Electrical Resistivity Primer

OutlineMotivationGeophysical ImagingSubsurface Electrical PropertiesThe Electrical Resistivity MethodSurveys and Data DisplayTimelapse Electrical Resistivity

Motivation: the need for information on the subsurface

Different professions need to have information on the subsurface. This information need varies by profession, as each profession will typically look at the subsurface from a different perspective. Motivation figure 1 For instance, if one considers the simple subsurface profile on the top of the figure on the left a civil engineer (who may want to build a building, and who would be interested in the bearing capacity and stability of the subsurface) may describe this profile in terms of bedrock and overburden and strength. A hydrologist (who is more interested in the flow and behaviour of water, and may want to understand the effect of irrigation and pumping) may describe the same profile in terms of the saturated vs. the unsaturated zone and porosity and permeability.

Similarly, if we consider the subsurface profile on the bottom of the figure on the left (which shows a leak from a pipeline which is connected to a storage tank) a remediation professional (who would be interested in remediating the subsurface) would describe this in terms of contaminant source zone and plume, and the associated biogeochemical and hydrological properties which would affect remedial efforts. An engineer working for the company who owns the infrastructure would describe this same profile in terms of depth and type of storage tanks and connecting pipes.

It is obvious that in order to do their work effectively each of these groups will need to have information on the subsurface. This information need can be classified in two types of questions: Motivation figure 2

  • Questions about what is where
  • Questions about what is changing (and possibly how and why) spatially and temporally

To answer these questions , there are two types of approaches: invasive approaches, and non invasive approaches. These two types of approaches are discussed in the next section.