P. Schmoldt, PhD - MTNet - DIAS

A.3. Auxiliary inversion results for the synthetic 3D subsurface model
A.3.2. Anisotropic 2D inversion
This Section contains a collection of figures displaying results of anisotropic 2D inversion
for the synthetic 3D model that, for the sake of clarity, are only referred to or partly shown
in Section 8.3.3. These models illustrate different aspects of the anisotropic 2D inversion
approach which are recapped here in brief.
Figure A.11 demonstrates the current limitation of the second approach for the anisotropic
2D inversion (isotropic inversion of long period data in the first sequence and
anisotropic inversion of short period data in the second sequence). Long period data are
sensitive not only to mantle but also to crustal structures and their isotropic inversion in
the first sequence yields an erroneous mantle region, which is not altered in the subsequent
anisotropic inversion of the second sequence. A third sequence, consisting of anisotropic
inversion of data from the whole period range can alter previous mantle structures but introduces
anisotropy to the mantle region, therefore contradicting the approach and failing
to reproduce mantle structures of the synthetic 3D model. As a result, the mantle region of
the anisotropic 2D inversion model is significantly different from the synthetic model and
any related responses exhibit an increased misfit. On the other hand, crustal structures are
recovered to some degree using anisotropy to image effects of the oblique strike direction
at crustal depth, with the highest anisotropy magnitude located at the crustal resistivity
interface (between stations pic009 and pic011). The recovery of crustal structures indicates
the potential of approach 2, which should be further exploited once recommended
anisotropy-zones are included in the inversion algorithm (cf. Sec. 8.3.3).
Figures A.12 – A.14 display different results of the anisotropic 2D inversion derived
using different sets of smoothness constraints. The best agreement between inversion
model and synthetic 3D model is achieved using resistivity gradient regularisation with a
lower smoothing parameter (τ=1).
Figures A.15 - A.18 show results of anisotropic 2D inversion for other profiles and stations
used to test reproducibility of findings for the 3D-crust profile with the pic-stations
(Fig. 8.17), of which only parts are shown in Section 8.3.3 (Fig. 8.19). Profiles 3Dcrust-west
and 3D-crust-east (Figs. A.17 and A.18) reproduce the resistivity distribution
of the 3D model in principle, however, the resistivity interface at mantle depth is less
constrained due to large station spacing. Profiles 3D-crust-NS and 3D-crust-EW (Figs.
A.15 and A.16), on the other hand, have an equidistant station spacing of 20 km and exhibit
an overall good agreement with the resistivity distribution of the synthetic 3D model.
Thus, the synthetic subsurface model can principally be recovered using anisotropic 2D
inversion given adequate station spacing.
303