The document discusses faults in terms of geology. It begins by defining a fault as a fracture between rock blocks that have moved relative to each other parallel to the fracture plane. It then discusses different types of faults including normal faults, strike-slip faults, and oblique slip faults. It provides examples of key features associated with different fault types, such as horsts and grabens associated with normal faults, and flower structures associated with strike-slip faults. The document also discusses methods for recognizing faults based on geological, fault plane, and physiographic evidence observed in the field.

1. FAULT IN TERMS OF GEOLOGY
RAJR
RAJA,BIBEK & PALLAVI
EARTH SCIENCE
NIT ROURKELA
RAJA,BIBEK & PALLAVI
EARTH SCIENCE
NIT ROURKELA

2. Main objectives
o What is fault ?
o Parts of the fault
o classification of faults
based on relative
movement between wall
o Some global examples
o Relation between slip and
separation
o Transform fault &
transcurrent fault
o Mechanism of
faulting(Anderson’s
Theory)
o Recognition of faults
o Relation with tectonics
o Focal mechanism
o Role of fluids in faulting
o Significance of fault
o others

3. • Brittle fault
> A fault is a discrete fracture between blocks of rock that have been displaced
relative to each other, in a direction parallel to the fracture plane.
> A fault zone is a region containing several parallel or anastomosing (i.e.
branching and reconnecting) faults.
> Any fault-bounded sliver in a fault zone is a horse. Fault and fault zones are
identified either when an earthquake occurs or by geological mapping showing
that motion across a discontinuity has occurred in the past. On geologic maps,
only faults that affect the outcrop pattern are usually shown.
FAULT- faults are defined when two adjacent blocks of rock have moved past
each other in response to induced stresses. The notion of localized movement leads
to two genetically different classes of faults reflecting the two basic responses of
rocks to stress: brittle and ductile.

4. Ductile fault
>Shear zones are the analogues in a ductile material of faults in a brittle material.
>Shear zones are regions of localised but continuous ductile displacement, formed
under conditions of elevated temperature and/or confining pressure, in contrast to
fault zones that are regions of localised brittle deformation.
>Shear zones are thus ductile faults, by contrast to the brittle faults.

5. Geometrical classification
Fault plane
Faults dipping more than 45° are called high angle faults; Faults dipping less than
45° are called low angle faults. In general, fault surfaces are curved. Undulation of
fault-surfaces is commonly seen in 3D seismic data. The fault corrugations thereby
identified are attributed to the linkage of fault-segments through time. A listric
fault is a curved, concave upward fault, that is, it gradually flattens with depth.
Where low-angle faults affect a set of nearly horizontal bedded rocks, they generally
follow a staircase path made up of alternating ramps and flats. The flats are where
the overlying rocks slide along a relatively weak bedding plane also called a
décollement plane, which refers to a surface across which there is a discontinuity in
displacement, strain or fold style. The ramps are fault sections climbing through the
stratigraphic sequence, typically at around 30° to the horizontal, across stiff,
competent layers. Ramps do not necessarily strike perpendicular to the movement
direction (frontal ramp) but are also found oblique or parallel to the transport
direction (lateral ramp or tear fault).

6. Parts of the Fault• Fault plane: Surface that the movement has
taken place within the fault.On this surface
the dip and strike of the fault is measured.
• Hanging wall: The rock mass resting on the
fault plane.
• Footwall: The rock mass beneath the fault
plane.
• Slip: Describes the movement parallel to the
fault plane.
• Dip slip: Describes the up and down
movement parallel to the dip direction of the
fault.
• Strike slip: Applies where movement is
parallel to strike of the fault plane.
• Oblique slip: Is a combination of strike slip
and dip slip.
• Net slip (true displacement): Is the total
amount of motion measured parallel to the
direction of motion

7. BRITTLE AND DUCTILE FAULTS
Brittle faults occur in the upper 5 to 10 km
of the Earth’s crust. In the upper crust
consist of :
Single movement
Anastomosing complex of fracture
surfaces.
The individual fault may have knife-sharp
contacts or it may consist of zone of
cataclasite.
At ductile-brittle zone 10-15km deep in
continental crust, faults are
characterized by mylonite. At surface
of the crust mylonite may also occur
locally where the combination of
available water and increased heat
permits the transition.
The two types of fault may occur within one
fault where close and at the surface
brittle the associated rocks are cataclasts
and at deep where ductile and brittle
zone mylonite is present

8. • Separation: The amount op
apparent offset of a faulted
surface, measured in
specified direction. There
are strike separation, dip
separation, and net
separation.
• Heave: The horizontal
component of dip separation
measured perpendicular to
strike of the fault.
• Throw: The vertical
component measured in
vertical plane containing the
dip.

9. DESCRIPTION OF FAULT DIP
Horizontal faults Faults with a dip of about 0°; if
the fault dip is between about10° and 0°, it is called subhorizontal.
Listric faults Faults that have a steep dip close to the Earth’s surface and have a
shallowdip at depth .Because of the progressive decrease in dip with depth, listric
faultshave a curved profile that is concave up.
Moderately dipping Faults with dips between about faults 30° and 60°.
Shallowly dipping Faults with dips between about
faults 10° and 30°; these faults are
also called low-angle faults.
Steeply dipping faults Faults with dips between about
60° and 80°; these faults are also called high-angle faults.
Vertical faults Faults that have a dip of about90°; if the fault dip is close to90° (e.g., is
between about 80°and 90°), the fault can be called sub vertical Rake angle Net slip Dip-
slip.

10. FAULT CLASSIFICATION AND TERMINALOGY
Faults: Are fractures that have
appreciable movement parallel to
their plane. They produced usually be
seismic activity.
Understanding faults is useful in design
for long-term stability of dams,
bridges, buildings and power plants.
The study of fault helps understand
mountain building.
Faults may be hundred of meters or a
few centimeters in length. Their
outcrop may have as knife-sharp
edges or fault shear zone. Fault
shear zones may consist of a serious
of interleaving anastomosing brittle
faults and crushed rock or of ductile
shear zones composed of mylonitic
rocks.

14. Normal Fault
• Maximum principal
stress σ3(compressive stress) vertical
• Minimum principal
stress σ1(tensile stress) horizontal
Normal fault have dominant dip slip component, where hanging wall
move down relative to the foot wall. The hanging wall of normal fault
either dipping in same direction or in the opposite direction these are
described as synthetic fault and antithetic fault.

15. Displacement On Normal Fault

16. Normal FaultNormal Fault: The hanging wall has moved down relative to
the footwall.
Graben: consists of a block that has dropped down between
two subparllel normal faults that dip towards each other.
Horst : consists of two subparallel normal faults that dip away
from each other so that the block between the two faults
remains high.
Listric: are normal faults that frequently exhibit (concave-up)
geometry so that they exhibit steep dip near surface and
flatten with depth.
Normal faults usually found in areas where extensional regime is present.

17. • Growth faults are faults that operate during sedimentation and
therefore displace an active surface of sedimentation. They are
dominantly listric. They form characteristically, but not exclusively, in
unconsolidated sediments freshly deposited in basins that are actively
growing in breadth and depth .As a clear result, sediments or specific
layers are thicker on the hanging-wall than sediments and layers of the
same age on the footwall.

18. Pure shear or simple shear??

20. Planar faults
Planar, rotational normal faults occur above a basal detachment or a brittle-
ductile transition. They separate juxtaposed and tilted blocks without internal
deformation. Both the faults and fault-blocks rotate simultaneously about an
axis roughly parallel to the strike of the faults (rigid body rotation resulting in
domino or bookshelf faulting).
Each fault block has its own half graben. Each fault must have the same
amount of displacement and tilting or there are space problems at the bottom
of the system (opening of voids). Planar, rotational faults and blocks generally
abut against transfer, scissors faults.

21. Structures at Divergent Boundaries
• Tensional Stresses cause brittle strain and
formation of sets of normal faults
• i.e., Horsts and Grabens

22. Horsts and Grabens
• Older Rocks are exposed along the ridges formed by
the horsts
• Younger rocks lie beneath the grabens
• Sediment fills in the linear valleys
Hr Horst
t
Graben
Horst
Graben
Horst
Graben

23. Nevada
• “Washboard topography”
is the result of Horsts and
Grabens
• A.k.a, Basin and Range
• E.g., Humbolt Range
• E.g., Death Valley
(Graben)

24. Horst and Graben, Nevada
Humboldt Range, Northern Nevada
Graben
Horst

26. Tectonic Settings for Extension
• Divergent plate motions
• Gravitational collapse
– Over-thickened crust
– Continental margins
• Salt Domes

27. Continental
Extension

28. Rifts
Bounded by
normal faults

29. Lithospheric Extension
•Thinning of the lithosphere
•Normal faulting at the surface
•High heat flow (rising of the isotherms)
•Thermal subsidence - > sedimentary basins
North Sea Extensional Basin

30. Normal Faults(global examples)
IRAN

31. STRIKE-SLIP FAULT & OBLIQUE SLIP FAULT

32. Strike-slip Fault
• Both maximum and
minimum principal
stresses horizontal
• Intermediate
principal stress σ2
Vertical.

33. Strike-slip fault which have dominant strike slip component. It is mainly
two type Dextral and Sinistral. If looking across the fault plane the opposite wall appears to
moved towards the right, is called “Dextral or right handed fault”.
If looking across the fault plane the opposite wall appear to move toward left, is called “Sinistral
or left handed fault”.
Example of strike-slip fault are Alpine Fault of New Zealand, San Andreas Fault of California etc.

34. Transform Faults
 Transform fault are a type of
strike-slip fault (defined by
Wilson 1965).
 Transform faults end at the
junction of another plate
boundary or fault type.
 In addition, transform faults
have equal deformation across
the entire fault line.
 They are basically occur
where type of plate boundary is
transformed into another.
Main types of transform faults are:
• Ridge-Ridge
• Ridge-Arc
• Arc-Arc

35. Transcurrent or Wrench Fault:-
 In strike-slip fault the relative
displacement of block is
horizontal.
The fault plane of a strike-slip
fault is vertical and often extends
for long distances.
Transcurrent faults have greater
displacement in the middle of the
fault zone and less on the margins.
Because these fault are strike
across they are called
“transcurrent”, or “wrench” fault.

36. Tear fault:- It is a strike slip fault that runs across the strike of a contractional
or extensional belt and accommodates differential displacement between
two segments of the belt.

37. Transfer fault:-
A transfer fault is a strike slip fault that
transfers displacement between two
similarly oriented fault segments (e.g.
two normal faults).
Transfer faults are usually confined to
hanging walls of detached systems (i.e.
not affecting the basement) and
terminate where they connect the linked
faults.
transfer faults linking two thrusts or
normal faults are therefore nearly parallel
to the movement direction .
Transfer zones (faults) usually terminate
where they connect to and terminate
other faults or structures .

38. Large strike slip faults are often curve or made up of zone of “ En echelon
faults” (short faults are overlap each other) movement on such fault
system can cause extension or shortening in the bent region of the fault.
Whether an extension or shortening will occur will depend on whether
the fault is right lateral or left lateral.

39. Development of a Pull-Apart Basin(Transtension):-
A right lateral -right stepping or left lateral-left stepping fault will produce extension
on bend zone causes large scale pull apart movement by produce normal fault on
this zone. Pull- apart may also underlain by flower structures(negative flower
structure) . The fault associated with these structure combination of Normal and
Strike slip faults .

40. Normal (-) Flower Structure - Tulip

41. Development of a Restraining Bend(Transpression):-
A right lateral- left stepping or left lateral-right stepping fault will produce shortening on
the bend zone causes uplift or push up with development of flower or palm tree structures
by produce reverse fault on this zone.
Similarly push apart may also contain flower structures(Positive flower structure). The fault
associated with this structure combination of reverse and strike slip faults.

42. Reverse (+) Flower Structure - Palm

43. Summary of Flower Structures - Palms & Tulips

44. Oblique Slip Fault:-
• Where the strike slip and dip slip displacements are similar in magnitude,
the fault can be called an oblique slip fault.
• Depending on whether the opposite wall moves towards right or left and
whether the hanging wall moves relatively up or down oblique slip fault
further sub divided into four type

45. Evidence of Faulting
• Recognition of fault in the field can divided into three group:- I)geological
evidences, II)Fault plane evidences, III) Physiographic evidences.
• A)Geological evidences:- The most imp geological evidences of faulting are:-
• 1)Offset of rock unit:- Displacement of rock bed, dyke, vein, etc. Occurs on opposite
site of a fault.
• Offset of quartz vein
• 2) Repetition and omission of strata:- In a traverse line, the outcrop of a bed may be
repeated in cyclic order or it may disappear. Such repetition or omission of bed often
establishes a fault.
• 3) Stratigraphic sequence:- The normal stratigraphic sequence of a region may
disturbed by faulting. When older strata occur above younger strata, this type
disturbence is mainly done by thrust fault.

46. B) Fault Plane Evidences:-
• Fault plane contain some structures which are found associated with faults. Most
imp evidences are :-
• 1)Feather joints:- Feather joint are the tension joint formed due to fault
movement, and is found in the fault plane. These joint intersect the fault plane at
an acute angle. This acute angle points towards the direction of movement along
fault plane.

47. 2)Slickensides:-The movement of one block against another block result polishing and
grooving of fault surfaces. These grooved and striations are called slickensides.
Slickensides are useful to knowing the direction of the last movement on a fault
surface. This also indicate the direction of the net slip on the fault plane.

48. 3)Drag:- This structure found in the fault zone. The end of strata may bend up
and down formed due to frictional resistance of the bed on the fault plane.
For normal dip slip fault the hanging wall dragging up and the foot wall
dragging down.

49. 4)Fault Breccia and Gouge
• Along some faults the rocks are highly
fracture or crushed to angular fragment.
• Angular grains are embedded in a finely
grounded rock are called “faulted breccia”.
• Secondary mineral such as quartz, calcite,
or some pyrite fill the open space of
faulted breccia.
• Faulted breccia are crused again by
faulting it may be ground to fine clay like
powder called “Gouge”. The gouge is
frequently polished and striated by fault
movement.
Fault Breccia

50. 5)Silicification and
Mineralization:-
Fault are basicaly fracture they
often act as a channel way of
moving solution. The solution
may replace the country rock
with quartz grain in called
silicification. Fault plane also
act as passages for mineralizing
solution and many mineral
deposit are formed in the fault
plane is called mineralization.

51. Shiny slickensided surface in Paleozoic
strata of the Appalachians (Maryland, USA);
coin for scale.
(b) Slip fibers on a fault surface, showing steps
that indicate
sense of shear; compass for scale
(b)
Banded clay gouge from the
Lewis Thrust (Alberta, Canada).
(a) Fault breccia from the Buckskin
detachment (Battleship Peak, Arizona,
USA)

52. C) Physiographic Evidences
 The physiographic evidences are seen clearly from a distance or an aerial
photograph . The chief physiographic evidences are i) Fault scrap, ii)Fault line
scrap, iii)Fault Control of Streams.
 I) Fault Scrap:- A steep straight slope is called the scrap. It formed as a result of
faulting. It found only in those area where fault has been geologically very recent.
Fault scrape face in the direction of down throw side.
A reverse-motion, fault-line
scarp from Mongolia.

53. II)Fault Line Scrap:- Fault frequently bring together resistant and non resistant
rock beds. A ridge may formed along a fault due to process of unequal erosion.
Such ridge are called the “fault line scrap.

54. MECHANISM OF FAULT
(ANDERSON’S THEORY)

55. Anderson’s theory of faulting
• Anderson has proposed a theory which explain a large number of fault in
the shallow crust.
• Anderson argues that there can not be any shear stress on the free
surface of the earth, one of the principle stress axes should be vertical,
consequently the other two stress axes are horizontal.
• We get three type of fault depending on whether the tensile stress
axis(o3), the compressive stress axis(o1),the intermidiate stress axis(o2).
• A) Normal fault:- In this case, the compressive stress(o1) will be
vertical and hence the fault will be at an angle with the vertical. Thus, the
fault will strike parallel to the o2 axis and will dip at angle 60-70°. The
upper block will move down along the dip direction and will give rise to
dip slip normal fault.

56. B) Reverse fault:- In this case, the tensile stress (o3) is vertical and the stresses o2 and o1 in
the horizontal direction will be unequal. The fracture will strike parallal to o2 and inclined to the
horizontal o2 axis. So the upper block move up along the dip direction and will give rise to dip slip
reverse fault. Moreover, the upper block will move up the slope in a direction perpendicular to o2 .
Thus, trust fault dipping at an angle of abut 20-30° will be produced.
C) Strike- slip fault:- In this case , the intermediate o2axis is vertical, the fault s will also be
vertical. The movement along fracture will be at right angle to the o2 axis, the fault will be strike-
slip fault.
The general conclusion of Anderson’s theory is that among three types of faults in the shallow crust,
the reverse fault will be low dipping(<45°), the normal fault will moderately dipping(>45°), and
strike-slip fault will be vertical.

58. REVERSE FAULTREVERSE FAULT
If the hanging wall has moved up with respect to
the foot wall then the fault is called reverse fault.
Reverse fault are those which have dominant dip-
slip component.
 Here older rocks occure above younger rocks.
Reverse fault with a low angle (<45) are called
thrust fault.
 Low angle thrust fault is called overthrust (here
net slip is large).

59. Reverse fault results by compression

60. Older rocks above younger rocks
here in over thrust , net slip= stratigraphic throw/dip of
the fault plane

61. TERMINOLOGY
• Klippe :- A closed
outcrop of a thrust sheet
isolated from the main
mass by erosion is called
klippe (outlier)
• Window:- A closed
outcrop of the
substratum of a thrust
sheet framed on all sides
by the thrust surface is
known as window(inlier)

62. Autochthonous:-
The rocks of the foreland are essentially found where
they were deposited.
Allochthonous:-
The rocks in the overthrust sheets have traveled many
miles from their original place of deposition.

64. LEADING IMBRICATE FAN- Here the thrust infront
has the maximum slip.
TRAILING IMBRICATE FAN- Here the thrust at the
rear shows the maximum slip.

65. DUPLEX
. Duplex is a thrust mass which is bounded by
a floor thrust and a roof thrust.
Duplex structure are imbricated.
A prominant low angle thrust occure beneath
some thrust system is called floor thrust or
sole thrust.
The upper thrust is called roof thrust

66. DUPLEX STRUCTURE

67. DEVELOPMENT OF THRUST DUPLEX

68. HINTERLAND-DIPPING DUPLEX
The imbricate faults in a
duplex dip towards the
hinterland is called a
hinterland dipping
duplex.
Blocks are surrounded
by thrust are called
horses.
Usually composed of
upward facing horses.
Here
displacement<length of
horse

69. ANTIFORMAL STACK
Here displacement in
the individual horses is
greater such that each
horses lies more or less
vertically above the
other.
Horses are bunched up
in the form of antiform.
Displacement=Length of
horse.

70. FORELAND-DIPPING DUPLEX
 Usually composed of
downward facing horses.
 Here
displacement>length of
horse
 If the individual
displacement is greater
still then the horses have
a foreland dip.

71. THRUST GEOMETRY
Tip line- The relative
displacement must fade
out outward,where it
drops to zero is called
tip line.
Tip line separates
slipped rocks from non-
slipped rocks.

72. Branch line-Two faults meet along a branch line.
A tip line and branch line meet along a tip point
and branch point.
A subsidiary thrust may branch out as a splay
from the main thrust.
4 types of splay- Isolated splay
 Diverging splay
 Rejoining splay
 Connecting splay

73. • Isolated splay-Two tip points of
the splay are exposed. Trace of
the fault is isolated from the
main fault.
• Diverging splay-Here single tip
point and branch point are
exposed on the erosion
surface.
• Connecting splay-It connects
two different faults. Two
branch point of the splay are
exposed.
• Rejoining splay-Tip line is not
exposed. The ground surface
meets the main fault at two
branch points.

74. RAMP AND FLAT
• Ramps and flats are step like structure.
• Flats are fault surfaces that form parallel to the
strata(usually weak rock units evaporites and shale).
• Ramps cut across a dip angle of 30 to 45(usually
resistant rock units sand stone and lime stone).
• Ramps are classified in to 3 types(according to
transport direction).
1. Frontal ramp
2. Lateral ramp
3. Oblique ramp

75. • Frontal ramp- Strikes roughly perpendicular
to the transport direction(dominant reverse
dip slip).
• Lateral ramp- Strikes roughly parallel to the
transport direction(dominant strike slip).
• Oblique ramp- Strikes oblique to the
transport direction(both strike slip and reverse
dip slip).

77. THRUST RELATED FOLDS
• Backlimb thrust:-
A thrust cutting across
gentler backlimb of an
asymmetric fold is called
backlimb thrust.
Forelimb thrust:-
A thrust cutting across
steeper forelimb of an
asymmetric fold is called
forelimb thrust.

78. • Stretch thrust:-
It developes at an advance
stage of folding by
stretching and shearing
out of overturned limbs.
Break thrust:-
Here the thrust cuts the
forelimb at a large angle.

79. FAULT PROPAGATION FOLD
 A fold generated by propagation of
a thrust tip over a ramp in to
undeformed strata.It forms at the
tip of a thrust fault where
propagation along the decollement
has ceased but displacement on
the thrust behind the fault tip is
countinuing.
• The countinuing displacement is
accomodated by the formation of
an asymmetric anticline syncline
pair.
• As displacement continues the
thrust tip starts to propagate along
the axis of syncline. Such str is also
known as tip line fold.

80. FAULT BEND FOLD
• Fault bend fold:- Fold generated by movement
of a thrust sheet over a ramp.

81. POP UP STRUCTURE
• It is a lifted up triangular
area.
• A section of hanging wall
strata that has been uplifted
by the combination of
foreland thrust and hinter
land thrust.

82. • There are two models of
thrust propagation:-
 Piggy-back model:-older
thrust are structurally
higher up and younger
thrust are lower in
sequence.
 It is consider the normal
mode of propagation in
thrust system.
 Over step model:- Opposite
to piggy-back model.

83. Other types of fault
• en-echelon faults: Faults that are
approximately parallel one another
but occur in short unconnected
segments, and sometimes
overlapping.
• Radial faults: faults that are
converge toward one point
• Concentric faults: faults that are
concentric to a point.
• Bedding faults (bedding plane
faults): follow bedding or occur
parallel to the orientation of
bedding planes.

84. (a) Microscopic
faults, showing fractured and
displaced feldspar grains.
(b) Mesoscopic faults cutting thin layers
in an outcrop.

85. SHEAR-SENSE INDICATORS FOR
BRITTLE FAULTS AND FAULT ZONES
Steps on slickensides Microscopic steps develop along slickensided surfaces.
Typically the face of the step is rougherthan the flat surface. However,
slickenside steps may be confused with the intersection between pinnate
fractures and the fault, giving an opposite shear sense.
Offset markers You can define shear sense if you are able to define the relative
displacement of two piercing points on opposite walls of the fault, or can calculate
the net-slip vector based on field study of the separation of marker horizons.
Fault-related folds The sense of asymmetry of fault-related folds defines the shear
sense. Typically, fault-inceptionfolds verge in the direction of shear (see Chapter 11
for a definition of fold vergence). If the hingesof folds in a fault zone occur in a range
of orientations, you may need to use the Hanson slip-linemethod to determine shear
sense. Note that the asymmetry of rollover folds relative to shearsense is opposite to
that of other fault-related folds.
Fiber-sheet imbrication The imbrication of slip-fiber sheets on a fault provides a clear
indication of shear sense. Fibersheets tilt away from the direction of shear.

86. Carrot-shaped grooves Grooves on slickensides tend to be deeper and wider at one
end and taper to a point at the other,thus resembling half a carrot. The direction in
which that “carrot” points defines the direction of shear.
Chatter marks As one fault block moves past another, small wedge-shaped blocks
may be plucked out of theopposing surface. The resulting indentations on the fault
surface are known as chatter marks.
Pinnate fractures The inclination of pinnate fractures with respect to the fault
surface defines the shear sense
En echelon veins En echelon veins tilt toward the direction of shear. If the veins are
sigmoidal, the sense of rotationdefines the shear sense.

87. Faulting & Stress

89. Focal Mechanism

90. Role of fluids in faulting
Fluids plays an important role in faulting. They
have a lubricating effect in the fault zone as
buoyancy that reduces the shear stress
necessary to permit the fault to slip. The
effect of fluid on movement is represented as
in landslide and snow avalanches.

91. Other factor that control the type of movement is
the curvature of the fault surface.
• Withdrawal of ground water may cause near surface
segments of active faults to switch mechanisms from
stable sliding to stick slip, thereby increasing the
earthquake hazard.
• Pumping fluid into a fault zone has been proposed as a
way to relieve accumulated elastic strain energy and
reduce the likelihood of large earthquake, but the rate at
which fluid should be pumped into fault zone remains
unknown.

92. Fault Surfaces and Frictional sliding
Fault surfaces between two large
blocks are always not planar
especially on the microscopic
scale. This irregularities and
imperfections are called
asperities increase the
resistance to frictional sliding.
They also reduce the surface
area actually in contact. The
initial contact area may be as
little as 10%, but as
movement started the
asperities will break and
contact will be more.

93. Shear (frictional) Heating in Fault zonesDuring movement of faults frictional heat
is generated due to the mechanical
work. The heat generated can be
related to an increase in temperature.
This friction heat is indicted by the
formation of veins pseudotachylite
(false glass) in many deep seated fault
zones and the metamorphism along
subduction zones (greenschist and
blueschist facies).
In some areas there is indication of
temperature of 800ºc and 18 to 19 kb
(60km depth). This indicate that they can
form in the lower crust or upper mantle.
Fault zones may also serve as conduit for
rapid fluxing of large amounts of water
and dissipation of heat during
deformation.
Generally friction-related heating along
faults is a process that clearly occurs in
the Earth, but difficult to demonstrate.

94. Structural Oil Traps

95. • REFERENCES-
S.K.GHOSH-STRUCTURAL GEOLOGY
ROBERT J. TWISS ELDRIDGE M.MOORES-
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