P. Schmoldt, PhD - MTNet - DIAS

A.3. Auxiliary inversion results for the synthetic 3D subsurface model
A.3. Auxiliary inversion results for the synthetic 3D
subsurface model
In addition to the results shown in Section 8.3, auxiliary inversion results are derived for
multiple profiles over the synthetic 3D model (cf. Fig. 8.5). For the sake of clarity, these
additional inversion results are placed in this Appendix, sorted by inversion approach. In
general, anisotropic inversion models excel their isotropic counterparts, confirming conclusions
presented in Chapter 8 by demonstrating that respective results for the PICASSO
Phase I profile can be reproduced for other profiles and stations.
Electric resistivity anomalies of profiles parallel to the strike direction of crust or mantle
(Figs. A.5 – A.7 and A.9 – A.10) are due to distortion by off-profile features (as opposed
to effects of oblique strike direction of regions below the mantle). Distortion owing to offprofile
features is a known issue in 2D MT investigation and has been previously studied
by a number of authors, e.g. Ledo [2005]; Siripunvaraporn et al. [2005b], and is not the
topic of this investigation. Respective models are not discussed at great length in this
study, but are included in the appendix for completeness and to confirm results of profiles
intersecting both regions with oblique geoelectric strike directions.
A.3.1. Isotropic 2D inversion
Inversion for the profiles in this Section is carried with the same choice of parameters
that were determined in Section 8.3.1 to yield models closest to the subsurface of the
synthetic 3D model. Results of isotropic 2D inversion generally exhibit a low RMS misfit
(< 3 with a 5% error floor for phases and 10% error floor for apparent resistivities);
increased misfits originate for most models from smoothing constraints of the inversion
process contradicting the sudden changes of electric resistivity in the synthetic 3D model.
Despite the low misfit, the isotropic 2D inversion model are not an adequate reproduction
of the 3D model subsurface. Inversion results for the 3D-mantle profile with stations
synE02 – synL09 (Fig. A.4), decomposed according to the strike direction of the mantle
(N45E), support the findings of the same profile using stations pic001 – pic020 (cf. Fig.
8.8). Inversion models for the 3D-crust profile with stations synE02 – synL09 (Fig. A.8)
decomposed according to the strike direction of the crust (N45W), differ significantly
from the synthetic model subsurface. Instead, 3D-crust profile inversion models exhibit
values similar to the results of profiles parallel to the mantle strike direction (cf. Figs.
A.9 and A.10). Therefore, these models indicate the insensitivity of data decomposed
according to the strike direction of the crust to the electric conductivity distribution of
the mantle, hence the inadequacy of isotropic 2D inversion for a subsurface with oblique
geoelectric strike directions.
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