P. Schmoldt, PhD - MTNet - DIAS

6.3. Deriving subsurface structure using magnetotelluric data
2005b]). Those inversions are able to cope with distortion effects by small-scale bodies
(cf. Sec. 4), but they might exhibit an inferior performance (in terms of speed or resolution)
due to a set-up that is adjusted to the respective dimensionality. It is therefore
advised to first determine the dimensionality for the dataset (cf. Sec. 4.2) and then apply
the adequate inversion tool. Using an inversion program for a case of higher dimensionality,
e.g. 2D inversion of 3D structures, could significantly reduce computation time,
therefore allowing for higher resolution. However, such inversion can result in serious
misinterpretations of the subsurface when the effects of 3D structures are not adequately
accounted for [e.g. Jones, 1983a; Wannamaker et al., 1984; Garcia et al., 1999; Ledo
et al., 2002; Ledo, 2005] (cf. Sec. 4). Recent inversion programs (1Dai, in Tab. 6.3;
MT2Dinv v6.7 [Baba et al., 2006]) also consider effects of anisotropic structures on MT
responses. These inversion programs account for advances in instrumentation and the
resulting enhanced resolution, as well as revised theoretical concepts. However, such
inversion processes have to be carried out with caution in order to prevent mixing up dimensionality
and anisotropy; e.g. anisotropic 1D instead of isotropic 2D, or anisotropic
2D instead of isotropic 3D (cf. Sec. 4.1.3).
For all types of MT inversion, it has to be kept in mind that the resulting model is only a
fit to the response data and is highly non-unique. Therefore, additional information from
other geological and geophysical studies should be used wherever possible and careful
considerations should be given to the physical implications of the model.
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