Geology Reference
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resistivity cross-section can be obtained. As a result, high-definition pseudo-
section with dense sampling of apparent resistivity variation at shallow depth
(0-100 m) is obtained in a short time. It allows the detailed interpretation of
2D resistivity distribution in the ground (Loke and Barker, 1996).
Figure 3 shows comparison of different configurations along a profile. As
seen from the resistivity image, the following are observed.
The pole-dipole arrays bring rather distorted images at depth. The resistivity
of the bedrock is overestimated at the end opposite to the current electrode.
Only the pole-pole array has sufficient depth of investigation to effectively
image the bedrock with resistivity higher than 1500 Ohm.m.
But with respect to Wenner configuration the image at the surface is much
poorer. For instance, the lateral extension at shallow depth of the two
conductive anomalies is clearly detected with the Wenner array, but is not
seen with the pole-pole array.
From another point of view, the high depth of investigation of the pole-
pole array is counter balanced by a large model uncertainty.
MER2D data interpreted with the help of RES2D inversion software and
model uncertainty obtained along two profiles in Mohabatnagar are shown
in Fig. 4 and described below. As seen in Fig. 4, there are two clear conductive
faults respectively located at distance 55 m and 190 m along line A. The
second fault located at 190 m from the profile and at a depth of 20 m seems
to be more prominent compared to the first one, located at 55 m. The second
one presents a lateral extension at shallow depth. The prominent anomaly
also corresponds to large weathered thickness of resistivity 100
m. There
is a clear bedrock raise with a resistivity of around 600
m, to the surface
at distance 45 m. The second conductive anomaly corresponds to a lineament
detected on aerial photography. All the other anomalies observed at depth
are not corresponding to geomorphological features. The presence of
conductive body at the surface raises the uncertainty of the model at depth.
The same anomaly was also prominent in other configurations like Wenner,
and pole-pole array and the basement upliftment is more prominent in the
pole-pole array with extension of conductive zone about 40 m, which could
indicate the fracture in granite.
The bedrock presents a regular deepening from the eastern to the western
part along line B (Fig. 4). No faults are detected as interpreted from the
inverse model. The result shows low resistivity of 60-100
m, which indicates
the weathered fractured granite. At the surface a conductive area is located
between distances 160 and 270 m. This conductive area is not corresponding
to the black shrinking clayey soils of the paddy fields but to the reddish
clayey soils covering the end of a gentle hill slope.
In addition to this, the intrusive lineaments like dykes or quartz veins,
which behave resistive to the groundwater flow, can be taken as an indicative
tool for exploring the groundwater potential zones. The contact zones of the
intrusive material and the host material become weak because of their
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