Geology 360 - Geology 360 - Introduction to Thrust FaultsIntroduction to Thrust Faults

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Thrust faultsThrust faults

• Terminology

• Calculating stretch and shortening

• Throw, heave, and slip

• Stratigraphy and thrust faults

Thrust FaultThrust Fault

Thrust Fault TerminologyThrust Fault Terminology

Original layer cake templateOriginal layer cake template

Thrust Fault TerminologyThrust Fault Terminology

Transport DirectionTransport Direction

ForelandForeland HinterlandHinterland

Fault achieves trajectory rapidlyFault achieves trajectory rapidly

Fault Bend Fold MovieFault Bend Fold Movie

Thrust Fault TerminologyThrust Fault Terminology

Calculating Shortening for Thrust Calculating Shortening for Thrust

FaultsFaults

lo lf

50 km 40 km

Shortening =Shortening = llo o

llf f - l- loo * 100%* 100%

If Stretch [S] = lIf Stretch [S] = lff/l/loo, then , then shortening =shortening = llo o

llff -1 * 100%-1 * 100% ( )

Calculating Shortening for Thrust Calculating Shortening for Thrust

FaultsFaults

lo lf

50 km 40 km

Shortening =Shortening = llo o

llf f - l- loo * 100% = * 100% = 40 - 5040 - 50

5050* 100% = -20%* 100% = -20%

A Caution Regarding ShorteningA Caution Regarding Shortening

Choosing a minimum lChoosing a minimum loo value yields maximum shortening value yields maximum shortening

lo lf

50 km 40 km

Shortening =Shortening = llo o

llf f - l- loo * 100% = * 100% = 40 - 5040 - 50

5050* 100%= -20%* 100%= -20%

Shortening CalculationShortening Calculation

lo lf

40 km 30 km

Shortening =Shortening = llo o

llf f - l- loo * 100% = * 100% = 30 - 4030 - 40

4040* 100% = -25%* 100% = -25%

Thus “shortening” is relative to the baseline you pickThus “shortening” is relative to the baseline you pick

Throw, Heave, and SlipThrow, Heave, and Slip

Throw

Heave

Slip

(Throw)(Throw)22 + (Heave) + (Heave)22 = (Slip) = (Slip)22

SinSin = (Throw/Slip) = (Throw/Slip)

CosCos = (Heave/Slip) = (Heave/Slip)

Increasing Stratigraphic ThicknessIncreasing Stratigraphic Thickness

Evidence for Thrust Faulting in Evidence for Thrust Faulting in

BoreholesBoreholes

Evidence for Thrust Faulting in Evidence for Thrust Faulting in

BoreholesBoreholes

Evidence for Thrust Faulting in Evidence for Thrust Faulting in

BoreholesBoreholes

ReferencesReferences

Slides 3-9

http://earth.leeds.ac.uk/faults/thrust/rampflat/index.htm

Slides 10-14

Twiss, R. J. and E. M. Moores, Structural Geology, W. H. Freeman & Co., New York, 532 p., 1992.