Resistivity surveys application for detection of shallow caves in a case example from Western Iraq

Abstract

The 2-D and 3-D imaging resistivity techniques were used in the current study to determine the shallow subsurface caves in the Haditha region, western Iraq. The 2-D resistivity imaging has been applied at five locations. The dipole-dipole arrangement was selected with an electrode spacing of 2 m. The inverted models show the anomalous resistivity variation between the background rocks and the voids. Which showed shallow cavities at 1 to 6 m depth, whereas some of them are extending to a depth of 23 m. The unconformity layer between Anah and Euphrates formations is the lowest cohesive than the rocks beneath and above it. Providing the best area for the caves to be formed resulted from dissolving its rocks by leaking rainwater and groundwater. The 3-D resistivity imaging technique was selected near some visible caves by collating seven 2D imaging lines in mapping the subsurface extent of such cavities. 3D imaging draws a sub-surface image in presence of 3D inhomogeneity such as caves. The horizontal slices of 3D models show up these caves with anomalous high resistivity at 0-0.80 m, 0.80-1.72 m, 1.72-2.78 m, and 2.78-3.99 m depths. It also shows a group of small caves, such as the sink-hole canals that connect the main cave to the surface. Both 2-D and 3-D resistivity models have marked a very similar spread of subsurface caves in the study area and show some caves, in the upper part of the unconformity layer. The large values of RMS error for models, attributed to the presence of large homogeneities in the study area. Such heterogeneities are mainly caused by a large variation in the subsurface resistivity of the rocks surrounding the caves and the large spread of shallow caves.