Inversion of resistivity profiling data over hemispherical sinks: Dual electrode configuration

Abstract

The successful application of intersection of two apparent resistivity curves due to two symmetrical electrode configurations for finding the edges of the dike model (Chunduru et&1991) suggests that a similar technique could be devised for other models. In the present study a quantitative technique to find the projections of a hemispherical sink embedded in a semi-infinite space, on the surface is suggested making use of the dual electrode configuration method. Hemispherical sink problem is very useful in mining geophysics. The apparent resistivity over a outcropping hemispherical sink is computed covering the thin and thick hemispherical sink situations with matrix resistivities on either side of the sink are same and different from the resistivity of the sink, for various offsets. Nomograms based on characteristic apparent resistivity anomaly and width parameters are generated for estimating the geometric parameters of the conducting and resistive sinks. Figure 1. shows a vertical section of the sink model and the electrode configuration parameters for a collinear four electrode setup. A and B are the positive and the negative current electrodes while M and N are the positive and the negative potential electrodes respectively. The current passed through A and B is I and the potential difference between M and N is AV. The left edge of the sink is denoted as 0, and the right edge as 0,. Oz is midway between Or and 03. 0 is the reference point of the four electrode system (generally this is taken as the midpoint of the two outermost active electrodes). PZ is the resistivity of the hemispherical sink and PI is the resistivity of the host rock.