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Geophysical Exploration 2011-GE-56
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Lab#01
STATEMENT:
INTRODUCTION TO GEOPHYSICAL LAB EQUIPMENTS
SCOPE:
To know and familiar with the geophysical lab equipment’s and their uses in the field
THEORY:
GEOPHYSICS:
Geophysicists study a variety of natural phenomena, including the Earth's shape, the
dynamics of its interior, and atmospheric processes.
APPLICATIONS OF GEOPHYSICS:
Geophysics is a vast field and its uses are countless. The following are some of the
applications of geophysical exploration:
 Mineral exploration
 Oil and gas exploration
 Civil engineering projects
 Archeology
 Unexploded ordnance detection
 Interior of earth
 Finding problematic zones in tunnels and mines
Specification and accessories of each of the equipment are given as:
1) TERRAMETER SAS 4000:
Terrameter SAS 4000 has the ability to measure Resistivity and Induced Polarization as
well as Self Potential, making the Terrameter SAS 4000 a highly competent and flexible solution
for near investigations. All measured data is stored into a database which allows for export or
other suitable programs for interpretation and analysis. A Borehole log option is also available.
ADVANTAGES:
- Groundwater resource management and vulnerability assessment,
- Mapping and monitoring of contaminated ground/groundwater
- Geotechnical pre-investigation
- Geological mapping
- Mapping/prospecting of natural resources
- Geothermal prospecting
- Sub-bottom mapping at sea and in lakes
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Figure 1.1
Figure 1.2
- Mapping of frozen ground/permafrost
- Archaeology
- Resistivity Imaging a Robust Method
ACCESSORIES OF TERRAMETER:
 Electric cables:
Cables are used extensively in electronic
devices for power and signal circuits.
 Connectors:
An electrical connector is an electro-
mechanical device for joining electrical circuits as
an interface using a mechanical assembly.
Connectors consist of plugs (male-ended) and jacks
(female-ended).
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Figure 1.3
Figure 1. 4
Figure 1.5
 Polarized electrodes:
A metallic conductor behaves as a polarized electrode if it allows no movement of charge
between itself and the solution phase.
 12 volt battery:
An electric battery is a device consisting of one or more electrochemical cells that
convert stored chemical energy into electrical energy.
 Connecting cables:
Connecting cables are used to connect two or more devices.
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Figure 1.6
Figure 1.7
 Steel electrodes:
A type of steel resistant to corrosion as a result of the presence of large amounts of
chromium (12 to 15 percent). The carbon content depends on the application.
 Electrode Selector:
Resistivity imaging technique in which overall 64 resisters can be read out.
2) TERRALOC MK-6:
Terraloc MK-6 is an instrument used in geophysical exploration. It is used seismic survey
and is an old version. Terraloc MK-6 has the following specifications:
Up hole channel Channel 12 or 24, redirectable to a separate connector
Sampling Rate 25, 50, 100, 250, 500 µs, 1, 2 ms
Minimum Input Signal ±0.24 µV
Maximum Input Signal ±250 mV
Frequency Range 2-4000 Hz
Processor 386/486 (Depending on model)
Memory 4 to 32 MB RAM (Depending on model)
Power 10 to 30V DC External battery or internal battery
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Figure 1. 8
Figure 1. 9
Figure 1.10
ACCESSORIES FOR TERRALOC MK-6:
 5-6kg hammer:
Hammer is used to produce seismic waves in the ground. The hammer is striked against
the rubber plate.
 Rubber/metal/fiber plate:
Plate provide concentration to seismic waves. A hammer is used to hit it.
 Explosives:
Explosive is used for the generation of seismic waves. The explosives are used in holes
and the length and diameter of the holes are calculated according to the geology and depth.
Explosives are mostly used in areas where seismic reflection survey is used. Extra care must be
taken while using explosives.
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Figure 1.11
Figure 1.12
Figure 1.13
 Seismic cable:
It is used to connect all the geophones which record the seismic waves resulting from
either Vibroseis or dynamite when recording seismic data.
 Geophones:
A geophone is a device that converts ground movement (displacement) into voltage,
which may be recorded at a recording station. Types of geophones w.r.t sensitivity:
- SG-5 (high-sensitive geophone)
- SG-10 (high performance geophone sensor)
- jF-20DX (conventional geophone sensor)
 Triggering device:
It is used to initiate the whole system.
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Figure 1.14
Figure 1.15
3) SHIELDED ANTENNA GPR:
GPR means Ground Penetrating Radar. It works on electromagnetism principle.
RAMAC/GPR shielded antennas are primarily used for medium to high resolution surveys. The
shielded antenna construction makes the antennas especially suitable for urban investigations or
at sites with a lot of background noise.
A GPR measurement system consists of a transmitter and a receiver antenna and a control
unit. In the system applied in this practical course both antennas are placed in one box. The main
part of the GPR system is the control unit which generates the GPR signal and also receives the
signals after their passage through the ground. The complete system is computer controlled. The
measurement wheel at the back of the antenna box measures the distance along the survey track
and triggers the emittance of the electromagnetic pulses.
SPECIFICATIONS:
The shielded 100MHz antenna is the lowest shielded antenna frequency commercially
available. It is used for medium to low resolution. It is suitable for geological and geotechnical
applications. Dimensions: 1.25 x 0.78 x 0.20 m, Weight: 25.5 kg.
ACCESSORIES FOR GPR:
 Distance measuring wheel:
This small, lightweight distance-measuring wheel is designed with flexible mounts to
attach to most GSSI antennas with the mounting bolts. It measures distance.
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Figure 1.16
Figure 1.17
Figure 1.18
 Single button monitor:
Single button monitor is an old type of monitor in which the whole process is controlled
by using a single button present on the monitor.
 Rods/Extension Rods:
It is an instrument used to cause the sharpened sampler edge to cut through the soil.
4) GRAVIMETER:
It is used for gravity survey. It is easy to operate and has excellent field repeatability. It is
fully portable and it automatically rejects the noise. It transfers data quite easily.
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Figure 1.20
Figure 1.19
SPECIFICATIONS FOR GRAVIMETER:
ACCESSORIES FOR GRAVIMETER:
 Tripod stands:
A stand with three geophones attached with it. It has a level bubble for leveling the
tripod.
5) MAGNETOMETER:
It is used for magnetic survey. It gives the magnetic information of the subsurface
formations. Magnetometers are measurement instruments used for two general purposes: to
measure the magnetization of a magnetic material like a Ferro magnet, or to measure the strength
and, in some cases, the direction of the magnetic field at a point in space.
USES OF MAGNETOMETER:
SENSOR TYPE Fused quartz using electrostatic nulling
READING RESOLUTION 1microGal
POWER CONSUMPTION 4.5Watts at 25°C
WEIGHT 8kg (17.5lbs) including battery
GPS ACCURACY Standard
OPERATING RANGE Worldwide (8,000mGal without resetting)
STANDARD DEVIATION < 5microGal
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Figure 1.21
Magnetometers are widely used for measuring the Earth's magnetic field and
in geophysical surveys to detect magnetic anomalies of various types. They are also used
militarily to detect submarines.
In archaeology and geophysics, where the sensor sweeps through an area and many
accurate magnetic field measurements are often needed, cesium and potassium magnetometers
have advantages over the proton magnetometer.
6) PORTABLE WELL LOGGER:
It is used for well logging purposes for shallow depth. It is a portable well logger that can
be transported from one place to other easily.
FEATURES OF WELL LOGGER:
 For upward logging, also for downward logging
 Can receive digital / analog / pulse signal
 Winch automatically stops upon reaching the logging termination depth
 Indoor simulation logging, repeatability observation of instruments and probes
 Integration of depth control system and data acquisition system
 Digital real-time display of frequency, voltage for supply voltage
 Real-time display of working voltage, working current for down hole probe
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Figure 1.22
Figure 1.23
ACCESSORIES OF WELL LOGGER:
 Probe:
Probes used for gamma ray and SP resistivity logs. Different types of probes are used for
different purposes. Some of them are given as:
 Natural Gamma Logging
 Caliper Logging
 Spontaneous Potential Logging
 Nature Gamma Probe
 Acoustic Wave Probe
 Temperature and Liquid Resistance probe
7) MINI-SEIS:
The Mini-Seis is the very definition of a great blast monitoring seismograph for an
affordable cost. It is ideal for all kinds of blast vibration monitoring and for most continuous
vibration monitoring in bargraph mode. Rugged, reliable and very easy to use, the Mini-Seis sets
the standard for value in a seismograph. This device measures and detects surface waves, mostly
earthquake waves are detected.
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Figure 1.24
FEATURES OF MINI SEIS:
 Lightweight and easy to use.
 Costs much less than comparable seismographs.
 Maintenance and calibration costs are also less.
 Keypad and display for easy field setup and data review.
 Selectable seismic and acoustic recording range, seismic and acoustic trigger level, sample
rate and record duration.
 Can use either AC or DC power for long term monitoring.
 Sophisticated, non-loss data compression results in small record sizes and fast data transfer.
REFERENCES:
- http://shop.modelis-gis.com/shop/product.php?id_product=273&id_lang=1
- Ebooks from google
- Wikipedia search
- http://en.wikipedia.org/wiki/Exploration_geophysics
- http://www.geophysicalmethodsofexploration.com/
- http://en.wikipedia.org/wiki/Reflection_seismology
- http://en.wikipedia.org/wiki/Magnetometer
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LAB#02
INTRODUCTION TO TERRALOC MK-6
STATEMENT:
To study and describe Terraloc ABM Mk-6 and its reliability in the field
SCOPE:
 It is used to conduct seismic refraction and reflection surveys.
 Terraloc is a compact and complete seismograph with all we need to collect our seismic data
in single casing.
 It is used to explore the sub-surface feature of the earth.
 Ideal for all types of applications in shallow seismic as refraction, reflection, crosshole,
surface wave investigations.
THEORY:
TECHNICAL SPECIFICATIONS:
Up hole channel Channel 12 or 24, redirectable to a separate connector
Sampling Rate 25, 50, 100, 250, 500 µs, 1, 2 ms
Minimum Input Signal ±0.24 µV
Maximum Input Signal ±250 mV
Frequency Range 2-4000 Hz
Processor 386/486 (Depending on model)
Memory 4 to 32 MB RAM (Depending on model)
Data Storage 80 to 250 MB hard disk and 1.44 MB floppy disk drive 3.5 in.
Power 10 to 30V DC External battery or internal battery
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Figure 2.1 Terraloc MK-6
TYPES OF GEOPHONE SPREADS:
Split Spread:
Type of spread in which the source is in between regularly spaced receivers.
End-on Spread:
Type of spread in which the source is at one end of regularly spaced receivers.
In-line Offset:
In which the source away from the first receiver (i.e., Distance of source may vary).
Cross Spread:
In which two lines of geophones are laid out roughly at right angle and one source is fired at the
intersection point.
L Spread:
In which the source is at Centre and geophones are at sides,
forming an L shape.
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PROCEDURE:
Terraloc MK-6 is an instrument which records seismic waves generated by either hammer,
explosives, earth quake or any other source. The procedure is simple and easy. The connection is
being built between the Terraloc and seismic cables. The geophones are connected with the
cables and is recording the seismic waves being generated. The source may kept at either ends or
at the middle of the geophones. The battery is used to power the Terraloc. Before starting the
survey triggering is done which removes the error in the apparatus. The wiggles are recorded and
is saved in the system for further calculations.
APPLICATIONS OF TERRALOC MK-6:
 Terraloc MK 6 is the best one instrument to find out the depth of bed rock.
 It helps to locate the water table.
 It also helps to determine the velocities of waves through different layers.
 We can also compute depth of layer boundaries and so their thicknesses too.
 Real time noise monitoring.
 Frequency spectrum analysis.
 Refractor velocity indication.
REFRENCES:
Terraloc-MK-6-Manual-1994-02-24
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LAB#03
STATEMENT:
SEISMIC REFLECTION SERVEY IN UET STADIUM GROUND
OBJECTIVE:
Main objective of this lab is to acquire data for 80 ft. subsurface depth
PRINCIPAL:
This test method is based on refraction of waves according to Snell’s Law. A refraction survey
uses refracted (or head) waves to deduce velocities of the layered-earth model. So called first
arrival information is used for the analysis. More generalized methods based on the turning
waves from an arbitrary velocity model have also been used in recent days. This is called seismic
refraction tomography.
APPARATUS:
 Terraloc Mark 6
 25 Geophones
 12 V Battery
 Seismic cable
 Extension Cable
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Figure 3.1 Terraloc Setup
PROCEDURE:
 Setup the geophones according to the acquisitive design.
 Make all the connections with the help of seismic cables.
 Also attach a trigging geophone with the Terraloc.
 To check the geophones send signals by hammering to the geophones.
 See on Terraloc if we are getting signals on all geophones then ok otherwise check all the
connections of geophones and try again until u get signals on all geophones.
 Send signals to the geophones by generating seismic by hammering.
 We get a data of the subsurface read the data from the Terraloc or save it.
 Then we have to plot the data
THEORY:
 FARWARD SHOT:
In farward shot the source is near to the first geophone (may be at the last one. Actually farward
and reverse shot are opposite of each other).
 MID SHOT:
When the source is placed in the middle of geophones then it is called mid shot.
 REVERSE SHOT:
The source is placed in opposite to the
farward shot. (may be at the end of
geophones).
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Figure 3.2 Geophones Setup
COMMANDS OF TERRRALOC:
 First of all <ARM> the apparatus.
 Then for triggering press <Ctl + ARM> then <DISARM> the
apparatus
 Then start the
hammering at any required point mid or farwad.
 Then select the <file> and then the files as (File#00014.SG2).
 Then enter and save the file and open the new file and repeat the
same procedure for next shot.
DATA ACQUIRED IN THE STADIUM:
FOR 3 ft. INTERVAL:
 72 ft. Spread giving 36 ft. Subsurface Depth:
Farward Shot:
File #000142.SG2
Mid Shot:
File#000143.SG2
Reverse Shot
File#00044.SG2
FOR 5 ft. INTERVAL:
 120 ft spread giving 60 ft. subsurface depth:
Farward Shot:
File #000145.SG2
Reverse Shot:
File #000146.SG2
FOR 7 ft. INTERVAL:
 168 ft. spread giving 82 ft. subsurface depth:
Farward Shot:
File #000147.SG2 & File #000148.SG2
Reverse Shot:
File #000146.SG2
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Mid Shot:
File#000149.SG2
LAB#04
TO CALCULATE THE THICKNESS OF DIFFERENT LAYERS BY USING GRAPH
PAPER
GIVEN DATA:
GEOPHONE# TIME (ms)
12 8
11 14
10 22
9 24
8 28
7 30
6 31
5 36
4 38
3 40
2 42
1 44
Using Graph#01
Slope (m1) = 5 ms/m
Velocity (V1) = 1/5×1000 = 200 m/sec
Slope (m2) = 2 ms/m
Velocity (V2) = 500 m/sec
Intercept Time = 0.021 sec
XCross over = 7.7
THICKNESS OF LAYER:
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h1 =
√
h1 = 2.29m
GIVEN DATA:
USING GRAPH#02:
There are 3 layers and 2 interfaces in the given data.
Also we have calculated:
- Slope (m1) = 1×10-3
sec/m
- Velocity (V1) = 1000 m/sec
- Slope (m2) = 4×10-4
sec/m
- Velocity (V2) = 2500 m/sec
- Slope (m3) = 2×10-4
sec/m
- Velocity (V3) = 5000 m/sec
- Xcross-over for 1st
= 40 m
- Xcross-over for 2nd
= 123 m
- Intercept Time T1 = 0.024 sec
DISTANCE
(meter)
TIME (sec)
10 0.010
20 0.020
30 0.030
40 0.040
50 0.045
75 0.055
100 0.065
125 0.075
150 0.080
175 0.085
200 0.090
250 0.100
300 0.110
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- Intercept Time T2 = 0.049 sec
THICKNESS OF 1ST
LAYER:
h1 =
√
h1 = 13.09 m
Another formula for finding thickness of layer:
h1 = √
h1 = 13.10 m
THICKNESS OF 2ND
LAYER:
h = √
h2 = 36.08 m
2nd
layer thickness can also be find from the following formula:
h2 = ( )
RESULTS:
Thickness for graph#01 = 2.29m
Thickness of 1st
layer for graph#02 = 13.10m
Thickness of 1st
layer for graph#02 = 36.08m
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Figure 5.125
LAB#05
STATEMENT:
SEISMIC REFLECTION DATA INTERPRETATION
SCOPE:
Time can be calculated from the seismic reflection data. Surfer is used to draw the contour map
by using time, latitude and longitude.
APPARATUS:
 Final filtered migrated stack
 Magnifying glass
 Pencil
 Scale
 Base map
THEORY:
BASE MAP:
A base map contains seismic line and source points with coordinates (latitude and
longitude).
CONTOUR MAP:
A contour map uses contour lines which are often just called a "contour", to join points of
equal elevation (height) and thus this shows valleys and hills, and the steepness of slopes.
The relative spacing of the lines indicates the relative slope of the surface.
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Figure 5.2
STEPS FOR DRAWING CONTOUR MAP:
STEP 1:
COLLECT THE SEISMIC SECTIONS:
Example: Line= 915-MWI-81
From the above:
91= Year at which data is collected
5= Seismic party no.
MWI= Abbreviation for area
81= Seismic line no.
Full details are given at the header which are at the right side of the Final filtered migrated stack.
Like channels, source type, source interval etc.
STEP 2:
INTERPRETATION STEPS:
At Y-axis= Time ( Mostly in ms)
At X-axis= Source points (Shot points)
Source point no. = First shot no. and last shot no. should be given
Example: 318-110= 208 (Last shot - First shot)
Multiplying the shot no. difference with the interval
Example: 208×50 (Interval) = 10900
Check the parameters
1) Pick seismic time of different seismic horizons:
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- Continuous reflectors are called seismic horizons (Dark Lines)
- Pick times of horizons at different points
2) Seismic well tie:
Collect the data from well logs (Sonic and density). Comparing well log data with
synthetic seismogram by calculating its reflection coefficient and acoustic impedence.
R.C=
- Then making a graph between depth and R.C. A wiggle is generated from this graph.
- This wiggle is compared with the seismic wiggle.
- If the well is not present then the geological report which contains the extend of layers and
outcrops will help us.
- Then converting the seismic data to depth from time and velocity relation.
3) Mapping of the seismic Horizon:
- Note the latitude and longitude of the required seismic line from the base map.
- Entering the latitude, longitude and time into the surfer software.
- A contour map is drawn from that data.
OBSERVATION AND CALCULATIONS:
Data for Formation No.1:
SP # LATITUDE LONGITUDE TIME
480 71.3 32.65 -1.44
470 71.29 32.65 -1.46
460 71.285 32.65 -1.46
450 71.28 32.65 -1.45
440 71.275 32.65 -1.43
430 71.27 32.65 -1.42
420 71.26 32.65 -1.41
410 71.25 32.65 -1.38
400 71.245 32.65 -1.37
390 71.24 32.65 -1.35
380 71.235 32.65 -1.32
370 71.23 32.65 -1.30
360 71.225 32.65 -1.29
350 71.22 32.65 -1.26
340 71.215 32.65 -1.25
320 71.205 32.65 -1.14
310 71.2 32.65 -1.10
300 71.19 32.65 -1.07
290 71.185 32.65 -1.02
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Contour Map For Formation#01:
Contour Map (3D) For Formation#01:
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SP # LATITUDE LONGITUDE TIME
480 71.3 32.65 -1.93
470 71.29 32.65 -1.94
460 71.285 32.65 -1.94
450 71.28 32.65 -1.93
440 71.275 32.65 -1.91
430 71.27 32.65 -1.9
420 71.26 32.65 -1.87
410 71.25 32.65 -1.88
400 71.245 32.65 -1.84
390 71.24 32.65 -1.82
380 71.235 32.65 -1.79
370 71.23 32.65 -1.78
360 71.225 32.65 -1.77
350 71.22 32.65 -1.73
340 71.215 32.65 -1.68
330 71.21 32.65 -1.64
320 71.205 32.65 -1.61
310 71.2 32.65 -1.61
300 71.19 32.65 -1.61
Contour Map For Formation#02:
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Contour Map (3D) For Formation#02:
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LAB#06
STATEMENT:
INTRODUCTION TO RESISTIVITY SURVEY
SCOPE:
 Resistivity survey is used to measure the depth and thickness of geologic strata.
 It is used to detect changes and locate the anomalous geologic conditions.
 It measures the soil resistivity and soil corrosion rates and designing the grounding girds.
 It maps salt water intrusion and contaminant plumes
 It locates buried wastes e.g. locates landfill boundaries.
APPARATUS:
Terrameter SAS 4000
ACCESSORIES:
 Electrodes
 Measuring tape
 Crocodile connectors
 Electric cables
 Connecting cables
 External battery
 Jumpers
THEORY:
RESISTIVITY SURVEY:
Electrical resistance survey (also called earth resistance or resistivity survey) is one of a number of
methods used in archaeological geophysics. In this type of survey electrical resistance meters are
used to detect and map subsurface archaeological features and patterning.
TYPES OF RESISTIVITY SURVEY ARRANGEMENTS:
The types of electrode arrays that are most commonly used in resistivity survey are
Schlumberger, Wenner, and dipole-dipole. There are other electrode configurations that are used
experimentally or for non-geotechnical problems or are not in wide popularity today. Some of
these include the Lee, half-Schlumberger, polar dipole, bipole dipole, and gradient arrays. The
description of these configurations are given below.
Techniques:
1. Vertical Electrical Sounding (VES)
2. Vertical Electrical Profiling (VEP)
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Figure 6.1 Wenner onfiguration
Figure 6.2 Schlumberger Configuration
VERTICAL ELECTRICAL SOUNDING (VES):
Vertical electrical sounding (VES) is a geophysical method for investigation of a geological
medium. The method is based on the estimation of the electrical conductivity or resistivity of the
medium. The estimation is performed based on the measurement of voltage of electrical field
induced by the distant grounded electrodes (current electrodes).
CONFIGURATION:
There are four types of configurations used in electrical resistivity survey. They are:
1. Wenner Configuration
2. Schlumberger Configuration
3. Pole-dipole Configuration
4. Dipole-dipole Configuration
Mostly the first two configurations are widely used
WENNER CONFIGURATION:
This array consists of four electrodes in line, separated by equal intervals, denoted a. By using
the formula of apparent resistivity the user will find that the geometric factor K is equal to a, so
the apparent resistivity is given by:
SCHLUMBERGER CONFIGURATION:
The Schlumberger array consists of four collinear electrodes. The outer two electrodes are
current (source) electrodes and the inner two electrodes are the potential (receiver) electrodes.
The potential electrodes are installed at the center of the electrode array with a small separation,
typically less than one fifth of the spacing between the current electrodes.
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Figure 6.4 Double Dipole Configuration
Figure 6.3 Pole dipole Configuration
Pole-dipole Configuration:
The pole-dipole array contains four collinear electrodes. One of the current (source)
electrodes is installed at an “effective infinity” distance, which is approximately five to ten times
the survey depth. The other current electrode is placed in the vicinity of the two potential
(receiver) electrodes. This geometry is utilized because it reduces the distortion of equipotential
surfaces.
DOUBLE DIPOLE:
The dipole-dipole electrode array consists of two sets of electrodes, the current (source) and
potential (receiver) electrodes. A dipole is a paired electrode set with the electrodes located
relatively close to one another; if the electrode pair is widely spaced it is referred to as a
bipole. The convention for a dipole-dipole electrode array is to maintain an equal distance for
both the current and the potential electrodes (spacing = a), with the distance between the current
and potential electrodes as an integer multiple of a. The electrodes do not need to be located
along a common survey line.
APPLICATION OF RESISTIVITY SURVEY:
There are different applications of resistivity survey such as;
 It measures bedrock & water table depth.
 It detects sinkholes & hidden voids.
 It geophysical maps buried alluvial channels.
 It profiles landslip geometry.
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 It characterizes fracture zones & discontinuities.
 It defines landfill sites and leachate contamination.
REFERENCES:
 http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity
 http://www.epa.gov/esd/cmb/GeophysicsWebsite/pages/reference/methods/Surface
 Class Notes
 http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html
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LAB#07
STATEMENT:
TO PERFORM THE RESISTIVITY SURVEY IN UET GROUND
SCOPE:
Resistivities and no. of layers can be calculated from resistivity survey
APPARATUS:
 Terrameter SAS 4000
ACCESSORIES:
 Electrodes
 Measuring tape
 Crocodile connectors
 Electric cables
 Connecting cables
 External battery
 Jumpers
TECHNIQUES USED:
 VERTICAL ELECTRICAL SOUNDING:
 Wenner
 Schlumberger
PROCEDURE:
The following procedure is generic and will work with all meters. The meter’s manual should be
consulted for operational details.
 Verify that the metal strip between the meter’s C1 and P1terminals is disconnected (used for
3-Point testing)
 Install the 4 test probes in the ground equally spaced in straight line. Generally the shorter
spacing is done first.
 Using the conductors, connect the C1, P1, P2 and C2terminals to the electrodes. The
electrodes must be connected in order from the end, to the C1, P1, P2 and C2 terminals. The
test results will be invalid if the electrodes are not connected properly.
 Press the test button and read the digital display. Record the reading on the worksheet at the
appropriate location. If the reading is not stable or displays an error indication, double check
the connections. For some meters, the RANGE and TEST CURRENT settings may be
changed until a combination that provides a stable reading without error indications is
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Figure 7.1
reached. The addition of moisture is insignificant for the reading; it will only achieve a better
electrical connection and will not influence the overall results. Also a longer probe or
multiple probes (within a short distance) may help.
 Place the probes at each of the spacing indicated above and record the readings on the
worksheet
 All above steps of this procedure must be repeated at multiple locations on the site to obtain a
reliable soil profile.
OBSERVATION AND CALCULATIONS:
LOCATION MAP:
Figure 7.2 UET Lahore
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Figure 6.2
TARGET DEPTH:
40 ft.
CONFIGURATION:
1) WENNER CONFIGURATION:
Spacing (a) = 5,10,15,20,25,30,35,40
TABLE#6.1
Spacing (a) meter Resistivity (Ω-m)
1 99
2 110
3 112
4 118
5 130
6 155
7 165
8 200
9 215
10 235
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WENNER GRAPH:
LOG GRAPH FOR WENNER:
INTERPRETATION FROM GRAPH:
Two layers and single interface.
0
50
100
150
200
250
0 2 4 6 8 10 12
apparentresistivity(ρa)Ὡm
spacing (a) m
Electrode spacing (a) VS Apparent resistivity (ρa)
10
100
1000
1 10
resistivity(ρa)Ὡm
spacing (a) m
Electrode spacing (a) VS apparant resistivity (ρa)
wenner configration (VES)
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Figure 7.4
2) SCHLUMBERGER CONFIGURATION:
Spacing b/w potential electrodes= a= 3,6,9,12,15,18,21,24
Total spread is = 5a
Investigated depth = 5a/3
TABL#6.2
Spacing (a) Effective depth
(5a/2)
Resistivity
1 2.5 95
2 5 105
3 7.5 110
4 10 115
5 12.5 120
6 15 145
7 17.5 165
8 20 185
9 22.5 200
10 25 225
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GRAPH FOR SCHLUMBURGER:
LOG GRAPH FOR SCHLUMBURGER:
INTERPRETATION:
Two layers and a single interface.
0
50
100
150
200
250
0 5 10 15 20 25 30
Resistivity(ρa)Ὡm
Effective depyh (5a/2) m
Effective depth (5a/2) VS apparent resistivity (ρa)
schlmbergr configration (VES)
10
100
1000
1 10
Resistivity(ρa)Ὡm
Effective depyh (5a/2) m
Effective depth VS Apprent resistivity of Schlumberger
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BOREHOLE DATA:
The above data are collected from the borehole that were taken in UET ground.
COMMENTS:
The borehole data doesn’t coincides with the field data which shows that there exist some
problem in the field data.
10
m
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Figure 8.1
LAB#08
STATEMENT:
INTRODUCTION TO 2D AND 3D RESISTIVITY SURVEY
SCOPE:
To perform and understand the layout of 2D and 3D Resistivity Survey.
APPARATUS:
 Terrameter SAS 4000
ACCESSORIES:
 Electrodes
 12 V battery
 Imaging Cable
 Electrode Selector
 Hammer
 Tape
 Connectors
THEORY:
The purpose of electrical surveys is to determine the subsurface resistivity distribution by
making measurements on the ground surface. From these measurements, the true resistivity of
the subsurface can be estimated. The ground resistivity is related to various geological
parameters such as the mineral and fluid content, porosity and degree of water saturation in the
rock. Electrical resistivity surveys have been used for many decades in hydrogeological, mining
and geotechnical investigations. More recently, it has been used for environmental surveys.
We have seen the greatest limitation of the resistivity sounding method is that it does not take
into account horizontal changes in the subsurface resistivity. In many situations, particularly for
surveys over elongated geological bodies, this is a reasonable assumption. In theory, a 3-D
resistivity survey and interpretation model should be even more accurate. However, at the
present time, 2-D surveys are the most practical economic compromise between obtaining very
accurate results and keeping the survey costs down.
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Figure 8.2
1D SURVEY:
It is along a single axis y i.e, this survey measure only reading of resistivity with depth along a
straight line in y-axis direction. In order to locate a water supply tube-well that can serve the
congregation of thousands of worshippers patronizing the camp on weekly basis, a major
geophysical mapping of the camp was carried out. This involved both 1D and 2D surveys. 1D
electrical method using Vertical Electrical Sounding has been employed over the years to
characterize aquifer in different geologic environments and to map fractures in basement areas.
2D SURVEY:
It is along the two axis x, y. recently, attention is shifting to a more accurate method of imaging
the subsurface. 2D resistivity images are created by inverting hundreds to thousands of
individual resistivity measurements to produce an appropriate model of the subsurface resistivity.
3 D SURVEY:
It is along the three axis x, y and z. Since all geological structures are 3-D in nature, a fully 3-D
resistivity survey using a 3-D interpretation model (Figure 3c) should in theory give the most
accurate results. At the present time 3-D surveys is a subject of active research. However it has
not reached the level where, like 2-D surveys, it is routinely used. The main reason is that the
survey cost is comparatively higher for a 3-D survey of an area which is sufficiently large. There
are two current developments that should make 3-D surveys a more cost-effective option in the
near future.
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PROCEDURE:
 Select the suitable site for the experiment of resistivity survey.
 42 electrodes are placed at 5 ft interval depth..
 Instrument is attached with the battery.
 Instrument is started and readings are taken.
INTERPRETATION:
2D = we make simple contour map of resistivity.
3D = volumetric based map is formed for interpretation
COMMENTS:
The configuration were spread to know about the survey but due to the fault in battery the survey
were not done.
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LAB#09
STATEMENT:
TO PERFORM 2D RESISTIVITY SURVEY USING LUND IMAGING SYSTEM AT
UET AUDITORIUM GROUND
SCOPE:
To identify the different soil layers in UET auditorium ground
APPARATUS:
 Terrameter
 Battery
 Electrode
 Wires
 Connectors
 Jumper
 Crocodile connector
 Lund imaging selector
 Lund imaging wire
RELATED THEORY:
TERRAMETER SAS 4000 WITH LUND IMAGING SYSTEM:
It provides a system for automatic Resistivity and IP Imaging. ABEM Terrameter SAS 4000
with LUND Imaging System provides optimum versatility in infrastructure projects and
environmental studies.
FEATURES OF LUND IMAGING:
 It allows number of arbitrary cable arrangements and electrode arrays for Resistivity and
Induced Polarization survey (like Wenner, Schlumberger, gradient, dipole-dipole, pole-
dipole, pole-pole, square array, borehole etc.).
 It is also provided with some supporting softwares like software for data transfer from
instrument to PC, protocol generation software, file conversion software and pseudo section
plotting.
 Terrameter SAS 4000 allows number of geo-electrical surveys which include Resistivity
Sounding and Profiling (with different arrangements) and IP Survey and Subsurface Imaging.
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FIELD APPLICATIONS:
 Ground water resource management vulnerability assessment
 Mapping and monitoring of contaminated ground/groundwater
 Geotechnical pre-investigation
 Geological mapping
 Mapping/prospecting of natural resources
 Geothermal prospecting
 Sub-bottom mapping at sea and in lakes
 Mapping of frozen ground/permafrost.
 Archaeology
MAJOR ADVANTAGE:
A major advantage of the electrical imaging method is that it produces continuous images of the
variation in properties in the subsurface. This method can serve as an excellent basis for planning
detail investigations via for example a drilling and sampling programme with optimized
sampling locations. The detail investigation results can then in turn be used as a base for a
refined interpretation of the electrical imaging data, leading to a comprehensive and reliable
model of the underground.
Figure 9.26
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PROCEDURE:
 41 electrodes are connected at 5 ft. distances.
 The place where the electrodes are connected should be sprayed with water.
 Pocket multimeter may be used to check the error.
 The total spread was 210 ft. and the subsurface depth was 28 ft.
 After the connection the apparatus is started.
 The no. of cycles were 190.
 Electrode test is set to run for the whole electrodes.
 When the cycles are completed, the whole file is loaded to the software.
PROCEDURE TO LOAD THE DATA:
Softwares:
1) Res 2D inv.
2) SAS 4000
 The file is first loaded to the PC with a USB connecter from the terrameter.
 This file is in S4K extension.
 To convert the S4K file to .dat file, we will use the Res 2D inv. software.
 In this software go to the File menu and select New and then select Lund conversion
 Now press F8 to convert it to the .dat file extension
 After conversion load the same file to SAS 4000 software.
 Three models will be created, select the one that the last and least final model.
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FINAL MODELS FOR RESISTIVITY SURVEY IN UET GROUND:
INTERPRETATION:
There are four layers identified from the data (from 3.7m to 6m), The different colour in the
image shows different resistivity levels. Also with the increase in depth the resistivity is
increasing which shows that either there exists lower moisture content or anomalies are present.
There is an error of 9% which shows that the data is not a good one but may be acceptable.
PRECAUTIONS:
 The surface should not be too dry or too wet
 The electrodes should be connected properly
 Battery should be fully charged
REFRENCES:
Instruction manual of ABEM Terrameter SAS 4000 / SAS1000
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LAB#10
STATEMENT:
INTRODUCTION TO GPR SURVEY
SCOPE:
GPR uses electromagnetic wave propagation and scattering to image and identify changes in
electrical and magnetic properties in the ground.
SHIELDED ANTENNA GPR:
GPR means Ground Penetrating Radar. It works on electromagnetism principle. RAMAC/GPR
shielded antennas are primarily used for medium to high resolution surveys. The shielded
antenna construction makes the antennas especially suitable for urban investigations or at sites
with a lot of background noise.
A GPR measurement system consists of a transmitter and a receiver antenna and a control unit.
In the system applied in this practical course both antennas are placed in one box. The main part
of the GPR system is the control unit which generates the GPR signal and also receives the
signals after their passage through the ground. The complete system is computer controlled. The
measurement wheel at the back of the antenna box measures the distance along the survey track
and triggers the emittance of the electromagnetic pulses.
Figure 270.1 GPR Bag Figure10.28 GPR with Accessories
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SPECIFICATIONS:
The shielded 100MHz antenna is the lowest shielded antenna frequency commercially
available. It is used for medium to low resolution. It is suitable for geological and geotechnical
applications.
GPR SPECIFICATIONS
Antenna Frequency
MHZ
Radial Resolution
m/µs
Maximum Penetration Depth
m
25 100 50
50 50 40
100 25 25
200 12.5 12
250 10 8
500 5 6
800 3 2.5
1000 2.5 1.5
1200 2.1 1
1600 1.6 0.5
2000 1.3 0.4
PARTS OF GPR
 Distance measuring wheel
 Monitor
 7.5 V 2 batteries
 Transmitter
 Receiver
 Cables
 Wear plate
 Pulling handles
Figure10. 3 Battery place Figure 10.4 Wheel
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HOW GPR WORKS:
When a wave impinges on interface, it scatters the energy according to the shape and roughness
of the interface and the contrast of electrical properties between the host material and the object.
Part of the energy is scattered back into the host material, while the other portion of the energy
may travel into the object. The portion of the wave that propagates into the object is said to be
refracted. The angle that the wave enters into the object is determined by Snell’s law, which can
be stated as follows:
V1 / V2 = sin Φ1 / sinΦ2
Where,
V1 and V2 are the velocities of the wave through the upper and lower materials, respectively,
and Φ1and Φ2 are the angles of the ray path for the incident and refracted waves, respectively.
FIELD APPLICATIONS:
The system supports a number of subsurface investigations. Some of which are given below:
- Archeological site assessment
- Measuring bridge deck thickness
- Underground mining mapping
- Underground storage tank location
- Excavation planning
- Utility detection
- Hazardous waste site assessment
- Void detection and location
LIMITATIONS:
 The most significant performance limitation of GPR is in high-conductivity materials such as
clay soils and soils that are salt contaminated.
 Considerable expertise is necessary to effectively design, conduct, and interpret GPR
surveys.
 Relatively high energy consumption can be problematic for extensive field surveys.
REFRENCES:
- http://en.wikipedia.org/wiki/Ground-penetrating_radar
- http://www.geophysical.com/whatisgpr.htm
- http://www.geophysical.com/
- http://mysite.du.edu/~lconyers/SERDP/variablesaffecting2.htm
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LAB#11
STATEMENT:
GPR DATA PROCESSING AND INTERPRETATION
SOFTWARE USED FOR THE INTERPRETATION:
GV (GROUND VISION) RAMAC
MALÅ Ground Vision Software is a data acquisition software platform designed by MALÅ
Geoscience for MALÅ GPR systems with Ethernet communication. This softwares primary
function is data acquisition, but also includes tools for filtering, printing of GPR data
and includes support for multi-channel operation.
Ground Vision is the dedicated data acquisition software platform for MALÅ's single or multi-
channel GPR systems. As Window based software (running under W2000 or later), Ground
Vision offers an easy-to-use user interface with file management, printing and other key features.
Each measurement and its associated settings are stored in files. Filtering can be performed
during data acquisition measurements, or afterwards during post-processing. Ground Vision
software supports GPS coordinate logging during measurement. All radar grams can be printed
as such, or post-processed by further software.
DATA FROM GPR SURVEY:
File # DAT_0101
Frequency= 500 MHZ (6m penetration depth)
Velocity= 100 m/µs
STANDARD CHART FOR THE DIELECTRIC CONSTANT VALUES:
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GPR DATA FILE IN MALA SOFTWARE:
FROM THE FIRST PICK UP TIME THE FOLLOWING DATA IS COLLECTED:
Distance Time
3.5 10.2
20 9.8
25 9.9
59.5 10.1
64 10.2
92 9.5
129 10.5
144.5 9.8
145 10
147.5 10.2
178.5 11
186 10.5
194.5 10.8
195 9
195.5 9.9
227 10.5
248 12
260.5 10.8
262 10.5
267 10.6
278 10.5
286 10.2
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Graph#11.1 Graph B/W Time and Distance:
Graph 11.29
Velocity can be calculated using:
V=
9
9.5
10
10.5
11
11.5
12
0 50 100 150 200 250 300 350
Time
Distance
Figure 10.30Borehole data
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Depth of specific layer can be calculated by using:
S= vt
INTERPRETATIONS:
There are 4 layers that is mostly found from the GPR data. There is a change in data from 120m
to 200m which shows that there exist some anomalies. The anomaly may be pipe or concrete
slab present near the cricket ground.
COMMENTS:
In actual field we know that there is a pipe and a concrete slab present near the cricket ground so
we have a clue from the real data. By comparing it with the GPR data we are sure that there is
anomaly present. Also the data shows that the GPR is working great.
REFRENCES:
- http://www.malags.com/products/mala-groundvision-2
- http://hyperphysics.phy-astr.gsu.edu/hbase/tables/diel.html
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LAB#12
STATEMENT:
INTRODUCTION TO GRAVITY SURVEY
SCOPE:
To understand the gravity survey and to familiar with its applications
EQUIPMENT:
CG-5 Autograv (Gravimeter)
RELATED THEORY:
CG-5 AUTOGRAV (GRAVIMETER):
A gravimeter is an instrument used in gravimetry for measuring the local gravitational field of
the Earth. A gravimeter is a type of accelerometer, specialized for measuring the constant
downward acceleration of gravity, which varies by about 0.5% over the surface of the Earth.
The CG-5 is the latest, gravity meter. It offers all of the features of the low noise industry
standard CG-3M micro-gravity, but is lighter and smaller, has a larger screen which gives a
superior user interface. The CG-5 can be operated with minimal operator training, and automated
features significantly reduce the possibility of reading errors.
Data down load bottlenecks have been eased with the provision of a fast USB interface and
flexible data formats. Noise rejection has been improved.
TYPES OF GRAVIMETER:
ABSOLUTE GRAVIMETER:
Absolute gravimeters, which nowadays are made compact so they too can be used in the field,
work by directly measuring the acceleration of a mass during free fall in a vacuum, when the
accelerometer is rigidly attached to the ground.
Figure 12.1 Gravimeter
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RELATIVE GRAVIMETERS:
Most common relative gravimeters are spring-based. They are used in gravity surveys over large
areas for establishing the figure of the geoid over those areas. A spring-based relative gravimeter
is basically a weight on a spring, and by measuring the amount by which the weight stretches the
spring, local gravity can be measured. However, the strength of the spring must be calibrated by
placing the instrument in a location with a known gravitational acceleration.
SPECIFICATION OF CG-5 AUTOGRAV:
Sensor Type Fused Quartz using electrostatic nulling
Reading Resolution 1 microGal
Standard Field
Repeatability
<5 microGal
Operating Range 8,000 mGal without resetting
Residual Long-Term Drift : Less than 0.02 mGal/day (static)
Tares Typically less than 5 microGals for shocks up to 20 G
Automated Corrections Tide, Instrument Tilt, Temperature, Drift, Near Terrain,
Noisy Sample, Seismic
Noise Filter
Operating Temperature -40°C to +45°C
Ambient Temperature
Coefficient
0.2 microGal/°C
Pressure Coefficient 0.15 microGal/kPa
Magnetic Field Coefficient 1 microGal/Gauss
Power Consumption : 4.5 W at +25°C
Standard System CG-5 Console, Tripod base, 2 rechargeable batteries,
Battery Charger
110/240 V, External Power Supply 110/240 V, RS-232 and
USB Cables
GRAVITY OBSERVATIONS AND LEVELLING:
When performing manual gravity observations with relative gravimeters different circumstances
have to be considered. Important aspects relate to the actual measuring site, the specific
instrument and handling of it, natural conditions and of course, since the reading is carried out
manually, the observer himself. Because gravity measurements are normally conducted in loop
sequences higher order stations (as a minimum) are normally measured several times during a
working day.
It is essential that the gravimeter is kept strictly levelled during each observation sequence. This
requires continuous monitoring and frequent adjusting of the instrument level. The procedure
associated with most manually operated gravimeters may be rather demanding with respect to
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time and mental concentration of the observer. Especially during hot summer days when stations
are located on asphalt-paved ground this task are often really cumbersome and time-consuming
while the “legs“ of the meter base “pan“ may slowly sink into the warm asphalt thereby
distorting the measurements. Similar problems may arise if the underground is wet. With
automatic gravimeters like the Scintrex CG-5 Autograv the problem of levelling the instrument
are automatically handled by electronic tilt sensors. Along with automatic reading and logging of
the data into the gravimeters memory measuring becomes less demanding as regards the
involvement and skills of the observer.
STEPS TO FOLLOW:
STEP#01
GEOLOGICAL REPORT OF AN AREA:
Includes tectonic setting, outcrop mapping, topography, structure and stratigraphy. From these
values we can prepare the geological report.
STEP#02
3D GEOLOGICAL MODEL:
For 3D model we have to know about the orientation, structure etc. The geological report is
necessary for 3D model. From these features the 3D geological model is prepared.
STEP#03
PLOTTING GRAVITY LINES:
Perform proper grids and acquire data from grids. The grids are easy to read and give accurate
readings.
STEP#04
DEFINE GRAVITY BASE STATION:
Point of known coordinates and from IGSN71 taking a base station and define gr value. The
values of the base stations are already known.
IGSN71: International gravity standardization network.
STEP#05
PREPARE EQUIPMENT:
Time is very important (day/night).
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Tide correction:
Tide correction is applied for time. The apparatus have its own tide correction in it.
Drift Correction:
It is also called mechanical correction. As the equipment is used for a long time so the apparatus
starts to show error. This error can be removed by applying the drift correction.
STEP#06
DEFINE THE READING INTERVAL:
On the base of experience and geology define the intervals. The coordinates can also be defined.
STEP#07
ELEVATION OF AREA WITH RESPECT TO MEAN SEA LEVEL:
The values are feeded in the instrument country wise.
Latitude adjustment:
It can be calculated by subtracting the normal gravity values from the observed gravity values.
USES:
- Basement rock identification
- Igneous body on regional scale
- Anticline structures
- Mineral ores identification
- Also used for the contrast of sedimentary and igneous body
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LAB#13
STATEMENT:
SURFER GRAVITY CONTOUR MAP
SCOPE:
To draw the surfer map and to interpret the gravity and density changes in different zones from
the surfer map.
PROCEDURE:
1) Copy the data from surfer to the New work sheet in the surfer.
2) The data consists of longitude, latitude and bouguer gravity values. The grid file can be
created from this data by using the same file saved in .bln extension.
3) After it go to the contour map option and select the
same grid file that is generated and contour map is drawn.
4) Now selecting the same grid make a 3D surface map and overlay the contour map and the 3d
surface map. Colour can changed from its properties. The final results will be:
INTERPRETATION FROM GRAVITY CONTOUR MAP:
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ZONE 1: (N-E DIRECTION)
There is a decrease in density but overall density doesn’t changes. This shows that either there is
a loose material, limestone cavity or sink hole present.
ZONE 2: (N-W DIRECTION)
The density contrast increases and decreases rapidly, so there is a change in the density at this
zone. This shows that there is an anomaly present in this zone.
ZONE 3: (S-E DIRECTION)
There is a high density contrast at this zone. The density increases rapidly in this zone. This
shows that either there is an igneous intrusion or mineral ore etc. present.
ZONE 4: (S-W DIRECTION)
The variation doesn’t seem to be high at this zone. There is no abrupt change happen here. This
shows that there is a continuous strata deposited here.
SURFER GRAVITY CONTOUR MAP:
Figure 13.31 Surfer Gravity Contour Map
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LAB#14
STATEMENT:
INTRODUCTION TO PORTABLE WELL LOGGER AND MAGNETOMETER
RELATED THEORY:
WELL LOGGING:
Well logging, also known as borehole logging is the practice of making a detailed record (a well
log) of the geologic formations penetrated by a borehole. The log may be based either on visual
inspection of samples brought to the surface (geological logs) or on physical measurements made
by instruments lowered into the hole (geophysical logs). Some types of geophysical well logs
can be done during any phase of a well's history: drilling, completing, producing, or abandoning.
Well logging is performed in boreholes drilled for the oil and gas, groundwater, mineral and
geothermal exploration, as well as part of environmental and geotechnical studies.
TYPES OF LOGS:
 Resistivity logs
 Porosity logs
 Sonic logs
 Gamma ray log
 Density log
 Neutron log
Figure 14.32 Well Logging software
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PORTABLE WELL LOGGER:
Borehole logging provides in situ measurements of the physical properties of the subsurface
layers. The Mount Sopris MGX II borehole logging system is a portable system controlled by a
notebook computer that allows for the acquisition of up to 9 logs simultaneously, using Poly
probe technology. The motorized winch, efficiency of data acquisition, and the amount of
information available from one logging run make this a very economical survey tool. The system
logs include natural gamma, self-potential, single point resistance, normal resistivity (using 8,
16, 32 and 64 inch arrays), a lateral log, induced polarization, magnetic susceptibility, acoustic
velocity, temperature, fluid resistivity, electromagnetic induction, flow meter, caliper, and
borehole deviation.
DATA ACQUISITION:
The software used for the data acquisition is Ms Well. This software shows proper reading when
the logger is moving in the well bore. It also shows that either any of the error is present in the
connection of the apparatus.
DATA INTERPRETATION:
The software used for the data acquisition is Well cad. It consists of different modules like core
and cutting module, 3D module and many others which can be used to interpret the data from it.
Figure 14.33 MS Well
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APPLICATIONS:
- In environmental and groundwater investigations, locations of greatest groundwater flow are
determined using temperature and/or self-potential logs, flow meters and caliper logs.
Natural gamma, electrical, and magnetic logs characterize the lithology in terms of grain size
and clay volume.
- Fluid and formation resistivity logs are used to delineate areas of groundwater contamination.
An acoustic velocity log provides information on porosity and well completion to help
minimize cross-contamination in remediation programs. The determination of exact depths
and the physical characteristics of each layer decrease the uncertainties in groundwater
modeling and allow for the accurate placement of well screens for sampling, or groundwater
extraction.
- In geotechnical investigations, borehole logs provide a direct measure of the physical
properties of the subsurface with accurate delineation of each horizon. The full waveform
sonic log provides compressional wave velocities, and the sonic porosity of each layer.
Companion surveys provide shear wave velocities for dynamic moduli determinations.
- In mining applications, a variety of tools are used to determine petrophysical properties and
physical boundaries not visible in the drill core. The sonic log is used in conjunction with
seismic reflection surveys to provide accurate interval velocities of subsurface layers for
interpretation.
- The natural gamma log is a standard parameter used in coal evaluation, and uranium
exploration, as well as in geological mapping of igneous and metamorphic environments.
This log shows variations in natural radioactivity which are correlated with changes in
lithology.
Figure 14.34 Well cad
Geophysical Exploration 2011-GE-56
62 | P a g e
INTRODUCTION TO MAGNATOMETER:
- TAGS-6 (click on the above image for a detailed view) represents the latest development in a
long line of LaCoste-based airborne gravity systems, stretching back to the first successful
airborne gravity flights in 1958 and building on the success of the TAGS System. For over
50 years, LaCoste gravimeters have acquired hundreds of thousands of line kilometers of
gravity data during academic, government, and commercial surveys. TAGS-6 blends the
latest in GPS and data acquisition technology with the solid foundation of the LaCoste
dynamic gravimeter.
- TAGS-6 is an upgrade to the TAGS/Air III gravity meter, and is designed specifically for
airborne operations. The system incorporates a time-tested, low-drift, zero-length-spring
gravity sensor mounted on a gyro-stabilized gimbal platform. The sensor has a worldwide
gravity measuring range (no reset necessary) of 500,000 milliGals.
Figure 14.35 Magnetometer
HISTORY:
The first magnetometer was invented by Carl Friedrich Gauss in 1833 and notable developments in
the 19th century included the Hall Effect which is still widely used.
THEORY:
Magnetometers are measurement instruments used for two general purposes: to measure
the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in
some cases, the direction of the magnetic field at a point in space.
Geophysical Exploration 2011-GE-56
63 | P a g e
USES:
Magnetometers are measurement instruments used for two general purposes: to measure
the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in
some cases, the direction of the magnetic field at a point in space.
COMMENTS:
The apparatus were out of order so we did not get any readings.
REFRENCES:
- http://scintrexltd.com/internal.php?storeCategoryID=4&s_page=airborne
- http://www.geomatrix.co.uk/products/land-geophysical-equipment/gravity/cg5/

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Geophysics Labs

  • 1. Geophysical Exploration 2011-GE-56 1 | P a g e Lab#01 STATEMENT: INTRODUCTION TO GEOPHYSICAL LAB EQUIPMENTS SCOPE: To know and familiar with the geophysical lab equipment’s and their uses in the field THEORY: GEOPHYSICS: Geophysicists study a variety of natural phenomena, including the Earth's shape, the dynamics of its interior, and atmospheric processes. APPLICATIONS OF GEOPHYSICS: Geophysics is a vast field and its uses are countless. The following are some of the applications of geophysical exploration:  Mineral exploration  Oil and gas exploration  Civil engineering projects  Archeology  Unexploded ordnance detection  Interior of earth  Finding problematic zones in tunnels and mines Specification and accessories of each of the equipment are given as: 1) TERRAMETER SAS 4000: Terrameter SAS 4000 has the ability to measure Resistivity and Induced Polarization as well as Self Potential, making the Terrameter SAS 4000 a highly competent and flexible solution for near investigations. All measured data is stored into a database which allows for export or other suitable programs for interpretation and analysis. A Borehole log option is also available. ADVANTAGES: - Groundwater resource management and vulnerability assessment, - Mapping and monitoring of contaminated ground/groundwater - Geotechnical pre-investigation - Geological mapping - Mapping/prospecting of natural resources - Geothermal prospecting - Sub-bottom mapping at sea and in lakes
  • 2. Geophysical Exploration 2011-GE-56 2 | P a g e Figure 1.1 Figure 1.2 - Mapping of frozen ground/permafrost - Archaeology - Resistivity Imaging a Robust Method ACCESSORIES OF TERRAMETER:  Electric cables: Cables are used extensively in electronic devices for power and signal circuits.  Connectors: An electrical connector is an electro- mechanical device for joining electrical circuits as an interface using a mechanical assembly. Connectors consist of plugs (male-ended) and jacks (female-ended).
  • 3. Geophysical Exploration 2011-GE-56 3 | P a g e Figure 1.3 Figure 1. 4 Figure 1.5  Polarized electrodes: A metallic conductor behaves as a polarized electrode if it allows no movement of charge between itself and the solution phase.  12 volt battery: An electric battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy.  Connecting cables: Connecting cables are used to connect two or more devices.
  • 4. Geophysical Exploration 2011-GE-56 4 | P a g e Figure 1.6 Figure 1.7  Steel electrodes: A type of steel resistant to corrosion as a result of the presence of large amounts of chromium (12 to 15 percent). The carbon content depends on the application.  Electrode Selector: Resistivity imaging technique in which overall 64 resisters can be read out. 2) TERRALOC MK-6: Terraloc MK-6 is an instrument used in geophysical exploration. It is used seismic survey and is an old version. Terraloc MK-6 has the following specifications: Up hole channel Channel 12 or 24, redirectable to a separate connector Sampling Rate 25, 50, 100, 250, 500 µs, 1, 2 ms Minimum Input Signal ±0.24 µV Maximum Input Signal ±250 mV Frequency Range 2-4000 Hz Processor 386/486 (Depending on model) Memory 4 to 32 MB RAM (Depending on model) Power 10 to 30V DC External battery or internal battery
  • 5. Geophysical Exploration 2011-GE-56 5 | P a g e Figure 1. 8 Figure 1. 9 Figure 1.10 ACCESSORIES FOR TERRALOC MK-6:  5-6kg hammer: Hammer is used to produce seismic waves in the ground. The hammer is striked against the rubber plate.  Rubber/metal/fiber plate: Plate provide concentration to seismic waves. A hammer is used to hit it.  Explosives: Explosive is used for the generation of seismic waves. The explosives are used in holes and the length and diameter of the holes are calculated according to the geology and depth. Explosives are mostly used in areas where seismic reflection survey is used. Extra care must be taken while using explosives.
  • 6. Geophysical Exploration 2011-GE-56 6 | P a g e Figure 1.11 Figure 1.12 Figure 1.13  Seismic cable: It is used to connect all the geophones which record the seismic waves resulting from either Vibroseis or dynamite when recording seismic data.  Geophones: A geophone is a device that converts ground movement (displacement) into voltage, which may be recorded at a recording station. Types of geophones w.r.t sensitivity: - SG-5 (high-sensitive geophone) - SG-10 (high performance geophone sensor) - jF-20DX (conventional geophone sensor)  Triggering device: It is used to initiate the whole system.
  • 7. Geophysical Exploration 2011-GE-56 7 | P a g e Figure 1.14 Figure 1.15 3) SHIELDED ANTENNA GPR: GPR means Ground Penetrating Radar. It works on electromagnetism principle. RAMAC/GPR shielded antennas are primarily used for medium to high resolution surveys. The shielded antenna construction makes the antennas especially suitable for urban investigations or at sites with a lot of background noise. A GPR measurement system consists of a transmitter and a receiver antenna and a control unit. In the system applied in this practical course both antennas are placed in one box. The main part of the GPR system is the control unit which generates the GPR signal and also receives the signals after their passage through the ground. The complete system is computer controlled. The measurement wheel at the back of the antenna box measures the distance along the survey track and triggers the emittance of the electromagnetic pulses. SPECIFICATIONS: The shielded 100MHz antenna is the lowest shielded antenna frequency commercially available. It is used for medium to low resolution. It is suitable for geological and geotechnical applications. Dimensions: 1.25 x 0.78 x 0.20 m, Weight: 25.5 kg. ACCESSORIES FOR GPR:  Distance measuring wheel: This small, lightweight distance-measuring wheel is designed with flexible mounts to attach to most GSSI antennas with the mounting bolts. It measures distance.
  • 8. Geophysical Exploration 2011-GE-56 8 | P a g e Figure 1.16 Figure 1.17 Figure 1.18  Single button monitor: Single button monitor is an old type of monitor in which the whole process is controlled by using a single button present on the monitor.  Rods/Extension Rods: It is an instrument used to cause the sharpened sampler edge to cut through the soil. 4) GRAVIMETER: It is used for gravity survey. It is easy to operate and has excellent field repeatability. It is fully portable and it automatically rejects the noise. It transfers data quite easily.
  • 9. Geophysical Exploration 2011-GE-56 9 | P a g e Figure 1.20 Figure 1.19 SPECIFICATIONS FOR GRAVIMETER: ACCESSORIES FOR GRAVIMETER:  Tripod stands: A stand with three geophones attached with it. It has a level bubble for leveling the tripod. 5) MAGNETOMETER: It is used for magnetic survey. It gives the magnetic information of the subsurface formations. Magnetometers are measurement instruments used for two general purposes: to measure the magnetization of a magnetic material like a Ferro magnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space. USES OF MAGNETOMETER: SENSOR TYPE Fused quartz using electrostatic nulling READING RESOLUTION 1microGal POWER CONSUMPTION 4.5Watts at 25°C WEIGHT 8kg (17.5lbs) including battery GPS ACCURACY Standard OPERATING RANGE Worldwide (8,000mGal without resetting) STANDARD DEVIATION < 5microGal
  • 10. Geophysical Exploration 2011-GE-56 10 | P a g e Figure 1.21 Magnetometers are widely used for measuring the Earth's magnetic field and in geophysical surveys to detect magnetic anomalies of various types. They are also used militarily to detect submarines. In archaeology and geophysics, where the sensor sweeps through an area and many accurate magnetic field measurements are often needed, cesium and potassium magnetometers have advantages over the proton magnetometer. 6) PORTABLE WELL LOGGER: It is used for well logging purposes for shallow depth. It is a portable well logger that can be transported from one place to other easily. FEATURES OF WELL LOGGER:  For upward logging, also for downward logging  Can receive digital / analog / pulse signal  Winch automatically stops upon reaching the logging termination depth  Indoor simulation logging, repeatability observation of instruments and probes  Integration of depth control system and data acquisition system  Digital real-time display of frequency, voltage for supply voltage  Real-time display of working voltage, working current for down hole probe
  • 11. Geophysical Exploration 2011-GE-56 11 | P a g e Figure 1.22 Figure 1.23 ACCESSORIES OF WELL LOGGER:  Probe: Probes used for gamma ray and SP resistivity logs. Different types of probes are used for different purposes. Some of them are given as:  Natural Gamma Logging  Caliper Logging  Spontaneous Potential Logging  Nature Gamma Probe  Acoustic Wave Probe  Temperature and Liquid Resistance probe 7) MINI-SEIS: The Mini-Seis is the very definition of a great blast monitoring seismograph for an affordable cost. It is ideal for all kinds of blast vibration monitoring and for most continuous vibration monitoring in bargraph mode. Rugged, reliable and very easy to use, the Mini-Seis sets the standard for value in a seismograph. This device measures and detects surface waves, mostly earthquake waves are detected.
  • 12. Geophysical Exploration 2011-GE-56 12 | P a g e Figure 1.24 FEATURES OF MINI SEIS:  Lightweight and easy to use.  Costs much less than comparable seismographs.  Maintenance and calibration costs are also less.  Keypad and display for easy field setup and data review.  Selectable seismic and acoustic recording range, seismic and acoustic trigger level, sample rate and record duration.  Can use either AC or DC power for long term monitoring.  Sophisticated, non-loss data compression results in small record sizes and fast data transfer. REFERENCES: - http://shop.modelis-gis.com/shop/product.php?id_product=273&id_lang=1 - Ebooks from google - Wikipedia search - http://en.wikipedia.org/wiki/Exploration_geophysics - http://www.geophysicalmethodsofexploration.com/ - http://en.wikipedia.org/wiki/Reflection_seismology - http://en.wikipedia.org/wiki/Magnetometer
  • 13. Geophysical Exploration 2011-GE-56 13 | P a g e LAB#02 INTRODUCTION TO TERRALOC MK-6 STATEMENT: To study and describe Terraloc ABM Mk-6 and its reliability in the field SCOPE:  It is used to conduct seismic refraction and reflection surveys.  Terraloc is a compact and complete seismograph with all we need to collect our seismic data in single casing.  It is used to explore the sub-surface feature of the earth.  Ideal for all types of applications in shallow seismic as refraction, reflection, crosshole, surface wave investigations. THEORY: TECHNICAL SPECIFICATIONS: Up hole channel Channel 12 or 24, redirectable to a separate connector Sampling Rate 25, 50, 100, 250, 500 µs, 1, 2 ms Minimum Input Signal ±0.24 µV Maximum Input Signal ±250 mV Frequency Range 2-4000 Hz Processor 386/486 (Depending on model) Memory 4 to 32 MB RAM (Depending on model) Data Storage 80 to 250 MB hard disk and 1.44 MB floppy disk drive 3.5 in. Power 10 to 30V DC External battery or internal battery
  • 14. Geophysical Exploration 2011-GE-56 14 | P a g e Figure 2.1 Terraloc MK-6 TYPES OF GEOPHONE SPREADS: Split Spread: Type of spread in which the source is in between regularly spaced receivers. End-on Spread: Type of spread in which the source is at one end of regularly spaced receivers. In-line Offset: In which the source away from the first receiver (i.e., Distance of source may vary). Cross Spread: In which two lines of geophones are laid out roughly at right angle and one source is fired at the intersection point. L Spread: In which the source is at Centre and geophones are at sides, forming an L shape.
  • 15. Geophysical Exploration 2011-GE-56 15 | P a g e PROCEDURE: Terraloc MK-6 is an instrument which records seismic waves generated by either hammer, explosives, earth quake or any other source. The procedure is simple and easy. The connection is being built between the Terraloc and seismic cables. The geophones are connected with the cables and is recording the seismic waves being generated. The source may kept at either ends or at the middle of the geophones. The battery is used to power the Terraloc. Before starting the survey triggering is done which removes the error in the apparatus. The wiggles are recorded and is saved in the system for further calculations. APPLICATIONS OF TERRALOC MK-6:  Terraloc MK 6 is the best one instrument to find out the depth of bed rock.  It helps to locate the water table.  It also helps to determine the velocities of waves through different layers.  We can also compute depth of layer boundaries and so their thicknesses too.  Real time noise monitoring.  Frequency spectrum analysis.  Refractor velocity indication. REFRENCES: Terraloc-MK-6-Manual-1994-02-24
  • 16. Geophysical Exploration 2011-GE-56 16 | P a g e LAB#03 STATEMENT: SEISMIC REFLECTION SERVEY IN UET STADIUM GROUND OBJECTIVE: Main objective of this lab is to acquire data for 80 ft. subsurface depth PRINCIPAL: This test method is based on refraction of waves according to Snell’s Law. A refraction survey uses refracted (or head) waves to deduce velocities of the layered-earth model. So called first arrival information is used for the analysis. More generalized methods based on the turning waves from an arbitrary velocity model have also been used in recent days. This is called seismic refraction tomography. APPARATUS:  Terraloc Mark 6  25 Geophones  12 V Battery  Seismic cable  Extension Cable
  • 17. Geophysical Exploration 2011-GE-56 17 | P a g e Figure 3.1 Terraloc Setup PROCEDURE:  Setup the geophones according to the acquisitive design.  Make all the connections with the help of seismic cables.  Also attach a trigging geophone with the Terraloc.  To check the geophones send signals by hammering to the geophones.  See on Terraloc if we are getting signals on all geophones then ok otherwise check all the connections of geophones and try again until u get signals on all geophones.  Send signals to the geophones by generating seismic by hammering.  We get a data of the subsurface read the data from the Terraloc or save it.  Then we have to plot the data THEORY:  FARWARD SHOT: In farward shot the source is near to the first geophone (may be at the last one. Actually farward and reverse shot are opposite of each other).  MID SHOT: When the source is placed in the middle of geophones then it is called mid shot.  REVERSE SHOT: The source is placed in opposite to the farward shot. (may be at the end of geophones).
  • 18. Geophysical Exploration 2011-GE-56 18 | P a g e Figure 3.2 Geophones Setup COMMANDS OF TERRRALOC:  First of all <ARM> the apparatus.  Then for triggering press <Ctl + ARM> then <DISARM> the apparatus  Then start the hammering at any required point mid or farwad.  Then select the <file> and then the files as (File#00014.SG2).  Then enter and save the file and open the new file and repeat the same procedure for next shot. DATA ACQUIRED IN THE STADIUM: FOR 3 ft. INTERVAL:  72 ft. Spread giving 36 ft. Subsurface Depth: Farward Shot: File #000142.SG2 Mid Shot: File#000143.SG2 Reverse Shot File#00044.SG2 FOR 5 ft. INTERVAL:  120 ft spread giving 60 ft. subsurface depth: Farward Shot: File #000145.SG2 Reverse Shot: File #000146.SG2 FOR 7 ft. INTERVAL:  168 ft. spread giving 82 ft. subsurface depth: Farward Shot: File #000147.SG2 & File #000148.SG2 Reverse Shot: File #000146.SG2
  • 19. Geophysical Exploration 2011-GE-56 19 | P a g e Mid Shot: File#000149.SG2 LAB#04 TO CALCULATE THE THICKNESS OF DIFFERENT LAYERS BY USING GRAPH PAPER GIVEN DATA: GEOPHONE# TIME (ms) 12 8 11 14 10 22 9 24 8 28 7 30 6 31 5 36 4 38 3 40 2 42 1 44 Using Graph#01 Slope (m1) = 5 ms/m Velocity (V1) = 1/5×1000 = 200 m/sec Slope (m2) = 2 ms/m Velocity (V2) = 500 m/sec Intercept Time = 0.021 sec XCross over = 7.7 THICKNESS OF LAYER:
  • 20. Geophysical Exploration 2011-GE-56 20 | P a g e h1 = √ h1 = 2.29m GIVEN DATA: USING GRAPH#02: There are 3 layers and 2 interfaces in the given data. Also we have calculated: - Slope (m1) = 1×10-3 sec/m - Velocity (V1) = 1000 m/sec - Slope (m2) = 4×10-4 sec/m - Velocity (V2) = 2500 m/sec - Slope (m3) = 2×10-4 sec/m - Velocity (V3) = 5000 m/sec - Xcross-over for 1st = 40 m - Xcross-over for 2nd = 123 m - Intercept Time T1 = 0.024 sec DISTANCE (meter) TIME (sec) 10 0.010 20 0.020 30 0.030 40 0.040 50 0.045 75 0.055 100 0.065 125 0.075 150 0.080 175 0.085 200 0.090 250 0.100 300 0.110
  • 21. Geophysical Exploration 2011-GE-56 21 | P a g e - Intercept Time T2 = 0.049 sec THICKNESS OF 1ST LAYER: h1 = √ h1 = 13.09 m Another formula for finding thickness of layer: h1 = √ h1 = 13.10 m THICKNESS OF 2ND LAYER: h = √ h2 = 36.08 m 2nd layer thickness can also be find from the following formula: h2 = ( ) RESULTS: Thickness for graph#01 = 2.29m Thickness of 1st layer for graph#02 = 13.10m Thickness of 1st layer for graph#02 = 36.08m
  • 22. Geophysical Exploration 2011-GE-56 22 | P a g e Figure 5.125 LAB#05 STATEMENT: SEISMIC REFLECTION DATA INTERPRETATION SCOPE: Time can be calculated from the seismic reflection data. Surfer is used to draw the contour map by using time, latitude and longitude. APPARATUS:  Final filtered migrated stack  Magnifying glass  Pencil  Scale  Base map THEORY: BASE MAP: A base map contains seismic line and source points with coordinates (latitude and longitude). CONTOUR MAP: A contour map uses contour lines which are often just called a "contour", to join points of equal elevation (height) and thus this shows valleys and hills, and the steepness of slopes. The relative spacing of the lines indicates the relative slope of the surface.
  • 23. Geophysical Exploration 2011-GE-56 23 | P a g e Figure 5.2 STEPS FOR DRAWING CONTOUR MAP: STEP 1: COLLECT THE SEISMIC SECTIONS: Example: Line= 915-MWI-81 From the above: 91= Year at which data is collected 5= Seismic party no. MWI= Abbreviation for area 81= Seismic line no. Full details are given at the header which are at the right side of the Final filtered migrated stack. Like channels, source type, source interval etc. STEP 2: INTERPRETATION STEPS: At Y-axis= Time ( Mostly in ms) At X-axis= Source points (Shot points) Source point no. = First shot no. and last shot no. should be given Example: 318-110= 208 (Last shot - First shot) Multiplying the shot no. difference with the interval Example: 208×50 (Interval) = 10900 Check the parameters 1) Pick seismic time of different seismic horizons:
  • 24. Geophysical Exploration 2011-GE-56 24 | P a g e - Continuous reflectors are called seismic horizons (Dark Lines) - Pick times of horizons at different points 2) Seismic well tie: Collect the data from well logs (Sonic and density). Comparing well log data with synthetic seismogram by calculating its reflection coefficient and acoustic impedence. R.C= - Then making a graph between depth and R.C. A wiggle is generated from this graph. - This wiggle is compared with the seismic wiggle. - If the well is not present then the geological report which contains the extend of layers and outcrops will help us. - Then converting the seismic data to depth from time and velocity relation. 3) Mapping of the seismic Horizon: - Note the latitude and longitude of the required seismic line from the base map. - Entering the latitude, longitude and time into the surfer software. - A contour map is drawn from that data. OBSERVATION AND CALCULATIONS: Data for Formation No.1: SP # LATITUDE LONGITUDE TIME 480 71.3 32.65 -1.44 470 71.29 32.65 -1.46 460 71.285 32.65 -1.46 450 71.28 32.65 -1.45 440 71.275 32.65 -1.43 430 71.27 32.65 -1.42 420 71.26 32.65 -1.41 410 71.25 32.65 -1.38 400 71.245 32.65 -1.37 390 71.24 32.65 -1.35 380 71.235 32.65 -1.32 370 71.23 32.65 -1.30 360 71.225 32.65 -1.29 350 71.22 32.65 -1.26 340 71.215 32.65 -1.25 320 71.205 32.65 -1.14 310 71.2 32.65 -1.10 300 71.19 32.65 -1.07 290 71.185 32.65 -1.02
  • 25. Geophysical Exploration 2011-GE-56 25 | P a g e Contour Map For Formation#01: Contour Map (3D) For Formation#01:
  • 26. Geophysical Exploration 2011-GE-56 26 | P a g e SP # LATITUDE LONGITUDE TIME 480 71.3 32.65 -1.93 470 71.29 32.65 -1.94 460 71.285 32.65 -1.94 450 71.28 32.65 -1.93 440 71.275 32.65 -1.91 430 71.27 32.65 -1.9 420 71.26 32.65 -1.87 410 71.25 32.65 -1.88 400 71.245 32.65 -1.84 390 71.24 32.65 -1.82 380 71.235 32.65 -1.79 370 71.23 32.65 -1.78 360 71.225 32.65 -1.77 350 71.22 32.65 -1.73 340 71.215 32.65 -1.68 330 71.21 32.65 -1.64 320 71.205 32.65 -1.61 310 71.2 32.65 -1.61 300 71.19 32.65 -1.61 Contour Map For Formation#02:
  • 27. Geophysical Exploration 2011-GE-56 27 | P a g e Contour Map (3D) For Formation#02:
  • 28. Geophysical Exploration 2011-GE-56 28 | P a g e LAB#06 STATEMENT: INTRODUCTION TO RESISTIVITY SURVEY SCOPE:  Resistivity survey is used to measure the depth and thickness of geologic strata.  It is used to detect changes and locate the anomalous geologic conditions.  It measures the soil resistivity and soil corrosion rates and designing the grounding girds.  It maps salt water intrusion and contaminant plumes  It locates buried wastes e.g. locates landfill boundaries. APPARATUS: Terrameter SAS 4000 ACCESSORIES:  Electrodes  Measuring tape  Crocodile connectors  Electric cables  Connecting cables  External battery  Jumpers THEORY: RESISTIVITY SURVEY: Electrical resistance survey (also called earth resistance or resistivity survey) is one of a number of methods used in archaeological geophysics. In this type of survey electrical resistance meters are used to detect and map subsurface archaeological features and patterning. TYPES OF RESISTIVITY SURVEY ARRANGEMENTS: The types of electrode arrays that are most commonly used in resistivity survey are Schlumberger, Wenner, and dipole-dipole. There are other electrode configurations that are used experimentally or for non-geotechnical problems or are not in wide popularity today. Some of these include the Lee, half-Schlumberger, polar dipole, bipole dipole, and gradient arrays. The description of these configurations are given below. Techniques: 1. Vertical Electrical Sounding (VES) 2. Vertical Electrical Profiling (VEP)
  • 29. Geophysical Exploration 2011-GE-56 29 | P a g e Figure 6.1 Wenner onfiguration Figure 6.2 Schlumberger Configuration VERTICAL ELECTRICAL SOUNDING (VES): Vertical electrical sounding (VES) is a geophysical method for investigation of a geological medium. The method is based on the estimation of the electrical conductivity or resistivity of the medium. The estimation is performed based on the measurement of voltage of electrical field induced by the distant grounded electrodes (current electrodes). CONFIGURATION: There are four types of configurations used in electrical resistivity survey. They are: 1. Wenner Configuration 2. Schlumberger Configuration 3. Pole-dipole Configuration 4. Dipole-dipole Configuration Mostly the first two configurations are widely used WENNER CONFIGURATION: This array consists of four electrodes in line, separated by equal intervals, denoted a. By using the formula of apparent resistivity the user will find that the geometric factor K is equal to a, so the apparent resistivity is given by: SCHLUMBERGER CONFIGURATION: The Schlumberger array consists of four collinear electrodes. The outer two electrodes are current (source) electrodes and the inner two electrodes are the potential (receiver) electrodes. The potential electrodes are installed at the center of the electrode array with a small separation, typically less than one fifth of the spacing between the current electrodes.
  • 30. Geophysical Exploration 2011-GE-56 30 | P a g e Figure 6.4 Double Dipole Configuration Figure 6.3 Pole dipole Configuration Pole-dipole Configuration: The pole-dipole array contains four collinear electrodes. One of the current (source) electrodes is installed at an “effective infinity” distance, which is approximately five to ten times the survey depth. The other current electrode is placed in the vicinity of the two potential (receiver) electrodes. This geometry is utilized because it reduces the distortion of equipotential surfaces. DOUBLE DIPOLE: The dipole-dipole electrode array consists of two sets of electrodes, the current (source) and potential (receiver) electrodes. A dipole is a paired electrode set with the electrodes located relatively close to one another; if the electrode pair is widely spaced it is referred to as a bipole. The convention for a dipole-dipole electrode array is to maintain an equal distance for both the current and the potential electrodes (spacing = a), with the distance between the current and potential electrodes as an integer multiple of a. The electrodes do not need to be located along a common survey line. APPLICATION OF RESISTIVITY SURVEY: There are different applications of resistivity survey such as;  It measures bedrock & water table depth.  It detects sinkholes & hidden voids.  It geophysical maps buried alluvial channels.  It profiles landslip geometry.
  • 31. Geophysical Exploration 2011-GE-56 31 | P a g e  It characterizes fracture zones & discontinuities.  It defines landfill sites and leachate contamination. REFERENCES:  http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity  http://www.epa.gov/esd/cmb/GeophysicsWebsite/pages/reference/methods/Surface  Class Notes  http://hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html
  • 32. Geophysical Exploration 2011-GE-56 32 | P a g e LAB#07 STATEMENT: TO PERFORM THE RESISTIVITY SURVEY IN UET GROUND SCOPE: Resistivities and no. of layers can be calculated from resistivity survey APPARATUS:  Terrameter SAS 4000 ACCESSORIES:  Electrodes  Measuring tape  Crocodile connectors  Electric cables  Connecting cables  External battery  Jumpers TECHNIQUES USED:  VERTICAL ELECTRICAL SOUNDING:  Wenner  Schlumberger PROCEDURE: The following procedure is generic and will work with all meters. The meter’s manual should be consulted for operational details.  Verify that the metal strip between the meter’s C1 and P1terminals is disconnected (used for 3-Point testing)  Install the 4 test probes in the ground equally spaced in straight line. Generally the shorter spacing is done first.  Using the conductors, connect the C1, P1, P2 and C2terminals to the electrodes. The electrodes must be connected in order from the end, to the C1, P1, P2 and C2 terminals. The test results will be invalid if the electrodes are not connected properly.  Press the test button and read the digital display. Record the reading on the worksheet at the appropriate location. If the reading is not stable or displays an error indication, double check the connections. For some meters, the RANGE and TEST CURRENT settings may be changed until a combination that provides a stable reading without error indications is
  • 33. Geophysical Exploration 2011-GE-56 33 | P a g e Figure 7.1 reached. The addition of moisture is insignificant for the reading; it will only achieve a better electrical connection and will not influence the overall results. Also a longer probe or multiple probes (within a short distance) may help.  Place the probes at each of the spacing indicated above and record the readings on the worksheet  All above steps of this procedure must be repeated at multiple locations on the site to obtain a reliable soil profile. OBSERVATION AND CALCULATIONS: LOCATION MAP: Figure 7.2 UET Lahore
  • 34. Geophysical Exploration 2011-GE-56 34 | P a g e Figure 6.2 TARGET DEPTH: 40 ft. CONFIGURATION: 1) WENNER CONFIGURATION: Spacing (a) = 5,10,15,20,25,30,35,40 TABLE#6.1 Spacing (a) meter Resistivity (Ω-m) 1 99 2 110 3 112 4 118 5 130 6 155 7 165 8 200 9 215 10 235
  • 35. Geophysical Exploration 2011-GE-56 35 | P a g e WENNER GRAPH: LOG GRAPH FOR WENNER: INTERPRETATION FROM GRAPH: Two layers and single interface. 0 50 100 150 200 250 0 2 4 6 8 10 12 apparentresistivity(ρa)Ὡm spacing (a) m Electrode spacing (a) VS Apparent resistivity (ρa) 10 100 1000 1 10 resistivity(ρa)Ὡm spacing (a) m Electrode spacing (a) VS apparant resistivity (ρa) wenner configration (VES)
  • 36. Geophysical Exploration 2011-GE-56 36 | P a g e Figure 7.4 2) SCHLUMBERGER CONFIGURATION: Spacing b/w potential electrodes= a= 3,6,9,12,15,18,21,24 Total spread is = 5a Investigated depth = 5a/3 TABL#6.2 Spacing (a) Effective depth (5a/2) Resistivity 1 2.5 95 2 5 105 3 7.5 110 4 10 115 5 12.5 120 6 15 145 7 17.5 165 8 20 185 9 22.5 200 10 25 225
  • 37. Geophysical Exploration 2011-GE-56 37 | P a g e GRAPH FOR SCHLUMBURGER: LOG GRAPH FOR SCHLUMBURGER: INTERPRETATION: Two layers and a single interface. 0 50 100 150 200 250 0 5 10 15 20 25 30 Resistivity(ρa)Ὡm Effective depyh (5a/2) m Effective depth (5a/2) VS apparent resistivity (ρa) schlmbergr configration (VES) 10 100 1000 1 10 Resistivity(ρa)Ὡm Effective depyh (5a/2) m Effective depth VS Apprent resistivity of Schlumberger
  • 38. Geophysical Exploration 2011-GE-56 38 | P a g e BOREHOLE DATA: The above data are collected from the borehole that were taken in UET ground. COMMENTS: The borehole data doesn’t coincides with the field data which shows that there exist some problem in the field data. 10 m
  • 39. Geophysical Exploration 2011-GE-56 39 | P a g e Figure 8.1 LAB#08 STATEMENT: INTRODUCTION TO 2D AND 3D RESISTIVITY SURVEY SCOPE: To perform and understand the layout of 2D and 3D Resistivity Survey. APPARATUS:  Terrameter SAS 4000 ACCESSORIES:  Electrodes  12 V battery  Imaging Cable  Electrode Selector  Hammer  Tape  Connectors THEORY: The purpose of electrical surveys is to determine the subsurface resistivity distribution by making measurements on the ground surface. From these measurements, the true resistivity of the subsurface can be estimated. The ground resistivity is related to various geological parameters such as the mineral and fluid content, porosity and degree of water saturation in the rock. Electrical resistivity surveys have been used for many decades in hydrogeological, mining and geotechnical investigations. More recently, it has been used for environmental surveys. We have seen the greatest limitation of the resistivity sounding method is that it does not take into account horizontal changes in the subsurface resistivity. In many situations, particularly for surveys over elongated geological bodies, this is a reasonable assumption. In theory, a 3-D resistivity survey and interpretation model should be even more accurate. However, at the present time, 2-D surveys are the most practical economic compromise between obtaining very accurate results and keeping the survey costs down.
  • 40. Geophysical Exploration 2011-GE-56 40 | P a g e Figure 8.2 1D SURVEY: It is along a single axis y i.e, this survey measure only reading of resistivity with depth along a straight line in y-axis direction. In order to locate a water supply tube-well that can serve the congregation of thousands of worshippers patronizing the camp on weekly basis, a major geophysical mapping of the camp was carried out. This involved both 1D and 2D surveys. 1D electrical method using Vertical Electrical Sounding has been employed over the years to characterize aquifer in different geologic environments and to map fractures in basement areas. 2D SURVEY: It is along the two axis x, y. recently, attention is shifting to a more accurate method of imaging the subsurface. 2D resistivity images are created by inverting hundreds to thousands of individual resistivity measurements to produce an appropriate model of the subsurface resistivity. 3 D SURVEY: It is along the three axis x, y and z. Since all geological structures are 3-D in nature, a fully 3-D resistivity survey using a 3-D interpretation model (Figure 3c) should in theory give the most accurate results. At the present time 3-D surveys is a subject of active research. However it has not reached the level where, like 2-D surveys, it is routinely used. The main reason is that the survey cost is comparatively higher for a 3-D survey of an area which is sufficiently large. There are two current developments that should make 3-D surveys a more cost-effective option in the near future.
  • 41. Geophysical Exploration 2011-GE-56 41 | P a g e PROCEDURE:  Select the suitable site for the experiment of resistivity survey.  42 electrodes are placed at 5 ft interval depth..  Instrument is attached with the battery.  Instrument is started and readings are taken. INTERPRETATION: 2D = we make simple contour map of resistivity. 3D = volumetric based map is formed for interpretation COMMENTS: The configuration were spread to know about the survey but due to the fault in battery the survey were not done.
  • 42. Geophysical Exploration 2011-GE-56 42 | P a g e LAB#09 STATEMENT: TO PERFORM 2D RESISTIVITY SURVEY USING LUND IMAGING SYSTEM AT UET AUDITORIUM GROUND SCOPE: To identify the different soil layers in UET auditorium ground APPARATUS:  Terrameter  Battery  Electrode  Wires  Connectors  Jumper  Crocodile connector  Lund imaging selector  Lund imaging wire RELATED THEORY: TERRAMETER SAS 4000 WITH LUND IMAGING SYSTEM: It provides a system for automatic Resistivity and IP Imaging. ABEM Terrameter SAS 4000 with LUND Imaging System provides optimum versatility in infrastructure projects and environmental studies. FEATURES OF LUND IMAGING:  It allows number of arbitrary cable arrangements and electrode arrays for Resistivity and Induced Polarization survey (like Wenner, Schlumberger, gradient, dipole-dipole, pole- dipole, pole-pole, square array, borehole etc.).  It is also provided with some supporting softwares like software for data transfer from instrument to PC, protocol generation software, file conversion software and pseudo section plotting.  Terrameter SAS 4000 allows number of geo-electrical surveys which include Resistivity Sounding and Profiling (with different arrangements) and IP Survey and Subsurface Imaging.
  • 43. Geophysical Exploration 2011-GE-56 43 | P a g e FIELD APPLICATIONS:  Ground water resource management vulnerability assessment  Mapping and monitoring of contaminated ground/groundwater  Geotechnical pre-investigation  Geological mapping  Mapping/prospecting of natural resources  Geothermal prospecting  Sub-bottom mapping at sea and in lakes  Mapping of frozen ground/permafrost.  Archaeology MAJOR ADVANTAGE: A major advantage of the electrical imaging method is that it produces continuous images of the variation in properties in the subsurface. This method can serve as an excellent basis for planning detail investigations via for example a drilling and sampling programme with optimized sampling locations. The detail investigation results can then in turn be used as a base for a refined interpretation of the electrical imaging data, leading to a comprehensive and reliable model of the underground. Figure 9.26
  • 44. Geophysical Exploration 2011-GE-56 44 | P a g e PROCEDURE:  41 electrodes are connected at 5 ft. distances.  The place where the electrodes are connected should be sprayed with water.  Pocket multimeter may be used to check the error.  The total spread was 210 ft. and the subsurface depth was 28 ft.  After the connection the apparatus is started.  The no. of cycles were 190.  Electrode test is set to run for the whole electrodes.  When the cycles are completed, the whole file is loaded to the software. PROCEDURE TO LOAD THE DATA: Softwares: 1) Res 2D inv. 2) SAS 4000  The file is first loaded to the PC with a USB connecter from the terrameter.  This file is in S4K extension.  To convert the S4K file to .dat file, we will use the Res 2D inv. software.  In this software go to the File menu and select New and then select Lund conversion  Now press F8 to convert it to the .dat file extension  After conversion load the same file to SAS 4000 software.  Three models will be created, select the one that the last and least final model.
  • 45. Geophysical Exploration 2011-GE-56 45 | P a g e FINAL MODELS FOR RESISTIVITY SURVEY IN UET GROUND: INTERPRETATION: There are four layers identified from the data (from 3.7m to 6m), The different colour in the image shows different resistivity levels. Also with the increase in depth the resistivity is increasing which shows that either there exists lower moisture content or anomalies are present. There is an error of 9% which shows that the data is not a good one but may be acceptable. PRECAUTIONS:  The surface should not be too dry or too wet  The electrodes should be connected properly  Battery should be fully charged REFRENCES: Instruction manual of ABEM Terrameter SAS 4000 / SAS1000
  • 46. Geophysical Exploration 2011-GE-56 46 | P a g e LAB#10 STATEMENT: INTRODUCTION TO GPR SURVEY SCOPE: GPR uses electromagnetic wave propagation and scattering to image and identify changes in electrical and magnetic properties in the ground. SHIELDED ANTENNA GPR: GPR means Ground Penetrating Radar. It works on electromagnetism principle. RAMAC/GPR shielded antennas are primarily used for medium to high resolution surveys. The shielded antenna construction makes the antennas especially suitable for urban investigations or at sites with a lot of background noise. A GPR measurement system consists of a transmitter and a receiver antenna and a control unit. In the system applied in this practical course both antennas are placed in one box. The main part of the GPR system is the control unit which generates the GPR signal and also receives the signals after their passage through the ground. The complete system is computer controlled. The measurement wheel at the back of the antenna box measures the distance along the survey track and triggers the emittance of the electromagnetic pulses. Figure 270.1 GPR Bag Figure10.28 GPR with Accessories
  • 47. Geophysical Exploration 2011-GE-56 47 | P a g e SPECIFICATIONS: The shielded 100MHz antenna is the lowest shielded antenna frequency commercially available. It is used for medium to low resolution. It is suitable for geological and geotechnical applications. GPR SPECIFICATIONS Antenna Frequency MHZ Radial Resolution m/µs Maximum Penetration Depth m 25 100 50 50 50 40 100 25 25 200 12.5 12 250 10 8 500 5 6 800 3 2.5 1000 2.5 1.5 1200 2.1 1 1600 1.6 0.5 2000 1.3 0.4 PARTS OF GPR  Distance measuring wheel  Monitor  7.5 V 2 batteries  Transmitter  Receiver  Cables  Wear plate  Pulling handles Figure10. 3 Battery place Figure 10.4 Wheel
  • 48. Geophysical Exploration 2011-GE-56 48 | P a g e HOW GPR WORKS: When a wave impinges on interface, it scatters the energy according to the shape and roughness of the interface and the contrast of electrical properties between the host material and the object. Part of the energy is scattered back into the host material, while the other portion of the energy may travel into the object. The portion of the wave that propagates into the object is said to be refracted. The angle that the wave enters into the object is determined by Snell’s law, which can be stated as follows: V1 / V2 = sin Φ1 / sinΦ2 Where, V1 and V2 are the velocities of the wave through the upper and lower materials, respectively, and Φ1and Φ2 are the angles of the ray path for the incident and refracted waves, respectively. FIELD APPLICATIONS: The system supports a number of subsurface investigations. Some of which are given below: - Archeological site assessment - Measuring bridge deck thickness - Underground mining mapping - Underground storage tank location - Excavation planning - Utility detection - Hazardous waste site assessment - Void detection and location LIMITATIONS:  The most significant performance limitation of GPR is in high-conductivity materials such as clay soils and soils that are salt contaminated.  Considerable expertise is necessary to effectively design, conduct, and interpret GPR surveys.  Relatively high energy consumption can be problematic for extensive field surveys. REFRENCES: - http://en.wikipedia.org/wiki/Ground-penetrating_radar - http://www.geophysical.com/whatisgpr.htm - http://www.geophysical.com/ - http://mysite.du.edu/~lconyers/SERDP/variablesaffecting2.htm
  • 49. Geophysical Exploration 2011-GE-56 49 | P a g e LAB#11 STATEMENT: GPR DATA PROCESSING AND INTERPRETATION SOFTWARE USED FOR THE INTERPRETATION: GV (GROUND VISION) RAMAC MALÅ Ground Vision Software is a data acquisition software platform designed by MALÅ Geoscience for MALÅ GPR systems with Ethernet communication. This softwares primary function is data acquisition, but also includes tools for filtering, printing of GPR data and includes support for multi-channel operation. Ground Vision is the dedicated data acquisition software platform for MALÅ's single or multi- channel GPR systems. As Window based software (running under W2000 or later), Ground Vision offers an easy-to-use user interface with file management, printing and other key features. Each measurement and its associated settings are stored in files. Filtering can be performed during data acquisition measurements, or afterwards during post-processing. Ground Vision software supports GPS coordinate logging during measurement. All radar grams can be printed as such, or post-processed by further software. DATA FROM GPR SURVEY: File # DAT_0101 Frequency= 500 MHZ (6m penetration depth) Velocity= 100 m/µs STANDARD CHART FOR THE DIELECTRIC CONSTANT VALUES:
  • 50. Geophysical Exploration 2011-GE-56 50 | P a g e GPR DATA FILE IN MALA SOFTWARE: FROM THE FIRST PICK UP TIME THE FOLLOWING DATA IS COLLECTED: Distance Time 3.5 10.2 20 9.8 25 9.9 59.5 10.1 64 10.2 92 9.5 129 10.5 144.5 9.8 145 10 147.5 10.2 178.5 11 186 10.5 194.5 10.8 195 9 195.5 9.9 227 10.5 248 12 260.5 10.8 262 10.5 267 10.6 278 10.5 286 10.2
  • 51. Geophysical Exploration 2011-GE-56 51 | P a g e Graph#11.1 Graph B/W Time and Distance: Graph 11.29 Velocity can be calculated using: V= 9 9.5 10 10.5 11 11.5 12 0 50 100 150 200 250 300 350 Time Distance Figure 10.30Borehole data
  • 52. Geophysical Exploration 2011-GE-56 52 | P a g e Depth of specific layer can be calculated by using: S= vt INTERPRETATIONS: There are 4 layers that is mostly found from the GPR data. There is a change in data from 120m to 200m which shows that there exist some anomalies. The anomaly may be pipe or concrete slab present near the cricket ground. COMMENTS: In actual field we know that there is a pipe and a concrete slab present near the cricket ground so we have a clue from the real data. By comparing it with the GPR data we are sure that there is anomaly present. Also the data shows that the GPR is working great. REFRENCES: - http://www.malags.com/products/mala-groundvision-2 - http://hyperphysics.phy-astr.gsu.edu/hbase/tables/diel.html
  • 53. Geophysical Exploration 2011-GE-56 53 | P a g e LAB#12 STATEMENT: INTRODUCTION TO GRAVITY SURVEY SCOPE: To understand the gravity survey and to familiar with its applications EQUIPMENT: CG-5 Autograv (Gravimeter) RELATED THEORY: CG-5 AUTOGRAV (GRAVIMETER): A gravimeter is an instrument used in gravimetry for measuring the local gravitational field of the Earth. A gravimeter is a type of accelerometer, specialized for measuring the constant downward acceleration of gravity, which varies by about 0.5% over the surface of the Earth. The CG-5 is the latest, gravity meter. It offers all of the features of the low noise industry standard CG-3M micro-gravity, but is lighter and smaller, has a larger screen which gives a superior user interface. The CG-5 can be operated with minimal operator training, and automated features significantly reduce the possibility of reading errors. Data down load bottlenecks have been eased with the provision of a fast USB interface and flexible data formats. Noise rejection has been improved. TYPES OF GRAVIMETER: ABSOLUTE GRAVIMETER: Absolute gravimeters, which nowadays are made compact so they too can be used in the field, work by directly measuring the acceleration of a mass during free fall in a vacuum, when the accelerometer is rigidly attached to the ground. Figure 12.1 Gravimeter
  • 54. Geophysical Exploration 2011-GE-56 54 | P a g e RELATIVE GRAVIMETERS: Most common relative gravimeters are spring-based. They are used in gravity surveys over large areas for establishing the figure of the geoid over those areas. A spring-based relative gravimeter is basically a weight on a spring, and by measuring the amount by which the weight stretches the spring, local gravity can be measured. However, the strength of the spring must be calibrated by placing the instrument in a location with a known gravitational acceleration. SPECIFICATION OF CG-5 AUTOGRAV: Sensor Type Fused Quartz using electrostatic nulling Reading Resolution 1 microGal Standard Field Repeatability <5 microGal Operating Range 8,000 mGal without resetting Residual Long-Term Drift : Less than 0.02 mGal/day (static) Tares Typically less than 5 microGals for shocks up to 20 G Automated Corrections Tide, Instrument Tilt, Temperature, Drift, Near Terrain, Noisy Sample, Seismic Noise Filter Operating Temperature -40°C to +45°C Ambient Temperature Coefficient 0.2 microGal/°C Pressure Coefficient 0.15 microGal/kPa Magnetic Field Coefficient 1 microGal/Gauss Power Consumption : 4.5 W at +25°C Standard System CG-5 Console, Tripod base, 2 rechargeable batteries, Battery Charger 110/240 V, External Power Supply 110/240 V, RS-232 and USB Cables GRAVITY OBSERVATIONS AND LEVELLING: When performing manual gravity observations with relative gravimeters different circumstances have to be considered. Important aspects relate to the actual measuring site, the specific instrument and handling of it, natural conditions and of course, since the reading is carried out manually, the observer himself. Because gravity measurements are normally conducted in loop sequences higher order stations (as a minimum) are normally measured several times during a working day. It is essential that the gravimeter is kept strictly levelled during each observation sequence. This requires continuous monitoring and frequent adjusting of the instrument level. The procedure associated with most manually operated gravimeters may be rather demanding with respect to
  • 55. Geophysical Exploration 2011-GE-56 55 | P a g e time and mental concentration of the observer. Especially during hot summer days when stations are located on asphalt-paved ground this task are often really cumbersome and time-consuming while the “legs“ of the meter base “pan“ may slowly sink into the warm asphalt thereby distorting the measurements. Similar problems may arise if the underground is wet. With automatic gravimeters like the Scintrex CG-5 Autograv the problem of levelling the instrument are automatically handled by electronic tilt sensors. Along with automatic reading and logging of the data into the gravimeters memory measuring becomes less demanding as regards the involvement and skills of the observer. STEPS TO FOLLOW: STEP#01 GEOLOGICAL REPORT OF AN AREA: Includes tectonic setting, outcrop mapping, topography, structure and stratigraphy. From these values we can prepare the geological report. STEP#02 3D GEOLOGICAL MODEL: For 3D model we have to know about the orientation, structure etc. The geological report is necessary for 3D model. From these features the 3D geological model is prepared. STEP#03 PLOTTING GRAVITY LINES: Perform proper grids and acquire data from grids. The grids are easy to read and give accurate readings. STEP#04 DEFINE GRAVITY BASE STATION: Point of known coordinates and from IGSN71 taking a base station and define gr value. The values of the base stations are already known. IGSN71: International gravity standardization network. STEP#05 PREPARE EQUIPMENT: Time is very important (day/night).
  • 56. Geophysical Exploration 2011-GE-56 56 | P a g e Tide correction: Tide correction is applied for time. The apparatus have its own tide correction in it. Drift Correction: It is also called mechanical correction. As the equipment is used for a long time so the apparatus starts to show error. This error can be removed by applying the drift correction. STEP#06 DEFINE THE READING INTERVAL: On the base of experience and geology define the intervals. The coordinates can also be defined. STEP#07 ELEVATION OF AREA WITH RESPECT TO MEAN SEA LEVEL: The values are feeded in the instrument country wise. Latitude adjustment: It can be calculated by subtracting the normal gravity values from the observed gravity values. USES: - Basement rock identification - Igneous body on regional scale - Anticline structures - Mineral ores identification - Also used for the contrast of sedimentary and igneous body
  • 57. Geophysical Exploration 2011-GE-56 57 | P a g e LAB#13 STATEMENT: SURFER GRAVITY CONTOUR MAP SCOPE: To draw the surfer map and to interpret the gravity and density changes in different zones from the surfer map. PROCEDURE: 1) Copy the data from surfer to the New work sheet in the surfer. 2) The data consists of longitude, latitude and bouguer gravity values. The grid file can be created from this data by using the same file saved in .bln extension. 3) After it go to the contour map option and select the same grid file that is generated and contour map is drawn. 4) Now selecting the same grid make a 3D surface map and overlay the contour map and the 3d surface map. Colour can changed from its properties. The final results will be: INTERPRETATION FROM GRAVITY CONTOUR MAP:
  • 58. Geophysical Exploration 2011-GE-56 58 | P a g e ZONE 1: (N-E DIRECTION) There is a decrease in density but overall density doesn’t changes. This shows that either there is a loose material, limestone cavity or sink hole present. ZONE 2: (N-W DIRECTION) The density contrast increases and decreases rapidly, so there is a change in the density at this zone. This shows that there is an anomaly present in this zone. ZONE 3: (S-E DIRECTION) There is a high density contrast at this zone. The density increases rapidly in this zone. This shows that either there is an igneous intrusion or mineral ore etc. present. ZONE 4: (S-W DIRECTION) The variation doesn’t seem to be high at this zone. There is no abrupt change happen here. This shows that there is a continuous strata deposited here. SURFER GRAVITY CONTOUR MAP: Figure 13.31 Surfer Gravity Contour Map
  • 59. Geophysical Exploration 2011-GE-56 59 | P a g e LAB#14 STATEMENT: INTRODUCTION TO PORTABLE WELL LOGGER AND MAGNETOMETER RELATED THEORY: WELL LOGGING: Well logging, also known as borehole logging is the practice of making a detailed record (a well log) of the geologic formations penetrated by a borehole. The log may be based either on visual inspection of samples brought to the surface (geological logs) or on physical measurements made by instruments lowered into the hole (geophysical logs). Some types of geophysical well logs can be done during any phase of a well's history: drilling, completing, producing, or abandoning. Well logging is performed in boreholes drilled for the oil and gas, groundwater, mineral and geothermal exploration, as well as part of environmental and geotechnical studies. TYPES OF LOGS:  Resistivity logs  Porosity logs  Sonic logs  Gamma ray log  Density log  Neutron log Figure 14.32 Well Logging software
  • 60. Geophysical Exploration 2011-GE-56 60 | P a g e PORTABLE WELL LOGGER: Borehole logging provides in situ measurements of the physical properties of the subsurface layers. The Mount Sopris MGX II borehole logging system is a portable system controlled by a notebook computer that allows for the acquisition of up to 9 logs simultaneously, using Poly probe technology. The motorized winch, efficiency of data acquisition, and the amount of information available from one logging run make this a very economical survey tool. The system logs include natural gamma, self-potential, single point resistance, normal resistivity (using 8, 16, 32 and 64 inch arrays), a lateral log, induced polarization, magnetic susceptibility, acoustic velocity, temperature, fluid resistivity, electromagnetic induction, flow meter, caliper, and borehole deviation. DATA ACQUISITION: The software used for the data acquisition is Ms Well. This software shows proper reading when the logger is moving in the well bore. It also shows that either any of the error is present in the connection of the apparatus. DATA INTERPRETATION: The software used for the data acquisition is Well cad. It consists of different modules like core and cutting module, 3D module and many others which can be used to interpret the data from it. Figure 14.33 MS Well
  • 61. Geophysical Exploration 2011-GE-56 61 | P a g e APPLICATIONS: - In environmental and groundwater investigations, locations of greatest groundwater flow are determined using temperature and/or self-potential logs, flow meters and caliper logs. Natural gamma, electrical, and magnetic logs characterize the lithology in terms of grain size and clay volume. - Fluid and formation resistivity logs are used to delineate areas of groundwater contamination. An acoustic velocity log provides information on porosity and well completion to help minimize cross-contamination in remediation programs. The determination of exact depths and the physical characteristics of each layer decrease the uncertainties in groundwater modeling and allow for the accurate placement of well screens for sampling, or groundwater extraction. - In geotechnical investigations, borehole logs provide a direct measure of the physical properties of the subsurface with accurate delineation of each horizon. The full waveform sonic log provides compressional wave velocities, and the sonic porosity of each layer. Companion surveys provide shear wave velocities for dynamic moduli determinations. - In mining applications, a variety of tools are used to determine petrophysical properties and physical boundaries not visible in the drill core. The sonic log is used in conjunction with seismic reflection surveys to provide accurate interval velocities of subsurface layers for interpretation. - The natural gamma log is a standard parameter used in coal evaluation, and uranium exploration, as well as in geological mapping of igneous and metamorphic environments. This log shows variations in natural radioactivity which are correlated with changes in lithology. Figure 14.34 Well cad
  • 62. Geophysical Exploration 2011-GE-56 62 | P a g e INTRODUCTION TO MAGNATOMETER: - TAGS-6 (click on the above image for a detailed view) represents the latest development in a long line of LaCoste-based airborne gravity systems, stretching back to the first successful airborne gravity flights in 1958 and building on the success of the TAGS System. For over 50 years, LaCoste gravimeters have acquired hundreds of thousands of line kilometers of gravity data during academic, government, and commercial surveys. TAGS-6 blends the latest in GPS and data acquisition technology with the solid foundation of the LaCoste dynamic gravimeter. - TAGS-6 is an upgrade to the TAGS/Air III gravity meter, and is designed specifically for airborne operations. The system incorporates a time-tested, low-drift, zero-length-spring gravity sensor mounted on a gyro-stabilized gimbal platform. The sensor has a worldwide gravity measuring range (no reset necessary) of 500,000 milliGals. Figure 14.35 Magnetometer HISTORY: The first magnetometer was invented by Carl Friedrich Gauss in 1833 and notable developments in the 19th century included the Hall Effect which is still widely used. THEORY: Magnetometers are measurement instruments used for two general purposes: to measure the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space.
  • 63. Geophysical Exploration 2011-GE-56 63 | P a g e USES: Magnetometers are measurement instruments used for two general purposes: to measure the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space. COMMENTS: The apparatus were out of order so we did not get any readings. REFRENCES: - http://scintrexltd.com/internal.php?storeCategoryID=4&s_page=airborne - http://www.geomatrix.co.uk/products/land-geophysical-equipment/gravity/cg5/