Geology
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Item Smooth and sharp-boundary inversion of two-dimensional pseudosection data in presence of a decrease in resistivity with depth(Geophysical Press, 2002) Olayinka, A.I.; Yaramanci, U.The smooth and sharp-boundary inversion of two-dimensional (2D) apparent resistivity pseudosection data in cases where the half-space has a lower resistivity than the overburden is investigated. The study entailed calculation (by forward modelling) of the synthetic data over simple 2D geologic models and inversion of the data. The 2D structures modelled include vertical fault, graben and horst. The Wenner array was used. The results show that there is generally an improvement in the model misfit with iteration number in smooth inversion; the algorithm can then be expected to iterate to the best solution at a high iteration number where the model resistivity of the substratum approaches the true bedrock resistivity. Inversion of the data using sharp boundaries indicates that the range of 2D equivalence, for which a reasonable interpretation could be attained, is relatively narrow. For the equivalent solutions, the data misfit between the observed and the calculated data is very small while model interpretations that are wrong can be readily identified on account of very large data misfits. A field example is given from Nauen, northern Germany, where partly-saturated sand of high resistivity is underlain in succession by less resistive saturated sand and glacial till; the smooth and sharp-boundary inversion results are in good agreement with the geo-radar and surface magnetic nuclear resonance (SNMR) and borehole informationItem Use of block inversion in the 2-D interpretation of apparent resistivity data and its comparison with smooth inversion(Elsevier, 2000) Olayinka, I. A.; Yaramanci, U.The ability of a block inversion scheme, in which polygons are employed to define layers and/or bodies of equal resistivity, in determining the geometry and true resistivity of subsurface structures has been investigated and a simple strategy for deriving the starting model is proposed. A comparison has also been made between block inversion and smooth inversion, the latter being a cell-based scheme. The study entailed the 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. The Wenner array was used. The results show 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. It is shown that the starting model for block inversion can be based on a plane layer earth model. 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. Field examples from a crystalline basement area of Nigeria are presented to demonstrate the versatility of the two resistivity inversion schemes.Item Smooth and sharp-boundary inversion of two- dimensional pseudosection data in presence of a decrease in resistivity with depth(ELSEVIER, 2002) Olayinka, A.I.; Yaramanci, U.The smooth and sharp-boundary inversion of two-dimensional (2D) apparent resistivity pseudosection data in cases where the half-space has a lower resistivity than the overburden is investigated. The study entailed calculation (by forward modelling) of the synthetic data over simple 2D geologic models and inversion of the data. The 2D structures modelled include vertical fault, graben and horst. The Wenner array was used. The results show that there is generally an improvement in the model misfit with iteration number in smooth inversion; the algorithm can then be expected to iterate to the best solution at a high iteration number where the model resistivity of the substratum approaches the true bedrock resistivity. Inversion of the data using sharp boundaries indicates that the range of 2D equivalence, for which a reasonable interpretation could be attained, is relatively narrow. For the equivalent solutions, the data misfit between the observed and the calculated data is very small while model interpretations that are wrong can be readily identified on account of very large data misfits. A field example is given from Nauen, northern Germany, where partly-saturated sand of high resistivity is underlain in succession by less resistive saturated sand and glacial till; the smooth and sharp-boundary inversion results are in good agreement with the geo-radar and surface magnetic nuclear resonance (SNMR) and borehole informationItem Integrated use of geoelectrical imaging and hydrochemical methods in delineating limits of polluted surface and ground water at a landfill site in Ibadan area, Southwestern Nigeria(Nigerian Mining and Geosciences Society, 2001) Olayinka, A.I.; Olayiwola, M.A.The Impact of solid waste disposal at the Ring Road district of Ibadan metropolis, southwestern Nigeria, on the adjoining surface and ground-water sources, has been Investigated. The basement rocks include Precambrian quartzites and quartz-schists that have been extensively weathered. In this study, the geophysical survey Involved 5 electrical imaging lines, while the hydrochemical database comprised 4 samples of surface water and 6 samples of groundwater from dug wells. The samples were analysed for turbidity, pH, conductivity, total hardness, total dissolved solids (TDS), alkalinity, Cl, No3, SO42, PO43, Na, K+, Mg2 and Fe2. The results show that water bodies located in a down gradient direction and in close vicinity of the landfill, has received significant inputs of inorganic pollutants. Statistical analyses indicate positive correlation (p<0.05) between the following pairs of parameters: Ca2 and Mg2. (R=0.83; Na+ and K+ (R=0.95); (Na2+Mg2) and Cl (R = 0.92); (Na2 + K2) and Ca2 (R=0.96); pH and Cr (R = 0.87). Moreover. the electrical conductivity shows a positive correlation (p<0.05) with the concentrations of K+ (R = 0.97); Na+ (R = 0.96); Ca2+ (R = 0.93); Mg2+ (R = 0.82); Fe2+ (R = 0.85); Cl (R = 0.91) and TDS (R = 0.98). On the other hand, the conductivity shows a negative correlation with SO42 (R = 0.78). Corroborating evidence was provided from the geoelectrical imaging data which Indicate that the thickness of the waste dump ranges between about 2m to 17m, while its resistivity is low at between 4 and 8ohm-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 delineation of the limits of the probable polluted zone.Item Aspects of equivalence in two-dimensional resistivity imaging and modelling(Nigerian Mining and Geosciences Society, 2000) Olayinka, A.I.The possibility for geoelectrical equivalence in two-dimensional (2-D) inversion of apparent resistivity data has been investigated. This involved the calculation of synthetic pscudosection data for simple geological structures using a finite difference approach. With the aid of statistical F-test, it is shown that identical or near-identical pseudosections can be generated from more than one 2-D model. In particular, the apparent resistivity pscudosection measured over2-D structures like basement fault, trough and horst resemble those arising from lateral variations In the overburden resistivity.Item Strengthening academic linkages and collaboration in universities(The Graduate School, University of Calabar, Calabar, Cross River State, 2004-07-28) Olayinka, I.Item Methodology of basic and applied research(The Postgraduate School University of Ibadan, 2006) Olayinka, A. I.; Taiwo, V. O.; Raji-Oyelade, A.; Farai, I. P.Item A Guide to preparing geoscience research proposals(Mosuro Publishers, 2006) Olayinka, A. I.Item Hand-over notes(2006) Olayinka, A. I.Item Preparing a research proposal(The Postgraduate School, University of Ibadan, Ibadan, 2006) Olayinka, A. I.; Owumi, B. E.
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