Geophysical Assessment of Soil Liquefaction Potential in the Flood-Prone Lowlands of Awka-Etiti, Anambra State

Flood-prone lowlands in Awka-Etiti, Anambra State, are underlain by loose sand and silt deposits that may be prone to liquefaction during seismic shaking, posing risk to infrastructure and human settlements. This study assesses soil liquefaction potential in the lowlands of Awka-Etiti using geophysical and geotechnical data. Multichannel analysis of surface waves (MASW) was performed at twenty-three sites to derive shear wave velocity profiles to depths of approximately 30 m. Standard penetration test data from nine boreholes within the study area were used to supplement and validate the MASW-derived velocity profiles. Shear wave velocity profiles reveal soft sediment units with Vs values below 180 m/s at depths of 2 to 12 m, consistent with loose unconsolidated material susceptible to liquefaction. The cyclic stress ratio method was applied using Vs-based empirical correlations to evaluate liquefaction potential at each site for a range of design earthquake magnitudes. Factor of safety against liquefaction values below 1.0 are computed for twenty percent of the investigated sites when subjected to a Ml 5.5 earthquake, indicating significant liquefaction susceptibility. The highest risk zones are concentrated along the margins of active flood channels where saturated fine sand is present at shallow depth. Liquefaction potential index values computed from the Vs profiles classify the high-risk sites as having moderate to high liquefaction severity. These findings are directly applicable to foundation engineering decisions for infrastructure in the Awka-Etiti lowlands.

Keywords: MASW, shear wave velocity, liquefaction potential, Awka-Etiti, geotechnical geophysics