P. Schmoldt, PhD - MTNet - DIAS

ections from enhanced one-dimensional (1D) and 2D inversion procedures for which
otherwise 3D inversion is required. Relations between effects of electric anisotropy and
regional-scale heterogeneities on MT have been discussed, among others, by Heise and
Pous [2001] and Pek and Santos [2006]; previously, however, the focus has only been
on how to distinguish between anisotropy and regional-scale heterogeneities. There has
been no published report about the use of anisotropic inversion codes for the recovery of
oblique strike directions so far, meaning that this study breaks new ground. Performance
of this novel approach is examined in this thesis in a synthetic model study and subsequently
used to investigate the Tajo Basin subsurface. The synthetic model comprises
orthogonal geoelectric strike directions at depths associated with crust and mantle. MT
response data are modelled for numerous locations on top of the model, thereby facilitating
inversions along various profiles and a comprehensive assessment of results for the
different inversion approaches.
In addition to the development of a novel inversion approach, this thesis comprises an
investigation of tectonic processes that shaped the Iberian Peninsula. Therein, models
of the Tajo Basin subsurface are presented that were obtained with the anisotropic inversion
approach developed in this thesis as well as from isotropic 2D and 3D inversions of
the PICASSO Phase I dataset. Results of the different inversion schemes are contrasted
and petrological implication of model features are discussed. Obtained models provide
a remarkable new insight into the local geology of central Spain, permitting conclusions
about a reservoir that is responsible for volcanic events throughout Europe as well as
about interaction between the Tajo Basin subsurface and subducted lithospheric material
beneath the western Mediterranean Sea and Betic Cordillera.
The content of this thesis is divided into five parts, which illustrate the different aspects
related to this work.
A thorough discussion of the MT method is given in Part I: Theoretical background of
magnetotellurics. Therein, sources of the MT method (Chapter 2) and related mathematical
relations (Chapter 3) as well as effects of subsurface characteristics (Chapter 4) are
illustrated, followed by descriptions of Earth’s electric conductivity properties (Chapter
5) and application of the MT methods in order to derive subsurface structures (Chapter
6).
In Part II: Geology of the study area the tectonic evolution of the Iberian Peninsula is examined
and results of previous geological and geophysical studies in the Betic Cordillera
and central Spain are discussed (Chapter 7). In this Part, the two regions along the profile,
Betics Cordillera and Tajo Basin, are discussed individually accounting for their very
distinct geology.
The novel inversion approach for MT data, motivated by the significantly oblique geoelectric
strike directions of the Tajo Basin crust and mantle is presented in Part III: A novel
inversion approach for oblique geoelectric strike directions in crust and mantle. The approach
is first tested in a synthetic model study and results are compared with results
of commonly used isotropic 2D inversions (Chapter 8). Satisfactory performance in the
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