Faults are fractures along which the rock masses on either side have moved relative to each other. A fault occurs when movement happens along a discontinuity due to brittle deformation from stress. Faults can be classified in different ways, including based on the apparent movement, dip angle, pattern of faults, and more. Common fault types include normal faults, reverse faults, strike-slip faults, and oblique slip faults. Normal faults occur when the hanging wall block moves downward relative to the footwall, while reverse faults occur when the hanging wall moves upward.

1. Fault

2.  What is faults?
Faults are well-defined cracks along which the rock
masses on either side have relative displacement .There
can be no fault if there is no fracture or clear movement.
A fault is a surface or narrow zone across which there has
been relative displacement of the two sides parallel to the
zone (after Bates and Jackson 1987). The term
displacement is the general term for the relative movement
of the two sides of the fault, measured in any chosen
direction.

4. FOOT WALL
BLOCK
HANGING
WALL
BLOCK
FOOT WALL
BLOCK
HANGING
WALL
BLOCK
FIG: NORMAL FAULT FIG: REVERSE FAULT

5. Fault
• A fault is a mesoscopic to macroscopic plane
(listric faults are curved at large scale!) along
which the two blocks on either side have displaced
(slipped) relative to one another
• The slip is primarily due to brittle deformation
• This distinguishes faults from fault/shear zone
• Deformation in a fault zone is distributed along a set of
closely-spaced faults within a zone
• Deformation in a shear zone is ductile (i.e., high strain
without macroscopic loss of cohesion), involving either
crystal plastic or catraclastic flow mechanisms (or a
combination = semibrittle)

6. Scale of Faults
• The range of size for faults is from:
• microscopic, mm scale (10-3 m), to
• thousands of kilometer (106 m)
• (regional, lithospheric)
• A fault is called a shear fracture if its dimensions are
smaller than one meter

7. Fig: General terminology for a surface (patterned) offset by a fault. Heavy
lines are hangingwall and footwall cutoff lines

8.  DIFFERENT PARTS OF A FAULT
Fault Plane - The plane along which the rock or crustal
material has fractured.
Hanging Wall Block - The rock material which lies above the
fault plane.
Footwall Block - The rock material which lies below the fault
plane.
Dip- It is the angle between fault plane and the horizontal.
Hade- It is angle between fault plane and the vertical.

11. The main terminations related to a fault are given below
throw heave
Fault plane
Foot wall
Hanging wall

12. Fig. Fault separation terminology

13. Fig: Fault slip is the displacement of points (open circles) that were originally in
contact
across the fault. Here the correlated points represent the intersection line of a dike
and
Slip
Fault slip is the relative displacement of formerly adjacent
points on opposite sides of the fault, measured along the
fault surface . Slip can be subdivided into horizontal and
vertical components, the strike slip and dip slip components,
respectively.

15. Strike and Dip
• Strike of the fault is the trend of a horizontal line in
the plane of the faults.
• Dip is the angle that the faults plane makes with a
horizontal surface.

19. Defining Fault Orientation
• Strike of fault plane parallels
the
• fault trace
• fault scarp
• Direction of Dip of the fault
plane indicates the Hanging
wall block
19

20. Fault:
• Movement occurring along a discontinuity
• Brittle strain and subsequent movement as a result of stress
• Fault terminology
20

21. Faults
• Fault: When
movement
occurs along a
discontinuity
• Fault type
depends on the
type of stress
21

22. Normal Faults
22

23. Normal Faults, Horsts and Grabens
23

24. Reverse and Thrust Faults
• Compressive stress causes
the hanging wall to move
upward relative to the foot
wall  Reverse Fault
• At convergent plate
boundaries ancient rocks
can be thrust over younger
rocks  Thrust Fault
24

25. Thrust Fault: Glacier NP, Montana
Old
Younger
25

26. Strike Slip Faults
• Physiographic Features
26

27. Classification of Faults
 Geometrical classification
 Genetic classification

28. Classification of geometrical
faults:-
The bases of five different geometrical
classifications are……………
 The rake of the net slip.
 The attitude of the faults relative to the
attitude of the adjacent rocks
 The pattern of the faults.
 The angle at which the faults dip.
 The apparent movement on the faults.

29.  CLASSIFICATION OF FAULTS
Faults occur in a great variety. It is possible to classify
them into different types on the basis of some common
characters. Among them some are mentioned below:-
 Based on the rake of net slip
Strike slip fault
Dip slip fault
Oblique slip fault

31. On the basis of the movement of rock blocks faults may classified
as follows-
Dip-slip fault
a. Normal fault
b. Reverse fault
Strike-slip fault
a. Dextral or right lateral
b. Sinistral or left lateral
Oblique slip fault
a. Right normal oblique fault
b. Right reverse oblique fault
c. Left normal oblique fault
d. Left reverse oblique fault

32. Normal fault
Reverse fault
Dextral s.s fault
Sinistral s.s fault
Right normal oblique fault
Left normal oblique fault Left reverse oblique fault Right reverse oblique fault

33. Based on amount of dip angle
High angle fault
Low angle fault

34.  Based on attitude of fault relative to attitude of adjacent
beds
Strike fault
Dip fault
Oblique fault
Bedding fault
Longitudinal fault
Transverse fault

35. Strike Fault
• A strike fault is one that strikes essentially parallel to
the strike of the adjacent rocks.

36. Dip Fault
• A fault which strike is perpendicular to the
strike of the adjacent beds.

37. Oblique Faults
• An oblique fault is one that strikes
obliquely or diagonally strike of the
adjacent rocks.

38. Bedding Faults
• Bedding fault is variety of strike fault that is
parallel to the bedding .

39. Longitudinal Fault
• A longitudinal fault strikes parallel to the
strike of the regional structure.

40. Transverse Fault
• A transverse fault strikes perpendicularly
or diagonally to the strike of the regional
structure.

41.  Based on fault pattern
This classification is based by the pattern shown by a fault
on a map i.e. on a horizontal surface or also on a vertical
section.
These are namely:-
Parallel fault
Radial fault
En echelon fault
Peripheral fault

42.  PARALLEL FAULT
If a set of faults have essentially the same dip and strike
they are called parallel faults. If in a series of
parallel faults, whether vertical or inclined, the successive
blocks are downthrown more and more towards a particular
direction, the resulting structure looks more or less like the
steps in a staircase and is known as step fault.

43.  RADIAL FAULT
The word “Radial” comes from the word “Radius”. A
group of faults that appear emerging outward from a
common central region are classed as radial fault.

44.  EN ECHELON FAULT
This may be defined as a group of small size faults that
overlap each other in the region of their occurrence. A
second fault appears on the surface at a distance before
the first fault ends and so on.

45.  PERIPHERAL FAULT
The word “Peripheral” comes from the term “Periphery”.
These are circular or arcuate faults that bound a circular
area or part of a circular area. In such type majority of
faults are concentrated along the border or margin of the
area.

46. On the basis of apparent
movement of fault
1.Normal fault
2.Reverse fault

47. Genetic classification of fault
1 . Normal (gravity) fault
2. Thrust fault
3. Reverse fault
4. Over thrust fault
5. Horst
6. Graben

48. NORMALFAULT
• NORMAL FAULTS are the dip slip fault along
which hanging wall block has moved down with
respect to the footwall block.

50. NORMAL FAULT AT THE MOAB ROADCUT

51.  Normal faults are also called EXTENTION
FAULT.
 Normal fault shows YOUNGER-ON-OLDER
relationship.

52. The red line marks equivalent layers on opposite side
of the fault. Since the hanging wall dropped relative to
the footwall, this is clearly a normal fault.
Thick limestone beds in northerm Mexico,
by Norris W. Jones

53. TYPES OF NORMAL FAULT
• BOX FAULT : A network of faults, that developed
between two overlapping normal fault.
• BASEMENT FAULT: A fault that cuts the basement of a
rock layer. This fault is originated before deposition of
upper sediments and that may be reactivated.
• DECOLLEMENT FAULT: A bedding or layer parallel
fault above which the rock may be deformed.

54. • SYNTHETIC FAULT: A minor fault that is dipping
in the same direction to the master fault.
• ANTITHETIC FAULT: A minor fault that is
dipping in the opposite direction to the master fault.

55. THE SYNTHETIC AND ANTITHETIC NORMAL
SYNTHETIC
ANTITHETIC

56. • GROWTH FAULT: Growth fault is a particular type of normal
fault that develops during ongoing sedimentation, so the strata
on the hanging wall side of the fault tend to be thicker than
those on the footwall side.
Schematic diagram of growth fault

57. • DETACHMEMT FAULT: It is a low angle normal fault, along
which there has been considerable horizontal displacement.

58. IMBRICATE FAULTS: Imbricate faults are closely spaced parallel
faults of the same type that either terminate against or merge
with the detachment fault.

59. STRUCTURAL ASSOCIATION OF NORMAL FAULT:
HORST ANDGRBANSTRUCTURe :
An elongated faulted block, which goes down
between two oppositely dipping normal fault is
called GRABEN.
A linear uplifted block between two normal
fault is called HORST.

60. HORST AND GRABEN STRUCTURE

61.  Sometime Graben may form because of the
downthrow on a single fault or a single set of
fault, such graben are known as HALF GRABEN
HALF GRABEN

63. Fault Type
• Listric fault:
• The dip of the fault varies with depth.
• Fault bend:
• Is where both the dip and strike of a fault changes.
• Flat:
• A fault which is locally parallel to the bedding (in the
hanging wall or the footwall).
• A fault parallel to bedding in the hanging wall may
be across the bedding in the footwall, and vice
versa!
• Ramp: A fault which is locally across bedding

64. Ramps/Flats before & after Thrusting

65. Fault Surface Structures
• Fault displacement produces friction-related striations
(polishing and grooving) indicating the latest, local direction
of movement and sometimes absolute direction of
movement
• The slip lineation are called slickensides or slickenlines
• Fiber growth in the direction of fault displacement, on the
slickensided surface, provide clear indications of relative
offset
• Extensional fractures occur at a high angle to slip direction
and dip steeply into fault plane

66. Structural features to Recognize Faults
• polishing and grooving
• slickensides
• breccia
• gouge
• mylonite
• shear zone
• associated fractures
• drag of layers adjacent to fault
• juxtaposition of dissimilar rock types
• displacement of planar structures

67. Fault
Breccia

68. Clay
Gouge

69. Mylonite vs. Cataclasite

70. Geomorphic features
• fault scarp
• fault-line scarps
• triangular facets
• alignment of facets
• increase of stream gradients at the fault line
• hanging valleys
• aligned springs and vegetation
• landslides
• displaced stream courses

71. Fault Scarp

72. Fault-line scarp caused by
faulting of a resistant layer

73. EFFECTS OF FAULTING:-
 Effects of strike faults:-
1. Repetition
2. Omission

74. Effect of Dip Fault
• Horizontal shifting

75. Causes of these Faulting:-
These faults are generally caused under the
influence of stresses acting upon the rocks
of the crust on the earth from within.

76. Mechanics of faulting
Fault is a fracture discontinuity in rock along which the rock blocks
of each side have move past each other.
Fault is the result of brittle deformation in rock..
s
t
r
a
i
n
stress
brittle
Brittle- ductile
Ductile

77. For formation of fault a rock must have some fracture on its
surface due to the action of stress.
Fracture are mainly of two types.
A. Extension fracture
B. Shear fracture or Conjugate fracture
MECHANICAL ASPECTS OF FAULTING

78. Fig- Extension fracture
σ1
σ2
σ3
Extension fracture develops
Due to axial extension stress.
i.e in a condition
σ1=σ2>σ3>0

79. σ1
σ2
σ3
Fig- Shear fracture
Shear fracture are developed
Mainly due to the axial
compression Stress.
i.e in a condition where
σ1>σ2=σ3>0

80. Fault is nothing but a shear fracture.
σ1
Θ
Ø
It is experimentally proved that
In shear fractures the angle
Between the maximum principal
Stress and fault plane ( ) is
always less than 45 ⁰
Θ

81. Fig- normal fault
Ø
Here the dip of the fault plane ( ) is
always greater than 45⁰ .
Ø
σ1
σ1
σ2
σ3

82. Ø
Maximum
Compression
+ σ1
σ3
σ1
σ2
Fig- reverse fault
Here dip of the fault plane( ) is
Always less then 45⁰
Ø

83. Fig- strike- slip fault
σ1
σ2
σ3
Here the fault planes are vertical

84. In laboratories fault can be created with a instrument called triaxial rock
testing system.

85. Outer piston
Inner piston
Pressure vessel
Rock specimen
Yoked
Base plate
Fig- Triaxial testing system

86. With this apparatus we can measure the strength of any rock, which is
called the shearing resistance of the rock under geologically realistic
Stress conditions. Such conditions are those in which all three principal
stress have nonzero magnitudes, and accordingly the test is called
Triaxial test.
There are two types of triaxial test
σ1
σ3
σ3 σ1
Triaxial compression
Triaxial extension

87. The shearing resistance or the range of mechanical stability of
a particular rock in any confining stress can be examined by
triaxial test and it can also established with MOHR STRESS
DIAGRAM.
Suppose we want to establish the range of mechanical stability of
limestone for several different confining pressure conditions.
For this purpose we have to take three limestone specimen..
Specimen-1 Specimen-2 Specimen-3
Confining pressure 4,000 Pa 15,000 Pa 30,000 Pa
Differential stress at
failure
18,000 Pa 46,000 Pa 80,000 Pa
σ1 at failure 22,000 Pa 61,000 Pa 110,000 Pa
σ3 at failure 4,000 Pa 15,000 Pa 30,000 pa
Θ between fault plane
& σ1
25⁰ 30⁰ 33⁰

88. σ1
σ3
σN σs
& at failure
0 15 30 60 105 σN
σs
15
30
60

89. Now with the help of this Mohr failure envelope we can find the magnitude
of the greatest principal stress that would be required to create faulting
in limestone under any confining pressure.
Mohr- coulomb law of failure
The characteristics of failure envelope can be understood in the context
Of Mohr- Coulomb law of failure. A law based on the dynamic models
presented by Charls Coulomb (1773) and Mohr (1900).
The law describes the critical shear stress level ( ) which is required to
break a rock.
Mathematical expression of the law
σs σN
Ø
=C+tan ( )
σs
Where, σs= Shear stress at the failure point
C = Cohesive strength of the rock
σN = Normal stress(σ1 ) at instant of failure
tan( )
Ø = Coefficient of internal friction
Ø = Slope of the failure envelope

90. CONCLUSION
From the above discussion we can understand Mechanical analysis of
faulting is concerned both with the orientation of faults relative to stress
patterns.
Why faults can be so conveniently separated into normal, reverse and
strike slip categories.
We learn that there is a mechanical fact that on average strike-slip fault
Dip vertically, normal faults dip at 50-60⁰ and reverse fault dip at 30⁰ .

91. BIBLIOGRAPHY
www.google.com
www.wikipedia.com
Structural geology – By: Billings
Engineering & general geology- By: Parbin Singh

92. Classification of Faults (1)
• Faults are classified according to:
• The dip of the fault.
• The direction of relative movement. (slip)
• Normal faults (正斷層) are caused by
tensional stresses that tend to pull the crust
apart, as well as by stresses created by a push
from below that tend to stretch the crust. The
hanging-wall block moves down relative to
the footwall block.

93. Figure 9.13

94. Figure 9.13B

95. San Andreas Fault

96. Classification of Faults (2)
• A down-dropped block is a graben (地塹), or a rift (張裂), if
it is bounded by two normal faults.
• It is a half-graben (半地塹) if subsidence occurs along a
single fault.
• An upthrust block is a horst (地壘).

97. Figure 9.14

98. THANK YOU