P- and S-Waves Vs. ERT Method for Extremely Shallow Water Table

We address the importance of mapping P- and S-wave velocity changes compared to electrical resistivity tomography (ERT) results at Coastal Sabkha of Abu Dhabi (CSAD). Sabkha is characterized by a very shallow water table (<1m) and high shallow heterogeneity. Such complexity often involves alternations in the degree of saturation, water table depth, and lithological boundaries. Therefore, an accurate estimation of water table depth is essential for different applications, including urban development and hydrological studies. In this study, we conducted a geophysical survey, including seismic and ERT, at one of the largest sabkhas in the UAE. The acquired seismic data underwent processing to derive P- and S-wave velocity profiles. The computed velocity profiles were employed to estimate Poisson’s ratio. The obtained results from seismic unveiled three layers present, comprising a dry sabkha sediment layer, a partially saturated layer, and a fully saturated layer. However, the ERT method only highlights the dry-saturated layer boundary. This configuration highlights the unique hydrological system of Sabkhas, featuring a distinctive partially wet transition zone. We highlight the sensitivity of P-wave velocity to near-surface water table, emphasizing the potential for low-velocities at partially saturation zones or inaccurate water table depth mapping in comparison to ERT method.