Understanding the behaviour of seismically derived Poisson's ratio in near-surface characterization

Abstract

Near-surface characterization is often challenging using a single geophysical technique. We show that seismic refraction is an effective tool by combining P- and S-wave velocity models in the form of V P / V S and Poisson's ratio ( σ ) to detect buried targets along with electrical resistivity imaging (ERI). We acquired vertical and horizontal component seismic data along a 2D profile over two known targets. The first is a water pipe of c . 0.8 m diameter located c . 1.5 m below the surface and the second is a storm drainage pipe (SDP) of c . 1 m diameter at c . 2 m depth. The first arrival times of vertical and horizontal component data were picked and inverted using grid-based tomography. The resulting velocity models have smoothly varying structures and could not identify any of the target features. However, when combined as V P / V S and Poisson's ratio models, the features clearly appeared as anomalous zones. A collocated 2D electrical resistivity model shows the presence of anomalies around the same locations. Our study suggests that anomalous V P / V S and Poisson's ratio values derived from seismic velocities are indicative of the relative changes owing to the disturbances in the soil because of construction with respect to the background instead of the anomaly.