P. Schmoldt, PhD - MTNet - DIAS

1D
2D
local
3D/1D
3D/2D
regional
4.2. Dimensionality
Fig. 4.14.: Responses for the magnetotelluric (MT) station on top of the 3D/2D model (left-hand side in Figure 4.13). Response curves
comprises four regimes of different dimensionality for different period ranges. For the shortest periods (located on the left-hand side)
the regime exhibits 1D characteristics, changing to 2D, 3D/1D, and 3D/2D for longer periods, when additional boundaries are sensed.
A detailed description of the different regimes and related processes are given in the text.
shift of the apparent resistivity curves and similar phase values for the two modes. The
shift is due to galvanic distortion at the boundaries of the local distorter (cf. Sec. 4.1.1);
this is herein referred to as 3D/1D regime. Due to the distorting nature of the smallscale
body, curves do not adjust to the resistivity of the host mediums (1000 Ωm) but
instead exhibits a decreased conductivity, owing to the additive secondary currents over
the distorter. For comparison, the same station over the conductive dyke in the reference
model (right-hand side in Fig. 4.13) shows the similar distortion for the TM mode but
an adjustment to the host resistivity by the TE mode (cf. Fig. 4.15). This behaviour is
related to the electric component of the TE mode that is parallel to the orientation of the
conductor, thus unaffected by charge build-up on its boundaries (cf. Sec. 3.4.2). For the
longest periods, greater than 10 2 s, responses exhibit another split of the phase data and a
deviation from the parallel nature of the apparent resistivity curves. This response curve
behaviour is due to a superposition of effects from the small-scale body and the regional
2D structure, referred to as 3D/2D regime.
An additional observable feature here is the different trends of TE and TM mode at the
longest periods. Whereas the TM mode approaches the apparent resistivity value of the
host medium and phase values of 45 degrees, the TE mode exhibits a further decrease of
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