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Fig. 12.16
The two-dimensional TS model; resistivity values in Ohm
m are shown within blocks;
blocks of lower crustal resistivities are shaded; A, B, and C are local conductive zones in the crust
·
sites (
y
=45kmforReW
zy
and
y
=
45, 55, 100 km for Im W
zy
), the Re
W
zy
and
Im
W
zy
curves obtained for models with inhomogeneous and homogeneous upper
layers merge together at periods of order 100 s and even less. These periods relate
to the low-frequency range, in which the near-surface MV anomalies attenuate and
effects of deep conductive zones come to the forefront.
The integrated interpretation of the synthetic data obtained in the TS model has
been performed by the method of partial inversions.
Constructing the interpretation model, we assumed that the following a priori
information was available: (1) the sedimentary cover is inhomogeneous, with an
average thickness of 1 km, (2) the consolidated crust is inhomogeneous and can
contain local conductive zones, its resistivity can experience regional variations, and
an inhomogeneous conductive layer can exist near or within the seismic waveguide
(35-50 km), (3) the upper mantle consists of homogeneous layers, and its resistivity
at depths below 200 km can amount to 20 Ohm
−
m, (4) the profile under observation
is bordered on north and south by vast asymmetric media which slowly vary with
distance.
To detail these assumptions, we performed a trial inversion of the tippers using
a smoothing program capable of revealing crustal conductive zones. We applied the
REBOCC program (Siripunvaraporn and Egbert, 2000) and take a homogeneous
half-space with a resistivity of 100 Ohm
·
m as an initial approximation. Figure 12.18
presents this trial model TS-1, resulting from the inversion of Re
W
zy
and Im
W
sy
.It
shows clear evidences of three local crustal conductors A, B, and C (
·
<
30 Ohm
·
m)
but fails to stratify the crust and upper mantle.
The a priori information complemented with data on local crustal conductors
provides the construction of a blocky interpretation model. On this way, we tested
