P. Schmoldt, PhD - MTNet - DIAS

8. Recovering a synthetic 3D subsurface model using lower-dimensional inversion schemes
P-wave velocity pertubation (%)
-3.0 0.0 +3.0
Fig. 8.2.: Left: group velocity map of the Iberian Peninsula subsurface, obtained from ambient noise tomography using Rayleigh
waves at periods of 20 s, related to structures between 15 km and 30 km (cf. Sec. 7.3.2), with the thick black contour line indicating
the region in which features with a lateral extend greater than 100 km are well resolved; modified after Villaseñor et al. [2007]. Right:
body wave tomography map of the Iberian Peninsula and surrounding regions; modified after Villaseñor et al. [2003]. In both figures
dashed red lines denote the approximated course of lateral changes in the Tajo Basin at the respective depth, green lines denote the
location of the PICASSO Phase I profile, and the highlighted area indicates the region associated with the synthetic 3D model used in
this study (Fig. 8.3).
Mesh dimensions Forward response generation
Number of cells (x,y,z): 61, 58, 49 Min. error: 10 −5
Number of air layers: 10 Relaxations: 75
Dimension (x,y,z) (km):
100, 100, 105 Number of airlayers: 10
(rounded) Convergence factor: 5
Period range (s): 10 −3 –10 5
Tab. 8.1.: Left: parameters of the 3D model used to investigate the optimal inversion setting for the case of two very different
geoelectric strike directions in crust and mantle. Right: settings used to generate the forward response of the model; for details about
the forward response generation see WinGLink [2005].
The model features four blocks of different electric resistivity, with geoelectric strike directions
of N45E (+45° ) for the top 30 km and N45W (-45° ) for the region below; further
details about the model and the generation of the forward response are given in Table 8.1
and Section A.2.1. The model is rotated clockwise by 45 degrees to accommodate straight
mesh lines at an angle +45° and -45°, thereby avoiding edge effects of the rectangular
mesh used for the finite difference (FD) modelling (cf. Sec. 6.3.2). MT responses are
modelled for stations arranged in a grid on top of the synthetic model as well as for 13
additional sites, which are a projection of the PICASSO Phase I stations (cf. Fig. 8.4).
Arranging the stations in a grid facilitates evaluation of inversion results along a range of
2D profiles; the course of a selection of profiles is indicated in Figure 8.5.
8.2.2. Data preparation and analysis
Data obtained through forward modelling responses for stations on top of the 3D subsurface
(cf. Fig. 8.4) are modified in order to meet requirements of the different inversion
programs used in this investigation. First, a minuscule uncertainty level is assigned to the
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