An Empirical Method of Interpretation of Earth-resistivity Measurements

Abstract

A graphical method of analyzing the data obtained from shallowearth-resistivity depth tests is presented. The method is based upon empiricalresults and has no theoretical basis. The usual apparent resistivity-electrodespacing curve is used together with a cumulative resistivity-electrode spacingcurve plotted on the same sheet. The greatly reduced scale required forplotting the cumulative values of resistivity together with the effect of thesummation of the individual resistivity values serves to minimize the effect ofpurely local surface anomalies and inadvertent errors of measurement. The pointof intersection of tangents or straight lines drawn to intersect at zones ofmaximum curvature in the cumulative curve indicates the depth to the underlyingmaterial. Numerous figures are presented in which data from published reportsand from recent field studies are analyzed and the results compared with actualdepths established by borings or with depth values obtained by the use oftheoretical methods of analysis. Smoothly rounded curves of apparentresistivity such as are often obtained in the field, and which have been aserious drawback to attempts to analyze the data empirically heretofore, appearto be susceptible to rather accurate analysis by the method described. The method is best suited to analyses involving shallow two-layerformations. It has been applied successfully, however, in analyzing the dataobtained from tests made over shallow three-layer formations. As with mostempirical methods, its chief advantage is its simplicity and ease ofapplication. Introduction There have been published many papers that discuss the interpretation ofdata obtained from earth-resistivity tests when using the four-terminal methodof electrode spacing developed by Wenner. The majority of these have dealt withtheoretical analyses for two-layer and three-layer formations. Some sets of"master curves" have been presented for use in analyzing field data todetermine the depth to the first and possibly the second horizon below theearth's surface. Although practically all of these theoretical methods ofanalysis have appeared to have particular merit and some have been usedsuccessfully in practice, they have been found to be of little value where thelocal conditions surrounding the test failed to conform to those assumed in thetheory. In certain fields, particularly in civil engineering, relatively shallowexplorations are often involved and geophysical methods of test must competewith the direct methods of exploration ordinarily used. Only when it can bedemonstrated that geophysical methods of test can materially reduce the timeand cost of a given exploration project will the civil engineer abandon directmethods in favor of the interpretations of geophysical exploration data. T.P. 1743

Geoelectric stratigraphy and subsurface evaluation of quaternary stream sediments at the Cooper Basin, NE Texas

“…Soundings were conducted at 0.5 m increments and progressively expanded to 20 m electrode separations. From these data, an empirical technique, Moore's (1945) cumulative resistivity method, was applied, which allowed estimation of depth to horizontal interfaces from Wenner sounding data (Moore, 1945). Cumulative curves (Cum pa) were constructed from the sounding data by plotting p, as a function of electrode spacing, where…”

“…method toMoore's (1945) Cum pa horizons makes it possible to estimate the resistivities of each individual lithologic package identified. Values derived from this technique ranged from 20 to 113.0 Rm.…”

Freshwater reserves of mid-atlantic coast barrier Islands

“…To provide data to test the adequacy of the extrapolation from the Outer Banks to Assateague, water-table height at each of the 15 island sections was estimated using a surface resistivity instrument. The Winner probe configuration was used (see Kelley 1962 for a discussion of the method) and the results were interpreted using the Moore cumulative method (Moore 1945). The accuracy of the resistivity-determined water table was checked by direct comparison with water levels in shallow hand-dug and/or augered excavations and agreement was found to be excellent (Table 3).…”

Integrated approach for identification of potential groundwater zones in Seethanagaram Mandal of Vizianagaram District, Andhra Pradesh, India

“…Some empirical, analytical and numerical methods have been developed for determining resistivity characteristics of the various subsurface formations (Tagg 1934;Roman 1934;Moore 1945 Ghosh 1971; Patra and Nath 1999). In the meantime Narayan and Ramanujachary (1967) showed that it is possible to solve the field equation directly to get resistivities and thicknesses of the subsurface layers from the field data by inverse slope method.…”