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⊥
shows the transverse
0) from
analytical solution (9.4) and finite element solution (Wannamaker et al. 1987). Note
that both the solutions virtually coincide. In the absence of faults (q = 0) we observe
the strong
S
- effect: the descending branch of the
- curves obtained at the centre of the model (
y
=
⊥
- curve is dramatically shifted
upward with respect to the locally normal ¨
n
- curve, its static shift being about two
decades. But with conductive faults the situation essentially changes. In the case
f
=
3Ohm
·
m the static shift considerably diminishes, while in the case
f
=1
⊥
Ohm
·
mthe
- curve practically merges with locally normal ¨
n
- curve.
9.2 Deep Inhomogeneity in the Presence
of Conductive Faults
In the previous section we saw that the deep faults normalize the apparent-resistivity
curves distorted by near-surface
S
-inhomogeneity. Now we will show that the deep
faults increase the sensitivity of the apparent-resistivity curves to deep conductive
zones.
Figure 9.3 presents a two-dimensional model consisting of five layers. Here the
homogeneous conductive sediments (
1
) and resistive lithosphere (
2
,
3
,
4
)rest
5
). The lithosphere contains a conductive crustal zone
on the conductive mantle (
3
)ofwidth2
(
ν
bordering by vertical conductive channels (faults) of resistivity
f
and width
q
that connect sediments with conductive mantle.
The
⊥
- curves obtained over the midpoint of the conductive zone (
y
=
0) are
shown in Fig. 9.4. The calculations have been performed for fixed parameters
1
=
,
3
10 Ohm
·
m
,
h
1
=
1km
,
2
=
100000 Ohm
·
m
,
h
2
=
19 km
=
1000 Ohm
·
,
3
m
=
10 Ohm
·
m
,
h
3
=
15 km
,
4
=
1000 Ohm
·
m
,
h
4
=
65 km
,
5
=
10 Ohm
·
m and variable parameters q
=
0
,
5km
,ν
=
25
,
100
,
250
,
500 km;
f
=
1
m. Note that in the model under consideration the lithosphere resis-
tance is about 10
9
,
5
,
10 Ohm
·
m
2
Ohm
·
which is typical for stable regions. In the absence of
faults (
q
0) the conductive zone is strongly screened by highly resistive layers
of the llithosphere. Thus, at
=
⊥
- curves practically
ν
=
25
,
100 km the transverse
coincide with the locally normal ˙
n
- curve connected with a normal background.
Fig. 9.3
The
two-dimensional model with
conductive faults bordering
the deep conductive zone
