Geology 3120 Geology 3120 --Introduction to StrikeIntroduction to Strike--Slip FaultsSlip Faults

Levant StrikeLevant Strike--Slip FaultsSlip Faults

OutlineOutline

• Stick-Slip and Creep

• Andersonian Theory

• Kinematics

• Strike-Slip Faults on Continental Margins

• Strike-Slip Faults on Mid-Ocean Ridges

StickStick--Slip: Elastic Rebound TheorySlip: 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. the fault does not break.

••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

••Note that farNote that far--field strain may limit 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

QuickTime™ and a Cinepak decompressor are needed to see this picture.

Creep (Creep (Aseismic Aseismic Slip)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.continually over time.

•• Creeping faults do not store Creeping faults do not store

elastic energy that might be elastic energy that might be

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

earthquake)earthquake)

Andersonian Andersonian TheoryTheory

Conjugate StrikeConjugate Strike--Slip FaultsSlip Faults

Determining Sense of SlipDetermining Sense of Slip

RightRight--Lateral (Dextral)Lateral (Dextral)

LeftLeft--Lateral (Lateral (SinistralSinistral))

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

RightRight--lateral or leftlateral or left--lateral?lateral?

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

LeftLeft--laterallateral

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

Sinistral Sinistral or Dextral?or Dextral?

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

DextralDextral

StrikeStrike--Slip Faulting: Shallow Brittle Slip Faulting: Shallow Brittle vsvs Deep ShearDeep Shear

StrikeStrike--Slip Faulting: Slip Faulting: EQ’sEQ’s = dislocations= dislocations

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

Landers rupture propagation movies

StrikeStrike--Slip Faults on Continental MarginsSlip Faults on Continental Margins

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

N50 m

StrikeStrike--Slip Faults on Continental MarginsSlip Faults on Continental Margins

RightRight--lateral (dextral)lateral (dextral)

N50 m

TranstensionTranstension

Development of a PullDevelopment of a Pull--Apart BasinApart Basin

PullPull--Apart BasinApart Basin

Initial Releasing BendInitial Releasing Bend

Evolution of a Releasing BendEvolution of a Releasing Bend

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

TranspressionTranspression

Development of a Restraining BendDevelopment of a Restraining Bend

Initial Restraining BendInitial Restraining Bend

Evolution of a Restraining BendEvolution of a Restraining Bend

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

Summary of Flower Structures Summary of Flower Structures -- Palms & TulipsPalms & Tulips

Oceanic Strike Slip fault: TransformsOceanic Strike Slip fault: Transforms

StrikeStrike--Slip Faults on MidSlip Faults on Mid--Ocean RidgesOcean Ridges

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

StrikeStrike--Slip Faults on MidSlip Faults on Mid--Ocean RidgesOcean Ridges

RightRight--lateral (Dextral)lateral (Dextral)

PacificPacific--Antarctic RidgeAntarctic 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