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Fig. 12.33
Interpretation of
A
-curves in the mantle-diapir model class. (
a
) starting model; Roman
numerals - numbers of zones, Arabic numerals - values of resistivity in Ohm
·
m; (
b
) correction of
-curves, 1 - theoretical
-curve calculated from starting model, 2 - experimental
longitudinal
-curve, 3 - corrected
-curve
synthetic
in all zones, except for zone IV (Barguzin synclinorium), thereby confirming the
validity of the starting model. The
-curves are corrected through their vertical
translaton that fits the low-frequency branches to the model
sm
-curves. The shift is
generally small which indicates a weak regional
S
-effect.
The TE inversion of corrected
-curves is illustrated in Fig. 12.34. It optimizes
the resistivities of the crust. The initial structure of the sedimentary cover and upper
mantle was fixed during the entire cycle of iterations. The inversion clearly reveals
a continuous conductive layer in the middle crust whose resistivity decreases from
200 Ohm
·
m in the platform area I, II to 30-15 Ohm
·
m in the rift zone III, IV and 60
Ohm
m in the southeastern Trans-Baikal region V, VI (Fig. 12.31). The accuracy of
inversion is rather high. The general
rms
misfit does not exceeds 12%.
Going to the TM inversion, we insert narrow near-surface conductive zones in
the sedimentary cover to simulate the static shift of the transverse
·
⊥
-curves. The
TM inversion optimizes the resistivities of the upper crust, crustal conductive layer
and upper mantle. The result of 25 iterations is presented in Fig. 12.35. The crustal
conductive layer changes insignificantly. Considerable variations are observed in the
