Browsing by Author "Mamo, Tilahun (PhD)"

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    Delineating the Omo Basin Using Geophysical Methods
    (Addis Ababa Universty, 2006-07) Solomon, Salih; Mamo, Tilahun (PhD)
    Gravity field survey has been carried out in the Omo basin over the detail grid. The grid comprise nine, 48 km long gravity traverses, 4 km apart with gravity stations on a 1 km interval. The gravity data have been collected with the La-coste and Romberg Model G-1105 geodetic gravimeter occupation in conjunction with the post processed Fast static GPS-data acquisition using Trimble 5700. The data were processed, analyzed and presented in contour maps and therefore are interpreted to draw conclusions in terms of basin formation. The result shows a well-defined sedimentary basin bounded by northsouth striking major structures. The Omo basin sedimentary potential has thickness of more than 3 km as deduced from the processed results, besides; its width is about15870.5 m. In addition to its academic importance, the study will have a considerable contribution in exploring the country’s hydrocarbon potential.
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    Engineering rock mass characterization – An integrated approach through Rock Mass Classification and Seismic Refraction; a case of TAMS Hydroelectric power Dam Project in Gambella, Ethiopia
    (Addis Ababa Universty, 2017-05) Gebremichael, Daniel; Mamo, Tilahun (PhD)
    In the present study, an integrated geotechnical and geophysical approach was followed to characterize the dam foundation of TAMS Hydropower dam, situated in South-western Ethiopia, in Gambella National Regional State, Gambella Woreda, 721 km south-west of Addis Ababa. The dam is being constructed for the purpose of hydropower generation and will have a height of 265 m. A systematic methodology was followed for the present study. This includes review of secondary reports on investigations and design and collection of primary data from surface on geological and geotechnical parameters at the dam site. The investigations carried out in this regard includes; surface mapping, Rock mass rating (RMR) data collection, insitu testing on rock properties, and laboratory testing on representative samples. Besides, secondary raw data on drill hole logs, water pressure test and Seismic refraction survey data was also utilized to analyze and characterize the rock mass at the dam foundation. Surface rock mass classification at exposed rocks have been conducted to characterize the rock mass at the dam foundation, accordingly, 50% of the foundation rock mass falls in RMR class 66 – 70, 40% falls in 61 – 65 and the rest 10% falls in class 70 – 80. The data analysis from the geological logs and the seismic refraction survey suggests that the bedrock in the dam foundation is fresh granite, granodiorite, metagranite and schist of different types which can be characterized as fresh, massive, strong, slightly fractured to unfractured rocks of high quality, represented by very high seismic velocities (>4500m/sec) from seismic refraction survey. With the exception of some very soft rocks and heavily jointed media, the majority of the rock mass can be classified as an excellent foundation material. Further, the permeability results from water pressure tests conducted in boreholes at both the abutments indicate very low to medium permeability. The permeability value on right abutment, in BH-3 borehole, demonstrated high to very high permeability in the top part of the dam foundation. The permeability in the intermediate reach on the right abutments is again high as the Lugeon value is more than 65. Therefore, the most effective means of checking seepage through the abutments and the river section would be a provision of a grout curtain. Finally, on the basis of findings of the present research, recommendations are forwarded to be adopted as solutions against geotechnical problems identified at the proposed dam site. Key Words: Rock Mass Rating, Seismic refraction, Lugeon, Permeability, Rock Quality Designation.
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    Integrated Geophysical Approaches for Geothermal Potential Assessment of the Arto Hot Spring, Alaba Woreda, Southern Ethiopia.
    (Addis Ababa University, 2020-06-06) Dessalegn, Wubayehu; Yirgu, Gezahegn (Professor); Mamo, Tilahun (PhD)
    In this research, integrated geophysical survey using electrical and magnetic methods was conducted to assess the geothermal energy potential of the Arto hot spring, Alaba special zone, southern Ethiopia. The study area is located 240km southward from Addis Ababa, and accessible through the Ziwaw - Shasemene- Alaba asphalt road. In Ethiopia, there exist some geothermal energy prospects, which have proved to have significant geothermal potential. Arto hot spring is one of the geothermal sites, about which prospection had not been carried out, yet. The main objective of the research is assessing the geothermal potential of the area, Arto hot spring, by employing geophysical methods, apart from describing geological features (both structures & lithology), and geothermal manifestations, such as hot springs, mud pool and swamps. Totally, the geophysical data has been gathered at -nine vertical electrical sounding (VES) data points using Schlumberger electrode array with a maximum half electrode spacing, AB/2=750m in three traverse lines; and 311magnetic data points with station spacing 10m. The analysis result of the resistivity data was presented in the form of interpreted VES curves, pseudo depth section, stacked section, and geoelectric section maps. Whereas the magnetic data was presented in terms of total magnetic, residual magnetic anomaly, analytical signal, tilt derivative, Euler deconvolution magnetic and magnetic profile maps. From the electrical resistivity analysis, the low resistivity, which is less than 10Ω-m, and observed on the pseudo depth & geoelectric sections along Line-1, depicts that the geothermal manifestations. The result indicates that the low resistivity is due to the combined effects of the lithology of the subsurface rocks, the thermal heat, and the high salinity of the subsurface fluid. In the analysis, low magnetic anomaly coincides with low electrical resistivity results, showing that there exists anomalous subsurface heat. The magnetic anomaly map depicts the subsurface geological structures, trending NE-SW and NW-SE. The dominant structures, observed in the study area is correspondingly aligned with the general trend of the Main Ethiopian Rift (i.e., NE - SW). The main thermal manifestations in the study area are situated parallel with the Main Ethiopian Rift structure. According to the result acquired from the geophysical methods and the thermal manifestations, the area is proved to be potential from geothermal energy resource point of view. However, more detailed-geophysical surveys should be conducted.
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    Integrated Geophysical Investigations for Ground Water Exploration in Legedadi, Addis Ababa Ethiopia
    (Addis Ababa University, 2013-06-06) Belay, Abel; Haile, Tigistu (PhD); Mamo, Tilahun (PhD)
    In this thesis, Geophysical investigating for ground water exploration were carried out at Legedadi, Addis Ababa, Ethiopia. The methods employed were electrical vertical electrical sounding, and magnetic mapping survey. The thesis work mainly focuses on the evaluation of the deep groundwater potential in order to identify the potential area for groundwater and indicate the most promising sites of waterways for drilling capable of supplying potable water on continuous basis. On this work the conducted vertical electrical sounding was processed by using different soft wares and from that apparent resistivity pseudo-section, resistivity inversion curves, 2D-depth model, apparent resistivity contour and also layer thickness depth, were done. And the magnetic model was also processed by using software’s and from it grid map, trend map, analytic map, vertical and horizontal derivative map, magnetic intensity model etc. was done. These results were correlated and interpreted and additional geological information was acquired. Generally the result obtained was interpreted based on in geophysical and geological languages. Finally conclusions and recommendations are given.