P. Schmoldt, PhD - MTNet - DIAS

5. Earth’s properties observable with magnetotellurics
Fig. 5.5.: Typical electric conductivity structures below a continental shield (solid line) and oceanic lithosphere (dashed line); from
Heinson [1999]
Earth’s conductivity structures, different models have been proposed (e.g. Figs. 5.5 and
5.6). The different models are based on (long-term) Earth bound MT and GDS measurements
[e.g. Bahr et al., 1993; Schultz et al., 1993; Olsen, 1998; Heinson, 1999; Neal et al.,
2000; Utada et al., 2003; Tarits et al., 2004; Kuvshinov et al., 2005], satellite supported
geomagnetic experiments [e.g. Kuvshinov and Olsen, 2006, 2008], laboratory studies on
Earth’s materials [e.g. Xu et al., 1998a, 2000a; Nover, 2005; Yoshino et al., 2008], and
theoretical considerations [e.g. Ledo and Jones, 2005; Jones et al., 2009].
More recent models, incorporating step like changes of conductivity, are favourable
over previous smooth models as they have been proven to demonstrate better agreement
with assumed phase changes within the Earth. Phase changes of Earth materials are a
consequence of moving across boundaries in the P-T space. Lab studies (Sec. 5.3) aim to
derive the conditions at which these phase changes occur for certain materials and their
results can be used to guide interpretations of magnetotelluric and seismic investigations.
The depth of the different step changes for certain regions of the Earth is strongly dependent
on the geological history of the region; today it is commonly assumed that interfaces
of the mantle transition zone (MTZ) and below are comparatively flat, whereas shallower
interfaces are thought to exhibit a more pronounced topography. This conclusion, however,
is certainly biased by the reduced resolution of deep-seated features.
88