Evaluation of Reliability in Computerized Geotomographic Image Model Selection by Electrical Methods

Abstract

The recent development of the geoelectrical methods has been able to extract reliable subsurface information from its applications to the earth structure and the environmental earth field data obtained under more complex geological structure environments. This would include weathered overburden layers, vertical contacts, faults, fracture zones, deep bed rocks or host rocks, near-surface lateral or local inhomogeneities and various topographies. The most commonly used controlled source electrical methods, including direct current resistivity measurements for exploration and evaluation of the earth structures and their environments, may be those in which a great variety of electrode arrays may be grouped into two main systems : the surface electrode array system and the solid electrode array system. The surface electrode array system can be divided into vertical sounding and horizontal profiling techniques. The solid electrode array system may be divided into hole (or tunnel)-to-surface and cross-hole measuring techniques. The vertical sounding technique has extended its two-dimensional (2D) interpretation ability by use of continuous vertical sounding (CVES). The horizontal profiling has extended its ability for automatic, high resolution inversion. The solid electrode array measuring has become a new useful tool as an aid to extraction and enhancement of signals due to small or deep, and complex target inhomogeneities. In the resistivity interpretation method, including the so-called computerized geoelectrical image model construction, such as resistivity tomographic section reconstruction and computer animation of resistivity maps, it is worth special mention that evaluating the extraction and enhancement of subsurface information due to target inhomogeneities, or evaluating the effects of electrical arrays found to be sensitive to the reasonable subsurface model reconstructions. Especially, it is very important that one analizes and integrates the effective elements for the reliable evaluation of resistivity interpretation procedures. In this paper, at first, a significance of traditional and newly developed electrical geophysical pseudosections based on sensitivity distributions of the surface and solid electrode array systems are described. Next, we reviewed a model optimization in electrical prospecting by use of Akaike's Information Criterion, which can be considered as the statistical estimator of the entropy or the Kullback-Leibler information measure. Finally, two field examples of evaluation of the computerized image model selection procedure by using pseudosection and AIC are discussed.