Estimation of Shear Wave Velocity for Near-surface Characterisation; Case Study: Ifako/Gbagada Area of Lagos State, S.W. Nigeria

Near-surface shear–wave velocity profiles were acquired at four locations; these at strategic stations in Ifako/Gbagada a sub-urban area in Lagos State. The geophysical surveyed obtained the shear-wave velocity data using Multichannel Analysis of Surface Waves (MASW) technique. These data were acquired with a view to delineating the existing or potential hazards relating to subsidence, distressing and weakening of structures above the earth which is important to public safety, mitigation of property damage and to see the effectiveness of MASW technique in engineering site investigation. The processing method was fully automated by software called SURFSEIS. The study showed that the entire profiles depicted a very low shear-wave velocity (~80m/s to 160m/s) region down to 15m, a signature of saturated peaty/clayey formation. Thus, subsidence, distressing and weakening of structures were inferred to probably resulted from the loose nature of the subsurface soil.