Faults and its classification in structural geology.pdf

fault geometry and its classification on various types

1. 1
By
Dr. Harish Kapasya
Faculty of Earth Sciences
Department of Geology
Udaipur
Fault

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Faults are ruptures along
which the opposite walls
have moved over each
other parallel to the
surface of fracture.
A fault may be
defined as a fracture
along which blocks
of rocks have been
displaced relative to
each other.
FAULT

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•Translational Movement
•There is no rotation of the block relative
to each other. The straight line on opp.
Side of the fault and outside the
dislocated zone that were parallel before
the displacement are parallel afterwards.
•Rotational Movement
•Are those in which some straight line on
opp. Sides of the fault & outside the
dislocated zone parallel before the
displacement are no longer parallel
afterwards.
Nature of movement along Fault

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Fault plane:-The fracture surface
along which relative displacement
takes place during the process of
faulting, is called “Fault -Plane”.
Footwall :-The side or wall
that below the fault plane is
called footwall.
Hanging wall :-If the fault
plane is inclined the side or
wall that rest above the fault
plane is called the hanging
wall.
Hade:-The hade of
a fault is the angle of
inclination of fault
plane, measured
from the vertical.
Heave:-The horizontal
component of dip
separation between up
throw side and down throw
side is called “Heave”

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Throw:-The vertical component of the displacement of fracture rock
blocks, is called “Throw of Fault”
The side on which blocks appear to have
been throw down is called “Down throw
side”
The side on
which strata
appear have
been gone up
is called “Up
throw side”.

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•Dip:-Thedipistheanglebetweenhorizontalsurface
andfaultplane.
•Strike:-Thestrikeistrendofthehorizontallineinthe
faultplane.

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•NetSlip:-ThetotalDisplacementmeasuredalongfault
plane.
•DipSlip:-Displacementisparalleltothedipoffaultplane.
•StrikeSlip:-DisplacementisparalleltotheStrikeoffault
plane.
•ObliqueSlip:-Displacementinanydirection.
•FaultZone:-Mostfaultplanearerelatedwithazoneof
crushedorchangedrocks,thiszoneiscalled“FaultZone”.
•FaultLine:-Thelineofintersectionofthefaultplanewith
theearth’ssurface.

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Geometrical Classification
GeometricalClassificationoffaultisbasedon:
1.TherakeoftheNetSlip.
2.Theattitudeoffaultrelativetoadjacentrock.
3.Thepatternoffault.
4.Theangleatwhichfaultdips.
5.Theapparentmovementonthefault.

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TheRakeoftheNetSlip
•Angleofnetslipwithstrikemeasuredonfaultplaneis
0°-90°.
1.Strikeslipfault:-Netslipisparalleltothestrikeof
thefaultplane&therewillbenodipslipandrakeis0.
2.Dipslipfault:-Netslipisupordownthedipofthe
fault.Dipslipisequaltothenetslip.Strikeslip=0and
rakeoftheslipis90°.
3.Diagonalslipfault:-Netslipisdiagonallyupordown
ofthefault.Wehavestrikeslip&dipslipcomponent.
Rake=between0and90°.
AlsocalledasObliqueSlipFault.

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Theattitudeoffaultrelativetoadjacentrock
1.Dipfault:-
Afaultwhichstrikeapproximatelyparalleltothedipdirectionof
bedsiscalledthe“Dipfault.”
2.StrikeFault:-
Afaultwhichrunsparalleltothestrikeofbed,iscalledthe“Strike
fault”.
3.ObliqueFault:-
Afaultwhichobliquetothestrikeanddipdirectionsofbedis
calledthe“Obliquefault.”

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3.BeddingFaults:-
Abeddingfaultisonewhichoccursalongacontact
betweenbedsofdifferentorsameLithology.
5. Tear Fault & Wrench Fault:-
Instrike slip faulting the relative displacement of the
blocks is horizontal.

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Fault Pattern
1.Parallelfaults:-
Aseriesoffaultsthathavesamestrike&diparecalled“Parallel
faults”.Suchfaultsrunparalleltoanotherandallhadeinthe
samedirectionwiththesameangle.

14. 2.Stepfaults:-
Inthesefaultstheinterveningblocksaredownthrownin
samedirection.Inthesefaultsdownthrownblocks
produceastep-like
structure.
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15. 3.GrabenorRiftfault:-
Whenthetwoparallelfaultshadetowardseachotherandrock
bedsbetweenthemarethrowndown,suchstructurecalled
“Graben&Rift.”
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4.Horst:-
Whentwoparallelnormalfaultshadeawayfromone
anotherandrockblockbetweenthemisupliftedto
fromaridge,
thestructure
iscalleda
“Horst.”

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5.RadialFaults:-
Anumberoffaultsexhibitingaradialpatternonthe
groundsurfacearecalled“RadialFaults.”
6.EnechelonFaults:-
Thesearerelativelyshortfaultswhichoverlapeachother.

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7.PeripheralFaults:-
Thecurrentfaultswhichhavenearlycircularand
arc-likeoutcropsonthegroundsurface,arecalled
“PeripheralFaults.”

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The angle at which Fault Dips
1.High angle fault:-Dip greater than 45°
Ex. Normal fault
2.Low angle fault :-Dip less than 45 °
Ex. Thrust fault

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The apparent movement on the fault
1-Normalfault:-
Inthisfaultthehangingwallhavemoveddownwardrelativeto
thefootwall.Inthiscasefaultplanedipstowardthedown
throwside.

21. 2-Reversefault:-
Inthisfaultthehangingwallhavemovedupward
relativetothefootwall.Inthiscasefaultplanedips
towardtheupthrowside.
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22. Onthebasisofforcesresponsiblefortheformationoffaults.
1.Gravity&Tensionfaults:-
Thesefaultsarecomposedbytensionforces.Ex.Normal
Fault
2.CompressionalFaults:-
Thesefaultsareformedbycompressionforces.Ex.
ReverseFault
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3.Transcurrentfaults:-
Thesefaultsareformedbylateralthrust.
Transcurrentfaultsshowmainlyhorizontal
movement.

24. Thank You