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the symmetric or asymmetric bordering background that is composed of horizon-
tally homogeneous layers.
Partial inversions of the synthetic data have been carried out in the class of blocky
media with the use of the II2DC program (Varentsov, 2002) in the following suc-
cession: (1) Re W zy and Im W zy inversion
(2)
inversion
(3)
and
inversion. All the inversions were conducted automatically.
Below, we consider each inversion separately.
1. Inversion of the real and imaginary tippers, Re W zy and Im W zy . Starting resis-
tivities for this inversion are shown in Fig. 12.19. The tipper inversion results in
the model presented in Fig. 12.20. It is referred to as the TS-2 model. The model
agrees well with the initial TS model. The divergence between the tippers calculated
from both models in the period range from 1 to 10000 s is generally no more than
0.02 (Fig. 12.21). Using the MV data alone, we have successfully reconstructed the
most significant elements of the initial model, including the inhomogeneous sedi-
mentary cover, the local crustal conductors A, B, and C, and the inhomogeneous
crustal conductive layer whose resistivity varies from 234 Ohm
·
m in the north to
16 Ohm
m in the initial model). Also resolved
was the contrast between the nonconductive and conductive mantle (1667 Ohm
·
m in the south (from 300 to 10 Ohm
·
·
m/
109 Ohm
m in the initial TS
model). We see that the MV response functions measured on a 200 km profile enable
not only to detect the local conductive zones but to stratify the medium as well (with
an accuracy sufficient for obtaining some petrophysical estimates).
2. Inversion of the longitudinal-impedance phases,
·
m in the TS-2 model against 1000 Ohm
·
m/10Ohm
·
. At this stage, without
going beyond the TE-mode, we control the tipper inversion and gain additional
constraints on the stratification of the medium. The point is that the longitudinal
apparent-resistivity
curves are distorted by static shift caused by near-surface
3-D inhomogeneities. We avoided this difficulty by restricting ourselves to the
Fig. 12.20 Model TS-2; inversion of the tippers Re W zy and Im W zy has been performed using
the blocky II2DC program; resistivity values in Ohm
·
m are shown within blocks; blocks of lower
crustal resistivity are shaded (cf. Fig. 12.16)
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