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shows that the fold involves a steep uprise of resistive layers. But at T
40 s the
phase contours become horizontal, which suggests that the basement of the fold is
flat-layered. The
>
eff pseudo-section is less indicative. At T
>
40 s the NE side of
the fold is marked by higher values of
eff reflecting an uprise of resistive layers.
There is no evidence of the flat-layered basement. A characteristic feature of the
eff
pseudo-section is that the near-surface inhomogeneity generates the vertical static
anomaly that runs between the two sides of the fold through the entire
eff pseudo-
section (the
-effect) and spoils information on the fold.
Now we consider several examples of the pseudo-topography. This pictorial
technique is a three-dimensional generalization of the pseudo-sections. We present
pseudo-topographies plotted from synthetic data.
An initial three-dimensional model is shown in Fig. 11.48. In this seven-layer
model, the first, second and third layers imitate sediments, whereas the fourth, fifth,
and sixth layers are identified with the high-resistivity lithosphere. A conductive
mantle serves as the base of the model. The first sedimentary layer contains a
Fig. 11.48 Three-
dimensional synthetic model
containing a near-surface
(NP), crustal (CP), and
mantle (MP) 2-D prisms;
is
the prism strike azimuth, w is
the prism width, and the
numbers in the frontal and
lateral faces of the model are
resistivities of the layers and
prisms in Ohm
α
·
m
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