Real Madridhjrhgj

UNIVERSITY OF LAGOS

AKOKA, YABA

FACULITY O F SCIENCE

DEPARTMENT OF GEOSCIENCES

A FIELD REPORT ON THE INDEPENDENT GEOPHYSICAL STUDY CARRIED OUT AT IGARRA GIRLS JUNIOR GRAMMAR, IGARRA, EDO STATE,

SOUTH-WEST NIGERIA.

BY

NAME: AKILLO OLANIYI MOSHOOD

MATRIC NO: 110813006

DEPARTMENT: GEOSCIENCES/GEOPHYSICS

COURSE CODE: GPS 306

COURSE TITLE: FIELD TECHNIQUES

GROUP: 6

DATE: 28th of March – 16th of March 2014

AKILLO OLANIYI MOSHOOD 110813006 Page1

REPORT OUTLINE

ABSTRACT

1.0 CHAPTER 1: INTRODUCTIONLocation of the area. Size of the area. Purpose of investigation.

2.0 CHAPTER 2: THEORY/PRINCIPLE OF THE METHODGeophysical Method

3.0 CHAPTER 3: DATA PROCESSING AND DATA INTERPRETATION

Geophysical Results - Data Obtained Data Interpretation and Discussion

4.0 CHAPTER 4: ECONOMIC CONSIDERATIONS

5.0 CHAPTER 5: CONCLUSION

6.0 CHAPTER 6: BIBLIOGRAPHY


ABSTRACT

Geophysical field mapping has been carried out in IGARRA GIRLS JUNIOR GRAMMAR SCHOOL,Igarra, Akoko Edo, Edo State. North-West Nigeria to study the rock distribution, rock type and rock features and also to determine the physical characteristics and structural settings of the sub-surface materials using various geophysical methods.

For the geophysical survey, a traverse measuring 140 metres with a station-station interval of 10 metres was used for the survey. Measurements using seven (9) different geophysical methods and various sophisticated equipment were used for the survey.

From the geophysical survey, the depth to the basement was determined to be about 3 m – 7 m beneath the sub-surface by using various geophysical methods namely – Self-Potential (SP), EM 34-3, Very low frequency(VLF), Magnetics, Gravity, Resistivity method(VES and CST),Time Domain(TDM) and Seismic Refraction.

The results were able to support the fact that Igarra is a town sitting majorly on a basement complex though sediments have been deposited on some parts of the town. In order to get more detailed information about the basement complex beneath, regional geological and geophysical survey of the area has to be carried out.


CHAPTER ONE 1. 0INTRODUCTION

The objective of this survey was to delineate the subsurface characteristics and properties of rocks present in Igarra. As a result of the basement complex, the depth to ground water in Igarra would be large and the cost of drilling for ground water would be expensive. From this survey, we were hoping to get the depth to the basement complex and if possible, locate zones of easily reachable ground water by delineating fracture zones in the subsurface, layer thickness and number of layers in the subsurface, density variations in the subsurface, magnetic properties of the subsurface, the conductivity and resistivity of the subsurface e.t.c. Another important objective of this survey was for students to gain quality learning experience on how to carry out field survey processes and their interpretation.

The main objectives of this study were achieved using various geophysical methods. The geophysical methods employed include;Vertical Electrical Sounding (VES), Magnetics, Very Low Frequency (VLF), Spontaneous Potential (SP), Constant Separation Traversing (CST), Frequency Domain (EM 34-3), Seismic Refraction, Gravity, and Time Domain Electromagnetic (TDEM). . All these methods were used on the field to better characterize the subsurface behaviour of Igarra. The traverse ran East - West and was made to accommodate all the geophysical methods used.

The gravity method was used to check for density variations in the subsurface. The seismic method was used to delineate the number of layers present depending on the energy source, the thicknesses of these layers, the possible components of these layers and the depth to the last layer. The magnetic method was used to check for the variations in the magnetic susceptibility of the subsurface depending on the mineral contents of the soil and the basement. The self-potential method was used to delineate the variations in the potential difference of the subsurface. The VLF, TDEM and EM-34methods were used to


check for the horizontal and vertical variations in conductivity of the subsurface and the profiling and VES methods were used to delineate the lateral and vertical variations in resistivity of the subsurface.

1.0 GEOGRAPHICAL SETTING OF THE AREA

Location

Igarra lies in the northern part of Edo State and is the headquarters of Akoko Edo Local Government Area. The Igarra area lies within Latitudes 7024’5’’N-7030N and Longitudes 6000’E-6010’5’’E at the northern fringe of Edo State. The major highway in the area runs from Auchi through, Sobe- Ogbe, Ikpeshi, Igarra to Ibillo. Both the old and new roads were used as access paths for the exercise. There are

also other major footpaths which are indicated in the accessibility map below.

Location map of Igarra

Climate


The climatic condition of Igarra fall within the warm-humid tropical climate belt where the wet and dry seasons are noticed prominently in the area. The rainy seasons are mostly between April and October while the dry season is between November and February. Average rainfall is believed to be between 1450-950mm, with mean annual temperature of about 30°c.

Topography

The study plot is characterized by extremely high hills located on both the western and the eastern portion of the plot. Some isolated hills also occur in other portion of the plot. Gentle slope are also found in the eastern section of the plot.

A picture showing the topography of the survey area

Vegetation

Igarra and its environs fall under the Guinea savannah vegetation belt. The vegetation here is prominently made up of sparsely distributed trees, herbs, shrubs, and grasses. Trees in this area are mostly concentrated along fracture zones within the plutonic bodies and on the Quartzite ridges were adequate soil cover has resulted and there is adequate groundwater retention. The


vegetation in this area is mostly secondary i.e. the natural vegetation is being altered and such agricultural crops such as Maize, Yam, Cocoa, Cassava, Pineapple, Cashew, Mango, and Sugar cane are grown here.

SURVEY LAYOUT

A picture of a base map showing were the survey was carried out


CHAPTER TWO

THEORY/PRINCIPLE OF THE METHOD

Geophysical Method The geophysical survey was carried out within Igarragirls junior grammer School, Akoko Edo State. There were Ten (10) traverses for the survey, my group 6 used traverse seven (6) .In total, eight (9) methods were used namely: Vertical Electrical Sounding (VES), Magnetics, Very Low Frequency (VLF), Spontaneous Potential (SP), Constant Separation Traversing (CST), EM 34-3, Seismic Refraction, Gravityand time domain electromagnetic (TDEM)

1. GRAVITY SURVEY : Gravity method is the measurement of variations in the gravitational field of the earth, with the aim of locating local masses of greater or lesser density (called anomaly) than the surrounding formations. These variations in gravity depend upon lateral changes in the density of the subsurface in the vicinity of the measuring point. Because density variations are very small and uniform, the instruments used are very sensitive. These measurements are normally made on the earth’s surface, but underground surveys also are carried out occasionally.

A gravimeter is the instrument used to measure variations in the earth’s true gravitational field at a given location. The standard unit with which gravity measurements are taken is the milligal (mgal) or gravity unit (g.u.) [10g.u. =1mgal].

Gravity method is used as a reconnaissance tool in oil exploration, mineral exploration during integrated base-metal surveys, delineating buried valleys, bedrock topography, geologic structure, voids, engineering and archaeological studies.


BASIC THEORY

The basis on which the gravity method depends is encapsulated in two laws namely;

1.Newton’s Law of Universal Gravitation which states that the force of attraction between two masses and which is separated by distance is given by:

…………………………………….1

Where G is the gravitational constant (6.67x10-11 m3 kg2s2)

2.Newton’s Second Law of Motion which that the force acting on a body is equal to the product of mass and acceleration . If the acceleration is in a vertical direction, it is then due to gravity .

……………………………2

Equations (1) and (2) can be combined to obtain another simple relationship

This shows that the magnitude of the acceleration due to gravity on Earth is directly proportional to the mass of the Earth and inversely proportional to the square of the Earth’s radius .

Theoretically, acceleration due to gravity should be constant over the Earth, however, the earth’s ellipsoidal shape, rotation,


irregular surface relief and internal distribution cause gravity to vary from place to place.

METHODOLOGY

A total of 21 gravity stations comprise the data set. The gravity stations were surveyed on 105m traverse with the base station on an elevation of 314m. The used equipment include the gravimeter (for measuring the gravimeter anomalies), altimeter (for elevation readings), GPS (for longitude and latitude readings). Showing below

ALTIMETER (for elevation measurement) GRAVIMETER (gravity anomalies)

AGRAAeeSA

AAA

FIELD PROCEDURE

The gravity survey method is a very stressful survey method. All we did was take the gravimeter from one station to another, level it and wait for it to take readings so we can record. The time to return to the base station to take base station readings was stipulated to be every 1 hour. After 1 hour along the traverse taking gravimeter readings, we return to the base station. The


base station readings are taken to correct for drift. The altimeter readings were also taken by placing the altimeter on the station and leveling it. The longitude and latitude readings were taken by holding the GPS and standing on the station to record the longitude and latitude. All these data were recorded and taken home for processing and interpretation.

2.MAGNETIC SURVEY METHOD:Magnetic survey investigates subsurface geology on the basis of anomalies in the Earth’s magnetic field resulting from the magnetic properties of the underlying rocks. There is much uncertainty about the origin and nature of the Earth’s magnetic field, modern theories suggest the magnetic field is caused by flow of material in the outer core which generates a flow of electrical current, alongside current external to the Earth in the ionosphere and magnetosphere associated with the Van Allen radiation belts, are possible causes of overall geomagnetic field.

A magnetometer is an instrument which measures magnetic field strength in units of gammas or nanoteslas (1 gammas = 1 nanotesla = 0.00001 gauss). A buried ferrous object, such as a steel drum or tank, causes local distortion of the earth’s magnetic field and results in a magnetic anomaly. The common objective of conducting a magnetic survey is to map these anomalies and delineate the areas of burial of the sources of these anomalies. Analysis of magnetic data estimate the regional extent of buried ferrous targets, such as a steel tank, canister or drum and depth of burial.

Magnetic method measurements are made easier and cheaper than most geophysical measurements and corrections are practically minima. It is used at a site to map various geologic features, such as igneous intrusions, faults, and some geologic


contacts that may play an important role in the hydrogeology of a ground water pollution site.

BASIC THEORY

The force F between two magnetic poles of strength m1 and m2

separated by a distance r is given as

F= µ0m1m2

4 π µR r2 ………………….1

Where µ0and µR are constants corresponding to the magnetic permeability ofvacuum and the relative magneticpermeability of the medium separating the poles. The magnetic flux densityB(Wb/m2) due to a pole of strength m at a distance r from the pole is the force exerted on a unit positive pole at that point.

B = µ0m

4 π µR r2……………..2

The magnetic field in terms of a force field which is produced by electric current is called the magnetic field strengthH (A/m).

The ratio of the flux densityB to the magnetic field strength H resistivity r is a constant called the absolute magnetic permeability (µ)

Magnetic susceptibility k, which is a measure of how a material(rocks) become magnetized, is the geological parameter of interest and result in induced magnetization J of targeted magnetic material after its interaction with the geomagnetic field.

The relationship between k , B , and H is given below;

B = µ0H (1+k)………….3

Where J= kH


All magnetic anomalies caused by rocks are superimposed on the geomagnetic field, which varies in both amplitude and direction. The components of this geomagnetic field are what could be measured in any magnetic survey. There are three components of this geomagnetic field which can be measured in magnetic survey, they are;

Strength of the total field vector, B Horizontal component of the Earth’s magnetic field, H Vertical component of the Earth’s magnetic field, Z

METHODOLOGY

The traverse surveyed was 140m long with a total of 29 stations. We took our magnetic data at every 2.5m making a total of 29 stations. The equipment used was the magnetometer (for recording the magnetic susceptibility) and gps (for coordinates). A proton precession magnetometer was used.

FIELD PROCEDURE

It is a very stress free data acquisition method. We moved 2.5m on our traverse and took measurements till we were done with the traverse. We stripped ourselves off all metallic materials so that they won’t influence our data. We kept a constant distance of 2.5m between the precession rod and the recording device. A base station was chosen close to the traverse and we returned back to the base station every 5minutes to take readings. Not more than two persons carried out the survey. One person was with the rod and was leading while the other was with the measuring device and was behind. The rod was aligned with the magnetic north. The time of measurement was also recorded as we movedalong the traverse.


A picture showing magnetometer and how the survey was carried out

3.VERY LOW FREQUENCY METHOD:VLF method is electromagnetic radiation generated in the low-frequencyband of 15-30 KHz by a powerful radio transmitter used in long-range communications and navigational systems. The VLF method has the advantages that the field equipment is small and light, being conveniently operated by one person, and that there is no need to install a transmitter. The disadvantage is that the depth of penetration is somewhat less than that attainable by tilt-angle methods using a local transmitter. It is used for exploration of subsurface geological features, such as ore bodies, groundwater deposits, plume delineation, geologic mapping and location of buried object.


A DIAGRAM SHOWING THE PRINCIPLE OF VLF METHOD

Basic Theory

The principle of VLF geophysical surveying is the study of the interaction of radio waves with electrically conductive geological structures. This interaction induces secondary electrical and magnetic fields which can be measured at the surface of the Earth. This, in turn enables the measurement of VLF waves and their interactions with Earth materials.

At large distances from the source of the radio wave, the electromagnetic field is essentially planar and horizontal. A conductor that strikes in the direction of the transmitter is cut by the magnetic vector and the induced eddy currents produce a secondary electromagnet field.

Field Procedure

The instrument is a radio receiver tuned to receive the particular transmitter selected; because a transmitter does not have to be provided, the instrument is lightand compact .


EM-16R an instrument use for VLF survey

Our VLF data was acquired using a VLF receiver which was aligned parallel to a distant transmitting station. This was accomplished by careful observation of the direction of lowest frequency. The direction in which the frequency is lowest will be the direction of our traverse. The VLF traverses used during the survey were tilted at an angle from our original traverse used for other method. Thus our VLF traverse each 140m long, ran from the north-eastern to the south-western part of our survey area as opposed to the north-south orientation of our original traverse. Our data was collected at a station interval of 10 m along the traverse. At every station, the VLF receiver will be moved up and down in the vertical plane until a point of lowest frequency is reached, at this point the quadrature and in phase values are derived.


A picture showing how the EM-VLF survey was carried out on the field

4.ELECTRICAL RESISTIVITY METHOD:Electrical resistivity method utilizes direct currents or low frequency alternating currents to investigate the electrical properties of the subsurface geology. Resistivity, which is the resistance per unit length of unit cross-sectional area of the material concerned, is the physical property that is to be measured in electrical resistivity method. In resistivity survey, artificially-generated electric currents are introduced into the ground through the means of electrodes and the resulting potential differences are measured at the surface. The resistivity survey is used in the study of horizontal and vertical discontinuities in the electrical properties of the ground and also in the detection of three dimensional bodies of anomalous electrical conductivity. It is routinely used in engineering and hydrogeological investigation.

Basic Theory

Rocks are mostly insulators; electrical conduction in rocks is electrolytic rather than electronic. Thus, resistivity of rocks depends on the porosity, fluid content and rock type.is Resistivity is one of the most variable of physical properties. The effective resistivity of a rock; that is, the resistivity of the rock and its pore water, is given by Archie (1942) empirical formula:


P = aØ-bf-cpw…………………………….4

WhereØ=-porosity

f=fraction of pores containing water

w=water resistivity

a,b and care empirical constants.

If we consider a single current electrode on the surface of a medium of uniform resistivity, p, as shown below,

the circuit is completed by current sink at a large distance from the electrode. At a distancerfrom the electrode the shell has a surface area of 2πr 2thus, the current density igiven by

i= I

2π r2 ………………………….6

The associated potential gradient with this current density is given by

∂ y∂ x

=−pi= −pI2 πr 2………….7

The potential Vrat distance r is thus

Vr = pI2πr…………………………8

the constant of integration is zero since Vr =0 when r =∞


The potential VCat an internal electrode C is the sum of the potential contributions VA and VBfrom the current source at A and the sink at B.

VC = VA + VB…………………………..9

VC = pL2π ( 1

R A−

1RB ) ……………….10

Similarly,

VD= pL2π ( 1

R A−

1RB )………………...11

The potential difference between electrodes C and D is


4.1Vertical Electrical Sounding (VES)

Vertical electrical sounding (VES) is one of the two main modes of electrode arrays, which study of horizontal or near-horizontal interfaces. The current and potential electrodes are maintained at the same relative spacing and the whole spread is progressively expanded about a fixed central point.

VES using four electrodes.

VES is based on the fact that the wider the current electrode separation the deeper the current penetration and the apparent resistivity values observed at large separations are governed by the resistivity of deeper layers The technique is extensively used in geotechnical surveys to determine overburden thickness and also in hydrogeology to define horizontal zones of porous strata.


Resistivity Survey Equipment and Field Procedure

The equipment consists of four reel cables, ABEMTerrameter, 12V Lead-Acid battery, minimum of four electrodes and hammer

EQUIPMENT USED FOR VES SURVEY

The survey was carried on 0NE traverse, with two soundings each on a traverse. Schlumberger configuration was applied. The potential electrodes M and N are kept fixed initially at 0.25m separation, and current electrodes A and B are moved outwards symmetrically in steps while the apparent resistivity are taken progressively starting from 1m. At some point, the potential voltage generally fell below the reading accuracy of the voltmeter in the Terrameter. Thus, the distance between the potential electrodes MN is increased to 0.5m. At this point; there was an overlap in the two readings with the current electrodes and the new as well as the old potential electrodes distance. The process


was carried out progressively until the distance of 125m was covered.

A Wenner VES survey


4.2. Constant Separation Traversing (CST ): Electrical profiling, which is also Constant Separation Traversing (CST), is electrical resistivity survey which to determine lateral variations of resistivity. It is a method offield procedure in electrical resistivity in which the current and potential electrodes are maintained at a fixed separation and progressively moved along a profile. Thus, its principle is electrical resistivity as introduced in chapter four. This method is employed in mineral prospecting to locate faults or shear zones and to detect localized bodies of anomalous conductivity. It is also used in geotechnical surveys to determine variations in bedrock depth and the presence of steep discontinuities.

FIELD PROCEDURE

Like Vertical Electrical Sounding, the equipment consists of four reel cables, ABEMTerrameter, 12V Lead-Acid battery, minimum of four electrodes and hammers.

A PICTURE SHOWING THE EQUIMENT USED IN CST SURVEY


Constant Separation Traversing uses a manual electrode array, usually the Wenner configuration for ease of operation, in which the electrode separation is kept fixed. The entire array is moved along a profile and values of apparent resistivity determined at discrete intervals along the profile. In this report, the data was acquired for 2.5m, 5m, 10m, 15m and 20m spacing along traverse.

5.ELECTROMAGNETIC METHOD:Electromagnetic (EM) surveying methods make use of the response of the ground to the propagation of electromagnetic field. This response varies according to the conductivity of the ground. In electromagnetic method, a primary EM field is generated using an alternating current in a loop wire (coil) or a natural EM source; the response of the ground to this primary field is the generation of a secondary EM field.

A diagram showing a general principle of electromagnetic surveying

The resultant field is detected by the alternating currents that they induce in a receiver coil. Thus, electromagnetic method is a geophysical technique based on the physical principles of inducing and detecting electrical current flow within geologic


strata. In the electromagnetic method, currents are induced in the subsurface by the application of time-varying magnetic field. The electromagnetic method measures the bulk conductivity (inverse of resistivity) of subsurface material beneath the transmitter and receiver coils. Electromagnetic readings are commonly expressed in conductivity units of millimhos/meter or milliseimens/meter (1 millimho = 1 milliseimen). A “mho” is the reciprocal of an ohm.Electromagnetic method can be used to locate buried pipes, utility lines, cables, buried steel drums, trenches, buried waste, and concentrated contaminant plumes. In exploration of metallic ferrous deposits, engineering/construction site investigation, archaeological investigations and sedimentary thickness in fossil fuel search. The method can also be used to map shallow geologic features such as lithologic changes, clay layers, and fault zones.

Basic Theory Electromagnetic (EM) survey makes use of the response of the ground to the propagation of electromagnetic fields which are composed of an alternating electric intensity and magnetizing force. Primary electromagnetic fields may be generated by passing alternating current through a small coil made up of many turns or through a large loop of wire. The response of the ground is the generation of secondary electromagnetic field and the resultant field may be detected by the alternating currents that they induce to flow in a receiver coil by the process of electromagnetic induction. In general a transmitter coil is used to generate a primary EM field which propagates above and below the ground. When the EM radiation travels the subsurface media, it is modified slightly relative to that which travels through the air. The transmitter induces an electrical current into the subsurface, which produces secondary fields. These secondary fields are sensed and recorded by the receiver coil.

Field Instrument and Procedure


The electromagnetic instrument used during the survey consists of a transmitter coil(fig a)which generates the primary field and

receiver coil(fig b)

Fig(a) transmitter coil and a battery fig(b) receiver coil and a battery

Our traverse are establish normal to geologic strike and the coils were linked by a cable which carries a reference signal and also allows the coil separation to be accurately maintained at 10m, 20m and 40m intervals and move along the traverse. The transmitter coil, receiver coil is also connected to EM-34 that takes the readings. A primary field is null so that the field can be accurately measured. Both the vertical dipole (VD) and horizontal dipole (HD) readings were taken for 10m, 20m and 40m spacing.

6.SELF-POTENTIAL(SP ) :This is the measurement of natural electrical potential caused by electrochemical reaction of buried conductors (rocks) with differences in soil moisture chemistry,


by seeping water, and by other causes. Thus, it is caused by electrochemical action between minerals and groundwater solutions. When this action occurs in the oxidizing zone above the water table, current is generated. An ore body containing metallic minerals, acting as a conductor, carries the current downward towards the reducing zone below the water table. The overall effect is to create a negative potential in the rocks around the ore body as the electrons move downward. Pyrite (iron sulfide) oxidizes readily to hematite (iron oxide) in the groundwater environment. Therefore, ore deposits containing pyrite develop very strong negative self-potentials. Other minerals which are known to generate strong negative potentials arepyrrhotite and magnetite. Lead and zinc sulfides do not develop strong self-potential fields.

BASIC THEORY

Studies show that for a self-potential anomaly to occur its causative body must lie partially in a zone of oxidation. According to Sato & Mooney 1960, the causative body must straddle the water table.

Below the water table electrolytes in the pore fluids undergo oxidation and release electrons which are conducted upwards


through the ore body. At the top of the body the released electrons cause reduction of the electrolytes. A circuit thus exists in which current is carried electrolytically in the pore fluids and electronically in the body so that the top of the body acts as a negative terminal. This explains the negative SP anomalies that are invariably observed and, also their stability as the ore body itself undergoes no chemical reactions and merely serves to transport electrons from depth. As a result of the subsurface currents, potential differences are produced at the surface.

FIELD PROCEDURE

The equipment consists of a pair of non-porous electrode, a high-impedance millivolt meter, pegs, hammer and long connecting wires, which is just 80m in length.

Diagram showing aschematic of the procedure used to collect SP data.

Two field layouts were used, and they are: fixed electrode and constant spacing.For fixed electrode, an a non- polarizing electrode was dipped into the first station of a 140m traverse and connected to a AKILLO OLANIYI MOSHOOD 110813006 Page28

voltmeter and kept fixed while the other electrode was moved from the second to the third and so on. For constant spacing, in this layout they were moved at the same time at constant spacing.

A picture showing how the survey was carried out and showing the

instrument used.

7.SEISMIC REFRACTION: The seismic refraction surveying method uses seismic energy that returns to the surface after traveling through the ground along the refracted ray paths. The first arrivals of the seismic energy at a detector offset from a seismic source always represent either a direct or refracted ray. This fact allows simple seismic surveys to be performed in which attention is concentrated solely on the first arrivals (or onset) of seismic energy and time distance plots of these first arrivals are interpreted to derive information on the depth to refracting surface.


Exploration using refraction method covers a very wide range of application which includes engineering and environmental survey, hydrological surveys and crustal seismology.

Basic Theory

In seismic refraction surveying, seismic waves are generated by a controlled source (hammer and blow) and propagated through the subsurface. These waves are refracted at geological boundaries within the subsurface. Geophones distributed along the surface detect the ground motion caused by these returning waves and hence measure the arrival times of the waves at different ranges from the source. The geometry of the various refracted waves relative to the incident waves can be described using shell’s law of refraction. For any ray at the point of incidence upon an interface, the ratio of the sine of the angle of incidence to the velocity of propagation within that medium remains a constant which is known as the ray path parameter. In refraction seismology, for a simple horizontal refractor, as in diagram below


Shown above is a horizontal refraction separating two beds of

velocities and where, > and the refracting interface is at depth ( ). For a geophone at D, the path of refracted wave is SABD. The travel time ( ) can be written as

; Recall that

Therefore

Where

Solving for the depth of reflector ( );

Thus, by analysis of the travel-time curves of direct and refracted

arrival and could be derived (the reciprocal of the gradient)

and from theintercept ( ) the refractor depth could be determined.

METHODOLOGY


Survey was designed to identify anomalies in the subsurface. The traverse; 140m long were mapped. Equipment such as; a seismic source (used to send seismic waves into the ground, Consists of various types but a sledgehammer was used on this occasion), a metal base plate (this plate is hit by the sledgehammer instead of hitting the ground directly), seismometer (an electromechanical transducer plugged into the ground to convert ground motion caused by the propagated seismic waves into electric signals), seismograph (for recording electric signals sent from the seismometers/geophones), geophone cables (to connect the geophones to the seismograph), battery (to power the seismograph), a sensor (taped to the sledgehammer so that the time of delivery can be sensed and controlled by the seismograph), a connecting cable (to connect the sensor on the sledgehammer to the seismograph). A 24 geophone layout was used and the geophone layout was moved four times on a traverse. The methodology of seismic refraction analysis consists of three parts; instrumentation set up measurement and data interpretation.

SET UP MEASUREMENT

The layout of the seismic refraction set up is schematically shown with the figure below. The 24 geophones were placed along the traverse and the seismograph was set to connect the 12th and the 13th geophones. The spread line employed was 48m based on 2m geophone spacing so a traverse was mapped four times.


Figure: Typical setup of seismic refraction

The sledgehammer was also connected the seismograph and was moved to strategic shot points during survey. The numbers in the diagram represent the several shot points of the impact sledgehammer.

DATA PROCESSING

The data processing technique of seismic refraction method is explained systematically in the diagram below. The analogue electrical signals transferred to the seismograph by the geophones are reconverted into digital data. This data is what is printed out of the seismograph for processing. The important information needed is the arrival time of the various waves to the various geophones. The arrival times are plotted against their corresponding geophone positions. From theses graphs, the velocities of the mapped layers and their thicknesses can be delineated. These parameters are then interpreted for the desired result. The seismic section of the survey area was also drawn.

8. TIME DOMAIN ELECTROMAGNETIC: in TDEM systems, an alternative approach to detecting weak secondary magnetic fields. This works by simply switching the primary field off and observing the decay of the secondary magnetic fields. This method is often referred to as transient electromagnetic exploration (TEM) or time domain electromagnetic (TDEM) exploration. By the transient


electromagnetic method, TEM, the electrical resistivity of the underground layers down to a depth of several hundred meters can be measured. Ground based measurements as well as airborne surveys (SkyTEM) to cover large areas are possible. The method was originally designed for mineral investigations. Over the last two decades the TEM method has become increasingly popular for hydrogeological purposes as well as general geological mapping. The electromagnetic geophysical methods are all based upon the fact that a magnetic field varies in time – the primary field – and thus, according to the Maxwell equations, induces an electrical current in the surroundings – e.g. the ground which is a conductor. The associated electrical and magnetic fields are called the secondary fields.

fig A.B (A)the form of an eddy current immediately after turn off of the primary field and (B) downward and outward preparation of the eddy current filament at

successive interval of time.

Measuring technique

The TEM method applies an ungrounded loop as transmitter coil. The current in the coil is abruptly turned off, and the rate of change of the secondary field due to the induced eddy currents in the ground is measured in the receiver coil, usually an induction coil. The primary field is therefore absent while measuring.


summarizes the basic nomenclature and principles. Typical measuring parameters for a groundbased system are: 1 – 20ms on-time, 1 – 30 μs turn-off ramp and 1 – 20 ms off-time for measuring. The depicted waveform is often referred to as a square waveform. Other waveforms with sine or triangular shapes are used, but mainly in airborne systems.

Basic nomenclature and principles of the TEM method. (a) Shows the current in the transmitter loop. (b) Is the induced electromotive force in the ground, and (c) is the secondary magnetic field measured in the receiver coil. For the graphs of the induced electromotive force and the secondary magnetic field, it is assumed, that the receiver coil is located in the centre of the transmitter loop.

The datasets are recorded in decay-time windows, often called gates. The gates are arranged with a logarithmically increasing width to improve the signal/noise (S/N) ratio especially at late-times. This recording principle is called log-gating and 8–10 gates per decade in decay time are commonly used.

Field procedures


When performing fieldwork, a transient electromagnetic sounding can be conducted by placing a wire in a square loop on the ground as the transmitter coil, Tx-coil. When investigating the upper 150 m of the ground, a square loop Field proceduresWhen performing fieldwork, a transient electromagnetic sounding can be conducted by placing a wire in a square loop on the ground as the transmitter coil, Tx-coil. When investigating the upper 150 m of the ground, a square loop


3.0 CHAPTER THREE

DATA PROCESSING AND DATA INTERPRETATION

1.Gravity method

The gravity data were acquired and recorded. The data is then duly corrected. The data is taken through the following processing steps. The latitude measured is used to correct for the latitude correction with the IGF formula (9.7803815(1+0.00527885sin^2λ-0.000023462sin^4 λ)). The survey was a localized survey so there was no need for latitude correction because the survey area was not regional. The elevation readings can be used to make the bouguer corrections, free-air corrections and terrain corrections. Terrain correction was not needed for our data because our survey area was fairly smooth. The bouguer correction was made with (0.4191hρgu), where h=elevation and ρ=density. We assumed the average density of crustal rocks to calculate the bouguer correction. The free-air correction was also calculated with (3.086h gu), where h=elevation. The drift curve was plotted and the gravity data was also plotted against time. The gravity data graph was removed from the drift curve so as to get the drift correction for each recording time. After all the necessary corrections had been made, they were either added or subtracted from the gravity data. The base station readings were then subtracted from the duly corrected gravity data to give us the bouguer anomaly. The bouguer anomaly was plotted against station position to give the bouguer anomaly graph. The general or obvious trend reflecting a long wavelength gravity anomaly on the graph was traced out. That was chosen as the regional anomaly. The one left behind is noticed to be the short wavelength anomaly. This is the residual


anomaly and is the needed result for interpretation. A gravity residual map was also plotted.

Data Sheet Showing Gravity Data Measurement

Traverse six at 5m station spacing

Station time (H:m)

lat. Cor. Average(mGAL)

drift FAC(mgal)

BC(mGal)

FAA(Mgal)

BA(Mgal)

ResidualMgal

BS 15.63 9781149TR6 0 15.96 9781149 2574.284 2.51124 102.4552 373.74 2670.076 3043.816 0TR6 5 16.15 9781149 2574.881 4.68 102.1466 371.54 2670.056 3041.566 2.25BS 16.38 9781149 2575.328 5.00616 102.7638 370.39 2670.195 3040.585 3.231TR6 15 16.8 9781149 2575.857 6.0894 102.7638 372.62 2671.341 3043.961 0.145TR6 20 8.58 9781149 2576.862 8.41296 102.7638 372.62 2672.346 3044.966 1TR6 25 8.98 9781149 2577.865 10.65084 103.381 374.86 2673.963 3048.823 5.007TR6 30 9.2 9781149 2578.597 12.31752 103.0724 373.74 2673.698 3049.558 5.742BS 9.43 9781149 2578.973 13.2988 102.4552 371.51 2674.765 3048.50

54.6894

TR6 35 9.65 9781149 2579.385 14.3473 103.381 374.86 2674.56 3046.07 2.254TR6 40 9.86 9781149 2579.851 15.402 102.7638 372.62 2675.952 3050.812 6.996TR6 45 10.16 9781149 2580.398 16.4648 103.381 374.86 2676.316 3048.936 5.12TR6 50 10.42 9781149 2581.3 18.972 103.982 377.1 2676.784 3049.404 5.588TR6 55 10.57 9781149 2582.101 20.899 103.982 377.1 2678.202 3053.062 9.246TR6 60 10.73 9781149 2582.608 22.1707 103.381 374.86 2679.326 3056.426 12.61TR6 65 10.95 9781149 2582.113 23.3682 103.381 374.86 2679.831 3056.931 13.115TR6 70 11.13 9781149 2633.941 32.9072 103.0724 373.74 2731.014 3105.874 62.058BS 11.35 9781149 2634.843 35.5164 102.4552 371.74 2731.367 3106.22

762.411

TR6 75 11.06 9781149 2635.266 36.5588 103.381 374.86 2731.696 2769.556 274.26TR6 80 11.78 9781149 2635.595 37.44624 103.381 374.86 2731.769 3105.509 61.693TR6 85 11.97 9781149 2636.48 38.4316 102.4552 374.86 2731.276 3102.786 58.97TR6 90 12.15 9781149 2636.101 39.3026 103.381 375.98 2733.582 3108.442 64.626TR6 95 12.37 9781149 2637.481 40.2043 103.381 378.22 2733.962 3108.822 65.006TR6 100 12.53 9781149 2637.861 42.017 103.381 374.86 2734.323 3109.183 65.367BS 12.72 9781149 2638.222 43.0419 103.6896 377.1 2734.989 3110.96

967.153

TR6 105 12.92 9781149 2638.58 44.0681 104.3068 374.86 2734.954 3111.101 67.285

Table 1.0

The Bouguer Anomaly is plotted against the Stations using Microsoft Excel Software, this produced the Bouguer Anomaly Profile as shown below


A graph showing the relationship between bouguer anomaly and station (m)

0 20 40 60 80 100 120 1400

50

100

150

200

250

300

STATION(m)

boug

uer a

nom

aly(M

gal)

Graph 1.0

Direct InterpretationFor this report, direct method of interpretation was used and different shapes were assumed for the subsurface anomaly from each of the residual gravity anomaly as follows:Traverse six (6) Spherical Body

Limiting Depth Limiting depth is the maximum depth at which the top of a body could lie and still produce an observed gravity anomaly. Using the half-width

method, the half-width x 12and gravity anomaly amplitude Amaxwere recorded

as follows:

For Traverse One, Sphere;

x 12= 4m Assumed density= 2.64g/cm3 Amax = 275mgal

z = 1.305x 12


z = 1.305 x 4m

Therefore z = 5.22m (Depth of anomaly)

Amax = 4 πGr 3

3 z2

275 = 2(0.042)(2.64)r3

3¿¿

Therefore r = 46.63m (Radius of the anomaly)

Excess Mass Excess mass is the difference in mass between the body and the mass of country rock that

would otherwise fill the space occupied by the body.

For Traverse One, Sphere;

Total mass M = 255Amax ¿)

= 255(275) 4

= 280,500 tonnes

Assumed density = 2.64g/cm3 r=46.63m (Radius of the anomaly0

Mass of the anomaly = density x volume

= (2.64)(4 π3

¿(46.63)3

= 112,122 tonnes

Discussion and Conclusion


From the residual Bouguer anomaly of the traverse six, traverse six reflect a simple dual symmetrical anomaly between 80m - 90m which suggest a spherical highly denser mass sandwich by the higher amplitude . The radius of each of the spherical body was estimated to be 46.63m, with the rock locate at about 5.22m deep, the mass was estimated to be 280,500tonnesfor an assumed density of 2.64g/cm3

Data Sheet Showing Magnetic Data MeasurementThe data were acquired and recorded with their corresponding time. The magnetometer gave us 4 readings. The average of these readings was calculated and recorded. The drift of the magnetic data was calculated with the following formula; Drift = ((Bend-Bstart) / (tend-tstart))*(tstation-tstart). The drift was calculated for all the acquired data. The resulting drift was subtracted from the average readings at each station to get the Bcor (drift corrected reading at station position. The Bcor was plotted against station position. From the resulting graph, a trend reflecting a long wavelength of magnetic anomaly (regional) was traced out and the short wavelength anomaly (residual) was removed. The residual anomaly is what we need to interpret magnetic properties of features in the shallow depth. A map of the residual anomaly was also plotted.

MAGNETIC DATA AND INTERPRETATIONMAGNETIC DATA (2.5m)

S/NAverage reading

Time(sec) Drift Anomaly Residual

BS 22409.43 36720 0 22409.433 6769.03462


0 23481.73 36900 220.211538 23261.522 7621.12308

2.5 23889.57 36960 293.615385 23595.951 7955.55256

5 22136.03 37020 367.019231 21769.014 6128.61538

7.5 19049.2 37080 440.423077 18608.777 2968.37821

10 19952.2 37080 440.423077 19511.777 3871.37821

12.5 19487.77 37140 513.826923 18973.94 3333.54103

15 27084.43 37200 587.230769 26497.203 10856.8038

17.5 22394.13 37260 660.634615 21733.499 6093.1

20 16301.03 37260 660.634615 15640.399 0

22.5 21949.8 37320 734.038462 21215.762 5575.36282

25 20598.07 37380 807.442308 19790.624 4150.22564

27.5 22170.7 37380 807.442308 21363.258 5722.85897

30 23394.57 37440 880.846154 22513.721 6873.32179

32.5 20361.1 37500 954.25 19406.85 3766.45128

35 22145.9 37560 1027.65385 21118.246 5477.84744

BS 25784.27 37680 1174.46154 24609.805 8969.40641

37.5 24811.33 37740 1247.86538 23563.468 7923.06923

40 19126.2 37800 1321.26923 17804.931 2164.53205

42.5 19920.5 37920 1468.07692 18452.423 2812.02436

45 19205.8 37980 1541.48077 17664.319 2023.92051

47.5 19640.03 37980 1541.48077 18098.553 2458.15385

50 23404.23 38040 1614.88462 21789.349 6148.95

52.5 21443.47 38040 1614.88462 19828.582 4188.18333

55 20796.33 38100 1688.28846 19108.045 3467.64615

57.5 22892.03 38160 1761.69231 21130.341 5489.94231

60 22923.6 38160 1761.69231 21161.908 5521.50897

62.5 25228.5 38220 1835.09615 23393.404 7753.00513

65 25440.67 38280 1908.5 23532.167 7891.76795

67.5 21437.93 38340 1981.90385 19456.029 3815.63077

70 20971.53 38400 2055.30769 18916.226 3275.82692

72.5 20255.6 38400 2055.30769 18200.292 2559.89359

75 27390.57 38460 2128.71154 25261.855 9621.45641

77.5 21288.13 38520 2202.11538 19086.018 3445.61923

80 21753.97 38520 2202.11538 19551.851 3911.45256

BS 20752.63 38580 2275.51923 18477.114 2836.71538

82.5 23042.37 38640 2348.92308 20693.444 5053.04487


85 22430.4 38700 2422.32692 20008.073 4367.67436

87.5 22594.33 38760 2495.73077 20098.603 4458.20385

90 21979.93 38760 2495.73077 19484.203 3843.80385

92.5 19415.03 38820 2569.13462 16845.899 1205.5

95 21312.87 38880 2642.53846 18670.328 3029.92949

97.5 22019.1 38880 2642.53846 19376.562 3736.16282

100 24423.63 38940 2715.94231 21707.691 6067.29231

102.5 21283.2 39000 2789.34615 18493.854 2853.45513

105 20306.63 39000 2789.34615 17517.287 1876.88846

107.5 26783.43 39060 2862.75 23920.683 8280.28462

110 22800.87 39120 2936.15385 19864.713 4224.3141

112.5 22598.07 39120 2936.15385 19661.913 4021.5141

115 22369.53 39180 3009.55769 19359.976 3719.57692

117.5 23465.1 39240 3082.96154 20382.138 4741.73974

120 23714.33 39240 3082.96154 20631.372 4990.97308

122.5 21244.47 39330 3193.06731 18051.399 2411.00064

125 22306.93 39360 3229.76923 19077.164 3436.76538

127.5 20914.73 39360 3229.76923 17684.964 2044.56538

130 30559.87 39420 3303.17308 27256.694 11616.2949

BS 25054.77 39480 3376.57692 21678.19 6037.79103

132.5 22559.93 39600 3523.38462 19036.549 3396.15

135 22296.23 39600 3523.38462 18772.849 3132.45

137.5 24071 39660 3596.78846 20474.212 4833.81282

140 33795.5 39720 3670.19231 30125.308 14484.909

BS 22700.93 39840 3817 18883.933 3243.53462Table 1.1

MAGNETIC DATA (2.5m)


0 20 40 60 80 100 120 140 1600

5000

10000

15000

20000

25000

30000

35000

STATION(m)

MAG

NETIC

ANO

MAL

Y (n

T)

Graph 1.1 showing relationship between magnetic anomaly (nT) and station (m)

MAGNETIC DATA (5m)

S/NAverage reading(nT) Time(sec) Drift Anomaly Residual

BS 24329.5 31920 0 24329.5 5623.260 28250.13333 32040 -136.5022 28386.6355 9680.395555 23164.66667 32100 -204.7533 23369.42 4663.1810 25638.93333 32160 -273.00444 25911.93778 7205.69777815 25118.76667 32220 -341.25556 25460.02222 6753.78222220 30051.9 32280 -409.50667 30461.40667 11755.1666725 24129.8 32340 -477.75778 24607.55778 5901.31777830 23422.86667 32340 -477.75778 23900.62444 5194.38444435 30119.36667 32400 -546.00889 30665.37556 11959.1355640 23462.13333 32400 -546.00889 24008.14222 5301.90222245 23791.6 32400 -546.00889 24337.60889 5631.36888950 23891.53333 32460 -614.26 24505.79333 5799.55333355 22094.3 32520 -682.51111 22776.81111 4070.57111160 23365.13333 32580 -750.76222 24115.89556 5409.65555665 26194.03333 32640 -819.01333 27013.04667 8306.806667


70 21163.53333 32700 -887.26444 22050.79778 3344.55777875 22315.06667 32760 -955.51556 23270.58222 4564.34222280 23417.13333 32760 -955.51556 24372.64889 5666.408889BS 25353.26667 32820 -1023.7667 26377.03333 7670.79333385 22527.3 32940 -1160.2689 23687.56889 4981.32888990 22390.36667 32940 -1160.2689 23550.63556 4844.39555695 21359.93333 33000 -1228.52 22588.45333 3882.213333100 24823.6 33060 -1296.7711 26120.37111 7414.131111105 33994.86667 33060 -1296.7711 35291.63778 16585.39778110 41935.6 33120 -1365.0222 43300.62222 24594.38222115 17272.96667 33180 -1433.2733 18706.24 0120 17294.63333 33240 -1501.5244 18796.15778 89.91777778125 30446.56667 33240 -1501.5244 31948.09111 13241.85111130 25333.2 33300 -1569.7756 26902.97556 8196.735556135 33509.53333 33300 -1569.7756 35079.30889 16373.06889140 26448.2 33360 -1638.0267 28086.22667 9379.986667

Table 1.2

MAGNETIC DATA (5m)

0 20 40 60 80 100 120 140 1600

5000

10000

15000

20000

25000

30000

STATION(m)

MA

GN

ETIC

AN

OM

ALY

(n

T)


MAGNETIC DATA (10m)


S/NAverage reading(nT)

Time(sec) Drift Anomaly Residual

BS 21598.86667 35520 0 21598.8667 3511.638095

0 20021 35640 -470.885714 20491.8857 2404.657143

10 48945.46667 35700 -706.328571 49651.7952 31564.56667

20 17380.9 35700 -706.328571 18087.2286 0

30 18571.36667 35760 -941.771429 19513.1381 1425.909524

40 24305.5 35820 -1177.21429 25482.7143 7395.485714

50 23637 35880 -1412.65714 25049.6571 6962.428571

60 22318.1 35940 -1648.1 23966.2 5878.971429

70 22450.33333 36000 -1883.54286 24333.8762 6246.647619

80 23072.03333 36060 -2118.98571 25191.019 7103.790476

90 23081.9 36060 -2118.98571 25200.8857 7113.657143

100 27383.5 36120 -2354.42857 29737.9286 11650.7

110 21921.36667 36180 -2589.87143 24511.2381 6424.009524

120 24368.9 36240 -2825.31429 27194.2143 9106.985714

130 21413.76667 36240 -2825.31429 24239.081 6151.852381

140 23240.03333 36300 -3060.75714 26300.7905 8213.561905

BS 24895.06667 36360 -3296.2 28191.2667 10104.0381Table 1.3

MAGNETIC DATA (10m)


0 20 40 60 80 100 120 140 1600

5000

10000

15000

20000

25000

30000

35000

AB/2(m)

Magnetic anomaly (nT)


Quantitative interpretation

In this report, only the fairly symmetric anomaly was considered from traverse six as shown below.At 5m spacing: Amax = 24594.38nT width (w) = 5m

Depth estimate (z) = w2 = 5

2

Therefore z= 2.5mAt 10m spacing: Amax = 31564.57nT width (w) =7m

Depth estimate (z) = w2 =7

2

Therefore z= 3.5m

Qualitative interpretation


The magnetic anomaly of traverse six (5m spacing) produce signature within station range 105-115m and also at 10m spacing at which the signature was pronounce range 4-18m;they are symmetrical which suggest a uniform shape, say sphere, since the survey line was along the East-West direction. This concurs with the similar signature range in residual gravity anomaly. The depths of the anomaly was estimated to be about 2.5m-3.5m respectively, which is a little shallower than that of gravity. The remaining magnetic anomaly are much more noise.

Data Sheet Showing VLF Data MeasurementThe measured in-phase and quadrature is presented in the table below.


Table 1.4

These data were processed by first plotting the In-phase and the Quadrature component against the stations for each of the traverse. Secondly, the data were processed using the KHFFILT program software to obtain the refined VLF data, Fraser filtering and the K-H contourVLF PROFILE SHOWING THE RELATIONSHIP BETWEEN IN-PHASE/QUADRATURE % WITH STATION (m)


TRAVERSE 6S/N Station In-Phase % Quadrature %

1 0 -25 -242 5 -35 63 10 -21 -84 15 -30 -65 20 -43 226 25 -37 267 30 -29 168 35 88 309 40 60 -1010 45 -37 -1011 50 -27 2012 55 -25 2813 60 -15 3014 65 -30 1015 70 -34 1016 75 -25 -2017 80 -23 1418 85 -17 -1119 90 -15 -1420 95 -16 -621 100 -24 -1822 105 -22 -1623 110 -59 1824 115 -21 2025 120 -17 1226 125 -29 2027 130 -37 1428 135 -34 1829 140 -33 18

0 20 40 60 80 100 120 140 160

-80

-60

-40

-20

0

20

40

60

80

100

In-PhaseQuad-rature

STATION(m)

IN-P

HASE

/QUA

DRAT

URE %

Graph 1.4

A picture showing VLF measurement response


.

Qualitative interpretationIn the plot of in-phase/quadrature component against stations for traverse six, there is a distinct envelope between 20m – 40m. This suggests the presence of a highly conductive body which is likely to be a weathered basement.The Fraser filtering for this traverse shows similar signature at this range. The VLF response plot at this range reflects a negative signature between 20m – 40m which suggests the presence of a conductive anomalous body. The K-H contour shows this anomalous high negative


component at 30m- 45m and also shows the depth of the conductive body at the range of 5m -19m .

Data Sheet Showing Electrical Resistivity Data Measurement.The field data of Traverse6 (VES1,VES2,VES3, VES4,VES5) are shown in the table below

VES1 VES2 VES3 VES4 VES5

ab/2 (m) mn/2 (m) Geometric Factor

Resistivity(ρ) Resistivity (ρ)

Resistivity (ρ)

Resistivity (ρ)

Resistivity (ρ)

1 0.25 5.89 547.181 125.457 258.571 141.36 307.458

2 0.25 24.74 235.03 66.798 306.776 111.33 304.302

3 0.25 56.156 202.1616 61.7716 308.858 101.0808 280.78

4 0.25 100.138 190.2622 74.112133 300.414 100.138 260.3588

6 0.25 225.802 190.938171 98.110969 293.5426 114.0525 202.7476

6 0.5 112.312 190.9304 105.83159 314.4736 112.312 235.8552

9 0.5 253.684 182.855427 117.78548 329.7892 128.6938 173.6213

12 0.5 451.604 160.409740 120.62342 312.14868 141.3068 157.0678

15 0.5 706.073 124.410062 106.26398 294.29122 158.4427 156.4657

15 1 351.858 142.432118 103.79811 270.08620 161.8194 155.4508

20 1 626.748 92.3199804 97.271289 271.88328 178.7485 131.9931

25 1 980.177 87.5298061 93.018797 240.43741 204.4649 129.2853

32 1 1606.925 80.667635 102.68250 217.57764 204.4008 152.8185

40 1 2511.703 80.8768366 96.700565 210.22954 211.9877 85.14673

40 2.5 1001.383 91.4262679 59.081597 255.05225 171.5369 99.63760

50 2.5 1566.869 98.5560601 103.09998 226.88263 191.9414 144.1519

65 2.5 2650.719 109.739766 131.47566 254.46902 200.6594 174.4173

80 2.5 4017.312 12453.6672 152.65785 311.74341 252.6889 228.9867

100 2.5 6279.258 167.656188 209.72721 403.12836 1812.1938 277.5432

100 5 3133.739 202.126165 404.5657 295.51158 315.56751 370.7213

Table 1.5

The apparent resistivity of each VES is plotted against its electrode spacings (AB/2) ona tracing paper using a log-log graph sheet underneath. Manual interpretation is thus done by using of master and auxiliary curves to model the subsurface layers from the plot. The data alongside the resistivities and thickness of the manually-modelled layers were further processed by computer iteration technique with the aid of geophysical interpretation


software called WinResist. The result of the computer iterated technique which was guided by the manual interpreted result is presented below

VES1

VES2


VES3

VES4


VES 5

The obtained VES curves above indicate the number of layers being probed at the point of sounding. The result presented below shows the resistivity of value of the layers, thickness, depth of the overburden layers and their inference lithology

STATION 1

LAYER RESISTIVITY VALUE (Ωm)

THICKNESS(m) DEPTH(m) LITHOLOGY

1 950.5 0.7 0.7 Top soil

2 54.1 0.6 1.3 Sandsoil

3 578.7 1.8 3.1 Weathered Basement

4 41.4 9.5 12.6 Saturated weathered layer

5 9248.3 ----- -----

STATION 2AKILLO OLANIYI MOSHOOD 110813006 Page55

LAYER RESISTIVITY VALUE(Ωm)


1 124.0 0.5 0.5 Top soil

2 27.6 0.8 1.3 Sand (wet/moist)


4 35.7 13.1 19.9 Fresh Basement

5 1557.0 ----- ------

STATION 3



1 107.8 0.7 0.7 Top soil

2 92.8 2.6 3.3 Sandy soil


4 1663.7 ----- ----- Fresh Basement

STATION 4




1 153.3 0.8 0.8 Top soil

2 79.9 2.4 3.2 Sandy soil


4 332.7 ----- ----- Fresh Basement

STATION 5



1 368.7 1.2 1.2 Top soil

2 217.9 4.6 5.7 Sand Soil


4 2877.6 ----- ----- Fresh Basement

Data Sheet Showing SP Data Measurement .


The table below shows the measured potential difference and the stations midpoints for each traverse and fixed spacing length.

TRAVERSE6 fixed spacing

SP SP SP SP Spacing: 5m Spacing 10m Spacing 15m Spacing 20m

Station SP(mV) Station SP(mV) Station SP(mV) Station SP(mV)0 - 5 -3.8 0 - 10 -4.8 0 - 15 -1 0 - 20 -25 - 10 1 5 - 15 -5.1 5 - 20 2.1 5 - 25 -5.110 - 15 2.1 10 - 20 -7.3 10 - 25 0.2 10 - 30 -11.515 - 20 1.6 15 - 25 0.3 15 - 30 -5.5 15 - 35 -3.620 - 25 -0.2 20 - 30 -12.8 20 - 35 5.9 20 - 40 6.525 - 30 -10.2 25 - 35 5.4 25 - 40 7.2 25 - 45 10.230 - 35 18.3 30 - 40 14.4 30 - 45 16.9 30 - 50 17.935 - 40 13.8 35 - 45 4.4 35 - 50 8.2 35 - 55 7.540 - 45 0.38 40 - 50 1.8 40 - 55 0.8 40 - 60 0.645 - 50 2.1 45 - 55 -2 45 - 60 1.3 45 - 65 -2.850 - 55 -2.7 50 - 60 -1.9 50 - 65 -2.8 50 - 70 -2455 - 60 3.2 55 - 65 -6.4 55 - 70 -19.4 55 - 75 -11.860 - 65 -10.4 60 - 70 -24.3 60 - 75 -12.4 60 - 80 -16.665 - 70 -21.7 65 - 75 -8.4 65 - 80 -6.9 65 - 85 -6.870 - 75 10.5 70 - 80 0.5 70 - 85 11.3 70 - 90 -1.675 - 80 -8.3 75 - 85 -3 75 - 90 -10.5 75 - 95 -9.580 - 85 -0.6 80 - 90 3.6 80 - 95 -11.9 80 - 100 -32.785 - 90 -6.6 85 - 95 -5.1 85 - 100 -2.3 85 - 105 -15.390 - 95 -9.2 90 - 100 11.2 90 - 105 -8.9 90 - 110 -24.495 - 100 12.2 95 - 105 -5.3 95 - 110 -28.9 95 - 115 -18100 - 105 -19.6 100 - 110 -45.8 100 - 115 -32.9 100 - 120 -24.8105 - 110 -23.7 105 - 115 -16.7 105 - 120 1.5 105 - 125 -11.5110 - 115 -4.6 110 - 120 26.4 110 - 125 -28.3 110 - 130 3.7115 - 120 23.3 115 - 125 -0.8 115 - 130 -21.6 115 - 135 24.5120 - 125 -65.2 120 - 130 -40.1 120 - 135 -12.7 120 - 140 25.4125 - 130 16.7 125 - 135 50.1 125 - 140 -4.5130 - 135 22.9 130 - 140 61.7135 - 140 20.7

Table 1.6


Using Microsoft Excel software, the SP Anomaly (measured potential difference) is plotted against the Station Midpoints for each traverse; this gives the SP profile below:Fixed spacing 5m

0 5 10 15 20 25 30

-70

-60

-50

-40

-30

-20

-10

0

10

20

30 AN SP LINE PROFILE

Station(m)

Pote

ntial

Diff

eren

ce (m

V)

Graph 1.5

FIXED SPACING 10m

0 5 10 15 20 25 30

-60

-40

-20

0

20

40

60

80

AN SP LINE PROFILE

station(m)

Pote

ntial

Diff

eren

ce (m

V)


Graph 1.6

FIXED SPACING 15m

0 5 10 15 20 25 30

-40

-30

-20

-10

0

10

20AN SP LINE PROFILE

Station (m)

Axi

s P

oten

tial

Diff

eren

ce (m

V)

Q

Graph 1.7

FIXED SPACING 20m

0 5 10 15 20 25 30

-40

-30

-20

-10

0

10

20

30AN SP LINE PROFILE

Station m

Po

ten

tial

Diff

ere

nce

(m

V)

Graph 1.8


FIXED ELECTRODE

The table below shows the measured potential difference and the stations midpoints for each traverse and fixed electrode spacing length.


FIXED ELECTRODE 20M SPACING


SP fixed electrode 5m spacing

Station S/N Potential Difference (mV)0 - 5 1 1.50 - 10 2 3.50 - 15 3 4.10 - 20 4 4.70 - 25 5 0.80 - 30 6 1.40 - 35 7 0.30 - 40 8 00 - 45 9 0.20 - 50 10 -0.10 - 55 11 0.30 - 60 12 0.10 - 65 13 00 - 70 14 0.10 - 75 15 0.10 - 80 16 00 - 85 17 1.80 - 90 18 0.10 - 95 19 0

0 - 100 20 0.10 - 105 21 0.10 - 110 22 4.80 - 115 23 9.20 - 120 24 00 - 125 25 0.10 - 130 26 2.30 - 135 27 3.40 - 140 28 2.1

Using Microsoft Excel software, the SP Anomaly (measured potential difference) is plotted against the Station Midpoints for the traverse; this gives the SP profile below:


0 5 10 15 20 25 30

-2

0

2

4

6

8

10

AN SP LINE PROFILE

STATION(m)

Pote

ntial

Diff

eren

ce (m

V)

Graph 1.8



SP Fixed Electrode

Station S/N Potential Difference (mV)0 - 20 1 -52.20 - 40 2 -40.60 - 60 3 -16.30 - 80 4 -14.3

0 - 100 5 -10.60 - 120 6 -8.60 - 140 7 -6.7

0 2 4 6 8 10 12 14 16

-30

-25

-20

-15

-10

-5

0

AN SP LINE PROFILE

STATION(m)

Pote

ntial

Diff

eren

ce (m

V)

Graph 1.9


0 1 2 3 4 5 6 7 8 9 10

-35

-30

-25

-20

-15

-10

-5

0

AN SP LINE PROFILE

Station (m)

Pote

ntial

Diff

eren

ce (m

V)

Graph 2.0



0 1 2 3 4 5 6 7 8

-60

-50

-40

-30

-20

-10

0

AN SP LINE PROFILE

STATION(m)

Axis

Pote

ntial

Diffe

renc

e (m

V)

Graph 2.1

QUALITATIVE INTERPRETATION

SP interpretation is purely qualitative, from the profile of the traverse; there is major negative anomaly signature between 20m – 25.6m in traverse four for fixed spacing survey, this suggest presence of conductive body within this area. Similarly, there is negative anomaly signature between 30m – 50m. For other profile, do not give a distinctive contrast as the profile is likely to be due to bioelectric activity of the plant in the survey area or groundwater movement.

QUANTITATIVE INTERPRETATION

FIXED SPACING

For 5m spacing: to calculate for the depth of the conductive body

Vmax=-66mV and Vhalf=-33mV X 12= 10.5m

h = X 1

2

√3 = 10.5

√3 = 6.06m (Depth of the anomaly).



X 12= 9m

h = X 1

2

√3 = 9

√3 = 5.2m(Depth of the anomaly).


X 12= 10m

h = X 1

2

√3 = 10

√3 = 5.78m(Depth of the anomaly).


X 12= 8.5m

h = X 1

2

√3 = 8.5

√3 = 4.90m (Depth of the anomaly)

FIXED ELECTRODE

For 5m fixed electrode: to calculate for the depth of the conductive body

X 12= 10.5m

h = X 1

2

√3 =

10.5


For 10m fixed electrode: to calculate for the depth of the conductive body

X 12= m

h = X 1

2

√3 =

9



Discussion and Conclusion

At 5m, 10m, 15m and 20m respectively for fixed spacing on traverse one, there is presence of negative anomaly signature for the four fixed spacing, which suggest there is conductive body. The depth of the anomaly was estimated to be at range of 4.90m-6.06m and for fixed electrode a well formed anomaly was found at 5m and 10m spacing, the depth of the conducing body was calculate to be at range of 5.15m-6.06m . For other profile, do not give a distinctive contrast as the profile is likely to be due to bioelectric activity of the plant in the survey area or groundwater movement.


Data Sheet Showing Electrical Resistivity Data Measurement . The measured apparent resistivity data for each of the traverses was rewritten (arranged) in RES2DINV format, so that it could be read by the software as shown below

CST DATA (a=10m)Geometric factor (K) = 62.832

A(m) M(m) N(m) B(m) AB/2(m) Resistance (Ω)

Apparent resistivity(Ωm)

0 10 20 30 15 0.1943 12.20825762.5 12.5 22.5 32.5 17.5 2.4 150.79685 15 25 35 20 2.6 163.36327.5 17.5 27.5 37.5 22.5 3 188.49610 20 30 40 25 3.7 232.478412.5 22.5 32.5 42.5 27.5 4.2 263.894415 25 35 45 30 10.5 659.73617.5 27.5 37.5 47.5 32.5 37.8 2375.049620 30 40 50 35 27 1696.46422.5 32.5 42.5 52.5 37.5 20.2 1269.206425 35 45 55 40 30.7 1928.942427.5 37.5 47.5 57.5 42.5 37.2 2337.350430 40 50 60 45 5.7 358.142432.5 42.5 52.5 62.5 47.5 19.5 1225.22435 45 55 65 50 45.9 2883.988837.5 47.5 57.5 67.5 52.5 0.1499 9.418516840 50 60 70 55 5.7 358.142442.5 52.5 62.5 72.5 57.5 10.4 653.452845 55 65 75 60 25.5 1602.21647.5 57.5 67.5 77.5 62.5 5.1 320.443250 60 70 80 65 5.8 364.425652.5 62.5 72.5 82.5 67.5 8 502.65655 65 75 85 70 5.4 339.2928


57.5 67.5 77.5 87.5 72.5 6.4 402.124860 70 80 90 75 12.7 797.966462.5 72.5 82.5 92.5 77.5 0.7546 47.413027265 75 85 95 80 2 125.66467.5 77.5 87.5 97.5 82.5 0.3277 20.590046470 80 90 100 85 15.9 999.028872.5 82.5 92.5 102.5 87.5 8.7 546.638475 85 95 105 90 19.1 1200.091277.5 87.5 97.5 107.5 92.5 20.6 1294.339280 90 100 110 95 13.6 854.515282.5 92.5 102.5 112.5 97.5 17 1068.14485 95 105 115 100 16.7 1049.294487.5 97.5 107.5 117.5 102.5 3.3 207.345690 100 110 120 105 4.9 307.876892.5 102.5 112.5 122.5 107.5 8.8 552.921695 105 115 125 110 25 1570.897.5 107.5 117.5 127.5 112.5 8 502.656100 110 120 130 115 13.9 873.3648102.5 112.5 122.5 132.5 117.5 5.6 351.8592105 115 125 135 120 33.6 2111.1552107.5 117.5 127.5 137.5 122.5 22.2 1394.8704110 120 130 140 125 32.1 2016.9072

CST DATA (a=15m)Geometric factor (K) =94.248

a(m) m(m) n(m) b(m) AB/2(m) Resistance (Ω)Apparent resistivity (Ωm)

0 15 30 45 22.5 2.6 245.0448

2.5 17.5 32.5 47.5 25 1.8 169.64645 20 35 50 27.5 23.2 2186.55367.5 22.5 37.5 52.5 30 2.7 254.469610 25 40 55 32.5 79.3 7473.8664

12.5 27.5 42.5 57.5 35 15.8 1489.1184

15 30 45 60 37.5 8.6 810.5328

17.5 32.5 47.5 62.5 40 0.7731 72.8631288

20 35 50 65 42.5 15.7 1479.6936


22.5 37.5 52.5 67.5 45 22.1 2082.8808

25 40 55 70 47.5 14.8 1394.8704

27.5 42.5 57.5 72.5 50 10 942.48

30 45 60 75 52.5 10.8 1017.8784

32.5 47.5 62.5 77.5 55 1.5 141.372

35 50 65 80 57.5 1.3 122.5224

37.5 52.5 67.5 82.5 60 27.9 2629.5192

40 55 70 85 62.5 30.4 2865.1392

42.5 57.5 72.5 87.5 65 3.3 311.0184

45 60 75 90 67.5 1.8 169.6464

47.5 62.5 77.5 92.5 70 23.1 2177.1288

50 65 80 95 72.5 19.7 1856.6856

52.5 67.5 82.5 97.5 75 18.6 1753.0128

55 70 85 100 77.5 1.3 122.5224

57.5 72.5 87.5 102.5 80 16.8 1583.3664

60 75 90 105 82.5 5.6 527.7888

62.5 77.5 92.5 107.5 85 8.4 791.6832

65 80 95 110 87.5 7.4 697.4352

67.5 82.5 97.5 112.5 90 22.9 2158.2792

70 85 100 115 92.5 17 1602.216

72.5 87.5 102.5 117.5 95 4.8 452.3904

75 90 105 120 97.5 1.4 131.9472

77.5 92.5 107.5 122.5 100 1.1 103.6728

80 95 110 125 102.5 28 2638.944

82.5 97.5 112.5 127.5 105 7.7 725.7096

85 100 115 130 107.5 16.8 1583.3664

87.5 102.5 117.5 132.5 110 9.7 914.2056

90 105 120 135 112.5 10.7 1008.4536

92.5 107.5 122.5 137.5 115 60.5 5702.004

95 110 125 140 117.5 44.4 4184.6112

CST DATA (a=20m)Geometric factor (K) =125.664

A(m) M(m) N(m) B(m) AB/2(m) Resistance (Ω) Apparent resistivity (Ωm)

0 20 40 60 30 1.9 238.7616


2.5 22.5 42.5 62.5 32.5 1.7 213.6288

5 25 45 65 35 0.6834 85.8787776

7.5 27.5 47.5 67.5 37.5 4.1 515.2224

10 30 50 70 40 1.2 150.7968

12.5 32.5 52.5 72.5 42.5 1 125.664

15 35 55 75 45 0.7467 93.8333088

17.5 37.5 57.5 77.5 47.5 32.8 4121.7792

20 40 60 80 50 2 251.328

22.5 42.5 62.5 82.5 52.5 4.2 527.7888

25 45 65 85 55 3.1 389.5584

27.5 47.5 67.5 87.5 57.5 51.6 6484.2624

30 50 70 90 60 32.7 4109.2128

32.5 52.5 72.5 92.5 62.5 29.6 3719.6544

35 55 75 95 65 17.5 2199.12

37.5 57.5 77.5 97.5 67.5 5.1 640.8864

40 60 80 100 70 6 753.984

42.5 62.5 82.5 102.5 72.5 12.7 1595.9328

45 65 85 105 75 21.5 2701.776

47.5 67.5 87.5 107.5 77.5 63.6 7992.2304

50 70 90 110 80 12.9 1621.0656

52.5 72.5 92.5 112.5 82.5 31.3 3933.2832

55 75 95 115 85 13 1633.63257.5 77.5 97.5 117.5 87.5 2 251.32860 80 100 120 90 19.1 2400.182462.5 82.5 102.5 122.5 92.5 40 5026.5665 85 105 125 95 37.8 4750.099267.5 87.5 107.5 127.5 97.5 10.2 1281.772870 90 110 130 100 13 1633.63272.5 92.5 112.5 132.5 102.5 18.6 2337.3504

75 95 115 135 105 14.8 1859.8272

77.5 97.5 117.5 137.5 107.5 8.6 1080.7104

80 100 120 140 110 2 251.328

Processing these data with RES2DINV software gives the inversed resistivity structures below

PSEUDO-SECTION PLOT FOR TRAVERSE 6



Withinthe range of 66m - 79m at a depth of 0.6m indicates a low resistivity zone. Also, within the range of 91m – 94m at a depth of 0.4m, lies a low resistivity zone which is not too pronounced. Noticeable also from the section is another region of low resistivity at a range of 116m – 124m at depth 0.7m.


At a depth of 1.7m is a high resistivity zone within a range of 16m to 28m, with even higher resistivity values recorded at depth 1.5m located within a range of a 100m and 110m.

Low resistivity values indicate a fractured zone or basement whereas high resistivity


Data Sheet Showing Electromagnetic Data Measurement.The table below shows the acquired data for both Vertical Dipole (VD) and Horizontal Dipole (HD) for traverse 6 in 10m, 20m and 40m spacing.


EM

SPACING 10M

Station S/N HD (mS/m) VD (mS/m) Remark0 - 10 1 19 225 - 15 2 19 2110 - 20 3 17 2015 - 25 4 17 2020 - 30 5 16 2125 - 35 6 16 2130 - 40 7 17 2135 - 45 8 18 1640 - 50 9 19 1845 - 55 10 18 1850 - 60 11 17 1755 - 65 12 16 1960 - 70 13 17 2265 - 75 14 17 2070 - 80 15 18 1875 - 85 16 19 1780 - 90 17 18 1985 - 95 18 19 20

90 - 100 19 18 2295 - 105 20 18 21100 - 110 21 17 23 Presence of goal post105 - 115 22 18 25 Presence of goal post110 - 120 23 19 23115 - 125 24 20 24120 - 130 25 19 28125 - 135 26 20 30130 - 140 27 20 30 Presence of electric cable

Traverse One at 10m spacing

0 5 10 15 20 25 300

5

10

15

20

25

30

35

HDVD

STATION(m)

APPA

REN

T CO

NDU

CTIV

ITY

(mS/

m)



EMSpacing: 20m

Station S/N HD (mS/m) VD (mS/m) Remark0 - 20 1 21 195- 25 2 19 19

10 - 30 3 18 2315 - 35 4 18 2620 - 40 5 18 2725 - 45 6 18 2530 - 50 7 19 2335 - 55 8 18 2140 - 60 9 19 2245 - 65 10 18 2450 - 70 11 19 2455 - 75 12 17 2360 - 80 13 18 2165 - 85 14 18 2070 - 90 15 18 1775 - 95 16 18 1880 - 100 17 18 2185 - 105 18 19 2290 - 110 19 20 23 Presence of goal post95 - 115 20 20 24 Presence of goal post

100 - 120 21 21 23105 - 125 22 20 22110 - 130 23 21 25 Electric cable and weathered rock115 - 135 24 23 28 Electric cable and weathered rock120 - 140 25 25 34 Electric cable and weathered rock

TRAVERSE SIX (20m)SPACING

0 5 10 15 20 25 300

5

10

15

20

25

30

35

40

HDVD

STATION(m)

APPA

REN

T CO

NDU

CTIV

ITY(

Ms/

m)



EMSPACING(40M)

STATION(m) S/N HD (mS/m) VD (mS/m) Remark0 - 40 1 22 215 - 45 2 21 26

10 - 50 3 20 3015 - 55 4 22 2720 - 60 5 19 3125 - 65 6 19 3130 - 70 7 18 3435 - 75 8 18 2640 - 80 9 18 2945 - 85 10 19 2350 - 90 11 18 2155 - 95 12 19 2260 - 100 13 18 2365 - 105 14 18 2370 - 110 15 21 2675 - 115 16 22 27 Presence of goal post80 - 120 17 20 2585 - 125 18 22 2090 - 130 19 25 3095 - 135 20 24 28

100 - 140 21 25 30

TRAVERSE six (SPACING 40M)

0 5 10 15 20 250

5

10

15

20

25

30

35

40

HDVD

STATION(m)

APPA

REN

T CO

NDU

CTIV

ITY(

Ms/

M)

Qualitative Interpretation

Traverse six, at 10m spacing the presence of crossover point indicating likely presence of conductive zone at 7.8m, 10m, 15m and at 16.7m and also at 20m spacing 2m ,14.5m and 16m and 1m, 17.5 and 18.5m respectively also shows the presence conductive zone due to the crossover pointLikely presence of conductive zone at 24m,18m and 22m due to high peak at 10m, 20, and 40m spacing respectively


Seismic Refraction Data InterpretationThe acquired data were interpreted using SeisImager software. The Pickwin of the SeisImager was used to pick first arrival of the primary seismic wave, which was grouped into five picks. The picked groups are then plotted and modeled into geological layers using Plotrefa of the SeisImager, the results are shown below

a table showing were the shot was taken and the file number gotten from the seismogram


TRAVERSE 6

Shot Point File No.

Offset 013745

Btw G6 and G7 013747

Btw G12 and G13 013750

Btw G18 and G19 013751

2m after G24 013752

Offset 013753

Btw G25 and G26 013754

Btw G30 and G36 013755

Btw G42 and G43 013756

2m after G48 013757

A graph showing the relationship between velocity and distance

The forward and reverse shots for each profile were plotted and the layer velocities, layer thicknesses and depths were obtained from the time-distance graphs. The seismic refraction results of the layer velocities and layer thicknesses are


A picture showing the seimictomograpy of the subsurface


A seismic refraction travel time

A graph showing the relationship between velocity and distance


A picture showing the lithology of the subsurface


In traverse six, result shows that threeseismicvelocitylayersweredelineatedwithvelocityrange from 300m/s – 340m/s for layer 1, 1000-1200m/s for layer two and 1600-2000m/s for layer 3. The thicknesses of layers are 3.8 and 6.7m for layers 1 and 2 respectively. Data also show that velocity increases with depth.


CHAPTER FOUR

ECONOMIC CONSIDERATIONS

Igarra is a town in Edo State, Nigeria in which the major occupation is farming. This means the soil here is very rich in both micro and macro nutrients for cultivation. The minerals found here are mainly muscovite mica, orthoclase feldspar, biotitemica andquartz. These minerals were not found in large economic quantities but they could still be exploited and used for various purposes such as construction, glass making, ceramics etc.

Also, the whole town is sitting on the basement complex with a system of ridges almost surrounding the whole town and this resource could be exploited for the purpose of tourism which would generate more income to both igarra East LGA and Edo State, Nigeria.


CHAPTER FIVE

GENERAL CONCLUSION

The VLF EM16R method, after it’s processing gave a signature which is also found in the Constant Spacing Traversing technique. This signature (between 20metres and 40metres) is a moderately resistive and moderately conductive anomaly in the constant spacing traversing technique and VLF method respectively.

At this point of the traverse, the was a spike up (showing an anomaly) representing a material of low magnetic susceptibility. This means that the anomaly present beneath the subsurface is not a magnetic material

The moderate resistivity and conductivity of this anomaly was noticed at depth below 6metres, suggests that the material may not be water saturated or a corrosive part of the subsurface

The spontaneous potential method plot of 10metres also shows an anomaly between the distance 20m- 40m, this also correlates with the anomalous zone of the VLF and CST technique. This 3 technique are definitely responding to the same anomaly

In the gravity method, there was a spike up of the plot at distance between 80m and 100m on the traverse, there was the presence of a quartz intrusion. At this distance of the traverse, the basement was seen to be closer to the subsurface along the traverse. This supported also by the presence of a pegmatitic intrusion at that point on the traverse. The magnetic signature of that section (80-100m) is spiking down, this could be as a result of the pegmatitic intrusion in that section.

The seismic refraction method shows three layers up to about 21metres depth, this is the weathered layer shown in the Geo- electric section during the VES technique. The differentiation of layers by both methods however shows a distinct difference due to the fact that the differentiate layers based on different physical properties, velocity of seismic wave by seismic refraction and apparent resistivity of each layer by VES. In basement complex, the lithologies are as follows; fresh basement, partly fractured basement, fractured base, partly weathered base,


weathered basement, top-soil. The resistivity values decreases in this order. Therefore the aquifer unit in the basement complex are either the weathered or fractured basement. From the VES curve obtained, the resistivity values are

The depth to basement was found to be 20m-40metres below the surface.


BIBLIOGRAPHYAmerican Geological Institute. (1957). Glossary of Geology and

Related Sciences; National Academy of Sciences for the American

Geological Institute, U.S.A

Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation.

Reynolds, J.M. (1997). An Introduction to Applied and

Environmental geophysics; John Wiley and Sons Ltd, West Sussex,

England.


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