IMAGING THE EARTH'S SUBSURFACE An Inaugural Lecture delivered at the University of Ibadan ~, 11February, 2010 By " ABEL IDOWU OLAYINKA Professor of Applied Geophysics, Faculty of Science, University of Ibadan, Ibadan, Nigeria. UNIVERSITY OF IBADAN UNIVERSITY OF IBADAN LIBRARY The Vice-Chancellor, Deputy Vice-Chancellor (Admini- stration), Deputy Vice-Chancellor (Academic), Registrar, Librarian, Provost, College of Medicine, Dean of Science, Dean of the Postgraduate School, Deans of other Faculties and of Students, Members of Senate, Heads of Departments; l~~Y lords, Spiritual, Temporal and Geological, Esteemed Colleagues, Distinguished Ladies and Gentlemen. Introduction I thank the Almighty God for giving me the opportunity to present this year's Professorial Inaugural Lecture (PIL) on behalf of the Faculty of Science. The Dean of Science, my brother and esteemed colleague, Professor Kayode O. Adebowale, has been most supportive in this regard. The tradition of inaugural lectures in this university is as old as . the institution itself. Available record shows that Paul Christopherson, a Professor of English, delivered the first lecture titled 'Bilingualism' on the Foundation Day, 17 November, 1948. The lecture, this evening, is coming a little ..•. over 10 years after I attained the professorial rank; I probably have no reason to complain. This is because many eminent scholar-researchers who have been professors for upward of 20 years have not yet had this opportunity, no thanks to the policy of one PIL per faculty per session in the University of Ibadan. I am aware that there are about 20 professors in the Faculty of Science waiting for the chance to deliver their Inaugurals. There are probably similar situations in other very big faculties. If the original intention of an inaugural was for each and every professor to use this platform to address the public on his/her area of specialization soon after attaining the full professorial rank, it is obvious we need to devise another procedure to give all our professors this benefit. Soyibo (1996) made a similar plea about 14 years agq. Up till now, however, not much seems to have changed.' But;' of course, this is Ibadan, reputed as one of the most conservative' universities in the world! The 'only consolation can be found I\ . UNIVERSITY OF IBADAN LIBRARY in the Yoruba adage that says 'there is no time a man sews a garment that he would not have an opportunity to wear it' . Geology was established as a unit in the Department of Geography of this university in 1959. It subsequently became a full-fledged department in 1962, thus becoming the first of such departments in any Nigerian University. It is gratifying to note that the first Inaugural. Lecture from our Department was delivered barely a year later by our First Head of Department, Prof R.A. Reyment, who studied virtually all the sedimentary basins of Nigeria and produced the first coherent synthesis of their biostratigraphy. The second inaugural came from our highly revered Professor M.a. Oyawoye, a petro- logist, in 1970. Subsequent inaugurals from the Department were presented by Professor E.A. Fayose, a biostratigrapher, in 1979; Professor T.A. Badejoko a geochemist in 1995, and Professor A.A. Elueze, an economic geologist, in 2002. Today's lecture is the sixth from our stable (see table 1). From the modest beginning, some 50 years ago, the Department of Geology at Ibadan has grown in leaps and bounds. We are delighted to report that as of today, we can boast of 19 academic members of staff, with a satisfactory staff mix. It is also gratifying to note that the members of staff are in various areas of specialization in basic and applied geology. 2 UNIVERSITY OF IBADAN LIBRARY Table 1: Inaugural Lectures from the Department of Geology, University of Ibadan, 1962-2010 SINo. Presenter Area of Topic Year Specialization 6. Prof. A. I. Olayinka Applied Imaging the 2010 Geophysics Earth's Subsurface 5. Prof. A. A. Elueze Economic Compositional 2002 Geology Character: Veritable Tool in the Appraisal of Geomaterials 4. Prof. T. A. Badejoko Geochemistry Geochemistry: 1995 The Heartbeat of Mineral Resources 3. Prof. E. A. Fayose Biostratigraphy Man and 1979 Minerals 2. Prof. M. O. Oyawoye Petrology Politics and 1970 Economics of Mineral e Resources in Developing Countries I. Prof. R. A. Reyment Biostratigraph y The Future of 1963 Geology in Nigeria Geology as a Discipline Geology is a branch of science involving the study of the Earth, the materials of which it is made, the structure of those materials and the processes acting upon them. It includes the study of organisms that have inhabited our planet. An important part of geology is the study of how Earth's materials, structures, processes and organisms have changed over time. Many processes, such as landslides, earthquakes, floods and volcanic eruptions can be hazardous to people. Geologists work to understand these processes well enough to avoid building important structures where they might be damaged. If geologists could prepare maps of areas that have been flooded in the past, they can prepare maps of areas that might be flooded in the future. These maps can be used to 3 UNIVERSITY OF IBADAN LIBRARY guide the development of communities and determine -where flood protection or flood insurance is needed. We use Earth materials everyday. We use oil that is produced from wells, metals that are produced from mines, and water that has been drawn from streams or from underground. Geologists conduct studies that locate rocks that contain important metals, plan the mines that produce them and the methods used to remove the metals from the rocks. They do similar work to locate and produce oil, natural gas and groundwater. Today, we are concerned about climate change. Many geologists are working to learn about the past climates of the Earth and how they have changed across time. This information is valuable to understand how our current climate is changing and what the results might be. Some Basic Geological Concepts Internal Structure of the Earth The Earth is spherical in shape with a radius of about 6,378 km (fig. 1). The internal structure of the earth can be subdivided into three main regions; namely, the crust, the mantle and the core. The crust is very thin, averaging 20 km. The thinnest parts are under the oceans (Oceanic Crust) that go to a depth of roughly 10 km. The thickest parts are the continents (Continental Crust) which extend down to 35 km on average. The continental crust in the Himalayas is some 75 -k,m deep. The interface between the crust and the mantle is called the Moho discontinuity. The mantle is the layer beneath the crust which extends about half-way to the centre. It is made of solid rock and behaves like an extremely viscous liquid. The convection of heat from the centre of the Earth is what ultimately drives the movement of the tectonic plates and causes mountains to rise. The interface between the mantle and the core is called the Gutenberg discontinuity. The outer core is the layer beneath the mantle. It is made of liquid iron and nickel. Complex convection currents give rise to a dynamo effect, which is responsible for the Earth's magnetic field. The inner core is the bit in the middle, and it is made of 4 UNIVERSITY OF IBADAN LIBRARY solid iron and nickel. Temperatures in the core are thought to 4 be in the region of 5000-6000 °C and it is solid due to the massive pressure. -'-i- Fig 1. Internal structure of the Earth Source: (http://www.moorlandschool.co.uk/earth/earths_structure.htm; retrieved 18 December, 2009). Crust is created at the mid-ocean ridges and is destroyed at the subduction zones. The processes are driven by the convection currents created by the heat produced by natural radioactive processes deep within the Earth. The crust and uppermost mantle down to a depth of about 70 to 100 km under deep ocean basins and 100 to 150 km under continents is rigid, forming a hard outer shell called the lithosphere. Beneath the lithosphere lies the asthenosphere, a layer in which seismic velocities often decrease, suggesting 5 UNIVERSITY OF IBADAN LIBRARY lower rigidity. It is about 150 km thick. This weaker layer is thought to be partially molten. The asthenosphere plays an important role in plate tectonics because it makes possible the relative motions of the overlying lithospheric plates. The brittle condition of the lithosphere causes it to fracture when strongly stressed. The rupture produces an earthquake, which is the violent release of elastic energy due to sudden displacement on a fault plane. We often hear or see, on television, incidents of earthquakes in various parts of the world, a most recent one being that in Haiti in January 2010, where a magnitude-7 quake struck, and an estimated 200,000 people lost their lives. A common feature of the report in the mass media is to highlight the magnitude of the earthquake. For instance, 'A 6.5 magnitude earthquake hits California' (CNN Breaking News, Sunday, 10 January, 2010). The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs (adjustments are included to compensate for the variation in the distance between the various seismographs and the epicenter of the earthquake). The original formula is: where A is the maximum excursion of the Wood-Anderson seismograph; the empirical function Ao depends only on the epicentral distance of the station, 8. In practice, readings from all observing stations are averaged after adjustment with station-specific corrections to obtain the ML value. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; in terms of energy, each whole number increase corresponds to an increase of about 31.6 times the amount of energy released. Events with magnitudes of about 4.6 or greater are strong enough to be recorded by any of the seismographs in the world, given that the seismograph's sensors are not located in an earthquake's shadow. An earthquake magnitude scale is shown in table 2. 6 UNIVERSITY OF IBADAN LIBRARY Table 2. Earthquake Magnitude Scale Magnitude (Md Earthquake effects Estimated number per year 8.0 or greater Great earthquake. It can totally One every 5.to destroy communities near the 10 years epicenter. 7.0 to 7.9 Major earthquake. It can cause 20 serious damage. 6.1 to 6.9 May cause a lot of damage in 100 very densely populated areas. 5.5 to 6.0 Slight damage to buildings and 500 other structures. 2.5 to 5.4 Often felt but only causes minor 30,000 damage. 2.5 or less Usually not felt but can be 900,000 recorded by seismograph. Source: (http://www.geo.mtu.edu/UPSels/maglUlude.htm/retneved 14 January 2010). An earthquake often appears to happen at a point which is referred to as the focus or hypocenter. It generally occurs at a focal depth many kilometers below the Earth's surface. The point on the Earth's surface vertically above the focus is called the epicenter of the earthquake. Earthquake epicenters are not uniformly distributed over the Earth's surface, but occur predominantly along narrow zones of interpolate seismic activity. Three of such zones can be identified (fig. 2). First, the circum-Pacific zone, in which 75 to 80% of the annual release of seismic energy takes place, forms a girdle that encompasses the mountain ranges on the west coast of the Americas and the island arc along the east coast of Asia and Australia. Second, the Mediterranean- trans asiatic zone, responsible for about 15 to 20% of the annual seismic energy release, begins at. the Azores triple junction in the Atlantic Ocean and extends along the Azores- Gibraltar ridge. After passing through North Africa, it makes a loop through the Italian peninsula, the Alps and the Dinarides; it then runs through Turkey, Iran, the Himalayan mountain chain and the island arcs of the southeast Asia 7 UNIVERSITY OF IBADAN LIBRARY which terminates at the circum-Pacific zone. Third, the system of oceanic ridges and rises accounts for 3 to 7% of the annually released seismic energy. In addition to their seismicity, each of these zones is also characterized by active volcanism. '."•• :; . - .• f •••• .1•..•• :. •••. ..•...•...• OIl .,','~.t..·...~6.0 '~ . ·S o '" ~ ~ m 00 ~ ~ ~ m ~ ~ ~ ~ mOIl" '" 0 • East "West Fig. 2: The geographical distribution of epicentres for 30,000 earthquakes for the years 1961-1967 (After Barazangi and Dorman, 1969). The remainder of the earth is considered aseismic. However, no region of the Earth can be regarded as completely earthquake-free. About 1% of the global seismicity is due to intraplate earthquakes, which occur remote from the major seismic zones. . Earthquakes can also be classified according to their focal depths. Earthquakes with shallow focal depths less than 70 km occur in all seismically active zones; only shallow earthquakes occur on the oceanic ridge systems. The largest proportion (about 85%) of the annual release of seismic energy is liberated in shallow-focus earthquakes. The remainder is set free by earthquakes with intermediate focal depths of 70 to 300 km (about 12%) and by earthquakes with deep focal depths greater than 300 km (about 3%). 8 UNIVERSITY OF IBADAN LIBRARY Geologic Time Scale The geologic time scale (fig. 3) is a chronologie scheme (or idealized model) relating stratigraphy to the time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth. The table of geologic time spans presented here agrees with the dates and nomenclature proposed by the International Commission on Stratigraphy, and it uses the standard colour codes of the United States Geological Survey . ..., _.rF l,E,i/-. ••• l:-:=~:-:~l-,-------,-, Millions of Years Fig 3. Geologic time scale (http://en.wikipedia.org/wikilGeologic_time_scale; retrieved 18 December, 2009). This clock representation shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga. Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, while the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale. 9 UNIVERSITY OF IBADAN LIBRARY Evidence from radiometric dating indicates that the Earth is about 4.570 billion years old. The geological or deep time of Earth's past has been organised into various units according to events which took place in each period. Different spans of time on the time scale are usually delimited by major geological or paleontological events such as mass extinctions. For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous-Tertiary extinction event, which marked the demise of the dinosaurs and of many marine species. Older periods which predate the reliable fossil record are defined by absolute age. Each era on the scale is separated from the next by a major event or change. The Rock Cycle The rock cycle is a fundamental concept in geology that describes the dynamic transitions through geologic time among the three main rock types: sedimentary, metamorphic and igneous. As illustrated in fig. 4, each type of rock is altered or destroyed when it is forced out of its equilibrium conditions. An igneous rock, such as basalt, may break down and dissolve when exposed to the atmosphere, or melt as it is subducted under a continent. Due to the driving forces of the rock cycle, plate tectonics and the water cycle, rocks do not remain in equilibrium and are forced to change as they encounter new environments. The rock cycle is an illustration that explains how the three rock types are related to each other and how processes change from one type to another over time. 10 UNIVERSITY OF IBADAN LIBRARY Fig 4. The Rock Cycle. Source: (http://n-ww.coif.eduletelmoduies/mseselearthsysflrlrock.htill/; retrieved 26 December, 2009). An igneous rock can change into a sedimentary rock or into a metamorphic rock. A sedimentary rock can change into metamorphic rock or into igneous rock, while a metamorphic rock can change into igneous or sedimentary rock. An example of metamorphic change from mud into shale (a sedimentary rock), into slate, phyllite, schist and gneiss (metamorphic rocks) is shown in fig 5. 1 1 UNIVERSITY OF IBADAN LIBRARY Mud Sh+ale + Slate I ••• Phylite (about 300DC) Sc+hist Gneiss (atut 400°C) Fig. 5. An example of metamorphic change Igneous rocks form when magma cools and makes crystals. Magma is a hot liquid made of melted minerals. The minerals can form crystals when they cool. An igneous rock can form underground, where the magma cools slowly, or, it can form above ground, where the magma cools quickly. When magma pours out on the Earth's surface, it is called lava. On the Earth's surface, wind and water can break rock into pieces. They can also carry rock pieces to another place. Usually, the rock pieces, called sediments, drop from the wind or water to make a layer. The layer can be buried under other layers of sediments. After a long time, the sediments can be cemented together to make sedimentary rock. In this way, an igneous rock can become a sedimentary rock. All rocks can be heated. But where does the heat come from? Inside the Earth, there is heat from pressure (push your hands together very hard and feel the heat). There is heat from friction (rub your hands together and feel the heat). There is also heat from radioactive decay (the process that gives us nuclear power plants that make electricity). The heat 12 UNIVERSITY OF IBADAN LIBRARY are stored as freshwater in lakes. Not all runoff flows into rivers, much of it soaks into the ground as infiltration. Some water infiltrates deep into the ground and replenishes aquifers, which store freshwater for long periods of time. Some infiltration stays close to the land surface and can seep back into surface-water bodies (and the ocean) as groundwater discharges. Some groundwater finds openings in the land surface and comes O\,1tas freshwater springs. Over time, the water returns to the ocean, where our water cycle started. Fig. 6. The Water Cycle ~ Source: (hllp://en.wikipedia.org/wiki/File:Water _cycle.pllg; retrieved 27 ; December, 2009). The residence time of a reservoir within the hydrologic cycle is the average time a water molecule will spend in the reservoir (table 3). It is a measure of the average age of the water in such a reservoir. Groundwater can spend over 10,000 years beneath Earth's surface before leaving. Particularly old groundwater is called fossil water. Water stored in the soil remains there very briefly, because it is spread thinly across the Earth, and it is 14 UNIVERSITY OF IBADAN LIBRARY readily lost by evaporation, transpiration, stream flow or groundwater recharge. After evaporating, the residence time in the atniosphere is about 9 days before condensing and falling to the Earth as precipitation. Table 3: Average Reservoir Residence Time Reservoir Average residence time Oceans 3,200 years Glaciers 20 to 100 years Seasonal snow cover 2 to 6 months Soil moisture 1 to 2 months Groundwater I shallow 100 to 200 yearsI deep 10,000 years Lakes 50 to 100 years Rivers 2 to 6 months Atmosphere 9 days Source: (PhysicafGeography.net. CHAPTER 8: Introduction to the Hydrosphere Retrieved on 24 October, 2006 Overview of Geology of Nigeria The surface area of Nigeria is about 923, 768 km2 and about 50% of this is underlain directly by various suites of crystalline rocks (igneous and metamorphic rocks) while the remainder is underlain by sedimentary rocks (fig. 7). The crystalline rocks are further divided into three main groups namely: • The Basement Complex of Precambrian age (over 570 Ma), • The Younger Granites of carboniferous to cretaceous (300-140 Ma), and • The Tertiary to Recent Volcanics (65 Ma- 0.01 Ma) • The sedimentary rocks are found in sedimentary basins which include the Eastern Dahomey (or Benin) Basin, the Niger Delta, the Anambra Basin, the Benue Trough, the Bornu Basin, the Middle Niger Basin and the Sokoto Basin. 15 UNIVERSITY OF IBADAN LIBRARY o· ,. ," .\ ••...•.•....~.~. ••••.•n. .b1•.•••J.•••• .'.Y:. 0 ('>"d_ O EJ ---...f:......... g• ,0' ~<':..,.. .•.•••••..•.'E•='.£. r: . - .. , ~ Fig. 7. Geological Map of Nigeria (Adapted from Whiteman, 1982). Rocks are resources that bring a lot of revenues for the technological take-off of a nation (Ekwueme, 2006). They are the sources of mineral wealth, and with a sound knowledge of their structures indications of possible areas of mineral occurrences can be reasonably predicted based on geological principles .. Some of the products include dimension stone, slate, roadstone, aggregate, bricks, tiles, cement, glass, plaster, plasterboard, insulating materials and bitumen. One of the major tools used in studying geological problems is by applying the principles of physics. An overview of geophysics is given in the following section. Definition of Geophysics Geophysics has been defined variously as: (i) The study of the earth by the quantitative physical method, especially by seismic reflection and refract- tion, gravity, magnetic, electrical, electromagnetic and radioactivity methods. (ii) The application of physical principles to the study of the earth. This includes the branches of • 16 UNIVERSITY OF IBADAN LIBRARY (a) seismology (earthquakes and elastic waves); (b) geo-thermometry (heating of the earth, heat flow, volcanology, and hot springs); (c) hydrology (ground and surface water, sometimes including glaciology); (d) physical oceanography; (e) meteorology; (f) gravity and geodesy (the earth's gravitational field and the size and form of the earth); (g) atmospheric electricity and 'terrestrial magnetism (including ionosphere, VanAllen belts, telluric currents, etc.); (h) tectonophysics (geological processes in the earth); and (i) exploration and engineering geophysics. Geochronology (the dating of earth history) and geo- cosmogony (the origin of the earth) are sometimes added to the foregoing list. Geophysics often refers to solid-earth geophysics only, thus excluding (c), (d), (e), and portions of other subjects from the above list. In this discourse, exploration geophysics is the use of methods such as seismic, gravity, magnetic, electrical and electromagnetic (table 4) in the search for oil, gas, minerals, groundwater, etc., with the objective of economic exploita- tion. Some geophysicists spend most of their time outdoors studying various features of the Earth, and others spend most of their time indoors using computers for modelling and calculations. Some geophysicists use these methods to find oil, iron, copper and many other minerals. Some evaluate earth properties for environmental hazards and evaluate areas for dams or construction sites, and for other structures such as buildings, tunnels and bridges. Research geophysicists study the internal structure and evolution of the earth, earthquakes, the ocean and other physical features using these methods. 17 UNIVERSITY OF IBADAN LIBRARY Table 4. Geophysical Methods, the Properties Involved and the Parameters Measured Method Nature Prooertyinvolved Value measured Gravity P Density Spatial variations in natural gravity field Magnetic P Magnetic susceptibility Spatial variations in natural magnetic field Radioactive P Abundance of radio Gamma radiation nucleides Heat flow P Thermal conductivitv Heat flow Electrical A Electrical conductivity Apparent resistivity Telluric current P Electrical conductivity Relative apparent resistivity Spontaneous P Oxidation potential, Natural polarization ion concentrations electrochemical potentials Induced A Electronic conductivity Polarization voltages polarization Electromagnetic A Electrical conductivity Alternating and/or magnetic electrical/magnetic permeability field phase and intensity relationships Seismic P Ground unrest Ambient seismic noise A Seismic travel time, Seismic travel times velocity. acoustic of different waves, impedance wave amplitudes, reflection patterns Remote sensing P Natural radiation Radiation intensity A Reflectivity (albedo) Reflected radiation Borehole P Natural radiation Natural voltages. natural gamma radiation A Electrical conductivity, Apparent resistivity, seismic velocity, travel times and nuclear reactions amplitudes, induced, back-scattered radiation Note: P, passive method involving measurement of natural effects; A, acuve method involving an artificial disturbance. Source: Sheriff, 1989 My Odyssey in the Geological Sciences For some inexplicable reasons, as a secondary school student at the famous and prestigious Ilesha Grammar School, all I wanted to become in life in terms of a career choice was a .-.'" geologist. Up till now, I cannot fathom exactly what 18 UNIVERSITY OF IBADAN LIBRARY motivated this choice, safe for, perhaps, the fact that I was very good in Geography, and I probably thought the next possible nice-sounding course to choose was Geology. Incidentally, a credit level pass in Geography at the Ordinarily LeveVWest African School Certificate examination was not a requirement for reading geology at the University of Ibadan when people of my generation were seeking admission by concessional entrance into Ibadan. Invariably, I got admitted into the University of Ibadan through the Preliminary Science class (now 100 Level) to read Geology during the 1977/78 session. One tough course I offered in my second year in the University was "PHY 102: Classical Physics 1" (now PHY 201). Somehow, the course lecturer, Dr S.c. Garde, informed me that my performance was outstanding, and that I led the class. He added that if I were a Physics major student, I would have been awarded one of the scholarships on offer by an international oil company. I felt most humbled with such encomium showered on me, and this, I believe, in retrospect, was the beginning of my romance with Geophysics. In our final year in 1980/81, we were given the opportunity to choose an area of specialization that we were interested in for the purpose of the "Project in Geology". I picked Applied Geophysics and was assigned to Dr Ofiafate Ofrey as my Supervisor. My project partner was my very good friend, the highly cerebral Dr George Ifechukwude Unomah, now a leading explorationist with Mobil Producing Nigeria Unlimited. We worked on a micro-gravity survey of the Physics Experimental Station at the University of Ibadan. A few years later when I joined the University of Ibadan as a lecturer in myoid department, some of my old secondary school mates teased me that it was a fait accompli, in so far as I had satisfied my childhood curiosity. I was admitted to read Geophysics (Pure and Applied) for my MSc degree at the Imperial College of Science and Technology, London, in 1983. The Geophysics Section of the Geology Department at Imperial College was then reputed to be the largest of its kind in Western Europe, with an 19 UNIVERSITY OF IBADAN LIBRARY unusually large number of postgraduate students. It was such an exciting experience studying in a postgraduate class of 23 students drawn from 11 different nationalities. On completion of the programme, I proceeded to the University of Birmingham. It was a great and rewarding experience working under some of the giants in our discipline. My thesis supervisor and mentor was Dr R.D. Barker, who invented the Offset-Wenner array (Barker 1979, 1981). His own PhD supervisor, Prof D.H. Griffiths, who co-authored with Dr R.F. King the world-acclaimed geophysics textbook, Applied Geophysics for Engineers and Geologists, was still very much around in the Department, albeit as an Emeritus Professor, when I arrived in Birmingham. As it later turned out, Professor Griffiths served as the Internal Examiner for my PhD thesis. In the following section, which is the longest in this lecture, an attempt is made to give a synopsis of my research endeavours. Areas of Specialization and My Modest Contributions to Scholarship My research interest is in Exploration Geophysics. The principal methods that my collaborators and I have employed till date comprise direct current surface geoelectrics, electromagnetics, seisrnics and borehole geophysics. The various research topics can be summarized in the following groups: Group I Microprocessor-Controlled Resistivity Traversing and its geophysical applications. Group II Regional Ground-water Resource Evaluation. Group III I-D Inversion of Resistivity Sounding Data. • Quantitative assessment of geoelectrical suppression • Errors in depth determination from resistivity soundings 20 UNIVERSITY OF IBADAN LIBRARY • Constraining the inversion of resistivity sounding data • Accuracy of partial curve-matching • Use of longitudinal resistivity • Fuzzy logic modelling Group IV 2-D Resistivity Imaging • Use of longitudinal conductances • Non-uniqueness and equivalence in 2-D imaging and modelling • Choice of the best model III 2-D geoelectrical imaging • Use of Block Inversion in the 2-D Interpretation of Apparent Resistivity Data and Comparison with Smooth Inversion. • Smooth and sharp-boundary inversion of 2-D pseudosection data in the presence of a decrease in resistivity with depth Group V Groundwater Occurrence in Ibadan Metropolis • Groundwater occurrence • Aspects of quality Group VI Environmental Geophysics • Geoelectric Imaging at an abandoned dump site . • Environmental Assessment of a Sewage Disposal System. • Corrosion potential along a pipeline route in the Niger Delta • Two-Dimensional Geoelectric Response of a Hydrocarbon-Impacted Sand formation UNIVERSITY OF IBADAN LIBRARY • Geophysical investigation of suspected springs Group VII: Engineering Geophysics Group VIII: Integrated Geophysical Investigation at a Geological Transition Zone Group IX Archaeological investigation Group X Geoelectric imaging of a valley bottom soil in relation to its agricultural significance Group XI : 3-D Geoelectric Imaging Group XII: Petroleum Geophysics • Stratigraphy and hydrocarbon potential of the Opuama Channel Complex, western Niger Delta. • Use of kriging for estimation of 2-D permeability distribution in a hydrocarbon reservoir. • Seismic impedance character of the weathering layer in Eastern Niger Delta. • Generation of rock property for seismic modelling. Group XIII: Research Methodologies Group I: Microprocessor-Controlled Resistivity Traversing (MRT) The conventional approach to electrical resistivity surveying entails injecting electrical current into the ground through a pair of electrodes and measuring the potential difference developed as a result, using another pair of electrodes (fig. 8). My PhD thesis involved the development of simple proce- dures for the interpretation of resistivity survey data collected, using the Microprocessor-Controlled Resistivity Traversing (MRT) System and an evaluation of the use of the technique in hydrogeological investigations in tropical basement areas of Africa and, in particular, southwestern Nigeria (Olayinka, 1988). The MRT technique is a multi- electrode resistivity array in which a small microprocessor is 22 UNIVERSITY OF IBADAN LIBRARY used to switch through the electrodes at different Wenner spacings and positions. This greatly simplifies the field operations, both in terms of the survey time and the manpower requirements. The layout of the MRT system is given in fig. 9, and the sequence of measurement of a pseudosection is presented in fig. 10 (Griffiths et al., 1990). One of the methods of deriving an initial interpretation involves averaging vertical sets of data to provide a summed profile from which dimensionless characteristics are subsequently measured. Another method is based on the estimation of the total longitudinal conductances of the weathered mantle from the vertical sets of data, and it is used with interactive computer graphics. The final step in the MRT interpretation consists of iterative two-dimensional computer modelling. Olayinka (1988) established that the accuracy of the Dey and Morrison's (1979) finite difference algorithm used for this purpose is affected by the resistivity contrast. Correction factors were subsequently determined. (1\ II I' i®- Ground Level C Pili IP C / ~""'l""""""""""~~""""""""""~~""""""""""I""""'~ a a a +--------+1+---------. +--------. a = Electrode spacing; I = Electnc current; tN= Potential difference; P = Potential electrode; C = Current electrode. Fig. 8: Typical field layout (Wenner) in electrical resistivity method. 23 UNIVERSITY OF IBADAN LIBRARY OAUM • SwrTCHING UNfT I 1 n[CTRODE Fig. 9: The Microprocessor-controlled Resistivity Traversing (MRT) System (after Griffiths et al., 1990). Stati, on 32 C1 3a P1 3a P2 3. C2I I I I Laptop H Station 18 Compute. C1 2a P1 2a P2 2a C2I I I I " Station 1 [ I I C1 P1 P2 C2 Electrode Number Oft t ft 1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 leuel -L~a~a~a~~~ __ L-~~-L-L~ __ L-L-~-L-L~~L-LJ n = 1 1 • n=2 18· n=3 n=4 43· n=5 51· n = 6 56· . Fig. 10: Sequence of measurements to build up a pseudosection (after Griffiths et al., 1990). Olayinka and Barker (1990a) described the versatility of the MRT system for siting water-supply boreholes with examples from several towns and villages in southwestern Nigeria (fig. 11). Deeply weathered sites and probable fracture zones, for which there are often no surface indications, and which can be missed altogether with conventional sounding techniques, were delineated. A study of the MRT results suggests a strong relationship between low-resistivity anomalies on the contoured MRT sections and productive boreholes. The MRT pseudo sections allow a visual appreciation of the structure of the subsurface not readily obtained with other geophysical techniques. The 24 UNIVERSITY OF IBADAN LIBRARY results suggest that the success of borehole drilling in Basement Complex areas is related to the identification of a sufficient thickness of regolith, a low clay content, and a high degree of saturation within the weathered zone, coupled with underlying fractured bedrock. In all of the productive boreholes, the depth to bedrock exceeds 15 m. A correlation of the surface-measured geoelectrical data with pumping test results suggests that for a weathered basement aquifer in this area to be water-yielding, its resistivity should lie within the range of 40 to 150 O-m. The most productive boreholes appear to penetrate regolith with a resistivity between 60 and 900-m. )OE ,. "E ~A'II,I¥I_ tAfTACEOl.5 1;::::::1 ~LQ:':1\:7.t:::;':!;-n tw:~'C. sl:ule,wr.~1 PRf-C.II!48Rr"", TO JPf:f.:;: ('~M.P.IJ.I ~lINIif1"~at ••tlr.etO"~IHh"'.1'\t f:-=-==:J OuortrjW DI>d't"U!z-.:I'Ii.t ,,. R;':~';~J=~).=:j~,~~!~r14~: i P(,l'lIh,roi:licstl(; ilWIU ~ ,•••• ·1 ~a:;I:~H==g:~~~i~:~ctr.t .. ''Itl'fl:/llote. Qmll"r~".!t. ,. o )-0 ... ..• _._.-. S~fl.I. oa"I'Idai"l' ,.. .. ,. ,.. Fig. 11: Geological map of parts of the Ilorin district (After Nigerian Geological Survey Agency). 25 UNIVERSITY OF IBADAN LIBRARY Some of the towns and villages where the MRT technique was used as part of a borehole siting programme are shown in fig. 12. .O! 5°E eO! .,°E IO"N aU••• IO"Wlu- N •••,•.J-•)•. NIGER N i f \ \ -ILOItIN \. OFI'A ~ tY"W .. l...!.!!~.".-O...o" --I.~J~ -IlOIIOV<"\OYO r r ' -.KAISA-S A E ,._('. oC,bftb-K4bbo 'C-OKENE 0 10 40 .c 10 100"11I. -'..•••.... '-. ! I ! I I I -'-'- SIIhI ••••d•et7 7"11 7"11 4"! lI"E rE .,.r. Fig. 12: Location map of some of the towns and villages where the MRT technique was tested. Our'work demonstrated the potential usefulness of the MRT imaging system to provide information from which the distribution of subsurface: resistivity in cross-section along a profile can be determined. The initial successes recorded in our pioneering studiesserved as the basis for multi-electrode resistivity arrays, a t{9hnique that is now used routinely in several parts of the y\0rld for hydrogeological, geotechnical and archaeOIOgiC~oses. _ / 26 UNIVERSITY OF IBADAN LIBRARY Group II: .Groundwater Resource Evaluation . Groundwater is an- important component of the earth's environment. The occurrence of groundwater in areas underlain by crystalline Basement Complex rocks is structurally-controlled, and· it is, therefore, amenable to investigation by geophysical techniques to furnish information on the geometry and hydrogeological characteristics of the aquifers. The object of such surveys include determination of depth to the hard, competent bedrock; indications of depth to water, extent of saturation and porosity of the regolith; location of steeply-dipping structures, such as faults and dykes; and mapping variations in overburden composition and bedrock lithology. A typical weathering profile developed upon crystalline Basement Complex rocks and variations in the hydraulic properties is shown in fig. 13. The electrical resistivity method is recognized as the most widely adopted approach on account of its cost effectiveness and ease of operation (Olayinka, 1998b). In particular, combined sounding/profiling surveys offer distinct advantages over the conventional methods in areas of complex geology. Efforts have been made towards developing simple methods to aid the interpretation of the apparent resistivity data. The emphasis of the research in this category has been how to improve on the content of information obtained from the use of geophysical surveying techniques (electrical soundings, multi-electrode resistivity profiling and electromagnetics) in routine surveys. Field evaluation has been conducted in several parts. of the Basement Complex terrain of Nigeria. Practical strategies to aid the improvement of the success rates of borehole drilling have been developed accordingly. 27 UNIVERSITY OF IBADAN LIBRARY HYDRAULIC PROPERTIES PROFILE DESCRIPTION I RELATIVE SCALES} ._. .. - $Qj""'hacpi'9D :lIltMrally l.a.than O.Srm-r--~ :~r-::~:~:'~.:_'-.~thi:ck~. ~C~lef,t.Yrai~l, :;0~rleiezl :lI:o,nody:i:M:i:l.:P:\~ig.hii~th:G:D:d~ ...•'-3~,0".. .•• . ," •••• forftla,ion of lo,.rit. W clI!cret •. Co 3 •• ';.-:-., TNckn"s varies up to 15m, ::..•. ...:•!.-.•~ - ~.20,",,,'9' (soil'C'zonel: hw '"thid: sanely .;r.:-;.::: etc.1 or clay sond,oUt'fI concretionary. ~ :::~~~~ - !:er.;~~I~\~O:!!Oo:.::~c:~;a:~;;(o 5.dlas),s} cr ~:--=••:•:!,.••.:';' ~ in •••••ich stobie primary minerall 11I0)' beUJ • 1- prul'nt in th.ir originol to"", :t: ,;\:._ •..i•. Low pltNMability ar'ld ~illh porosit)'. ~¥~}-~:';!·:~~~::;:t·::;":~:;i.~~:;;;:'~·:'1 o ,,:':0.:;:-- agar.9C1t~s ond rDc~ fr09f!'\t'nti. .. ~ " ....•. lntermedlct. porosity and perl!\eGbrloty. < W a: uz Fig. 13: Typical weathering profile developed upon crystalline basement rocks and variations in the hydraulic properties (adapted from Acworth, 1987; Chilton and Smith-Carington, 1984; Buckley and Zeil, 1984). A vertical section through the weathered profile developed above crystalline basement rocks in low-latitude regions comprises, from top to bottom, the soil layer, the saprolite (product of the in situ chemical weathering of the bedrock), the saprock (fractured bedrock) and the fresh bedrock (fig. 14). It is worth noting that the resistivity of the saprolite can be as low as 10 Q-m, especially when the regolith is rich in clay. The geoelectrical succession over a tropically-weathered regolith based on southwestern Nigerian conditions, is shown in table 5. 28 UNIVERSITY OF IBADAN LIBRARY RESISTIVITY } Collap •• d (OHH -HI f Zone 111IStone Imel 1.9.9.: .§Q.0_0 s C•:i. " }~,."'." }EGOLITH 10 -800e 0 '7 ------ 0 1 }.,,- '" WEATHEREBEDROCK 200 -1000------ FRESH BEDROCK > 2000 Fig, 14: Schematic weathered profile above crystalline basement rocks and the typical range of resistivity for each weathering grade Table 5, Geoelectrical Succession over a Tropically-weathered Regolith based on Sou thwes tern N'1gen,an Con dimtions Layer Thickness Resistivity Hydrogeological significance (m) (Q-m) I <5 <200 (wet) The residual soil. Up to 5000 Often forms lateritic cappings. Could be (dry) associated with deep weathering. 2 5-35 10-800 The saprolite zone. Often has a high clay content; good aquifers when permeable. 3 0-20 200-1000 The fractured basement sequence. Has low effective relative thickness, which makes its detection difficult fro surface geoelectrics. Often a transitional zone. Good aquifer when not too highly resistive 4 00 The semi-infinite bedrock. Poor aquifer unless when fractured. Olayinka (1990b) employed ground electromagnetic profiling, using a Geonics EM-34-3 instrument, to identify areas of high conductivity in parts of the Precambrian crystalline Basement Complex of southwestern Nigeria. The surveys, conducted as part of a rural water supply programme, indicate that the apparent conductivities are 29 UNIVERSITY OF IBADAN LIBRARY generally lower than about 60 mmho m-I. Subsequent borehole drilling suggests a good correlation between high EM34 anomalies, deep weathering and high well yield (> 1 1s I). On the other hand, boreholes sited on conductivity lows penetrated a thinner regolith with relatively lower yields. Olayinka (1990c) integrated electromagnetic profiling and resistivity soundings in ground-water investigations near Egbeda-Kabba (fig. 15). While the EM technique provided a rapid reconnaissance tool in identifying high conductivity anomalies thought to be due to deep weathering and/or bedrock fissuring, a quantitative interpretation of the sounding data indicated that the resistivity of the weathered zone varies over a wide range, from about 10 to 200 n -m, and that the overburden is generally less than 40 m thick (fig. 16). II t OKEHE o~ 101(11I Fig. 15: Orientation of geophysical traverses at the Egbeda-Kabba survey area (Inset: location of Egbeda-Kabba in relation to neighbouring towns). 30 UNIVERSITY OF IBADAN LIBRARY lEGEND ,U"'";' <0·";., I<';~=:::;' C__I.,., •• 'U;,.4f'." ••••...-:t:, •,...,.••••'...•.,••'k.e' •.••_t.~:;: - II ,,1M' ~ II _ e~ __ O ~-. (bl ~-Ie ,"" -":' e... •••.• ,;e.L 1I." ••• ".,i••. "' .. ~-.. ~•..,~ t., •...•.• ,•..u. ~ 11 ~--.-' • . 'I.''''G • , •• , ••• Fig. 16: Interpreted geological sequences along selected profiles at Egbeda- Kabba. A similar approach was adopted for groundwater exploration in Igbeti, southwestern Nigeria (Olayinka et al., 2004). The bedrock geology comprises a suite of metasediments, gneisses and intrusive granites (fig. 17). The three main targets for groundwater in the locality consist of the weathered zone, the fractured zone and vertical dykes. The fractured gneiss sequence was inferred from the YES data as relatively low model resistivity at less than 1500 n -m for the geoelectric basement. The vertical dykes were inferred from the large separation between the horizontal and vertical dipoles on the EM conductivity profiles, coupled with negative readings on the vertical dipole curves. The boreholes drilled, based on results of the geophysical surveys, penetrated a sequence of topsoil/laterite, moderately weathered granite, fractured gneisses and fresh bedrock (fig. 18). 31 UNIVERSITY OF IBADAN LIBRARY · . . .1:.:.:.'",,":">:.:. ~": .: tN ~~~~~t>J:C=~E....!!....!!....!!.~~~==~~~ •••.• [] ""_P'f"bol", Set •.•. ' ••• .1.••••• b ••••.••.•e• fa ...•.•C.••t. gron •• " ~"e.SS ~ C;abbo-o and o ..•• rl& gobbrv.O" .•. "" gGlu>ro ~ Hor"t-I.nd ·b.otll~ gr •• ut" 83 C.ar_ pl>rph,.r.l.c tIlG"'. OI'OC'b •• ht •• t'lo,. •• tIol~...:I'" !!t' •••••• ,. ~ PO"."')i',..blo ••. c ••••••• ~ (h.G"'" &,U'5c •~•••~d .~S.h.~ar :tZ..ne.IeI"'. 'Iuarf.lle.n. D 4r •••. te S""· ••~ ~~:;,·t:t~~ ho,.•• H_6& •••• 5. ~ •..a.nl. ?L- "''ikm Fig. 17: Geological map of Igbeti area. 32 UNIVERSITY OF IBADAN LIBRARY _25,,.------- ---------. ..!1. W VES2 BH2 E' !20' -?,;: .~158.. 1 C :! :"::5 - YES 1 t- s •••• of= 60:::> z0 0o 40 t- Z UJ UJ UJ «0:: 20 o, o, 0 200 400 600 800 1000 30 10.0 Source: Olaymka et al. 1997 36 UNIVERSITY OF IBADAN LIBRARY Table 7.Aiuui.£er Poten tiIal asa Func fIon 0fS anro linte Resi.s tiIVilttV Saprolite Aquifer characteristics Weighting resistivity (O-m) <20 Clayey; limited aquifer potential 7.5 20-100 Optimum weathering and 10.0 groundwater potential 100-150 Medium aquifer conditions and 7.5 potential 150-300 Limited weathering and poor 5.0 potential >300 Negligible potential 2.5 Source: Modified after Wright, 1992 Table 8. Aquifer Potential as a Function of the Fractured Bedrock Resistivity Saprock Aquifer characteristics Weighting resistivity (.Q-m) <750 High fracture permeability as a 10.0 result of weathering; high aquifer potential. 750-1500 Reduced influence of weathering; 7.5 medium aquifer potential. 1500-3000 Fairly low effect of weathering; 5.0 low aquifer potential. >3000 Little or no weathering of the 2.5 bedrock; negligible aquifer potential. Source: Olayinka et al. 1997 The geometric mean of the weighting from the three geoelectrical parameters varies between 3 and 9, with the modal class being 5 to 6. Weighted means less than 5 indicate low aquifer potential which can only support hand pumps. Weighted means between 5 and 7 represent medium aquifer potential and can support surface pumps. The weighted means higher than -7 are indicative of areas with high aquifer potential and can support submersible pumps. Okurumeh and Olayinka (1998) employed radial YES in the Okeho area to determine electrical anisotropy and map the trend of concealed structures (fig. 22). The results indicate that the concealed bedrock is anisotropic with the causative 37 UNIVERSITY OF IBADAN LIBRARY structural features compnsmg joints, foliations and faults. Dual structural trends were observed at some of the radial YES locations, and they were interpreted as the intersection of structural elements at depth (figs. 23 and 24). The coefficient of anisotropy varies from 1.02 to 1.54, with a mean of 1.21. The bedrock model resistivity shows an inverse relationship with the coefficient of anisotropy, and localities with low bedrock model resistivity may indicate a fractured zone which could favour groundwater storage. This is also true of sites 'with dual structural trends as the interconnected structures should aid groundwater movement. This study has shown that radial YES could complement surface geologic mapping and remotely sensed data in structural analysis of concealed basement structures. 24' . ·,·Nt·· I ~ '/ ••••.•1<. .. I / >: '" I LEGEND Strike and dip x Porphyritic granite /I of foliation »:>; Syenite . --F Fault ~ Buut-up.are a :'f Amphibole schist 'r . . Gneiss and schist (6) Radial VES~ ~ ~ Road Fig. 22: Geological map of Okeho area showing the position of radial soundings (after Okurumeh and Olayinka, 1998). 38 UNIVERSITY OF IBADAN LIBRARY o· 0" N N~ totion 01 / / Stotion as S-la-lio-n-06 HY tation 07 Station 08 Station 09 --- Sounding ~,.otj r'Q·.I Appcrc"lrui$.lio 10". cont01lrr'n..: LJ ;:.SCALE 0" PAOf1LE Fig. 23: Apparent resistivity polar diagrams for the respective radial YES stations at Okeho (After Okurumeh and Olayinka, 1998). 39 UNIVERSITY OF IBADAN LIBRARY J020'E 21 2. 80•."-I-.,.......,,-l.....,----2.2..l-r::o;~--L-r_ ••.•-.._.j N t WWI.tl. §s,rike .nddlpr : 01 foliationFauh r:::l 8u Ilf.~-a; reaShuc1uraltrend" (inferred) ~ Road. - Senile , Fig. 24: Superposition of the inferred structural trends on the solid geology at Okeho (After Okurumeh and Olayinka, 1998). Due to poor planning, most urban centres and metropolis in Nigeria do not have adequate and reliable public water supply schemes for domestic use. In an attempt to ameliorate this, an alternative is sought in the drilling of boreholes. However, the decision to drill a borehole is not made until the completion of building construction with most facilities, such as underground cables, pipes, septic tanks, and concrete surfaces, already in place. It then becomes very difficult to be able to conduct geophysical survey without extensive noise interference. Ironically, the lack of space often restricts the usefulness of surface geophysical techniques. It is recommended here that private housing developers, including individuals, should conduct surface geophysical surveys to decide on the best location for borehole sites on their property before the commencement of actual construction of other structures. Due to the irregular nature of the bedrock topography and the unpredictability of the nature of regolith materials, Olayinka (1998b) proposed that the separation between adjacent sounding centres should not exceed 100 m. This would permit an adequate sampling of the subsurface. 40 UNIVERSITY OF IBADAN LIBRARY Group III: I-D Inversion of Resistivity Sounding Data It is only through model studies, involving synthetic data in which the true solutions are known, that a realistic meaningful assessment of resistivity inversion schemes can be conducted. Consequent upon this, the investigations that we have carried out have relied greatly on synthetic data. The limitations of each scheme were evaluated in defining the geometry and true resistivity. The applicability of the inversion schemes was tested with real data from . southwestern Nigeria. Quantitative Assessment of Geoelectrical Suppression It was, hitherto, assumed that geoelectrical suppression should not constitute a major limitation in resistivity interpretation since the effect of the intermediate layer was expected to be incorporated into the adjacent layers. Using computer models, it has been shown that this may not always be the case, and consequently, if the possibility of suppression is overlooked, it could constitute a major source of mistie between inversion results and the true subsurface condition. The factors influencing geoelectrical suppression of the penultimate layer in a four-layer HA-type curve (PlP3P2A Fig. 29: MRT survey, Agbamu, southwestern Nigeria. (a) measured pseudosection (b) longitudinal conductance profile (c) initial model (d) final model (e) computed pseudosection. The values inside the plots are resistivities in O-m. (After Olayinka and Barker, 1990b). Olayinka (1991b) described how averaging vertical sets of Wenner pseudosection data, 'beneath' a sampling station to produce a summed profile, can aid in deriving a fast interpretation. We have also shown that the lateral variation index could be useful in inferring the probable positions of shallow and vertical (or near-vertical) contacts (Griffiths et aI., 1990)_ Non-uniqueness and Equivalence in 2-D Imaging and Modelling It is widely appreciated that the interpretation of geophysical data is hardly unique with more than one geologic model fitting the same set of field observations. Olayinka (1991a) 51 UNIVERSITY OF IBADAN LIBRARY and Olayinka (2000) investigated the possibility for geoelectrical equivalence in the 2-D inversion of apparent resistivity data. This involved the calculation of synthetic pseudosection data for simple geological structures, using a finite difference approach (Dey and Morrison, 1979). With the aid of statistical F-test, it has been shown that identical or near-identical pseudosections can be generated from more than one 2-D model. In particular, the apparent resistivity pseudosection measured over 2-D structures, like basement fault, trough and horst resemble those arising from lateral variations in overburden resistivity. An example for the dipole dipole array is shown in fig. 30 for a model with two vertical contacts in which the resistivity at the centre is 50 Q-m, while, at the flanks the resistivity is much higher at 200 Q-m. There is a low resistivity structure flanked by highs at shallow depths of the pseudosection. However, at depth, there is a resistivity high at the position of the low resistivity structure, flanked by highs. The highest apparent resistivities are of the order of 1000 Q-m, which is about one-third of the true bedrock resistivity. A similar pseudo section (fig. 30) was calculated for a basement trough structure in which the depth to the bottom of the trough is 27 m, while at the upthrown block the depth to the interface is 4.6 m. The F-ratio between the two pseudosections is 1.054, which is not statistically significant at the 95% confidence interval. 52 UNIVERSITY OF IBADAN LIBRARY (a) X(m) 0 40 80 120 160 200 240 280 320 360 400 440 480 520 I :[ E~ 200 On; I50 omI ! I 200m~:;Q.GO 3000 0 mQ i (b) :[Oo;-4~0 ~8~0~=120==16=0 =20=0=2=40~2=80=~32=0 =36~0=4=00==440==48=0a = 5~20==~~~==~ 20 GO " 40 -og 60 GO ~ 80~----------------~ Dipole length = 20 m (e) 40 80 120 160 200 240 280 320 360 400 440' 480 520 I I I I I I I I I I I :[ 2glO ~ .QI::.. 40 ~ 60 3000 Om I 80 ~---------------------------------------------- (d) F-ratio = 1.054 40 80 120 160 200 240 280 320 360 400 440 480 520 10 14 21 31 45 66 97 142 209 307 450 660 Fig. 30: Illustration of 2-D equivalence (a) 2-D model with lateral variation in overburden resistivity; (b) dipole dipole apparent resistivity pseudosection data calculated from the model in (a); (c) 2-D model representing a trough structure; (d) dipole dipole apparent resistivity pseudosection data calculated from the model in (c). Olayinka and Weller (1997) presented a methodology for the inversion of 2-D geoelectrical data for solving hydrogeological problems in crystalline basement areas. _The initial step entails compiling an earth model, using all available geological, borehole and geophysical information. This model served as the input to an algorithm based on the 53 UNIVERSITY OF IBADAN LIBRARY Simultaneous Iterative Reconstruction Technique (SIRT). The algorithm tries to find a model that is as dose as possible to the starting model. To demonstrate the usefulness of this procedure, several field examples, conducted as part of a borehole siting programme, were given. Borehole information regarding the thickness of the weathered zone overlying a gneissic bedrock was used to constrain the 1-D inversion of sounding data (fig. 31), and the model thus compiled was used as the starting model for 2-D inversion. The results indicated that if the starting model had incorporated all the available information as constraints, it is generally possible to compute a model that not only fits the measured data but is also a good approximation of the subsurface geology, more so when many 2-D models can fit the same set of field measurements on account of the limitations posed by equivalence. res Location: u layared pralie rtJ: VES38 Dep1tI RHO RHQ.Sit ()1mom ram i~Ohm'm 10' R' R' w' 'j 10.1 I I I I - me_rod v81ues228 I --- caJcuiaIed values 1.0 to· ___ LI ~• ----- 619 I II I 3.5 I I I I ___ . ...1I , I _ 110 I I I I 42.3 I I _____IL II I _ focal 10' I I a I I inm I Fig, 31: I-D interpretation of a YES curve from Agbamu used as starting model for inversion of the 2-D data. (After Olayinka and Weller, 1997). 54 , . UNIVERSITY OF IBADAN LIBRARY Choice of the Best Model in 2-D Geoelectrical Imaging The conventional approach in the inversion of vertical electrical sounding data is to accept the model which gives the minimum data rms misfit between the field and calculated data in the forward model. The model rms misfit was never considered in this approach. However, Simms and Morgan (1992) showed that the data rms misfit and the model rms misfit are not always simultaneously minimized in the 1-D inversion of vertical electrical sounding data. While the data rms misfit is a measure of the fit between the field data and the calculated data, the model rms misfit is a measure of the fit between the inverted model parameters and the known synthetic model. Olayinka and Yaramanci (2000a) investigated the reliability of inversion of apparent resistivity pseudosection data in order to accurately determine the true resistivity distribution over 2-D structures, using a common inversion scheme based on a smoothness-constrained non-linear least- squares optimization, for the Wenner array (Loke and Barker, 1996). This involved calculation of synthetic apparent resistivity pseudo section data, which were then inverted, and the model estimated from the inversion was compared with the original 2-D model. Over vertical structures, the resistivity models obtained from inversion are usually much sharper than the measured data. However, the inverted resistivities can be smaller than the lowest or greater than the highest true model resistivity. The data rms misfit always converges towards a limiting value representing the amount of noise in the data. However, the substantial reduction generally recorded in the data misfit is not always accompanied by any noticeable reduction in the model misfit. The response of the model rms misfit can be grouped into three classes (fig. 32). Firstly, as would be expected theoretically, the model rms misfit could decrease in response to a decrease in the data rms misfit for successive iterations. The diagonal line with a negative slope would then be applicable. This simultaneous minimization of 55 UNIVERSITY OF IBADAN LIBRARY the data rms misfit and the model rms misfit would yield an optimum model at a high iteration number as the outcome of the inversion procedure, and it is referred to as the 'ideal' behavior. Both the data rms misfit and the model rms misfit are very low in the optimum model. This situation arises at very low resistivity contrasts. Secondly, there are instances in which the model rms misfit remains, for all practical purposes, invariant. The plot of the Mrrns against the iteration number is represented by a horizontal line, and it is referred to as 'non-unique' behavior. None of the inverted models for the respective iteration numbers represents the true solution uniquely. The inverted model at any iteration step can be considered as good as that at any other iteration, since each and all of them have roughly the same model rrns misfit in spite of large differences in the .data rms misfit. Thirdly, there could be an increase in the model rms misfit for successive iterations. As the data rms misfit is being minimized for successive iterations, the model rms misfit is being maximized. This is represented by the diagonal line with a positive slope on the diagram. This is referred to as 'anti-ideal' behavior, and is often encountered at very large resistivity contrasts. This pattern would inadvertently lead to the attainment of the most sub-optimal model since the supposedly 'worst' model for which the Drrns is a maximum is, in fact, the 'best' model by virtue of having the lowest Mrrns• This would have grave implications when working with field data in which it is generally impossible to calculate the model rms misfit, and the best model is often taken as that for which the data rms misfit is the least. There are several modifications of these three basic patterns. In particular, there are instances where the model rms misfit begins by converging as the number of iteration increases only to start diverging at a high iteration number. 56 UNIVERSITY OF IBADAN LIBRARY T , II-- III> i;:'E III'E 'E" ... - - - -no-n--un-iqu!Oi;) -e - - - E "C Vo "C .~ E"C 'iii E .~ (5 'iii z E•.. , zo Iterationumber- Fig. 32: Variation in the data nns misfit (solid curve) and the model rms misfit (discontinuous curve) during the 2-D inversion of apparent resistivity data. The misfits are normalized with respect to the value at the first iteration. (After Olayinka and Yaramanci, 2000a). A case history to demonstrate the application of this approach was described from a waste dump site in Ibadan (Olayinka and Yaramanci, 1999). The solid geology comprises quartzite and quartz-schist that .have been extensively weathered and fractured (fig. 33). Inversion of the Wenner pseudosection data indicates that the model bedrock resistivities at about the second iteration are geologically realistic. The thickness of the waste dump varies from about 2 to 17 m, while its resistivity is low and lies between 4 to 8 11- m. The low resistivity is due to the presence of leachate emanating from the site, and this has also polluted the surface and ground waters in the immediate vicinity. It is concluded that geoelectric imaging, with appropriate geologic constraints, provided a realistic subsurface image for the noisy environment of the waste dump (fig. 34j. 57 UNIVERSITY OF IBADAN LIBRARY DUQb. +--;. L..E..G..E.HIl. .t--;. Wasl. Dump L.!:.L T"ven:. and electro!!e f;otilion • Wat~' sampling point .,. VES point oL-...J...--1I00 III (b) sw p LI LS Om + "-----.p5NE' :Soil cover + + R : Refuse (+Ieachate) + + ++ SP : Saprolite + + + we; W.atheredlfraetured 35mL:+~!::;:;:===::::.__ +!..._..:W::.:B_~+_+::"'':+b:oJdroci< Vertical uaggeration x3.4 Fig. 33: Enlarged map of the Ibadan Ring Road Refuse Dump Site (now inactive), showing (a) orientation of geoelectrical traverses and position of water sampling points. The edge of the polluted zone has been inferred from the geoelectrical imaging results, supplemented with hydrochemical data; (b) A SW-NE vertical cross-section across the study area. The positions of the resistivity traverse lines are indicated (after Olayinka and Yaramanci, 1999). 58 UNIVERSITY OF IBADAN LIBRARY NW X[m] SE (a) 0 50 100 L5 150 200 .§.1 sii:. 20 C•• 30 + + + + 0 50 100 150 200 L4(b) 0 ~ 10 '-60 nn 209 'n. -. + + ~ 20 wealhe red bedrock C•• 3 + + (quarlz schisl) + (c) a 50 100 150 200 250 300 l3 0 E. 010 + weathered bedrockt 20 + ++ 209 Qn (quart> schist] ~ 3C + + + + + + (d) l2 0 50 IDa 150 200 250 300 350 0 E. o San 0 010 0 + ~ 20 + 209 Qn + (quartz schist] ~ 30 + + + + + + + (e) 150 200 250 300 L1 ~, 0 refuse 0 209 Qn + + + ~2 + +wealhered bedrock .; 30 + + + + + (quartz schist) + Fig. 34: Integrated interpretation and geologic model of the resistivity images at the Ibadan Ring Road Waste, Dump Site (After OIayinka and Yaramanci, 1999). Use of Block Inversion in the 2-D Interpretation of Apparent Resistivity Data and Comparison with Smooth Inversion Studies conducted on smooth inversion of apparent resistivity pseudosection data have shown that such schemes can only 59 UNIVERSITY OF IBADAN LIBRARY provide an approximate guide of the true geometry of the subsurface. While this information is generally adequate for most hydrogeological and environmental investigations, it is often unsatisfactory in petrophysical evaluation where a more representative value of the true formation resistivity is generally desired. The largest model misfit is encountered in the zone immediately above and below a contact. The foregoing suggests that a block-type (or sharp boundary) inversion, in which polygons are used to define layers and/or bodies of equal resistivity, might be more suitable in determining the geometry and true resistivity of subsurface structures, especially as any a priori information can be introduced (Olayinka and Yaramanci, 2000b). An example of a smooth 2-D inversion algorithm is RES2DINV by Loke and Barker (1996), while the program RESIX IP2DI by Interpex (1996) is representative of a block inversion scheme. The study involved calculation, by forward modelling, of the synthetic data over 2-D geologic models and inversion of the data. The 2-D structures modelled include vertical fault, graben and horst, which are of significance in areas underlain by crystalline basement rocks. The results indicate that the images obtained from smooth inversion are very useful in determining' the geometry. However, they can only provide guides to the true resistivity because of the smearing effects. However" in the presence of sharp, rather than gradational, resistivity discontinuities, the model from block inversion more adequately represents the true subsurface geology, in terms of both the geometry and the formation resistivity. We devised a simple technique, based on a plane layer earth model, for deriving the initial model (Olayinka and Yaramanci, 2000b) (fig. 35). 60 UNIVERSITY OF IBADAN LIBRARY (a) -40 XJA XJA D =5%-20 o 20 40 (b) -40 -20 0 20nnso 40o 4 «2 ~ B N4 12 6 16-L-----' ~.~.!II~~~~ p [om) (e) 61 90 132 418 613 Drms = 102% Iteration3 « ~:~~~~~~~~~;;~~ N 4 (e) 6-L~~~~+~~3:2...:.....j OI~~~~~~~~~~~T N« 2:~=-=-=-=-~~~~~~~4 6~ __ •• ~~~~~~~~ (9) o·~~~~~~~~~~~-r -Nc 42ji===-=-=-=-~=---.- •••"•.•..,,=t6~ .:~~ __ ...:.....~~ (I) O~~~~~~~~~~~+ « 2 N :1:===:J!~mr;~==i m) O~~~~~~~~~~~+ 2 ~ :F=-=-=- __ jjjjii••••"•""'~i=='t B Fig. 35: (a) Synthetic pseudosection data calculated for a vertical fault structure, buried by a single overburden unit, with 5% Gaussian noise added. (b) resistivity image obtained from the smooth inversion algorithm. From (c) to (n), the left hand panel is the starting model used as input for block inversion while the right-hand panel is the inverted model (After Olayinka and Yaramanci,2000b). Field examples from a crystalline Basement Complex area of Nigeria were used to demonstrate the versatility of the two resistivity inversion schemes (fig. 36). The test data have shown that the block inversion method gives very good results if the actual subsurface consists of two homogeneous regions with a sharp interface and if the starting depth of the two-layer model is reasonably accurate. If the subsurface is 61 UNIVERSITY OF IBADAN LIBRARY more complicated with several regions, or if the starting depth is too shallow or too deep, the results can be unstable. We have shown that, in such cases, the depth of the interface of the lower resistive layer in the inverted model begins to undulate, as if a type of ringing occurs. Beard and Morgan (1991) and Oldenburg and Li (1999) also described such unusual inversion effects at the edge of 2-D structures. These weaknesses can be easily overcome by a combined use of a cell-based inversion method and the block inversion method. The cell-based inversion will at least give a rough idea of the bedrock depth, which will, prevent the starting depth in the block inversion to be too shallow or too deep, particularly with field data. The cell-based inversion model can also warn the user if the subsurface is more complex than the two regions model. The different inversion methods described can be viewed as complementary tools that an interpreter can employ to obtain the most consistent and reasonable results for a given data set. UNIVERSITY OF IBADAN LIBRARY X[m] X[m) Drms=12% SE (a) 100 200 300 (b) 0 100 200 300 o E 10 ;;; 20 (e) Ol1$.~~~~~~~ ;E;:10;£~~~~~~~~~~~~ I(e) D = 204% 1~lF~~;;~rms;;;;~;;~~~~ N:~======================:t (g) I1O0~~~--~~--~--~~~-r N20~~--------------------~ (I) Drms = 403% 4 Om Drms =482% ',,"~ f! ·-""'~~~i .. , '\:.~..L- 114 nrn ~ -.1'-. From (b) to (I) the vertical exaggeration = X3 Fig. 36: lnrc: prctauun of Wenner pseudosection data (line 3) from the Ibadan Ring Road Waste Dump. (a) Measured data. (b) model from smooth inversion. From (c) to (I), the left-hand panel is the initial model for block inversion while the right-hand panel is the respective inverted model (After Olayinka and Yaramanci, 2000b). Smooth and sharp-boundary inversion of 2-D pseudo- section data in the presence of a decrease in resistivity with depth Situations often arise in environmental, engineering and hydrogeological investigations in which there is a decrease in resistivity with depth. Olayinka and Yaramanci (2002) examined the performance of smooth and sharp-boundary inversion schemes in such cases by considen..g synthetic data over 2-D geologic models such as vertical fault, graben and 63 UNIVERS TY OF IBADAN LIBRARY horst. It was demonstrated that the starting model could be based on a plane layer earth model, which has the added advantage that only the depth to the interface(s) need be varied as the inversion result is for all practical purposes not dependent on the resistivity contrast in the starting model. Fortunately, the data rms misfit between the calculated and the synthetic 'observed' data is very diagnostic in identifying a reasonable interpretation. The bad inverted models are invariably attained after a very few iterations and accompanied by a high data misfit. On the other hand, the good models are attained after many iterations with much lower data misfit. With this interpretation procedure, it has been shown that the range of 2-D equivalence is very narrow for the case in which there is a decrease in resistivity with depth (figs. 37 and 38). 64 UNIVERSITY OF IBADAN LIBRARY XolA XloA Dnn5 =5%·20 20 . ·20 20 40 ..... (e) o~Drms = 38~ •...4. .: ",2 i'l4 wnm 6 ---! (e) Drms = 208% '" o2-~18'11 1ariR•• -=t. i'l4 6L- 50 Om ~ (9) Drm, = 192% .: •• EE:!j i'l4 6L- w__n_m ~ (i) Drms = 221% o~~~~~~~~~~ i",'2l4~~~~~~~~~~~ 6L-__~--~~~------~ (k) Drm,.= 281'/. o ",",42 6L- ~~ ~ m) o ~2 : 8 Fig. 37: Interpretation of dati!' over a vertical fault model. (a) Synthetic apparent resistivity pseudosection data containing 5% Gaussian noise; (b) Model obtained from smooth inversion; From (c) to (n), the left-hand panels are the initial models for sharp-boundary algorithm, while the right-hand panels are the corresponding inverted models. A is the minimum Wenner spacing (After Olayinka and Yaramanci (2002). 65 UNIVERSITY OF IBADAN LIBRARY (a) X1A (b) X1AIteration 1 Mmean = -31+118% -40 -30 -20 -10 o 10 20 30 40 -40 -30 ""-20 -10 o 10 20 30 40 o o N«24 N«42 6 "'--_-"-- 6 "--_""""'- (e) Iteration 2 (d) M mean = -26+/!.9% -40 -30 -20 -40 -20 o 20 40 «~ ~-iiii o N4 «N24 61...._..b~!:: 6~_..-S!-..:::.....J"'" «(e)-N4~It40 ~eration 3-30"-20"-"10 "o"1"0 i2•0 i••• (f) 30 -30 -20 -10 0 rt 6.1-_-.:!::=~~ (9) (h) Iteration 4 Mmean ::;-:21+'[4% -40 -30 -20 -10 0 -40 -30 -20 -10 0 10 20 30 40 o ~~~~~~ o N«42 N«24 6 6 -38 ·13 1e so Mmis 1%] Fig. 38: Inverted model (the left-hand panels) at various iteration steps in the smooth inversion of the data in fig. 35 and the corresponding model misfit (the right-hand panels) (After Olayinka and Yaramanci, 2002). A field example is given.from Nauen, northern Germany, where partly-saturated sand of high resistivity in the vadose zone (4000 O-m) is underlain in succession by less resistive saturated sand (150 O-m), which in turn is underlain by glacial till (100 O-m). The smooth and sharp-boundary inversion results are in agreement with the geo-radar and surface magnetic nuclear resonance (SNMR) and borehole information (figs. 39 to 42). 66 UNIVERSITY OF IBADAN LIBRARY !!"OO'E IO"OO'E 5!5'"OO'N !e'OO'E~·oo'N N ~'N S3"OO'N .~ f 51-00'/11 51"OO'N 2:1OfCm. ! Fig, 39: Sketch map showing the location of study area in northern Germany. X[m) o 50 100 150 200 o E 8 -;;;-16 24 Fig. 40:Ja) Measured pseudosection data at Nauen test site, northern Germany; (b) Smooth inversion resistivity model (After Olayinka and Yaramanci, 2002). 67 UNIVERSITY OF IBADAN LIBRARY Fig. 41: Model obtained from the sharp-boundary inversion of the measured pseudosection data at Nauen. The left-hand panels are the initial models prescribed by the interpreter while the right-hand panels are the corresponding inverted 2-D models. Note that the data rms misfit stays practically the same in all the equivalent model interpretations. (After Olayinka and Yaramanci, 2002). 68 UNIVERSITY OF IBADAN LIBRARY OIST "'NCE 1m} Fig. 42: Geo-radar section from the same traverse as the electrical image line from Nauen (After Olayinka and Yaramanci, 2002). Group V: Groundwater Occurrence in Ibadan Metropolis Groundwater Availability The provision of water for domestic and other uses in both rural and urban centers is one of the most intractable problems in Nigeria today. In recent times, the inadequacy of the pipe-borne water supply system in the country, generally, and Ibadan metropolis, in particular, coupled with the need to improve the supply and quality of potable water in these areas, has led to the increase in the construction and drilling of boreholes. Ibadan, located in the southwestern part of Nigeria, is the largest pre-colonial city in Nigeria and sub- Saharan Africa, with a total area of about 540 km2 and an estimated population of about 3.5 million in 2007. Nearly all houses in the medium and low density residential areas of Ibadan now have either large-diameter dug wells or boreholes. Ibadan metropolis is underlain by quartzites of the metasedimentary series and the migmatites complex comprising banded gneisses, augen gneisses and migmatites with minor intrusions of pegmatites, quartz, aplite, diorites and amphibolites (fig. 43). The low porosity and "negligible permeability of these crystalline basement rocks do not 69 UNIVERSITY OF IBADAN LIBRARY completely rule out the possibility of the presence of localized and productive aquifers from the saprolite and the saprock, if proper exploratory work is carried out. 46' (/l\ 7 0 7 Kilometers .~ r---~I~~~~~~~I~~~~~~~I----------, EXPLANATION [==:J Pegmatite & quartz vein iIlii Amphiboltte .i=ffiiii1 Quartztte quartz schist -- Geological boundary. r?~ Granite gneiss -L strike & dip. Migmatite & Banded gneiss Fault. _ Undifferentiated gneiss complex • Settlement.· Fig. 43: Geological Map of Ibadan and environs (After Okunlola et al., 2009). 70 UNIVERSITY OF IBADAN LIBRARY In an ongoing research, we have conducted about 516 Schlumberger YES in various parts of Ibadan metropolis to characterize the aquifer properties and groundwater potential. The survey locations cover the different rock types (fig. 44) (Oladunjoye and Olayinka, 2010). The data obtained were processed, using a 1-D algorithm to generate geo-electric parameters (table 9). ~~5iiOi __ ~~~~""""'I8 Kilometers LEGEND VESPoints Raitway Duel c:arriage way River Major rood Darn Fig. 44: Map of Ibadan metropolis showing YES locations. 71 UNIVERSITY OF IBADAN LIBRARY Table 9. Computer interpretation of representative YES,curves from Ibadan for different groundwater potential zones Loca-tion Layer Resistivity Layer Thickness (m) Depth to Ground-water (n-m) geoelectric potential basement (m) I 2 3 4 I 2 3 Oke-badan 171 122 41 191 1.1 5.7 23.4 30.1 High Estate Odo-Ona 204 58 527 1.9 12.4 14.1 Intermediate Elewe Ojoo 450 61 1440 1.0 3.6 4.6 Low 72 UNIVERSITY OF IBADAN LIBRARY Examples of YES curves from Ibadan are presented in fig. 45. From an analysis of the results of this extensive investigation, we have divided the study area into four groundwater potential zones, namely: high, medium, low and poor, respectively (fig. 46). The high groundwater potential zones tend to correlate with mostly the quartzite and quartz schist while the low groundwater potential zones were recorded in areas with very shallow overburden without evidence of basement fractures in the gneisses. However, field examples from geophysical data and borehole drilling report have shown that in areas delineated as low and poor groundwater potential yields, it is still possible to isolate localized anomalies, such as linear fractures, if detailed investigation is carried out. r~l 1. , "?>: ' • ~ ~CC: ~ .• _ •....•.• --- - .,.. - '" ci n "" 10+--~~;'-"-'~~f--,-~,..,....,.,j < 10 I 10 100 1000 I 10 100 1000 ABI~mJ - ABl2[m] (a) (b) fooO t .. ]e; • :; '.- . ~ 100 -- ------+----1 ]i c: c ~a. a. < 10 +__~~+__~~+__~~ 1 10 100 1000 AB/2[m] (c) Fig. 45: Representative YES curves from Ibadan. (a) Okebadan Estate (b) Odo- Ona Elewe (c) Ojoo. 73 UNIVERSITY OF IBADAN LIBRARY E 8 o Fig. 46: Map of Ibadan metropolis showing the groundwater zones. II represents high groundwater potential; 1\\ represents medium groundwater potential while L represents low groundwater potential. 74 UNIVERSITY OF IBADAN LIBRARY The groundwater potential will impact the choice of residential accommodation since a prospective tenant! occupier of a housing unit would be interested in the availability of water supply through borehole or dug well since the public water supply is generally unreliable (Olatubara, 2008) Aspects of Groundwater Quality An integrated study, involving geologic mapping, hydro- chemistry and electrical geophysics, was carried out in Ibadan to characterize the groundwater in a typical low-latitude environment underlain by Precambrian crystalline basement complex rocks (Olayinka et al., 1999). The water sampling points are shown in fig. 47. Chemical analyses of the groundwater show that the mean concentration of the cations is in the order Na+>Ca2+>Mg2+>K+,while that of the anions is Ci>HC0"3>N03>S02-4. Five different groundwater groups were identified in the metropolis, namely: (i) the Na-Cl, Na- Ca-CI, Na-Ca-(Mg)-Cl, (ii) the Ca-(Mg)-Na-HC03-Cl, Na- Ca-HC03-CI and Ca-HC03-CI; (iii) the Ca-(Mg)-Na-HC03, Ca-Na-HC03, (iv) the Ca-Na-CI-(S04)-HC03 and (v) the Ca- (Mg)-Na-S04-HC03. The respective groups reflect the diversity of bedrock types and consequently, of the products of weathering. Most of the water samples were unfit for drinking on account of the high N03-content. 75 UNIVERSITY OF IBADAN LIBRARY 7" 24' N Sample Location o R...uw.y / Road Built lip Area Fig. 47: Location map of Ibadan study area, showing the water sampling point (inset: Generalized map of Nigeria) (After Olayinka et al., 1999). The piezometric surface map prepared from the static water level values is presented in fig. 48. This can aid an understanding of the subsurface flow trend. Ground water flows from higher energy levels towards lower energy environments provided the energy is essentially the result of elevation and pressure (Davis and DeWiest, 1966). Accordingly, the groundwater elevation in the study area controls the direction and mode of the subsurface flow. That is, flow is generally from regions of increasing head to that of 76 UNIVERSITY OF IBADAN LIBRARY decreasing head. The entire area is dominated by a series of gently and steeply undulating rises and falls in the water level elevation. Since the subsurface flow direction is usually from the rises to the falls, the domes would be expected to act as points of recharge, while the basins are principally the discharge points. These suggest that the subsurface environment in the northeastern part has the highest potential for groundwater. Fig. 48: Piezometric-surface map of Ibadan metropolis. Values inside the plot are in metres above the mean sea level (After Olayinka et al., 1999). Group VI: Environmental Geophysics The knowledge obtained from the research in 2-D geo- electrical modeling and imaging has been applied to solving some problems related to the environment, notably those concerning waste disposal and groundwater occurrence and utilization. 77 UNIVERSITY OF IBADAN LIBRARY Geoelectric Imaging at an Abandoned Dump Site A geoelectrical imaging of an abandoned waste dump site (Orita Aperin) in Ibadan was carried out with the aim of determining how accurately surface electrical measurements could delineate the influx of leachate into groundwater and nearby surface water. The imaging is expected to reveal the heterogeneous material compositions as well as the attendant complex biogeomorphic processes in a landfillldumpsite environment. Eight electrical imaging lines were measured, using the Wenner Array and a Campus Tigre meter was employed for resistance measurements (fig. 49). The minimum electrode spacing was 5 m, and the maximum 30 m. Four traverses (T 1 - T4) were measured directly on the waste dumpsite with T2 being the longest at 140 m. Two traverses T5 and T6 were measured at the lower elevation of the dump site to ascertain the ingress of the leachate towards the lower side of the dump site. Traverse seven (T7) and eight (T8) was made at a primary school on the western side about 300 m from the waste dump site to serve as a control for the former data sets. To obtain the true two-dimensional distribution of soil resistivity, the apparent resistivity data were inverted using the program RES2DINV. The results of the inversion delineated regions of low resistivity (less than 20 n-m) believed to be leachates derived from decomposed waste for image lines conducted on the abandoned waste (fig. 50). On the other hand, the 2-D models obtained for the control lines (fig. 51) are a reflection of the lateral variations in the thickness of the regolith derived from the chemical weathering of the underlying crystalline bedrock. It should be noted that the RMS error in the calculated data is less than that for the lines measured over the waste dump. Considering the surface topography of the area, it can be expected that there would be high concentration of the leachate towards the lower elevation; hence the adjoining stream is prone to pollution. This, no doubt, can also influence pollution of groundwater system. 78 UNIVERSITY OF IBADAN LIBRARY ~ u:co_-" ao,o--,••_.•.a.0- -~ -.•c-•.r.-..~....•.D Cn_T_ 'h_ ••••••• •_•. Fig. 49: Orientation of traverses, Aperin waste dump site, Ibadan (upper diagram) and a vertical profile through a line. of section A-B. 79 UNIVERSITY OF IBADAN LIBRARY Black 175 Ipi at 45 degrees "~;i;'l'~''''',".'',;'0,,',,;.,''~ ,"...--- --..--,~_ •• 1>1.1.0(1. •• ~ 1-, Fig. 51: Inverted resi-uv ity section for ,""III,d line 8, Aperin Waste Dump Site (Oladunjoye and Olayinka, 20IOa). 80 UNIVERSITY OF IBADAN LIBRARY Environmental Assessment of Sewage Disposal System In Nigeria, sewage disposal constitutes an important source of environmental pollution. Apart from the design consideration, most systems are misused or overused. This is particularly the case in urban areas where, because of population and space limitation, systems designed for a single household are commonly used by two or more households. This often results in malfunctioning and a short life span of the system, and, in consequence, environmental problems. Unfortunately, there is no standard regulation on the operation and use of sewage disposal systems as well as their distance from water- supply wells. Thus, to forestall greater health hazards, efforts need to be directed toward developing a reliable approach for assessing and predicting environ-mental pollution arising from sewage disposal systems. Amidu and Olayinka (2006) evaluated a geophysical approach to mapping pollution from sewer systems. The study involved geoenvironrnental studies, using 2-D electrical-resistivity imaging and geochemical analysis around a septic tank in the Senior Staff Quarters on Sanders Road, within the University of Ibadan campus (figs.52 and 53). According to available data, household wastes have been discharged into this system daily since about 1961. Thus, some level of environmental impact was expected. Electrical resistivity techniques can be effective methods of imaging and clarifying subsurface structures and delineating contaminated zones. Corroborative evidence is often provided by geochemical analyses of soil, rock and water samples. However, previous researchers have focused largely on the chemistry of surface water and groundwater (Adepelumi et ai., 200i;flOI<\yinka and Olayiwola, 2001). The sampling of soils from pits dug at selected locations within the study area was the geochemical approach used in the work. The objectives of the study include assessing the impact of the sewage disposal system on the environment, determining the reliability of the electrical-resistivity method in imaging pollution' plumes' in areas underlain by the crystalline 81 UNIVERSITY OF IBADAN LIBRARY Basement Complex rocks, correlating subsurface geologic structures with geophysical anomalies, and making recommendations to improve the design and construction of septic tank systems in order to prevent or at least reduce environmental hazards. ~I ~~ ~ ~~Ub.;.'t<, =llmr Fig. 52: GCUlllgil'al Map of the University of Ibadan Campus (After Oladunjoye, 2010). 82 UNIVERSITY OF IBADAN LIBRARY • PrP", S ••nlplJnK piN 5 -- Tr."llrM 1111"" ::alld t~P""''''''•' ••i,"\ ttk't:tr'>llt"t,uhn:t~ 0- - - - - - - l'"d~f'Kn.u.d plPl",\ "i.h "C'plioo: hn~''-* 5"".&(1 p Fig. 75: Revised geological map of the Ijebu-Ode area (After Olayinka and Osinowo, 2009). GroupIx: Archaeological Investigation In the past, archaeological investigation generally utilized the trial and error method or random test pitting. This technique is time-wasting, tedious and not necessarily accurate. Thus the need to introduce faster and more accurate methods became evident (X~ and Noel, 1991). 107 UNIVERSITY OF IBADAN LIBRARY The use of geophysical methods for archaeological investigation is a recent development in Archaeology. The magnetic method has been used in the search for buried magnetic materials such as iron slag, buried ferrous materials and fired clay. Resistivity methods have been used in search of buried pits, trenches, tunnels, buried brick walls, iron slag, among others. At Ijaye-Orile, located within Southwestern Nigeria (fig. 76), an integrated geophysical technique involving magnetic and electrical resistivity surveys, was carried out to locate archaeological materials. Results of. the geophysical investigation were verified, using excavation (pitting). Two locations were selected for study within the site. At the first location, nine magnetic traverses, each 100 m long, were run north-south at station intervals ofL and 5 m spacing between traverses (fig. 77). Six resistivity traverse lines were taken, using the Wenner configuration. Four of the lines were parallel to the magnetic traverses and were 55 m long. The other two traverses were perpendicular, and they were 25 and 30 m long. TIi'e data obtained were used to construct pseudosections and isoresistivity contour maps. At the second location, which was 80 m southeast of The first, 12 magnetic and six resistivity profile lines were taken, using similar procedures. The data obtained were also used to construct pseudosections and contour maps. : I : i 108 UNIVERSITY OF IBADAN LIBRARY N t 3.1;45='-"'-::==.....:•....-.-----''--~....:..~:;....l......I...._l~_ _.Ili:._ __ ....JJ..__1.,.30' [§] Quartzi.e.ad quart.......... Major road< r.:;] M1o:matisftl UndllT•••••• i••••b•""~. ---- Geologic bouodary ~ "hiotitt'-hom~ ~1tJt Geologic boundary approximate mtm.'ablrd :amphibalik rg;;J trndllT•••••• ia' ••• 1:>1.'" COlUp"'X >- Strik. IUJd dip ~ p••••••b1r ••• 1nlyscbW _--- Faultassumed B Hombltndrwbiotik·lranite • Study a~a ~ Ptplath~ or quam vd. Y fkm Fig. 76: Geological map of the area around ljaiye (after Nigerian Geological SurveyAgency). 109 UNIVERSITY OF IBADAN LIBRARY ,.,7.89' . ; ~ ~ tN l~Location 1 %]4161" Location 2 IIII '""''''''1 II '" Tell Pi1- (Mj~hcDCl.io:TI'1I-'- t-----I (RjRc:si.llivity Tl'1Ivax lill(. '" ~ lroo S/.q Ocposil. t7lJ EWl •••• PII '''1 0 20 ••.. ! ! "! ! "' •••••••••••• 11I •• 11I •••• M7,1" 1<11112111.11111111112011 ........ ••••sr Fig. 77: Map of the Jjaye study area, showing magnetic and resistivity traverse lines and test pits. The geophysical results delineated the first location into two anomalous regions; one of these has a high magnetic field intensity and high resistivity, and the other has a low magnetic field intensity and low resistivity (figs. 78 to 80). At the second location, a high magnetic field intensity was generall y observed. Excavation carried out yielded a large . amount of archaeological materials (iron slag and pottery) at high magnetic field intensity and high resistivity regions, and a small amount of archaeological materials at low magnetic field intensity and low resistivity regions. Thus, geophysical anomalies correlated with the excavation results. The results demonstrate that geophysical methods hold great promise as a tool in archasological investigations. 110 UNIVERSITY OF IBADAN LIBRARY Litholog r"UN)' n.).",,:}I" Hr) tint a;rlllnf;(II .•••iI'"~·S"il ru Pfttttry(4.32kj!)in filiI.'" I;raincd Luamy wit ff1oUl.'ty O.Il,H;g) in rtee :,:r:linl'd sm~'~••u I 30 I'Ptlny(I.73k;)ill lint' Utholog :::rahllo'dSllt~ Mlil I__ Sl.It/.l.~lltlitt·mU ••• ~M
  • II Punl'~(V,"!=)i.ll rtne ~rllinl'dSOIlldyS(lIl I..-Sb;il.!k)11oo 11.•• ~<~i.....lJ.•"•,.~.." l'Olll'ry(IU.3"1J;I:. in medium 1'••••Sb.\~.tH.dloo"mtlu •• J::uinl'dSandy <,(,U. a:\h l,"*E....-.JI_",)!oMiI vIt•••Sfotl.l.~lc..,iMfI•••.I'uu ••ry' (J_W"lt) ill Cell"'" -' .•..•S•...t~·••~1 I!rajl acd SYnd~' wil I.-Sh"t1.ft\:.l_-.li_ ~."I•••I•s.-.~-= ! ,e ~ ~5 12 '?!~, 1 r : ',0 ;0 Fig. 92: Percentage error in the determination of permeability shown in fig. 91 (After Olayinka and Chapele-Oletu, 1998). The results have shown that the kriging technique provides a reliable and cost-effective alternative approach to estimate the 2-D permeability distribution, even when there is a paucity of well data, with the error within the prospective zones being less than 10%. Seismic Impedance Character of the Weathering Layer in Eastern Niger Delta Forty-nine uphole and refraction surveys were carried out at three prospect areas in eastern Niger delta in order to obtain information about the weathering thickness, weathering velocity and the impedance character of the weathering layer (Olayinka and Chukwuma, 1998). The data were acquired, using an ABEM Terraloc and a MC-SEIS 1600 m portable 24-channel seismograph system in the form of uphole velocity survey and refraction profile. The recorded slanting 127 UNIVERSITY OF IBADAN LIBRARY times were corrected to vertical time. Using the depth of the geophone, a time-depth curve is plotted and different velocity functions computed (fig. 93). Eleven of the experiments show typical three-layer cases comprising, the weathering layer, intermediate layer and the subweathering layers, respectively. Thirty seven of the profiles indicated two-layer cases, while one showed a single continuous layer. The driller's logs and experimental results used to define the near-surface stratigraphy indicated that the weathering layer is mainly mud, sand, or mixed sand/clay. The intermediate layer consists mostly clay, pebbly or coarse sand and gravel, while the subweathering layer is predominantly a sandy formation. The weathering thickness is highly variable, ranging from about 0.5 to about 27.8 m, with an average of 7.1 m. Areas with thin weathering layer are suspected to be stable areas or erosional surface. There is a general increase in the weathering thickness from the river channel to the swamp and towards the upland areas. The velocity and seismic impedance are also variable and show no relationship with the weathering thickness but depends largely on the environment of deposition and the composition of the weathered materials. 128 UNIVERSITY OF IBADAN LIBRARY t·) (0) ··..,.5>.::"'::-:-"----, . OJ Ocpth 1-] Fig. 93: Examples of time-depth plots from the uphole and refraction survey conducted in eastern Niger Delta (After Olayinka and Chukwuma, 1998). The average compressional wave velocity and the average seismic i~ance of the weathered layer are 751 m S-I and 1244 kg m' S-I, respectively. The second layer has an average compressional wave velocity of about 1585 m S-I and an average seismic impedance of 3093 kg m-2 S-I. The uphole time, weathered layer velocity and thickness, thus derived, are very useful for static correction against time anomalies caused by near-surface variations. The information provided on weathering layer characteristic could form part of a data base for seismic data processing and groundwater exploration, as well as in foundation investigations in the study area. 129 UNIVERSITY OF IBADAN LIBRARY Generation of Rock Property for Seismic Modelling While it is often required to choose realistic values of rock properties to use in seismic modeling, petrophysical relationships among rock properties exist in the literature. However, the fact that rocks in a particular region are unique in the manner these properties are distributed suggests the need for the determination of empirical relationships for the common sedimentary lithologies. Olayinka and Akinlabi (1999) examined the interdependence between seismic parameters and rock physical properties in a field offshore western Niger Delta. The seismic parameters, obtained from wireline logs include the compressional wave velocity (Vp), shear wave velocity (Vs), bulk density (p), Vp/Vs ratio and Poisson's ratio (a). The results show that the compressional wave velocity increases with depth; there is also an increase in the density and shear wave velocity with depth, while there is a decrease in both the Poisson's ratio and the VplVs ratio. The differences between the measured and predicted densities are less than 3%. Similarly, the predicted compressional wave velocities differ from measured velocities by less than 5%. These imply the reliability of the local trends in predicting the rock properties. The trends of the bivariate plots were compared with published trends, and they show that the local data follow similar trends but have different variabilities (figs. 94 to 99). 130 UNIVERSITY OF IBADAN LIBRARY 4' 0 6000 6000 10000 .~OOO ·"(DO ·5000 ·5COO e. §: §: .' e L c, ·6000 ~ -6COO 0 a -lOCO ·7[00 gu Ul'ld olu.nd -econ -sccc (e) Vplftls] (.) Vpl!IIS) (oon 60CO SOCO 10030 4000 ~ODO MOO 1QOOG t:< -400Q -<1(100 ·~UO(] -5000 = ~ !-6000 !·6(100 ·7000 ·701l0 w~lU"tI ·SOOO ...• Fig. 94: Compressional wave velocity-Depth cross plot for the study area, offshore western Niger Delta (After Olayinka and Akinlabi, 1999). (.J Oensiry 19m/cm3) (b) Oen,r.y [.",lom3] 1.8 2.0 2.Z 2' 2.6 l.R 2.0 2.~ 2.' 2.6 -4000 _.030 gas sand 011 SAtli3 ·5000 ·50JO .. ::. c ~~ '5000 ~ ·SOC!) t:":I -700(' -1000 R • 066 f\ .• 054 -.OOC -dOOO (O) (d) Density (gm/cm3t Density (grn/c.m3: 1.B 2.0 2.2 24 2.5 1.8 2.~ 22 2.4 2.6 -4000 '''000 W31~t Un -5000 ·5000 .- - ~ -6000 c -6100 a ~C .7D~0 ·7000 -secc "~ 1I.4~ R.:; D 6'·8JOO Fig. 95: Density-Depth crossplot for the study area (Olayinka and Akinlabi, 1999). 131 UNIVERSITY OF IBADAN LIBRARY (a) (b) gas cand oil sand 10000 10000 6000 ~o. ~~ 8000 '> :> 6000 GOOD H • 0.71 4000 400C R 'r 0.S5 1.5 2.0 2.2 2.4 2.8 1.8 2.0 2.2 2.4 2.6 Densily [gm/cm3j D,nolly [gm/cm3) (e) 10000 t (d)....wal.".,d $1I.le l.L....•. 1000'J t: ~~ 8000- .r-- : - 8000~a. :> :> 6000- 6000 ~OOO H.O."'9 f't- 0.804000 1.8 2.0 2.2 2.4 2.6 1.8 2.0 2.2 2.4 2.6 Density Igm/cm3} Donsity [Qrn/cm3] Fig. 96: Density-Compressional wave velocity crossplot for the study area. 132 UNIVERSITY OF IBADAN LIBRARY ". 0.4 R. ·O.QS Ii: ·0.94 c '" 0.2 - C:~ .• 0.2 ~ ~Q; 0 " 0.0 - o0c 0.0 .Q c: .Q , ~" "01: -0.2 - \ ~ -0.2- shalc-l]a5 sand -0.4 !ilU Ul'ld· QII ~o.l'td 1 -0.4 -0.4 1 1-0 .2 0.0 10 2 0.4 ·0.4 -0.2 0.0 0.2 0.4 I09tOIV,1V2) I09101V,1V (e) 2(d] 0.4 0.4 ~ • ·0.97 R • -0.95 C .~ 0.2- e ~ ~ 0.2-:u" ;;0 u 0.0--: 0c: u 0.0- .s c: (; .2 \ ~ -0.2- , (g; ~ -0.2- oil Un.CI • W _I sand ·0.4 gat SlI\C - wet .$and 1 -0.4 -0.4 -0.2 0 0 0.2 0.4 1 I·0.4 -0.2 0.0 0.2 0.4 I091(j(V,N 2) I0910(V,IV2) Fig. 97: Correlation between the reflection coefficient at interfaces and the respective compressional wave velocities. 10000 "ih : 80000=.. > 6000 4000 0 2000 4000 6000 BODO \' s'{fl/S] Fig. 98: Correlation of the compressional wave and shear wave velocities 133 UNIVERSITY OF IBADAN LIB ARY t20C)O 10000 • •• • • Q~ . 8000 > 6000 "• .. • 4000~--'---'-~r-~ __~ __'-__r-~r--4 -1.0 -c.s -0.6 -0.. -0.2 0_0 0.2 0.4 Poilion'. raUo 0.6 0.8 Fig, 99: Correlation between the P-wave velocity and the Poisson's ratio. Group XIII: Research Methodologies Beyond an Album of Acceptance Letters In the days before the internet became a widely available mode of communication, surface mails were in vogue in the University of Ibadan, and, in fact, in most parts of the world. As budding scholars, some of the happiest moments that we enjoyed so much here at Ibadan were those instances when we got to the Central Porters Lodge of our University to pick up our letters, only to receive a nice correspondence from some Editor-in-Chief of a journal in our field of specializa- tion conveying acceptance of a manuscript for publication. There was always that feeling of achievement, growing reputation and satisfaction. However, beyond this modest contribution to learning, as evidenced by journal articles, a teacher-scholar is also expected to contribute to community service and participate in value-added consultancy services. I must confess that my sojourn at the Postgraduate School, first from 1999-2001 as Sub-Dean, and second from 2002-2006 as Dean, has been most fulfilling and rewarding in this regard, As an academic who by providence has found himself i.n administration, I 134 UNIVERSITY OF IBADAN LIBRARY have, along with other scholars, made some modest contributions especially in aspects of research methodology. The original intention was to further expose our colleagues to recent developments in grantsmanship, by learning from the experience and expertise of leaders in such matters. Among others, I spoke with three highly 'respected members of our University community who supported the idea. These were Professor Olufemi A. Bamiro (now the Vice-Chancellor), Professor Adedoyin Soyibo (currently, Director, Centre for Enterpreneurship and Innovation) and Professor Oladimeji Oladepo (currently, Dean of Public Health). The workshop was eventually held on 16 and 17 July, 2003 and the first publication in this category was the one on the planning and writing of grant-winning research proposals (Bamiro et. al. 2003). It turned out to be a well-attended event, with the participants drawn from all the Faculties/Institutes/Centres, requesting that we mount follow-up programmes for the benefit of other colleagues who might not have had the opportunity to be part of the programme. During my first year as Dean, we had much difficulty at the Executive Committee of the Postgraduate School in considering the draft of abstracts of theses and dissertations. For many of our research students, the fear of the Executive Committee was literarily the beginning of wisdom! I still remember vividly that one evening in October 2003, when I was away to the Federal University of Technology, Akure, as External Examiner, I had cause to ruminate over this seemingly intractable problem. Then, I had a brain wave on a possible solution. I said to myself that as a community of scholars, the best way to tackle any knotty issue was to invite colleagues to a roundtable and brainstorm. On my return from the Akure trip, I broached the idea of organizing a workshop on the theme 'What is a PhD thesis?' to some of our colleagues, including the then Dean of the Faculty of the Social Sciences, and currently the Deputy Vice-Chancellor (Academic), Professor A.A.B Agbaje. All of them felt it was a good idea and promised to contribute in one way or the 135 UNIVERSITY OF IBADAN LIBRARY other to its actualization. I was naturally very excited by this and the workshop was eventually held in February 2004. From this emanated our publication on 'Guidelines to Writing a Doctoral Thesis' (Olayinka et. al. 2004). At one of the plenary sessions of that workshop, a Session Chair and then Deputy Vice-Chancellor (Administration), Professor Olusoji Ofi, while commending the organisers of the interactive session, did say that there was still something missing in what we had done, hitherto, in so far as writing a research thesis is just one of the major outcomes of research. In his well-considered view, it would be worth the while if we could look at the entire research process itself. About that same time, I came across an advert in The Guardian on a Workshop on Research Methodology by the National Postgraduate Medical College. It then became obvious that we should plan toward a major, more encompassing Workshop. It took us a lot of planning and we eventually held the Workshop from 1 to 5 November, 2004. The materials were subsequently published as a book on 'Methodology of Basic and Applied Research' with some 34 contributors drawn from all our various Faculties and the College of Medicine (Olayinka et al., 2006). One major outcome of these Workshops, which gladdens my heart till today, was our ability to evolve a uniquely home-grown University of Ibadan Manual of Style (UIMS). The ultimate objective of the guide is to achieve consistency in the presentation style of academic writing. As a composite simplification of some standard style sheets, this unified style of referencing is highly recommended for all postgraduate students within the University of Ibadan Postgraduate system, and their colleagues in sister universities. The credit for the design and development of the UIMS is due to three of my colleagues, Dr. Aderemi Raji-Oyelade, Professor Temitope Alonge and Dr. E. Oluwabunmi Olapade-Olaopa (Raji- Oyelade et al., 2006). Our professional cum learned society, the Nigerian Association of Petroleum Explorationists (NAPE) observed 136 UNIVERSITY OF IBADAN LIBRARY that not many Nigerian geoscience scholars were winning competitive research grants from international bodies. Based on our modest accomplishment at the University of Ibadan, I was commissioned to write a book to attempt to solve this problem. Eventually, we came up with 'A Guide to Preparing Research Proposals in the Geosciences' (Olayinka, 2005) which was published by Mosuro and funded by NAPE under her NAPE-University Assistance Programme. It is gratifying to note that since the publication came out and was widely disseminated by the association, a positive improvement in grant-winning ability of geosciences scholars has been reported (Kunle Adesida, 2009, personal communication). I have been teaching aspects of the course 'GEY 701: Methodology of Geological Research' to our MSc students in the Department of Geology for about 20 years now. It is gratifying to note that the experience one has acquired in Research Methodology, courtesy of our Postgraduate School, has been most beneficial in enriching the course. Since completing my tenure at the Postgraduate School, I have received invitation from many sister institutions in Nigeria, Ghana, Senegal, South Africa and the United Kingdom to share my thoughts on aspects of grantsmanship and University research management (Olayinka, 2006; Olayinka, 2007; Olayinka, 2008). Along with the work of several others, Ibadan is now rightly acknowledged as a leader in this emerging profession. Given the recognition that research management can contribute to better governance of research, increased impact and help to attract the much-desired external funds from abroad, there is need to develop internationally recognized professional skills base in the field. This can be provided through continuous professional development. However, these skills are usually not acquired through the regular University curricular. There is currently a dearth of training on practical issues. Ibadan is expected to provide leadership in this direction, and the fact that we host the secretariat of 137 UNIVERSITY OF IBADAN LIBRARY the West African Research and Innovation Management Association (WARIMA) is an advantage in this direction. Fieldwork is recognized as a basic tool in the training of students of Geology. Esso Exploration and Production Nigeria Limited organized a training-of-trainers workshop for lecturers of Geology from various Nigerian universities in Benin City in February 2007. The book of proceedings, co- edited by Dr. Daniel O. Lambert-Aikhionbare, FNMGS, FNAPE, and my humble self, have since been published. I also contributed a chapter on best practices in the planning and execution of geological field mapping (Olayinka, 2009). Discussions and Conclusions Sustainable development is on the front burner of Nigeria's agenda like in .most developing countries where serious challenges, in terms of health, resource and environmental sustainability, poverty alleviation, and related quality of life issues, are faced by citizens. The research challenges facing researchers in these regions are therefore extremely complex. They, in most cases, need an interdisciplinary or partnership . approach, and should be researched at a local level to ensure relevant outcomes. The research outputs need to be translated effectively for social benefit. The positive side to this is that we researchers are also perfectly positioned amongst a unique convergence of issues to be researched, and with improved access to support structures and resources, we can be world leaders in our fields, making a real impact on development through our research outputs. Water quality management is an issue that must be given top priority. One of the measures that can be taken for the protection of groundwater includes waterproofing the base of any leachate stream and the stream bed to prevent infiltration of the effluent. Secondly, there should be continuous monitoring using geoelectrical imaging to provide early warnings as to the presence of potential pollution. Thirdly, the effluents should be treated to meet the standards established by the National Environmental Standards and 138 UNIVERSITY OF IBADAN LIBRARY Regulations Enforcement Agency (NESREA), the Oyo State Environmental Protection Agency. Fourthly, there should be launching of public awareness campaigns and convincing the relevant authorities at the local, state and federal levels as to the need to undertake groundwater protection measures. Some 47 years ago, our foundation Head of Department had concluded his inaugural lecture in the following manner: I think these few words may have served to indicate the bright future for geology as a profession in Nigeria. I hope that they also may have indicated that the graduate from a Nigerian university is far better trained for the task before him than colleagues, Nigerian and expatriate, with degrees from overseas. He has not only a special knowledge of the geology of his country, but he is also adapted to operating in an environment in which he was born and has learnt to understand (Reyment, 1963). Perhaps, not much has changed since then. We currently have a crop of very bright students, and it is gratifying to note that the learning and teaching environment in our university is improving. I am happy to report that the quality of our intakes has improved considerably in the last three sessions. A major reason for this obviously is the post-UME screening which the university introduced about four years ago; thanks to a major policy shift of the Federal Ministry of education, then led by Mrs. Chinwe Obajias the Honourable Minister. FOl; the first time in recent memory, all the 38 students that registered for the 100 level in Geology during the 2008/2009 session passed and were eligible to proceed to the 200 level in the current session. I was extremely delighted when as the Acting Dean of Science I had cause to present their results to Senate at the meeting of Monday, 4 January, 2010 (See Senate Paper No 5377). It was also helpful that out class size is moderate and conforms with the prescription of the Council 139 UNIVERSITY OF IBADAN LIBRARY of the Nigerian Mining Engineers and Geoscientists (COMEG). Although one realizes that there is a lot of pressure on universities to expand access, we should not do this at the expense of quality. In simple words, Ibadan should resist pressure to admit students beyond our carrying capacity. I learnt reliably that one of the criteria employed by Esso Exploration and Production Nigeria Ltd (EEPNL) in selecting our department as one of the beneficiaries of the EEPNL-Universities Partnering Programme was our small class size. This has remained one of our major benefactions in recent years. Falase (2010) has discussed extensively on this in his valedictory lecture presented at this same venue exactly three weeks ago. Ibadan took a strategic decision a few years ago to reduce undergraduate intakes while at the same time expand the postgraduate intake. Ultimately a 60:40 postgraduate: undergraduate student mix is envisaged. This, in our humble view, should be adhered to in spite of the pressure to increase undergraduate admission. By the special grace of God, I earned my first degree in Geology from this university some 29 years ago, and I have also been on the academic staff for some 22 years now. I make bold to say that the curriculum that we run today in our Department is not in any way inferior to the one I passed through as an undergraduate. I am aware that our curriculum is well above the Minimum Academic Standard prescribed by the National Universities Commission (Nl.K'). It is also comparable to what obtains in reputable and famous sister departments elsewhere. This is the truth of the matter! Our current academic staff strength of 19 is respectable enough. We also have 10 members of the technical and administrative staff who provide necessary support. For this, I thank the current and the immediate past administrations of the University for allowing us to recruit many young and promising academics to strengthen the department. I am aware that some of these colleagues were head-hunted from sister Universities on account of their special talents and great 140 UNIVERSITY OF IBADAN LIBRARY potentials. However, like Oliver Twist, we ask for more, especially as there are many areas of specialization that one would ordinarily expect in any modem Department of Geology. These include FieldlRegional Geology, Igneous and Metamorphic Petrology, Sedimentology, Petroleum Geology, . Structural Geology, Geochemistry, Economic/Mining Geology, Biostratigraphy, Geophysics, Photogeology, Remote Sensing, Engineering Geology, Hydrogeology, and Environmental Geology, among others. As at the time of my appointment as a Lecturer Grade II in April 1988, there was no lecturer of Applied Geophysics in the Department due to staff retirements. My self-imposed mandate was to immediately take up teaching and research in this area and deepen it to become a viable area of specialization. I started teaching the only undergraduate and five postgraduate courses in this applied/exploration geophysics. By November 1990, I had successfully comple- ted the supervision of three MSc candidates. Till date, I have supervised a total of 76 MSc and 3 PhD candidates in Applied Geophysics, Hydrogeology and Petroleum Geology. Four other PhD candidates will soon start the registration formalities for their theses. The candidates have been mentored to present their research findings at local and international conferences, and some of them have won awards in the process. Many of them are now gainfully employed in various universities, oil exploration/production/ service companies, the Nigerian Geological Survey Agency (NGSA), mining companies, and the like. Along with other colleagues, we have built up the Applied Geophysics Group in the Department. I salute the industry, hardwork and perseverance of my three younger lecturers-colleagues in the group. Our MSc programme in Applied Geophysics is highly regarded and heavily subscribed. It has, perhaps, one of the most stringent entry requirements in the University of Ibadan Postgraduate School system: in the last 10 years or so, the minimum admission requirement has been a Second Class (Upper Division) .ESc in Geology or Applied Geophysics; in 141 UNIVERSITY OF IBADAN LIBRARY addition to satisfying all other conditions stipulated by the School. We will continue to strive to maintain this standard. During the last quarter of 2007, our Department had cause to prepare for NUC Accreditation as we earned an 'Interim Accreditation' with a disappointing Programme Score of 61% during the previous 2005 Accreditation exercise. I realized that one of the criteria is 'Employer's Rating' to which a maximum score of 3 points has been allotted by the NUC. I was determined to secure the maximum point from this, given what I knew of our pedigree. Among the people I contacted was the Head of Department of Geology, Baylor University, Waco, TX, USA, under whom one of our former students, Sikiru Arnidu, BSc (First Class) 2000, MSc 2005 (Ibadan), was then a research scientist and PhD student. He had replied, in an e-rnail which he sent directly to the Vice-Chancellor of the University of Ibadan, that: Sikiru is well-suited and exceptionally well- prepared to conduct research projects, given his previous geological and geophysical training acquired in his native Nigeria. He is very hard- working. He has given many public presentations on his research at regional, and national meetings. We are proud to have him as a member of our Geology Department and Geophysics Program at Baylor University. He has since completed his PhD. Similarly, Wasiu Olayinka Popoola, BSc (First Class) 2007, has just finished his MSc in Petroleum Geosciences, with distinction, at Imperial College. Both ex-students of ours, whom we are exceedingly proud of, are now employed with an international oil exploration! production company based in Lagos. There are many other success stories of our former students who are doing well in various areas of human endeavour, both at horne and abroad. This is a confirmation of the saying that 'if it is from Ibadan, it must be good quality'. It may be noted in passing that we 142 UNIVERSITY OF IBADAN LIBRARY scored the maximum 3 points under 'Employer's Rating', and we were granted Full Accreditation by the NUC as part of the 2007 exercise, with a more ,respectable Programme Score of 89%. I must confess that I felt deeply relieved when the outcome was announced. We have been involved in fund generation from alumni, alumnae, corporate institutions and friends of the Department of Geology. The money mobilized during such campaigns has been used to upgrade our teaching and learning facilities and the environment which is now more user-friendly. We believe that benefactions can play a vital role in supporting the training of successive generations of students. Many of our alumni and alumnae were requested to join the history of philantrophic support and help us continue to transform the lives of our students. Through this focused charitable programme of fund raising, many have joined our community of graduates who are proud to know they are supporting one of the finest teaching, research and life opportunities in the geosciences in the world. The Association of Ibadan University Geologists, better known as Ibadan Geologists, comprising alumni/alumnae of the Department provided a state-of-the-art Petrological Microscope Laboratory in the Department in March 2007. The endowment comprises two trinocular research microscopes and 21 binocular microscopes, with camera attachments, valued at Ten Million and Five Hundred Thousand Naira (NlO, 500,000.00). We are improving the teaching, learning and research environment. The entire departmental complex was re-painted and refurbished in March 2008 at a cost of Two Million, One Hundred Thousand naira (N2,100,000.00) which was raised from donations. We attracted the Esso Exploration and Production Ltd to fund a Field Mapping Project, in conjunction with the Nigerian Geological Survey Agency. Through this initiative, a brand-new 18-seater Toyota Hiace Field Vehicle, valued at Four Million, Five Hundred Thousand naira (N4,500,000.oO), 143 UNIVERSITY OF IBADAN LIBRARY was donated to the Department in February 2008. A thin- section machine was provided to the Department, and our senior Technologist was sponsored by Esso to undertake a week training course in Scotland in June 2008. The Department is benefiting to the tune of Seventy Five Million Naira (~75,000,000.00) over the three-year duration of this project. We have been very lucky with the Endowment of Prizes. At the last count, there are 13 such prizes and awards that have been endowed in perpetuity to the benefit of our deserving students. We created the Department of Geology Occasional Publications Series in March 2007, with three academic titles already published. The Mosobalaje Oyawoye Library, named after the foremost African Geologist and first African Head of our Department, Professor M. O. Oyawoye, DSc (Ibadan) (Honori causa) has received a major facelift, in terms of computer hardware and software, recent journal collections and current hooks. However, the challenges of geoscience education in Nigeria include the low level of funding, poor quality of students admitted into the universities on account of the declining quality of education at the primary and secondary school levels, poor quality and inadequate staff (both teaching and non-teaching), decaying and ageing facilities, limited access to ICT infrastructure and equipment, incessant power outage, limited exposure to fieldwork, poor orientation of students, indiscipline among staff and students, as well as cultism. Specific areas of collaboration between Nigerian Universities and the Oil and Gas Industry include fieldwork support, Students' Industrial Work Experience Scheme (SIWES), scholarship and bursary awards, staff exchange programme, consultancy, provision of infrastructure/equipment and instructional materials, endowment of professorial chairs, donation of field vehicles and sponsorship to academic and professional fora, ICT facilities, geoscientific database, development of appropriate 144 UNIVERSITY OF IBADAN LIBRARY curriculum in consultation with the NUC, COMEG and other stakeholders to serve as standard. Establishment and operation of Geoscience departments are capital intensive. However, the impact of the oil and gas industry, especially through the intervention of NAPE- University Assistance Programme, on geoscience education, has been salutary and positive. There are now individual and corporate sponsors, including oil companies and the Petroleum Technology Development Fund (PTDF), giving scholarship, equipment, field vehicles, and professorial chairs. ' The NGSA, under the indefatigable leadership of its Director-General, Professor Siyan Malomo, FNMGS, FAS, has been extremely pro-active in fostering a much desired collaboration and bridging the artificial bridge between the NGSA and tfierespective Departments of Geosciences in our Universities. Many senior academics now have the opportunity to spend their sabbatical/study leave at the NGSA, while countless NGSA geoscientists are also encouraged to register for higher degrees in our universities. This is most commendable, and there is no doubt in my mind that it is a win-win situation for all the parties involved. Although there is need to create more opportunities for young people who desire university education, in widening the access, efforts must be made to ensure a high standard of training. Proprietors of Universities (Federal and State Governments and "Private institutions) should increase their level of funding for Geoscience programmes. The Federal Government should increase the level of funding to her universities in order to complement funding from other sources. There is an urgent need to improve the working conditions in the universities in order to attract and retain bright scholars. There should be mentoring of emerging scholars by the more established academics. Alumni and alumnae of each University should participate actively in 145 UNIVERSITY OF IBADAN LIBRARY improving the teaching and research environment of their alma mater. Staff (teaching and non-teaching) in higher institutions should put in their best to ensure a very high quality of graduates who are employable and/or can be self-employed, while academic staff should strive to devote adequate time to research which would subsequently improve effectiveness in their other core mandates of teaching and value-added consultancy and services. Best practices in pedagogy, including methods developed for use in large, introductory- .level courses, need to be identified, communicated and broadly implemented. Geoscience curricular at all levels need to embrace the Earth System science approach. Geoscience curricular must be aligned with national priorities to increase impact and perceived importance of the Geosciences. Workforce skills need to be emphasized, including quantitative expertise, the ability to communicate complex information in writing and orally and the ability to work on interdisciplinary teams. Public-Private Partnerships should be strengthened in order to have more collaboration between the Universities and the Oil and Gas Companies. The establishment of Centers of Excellence and Centralised Research Laboratories in selected universities would attract better funding and consultancies from the private sector. The improvement of the basic research capabilities of universities would also enhance the Nigerian Content Development (NCD) drive of the government for the oil and gas industry. Students and faculties are enjoined to promptly apply for research grants. Information about workforce needs and career prospects should be provided to recruit qualified candidates into Geosciences disciplines and motivate students to excel. There is a need to re-examine the limited access to ICT infrastructure and equipment as this has created problem for the academics and students of the geosciences to tap from global network of ideas and knowledge. 146 UNIVERSITY OF IBADAN LIBRARY Library facilities should be updated. Students and staff must be able to use internet facilities to access resource materials, which may not be available locally. The focus should be the production of world-class graduates and not local champions. Each department of geology should have a functioning library. The classrooms must be fully integrated with cyber-infrastructures for effective teaching and learning. Sponsoring of Train- the- Trainers workshops, seminars and courses by companies' staff should be extended to University teaching and technical staff. The carrying capacity of each academic department should not be exceeded in order to maintain an optimum staff! student ratio, and the regulations on admissions and staff/student ratios stipulated by the NUC and professional bodies, like the Council of Nigerian Mining Engineers and Geoscientists (COMEG), should be strictly enforced. The post-UME screening of prospective students should be continued and fine-tuned to enhance quality intakes into the universities. Heads of Geosciences Departments should have effective input to the admission list of prospective students as is the case at the University of Ibadan. Inter-university exchange programmes with foreign universities should be encouraged. There is no doubt that this University acknowledges the importance and contribution of Professorial Inaugural Lectures (PIL) as a pinnacle in the production of knowledge in the everyday business of the University as one among many universities of world-wide reputation in research, teaching and research-based/value-added consultancy activities. Falase (2005) identified two critical roles PIL play in the life of a university. First, the lectures are expected to highlight some of the research findings that may be of great value to the academic world, budding entrepreneurs,· industrialists and government. Second, the lectures can showcase to the outside world (that is the town) the academic attainments of individual lecturers and the entire university (that is the gown). 147 UNIVERSITY OF IBADAN LIBRARY I wish to add other incidental roles. Our PIL contribute towards maintaining an active academic environment. They serve as proof or demonstration of the academic's leadership quality. Moreover, they serve as a source of inspiration and motivation for our undergraduate and postgraduate students, as well as emerging scholars, including faculty members in this and other sister universities, thus providing a veritable vehicle for mentoring. Nonetheless, one has observed that there is still a lacuna with the structure of our PIL, as there is neither a policy document nor a guideline moderating the preparation and presentation of the lecture. It, therefore, becomes apparent that we need to strengthen the process of organizing our inaugural lectures. To rectify this, I humbly propose that our University should establish a "Senate Committee on Professorial Inaugural Lectures". If I have in any way met some of the aforementioned functions of PIL, the efforts of this wonderful audience to attend the lecture would not have been in vain, and the confidence reposed in me by all those who have encouraged me in this enterprise would not have been misplaced. Acknowledgements I like to thank my creator, the Almighty God, through Jesus Christ, my Lord and Saviour, who has made today's lecture and our modest contributions possible. He has been especially kind and generous to an unworthy son like my humble self. To Him alone be all the honour, glory and adoration. I acknowledge, with gratitude;' my parents, Mr Gabriel Olayinka Ojimi and Mrs Florence Mopelola Olayinka, both of blessed memory, for my strict Christian upbringing, especi~lly during the form~t~~y~ars ~~".V~atis r,eferr~~;tQ,in geological parlance, as the Ilesha 'Schist Belt. They taught me the virtues of honesty, hardwork and the fear of God. These have stood me in good stead, both in times of peace and turmoil. I remain ever &rJ;lte£UI,·t~-;Ittami' -~'i~Y€~mi';. ,,' respectively. I wantto m~' one specialnote of~thaitf~to my 148 ' -~... 0- UNIVERSITY OF IBADAN LIBRARY mum. I am here today largely because of her aspirations and sacrifices for my siblings and me. Although I may not have been able to meet with her high expectations from me, I have tried to approximate them. My siblings, Mrs Alice Foluke Ajidahun, Niyi Olayinka, Niran Olayinka, Kehinde Olayinka and their spouses, have been very wonderful in their support all these years. They have always intervened at critical periods in my career, and I remain ever so grateful for the exceptional love, care and understanding. I have many devoted members of extended family, ably represented by Olumakinde Oni, Ternitayo Bakare, Busuyi Oni, Biderni Aluko, Johnson Oni, and Seun Oni. I am very grateful to you members of the Rebecca Obidahunsi Oni Dynasty of Ijesaland for the filial love. I thank my role models who mentored me when I was a young boy growing up in the 1960s and 1970s. These were people one looked up to, and they have never disappointed. In this regard, special mention must be made of Mrs Bola and Mr Adejumoke Oni, Mrs C. Nihinlola and Prof Olakanrni Abimbola, and Mrs Bola (of blessed memory) and Mr Segun Agboola. I thank my teachers at the University of Ibadan during my undergraduate days. I recall, with nostalgia, Mr Dugdale who taught us Mechanics as part of our Preliminary Year .Physics. He, in particular, impressed me with his punctuality in class, an attribute I so much appreciated then and have also tried to emulate and implement in my own little ways since I became a member of the Faculty some 22 years ago. Dr S.C. Garde taught me 'Classical Physics I' during the 1978/79 session and I enjoyed his classes which rekindled my interest in later years to specialize in Geophysics. I am grateful fb:)Dr Anna Thomas-Betts, my MSc Course Coordinator at Imperial College, who taught me Mathematics for Geophysicists and Exploration Geophysics, and believed much in my ability andpotesnot'ieal. She did much to encourageme to register f6r. a. Phd n after the Master programme, 149 UNIVERSITY OF IBADAN LIBRARY and in later years, she gave me a strong recommendation for the Humboldt Fellowship. I remain ever grateful to Dr Ronald D. Barker who supervised my PhD thesis at the University of Birmingham and in the process taught me how to conduct research. I acknowledge the contributions of the late Emeritus Professor D. H. Griffiths (1919-2007), for being such a father-figure throughout my stay in Birmingham. At the post-doctoral level in Germany, I thank Prof Dr Peter Weidelt and Prof Dr Andreas Weller, my co-hosts at the Technical University, Braunschweig and Prof Dr Ugur Yaramanci, my host at the Technical University, Berlin. It has been a rare privilege, an exceptional honour and divine luck for one to have had the opportunity to stand on the shoulders of these academic giants. I acknowledge, with gratitude, the sponsorship received from the Committee of Vice-Chancellors and Principals of United Kingdom Universities, the German Academic Exchange Services (DAAD), the Alexander von Humboldt Foundation and the Association of Commonwealth Universities. I thank my good friend, Dr Babajide Bamkole, for his comradeship during the good days we spent together in the West Midlands, when both of us were research students. Many individuals have made my stay at the University of Ibadan as a faculty member very interesting. They include my former teachers and my senior colleagues and bosses in the Department of Geology- Prof. T.A. Badejoko, Prof M.A. Olade (both of whom have since retired) and Prof A. A. Elueze. I publicly acknowledge the contribution of Prof T.A. Badejoko for believing in me and insisting on putting me up for Professorship in 1999, against my personal wish and ambition to apply for the grade of Reader and then possibly attempt the full professorship after at least three years. In his opinion, my publications in learned journals were far in excess of the minimum required for a full professorship. Thank God that the Faculty, and the University Appointments and Promotions Committees as well as all the Internal and 150 UNIVERSITY OF IBADAN LIBRARY External Assessors agreed with his sound judgment. I was subsequently promoted to the grade of Professor with effect from 1 October 1999. I remain eternally grateful, Sir. My colleagues in the Department who have contributed towards the creation of an enabling environment for me to thrive include Dr AF. Abimbola, Dr G.O Adeyerni, Dr I.M. Akaegbobi, Dr Moshood Tijani, Dr A T. Bolarinwa, Dr Mathew Nton, Dr Gbenga Okunlola, Dr Gbenga Ehinola, Dr Gbenga Boboye, Dr Bunmi Adeigbe, Dr A S. Olatunji, Mr Mutiu Adeleye, Mr Ibrahim Oyediran and Mr Ayo Jayeoba. I am also grateful to all the members of the non-teaching staff for their support. My postgraduate students have contributed in no small measure to my research profile, and this group is ably represented by Mrs Doja Ojelabi (nee Adejobi), Dr Moroff Adabanija, Michael Oladunjoye, Dr Sikiru Amidu Adetona, Wale Osinowo and Philips Aizebokhia. The invaluable contributions and support of Prof Ayodele Falase, FAS, NNOM, Prof Olufemi A. Bamiro, FAS, FNSE, Prof B.O. Fagbemi, Prof Labode Popoola, Prof V.O. Taiwo, Dr Victor Adetimirin, Dr Tanimowo Odunneye, rnni, Mrs Elizabeth Ette and Mrs Nkechi Egbunike made my sojourn at the Postgraduate School a memorable and much-cherished one. I thank my very senior friends and colleagues for their abiding interest in my welfare. This elite group is ably represented by Prof Abiodun O. and Prof Adeyinka G. Falusi, Prof Olabode Lucas, Prof. F.AA. Adeniyi, Prof Oluwole Akinboade, Prof Oluwole Osonubi, Prof Olusegun Ekundayo, Prof Oladele Osibanjo, Prof Ademola Ariyo, Prof Rotirni Oderinde, Prof Segun Omole (now late), Prof Isaac F. Adewole, Prof Oye Gureje, DSc, NNOM, Prof O.D. Olaleye, Prof Adeniyi Gbadegesin, Dr Gani Adeniran, Prof Oludele Itiola, Dr. O.A Fakolujo, Prof Labode Popoola, Prof Ternitope Alonge, Prof Victor O. Taiwo, Dr Victor Adetiniirin, Dr Segun Ademowo, Dr Oluwabunmi Olapade- Olaopa, Prof Francis Egbokhare, Prof. Abel Olorunnisola, 151 UNIVERSITY OF IB DAN LIBRARY Dr Aderemi Raji-Oyelade, Dr. R.O. Oriaku, Dr Ayobami Kehinde and Dr Adenike Akinjobi. I am grateful to Mr Mbat Akpan, FNMGS, FNAPE, for the financial support towards the preparation of this lecture. My assistants, Mrs M.A. Bademosi, Mrs S. O. Bamidele, Mrs Teju Ajao, Mrs Tosin Olowola, and Mr S.A. Adesina were helpful with the logistics. Ihave to place on record the support of members of my nuclear family who have had to put up with my incessant and sometimes prolonged absence from home on official cum professional duties. My jewel of inestimable value, Eyiwumi, and our wonderful and precious gifts from God, Olakeyede and Olaseeni, Iam ever very proud of you. You have been so understanding and wonderful these last 19 years. In closing, I give all the honour and adoration to my good God, the eternal rock of ages, my creator, who made me in His own image. He remains the greatest imager of all times. Without His protection, today's celebration would probably have remained all but a figment of my imagination. References Acworth, RI., 1987. The development of crystalline basement aquifers in a tropical environment. Quarterly Journal of Engineering Geology, 20, 265-272. Adabanija, M., Olayinka, A I., and Omidiora, E. 2008. 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