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Fig. 12.46
Illustrating the
resolution of the apparent-
resistivity curves in models
S
and
A
at distances of 15 and
85 km from the coast:
1 - locally normal curves
(
n
), 2 - transverse curve
(
⊥
), 3 - longitudinal
curve (
)
thick. In the same zone, the TE-mode clearly distinguishes between crustal and
crust-mantle conductors.
Next we will examine the behavior of the tipper. Figure 12.47 shows the curves of
W
zy
. The coast effect produces an extensive
W
zy
-anomaly extending for about 100
km in the ocean and 300 km on the continent. Note rather high resolution of tippers:
at periods of 100 and 1000 s, the difference between models A and S displays itself
quite distinctly even in the near-coast zone.
Evidently, the TE-mode (longitudinal apparent resistivities and tippers) is more
sensitive to deep conductive zones compared to the TM-mode (transverse apparent
resistivities). This statement, derived from the analysis of simplest models, needs
more detailed elaboration taking into account the structure of the subduction zone.
Figure 12.48 presents a blocky model of the subduction zone involving the fol-
lowing components: (1) ocean, (2) continental sediments, (3) oc - oceanic crust,
(4) oa - oceanic asthenosphere, (5) sp - subducting plate, (6) cc - continental
