SQUARE ARRAY ANISOTROPY MEASUREMENTS AND RESISTIVITY SOUNDING INTERPRETATION

Abstract

The use of geophysics in shallow investigations, such as in environmental, geotechnical and hydrogeological studies requires the development of fast, reliable, high-resolution field and interpretation techniques.When resistivity methods are used, limitations can be expected if ground inhomogeneities and anisotropy are present. In these cases, 1D surveys are not suitable and 2D approaches need geological information so that adequate survey line orientation is chosen. On the other-hand, 3D techniques could prove to be expensive and time-consuming, both in the field and at the interpretation stages.Nonconventional electrode arrays, such as the square array, have been proposed and could provide useful information on local inhomogeneities and anisotropy. However, interpretation material for these arrays is still difficult to obtain.In this paper, it will be shown how conventional resistivity sounding curves can be used to derive ground anisotropy parameters when square arrays are applied. At first, two-layer sounding model curves are interpreted with traditional 1D resistivity curves and estimates for the model apparent resistivity, anisotropy, and strike are derived. Then, several field curves for two, three and four layers are fully interpreted, and it is demonstrated how to obtain depths, apparent resistivity, strike and apparent anisotropy estimates for concealed earth layers.