The Auxiliary Point Method of Electrical Sounding Interpretation, and Its Relationship to the Dar Zarrouk Parameters

Abstract

The so‐called “auxilliary point” method for the interpretation of geoelectrical resistivity soundings has received considerable attention from the European geophysicists. However, almost no mention of it has been made in the American literature. It is the aim of this paper to introduce the method and to establish its mathematical relationship to the so‐called “Dar Zarrouk” parameters. The auxiliary point method is an empirical graphical method by which a multilayer problem is progressively reduced to the simple two‐layer case. Hence, to interpret a multilayer sounding curve, use is made of the available two‐ and three‐layer master curves in conjunction with one, or more, of four charts that represent families of auxiliary curves. The four charts are known as the Hummel (H‐chart), the Anisotropy (A‐chart), the Displaced‐Hummel (DH‐chart), and the Displaced‐Anisotropy (DA‐chart). The mathematical basis for the drawing of these charts is discussed, and furthermore the identity of the Dar Zarrouk point to the anisotropy point is shown. The relation between the various parameters of the auxiliary points and the Dar Zarrouk point is graphically illustrated. Other auxiliary methods for the interpretation of sounding curves, e.g., the Cagniard and the Ono charts are essentially the same as the auxiliary point charts. A theoretical four‐layer case illustrates the practical use of the method, its advantages, and its limitations.

Groundwater Potential and Vulnerability Assessment from Integrated Geophysical Methods, Borehole Logging, and Hydrogeological Measurement

“…The soundings were conducted at points of anomaly quantitatively delineated from the EM profiles. Seventy (70) depth soundings were conducted, with maximum half-current electrode spacing (AB/2) of 100 m. The field curves were manually interpreted [22], using master curves [23] and auxiliary point charts [24][25]. Geoelectric parameters obtained frommanual interpretation were later used as a starting model for computer-assisted interpretation [26].…”

Geoelectrohydraulic investigation of the surficial aquifer units and corrosivity in parts of Uyo L. G. A., Akwa Ibom State, Southern Nigeria

“…In reduction of the VES data to 1D geological models, manual and computer modeling techniques were utilized (Zohdy 1965;Zohdy et al 1974). Bi-logarithmic graphs were used to plot the computed apparent resistivities and curves were smoothened to remove the effects of lateral heterogeneities and other forms of noisy signatures (Chakravarthi et al 2007;Akpan et al 2006).…”

Integrated Geophysical Survey In A Refuse Dumpsite Of Aarada, Ogbomoso, Southwestern Nigeria.

“…4), with maximum half current electrode spacing (AB/2) of 65m. The field data was interpreted by applying partial curve matching technique (Koefoed, 1979) with the help of master curves (Orellana and Mooney, 1966) and sets of auxiliary charts (Zohdy, 1965;Keller and Frischnecht, 1966). From the preliminary interpretation, initial estimates of the resistivity and thickness of the various geoelectric layers at each VES locations were determined.…”