NUMERICAL INVESTIGATION ON DC RESISTIVITY ANISOTROPY MODELLING AND IMAGING FOR NEAR-SURFACE STRUCTURES

Electrical resistivity tomography (ERT) is a popular tool to a variety of near-surface applications, including mineral search, civil engineering site investigations, groundwater hydrology and contaminant explorations, because of the efficiency and low cost. The imaging for near-surface structures can provide more intuitive information. The common ERT often applies the assumption that the subsurface rocks are all isotropic, which means the conductivities of the rocks are constant in all directions. Unfortunately, the thin-layered or fracture-aligned sedimentary rocks do not satisfy the assumption, so the common ERT becomes no longer applicable. The anisotropic conditions are incorporated into few previous studies on imaging near-surface structures. These studies are mainly focused on the forward modeling, and the inversion problem is not solved. Thus, the project can make progress in this research area. We investigate how to use the observed potential data on the surface to reconstruct the near-surface geological structure which involves the anisotropic rock. For this goal, an advanced direct-current anisotropy modelling technique, called Gaussian quadrature grid approach and various multi-electrode surveying configurations will be employed, and a non-linear resistivity anisotropy inversion will be developed. We will validate computer program to realize the electric anisotropy inversion (imaging) and design geological models incorporating suitable heterogeneous conditions to optimize the computer program. With the new modelling and inversion program, we will carry out synthetic experiments and find an efficient and effective way to image the near-surface geological structures that may be composed of various media including anisotropic rocks.