Comparison between four electrode arrays in delineating sedimentary layers of alluvial fan deposits in eastern Iraq using a 2D imaging technique

Abstract

A resistivity survey is performed in the northern Badra area, eastern Iraq, using a two-dimensional (2D) imaging technique. The mean goal is to compare four electrode arrays (Dipole–Dipole, Wenner–Schlumberger, Schlumberger reciprocal, and Wenner) to examine their resolution and ability in delineating the layers in complex sedimentary deposits. Six 2D imaging stations applied in the study area. The first two stations (2DS1 and 2DS2) are selected to make the comparison. The comparison results showed that Wenner–Schlumberger’s inverse models provide optimal results corresponding to the deep subsurface layers and they show the best resolution with depth compared to the other arrays. Therefore, it is useful in determining the layers, especially in areas with high inhomogeneity and also with the long survey line. The Wenner array presents a high sensitivity to high background noise and/or a long survey line. Its inverse model is incapable of recognizing the layers (in 2DS1), but it gives good images when the noise level becomes small and/or a shorter long survey line is used. However, its resolution is still less than that of the Wenner–Schlumberger array. The Schlumberger reciprocal array successfully delineates the layers, but its inverse models do not show optimal matching with the lithology sections of the boreholes (BH1 and BH2). The Dipole–Dipole array is incapable of determining the underlying layers due to the decrease in its vertical resolution when there is an increase in depth and/or noise contamination. However, it is suitable to use in very shallow investigations (no more 30–40 m depth) and needs high-quality data measurements.