Structural Geology-Fault

Developed By : Prof. A. K. Baile
Assistant Professor of Engineering Geology

• Summary
CONTENTS

Unit 1
Unit 2
Unit 3

Unit 4:
Unit 5: Provides i

After navigating through this e-content and
actively interacting with it, you will be able to:
OBJECTIVES
1.0 Appreciate the background of study of faults
in Civil Engineering
1.1 Define Structural Geology
1.2 State reasons for use of structural
geology studies in civil Engineering
works

2.1 Explain relationship between geological
structure and plate boundaries
2.2 Explain different types of plate
boundaries
2.3 Describe tectonics stresses results
from Internal Energy
2.4 Define Dip and Strike
2.0 Describe various geotectonic forces
are responsible for structural
deformation in rocks
….OBJECTIVES

3.0 Explain Fault and elements of fault
3.1 Define Fault
3.2 Explain Elements of fault
….OBJECTIVES

4.1 Enlist types of fault
4.2 Classification of fault:
4.2.1 Classify fault on the basis of the
relationship between the direction of
slip and the attitude of the fault plane
4.2.2 Classify fault on the basis of
apparent movement of blocks
4.2.3 Classify fault on the basis of fault
pattern
4.0 Classify and describe the different types
of fault
….OBJECTIVES

5.0 Explain Reorganization of fault in the
field
5.1 Identify fault in the field
….OBJECTIVES

Structural geology: is a subfield within
geology which focuses on the study of
geological structures like fault, fold, joints and
unconformities, with the goal of learning how,
when, and why they formed.
FAULT

Geotectonic : is the study of processes
which control the structure and properties of
the Earth's crust, and its evolution through
time.
In particular, it describes the processes
of mountain building, the growth and behavior
of the strong, old cores of continents known
as cratons, and the ways in which the
relatively rigid plates that comprise the Earth's
outer shell interact with each other.

1.2 Reasons for use of structural geological
studies in civil Engineering works:
1. In the rock beds If the geological structure
like faults, joints, bedding planes folding
and solution channels are properly located
and suitably treated, then stability of civil
engineering structures can be increased.
2. Faults are most troublesome if they are en-
countered across the length of the dam,
therefore detail study of movements of fault
is important.

3. Many rocks contain structures like
stratification, foliation and lamination. Such
rocks bear greater loads if they are placed
in the construction parallel to the plane of
weakness.
4. Careful geological studies brings out the
advantages or disadvantages of a site and
such studies go a long way either in
reducing or in increasing the cost of
various civil engineering projects.

2.1 Geological structure and plate
boundaries:
 Each of the three different types of plate
boundaries produces different tectonic
stresses and therefore different kinds of
structures.
 Extensional stress at a divergent
boundary produces normal faults and
sometimes grabens, but little or no folding
of rocks.

 Where as transform boundary crosses
continental crust, shear stress bends and
fractures rock.
 Frictional drag between both sides of the fault
may fold, fault an uplift nearby rocks. Forces
of this type have formed the mountain ranges
of north of the Himalayas.
 In contrast, compressive stress commonly
dominates a convergent plate boundary. The
compression produces folds, reverse faults
and thrust faults.
boundaries:

 As a result of continent–continent
collisions i.e. Indian plate and Eurasian
plate. The rocks of Himalayan terrain get
folded as well as faulted.
boundaries:

2.2:Types of Plate Boundaries-
Depending on the relative motions of adjacent
plates, the plate boundaries are classified into
three groups:
Plate
boundaries
Divergent
boundary
Convergent
boundary
Transform
boundary

Plate
boundaries

…..Types of Plate Boundaries-
•Divergent plate boundaries: are boundaries along
which plates move away from each others. In this
process tensile stress is acting, which is responsible
for formation of faults and joints.
•Convergent plate boundaries: are boundaries along
which no plates approach each other and leading
edge of one slips down under the other low density
plate. In this process compressional forces are acting,
which is responsible for formation of folds.
Transform Boundaries: Transform Plate Boundaries
are locations where two plates slide past one
another.

2.3 Strains (deforms) the Mantle and
Crust:
Let us know how the rocks are deform
due to different strains-
 Due to ductile strain the rocks strata Bends and
form the undulation into the rocks i.e. folding
 Due to brittle strain the Rock breaks down and
creates no of fractures into it, if there is no
relative movements then it is called Joints.
 Due to brittle strain displacement of large rocks
blocks may cause the faulting

2.4 Tectonics stresses results from Internal
Energy:
 The Earth's mantle has convection currents
because the heat of the core acts similarly to
the light bulb in our lava lamp.
 The core's heat energy is transferred to the
mantle, causing it to rise towards the Earth's
surface, which is cooler.
 As the heated mantle transfers its heat energy
to the lithosphere, it becomes denser than the
surrounding magma and sinks back down
towards the core.

2.4 Tectonics stresses results from Internal
Energy:

2.5 Introduce to strike and dip: STRIKE:
The trend of a rock bed on the ground surface is called
the strike. The direction of the strike is measured by
compass with reference to the true north and south. For
example. If the strike direction of a particular beds is
40˚ east of north, strike will be recorded as N40˚E-S40˚W
Strike
Dip

3.1: INTRODUCTION TO FAULT
FAULT

3.2 TERMINOLGOY OF FAULT
Fault plane: The fracture
surface, along which
relative movement has
taken place, is called a
“fault plane”.
The word fault includes
both the fault plane and
the displacement that
has occurred along it.
A fault plain may be
markedly curved or in
some cases undulating.
Fault plane

Hanging wall: The rock mass resting on the
fault plane is called hanging wall.
Footwall: The rock mass beneath the fault
plane is called footwall
Hade: It is angle of inclination of fault plane
measured from the vertical. It includes
both angle & direction.
Throw: It is the vertical component of the
displacement of fractured rock blocks.
Heave: It is the horizontal component of
the displacement of fractured rock block.

Fault plane
Foot Wall
Hanging Wall
Hade
Heave
Up Throw Down Throw

4.1 LIST OF FAULT
The lists of faults are given hereunder:
•Strike slip fault
•Dip slip fault
•Oblique slip fault
•Normal fault
•Reverse fault
•Thrust fault
•Horst & Graben
•Step fault
NORMAL FAULT

4.2: Classification of fault
4.2.1 On the basis of the relationship
between the direction of slip and the attitude
of the fault plane the faults are classified into
three group :
•Strike slip fault
•Dip slip fault
•Oblique slip

DIP SLIP FAULT:
A fault, in which movement is
essentially downward along
the dip of fault, is called dip
slip fault.
OBLIQUE SLIP FAULT: A fault,
in which direction of
movements is diagonal to
both the dip and strike of
fault, is called oblique slip
fault.

4.2.2: On the basis of apparent movement
the faults are classified into four groups:
• Normal fault
• Reverse fault
• Thrust Fault
• Horst & Graben

Normal Fault
A normal fault is one in which the hanging wall
appeared to have moved downward relative to
the foot wall. In this case the fault plane dips
towards the down-throw side.
Generally normal fault are produced by tensional
forces and they are also called the gravity fault.
This fault is indicating lengthening of the earth
crust.

Reverse Fault
Is one in which the hanging wall appears to have
moved upward relative to the footwall. In this case
the fault plane dips towards the up-throw side.
The reverse faults are usually high angle faults.
They are produced by compressive forces. Theses
fault indicates shortening of the earth crust.

Normally reverse fault have dips of order
of 45 degree or more.
Intense compression produces low angle
reverse fault is called “the thrust fault”.
The thrust fault may curve at the bottom to
merge with a bedding plane.
Thrust Fault

If tectonic forces stretch the crust over a
large area, many normal faults may
develop, allowing numerous Graben to
settle downward between the faults.
The blocks of rock between the down
dropped Graben then appear to have
moved upward relative to the Graben;
they are called horsts.
Horst & Graben

4.2.3 Classify fault on the basis of
pattern of fault:
On the basis of pattern fault
classified into three groups:
• Parallel fault
• Step fault
• Radial Faults

3. Radial Faults: A number of faults
exhibiting a radial pattern are descried
as radial faults.

To recognize faults in the field, a number of
criteria are used. The fault may be directly seen
as river cutting, road cuttings etc. but in some of
the cases, faults are recognized by following
evidences as:
5.1 IDENTIFICATION OF FAULT IN THE FIELD:
I. Abrupt termination.
II. Repetition or omission of strata.
III. Silicification & Mineralization.
IV. Features characteristics of fault plane

Faults within the Earth's crust are the result of
the failure of rock or slip on an existing fault
under some applied natural load. Faults are
global structures of the Earth. They are the
source of earthquakes which can cause severe
damage to homes and even death. It is
important for you as a member of this blue
planet Earth, to have a basic understanding of
faults formation.
Summary

In Unit 1: you have learned reasons for uses of
structural geological studies in civil Engineering
works.
In Unit 2: you have learned roles of plate tectonic
boundaries in the formation of geological structures.
Different types of plate tectonics movements,
Tectonics stresses, strike and dip.
In Unit 3: fault and different elements of faults
In Unit 4: You have learned different fault types,
Classification of faults and
In Unit 5: you have seen identification of fault in field
Summary

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Summary

Structural Geology-Fault

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