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and
n . Summing up,
we can assume that the regional structure of near-surface rocks in the vicinity of
the Lincoln line is favorable for a 2D interpretation of MT and MV soundings. This
important result is consistent with the estimates obtained by Zhdanov and Spichak
(1992) and Spichak (1999).
xy , agree closely with the 1D locally normal curves
n and
12.7.5 Models EMSLAB-I and EMSLAB-II
Two models are of special interest in the discussion about the geoelectric structure
of the Cascadia subduction zone: the EMSLAB-I model (Wannamaker et al . , 1989b)
and the EMSLAB-II model (Varentsov et al . , 1996).
The EMSLAB-I model is shown in Fig. 12.52. This two-dimensional model has
been constructed by the trial-and-error method with a high priority to the TM-mode,
which, as the authors of the model believe, is tolerant to 3D deviations from the two-
dimensionality. This model minimizes the misfit of the curves of
, and virtu-
, . The most interesting elements in the
EMSLAB-I model are (1) the upper conductive part of the oceanic plate subducting
under the Coast Range, (2) a subhorizontal conductive layer in the continental crust
thickening under the High Cascades, and (3) a well-developed conductive astheno-
sphere under the ocean. The question of whether the downgoing plate is connected
with the crustal conductor is left open. No continental asthenosphere is present in
this model, although the shape of the experimental curves of
ally ignores the misfit of the curves of
,
indicates a
CB
NB
CR
WV
WC
HC
DP
150
100
50
0
50
100
150
200
km
0
5
25
4:1
50
1:1
100
150
200
1:4
300
400
km
resistivity (Ohm·m)
<1
<3
<10
<30
<100
<300
<1000
<3000
Fig. 12.52 The EMSLAB I model: CB - Cascadia Basin, NB - Newport Basin, CR - Coast Range,
WV - Willamette Valley, WC - Western Cascades, HC - High Cascades, DP - Deschutes Plateau
(Wannamaker et al., 1989b)
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