Application of Varying Geometric Spreads in Seismic Refraction Studies to Characterize the Overburden Strata on the Flanks of Zaria Dam, Northwestern Nigeria
A geophysical investigation was carried out on the flanks of Zaria Dam using Seismic Refraction Tomography. The aim was to analyze the data provided to characterize the different strata of the subsurface within the overburden. To this end, varying geometric spreads were used with optimum geophone spacing of 5 m reduced to 4, 3 and 2 m successively for different traverses on the same profile line. Using the Tomographic inversion, it was possible to derive the picture of the subsurface layering mapped from the Tomograms despite the geologically complex environment. The results gave velocities of 1356, 2543 and 3743 m/s for the overburden, weathered basement and fresh basement, respectively. However, the depth of probe differed as the geophone spacing varied. In some profiles, the model suggested a sedimentary thickness of not less than 20 m overlying the basement. The results showed that as the geometric spread is reduced, the shallow structures within the overburden strata become enhanced. Hence, making it possible to recover hidden and undetected layers with such ranges of velocities as 778–998 m/s and 2197–2439 m/s in the overburden and weathered basement, respectively.
KeywordsTomography Overburden deposits Varying geophone spacing Hidden layers Seismic refraction
- 1.ICOLD (International Commission on Large Dams): World Register of Dams. Version updates 1998–2009. ICOLD, Paris. www.icold-cigb.net (2009)
- 2.Indiana Dam Safety Inspection Manual: Dam management and maintenance (Part 2). Division of Water, Department of Natural Resources, Indianapolis, Indiana (2007a)Google Scholar
- 3.Indiana Dam Safety Inspection Manual: Dam safety inspections (Part 3). Division of Water, Department of Natural Resources, Indianapolis, Indiana (2007b)Google Scholar
- 4.Chinedu, A.D., Osazuwa, I.B.: Generalized reciprocal method applied in processing seismic refraction data from the basement terrain of Zaria, North-Western Nigeria. Niger. J. Phys. 20(2), 377–385 (2008)Google Scholar
- 5.Osazuwa, I.B., Chinedu, A.D.: Seismic refraction tomography imaging of high permeability zones beneath an earthen dam, in Zaria area, Nigeria. J. Appl. Geophys. 66, 44–58 (2008)Google Scholar