P. Schmoldt, PhD - MTNet - DIAS

10. Data inversion
(a)
Constrained Interfaces Fixed Interfaces Starting model
Depth (km)
Depth (km)
Depth (km)
(b)
(c)
0
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0
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0
7
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0 16 32 48 64 80 96 112 128 144
Distance (km)
Resistivity log10(Wm) 0.7 1.1 1.5 1.8 2.3
Fig. 10.5.: Results of isotropic 2D sharp-boundary inversion using conductivity interfaces (CI-inversion) to evaluate proposed levelled
layer structure of the Tajo Basin crust. Uppermost plot: RMS misfit for each station, with coloured symbols indicating the misfit for
the models shown below (red circles: model a, green squares: model b, blue diamonds: model c). Model (a) is created with layering
according to a compilation of results from seismic reflection studies. Models (b) and (c) are results of sharp-boundary inversion with
fixed and constrained conductivity interfaces, respectively; using model (a) as starting model. See text for further details.
to as CI-inversion), part of the MT2Dinv inversion software implemented in WinGLink
[WinGLink, 2005]. In CI-inversion, changes of electric resistivity (or its inverse, electric
conductivity) along the conductivity interfaces are not penalised by smoothing regularisation
(cf. Sec. 6.3). Therefore, in CI-inversion models, boundaries of regions with different
electric resistivity usually coincide with conductivity interfaces, and variations within the
different regions are small. The layered subsurface model derived in the previous Section
10.1.2 is used as a starting model for the CI-inversion with conductivity interfaces located
at the layer boundaries, coincident with layer depths proposed by seismic studies (upper
plot in Figure 10.5). Forward modelling of the starting model yields a RMS misfit of 5.34
(error floor: ρa = 10%, φ = 5% for the TM mode, and ρa = 20%, φ = 10% for the
TE mode), indicating that the model possesses a minor degree of similarity with the true
model.
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