agp report
TRANSCRIPT
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Chapter-1
Introduction
1.1AbstractThis technical report summarizes the various geophysical surveys carried out in
Bakreshwar from 6th
December to 24th
December.
We planned our Geophysical surveys in an area where the strike direction is NE-SW.
And hence the two profiles of length 400 meter each and with a profile separation of 20 meter are laid in
the direction NW-SE perpendicular to the strike using prismatic compass. Two holes, one is of 10cm
depth and other is of 50cm depth are made at each station in the profiles with the station spacing 5 meter
to perform our experiments.
Then various Geophysical methods such as Spontaneous Potential , Wenner Profiling and
sounding , Schlumberger sounding, Pole-dipole method, Frequency domain EM , Time domain EM,
Time domain IP methods and Refraction and reflection seismic survey are carried out in these two
profiles and the results are interpreted.
We also carried out Regional Gravity survey using Worden gravimeter in the surrounding
areas and the corresponding station coordinates are precisely measured using GPS model 1200 (LEICA)
In this Geophysical Field training we are trained to acquire our own data using different
Geophysical methods and we are guided to process the field data. The results interpreted by different
Geophysical methods are consistent with each other which makes us excited and encouraging.
The methods and their results are discussed chapter wise as mentioned in the table of contents.
1.2 Location of the area
Figure 1.1 Location of Bakreswar and its Geology
Bakreswar region is the
most promisinggeothermal system in
Eastern India. It is
located at Bakreswar
(2305248 N;
8702240 E) inBirbhum district, West
Bengal, India. The
elevation of the area isabout 84 meters.
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1.3 Geology of the area
Bakreswar hot spring is surrounded by alluvial and laterite soil with irregular exposures of the
basement consisting Archaean gneisses and schists belonging to the Chotanagpur Gneissic Complex.
The rocks are highly sheared, brecciated near the springs.
It is one of the few groups of geothermal areas in the Chotanagpur Granite Gneiss
Plateau of the eastern part of the Indian Peninsular Shield. The geothermal areas in the terrain are
characterized by surface manifestation of a cluster of springs with varied temperatures (35C88C) and
similar chemical compositions. The springs mostly issue out of fractures in a reactivated composite mass
comprising predominantly granitic rocks (Precambrian) with an EW belt of sparsely occurring
sedimentary outliers of Gondwana formation (Lower Permian to Middle Jurassic).
Figure 1.2 Local Geology of the area
Figure 1.3 Lithological sequence of the area
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1.4 Hydrology of the geothermal area
For a better understanding of the hydrology of Bakreswar geothermal area, geophysical
investigations reveal that the occurrence and movement of shallow non-thermal groundwater take place
mostly in the weathered and fractured rocks, constituting a single aquifer system in the area.
Groundwater occurs in water table condition (unconfined state). Water table condition in Bakreswar and
the surrounding villages is studied from the inventory of several dug wells in. Water table contour
pattern generated from dug well data indicates varying hydraulic conductivity of the heterogeneousaquifer system .Hydraulic gradients are mostly towards the spring site from the relatively high
topographic areas in the north, northeast and southwest, suggesting thereby, mixing of non-thermal
groundwater with deep-seated hot water.
A comparative study of thermal and chemical behaviours i.e. the presence of
sulpher,helium,calcium,potasium of the hot springs and the non-thermal groundwater of the adjoining
localities and isotopic signatures, viz. 18
O, 2H and tritium contents of surface water, non-thermal
groundwater, as well as hot spring water however, indicate insignificant mixing of spring water with
non-thermal groundwater at the spring site. Orifices of spring discharge are restricted in nature, being
controlled by fractures within the shallow basement crystalline. A nearly NS trending buried fault zoneprovides the major outlets for the emergence of hot water.
18O and
2H contents of spring water bear
resemblance with those of local meteoric water, even though its tritium content is remarkably lower than
in local meteoric water. From such observations, it can be reasonably inferred that circulation of
meteoric water along deep-seated active fractures augments its temperature, which, under suitable hydro
geological conditions, emerges as hot springs.
1.5 Other details
The heat flow of the area vary from 145 mW/m2 to 200m W/m2
The geothermal gradient near the hot spring is 900C/km.
Number of hot springs: 10
Helium present:2%by volume of water
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CHAPTER-2
GLOBAL POSITIONING SYSTEM (GPS)
2.2 Components of the GPS:
Satellite segment
Ground segment
User segment
Ground Segment
The ground segment consists of a global network of monitoring stations and a master control station
(MCS) in Colorado. Coordinates of the ground stations are all precisely determined. The monitoring
stations communicate with the satellite constellation, collecting location information about the satellites
and sending it to the MCS. The MCS processes the information, modeling the location of the satellites
2.1 GPS Introduction
GPS, which stands for Global Positioning System, is the
only system today able to show you your exact position on
the Earth anytime, in any weather, anywhere. GPS satellites,
24 in all, orbit at 11,000 nautical miles above the Earth.
They are continuously monitored by ground stations located
worldwide. The satellites transmit signals that can be
detected by anyone with a GPS receiver. Using the receiver,
you can determine your location with great precision.
. These spacecraft are placed in 6 orbit planes with fouroperational satellites in each plane.
2.1 Principle of GPS
Satellite Segment
The space segment of the GPS system consists of a
constellation of satellites in earth orbit, with at least four
visible anywhere in the world at any time. While only
twenty four satellites are needed to meet this requirement
(four satellites in each of six orbital planes), several more
are generally in service to provide backup. The satellites
primarily consist of antennas, a transmitter, and atomic
clocks. The transmitter sends a signal containing position
information, a time stamp (from the atomic clock) and the
pseudo-random code needed for distance determination.Figure 2.2
http://www.sco.wisc.edu/gps/system.php#sathttp://www.sco.wisc.edu/gps/system.php#groundhttp://www.sco.wisc.edu/gps/system.php#userhttp://www.sco.wisc.edu/gps/system.php#userhttp://www.sco.wisc.edu/gps/system.php#groundhttp://www.sco.wisc.edu/gps/system.php#sat -
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as a function of time and then sending the information out for uplink to the satellites. Orbital
information, atmospheric data, and other parameters are also monitored and maintained by the MCS.
User segment
The user segment consists of the person or system (car, airplane, etc) using a receiver to determine the
position of an unknown location. Receivers contain an antenna that captures signals from visible
satellites, a clock to internally generate signals to synchronize with the incoming satellite signal, and ahardware and software system to process signals and calculate position. Characteristics of receivers that
can impact accuracy are single- versus dual-frequency receivers, the number of channels available to
track satellites (i.e. how many satellites can be tracked simultaneously), whether they are differential-
ready, and whether they use carrier signals in some fashion. Other characteristics of receivers that may
be important include size, cost, battery life, and interoperability with other systems like personal
computers.
2.3 Measurement of distance using satellites
Velocity (mph) x Time (hours) = Distance (miles)
In the case of GPS we're measuring a radio signal so the velocity is going to be the speed of
light or roughly 186,000 miles per second.
Timing is tricky
We need precise clocks to measure travel time
The travel time for a satellite right overhead is about 0.06 seconds
The difference in sync of the receiver time minus the satellite time is equal to the travel time
Distance to a satellite is determined by measuring how long a radio signal takes to reach us from
that satellite.
To make the measurement we assume that both the satellite and our receiver are generating the
same pseudo-random codes at exactly the same time.
By comparing how late the satellite's pseudo-random code appears compared to our receiver's
code, we determine how long it took to reach us.
Multiply that travel time by the speed of light and you've got distance.
2.4 GPS model 1200 (Leica) and SR 20 (Leica)
Several modern surveying techniques like Satellite Remote Sensing, Photogrammetric,Field surveying procedures using digital theodolites, short and long-range EDM instruments like Total
Station etc., are available today. However, the advantages of using the satellite based GPS techniques
for surveying are:
GPS measurements do not require inter-visibility between points whereas the conventional surveying
tools require line of sight for measurements.
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GPS technique provides a three dimensional position for the point. That is in one go, we
get the horizontal and vertical position of the point, unlike in conventional surveying where we need two
operations viz., horizontal traverse for planimetric control and a level loop for height control.
A very high accuracy measurement can be made in a relatively short time for baseline
lengths of a few hundred meters to few hundred kilometers and can provide the same accuracy anywhere
on earth, in almost any weather condition and at any time of the day.
GPS offers many advantages compared with conventional survey methods. Because there
is no need for a rod person, each surveyor can work alone when necessary. GPS also requires much less
setup time than did traditional surveying equipment, so the crew can use its time more efficiently. It can
also keep a much more flexible schedule and move from one area to the next or one pit to another as
needed.
2.5 Operations and acquiring the data
The tripod stand of the GPS should be leveled coarsely before mounting the level table.
Once the tripod leveled coarsely, fine leveling should be done after mounting the level table.
The GPS data acquiring instrument should be connected to a circular disc shaped antenna and then it
should be mounted on the clip in the tripod.
The instrument should be placed in an open area.
Once the instrument setup is ready, we can easily acquire the data which is software guided.
Usually, the data will be acquired for 10 minutes, to avoid any redundancy associated with the
atmospheric disturbances for the radio signal coming from the satellites.
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STATION DATE & TIME LATITUDE LONGITUDE Elliptical Height Position + Height Qlty
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2.7 Map of the stations
The map of the stations produced using the LEICA-Geo Office software package
Figure 2.3 Map of the stations occupied by GPS
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Chapter-3
Self potential Method
3.1 Introduction to SP
SP is a passive method that employs measurements of naturally occurring electrical
potentials commonly associated with the weathering of sulfide ore bodies. Measurable electricalpotentials have also been observed in association with ground-water flow and certain biologic processes.
The groundwater plays a key role by acting as an electrolyte.
.
.
The self-potential associated with an ore body is called its mineralization potential.Self-potential (SP) anomalies across ore bodies are invariably negative, amounting usually to a few
hundred mill volts. They are most commonly associated with sulfide ores, such as pyrite, pyrrhotite, and
chalcopyrite, but also with graphite and some metallic oxides.
3.2 Basic theory:Self-potential depends on variations in oxidation (redox) potential with depth. The ground
above the water table is more accessible to oxygen than the submersed part, an electrochemical reactiontakes place at the surface between the ore body and the host rock above the water table. It results in
reduction of the oxidized ions in the adjacent solution. An excess of negative ions appears above thewater table. A simultaneous reaction between the submersed part of the ore body and the groundwatercauses oxidation of the reduced ions present in the groundwater. This produces excess positive ions in
the solution and liberates electrons at the surface of the ore body, which acts as a conductor connecting
the two half-cells.Potential difference between the upper and lower parts, causing a spontaneous electric polarization of
the body.
Figure 3.1
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3.3 Field equipment
1. Two porous pots
2. SP potential measurement meter
3. Two long cables winches.
4. Connecting wires with crocodile clips
5. water
6. Tool box
3.4 Field procedure
The method we have used for the survey is the gradient method. The gradient method employs
a fixed separation between the electrodes, of the order of 10 m. The potential difference is measuredbetween the electrodes, and then the pair is moved forward along the survey line until the trailing
electrode occupies the location previously occupied by the leading electrode.
One day before the day of survey the porous pots were filled with and immersed in coppersulphate solution.
In the field we have chosen the porous pots which have minimum mutual potential difference.
In the field small holes were drilled along the profile at an interval of 5meter and all the holeswere filled with distilled water.
Next the two porous pots were joined to potential measure unit with the help of the connectingwires and crocodile clips.
Fig 3.2 the gradient method for measuring self potential. The total potential V at a station in
the gradient method is found by summing the previous potential differences.
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3.5 SP DATA of Profile-1
Surface Measurements (at 5 cm depth) In a hole of depth 50 cm
AB/2(m) SP(mv) AB/2(m) SP(mv)
-112.5 -9.9 2.5 -14.4
-107.5 -4.8 7.5 -22.9-102.5 5.3 12.5 -15.13
-97.5 0.1 17.5 -26.5
-92.5 -4.9 22.5 -19.6
-87.5 -1.9 27.5 -19.5
-82.5 -9 32.5 -0.2
-77.5 1.5 37.5 -15
-72.5 1.3 42.5 -13.1
-67.5 1.1 47.5 -20.6
-62.5 5.6 52.5 -15.3
-57.5 -8.2 57.5 -17.7
-52.5 4.1 62.5 -16.9
-47.5 7.7 67.5 -23.7
-42.5 -0.5 72.5 -23.5
-37.5 3.9 77.5 -2.2
-32.5 7.8 82.5 -9.2
-27.5 4.9 87.5 -16.8
-22.5 -1.4 92.5 -22.6
-17.5 -7.8 97.5 -22.7
-12.5 12.1 102.5 -16.1
-7.5 6.8 107.5 -16.1
-2.5 -1.5 112.5 -14.8
2.5 -6.9 117.5 -19.4
7.5 -6.6 122.5 -14.9
12.5 -2.6 127.5 -19.6
17.5 15.7 132.5 -21.3
22.5 3.7 137.5 -16.6
27.5 4.7 142.5 -11.9
32.5 6.7 147.5 -10.3
37.5 -4.8 152.5 -17.7
42.5 -1.6 157.5 -19.1
47.5 6.2 162.5 -12.2
52.5 -9.3 167.5 -16
57.5 -2.7 172.5 -20.9
62.5 -13.8 177.5 -14.6
67.5 -4.8 182.5 -23.2
72.5 -2.1 187.5 -21.8
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77.5 4.2 192.5 -17.5
82.5 16.9 197.5 -14.3
87.5 2.9 202.5 -13.4
92.5 -6.6 207.5 -12.9
97.5 -13.5 212.5 -18.4
102.5 -24.5 217.5 -7.1
107.5 8.7 222.5 -12.3112.5 4.7 227.5 -16.2
117.5 -4.4 232.5 -14.5
122.5 -0.1 237.5 -13.6
127.5 5.7 242.5 -3.9
132.5 -1.2 247.5 8.6
137.5 7.6 252.5 -21
142.5 7.4 257.5 -13.8
147.5 4.9 262.5 -30.5
152.5 2.9 267.5 -27.8
157.5 -13.7 272.5 -17.5
162.5 -10.6 277.5 -29.6
167.5 -19 282.5 -2.5
172.5 7.5 287.5 -23.3
177.5 -20.9 292.5 -24.2
182.5 -15.4 297.5 -20
187.5 -13.8 302.5 -22.1
192.5 7.4 307.5 -19.6
197.5 -1.3
202.5 3.8
207.5 6.4
212.5 3.7
217.5 -2.2
222.5 3.1
227.5 22.6
232.5 -32.1
237.5 7.2
242.5 8.9
247.5 -6.8
252.5 5.1
257.5 6.1
262.5 8.3
267.5 2.7
272.5 1.5
277.5 1.7
282.5 -8.1
287.5 -15.4
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292.5 26.1
297.5 10
302.5 6.5
307.5 -1.4
3.6 Plot and Interpretation of profile-1
Figure 3.3 SP Vs Distance for profile-1
Interpretation of self potential data: The SP profile both
for 10cm & 50cm depth shows same nature.We observe three anomalies.
Between 120-220, we have observed two anomalies;these may be due to bio-electric activity.
Between 230-310 we have observed major anomalythis may be due to mineralized body.
Estimation of the depth: An estimation of depth can be
made from the shape of the profile .if X1/2 is the total width
of the profile at the half (negative) maximum, then the depth
of the top of the body is order of the order of half the
distance. Estimated depth = 20 meter
If the anomalous profile is wide, the source is also wide,
rather than deep, because the depth ofdetection in SP is
usually not greater than 60m.
Figure 3.4
Measuring
the depth
using half-
width method
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3.7 SP DATA of Profile-2
Surface Measurements (at 5 cm depth) In a hole of depth 50 cm
AB/2(m) SP(mv) AB/2(m) SP(mv)
-97.5 -5.08 -97.5 1.74
-92.5 8.74 -92.5 -0.48-87.5 -9.96 -87.5 6.8
-77.5 -24.12 -77.5 -4.54
-72.5 19.4 -72.5 1.62
-67.5 3.34 -67.5 7.98
-62.5 1.58 -62.5 1.8
-57.5 0.66 -57.5 0.64
-52.5 -6.76 -52.5 2.46
-47.5 4.26 -47.5 -0.7
-42.5 6.14 -42.5 2.66-37.5 15.46 -37.5 1.92
-32.5 -3.2 -32.5 5.7
-27.5 7.08 -27.5 2.98
-22.5 16.54 -22.5 5.38
-17.5 -4.38 -17.5 3.68
-12.5 -13.24 -12.5 -1.42
-7.5 6.32 -7.5 1.24
-2.5 29.04 -2.5 1.82
2.5 -24.9 2.5 7.567.5 -5.88 7.5 -0.24
12.5 -6.12 12.5 0.82
17.5 -9.38 17.5 1.3
22.5 -5.4 22.5 3.16
27.5 -1.9 27.5 6.7
32.5 5.84 32.5 5.34
37.5 9.42 37.5 5.64
42.5 -1.74 42.5 8.24
47.5 7.34 47.5 6.1252.5 -1.86 52.5 6.68
57.5 4.42 57.5 3.06
62.5 -7.96 62.5 1
67.5 -7.68 67.5 -4.6
72.5 13.78 72.5 7.42
77.5 -1 77.5 -7.52
82.5 6.64 82.5 -2.5
87.5 7 87.5 2.02
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92.5 0.58 92.5 -1.18
97.5 7 97.5 12.06
102.5 -1.2 102.5 -11.3
107.5 2.5 107.5 -7.78
112.5 -2.38 112.5 11.26
117.5 3.4 117.5 -4.5
122.5 0.68 122.5 -12.04127.5 7.38 127.5 3.86
132.5 1.92 132.5 -7.88
137.5 6.74 137.5 -5.26
142.5 6.3 142.5 -3.84
147.5 3.92 147.5 10.54
152.5 1.34 152.5 -1.88
157.5 6.28 157.5 -6.06
162.5 -0.7 162.5 -1.36
167.5 3.76 167.5 1.66172.5 -0.82 172.5 -2.22
177.5 -5.52 177.5 -4.52
182.5 -4.72 182.5 -14.1
187.5 -11.36 187.5 -3.9
192.5 -12.18 192.5 -11.66
197.5 -9.62 197.5 -15.26
202.5 -3.52 202.5 -14.46
207.5 -8.54 207.5 3.42
212.5 0.6 212.5 12.22217.5 -2.74 217.5 -9.66
222.5 0.4 222.5 11.8
227.5 -3.86 227.5 5.22
232.5 4.74 232.5 7.1
237.5 -2.74 237.5 7.8
242.5 2.26 242.5 -10.08
247.5 0.98 247.5 1.78
252.5 6.98 252.5 3.04
257.5 1.94 257.5 3.66262.5 7.54 262.5 -8.26
267.5 6.36 267.5 9.84
272.5 9.22 272.5 -2.3
277.5 8.36 277.5 -6.9
282.5 -1.24 282.5 -0.92
287.5 1.2 287.5 -2.18
292.5 10.54 292.5 1
297.5 5.36 297.5 8.52
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302.5 -4.32 302.5 -3.08
307.5 9.3 307.5 6.28
3.8 Plot and Interpretation
Fig.3.5: SP profile for 10cm whole depth
Fig.3.6: SP for 50cm depth hole
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Fig.3.7: comparison of SP profile for 10cm & 50cm depth hole
Fig.3.8: Estimate of the depth from the shape of the profile (in this plot the distance is form the position
marked by 0)
3.9 INTERPRETATION:
The SP profile both for 10cm & 50cm depth shows same nature. We observe two major anomalies
1. Between 100-150m, may be due to bioelectric activity in vegetation.
2. Between 250-300m, may be due to presence of mineralized body or fracture on the subsurface.
We can estimate the depth the top of the target from the SP profile. If x1/2 is the total width of the profile
at half the maximum, then the depth of the top of the body is of the order of half this distance. From
figure 3.8 we estimated the depth of the body is approximately 20m.
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Chapter-4
Resistivity Methods
4.1 Resistivity Method - Observation of electric fields caused by current introduced into the ground as a
means of studying earth resistivity in geophysical exploration. Resistivity is the property of a material
that resists the flow of electrical current.
4.2 The most common electrical method used are:
Resistivity Profiling - used to determine lateral changes in resistivity due to changes in geologicstructure.
Resistivity Soundings - used to determine vertical changes in resistivity due to geologic structure
assuming horizontal layering.
Some important arrays are:
Wenner Array
Schlumberger Array
Pole-Dipole
These arrays of current and potential electrodes measure apparent resistivity
Figure 4.1 General four-electrode configuration for resistivity measurement, consisting of a pair of current
electrodes (A, B) and a pair of potential electrodes (C, D).
4.3 Apparent resistivity
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4.4 Wenner Configuration and procedure
Profiling For lateral exploration or mapping the spacing remains constant and all four electrodesare moved along the line, then along another line.
Sounding: For depth exploration the electrodes are expanded about a fixed centre, increasing thespacing an in steps.
After each 5m spacing along the traverse marking was done.
For potential electrodes holes were dug at the corresponding marks.
Electrodes were placed.
All the connections were done as in above wenner array figure
SP was balanced
Power was switched on.
The current value was read with the current unit and for having the appropriate current valuethe battery voltage was changed.
The current value with the current unit and voltage (potential difference) with potential unitwere read.
After that the resistance was so adjusted that current becomes zero. Then the value ofresistance was noted.
Then system was shifted by 5m and similar procedure was applied for taking reading.
By measuring (V/I) for a particular position of electrodes apparent resistivity is calculated. Apparent
resistivity for each array position is plotted against the centre of the spread i.e. the midpoint of the
current electrodes. It gives the lateral variation of resistivity along the profile.
B
Figure 4.2
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4.5 Wenner Profiling data of Profile-1
AB/2(m) Resistivity(-m) AB/2(m) Resistivity(-m)
7.5 112.3 202.5 48.2
12.5 190.5 207.5 43.7
17.5 182.4 212.5 49.3
22.5 190.7 217.5 37.4
27.5 219.8 222.5 39.232.5 232.2 227.5 58.3
37.5 214.5 232.5 39.5
42.5 230.7 237.5 45.8
47.5 167.4 242.5 42.76
52.5 170.1 247.5 44.7
57.5 77.1 252.5 35.6
62.5 63.6 257.5 36.2
67.5 36.7 262.5 41.2
72.5 41.5 267.5 41.8
77.5 37.7 272.5 57.8
82.5 35.1 277.5 49.5
87.5 38.3 282.5 56.6
92.5 44.5 287.5 48.9
97.5 33.7 292.5 49.8
102.5 30.9 297.5 50.9
107.5 33.9 302.5 68.1
112.5 29.1 307.5 90.4
117.5 48.1 312.5 57.2
122.5 44.6 317.5 72.1
127.5 68.3 322.5 45.4
132.5 55.4 327.5 29.8
137.5 49.7 332.5 31.2
142.5 79.9 337.5 26.7
147.5 72.8 342.5 15.9
152.5 70.6 347.5 19.9
157.5 58.5 352.5 10.7
162.5 32.8 357.5 17.7
167.5 39.5 362.5 13
172.5 42.6 367.5 14.2177.5 42.8 372.5 15.4
182.5 45.1 377.5 15.4
187.5 67.1 382.5 17
192.5 73.8 387.5 18.5
197.5 49.7
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4.6 Plot and interpretation of profiling data
Interpretation
In general, if the wenner profile plot has the M shape plot it indicates the presence of thevertical contacts, if plot have the W shape plot it indicates the presence of the dyke.
Here we got two M shape curves around 45 and 320, which indicate the presence of thetwo vertical contacts.
4.7 Wenner Sounding Data at 320 meter
Figure 4.3
Profile-1 wenner
profiling plot
AB/2(m) Resistivity(-m)
10 60.3
20 142.3
30 257.2
40 400.95
50 577.6
60 681.2
70 881.2
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4.8 plot and interpretation of wenner sounding data
Interpretation:We have drawn cumulative resistivity vs spacing. The above plot indicates the three layers,
the resistivity and thickness of the layers are as follows.
Resistivity(-m) Thickness(m)
Layer 1 54 20
Layer 2 608 46
Layer 3 1165
4.9 Wenner Profiling Data of Profile-2
Plotting point in meter Apparent resistivity
(a in -m) 10cm depth
Apparent resistivity
(a in -m) 50cm depth
7.5 244.2 250.3286
12.5 302.1857 326.2286
17.5 346.3429 328.2714
22.5 221.2571 235.4
27.5 201.7714 215.2857
32.5 123.6714 132.6286
37.5 126.6571 125.7143
Figure 4.4
Cumulative
apparent
resistivity
Vs Distance
(AB/2)
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42.5 84.7 83.6
47.5 65.84286 67.00571
52.5 75.42857 75.58571
57.5 71.5 60.02857
62.5 73.54286 72.91429
67.5 82.97143 85.01429
72.5 81.87143 76.68571
77.5 76.21429 80.77143
82.5 83.91429 61.6
87.5 60.97143 79.51429
92.5 79.51429 64.74286
97.5 63.17143 81.08571
102.5 83.91429 63.64286
107.5 63.48571 65.21429
112.5 61.75714 55
117.5 74.8 77
122.5 55.94286 56.41429
127.5 53.58571 53.58571
132.5 76.37143 75.58571
137.5 85.48571 84.7
142.5 115.6571 111.7286
147.5 103.5571 108.1143
152.5 104.6571 106.2286
157.5 66 68.51429
162.5 70.08571 68.35714
167.5 64.74286 65.05714
172.5 62.54286 63.48571
177.5 63.17143 65.37143
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182.5 77.15714 73.7
187.5 93.81429 95.54286
192.5 62.85714 66
197.5 61.44286 105.7571
202.5 77.31429 95.54286
207.5 61.44286 82.65714
212.5 66.31429 92.71429
217.5 53.74286 64.74286
222.5 80.61429 55
227.5 82.02857 46.35714
232.5 69.14286 82.02857
237.5 82.97143 70.24286
242.5 93.02857 81.08571
247.5 100.8857 93.65714
252.5 106.2286 106.8571
257.5 94.28571 109.3714
262.5 97.74286 97.9
267.5 101.5143 98.21429
272.5 40.22857 102.7714
277.5 81.4 85.17143
282.5 83.75714 83.75714
287.5 78.1 85.8
292.5 75.9 77.15714
297.5 97.42857 76.37143
302.5 87.52857 93.97143
307.5 114.0857 91.14286
312.5 106.7 110
317.5 118.4857 106.7
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322.5 119.7429 118.3286
327.5 105.4429 104.5
332.5 108.4286 104.3429
337.5 111.4143 120.6857
342.5 81.71429 81.55714
347.5 113.1429 114.2429
352.5 66.31429 69.77143
357.5 66.31429 93.65714
362.5 55 56.25714
367.5 52.64286 52.48571
372.5 50.12857 51.54286
377.5 51.07143 49.34286
382.5 50.91429 51.38571
387.5 49.97143 52.8
392.5 51.22857 53.27143
397.5 51.54286 54.84286
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4.10 Plot and Interpretation of Profile-2 Data (wenner profiling data)
Figure 4.5 Wenner profiling (data 1:10cm depth, data-2:50cm depth)
Interpretation
A good anomalous body is located at 330 meter.
A further extension of profile along backward direction of profile required.
Figure 4.6 smoothened plot of Lateral wenner profiling (50cm hole data)
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4.11 Wenner Sounding Data (wenner sounding data in profile-2)
4.12 Plot and Interpretation (wenner sounding data in profile-2)
Interpretation
Layers Resistivity (ohm-meter) Thickness (meter)
First 96.737 25.5
second 165.85 infinity
Distance
(AB)
Distance
(AB/2)
Apparent
resistivity
5 2.5 102.05
15 7.5 77.71
25 12.5 102.05
35 17.5 92.3
45 22.5 114.45
55 27.5 127.8
65 32.5 149
75 37.5 155.43
85 42.5 170.81
95 47.5 190.91
Figure 4.7 Cumulative apparent resistivity Vs Distance (AB)
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4.13 Schlumberger configuration
Profiling:
Lateral profiling done in two ways. With a large fixed separation of the current electrodes, the potential
pair is moved between them, also with fixed spacing subject to the limitation (L-x) >> 3L.
Sounding:
The potential electrodes remain fixed while the current electrodes spacing is expanded symmetrically
about the center of the spread in the limitation of L5a
4.14 Schlumberger Sounding Data in profile-1 and profile-2
At 30 meter At 320 m At 320 m perpendicular to profile
AB/2(m) App Resistivity(-m)
1.5 551.42
2 339.34
3 226.22
4 201.09
6 169.67
8 201.09
10 392.75
15 353.5
20 314.2
25 392.75
30 282.75
40 502.75
50 78.55
60 113.31
80 155.34
100 210.5
120 261.63
140 285.59
160 289.57
180 300.31
200 309.49
AB/2(m) App Resistivity(-m)
1.5 551.42
2 339.34
3 226.22
4 201.09
6 169.67
8 201.09
10 392.75
15 353.5
20 314.2
25 392.75
30 282.75
40 502.75
50 78.55
60 113.31
80 155.34
100 210.5
120 261.63
140 285.59
160 289.57
180 300.31
200 309.49
AB/2(m) App Resistivity(-m)
1.5 551.42
2 339.34
3 226.22
4 201.09
6 169.67
8 201.09
10 392.75
15 353.5
20 314.2
25 392.75
30 282.75
40 502.75
50 78.55
60 113.31
80 155.34
100 210.5
120 261.63
140 285.59
160 289.57
180 300.31
200 309.49
Figure 4.8
Schlumberger
arrangement
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4.15 Plot and Interpretation of schlumberger sounding data in profile1 and profile2
Figure 4.9 Schlumberger sounding curve at 320 m Interpretation:From the wenner profiling we hav
choosen the sounding point at 320m.We got the H type sounding
curve,which represents the second laye
has less resistivity compared to the firs
and third layer.
The above plot indicates the thre
layers ,the resistivity and thickness of the
layers are as follows.
Resistivity(-
m)
Thickness
(m)
Layer 1 169 1.1
Layer 2 54 9.8
Layer 3 1080
When we carry out Schlumberger
sounding at point 320m, along the
strike and across the strike, we get A-
type resistivity curves but they arehaving a static shift. Hence we can't
surely say that the layer parameters
corresponding to a curve are exactly
correct.
Reason for static shift and its
solution. It is assumed that the rate of
accumulation of surface charge is
slower than the rate of evaporation butthis is an ideal case, and
when This condition is rarely obtained.
So we use the equation which solves the problem.
Therefore to solve this problem and
for better interpretation we go for
Electromagnetic survey.
Figure 4.10 shows Schlumberger sounding at 320 m, one along the strik
direction and other along the direction perpendicular to the strike
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4.16 POLEDIPOLE METHOD
In this method one of the current electrode id fixed at a great distance from the other
three, all of which can have various spacings.
Fig 4.12 pole dipole array
rAC =a; rAD=b; rCB = rDB= large spacing
When b=2a
This is the double the ratio of in the wenner array.
When the potential electrode spacing is very small compared to the distance of either potential electrode
from Athen
Large spacing
Figure 4.11 shows Schlumberger soundi
data at 30 meter. It shows a HKH-curve
because which cant be interpreted
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This arrangement is called half-Schlumberger array.
If we move one of the potential electrode to a distant point which is also remote from the another current
electrode
i.e. r3= b = then this arrangement is called half- wenner array.
x2 (in meter) rho x2 (in meter) rho
7.5 58.77 182.5 38.2
12.5 215.5 187.5 43.5
17.5 155 192.5 50.5
22.5 198.7 197.5 54.32
27.5 199.6 202.5 54.4
32.5 207.3 207.5 49.7
37.5 200.3 212.5 51
42.5 234.7 217.5 49.4
47.5 225.2 222.5 40.4
52.5 237 227.5 37.9
57.5 129.3 232.5 41.7
62.5 82.3 237.5 37.5
67.5 35.9 242.5 43
72.5 38.2 247.5 45.6
77.5 34.2 252.5 49
82.5 39.3 257.5 42
87.5 43.3 262.5 34
92.5 41.6 267.5 36
97.5 16.2 272.5 30.3
102.5 88.9 277.5 46.7
107.5 41.2 282.5 48.7
112.5 26.8 287.5 54.4
117.5 21.4 292.5 50
122.5 28.2 297.5 48
127.5 54.9 302.5 43.4
132.5 52.4 307.5 50.6
137.5 41.6 312.5 52
142.5 48.8 317.5 57
147.5 54.2 322.5 34.7
152.5 61.3 327.5 59.5
157.5 53.8 332.5 36.7
4.17 Pole dipole profiling data
162.5 57.3 337.5 40.8
167.5 41.4 342.5 15.8
172.5 45.1 347.5 23
177.5 36.4 352.5 28.9
357.5 17
4.18 Plotting of Pole-Dipole Profiling Data
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Chapter-5
Time domain IP survey
5.1 Theory: Induced polarization method is relatively new technique in geophysics, and has been
employed mainly in base metal exploration and to minor extent of ground water search. There aretwo types of measurements in IP one is time domain IP measurement (decay voltage is measured as
a function of time) and other is frequency domain IP measurement (decay voltage is measured as a
function of time).
To carry out induced polarization survey over the specified profile line with dipole-dipole
Arrangement
5.2 Instruments used:
1. Induced polarization transmitter unit2. Induced polarization receiver unit3. Generator4. Current electrodes5. Potential electrodes6. Winches with cables7. Connecting wires with clips and clamps8. Tool Box9. Hammer10.salt water11.Gloves
Time domain IP surveys involve measurement of the magnitude of the polarization voltage (Vp) that
results from the injection of pulsed current into the ground
5.3 Illustration of the IP-related decay of potential after interruption of the primary current
Figure 5.1 showing the principle of Time-
Domain IP
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5.4 Parameters measured in IP survey
Chargeability, Metal factor are the parameters which are commonly measured in an IP survey:
Chargeability: The area under the decay curve, expressed as a fraction of the steady-state voltage, is
called the chargeability M, defined asM has the dimensions of time and is expressed in seconds or
milliseconds. It is the most commonly used parameter in IP studies.
It is defined
M=1/v0
2
1
( )
t
t
v t d t
Where V0 - steady voltage & v(t) =residual voltage
5.5 Procedure
1. At first eleven electrodes (two for current and nine for potential) were planted in the ground atequal spacing.
2. One winch was kept near to each electrode and one end current electrode was connected to theelectrode and other was connected to transmitter (which was kept far from the profile line).
Similarly the one end of winch was connected to the potential electrode and other was connected
to the receiver with the corresponding places.3. The receiver was set up according to the manual.4. Then the transmitter was connected to the generator.5. Current of around 1amp was injected in the ground through the transmitter.6. Readings were taken and stored by the receiver unit.7. After taking the readings the current was put off, and receiver position was shifted to the next
electrode.
8. In this way the further readings were taken.
Figure 5.2 Measuring the parameters in
Time-Domain IP
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5.6 Time Domain IP Data of profile-1
Station Mx1 Mx2 Mx3 Mx4 Mx5 Mx6 Mx7 Mx8
0-10 7.19 8.36 8.51 5.8 5.73 6.93 8.67 8.76
10-20 8.37 8.57 5.5 5.24 6.53 8.4 6.02 5.31
20-30 9.34 6.36 5.86 6.49 8.44 6.55 5.72 6.07
30-40 9.2 8.56 9.01 10.93 9.1 8.04 7.63 10.9
40-50 7.23 8.11 10.31 8.57 7.65 7.3 9.34 6.41
50-60 6.12 8.51 6.73 5.78 5.43 7.52 4.78 5.09
60-70 8.33 6.76 5.93 5.48 7.4 4.87 5.88 8.33
70-80 8.33 7.85 7.26 8.86 6.47 7.43 9.34 9.19
80-90 8.28 8.07 9.83 7.52 8.45 10.85 9.72 11.84
90-100 5.98 7.44 5.19 6.06 8.57 8.14 7.81 6
100-110 7.06 4.8 5.69 8.27 7.77 7.54 5.75 3.48
110-120 5.41 6.04 8.9 8.1 7.71 5.96 4.31 5.46
120-130 8.52 11.97 11.04 11.24 8.74 7.95 9.5 11.73
130-140 8.81 7.86 8.38 5.85 3.6 6.36 8.57 -30.52
140-150 10.52 11.16 8.88 7.16 9.12 11.17 9.38 8.29
150-160 11.96 9.88 8.49 10.77 12.88 11.1 9.93 13.57
160-170 10.48 9.49 10.7 12.9 11.16 10.01 12.33 10.45
170-180 11.55 11.37 13.32 11.24 9.94 11.47 10.54 14.85
180-190 12.65 13.93 11.39 9.99 11.89 10.07 7.53 7.86
190-200 11.96 9.65 8.08 10.19 7.73 4.42 7.56 6.17
200-210 12.94 10.92 11.95 10.71 8.99 9.21 6.5 7.36
210-220 14.08 14.97 13.26 11.74 11.93 8.93 9.9 8.41
220-230 16.25 13.96 11.52 11.45 8.96 9.12 -2.65 28.85
230-240 13.33 10.82 10.53 9.43 8.68 7.18 6.68
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5.7 Time domain IP Pseudo-section
240-250 11.72 0.09 30.98 10.09 8.78 8.28
250-260 10.03 7.48 8.37 7.13 6.73
260-270 8.69 7.25 5.72 100.62
270-280 8.39 6.15 4.95
280-290 6.61 1.17
290-300 5.21
Chargeability
Distance (in meters) Scale: X-axis- 1 unit = 10 meter
Mx
Figure 5.3 Time domain IP pseudo section
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5.8 Time domain IP sounding data
AB/2(m) chargeability
4 10.92
6 12.2
8 12.51
10 12.37
15 11.61
20 10.58
25 10.15
40 8.31
50 8.09
60 9.21
80 8.5
100 7.87
120 8.57
140 7.49
160 7.9
180 7.47
200 7.77
250 8.27
300 8.59
TDIP sounding at 250
Figure 5.4 TDIP sounding plot
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5.10 Pseudo-plot of Time domain IP data of Profile-2 and Interpretation
INTERPRETATION:
The entire above diagrams represents IP pseudo section plot i.e. how the chargeability varies along the
profile. IP method is applicable for ground water search. We know water has lower chargeability. Here
we observe the presence of water which is indicated by the lower value of chargeability. Water is
trapped in an impervious rock. All figures indicate that water is associated with clay. Hence IP method
is suitable to distinguish between water and clay.
Chargeability
Distance (in meters)
Mx
Scale X-axis 1 unit = 10 meter and the
origin starts at 1 instead of 0
Chargeability
Scale X-axis 1 unit = 10 meter and the
origin starts at 1 instead of 0
Distance (in meters)
Mx
Figure 5.5 Pseudo-section TDIP profile-2 A
Figure 5.6 Pseudo-section TDIP profile-2 B
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5.11 Measurement of layer parameters using TDIP data
5.12 Interpretation for TDIP:
In the presence of chargeable medium apparent resistivity is given as:
a
a
m
1
*
The layer parameters are
1 = 172-m
1h = 1.1m 1m =17.8ms
2 = 56 -m
2h = 9.8m
2m = 37.2ms
3 = 1100-m 3h = 3m =18ms
Figure 5.7 Soundin
curves for TDIP an
schlumberger
For schlumberger
For TDIP
am = chargeability of the medium;
a = Apparent resistivity measured by Schlumberger
sounding method;
From the plot, we find that the resistivity curve for
Schlumberger sounding and TDIP sounding are
overlapping. This is due to low chargeability of the medium
AB/2 Ma (in s) rhoa
Ma (in
ms) rho'
5 9.42 32.2517 0.00942 32.5
10 9.06 34.1946 0.00906 34.50
15 8.29 33.3959 0.00829 33.67
20 8.27 35.7489 0.00827 36.04
25 8.59 33.912 0.00859 34.20
40 7.75 46.9823 0.00775 47.34
50 7.69 38.8575 0.00769 39.1560 7.425 54.95 0.007425 55.36
Data sheet prepared using the Formula
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Chapter-6
Electromagnetic Methods6.1 Introduction
Electromagnetic methods to get information about subsurface resistivity structure particularly
in volcanic and hydrothermal regions are considered highly effective to apply. This method can befurther divided into two parts depending on type of the signal used to energize the ground.
Frequency Domain Electromagnetic Method (FDEM)
Time Domain Electromagnetic Method (TDEM)
6.2 Frequency Domain Electromagnetic (Ground Conductivity) METHODS
Frequency Domain Electromagnetic (FDEM) involves generating an electromagnetic field which
induces current in the earth which in turn causes the subsurface to create a magnetic field. By measuring
this magnetic field, subsurface properties and features can be delineated. This method measures themagnitude and phase of induced electromagnetic currents, which are related to the subsurface electrical
conductivity. EM instruments provide two measurements simultaneously, the electrical conductivity data
and the phase component (in term of in-phase and quadrature), which responds to magnetic
susceptibility.These instruments provide bulk measurements of apparent conductivity values integrated
over a volume of the subsurface.
Figure 6.1 shows the generation of secondary field in subsurface conductive body.
FDEM has distinct advantages over many other techniques. Because no contact with the ground is
required, FDEM can cover a large area quickly and therefore economically. In certain cases, depths of
up to 50 meters can be mapped.
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6.3 Common applications of FDEM include the following,
Near-surface structures (faults)
groundwater investigations(identifying aquifers)
mapping lateral changes in natural geologic conditions
detecting and mapping contaminant plumes
mapping buried wastes, metal drums, tanks, and metal utilities
Factors affecting ground conductivity include the constituents, structure, and moisture content of the soil
or rock. Most soil and rock constituents (such as quartz, feldspar, mica, and iron and aluminum oxide
coatings) are electrical insulators of very high resistivity. In general the conductivity of both soils and
rocks is a function of:
Porosity
Moisture content
Concentration of dissolved electrolytes in the contained moisture
Temperature and phase state of the pore water
Amount and composition of colloids
6.4 Instruments used
Transmitter
Receiver
Cable
6.5 Coil systems for electromagnetic surveys
Figure 6.2 shows the different Geometry of coupling between Transmitter and Receiver
Field The EM survey was carried out in two lines. The profile length is 400m with station
spacing 10m and source receiver distance of 100m were chosen for the EM survey. The readings were
taken at four different frequencies i.e. 220 Hz, 880Hz, 3520 Hz and 14 kHz. The in-phase and out of
phase component were measured at four different frequencies. The survey is carried out on both the
profile-1 and profile-2.
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6.6 FDEM DATA SHEET for profile-1
X (Mid-point) 220Hz 800Hz , 3520Hz 7000Hz 14kHz
I I I I I
0 -7.2 -4.8 -9.5 -6.5 15
10 -6.6 -4.5 -7.3 29.5 19.9
20 -6.2 -4.1 1.1 39.2 19
30 -8.1 -5.4 5.3 13.7 -9.7
40 -7.7 -5.6 5.2 13.7 -17.3
50 -6.6 -4.3 -3.8 -9.6 -17.7
60 -8.6 -4.8 -2.3 -4.6 -40.9
70 -8 -6.2 -3.5 -13.5 -58.7
80 -10.7 -5.4 4.8 -7.4 -43
90 -11.3 -9 -4.9 -7.4 -53
100 -7 -6.4 -5.8 -12.4 -50.4
110 -9.7 -6 -2.3 -11.2 -36.5
120 -8.5 -6.2 -1.7 -8 -50.8
130 -4.9 -5.5 -1.9 -8 -35.8
140 -8.8 -5.8 7.8 -1 -28.9
150 -6.5 -4.6 3 7.4 -24.4
160 -7.9 -5.6 7.2 19.2 0.3
170 -5.2 -5.6 6.9 23.3 7
180 -7.8 -6.1 0.5 0.4 -28.6
190 -5 -4.8 0.4 1.7 -23.5
200 -5.7 -5.1 0.8 1.9 -24.1
210 -8 -3.7 -0.2 -0.3 -27.1
220 -7.9 -3.8 0 -0.7 -22.1
230 -5.2 -5.8 2.9 13.1 -0.2
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6.7 Plot and Interpretation of FDEM data of profile-1
Interpretation
Phase zero or cross over point indicates the position of the receiver or transmitter at the top ofthe body.
In general high frequencies resolve shallower bodies and lower frequencies resolve deeperbodies.
In the figure separation of crossovers for the 14 kHz and 7 kHz phase curve indicate the bedsare inclined.
6.8 FDEM Data for profile-2
Mid 220 Hz 880 Hz 3520 Hz 14000 Hz
I Q I Q I Q I Q0 -13.2 0.7 -6.3 4.9 12.2 3.1 5.1 -75.2
10 -8.5 1.6 -5.8 4 8.5 0.8 -6.8 -77.3
20 -9.5 0.3 -7.4 2.6 5.2 -3.5 -20.8 -78.1
30 -8.9 1.3 -7.8 2.1 3.9 -5 -26 -76.4
40 -8.9 0.6 -7.1 2.8 6.1 -2.3 -18.1 -79.4
50 -9.6 1.1 -7 3.3 6.1 -0.6 -17.2 -77.9
60 -10 1.6 -7.6 2 3.9 -5 -27 -76.6
70 -10 -1 -8.5 -2.8 -5.8 -19.2 65.4 -71.8
80 -9.7 -3.2 -5.7 -5.4 -8.1 27.3 -81.3 -71.2
Figure 6.3
Phase value (I
DistanceFor different
frequencies 2
Hz, 880 Hz, 35
Hz, 14 KHZ
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90 -6.8 -4.3 -8 -4.2 -7.6 -24.1 -75.2 -71.2
100 -8.1 -0.6 -5.6 -1.5 -2.5 -16.7 56.5 -73.1
110 -9.2 -0.3 -8.6 -3 -6.4 -21.3 -71.4 71.3
120 -10.4 -0.3 -8.2 -2.4 -4.9 -19 -65.6 -76.3
130 -9.6 -1.2 -8.4 -2.1 -3.7 -17.6 -63.1 -79.3
140 -10.3 -0.6 -7.7 0.8 2.5 -8.9 -14.2 -82.4
150 -8.4 -1 -7.3 0.8 2 -8.5 -13.6 -79160 -8.9 0.5 -7.1 -0.7 0.3 -12 -11.6 -80.9
170 -7.5 -2.4 -8.3 0.6 0.3 -9 -32.7 -75.5
180 -5.5 0.6 -5.1 1.4 4.2 -6.6 -21 -70.6
190 -8.2 -1.9 -6.8 -0.3 -2.3 -11.7 -44.9 -74.4
200 -9 -0.5 -6.6 -1.2 2.8 -12.5 -43.4 -69.8
210 -7.5 0.5 -5.4 0.6 0.2 -5.5 -24.2 -65.9
220 -8.6 1.6 -5.2 1.3 1.5 -2.6 -13.3 -56.9
230 -6 1.4 -4.2 2.1 3.3 0 -3.4 -55.9
240 -5 0.1 -3.8 -0.7 -0.6 -8.7 -26.8 -60.5
250 -4.9 1.2 -3.5 0.7 1.6 -4.5 -18.1 -61.9
260 -3.3 1.3 -2.5 2.4 5.3 1 1.4 -55.8
270 5 1.4 -2.2 5.7 10.8 12.4 44.3 -44.8
280 -4.2 2.8 -1.6 6.1 11.6 13.5 48.2 -40
290 -2.9 2.2 -1.5 6.7 12.9 17 64.5 -34.7
300 -3 2.1 -1.7 6.9 12.2 17.3 66.2 -30.6
310 -2 1.8 -1.7 7.6 13.5 18.5 69.2 -34.8
320 -4.4 2.1 -2.5 5.9 11.9 13.5 46.2 -53.5
330 -2.5 1.7 -1.3 4 9.8 7.3 27.3 -59.3
340 -3.3 1.9 -2.1 3.2 6.1 3.8 12.8 -58.1350 -4 1.4 -2.7 2.5 5.3 2.6 6.5 -58.8
360 -3.6 1 -2.1 0.8 2 -4 -24 -59.7
370 -3.8 0.5 -3 -0.5 -1.2 -7.9 -39.3 -55.2
380 0.9 1 4.1 -2.8 -2.2 -9.4 -43 -48.3
390 1 1.2 1.5 1.2 -1.9 -10.6 -47.3 -46.7
400 0.9 1.1 2.6 1.3 -3.1 -15.7 -58.9 -42.7
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6.9 Plot and Interpretation of FDEM data -profile-2
Distance (in meters)
I
Distance (in meters) I
1-220 Hz
2- 800 Hz
3- 3250 Hz4- 14 Hz
Figure 6.4 In-Phase
component Vs Distance
Figure 6.5 In-phase
component and Quadrature
Component Vs Distance
Figure 6.6
In-phase component
contours to easily
visualize the contact
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Interpretation
The anomaly becomes feeble as we go for low frequencies indicate the body causing the
anomaly is of shallow origin.
The contacts are found at 260 meter and 350 meter location in the profile
And also some unclear contacts are present at 50 meter and 100 meter location in the profile.
The contacts can be visualized by noting the zero contour in color map
6.10 Time Domain Electromagnetic Methods
Time domain electromagnetic sounding has a very peculiar advantage over other electrical prospecting
methods. So it provides a very good tool to resistivity structure of the earth. The advantages are stated
bellow:
It measures the secondary in the absence of primary.
It gives the value of a without measuring
E , rather it calculate a form
B .
6.11 Basic Principles
The time domain electromagnetic method employs a transmitter that drives an alternating current
through a square loop of insulated electrical cable laid on the ground. The current consists of equal
periods of time-on and time-off, with base frequencies that range from 1 to 32 Hz, producing an
electromagnetic field. Termination of the current flow is not instantaneous, but occurs over a very brief
period of time (a few microseconds) known as the ramp time, during which the magnetic field is time-
variant. The time-variant nature of the primary electromagnetic field creates a secondary
electromagnetic field in the ground beneath the loop, in accordance with Faraday's Law, that is a precise
image of the transmitter loop itself. This secondary field immediately begins to decay, in the process
generating additional eddy currents that propagate downward and outward into the subsurface like a
series of smoke rings. Measurements of the secondary currents are made only during the time-off period
by a receiver located in the center of the transmitter loop. Depth of investigation depends on the time
interval after shutoff of the current, since at later times the receiver is sensing eddy currents at
progressively greater depths. The intensity of the eddy currents at specific times and depths is
determined by the bulk conductivity of subsurface rock units and their contained fluids.
Instrument used:
Transmitter
Receiver
Sensors(3 magnetic coil)
Controler
Cable
Batteries
Figure 6.7
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6.12PROCEDURE FOR PROFILING
First of all the receiver should be switched on before one hour to provide enough time to the
quartz crystal to heated up. Then the receiver (Rx) and the transmitter are synchronized by the help of
the controller (XMT) by setting the phase difference around 0.2 degrees. By this we can make the pulse
shape of the transmitted and received signal exactly same or having phase difference with in tolerance
level. The XMT is then calibrated at 1Hz and 50% duty cycle.
Before taking reading the magnetic coils are calibrated form 1Hz to 32Hz and the contact
resistance is checked then a 30 X 30m loop of conducting wire is laid having the receiver at the centre.
The entire profile having 400m length is covered with 14 stations having 30m station spacing. The value
of the time window and the apparent resistivity are recorded which are then plotted. The plots are given
on the next page.
Figure 6.8 principle of TDEM
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6.13 TDEM profile-1 Data Sheet
As it can be seen the data is inconsistent with our geological knowledge. The data shows that top
weathered layered resistivity is above 60000 ohms and resistivity values decreases uniformly with the
depth. Thus there is some problem has occurred while acquiring the data, so we not processed this data.
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6.14 TDEM Profile-2 DATA SHEET
In order to plot the TDEM data into effective resistivity versus effective depth using theformulae given below,
Effective resistivity = Effective thickness = The data is processed and tabulated as given below.
6.15 Processed TDEM data sheet
x(station) y(eff_depth) z(eff_res) Station # Log(Eff_depth) Log(Eff_resistivity)1 32.978 114.37 1 1.518224314 2.058312121
1 25.851 35.453 1 1.412477348 1.549652991
1 50.44 90.249 1 1.702775078 1.955442398
1 92.754 229.29 1 1.967332648 2.360385114
1 186.69 743.81 1 2.271121056 2.871462013
1 211.43 795.08 1 2.32516661 2.900410829
1 197.65 557.89 1 2.295896819 2.746548577
1 240.45 651.39 1 2.381024781 2.813841087
1 205.15 391.66 1 2.312071521 2.59290922
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1 259.68 516.5 1 2.414438502 2.713070326
1 240.36 364.14 1 2.380862195 2.561268388
1 277.62 394.47 1 2.44345075 2.59601398
1 445.68 805.71 1 2.649023145 2.906178754
1 279.86 255.14 1 2.44694083 2.406778551
1 293.34 225.65 1 2.467371288 2.353435338
1 400.4 338.17 1 2.602494069 2.529135078
1 354.68 211.65 1 2.5498367 2.325618273
1 314.06 131.17 1 2.497012626 2.117834519
1 331.8 116.23 1 2.520876382 2.065318238
1 267.65 60.282 1 2.427567248 1.780187653
1 399.37 107.03 1 2.601375438 2.029505525
1 295.31 46.523 1 2.470278154 1.667667712
1 427.93 77.525 1 2.631372734 1.889441775
1 284.6 27.311 1 2.454234896 1.436337602
1 383.91 39.571 1 2.584229425 1.597377025
2 12.997 17.765 2 1.113843119 1.2495652122 10.347 5.6796 2 1.014814449 0.754317751
2 11.747 4.8951 2 1.069926969 0.689761568
2 18.571 9.1919 2 1.26883529 0.963405291
2 34.095 24.809 2 1.532690695 1.394609259
2 89.715 143.16 2 1.952865061 2.15582169
2 107.55 165.19 2 2.031610415 2.217983753
2 126.45 180.16 2 2.101918834 2.255658373
2 142.65 189.38 2 2.154271776 2.277334112
2 166.38 212.03 2 2.22110112 2.326397313
2 245.25 379.11 2 2.389609016 2.57876524
2 233.03 277.93 2 2.367411835 2.443935427
2 162.43 107.03 2 2.210666244 2.029505525
2 158.04 81.362 2 2.198767021 1.910421616
2 145.31 55.373 2 2.162295503 1.743298053
2 168.58 59.945 2 2.22680605 1.777752965
2 153.55 39.667 2 2.186249821 1.598429356
2 123.28 20.21 2 2.090892626 1.305566314
2 118.98 14.945 2 2.075473965 1.174495919
2 169.06 24.05 2 2.228040865 1.381115081
2 113.25 8.6065 2 2.054038211 0.934826573
2 182.69 17.804 2 2.261714776 1.250517586
2 136.06 7.8371 2 2.133730467 0.894155388
2 139.94 6.6039 2 2.14594187 0.819800488
2 121.93 3.9915 2 2.086110574 0.601136134
3 12.997 17.765 3 1.113843119 1.249565212
3 10.347 5.6796 3 1.014814449 0.754317751
3 13.357 6.3288 3 1.125708926 0.801321372
3 60.177 96.512 3 1.779430533 1.984581316
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3 48.115 49.407 3 1.68228049 1.693788484
3 40.801 29.61 3 1.610670807 1.471438407
3 365.68 1909.7 3 2.563101208 3.280965148
3 214.94 520.52 3 2.332317245 2.716437421
3 179.99 301.49 3 2.255248377 2.479272912
3 172.11 226.88 3 2.235806105 2.355796214
3 186.82 219.99 3 2.271423368 2.34240294
3 319.55 522.63 3 2.504538822 2.718194335
3 204.96 170.41 3 2.311669112 2.231495076
3 181.88 107.76 3 2.259784946 2.032457583
3 160.09 67.208 3 2.204364205 1.827420972
3 150.02 47.475 3 2.176149161 1.676464973
3 143.83 34.808 3 2.15784948 1.54167907
3 138.02 25.334 3 2.139942023 1.403703766
3 134.43 19.079 3 2.128496199 1.280555608
3 140.94 16.715 3 2.149034267 1.223106381
3 131.37 11.581 3 2.1184962 1.0637460623 136.61 9.9554 3 2.135482491 0.998058714
3 132.13 7.3914 3 2.121001435 0.868726706
3 127.64 5.4939 3 2.105986796 0.73988075
3 138.51 5.1512 3 2.141481129 0.711908412
4 20.64 44.8 4 1.314709693 1.651278014
4 27.466 40.02 4 1.438795416 1.602277084
4 51.638 94.589 4 1.712969413 1.975840634
4 97.328 252.46 4 1.988237799 2.402192578
4 123.42 325.11 4 2.091385542 2.512030328
4 126.23 283.39 4 2.101162582 2.452384521
4 137.68 270.68 4 2.138870857 2.432456168
4 159.6 286.99 4 2.203032887 2.457866764
4 157.62 231.2 4 2.197611323 2.36398783
4 178.33 243.58 4 2.25122441 2.386641626
4 209.22 275.89 4 2.320603198 2.440735959
4 208.45 222.39 4 2.319001899 2.347115255
4 232.93 220.1 4 2.367225427 2.342620043
4 266.9 232.07 4 2.426348574 2.365619002
4 245.17 157.62 4 2.389467327 2.197611323
4 326.4 224.73 4 2.51375015 2.351661052
4 304.93 156.44 4 2.484200154 2.194347807
4 640.87 546.19 4 2.806769942 2.737343745
4 424.89 190.59 4 2.62827651 2.28010011
4 349.69 102.9 4 2.543683213 2.012415375
4 375.35 94.545 4 2.57443642 1.975638566
4 512.17 139.94 4 2.709414136 2.14594187
4 236.28 23.635 4 2.373426962 1.373555607
4 323.09 35.199 4 2.509323516 1.546530325
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4 279.21 20.931 4 2.445930969 1.320789978
5 12.93 17.583 5 1.111598525 1.245092976
5 10.342 5.674 5 1.014604533 0.753889331
5 11.567 4.7464 5 1.063220736 0.676364335
5 15.949 6.779 5 1.202733458 0.831165634
5 32.946 23.165 5 1.517802694 1.364832305
5 80.972 116.62 5 1.908334866 2.066773037
5 136.94 267.79 5 2.136530324 2.427794355
5 148.36 248 5 2.171316825 2.394451681
5 146.08 198.6 5 2.16459076 2.297979244
5 172.5 227.9 5 2.236789099 2.357744325
5 201.09 254.88 5 2.303390474 2.406335758
5 283.35 410.94 5 2.452323217 2.613778417
5 158.03 101.3 5 2.19873954 2.005609445
5 129.14 54.328 5 2.111060782 1.735023717
5 133.45 46.699 5 2.125318578 1.669307581
5 116.75 28.751 5 2.067256889 1.4586529555 120.98 24.624 5 2.08271358 1.391358602
5 113.78 17.215 5 2.056065929 1.235907027
5 120.37 15.296 5 2.080518261 1.184577875
5 127.66 13.714 5 2.10605484 1.137164145
5 134.72 12.18 5 2.129432074 1.085647288
5 131.94 9.2859 5 2.12037648 0.967824002
5 106.22 4.7767 5 2.026206297 0.679127966
5 101.68 3.4859 5 2.007235538 0.542314924
5 185.93 9.2812 5 2.269349469 0.967604131
6 27.179 77.683 6 1.434233474 1.890325989
6 38.043 76.779 6 1.580274757 1.885242451
6 72.856 188.29 6 1.862465324 2.274827255
6 181.52 878.13 6 2.258924483 2.943558814
6 201.02 862.36 6 2.303239269 2.935688604
6 216.3 832.18 6 2.335056519 2.920217274
6 219.79 689.88 6 2.342007929 2.838773555
6 224.62 568.45 6 2.351448423 2.754692271
6 258.6 622.35 6 2.412628521 2.794034694
6 269.71 557.15 6 2.430897049 2.745972135
6 254.88 409.47 6 2.406335758 2.612222088
6 382.46 748.66 6 2.582586021 2.87428463
6 368.08 549.59 6 2.56594222 2.740038822
6 300.78 294.71 6 2.478248955 2.469394872
6 367.49 354.15 6 2.565245526 2.549187246
6 1165.1 2863.5 6 3.066363202 3.456897187
6 365.11 224.29 6 2.562423728 2.350809911
6 345.76 158.98 6 2.53877475 2.201342493
6 632.81 422.76 6 2.801273333 2.626093889
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6 381.13 122.23 6 2.581073135 2.087177812
6 653.09 286.23 6 2.814973034 2.456715151
6 366.06 71.482 6 2.563552275 1.854196695
6 395.93 66.366 6 2.59761841 1.821945643
6 292.35 28.82 6 2.465903098 1.459693976
6 328.43 28.961 6 2.51644282 1.461813554
7 12.997 17.765 7 1.113843119 1.249565212
7 10.347 5.6796 7 1.014814449 0.754317751
7 12.28 5.349 7 1.089198367 0.728272598
7 24.969 16.616 7 1.397401149 1.220526484
7 37.586 30.15 7 1.575026109 1.479287316
7 84.728 127.69 7 1.928026955 2.106156887
7 93.095 123.77 7 1.968926356 2.092615391
7 106.23 127.15 7 2.026247181 2.104316365
7 114.23 121.43 7 2.057780177 2.084325995
7 125.89 121.38 7 2.099991234 2.084147133
7 151.99 145.61 7 2.181815015 2.1631912027 198.8 202.28 7 2.29841638 2.305952945
7 255.47 264.75 7 2.407339908 2.422835969
7 161.6 85.077 7 2.208441356 1.929812167
7 164.42 70.896 7 2.215954644 1.850621733
7 139.06 40.788 7 2.143202225 1.610532411
7 131.68 29.174 7 2.119519818 1.464995979
7 133.13 23.57 7 2.124275932 1.372359583
7 126.55 16.907 7 2.102262149 1.228066553
7 121.94 12.512 7 2.086146191 1.097326736
7 125.3 10.536 7 2.097951071 1.022675762
7 116.11 7.1922 7 2.064869625 0.856861756
7 138.68 8.142 7 2.142013833 0.910731098
7 125.49 5.3104 7 2.098609119 0.725127235
7 125.73 4.2445 7 2.099438916 0.627826538
8 12.93 17.583 8 1.111598525 1.245092976
8 10.294 5.6212 8 1.012584164 0.749829038
8 12.32 5.3842 8 1.090610708 0.731121184
8 34.097 30.985 8 1.53271617 1.4911515
8 40.453 34.925 8 1.606950734 1.543136415
8 84.293 126.38 8 1.925791511 2.101678351
8 91.897 120.6 8 1.963301334 2.081347308
8 103.97 121.8 8 2.016908044 2.085647288
8 114.61 122.25 8 2.059222513 2.087248868
8 141.64 153.65 8 2.151185918 2.186532565
8 152.69 146.95 8 2.183810595 2.16716959
8 374.17 716.58 8 2.573068964 2.855264683
8 257.65 269.28 8 2.411030147 2.430204099
8 157.18 80.486 8 2.196397284 1.905720344
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8 136.42 48.804 8 2.134878045 1.688455418
8 124.49 32.692 8 2.095134467 1.51444149
8 120.41 24.395 8 2.080662556 1.387300822
8 121.15 19.518 8 2.083323418 1.290435314
8 121.7 15.635 8 2.085290578 1.194097886
8 112.7 10.688 8 2.051923916 1.028896445
8 132.23 11.734 8 2.121329998 1.069446084
8 119.79 7.6544 8 2.078420565 0.883911154
8 126.7 6.7961 8 2.102776615 0.832259761
8 131.42 5.8238 8 2.118661463 0.765206452
8 115.26 3.5666 8 2.061678615 0.552254405
9 27.169 77.625 9 1.434073654 1.890001613
9 50.656 136.13 9 1.704630893 2.133953845
9 135.39 650.25 9 2.131586588 2.813080361
9 175.18 817.84 9 2.243484522 2.912668348
9 419.69 3759.2 9 2.622928621 3.575095432
9 365.04 2370.1 9 2.562340456 3.374766679 207.54 615.11 9 2.317101812 2.788952788
9 540.81 3295.4 9 2.733044713 3.517908137
9 179.28 299.12 9 2.253531844 2.475845452
9 298.33 681.66 9 2.474696928 2.83356781
9 244.25 376.02 9 2.387834572 2.575210945
9 233.68 279.49 9 2.368621544 2.446366274
9 328.75 438.39 9 2.516865761 2.641860639
9 249.68 203.08 9 2.397383756 2.307667155
9 337.47 298.64 9 2.528235171 2.475147977
9 237.49 118.97 9 2.375645327 2.075437462
9 450.86 342.01 9 2.654041707 2.534038805
9 225.36 67.541 9 2.352876834 1.829567486
9 307.78 100.01 9 2.488240395 2.000043427
9 219.24 40.446 9 2.340919793 1.606875578
9 187.79 23.666 9 2.273672462 1.37412486
9 261.64 36.519 9 2.41770414 1.562518877
9 281.03 33.437 9 2.448752683 1.524227305
9 225.23 17.105 9 2.352626237 1.233123079
9 229.15 14.098 9 2.360119862 1.149157506
10 22.235 51.992 10 1.347037134 1.715936524
10 49.062 127.7 10 1.690745248 2.106190897
10 83.259 245.9 10 1.92043119 2.390758529
10 180.92 872.32 10 2.257486579 2.94067583
10 292.77 1829.3 10 2.466526573 3.262284934
10 212.03 799.68 10 2.326397313 2.902916234
10 88.197 111.09 10 1.945453813 2.045674967
10 303.34 1036.7 10 2.481929682 3.015653099
10 274.21 699.75 10 2.438083289 2.844942907
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10 506.09 1961.8 10 2.704227756 3.29265473
10 302.17 575.49 10 2.480251345 2.760037782
10 344.45 607.24 10 2.537126189 2.783360372
10 369.69 554.39 10 2.567837703 2.743815388
10 349.7 398.38 10 2.543695632 2.600297527
10 259.11 176.06 10 2.413484174 2.245660698
10 302.4 192.89 10 2.480581787 2.285309713
10 635.02 678.48 10 2.802787404 2.83153705
10 433.8 250.26 10 2.637289548 2.39839144
10 455.26 218.81 10 2.658259494 2.340067166
10 530.86 237.14 10 2.724980003 2.375004816
10 348.69 81.594 10 2.542439493 1.911658224
10 245.32 32.105 10 2.389732956 1.506572674
10 271.39 31.182 10 2.433593841 1.493903967
10 639.6 137.94 10 2.805908455 2.139690222
10 274.59 20.243 10 2.438684717 1.306274875
11 41.58 181.82 11 1.618884485 2.25964165311 62.49 207.17 11 1.795810525 2.316326866
11 97.612 337.99 11 1.989503211 2.528903851
11 151.72 613.5 11 2.181042834 2.787814567
11 152.01 493.18 11 2.181872159 2.693005456
11 147.26 385.74 11 2.168084796 2.586294676
11 408.08 2378.2 11 2.610745311 3.376248375
11 170.64 328.08 11 2.232080842 2.515979756
11 244.81 557.73 11 2.388829154 2.746424006
11 197.93 300.07 11 2.296511625 2.477222578
11 215.66 293.16 11 2.333769601 2.467104713
11 195.35 195.31 11 2.290813416 2.29072448
11 258.2 270.44 11 2.411956238 2.432070927
11 214.81 150.32 11 2.332054495 2.177016767
11 210.07 115.73 11 2.322364035 2.063445953
11 409.44 353.62 11 2.612190269 2.54853682
11 316.6 168.65 11 2.500510911 2.226986346
11 334.49 148.79 11 2.524383139 2.172573744
11 217.63 50.004 11 2.337718762 1.699004747
11 569.04 272.47 11 2.755142796 2.435318692
11 177.29 21.092 11 2.24868424 1.324117763
11 207.89 23.056 11 2.317833599 1.362783963
11 215.79 19.713 11 2.334031315 1.294752722
11 251.94 21.404 11 2.401297125 1.330494942
11 164.21 7.2397 11 2.215399601 0.85972057
12 32.583 111.65 12 1.512991068 2.047858727
12 160.39 1364.7 12 2.205177287 3.135037192
12 229.93 1875.4 12 2.361595639 3.273093912
12 131.01 457.46 12 2.117304447 2.660353126
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12 179.78 689.81 12 2.254741376 2.838729486
12 202.87 732.05 12 2.307217829 2.864540745
12 220.76 696 12 2.343920385 2.84260924
12 356.92 1435.4 12 2.552570884 3.156972942
12 217.16 438.86 12 2.336779833 2.642325999
12 337.72 873.59 12 2.528556781 2.941307654
12 276.43 481.65 12 2.441585174 2.682731565
12 462.21 1093.5 12 2.664839337 3.038818787
12 418 708.76 12 2.621176282 2.850499199
12 287.4 269.07 12 2.458486764 2.429865279
12 379.84 378.36 12 2.579600697 2.577905217
12 278.42 163.51 12 2.444700429 2.213544319
12 521.01 456.72 12 2.716846059 2.65965003
12 337.8 151.74 12 2.528659645 2.18110008
12 218 50.171 12 2.338456494 1.700452757
12 519.12 226.76 12 2.715267761 2.355566448
12 305.14 62.482 12 2.484499142 1.79575492312 491.27 128.75 12 2.691320244 2.109747238
12 325.84 44.949 12 2.513004397 1.652720034
12 533.74 96.061 12 2.727329751 1.982547103
12 273.65 20.105 12 2.437195452 1.303304077
13 12.638 16.796 13 1.101678351 1.225205866
13 10.294 5.6212 13 1.012584164 0.749829038
13 12.382 5.4387 13 1.0927908 0.735495104
13 31.813 26.972 13 1.502604625 1.430913151
13 40.407 34.845 13 1.606456608 1.542140469
13 92.161 151.08 13 1.964547178 2.179206976
13 98.005 137.17 13 1.991248233 2.137259139
13 109.31 134.62 13 2.038659894 2.129109586
13 116.38 126.04 13 2.065878353 2.100508395
13 127.62 124.75 13 2.10591874 2.096040554
13 151.32 144.33 13 2.179896333 2.159356612
13 202.53 209.93 13 2.306489363 2.322074506
13 214.67 186.93 13 2.331771356 2.271679006
13 162.93 86.474 13 2.212001058 1.936885548
13 150.83 59.659 13 2.178487731 1.775675969
13 137.05 39.62 13 2.13687904 1.597914471
13 130.41 28.613 13 2.115310895 1.456563395
13 124.24 20.526 13 2.094261443 1.312304325
13 121.18 15.502 13 2.083430948 1.190387733
13 119.78 12.073 13 2.078384309 1.081815201
13 121.7 9.9397 13 2.085290578 0.997373277
13 125.15 8.3548 13 2.097430854 0.921936058
13 116.87 5.7824 13 2.067703044 0.762108131
13 113.89 4.3738 13 2.056485593 0.64085892
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13 131.34 4.6312 13 2.118397012 0.665693537
14 34.66 126.33 14 1.539828558 2.101506496
14 157.16 1310.4 14 2.19634202 3.117403884
14 97.113 334.54 14 1.98727737 2.524448053
14 160.26 684.5 14 2.204825138 2.835373452
14 191.46 782.34 14 2.282078055 2.893395536
14 202.07 726.27 14 2.305501841 2.861098105
14 236.76 800.49 14 2.374308331 2.903355911
14 276.12 859.03 14 2.441097865 2.934008331
14 404.14 1520 14 2.606531837 3.181843588
14 261.93 525.5 14 2.418185243 2.72057272
14 583.4 2145.2 14 2.765966425 3.331467788
14 351 630.57 14 2.545307116 2.799733305
14 320.9 417.72 14 2.506369717 2.620885269
14 337.32 370.68 14 2.528042092 2.568999154
14 463.77 564.03 14 2.666302652 2.751302204
14 411.96 357.99 14 2.614855049 2.55387089514 516.08 448.12 14 2.712717029 2.651394327
14 321.9 137.79 14 2.507720977 2.1392177
14 314.31 104.29 14 2.497358199 2.018242667
14 602.54 305.5 14 2.779985883 2.485011215
14 573.27 220.54 14 2.758359215 2.34348737
14 235.26 29.525 14 2.371548093 1.470189906
14 344.79 50.327 14 2.537554661 1.701801043
14 281.79 26.774 14 2.449925577 1.427713259
14 403.34 43.677 14 2.605671294 1.640252801
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6.16 TDEM data Statistical Analysis to remove noisy data
The data tabulated is analyzed statistically by computing the mean and standard deviation of
effective resistivity. And the data which have higher standard deviation are removed.
It has been found that most of the data fall below the S.D value 14.89. And constricting ourselves to
the depth of investigation to 350 meter, we filtered the data set. I.e. we removed the data set whose
depth value greater than 350 meter
The station locations are converted into meters. The data set thus obtained is scattered data set.
This scattered data thus obtained are converted into the regular grid data by grid data function in
MATLAB which uses cubic spline method for interpolation
Figure 6.9 Standard deviation Vs Resistivity data ( data whose S.D more than 14.89 are removed )
Figure 6.10 showing conversion of scattered data to grid data
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6.17 Scattered Data set filtered on the basis standard deviation described above
and restricting ourselves to depth of 350 meter
X Y Z
STATION DEPTH EFFECTIVE RESISTIVITY
(in meter) (in meter) (in Ohm-meter)15 32.978 114.37
15 25.851 35.453
15 50.44 90.249
15 92.754 229.29
15 197.65 557.89
15 205.15 391.66
15 259.68 516.5
15 240.36 364.14
15 277.62 394.47
15 279.86 255.1415 293.34 225.65
15 314.06 131.17
15 331.8 116.23
15 267.65 60.282
15 295.31 46.523
15 284.6 27.311
45 12.997 17.765
45 10.347 5.6796
45 18.571 9.1919
45 34.095 24.809
45 89.715 143.16
45 107.55 165.19
45 126.45 180.16
45 142.65 189.38
45 166.38 212.03
45 245.25 379.11
45 233.03 277.93
45 162.43 107.03
45 158.04 81.362
45 145.31 55.373
45 168.58 59.945
45 153.55 39.667
45 123.28 20.21
45 118.98 14.945
45 169.06 24.05
45 113.25 8.6065
45 182.69 17.804
45 136.06 7.8371
45 139.94 6.6039
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75 12.997 17.765
75 10.347 5.6796
75 13.357 6.3288
75 60.177 96.512
75 48.115 49.407
75 40.801 29.61
75 214.94 520.52
75 179.99 301.49
75 172.11 226.88
75 186.82 219.99
75 319.55 522.63
75 204.96 170.41
75 181.88 107.76
75 160.09 67.208
75 150.02 47.475
75 143.83 34.808
75 138.02 25.334
75 134.43 19.079
75 140.94 16.715
75 131.37 11.581
75 136.61 9.9554
75 132.13 7.3914
105 20.64 44.8
105 27.466 40.02
105 51.638 94.589
105 97.328 252.46
105 123.42 325.11
105 126.23 283.39
105 137.68 270.68
105 159.6 286.99
105 157.62 231.2
105 178.33 243.58
105 209.22 275.89
105 208.45 222.39
105 232.93 220.1
105 266.9 232.07
105 245.17 157.62105 326.4 224.73
105 304.93 156.44
105 349.69 102.9
105 236.28 23.635
105 323.09 35.199
105 279.21 20.931
135 12.93 17.583
135 10.342 5.674
135 15.949 6.779
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135 32.946 23.165
135 80.972 116.62
135 136.94 267.79
135 148.36 248
135 146.08 198.6
135 172.5 227.9
135 201.09 254.88
135 283.35 410.94
135 158.03 101.3
135 129.14 54.328
135 133.45 46.699
135 116.75 28.751
135 120.98 24.624
135 113.78 17.215
135 120.37 15.296
135 127.66 13.714
135 134.72 12.18
135 131.94 9.2859
135 185.93 9.2812
165 27.179 77.683
165 38.043 76.779
165 72.856 188.29
165 269.71 557.15
165 254.88 409.47
165 300.78 294.71
165 345.76 158.98
165 292.35 28.82165 328.43 28.961
195 12.997 17.765
195 10.347 5.6796
195 24.969 16.616
195 37.586 30.15
195 84.728 127.69
195 93.095 123.77
195 106.23 127.15
195 114.23 121.43
195 125.89 121.38195 151.99 145.61
195 198.8 202.28
195 255.47 264.75
195 161.6 85.077
195 164.42 70.896
195 139.06 40.788
195 131.68 29.174
195 133.13 23.57
195 126.55 16.907
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195 121.94 12.512
195 125.3 10.536
195 116.11 7.1922
195 138.68 8.142
225 12.93 17.583
225 10.294 5.6212
225 34.097 30.985
225 40.453 34.925
225 84.293 126.38
225 91.897 120.6
225 103.97 121.8
225 114.61 122.25
225 141.64 153.65
225 152.69 146.95
225 257.65 269.28
225 157.18 80.486
225 136.42 48.804
225 124.49 32.692
225 120.41 24.395
225 121.15 19.518
225 121.7 15.635
225 112.7 10.688
225 132.23 11.734
225 119.79 7.6544
225 126.7 6.7961
225 131.42 5.8238
255 27.169 77.625
255 50.656 136.13
255 179.28 299.12
255 244.25 376.02
255 233.68 279.49
255 328.75 438.39
255 249.68 203.08
255 337.47 298.64
255 237.49 118.97
255 225.36 67.541
255 307.78 100.01255 219.24 40.446
255 187.79 23.666
255 261.64 36.519
255 281.03 33.437
255 225.23 17.105
255 229.15 14.098
285 22.235 51.992
285 49.062 127.7
285 83.259 245.9
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285 88.197 111.09
285 349.7 398.38
285 259.11 176.06
285 302.4 192.89
285 348.69 81.594
285 245.32 32.105
285 271.39 31.182
285 274.59 20.243
315 41.58 181.82
315 62.49 207.17
315 97.612 337.99
315 152.01 493.18
315 147.26 385.74
315 170.64 328.08
315 244.81 557.73
315 197.93 300.07
315 215.66 293.16
315 195.35 195.31
315 258.2 270.44
315 214.81 150.32
315 210.07 115.73
315 316.6 168.65
315 334.49 148.79
315 217.63 50.004
315 177.29 21.092
315 207.89 23.056
315 215.79 19.713
315 251.94 21.404
315 164.21 7.2397
345 32.583 111.65
345 131.01 457.46
345 217.16 438.86
345 276.43 481.65
345 287.4 269.07
345 278.42 163.51
345 337.8 151.74
345 218 50.171345 305.14 62.482
345 325.84 44.949
345 273.65 20.105
375 12.638 16.796
375 10.294 5.6212
375 31.813 26.972
375 40.407 34.845
375 92.161 151.08
375 98.005 137.17
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170 499.0 21.4 212.5 278.4 222.7 116.3 81.8 68.0 320.9 232.0 318.1 45.3 80.9 142.7
180 527.6 14.2 301.4 239.0 91.6 42.2 120.7 75.2 290.7 126.1 24.0 60.5 102.4 108.3
190 548.4 36.2 215.0 216.6 53.1 98.5 168.3 89.6 19.2 80.7 121.0 107.6 145.8 77.4
200 519.7 77.6 158.5 209.7 247.1 246.1 205.8 103.6 16.5 -9.0 253.1 272.3 197.3 51.7
210 390.9 132.5 356.8 280.1 288.1 281.3 234.3 121.8 29.6 -9.4 114.2 414.7 198.3 33.2
220 372.4 195.0 515.5 281.4 307.8 313.0 259.0 150.5 39.5 65.2 84.0 45.6 193.0 23.4
230 354.0 259.1 438.2 233.5 310.6 342.4 276.5 192.3 51.3 41.9 314.8 27.7 208.0 24.2
240 363.0 348.9 307.1 66.5 302.9 370.1 283.3 229.5 204.1 28.9 526.2 16.9 225.3 76.6
250 475.1 373.2 283.3 175.4 265.8 396.7 276.0 256.9 199.4 72.0 129.8 12.3 242.2 327.5
260 511.2 358.0 242.4 229.8 334.2 467.6 248.3 271.0 50.8 175.1 274.4 12.8 253.5 521.4
270 91.1 341.7 224.4 191.0 400.5 554.0 187.6 263.8 13.0 43.3 280.6 17.5 216.9 348.8
280 247.5 325.9 298.4 22.3 418.5 309.2 305.0 237.0 31.0 41.8 266.3 152.0 115.8 44.6
290 158.4 313.0 384.9 76.7 376.2 51.0 280.0 198.1 58.1 117.1 239.5 252.4 70.2 8.7
300 46.0 314.1 460.9 143.4 284.0 289.4 243.1 159.9 86.1 184.9 208.4 108.8 27.2 28.6
310 113.1 354.7 511.4 137.6 162.0 218.3 180.7 123.9 111.6 194.8 180.9 47.7 47.1 78.1
320 147.9 382.7 522.0 51.7 43.9 86.4 70.2 177.9 300.8 162.0 161.4 30.4 71.0 399.5
330 134.2 307.9 436.3 231.2 108.5 30.8 121.6 318.4 434.0 114.6 139.1 81.3 180.1 256.7
340 NaN NaN 205.6 185.1 160.8 114.4 171.9 248.3 306.7 80.0 201.8 158.2 153.8 281.3
Here along X-direction is profile distance in meter, along Y-axis is Depth in meter and Grid data are
effective resistance in Ohm-meter. NaN indicates non-availability of the data or the places where the
data cannot be computed.
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6.18 Plotting and Interpretation of TDEM data
We obtained the image of the subsurface by plotting in MATLAB
Interpretation:
Low resistivity regions may be water or clay are indicated by dark blue colour
High resistivity regions may be due to igneous intrusions are indicated by red colour, but thethose structure will not look like real igneous intrusions (dyke) due to interpolation errors ,approximations and smoothing done while processing the data.
This High resistivity regions are consistent with the anomalies obtained in other geophysicalmethods like SP, wenner profiling.
Effective
resistivity
Figure 6.10
Effective resistivity
plot using TDEM
method
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Chapter-7
Gravity survey
7.1 Gravity Survey Introduction: Gravity prospecting involves the measurement of subsurface
geology on the basis of variation in the Earths gravitational field generated by density contrasts
between the subsurface rocks.
7.2 Gravity Survey Theory:
The acceleration due to gravity is given by
g=GM/R2
Where, M=Mass of Earth, G=Gravitational constant, R=Radius of the Earth
In Gravity prospecting, we measure the relative variation in gravity with respect to a Base Station at
which gravity is known previously.
International gravity reference formula 1930 (IGRF)
The acceleration due to gravity at any latitude () is given by theInternational gravity formula
g= g0 (1+sin2+sin
22).
Where g0 = 978.049 Gal, gravity at the equator.
= 0.0052884, = -0.0000059, = latitude
This gives the theoretical value of gravity at the stations.
7.3 Corrections applied to the gravity data:
1. Drift correction: All spring mass system (e.g. gravimeter) changes null reading with time, even when
set up at fixed station. This is known as drift.
Drift rate = (b2-b1)/ (t2-t1) * C
Drift correction at time t = (t-t1) * Drift rate
g = observed reading + Drift correction
Where, b2 = gravimeter reading at time t2
b1 = gravimeter reading at timet1
C = dial constant of gravimeter
g =drift corrected gravimeter reading
2. Free Air correction (F.A.C):
Free air correction is given by: 2gh/R= -0.3086h mgal/m
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3. Bouguer correction (B.C):
Bouguer correction is given by: 2Gh= 0.112h mgal/m
Free Air anomaly = g (observed)-g (theoretical) +F.A.C
Bouguer anomaly = g (observed)-g (theoretical) +F.A.C-B.C
7.4 Field Procedure:
The gravity base station at Dubrajpur is taken as the primary base station for the gravity survey. For drift
corrections, a Secondary base station was prepared near Bakreswar lodge.
Preparation of Secondary Base:
Reading at Primary Base at time t1=R1
Reading at Secondary Base at time t2=R2
Reading at Primary Base at time t3=R3
By interpolation, Reading at Primary Base at time t2= R1 + ((R3-R1) / (t3-t2))*(t2-t1).
The students were divided into groups and each group carried out the survey in different places near
to the survey area. Every day at the beginning, the gravimeter was placed at the secondary base station
and the reading was taken after leveling the gravimeter. Readings were repeated at the base after two-
three hours. For accuracy, readings were repeated at each station.
Elevation, latitude and longitude of stations were determined through GPS survey.
7.5 OBSERVATIONS:
Value of the gravity at the primary base is 1035.1 div or 93.28321 mgal.
The elevation of the primary base from M.S.L is 36.215m.
Gravimeter used: Worden Gravimeter.
Instrument constant: 0.0912 mgal/div
Density taken, = 2.67 gm/cm
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7.6 Data sheet for Gravity survey with various corrections
S.No Stations
name
Field
gravity
value
(div)
Drift
correction
(div)
Drift
corrected
value
(div)
Drift
corrected
value
(mgal)
*Elevation
of station
(m)
Free air
correction
(mgal)
Bouguer
correction
(mgal)
**Bouguer
anomaly
(mgal)
1 ADU1 1068.6 1.9008 1066.8992 97.3012 6.7444 -2.0813 0.7553 -0.0283
2 ADU2 1055.6 3.0624 1052.5376 95.9914 8.6908 -2.6819 0.9733 -2.1567
3 ADU3 1067.3 3.6432 1063.6568 97.0055 2.3034 -0.7108 0.2579 1.54384 ADU4 1058.0 4.4352 1053.5648 96.0851 0.0992 -0.0306 0.0111 1.6151
5 ADU5 1071.3 5.5176 1065.7824 97.1993 -7.0103 2.1633 -0.7851 5.6550
6 ADU6 1064.6 6.072 1058.5280 96.5377 -1.1646 0.3593 -0.1304 2.5347
7 ADU7 1051.1 0.2865 1050.8130 95.8341 -1.1646 0.3593 -0.1304 1.8311
8 ADU8 1048.2 0.3655 1047.8340 95.5624 -6.9734 2.1519 -0.7810 4.0026
9 ADU9 1062.9 0.4287 1062.4712 96.8973 -2.9241 0.9023 -0.3275 3.6344
10 ADU10 1060.9 0.4564 1060.4535 96.7135 -6.5242 2.0133 -0.7307 4.9647
11 TNP1 1049.7 0.6629 1049.0124 95.6688 3.1126 -0.9605 0.03486 0.1331
12 TNP2 1071.8 1.5785 1070.2211 97.6041 0.1372 -0.0423 0.0154 3.0536
13 TNP3 1063.7 2.7465 1060.9531 96.7589 1.4915 -0.4603 0.1671 1.6387
14 TNP4 1060.1 3.4727 1056.6273 96.3644 7.8469 -2.4215 0.8788 -1.4288
15 TNP5 1051.5 4.7355 1046.7645 95.4649 10.5478 -3.2550 1.1814 -0.464316 CHR1 1093.6 0.1101 1093.4912 99.7263 5.3151 1.6402 0.59528 6.2784
17 CHR2 1021.2 0.1801 1021.0231 93.1170 -5.4050 1.668 -0.60536 0.89758
18 CHR3 1117.9 0.2202 1117.6842 101.932 -5.9551 1.8377 -0.66696 9.94424
19 CHR4 1106.5 0.2803 1106.2214 100.8873 -1.0553 0.3256 -0.11816 6.83824
20 CHR5 1109.6 0.3303 1109.6121 100.8943 -8.7952 2.7141 -0.98504 10.10062
21 RJN1 1058.5 1.2615 1057.238 96.4201 6.4336 -1.9854 0.7205 -0.7786
22 RJN2 1038.4 1.8922 1036.5078 94.5295 17.2918 -5.3362 1.9366 -7.2361
23 RJN3 1050.8 2.3758 1048.4242 95.6162 12.4245 -3.8342 1.3995 -4.1023
24 RJN4 1063.3 2.6492 1060.6508 96.7313 0.9471 -0.2922 0.1060 1.8402
25 RJN5 1060.9 2.9645 1057.9355 96.4837 9.1629 -2.8276 1.0262 -1.86290
*Elevation is given with respect to bench mark located at Dubrajpur, whose elevation with respect to
MSL is 36.215 m.
**Bouguer anomaly has been calculated with respect to gravity value at Dubrajpur base station, which
has a value of 1035.1 div or 93.28321 mgal as measured by gravimeter.
7.7 Bouguer Anomaly and corresponding Latitude and Longitude values Data sheet
STATION
BOUGUER
ANOMALY LATITUDE LONGITUDE
ADU 1 -0.02831 23.9182 87.3991
ADU 2 -2.15674 23.9123 87.3957
ADU 3 1.54387 23.9067 87.392
ADU 4 1.6152 23.9003 87.3859
ADU 5 5.6551 23.8873 87.3758
ADU 6 2.5348 23.8781 87.3693
ADU 7 1.8312 23.8781 87.3693
ADU 8 4.0027 23.8764 87.3711
ADU 9 3.6344 23.8751 87.3727
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ADU 10 4.9648 23.8734 87.3741
ADU 11 0.13312 23.8956 87.3752
ADU 12 3.0536 23.8848 87.3642
ADU 13 1.6387 23.9036 87.3564
ADU 14 -1.4288 23.9059 87.3479
ADU 15 -0.4643 23.9057 87.3373
ADU 16 -0.7786 23.9254 87.387
ADU 17 -7.236 23.929 87.3784
ADU 18 -4.1023 23.9312 87.3689
ADU 19 -1.8402 23.9356 87.3613
ADU 20 -1.8629 23.9198 87.3946
ADU 21 6.2784 23.9187 87.4124
CHRO 2 0.8975 23.9191 87.4259
CHRO 3 9.9442 23.9198 87.4323
CHRO 4 6.8382 23.9177 87.4433
CHRO 5 10.1006 23.9195 87.4517
7.8 plotting and interpretation
Based on the data the Bouguer Anomaly Map is generated using SURFER package and the results are
interpretedX-axisLatitude