Geophsics and Geology

ِ‫ن‬ ‫ه‬‫م‬ْ‫ح‬ٰ‫ٱلر‬ ِ ‫ه‬ٰ
‫ٱَّلل‬ ِ‫م‬ْ‫س‬ِ‫ب‬
ِ‫يم‬ ِ‫ح‬ٰ‫ٱلر‬

TECHNIQUES OF MINERAL
EXPLORATION
Pakistan Institute of Engineering & Applied Sciences
Department of Chemical Engineering
Chaudhary Muhammad Rizwan
MS Mineral Resource Engineering
2022-2024

DETAILED BASIC CONCEPT
AND SEISMIC METHOD
CHAUDHARY MUHAMMAD
RIZWAN

Department of
Chemical Engineering
Contents
• Part 1 : GEOPHYSICS AND BASIC PRINCIPLES
• Part 2 : SEISMIC REFRACTION
• Part 3 : SEISMIC REFLECTION
• Part 4 : EARTHQUAKE SEISMOLOGY
• Part 5 : RESISTIVITY METHOD
4

Part 1 : GEOPHYSICS AND
BASIC PRINCIPLES

Department of
Learning Objectives Part 1
1.The definition & divisions of geophysics.
2.The concept of elasticity.
3.The relationship between stress & strain.
4.Types of stress.
5.Hooke's law.
6.The elastic constants.
7.The definition & types of seismic waves.
8.The relationship between wave front & ray path.
9.Wave parameters.
10.Huygens's principle.
11.Snell's law.
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Department of
GEOPHYSICS
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Department of
GEOPHYSICS
Geophysics: is the science which deals with
investigating the earth, using the methods and
techniques of physics.
8
Geophysics = Geological Observations + Physical Laws

Department of
GEOPHYSICS
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Department of
GEOLOGY AND GEOPHYSICS
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Department of
DIVISIONS OF GEOPHYSICS
 Global Geophysics:
 Study of earthquakes, magnetic field, physical
oceanography, Earth's thermal state and meteorology.
 Exploration Geophysics:
 Physical principles are applied to the search for, and
evaluation of, resources such as oil, gas, minerals, water and
building stone.
There are many divisions of geophysics, including:
oceanography, atmospheric physics, climatology, petroleum
geophysics, environmental geophysics, engineering
geophysics and mining geophysics.
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Department of
GEOPHYSICAL EXPLORATION METHOD
 Passive Methods (Natural Sources):
 Incorporates of natural occurring fields or properties of the
Earth [i.e. Magnetotelluric, Telluric, Gravity, Magnetic].
 Active (Induced Sources):
 A signal injected into the earth and then measure how the
earth respond to the signal [i.e. Resistivity, Seismic
Refraction, GPR].
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Department of
COMMON APPLICATIONS
 Oil and gas exploration.
 Mineral exploration.
 Diamond exploration.
 Hydrogeology.
 Geotechnical and engineering studies.
 Tectonic studies.
 Earthquake hazard assessment.
 Archaeology.
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Department of
Chemical Engineering 14
ELASTICITY

Department of
THEORY OF ELASTICITY:
• Stress: is the ratio of applied force (F) to the area
across which it is acts.
• Strain: is the deformation caused in the body, and is
expressed as the ratio of change in length (or
volume) to the original length (or volume).
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Department of
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Department of
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Department of
TYPES OF STRESS:
1.Compression: causes a material to shorten.
2.Tension: causes a material to lengthen.
3.Shear: causes distortion of a material.
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Department of
TYPES OF STRESS:
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Department of
TYPES OF STRESS:
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Department of
PRESSURE:
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Department of
PRESSURE:
Pressure: Forces act equally in all directions
perpendicular to faces of body.
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Department of
PRESSURE:
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Department of
PRESSURE:
• Principal-stress axes: Three
mutually perpendicular axes
(designated, σ1, σ2, and σ3)
which are parallel to the
directions of maximum,
intermediate, and least principal
stress. Their separate lengths
and directions describe the state
of stress at a particular point.
24

Department of
PRESSURE:
• If all (3) principal stresses are
equal (σ1 = σ2= σ3), the body is
subjected to a pressure.
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Pressure = Sum of Principal Stresses/3

Department of
Hooke’s Law
• Hooke’s Law essentially states that stress is
proportional to strain.
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Department of
Hooke’s Law
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Department of
Hooke’s Law
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Department of
Hooke’s Law
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Department of
Elastic Constants
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• Elastic constants describes the strain of a
material due to applied stress.
Modulus = Stress/Strain
• The higher the value of the modulus, the
stronger the material, the smaller the strain
produced by a given stress.

Department of
Elastic Constants
31
• Young’s Modulus (E)
• Bulk Modulus (K)
• Shear Modulus ()
• Axial Modulus (ψ)
• Poisson’s Ratio ()

Department of
Young’s Modulus (E):
32

Department of
Bulk Modulus (K):
33
Measure of the capacity of the material to be compressed. It can
be carried out for solid, liquid, and gas.

Department of
Bulk Modulus (K):
34

Department of
Shear Modulus ():
35
Measure of the effort needed to change the shape of a
material without change of volume ( =0 for liquid or gas).

Department of
Axial Modulus (ψ):
36
Response to longitudinal stress, similar to Young’s Modulus
except that strain is uniaxial – no transverse strain associated
with the application of the longitudinal stress.

Department of
Poisson’s Ratio (σ):
37

Department of
Seismic Waves
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Department of
Seismic Waves
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Waves of energy that travel through the Earth's layers, and are
a result of an earthquake, explosion, or a volcano.

Department of
Seismic Waves
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Department of
Seismic Waves
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Department of
Seismic Waves
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Department of
Seismic Waves
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Department of
Seismic Waves
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S - waves
• Transverse.
• Slow moving.
• Travel through solids
only.
P-waves
• Longitudinal.
• Fast moving.
• Travel through liquids
and solids.

Department of
Relationship between Vp and Vs
45
Compressional Waves: Shear Waves:
• Averaged Vp/Vs = 1.732 for the
crust.
• For mafic rocks, Vp/Vs = 1.81.
• For felsic rocks, Vp/Vs = 1.70.

Department of
Relationship between Vp and Vs
46

Department of
Types of Seismic Waves
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Department of
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Department of
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Department of
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Department of
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Department of
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In general, velocity rises with increasing pressure.

Department of
Seismic Waves Propagation
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The wave front is the direct boundary between the seismic waves in the
earth material, and the material that the seismic energy has not yet
reached.
Ray is the vector perpendicular to a wave front.

Department of
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Department of
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Department of
56
-Huygens's Principle is a method of analysis applied to problems of
wave propagation.
-He proposed that every point on a wave-front may be considered a
source of secondary spherical wavelets which spread out in the forward
direction at the speed of light.

Department of
57
Snell's Law: describes how elastic waves are reflected and
refracted across a boundary separating layers of differing velocity.

Department of
58
When V2 is greater than V1, the angle of refraction is greater than the
angle of incidence, then the angle of incidence for which this occur us
called the critical angle.

Department of
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Department of
Calculations
60

Department of
Calculations
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Department of
Calculations
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Department of
Calculations
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Department of
1.The concept of seismic refraction & its applications.
2.The three main paths (direct, refracted, and
reflected).
3.The critical refraction (critical distance).
4.The cross over distance.
5.First break picking.
6.Travel time curves.
7.Detecting multiple layers.
8.Detecting dipping interfaces.
9.Survey types.
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Department of
Refraction vs Reflection
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Department of
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A signal, similar to a sound pulse, is transmitted into the earth. The
signal recorded at the surface can be used to infer subsurface
properties. There are two main classes of survey:
Seismic Refraction: the signal returns to the surface by refraction at
subsurface interfaces, and is recorded at distances much greater
than depth of investigation.
Seismic Reflection: the seismic signal is reflected back to the surface
at layer interfaces, and is recorded at distances less than depth of
investigation.

Department of
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Department of
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Department of
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Department of
Seismic Refraction
71



 


Department of
Applications for Seismic Refraction:
72
• Depth to bedrock.
• Groundwater exploration.
• Crustal structure and
tectonics.

Department of
Seismic Refraction
73
• When doing a seismic refraction survey, a recorded ray can come from three
main paths:
– The direct ray.
– The reflected ray.
– The refracted ray.
• Because these rays travel different distances and at different speeds, they
arrive at different times.
• The direct ray and the refracted ray arrive in different order depending on
distance from source and the velocity structure.

Department of
Critical refraction
74
Refraction surveys use the process of critical refraction to infer
interface depths and layer velocities.
Critical refraction (critical distance) requires an increase in velocity
with depth. If not, then there is no critical; refraction.

Department of
Direct Ray
75

Department of
Reflected Ray
76

Department of
Refracted Ray
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Department of
Crossover distance
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Department of
First Break Picking
79
First Break Picking
The onset of the first seismic wave, the first break, on each
seismogram is identified and its arrival time is picked.

Department of
Travel Time Curves
80
Travel Time Curves
• Analysis of seismic
refraction data is
primarily based on
interpretation of
critical refraction
travel times.
• Plots of seismic arrival
times vs. source-
receiver offset are
called travel time
curves.

Department of
Time (t) – Distance (x) Diagram
81

Department of
Multiple Layers
82

Department of
Multiple Layers
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Department of
Dipping Interfaces
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Department of
Dipping Interfaces
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Department of
Dipping Interfaces
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Department of
Seismic Refraction
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Department of
Survey Types
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Department of
Survey Types
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Department of
Survey Types
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Department of
Survey Types
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Department of
Calculations
92

Department of
Calculations
93

Department of
Calculations
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Department of
Calculations
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Department of
Calculations
96

Department of
Calculations
97

Department of
Calculations
98

Department of
Calculations
99

Department of
1.The concept of seismic reflection and its applications.
2.The difference between seismic refraction &
reflection.
3.The difference between signal & noise.
4.Reflection coefficient (R).
5.Transmission coefficient (T).
6.Acoustic impedance (Z).
7.Zoeppritz equations.
8.Negative polarity reflection.
101

Department of
102
A signal, similar to a sound pulse, is transmitted into the earth. The
signal recorded at the surface can be used to infer subsurface
properties. There are two main classes of survey:
Seismic Refraction: the signal returns to the surface by refraction at
subsurface interfaces, and is recorded at distances much greater
than depth of investigation.
Seismic Reflection: the seismic signal is reflected back to the surface
at layer interfaces, and is recorded at distances less than depth of
investigation.

Department of
Seismic Imaging Techniques
103
• Seismic reflection.
• Seismic refraction.
Geophones
Source
Direct
Reflected
Refracted
time

Department of
Seismic Imaging Techniques
104

Department of
Applications for Seismic Reflection:
105
• Detection of subsurface cavities.
• Shallow stratigraphy.
• Hydrocarbon exploration.
• Crustal structure and tectonics

Department of
Seismic Reflection
106

Department of
Diff. Refraction and Reflection
107

Department of
Seismic Reflection
108

Department of
Seismic Reflection
109

Department of
Seismic Reflection
110

Department of
Non- Vertical Reflection
111

Department of
Multiple Reflection
112

Department of
Signal and Noise
113

Department of
Calculations
114

Department of
Calculations
115

Department of
Calculations
116

Department of
Calculations
117

Department of
Calculations
118

Department of
Calculations
119

Department of
Calculations
120
Calculate the arrival time for the
wave?
Receiver

Department of
Calculations
121

Department of
Calculations
122
Calculate:
• R and T for interface A.
• R and T for interface B.
• Total arrival time.

Department of
Calculations
123
A. Z1= 8370 kg km s-1 m-3 Z2= 12150 kg km s-1 m-3
RA= 0.18 and TA= 0.82
Arrival time for interface A= 0.26 sec
B. Z2= 12150 kg km s-1 m-3 Z3= 18360 kg km s-1 m-3
RB=0.20 and TB=0.80
Arrival time for interface B = 0.4 sec
C. Total arrival time = 0.26 + 0.4 = 0.66 sec

PART 4 : EARTHQUAKE
SEISMOLOGY

Department of
1.Earth's internal structure.
2.The difference between continental crust & oceanic crust.
3.Plate tectonic theory, types of plate boundaries & faults.
4.Earthquake, seismic waves, focus (hypocenter), & epicenter.
5. How, why, & where earthquakes occur.
6.Wadati‐Benioff Zone.
7.Types & depths of earthquakes.
8.How to measure & locate earthquakes.
9.Richter scale & Mercalli scale.
10.Types of magnitudes.
11.Energy of earthquakes & moment magnitude.
12.Effects of earthquakes.
125

Department of
Rocks of the crust provide clues to Earth’s past. By
analyzing these clues we can infer events from
the past.

Department of
Earth radius is the distance from Earth’s center to
its surface which is about 6378 km.

Department of

Department of
A fault is a crack in the Earth's crust. Typically, faults are
associated with, or form, the boundaries between
Earth's tectonic plates.

Department of
Definitions
Earthquake: Vibration of the Earth produced by
the rapid release of energy.
Seismic waves: Energy moving outward from the
focus of an earthquake.
Focus (hypocenter): Location of initial slip on the
fault; where the earthquake origins.
Epicenter: Spot on Earth’s surface directly above
the focus.

Department of

Department of
Around (80%) of all earthquakes occur in
the Pacific belt.
Most of these result from convergent
margin activity.
 (10%) occur in the Asiatic‐European belt.
Remaining (5%) occur in the interiors of
plates and on spreading ridge centers.
More than (150,000) quakes strong enough
to be felt are recorded each year.

Department of

Department of
Types of Earthquakes:
The type of earthquake depends on the region
where it occurs and the geological make‐up of that
region.
1.Tectonic Earthquakes: these occur when rocks in
the earth's crust break due to geological forces
created by movement of tectonic plates.
2.Volcanic Earthquakes: occur in conjunction
with volcanic activity.
3.Collapse Earthquakes: are small earthquakes
in underground caverns and mines.
4.Explosion Earthquakes: result from the explosion
of nuclear and chemical devices.

Department of
Depth of Earthquakes:
1. Shallow earthquakes:
(Depth between 0 and 70 km).
2. Intermediate earthquake:
(Depth between 70 and 300
km).
3. Deep earthquakes:
(Depth is greater than 300 km).

Department of
Measuring Earthquakes:
Seismometers:
instruments
that detect
seismic waves.
Seismographs:
Record intensity,
height and
amplitude of
seismic waves.

Department of
Locating the
Epicenter
‐ In order to determine the location of an
earthquake, the earthquake needs to be
recorded on three different seismographs that
are at significantly different locations.
‐ The other piece of information needed is the time
it takes for P‐waves and S‐waves to travel
through the Earth and arrive at a seismographic
station.

Department of
A seismograph records earthquake activity by
plotting vibrations on a sheet of paper to create a
seismogram.

Department of

Department of
‐ If three arrival times are available at three
different seismic stations then triangulation can
be used to find the location of the focus or
epicenter and the time of occurrence of the
earthquake.
‐ The distance between the beginning of the
first P‐wave and the first S‐wave tells you how
many seconds the waves are apart.

Department of

Department of
Earthquake Size [two ways to measure]:
1) Magnitude (Richter Scale):
• Measures the energy released by
fault movement.
• related to the maximum amplitude of
the S wave measured from the
seismogram.
• Logarithmic‐scale; quantitative measure
• For each whole number there is a 31.5
times increase in energy.
• eg. an increase from 5 to 7 on the Richter scale =
an increase in energy of 992 times!!

Department of

Department of
2) Intensity (Mercalli Scale):
– What did you feel?
– Assigns an intensity or rating to measure an earthquake
at a particular location (qualitative).
– I (not felt) to XII (buildings nearly destroyed).
– Measures the destructive effect.
• Intensity is a function of:
• Energy released by fault.
• Geology of the location.
• Surface substrate: can magnify shock waves e.g.
Mexico City (1985) and San Francisco (1989).

Department of

Department of
Effects of Earthquakes:
1. Direct:
‐ Ground sliding.
‐ Ground tilting.
‐ Liquefaction.
‐ Differential
settlement.
2. Indirect:
‐ Tsunamis.
‐ Landslides.
‐ Floods & fires.

Department of
1.Electrical properties of the rocks.
2.Electrical and electromagnetic methods.
3.Application of electrical methods.
4.Resistance, resistivity, and conductivity.
5.Classification of materials according to resistivities values.
6.Rock & mineral resistivities.
7.Factors which control the resistivity.
8.Archie's Law.
9.Schlumberger Arrangement, Wenner Arrangement, and
Dipole – Dipole Array.
10.Current refraction.
11.Survey design.
182

Department of
ELECTRICAL PROPERTIES
183
• Resistivity (or conductivity), which govern the
amount of current that passes when a potential
difference is created.
• Electrochemical or polarizability, the response of
certain minerals to electrolytes in the ground.
• Dielectric constant or permittivity. A measure of the
capacity of a material to store charge when an electric
filed is applied.

Department of
184
Electrical methods utilize direct current or Low frequency
alternating current to investigate electrical properties of the
subsurface.
Electromagnetic methods use alternating
electromagnetic field of high frequencies.
Two properties are of primary concern in the
application of electrical methods:
• The ability of Rocks to conduct an electrical current.
• The polarization which occurs when an electrical current
is passed through them.

Department of
185
For a uniform wire or cube, resistance is
proportional to length and inversely proportional
to cross-sectional area. Resistivity is related to
resistance but it not identical to it. The resistance
(R) depends an length, Area and properties of the
material which we term resistivity (ohm.m).

Department of
186

Department of
RESISTIVITY
187

Department of
RESISTIVITY
188
Classification of materials according to resistivities values:
A) Materials which lack pore spaces will show high resistivity such as:
• Massive limestone.
• Most igneous and metamorphic (granite, basalt).
• Materials whose pore space lacks water will show high
resistivity such as: dry sand, gravel, and Ice.
B) Materials whose connate water is clean (free from salinity)
will show high resistivity such as:
• Clean sand or gravel, even if water saturated.
C) Most other materials will show medium or low resistivity,
especially if clay is present such as:
• Clay soil.
• Weathered rock.

Department of
RESISTIVITIES
189

Department of
RESISTIVITY
190

Department of
FACTORS FOR RESISTIVITY
191
Factors which control the resistivity:
(1) Geologic age.
(2) Salinity.
(3) Free-ion content of the connate water.
(4) Interconnection of the pore spaces (permeability).
(5) Temperature.
(6) Porosity.
(7) Pressure.
(8) Depth.

Department of
RESISTIVITY
192

Department of
RESISTIVITY
193

Department of
ELECTRODE CONFIGURATION
194

Department of
ELECTRODE CONFIGURATION
195
1 Schlumberger Arrangement:
This array is the most widely used in the
electrical prospecting. Four electrodes are
placed along a straight line in the same order.
2 Wenner Arrangement:
The four electrodes A , M , N , B are equally
spaced along a straight line.
3 Dipole – Dipole Array:
The distance between the current electrode A
and B (current dipole) and the distance between
the potential electrodes M and N (measuring
dipole) are significantly smaller than the
distance , between the centers of the two
dipoles.

Department of
CURRENT REFRACTION
196

Department of
SURVEY DESIGN
197
Two categories of field techniques exist for conventional
resistivity analysis of the subsurface:
1. Vertical Electric Sounding (VES): The object of (VES )is to
deduce the variation of resistivity with depth below a given
point on the ground surface and to correlate it with the
available geological information in order to infer the depths
and resistivities of the layers present.
2. Horizontal Electrical Profiling (HEP): The object of (HEP) is
to detect lateral variations in the resistivity of the ground,
such as lithological changes & near- surface faults.

Department of
REFERENCE BOOKS:
• An introduction to geophysical
exploration (3rd edition). P. Keary, M.
Brooks, and I. Hill, Blackwell
Publishing, (2002). ISBN: 0- 632-04929-
4
• Introduction to applied geophysics:
Exploring the shallow subsurface.
H.R. Burger, A.F. Sheehan, and C.H.
Jones, W.W. Norton and Company,
(2006). ISBN: 0- 393-92637-0
198

Department of

Presenter Name:
MUHAMMAD RIZWAN

Geophsics and Geology

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