Seismic Refraction Tomography for Engineering Site Characterization in Awka, Southeastern Nigeria

Subsurface characterization is crucial for safe and cost-effective civil engineering design, particularly in regions underlain by weak or heterogeneous geological formations. This study employs seismic refraction tomography (SRT) to evaluate the engineering properties of near-surface materials in Awka, the capital of Anambra State, Southeastern Nigeria. Six seismic profiles were acquired using an ES-3000 seismograph with 24 geophones spaced at 2 m intervals. Data processing and interpretation were performed using ReflexW software, enabling delineation of three major subsurface layers with P-wave velocities ranging from 400–745 m/s, 589–1518 m/s, and 797–2826 m/s, respectively. Engineering parameters including shear modulus, Young’s modulus, bulk modulus, oedometric modulus, and allowable bearing pressure were derived from the measured P- and S-wave velocities. Results show that seismic velocity and corresponding engineering parameters increase with depth, indicating progressive compaction and strength of subsurface materials. The calculated allowable bearing capacity ranges between 1.36 × 10² and 4.50 × 10² N/m², consistent with regional geotechnical data. Findings demonstrate that SRT provides a reliable and cost-effective approach for evaluating foundation conditions in Awka, and can serve as an alternative or complement to conventional laboratory testing. These results are recommended for application in urban planning, construction projects, and subsurface resource management in Southeastern Nigeria.