ORIGINAL PAPER Subsurface characterization using seismic refraction and surface wave methods: a case of Lagos State University, Ojo, Lagos State R. B. Adegbola & E. A. Ayolabi & W. Allo Received: 13 August 2012 / Accepted: 21 November 2012 # Saudi Society for Geosciences 2012 Abstract This study contains the finding of geophysical investigations conducted at the proposed science complex site at Lagos State University, Ojo, Lagos, Nigeria. Surface wave and seismic refraction tests are non-invasive seismic techniques and have been used to determine the shear wave velocity profile of soil deposits. The methods provide a simplified character- ization of subsurface in two-dimensional (2D) (distance and depth) profiles. Seismic records obtained were processed/ana- lyzed by Seis-Imager software to obtain one-dimensional shear wave velocity (Vs) distribution. Multiple Vs obtained were integrated and used to construct two-dimensional Vs map. The measured P- and S-wave velocities were also used to estimate Poisson’ s ratio, rigidity modulus, and N-values. The study had shown that the area investigated composed mainly of loose sediments (clay formation) to the depth of 12 m with P- wave velocity ranging between 125 and 205 m/s and corresponding S-wave velocity between 60 and 100 m/s. The results presented in this study will be vital information for the engineers in construction of the proposed science complex. Keywords Seis-Imager . Rigidity modulus . N-values . Shear wave velocity Introduction Recently, the management of Lagos State University pro- posed the construction of science complex on their Ojo campus in Ojo Local Government Area, Lagos. Seismic techniques are commonly used to determine site geology, stratigraphy, and rock quality. These techniques provide information about subsurface layering and rock geo-mechanical properties using acoustical waves. Seismic surveys play an important role in near-surface investigation for various purposes: engineering, environmental, etc. Seismic refraction survey is the geophysical method most closely related to rock mass properties because the longitudi- nal seismic wave velocity varies with the main features, which characterizes the rock mass. Therefore, the results from such seismic measurements may assist in rock mass engineering (Palmstrom 1996). The seismic refraction method can provide two-dimensional (2D) profile interpretations of subsurface horizon interface depths and compression wave (p-wave) velocities within those horizons (Rucker 2000).The method utilizes the propagation of compressional or primary seismic waves. The ratio of the shear and longitudinal sonic velocities can be used to determine the dynamic moduli of the rock (Sjögren et al. 1979; Sjögren 1984). Seismic refraction tech- nique provides a simplified characterization of subsurface in 2D (distance and depth) profiles. Information provided by seismic refraction includes compressional wave velocities within investigated subsurface profile. These velocities are interpreted to be present within layers or horizons whose depths are also interpreted. Limitations due to subsurface geometrics such as thin layers and lower velocity horizons underlying higher velocity must be understood. Seismic sur- veys commonly used for near-surface investigations imple- ment P- and S-wave reflection and refraction methods. The method has been gaining a growing popularity, mainly for estimating Vs distribution. Surface wave tests are non- invasive seismic techniques that have been traditionally used to determine the shear wave velocity profile of soil deposits (Lai et al. 2002). Seismic refraction continues to be the most frequently applied seismic technique for shallow subsurface investigations (Burger 1992). R. B. Adegbola Department of Physics, Lagos State University, Lagos, Nigeria e-mail: adegbolaji@yahoo.com E. A. Ayolabi (*) : W. Allo Department of Geosciences, University of Lagos, Lagos, Nigeria e-mail: eojelabi@yahoo.com Arab J Geosci DOI 10.1007/s12517-012-0784-2