Introduction to the resistivity surveying method. The resistivity of ...

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carry out the more data intensive 2-D and 3-D surveys. The second reason was the lack of
practical computer interpretation tools to handle the more complex 2-D and 3-D models.
However, 2-D and even 3-D electrical surveys are now practical commercial techniques with
the relatively recent development of multi-electrode resistivity surveying instruments
(Griffiths et al. 1990) and fast computer inversion software (Loke 1994).
Figure 3. The three different models used in the interpretation of resistivity measurements.
Figure 4. A typical 1-D model used in the interpretation of resistivity sounding data for the
Wenner array.
1.3 The relationship between geology and resistivity
Before dealing with the 2-D and 3-D resistivity surveys, we will briefly look at the
resistivity values of some common rocks, soils and other materials. Resistivity surveys give a
picture of the subsurface resistivity distribution. To convert the resistivity picture into a
geological picture, some knowledge of typical resistivity values for different types of
subsurface materials and the geology of the area surveyed, is important.
Table 1 gives the resistivity values of common rocks, soil materials and chemicals
(Keller and Frischknecht 1966, Daniels and Alberty 1966). Igneous and metamorphic rocks
typically have high resistivity values. The resistivity of these rocks is greatly dependent on the
degree of fracturing, and the percentage of the fractures filled with ground water. Sedimentary
Copyright (1999-2001) M.H.Loke