike-Slip Faulting: EQ’s = dislocations

http://www.data.scec.org/Module/links/landrupt.html

Landers rupture propagation movies

Strike-Slip Faulting: EQ’s = dislocationsStrike-Slip Faulting: EQ’s = dislocations

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Strike-Slip Faulting: EQ’s = dislocationsStrike-Slip Faulting: EQ’s = dislocations

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Strike-Slip Faults on Continental Strike-Slip Faults on Continental

MarginsMargins

What is the sense of slip?What is the sense of slip?

N50 m

Strike-Slip Faults on Continental Strike-Slip Faults on Continental

MarginsMargins

Right-lateral (dextral)Right-lateral (dextral)

N50 m

TranstensionTranstension

Development of a Pull-Apart Development of a Pull-Apart

BasinBasin

Pull-Apart BasinPull-Apart Basin

Initial Releasing BendInitial Releasing Bend

Evolution of a Releasing Evolution of a Releasing

BendBend

Normal (-) Flower Structure - Normal (-) Flower Structure -

Tulip Tulip

TranspressionTranspression

Development of a Restraining Development of a Restraining

BendBend

Development of a Restraining Development of a Restraining

BendBend

Initial Restraining BendInitial Restraining Bend

Evolution of a Restraining Evolution of a Restraining

BendBend

Reverse (+) Flower Structure - Reverse (+) Flower Structure -

PalmPalm

Summary of Flower Structures - Palms Summary of Flower Structures - Palms

& Tulips& Tulips

Summary of Step Overs - Strike-Slip Summary of Step Overs - Strike-Slip

FaultsFaults

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Los Angeles - Pull apart structureLos Angeles - Pull apart structure

Releasing Releasing bendbend

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Summary of Flower Structures - Palms Summary of Flower Structures - Palms

& Tulips& Tulips

Summary of Flower Structures - Palms Summary of Flower Structures - Palms

& Tulips& Tulips

Summary of Flower Structures - Palms Summary of Flower Structures - Palms

& Tulips& Tulips

Summary of Flower Structures - Palms Summary of Flower Structures - Palms

& Tulips& Tulips

Oceanic Strike Slip fault: TransformsOceanic Strike Slip fault: Transforms

Strike-Slip Faults on Mid-Ocean Strike-Slip Faults on Mid-Ocean

RidgesRidges

What is the sense of slip?What is the sense of slip?

Strike-Slip Faults on Mid-Ocean Strike-Slip Faults on Mid-Ocean

RidgesRidges

Right-lateral (Dextral)Right-lateral (Dextral)

Pacific-Antarctic RidgePacific-Antarctic Ridge

Magnetic anomalies from present to 9.9 MaMagnetic anomalies from present to 9.9 Ma

Warm colors indicate positive polarityWarm colors indicate positive polarity

Cool colors indicate reverse polarityCool colors indicate reverse polarity