Chapter 9: Resistivity, Induced Polarization, and Complex Resistivity
With only a few minor exceptions, electrical geophysical methods can be divided into two categories: (1) galvanic source methods, directly coupling or injecting electrical current into the ground via electrodes, and (2) inductive source methods, inducing eddy currents into the ground via time-varying magnetic fields using coils not in direct contact with the ground. Ground-penetrating radar (GPR) can be considered an extreme high-frequency, dielectric-properties–sensitive example of the latter. Self-potential (SP) effects, due to electrochemical mechanisms in the ground, and telluric current methods (where only ambient voltages, induced by natural EM sources such as the oscillating magnetosphere of the earth, are measured) can arguably be included in the former, but are both passive methods and are beyond the scope of this chapter.
Figures & Tables
Near-surface geophysics uses the investigational methods of geophysics to study the nature of the very outermost part of the earth’s crust. Man interacts with this part of the earth’s crust: he walks on it; he drills and excavates into it; he constructs structures on and in it; he utilizes its water and mineral resources; and his wastes are stored on and in it and seep into it. The very outermost part of the Earth’s crust is extremely dynamic-in both technical (physical properties) and nontechnical (political, social, legal) terms-which leads to both technical and nontechnical challenges that are much different than the challenges faced by “traditional” applications of geophysics for regional geologic mapping and for oil and gas exploration (see Chapter 2).