| Scope and method of study. Forward modeling of Electrical Resistivity Imaging was performed to define the limits present in the algorithms and grids. An analysis was completed of these limits by forward modeling 44 models with the Halihan-Fenstemaker method of acquisition and processing. Twenty four forward models were also run with other arrays and standard processing techniques. Field data was acquired at three field sites in the Arbuckle-Simpson study area. The first site was a saturated fault without water flow at the surface. The second site was a saturated fault with spring flow at the surface. The third site was an unsaturated fault, exposed, and had no water flow. These were examined to determine if resistivity can identify faults that are conduits to flow or barriers to flow.; Findings and conclusions. Electrical Resistivity Imaging is a viable technique to use for locating and identifying fault properties. Error is present in the method but can be minimized. There are three types of errors present from the numerical modeling of ERI data: grid error, depth error, and inversion error. Grid error is the result of the shape of the rectangular grid. This does not allow precise calculations for straight lines that are at an angle to the grid. Inversion error is the result of the grid values being calculated on the nodes of the grid and data being present in the grid center. Contrast error is a result of the averaging algorithm. As the contrast between two objects increases the averaging algorithm causing broadening of the contrast front further from the contact of the two resistivities. This has the effect of making the fault more apparent in the image but lowers the precision the fault location can be selected. Once these are understood more informed analysis can be performed on inverted images. This is shown in the field studies done in the Arbuckle-Simpson Aquifer study. Resistivity can be used to determine if a fault is saturated or unsaturated, and may be able to infer if the fault is hydraulically conductive. |
