Geology Reference
In-Depth Information
its depth of investigation. For higher electrode spacings, the depth of
investigation will be more.
When the apparent resistivity observations for all stations on a traverse
and for all such traverses spread over the entire area of the survey are made,
the resistivity values are plotted at their respective positions over a map.
After this, the contours of equal resistivity values for particular electrode
spacing are drawn and are called as equi-resistivity or contour maps. Thus
the representation is in the form of linear maps for several electrode spacings
or contour maps for a particular assumed depth section. The resistivity highs/
lows are marked to give an idea about the epicentral location of the target
(resistive or conductive zone) and its lateral extent. The resistivity profiles
taken across two dykes are shown in Fig. 1. The results show low resistivities
at shallow depths and high resistivities at deeper depths over the dyke thus
indicating the conductive nature due to weathering/fracturing of the dyke in
upper parts and hence suggests that this dyke is not acting as barrier for the
ground water to flow at shallow depths, whereas in deeper levels, the dykes
may be acting as barriers.
Figure 1.
Resistivity profiles in Maheshwaram watershed.
