P. Schmoldt, PhD - MTNet - DIAS
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P. Schmoldt, PhD - MTNet - DIAS

P. Schmoldt, PhD - MTNet - DIAS P. Schmoldt, PhD - MTNet - DIAS

mtnet.dias.ie
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10. Data inversion the model into upper (0 – 10 km), intermediate (10 – 24 km), and lower crust (24 – 31.5 km) as well as the mantle (≥ 31 km). • Features are manually removed or their resistivity values are modified in order to test whether they become re-established in subsequent inversion steps and are therefore likely to be data-supported structures. • Focussed inversions are carried out for specific regions of the model by individually inverting responses from selected stations 1 , namely – stations pic013 – pic017, to refine the shape of the resistive body beneath the Manchega plain (labelled ‘e’ in Figure 10.6); and – stations pic004 and pic005, to investigate the lateral extent of the upper crustal conductor in the north of the Tajo Basin (labelled ‘c’ in Figure 10.6). • Anisotropic 2D inversion is carried out using a range of isotropy parameters (τiso) in order to test for potential anisotropic structures with the results that even for relatively low constraints (τiso = 10) the anisotropy magnitude is overall low and mostly confined to the surficial conductive layer (cf. Fig. 10.7). Misfit and sensitivity to regions of the Tajo Basin crustal model (Fig. 10.6) are examined in the paragraphs below, followed by a discussion of model features and their geological implication in the next subsection (‘Features of the crustal model’, Page 239); deep-seated features at mantle depth are examined in the subsequent Section 10.2. Model misfit and sensitivity The concluding Tajo Basin crustal model fits observed MT data considerably well; the model exhibits a RMS misfit of 1.47 using error floors of 5% for the phases and 10% and 20% for the apparent resistivities of TM and TE mode, respectively. During the inversion, attention was also paid to the misfit distribution, assuring that the global misfit is not controlled by the misfit of a small number of confined regions. As a result, a relatively even distribution of the misfit is obtained using focussed inversions during the model identification process, which reduce the misfit of respective regions (cf. Fig. 10.8). It should be noted, however, that response data of stations in proximity of the DC train line had to be truncated due to high noise levels; thus, structures in this region are less constrained (indicate by white space in Figure 10.8). For the final crustal model (Fig. 10.6), all stations exhibit a RMS misfit of 2.5 or lower with a relatively uniform distribution of the misfit for all stations and periods. Detailed comparison of recorded data and model response for each stations is given in the Appendix (Section A.4.1). In order to determine reliability of regions within the inversion model, sensitivity analysis is carried out following the approach by Schwalenberg et al. [2002]. Therein, a 1 alteration of other model regions during that process is restricted by fixing respective regions and setting the parameter ‘solving for smoothest variation away from a priori model’ 236

S N Manchega Campo de Montiel Loranca Basin Plain Electric Resistivity Seismic zoning pic001 pic002 pic003 pic004 pic005 pic007 pic009 pic011 pic013 pic015 pic017 pic019 pic020 a 0 log10(r) Wm 3.5 Upper Intermed. Lower c b2 b1 6 12 Depth (km) 2.5 Crust Mantle f 18 1.5 24 e d 10.1. Inversion for crustal structures 30 0.5 36 0 15 30 45 60 75 90 105 120 135 Distance (km) Fig. 10.6.: Final model of the electric resistivity distribution at crustal depth beneath the Tajo Basin, derived through inversions of the magnetotelluric PICASSO Phase I profile data in the period range 10−2 – 103 s; see Figure 7.1 for the profile location. Also shown are the geological regions of the Tajo Basin (based on the USGS EnVision map for Europe, Figure 9.1), cross-over point locations of faults with the PICASSO Phase I profile (dotted black lines, cf. Sec. 7.3.1), different crustal and mantle layers derived by seismic studies in this region (thin white horizontal dashed lines, cf. Sec. 7.3.2), and regions of low resolution (shaded). A discussion of model features is given in subsection 10.1.5 (page 239) 237

S N<br />

Manchega<br />

Campo de Montiel Loranca Basin<br />

Plain<br />

Electric<br />

Resistivity<br />

Seismic<br />

zoning<br />

pic001<br />

pic002<br />

pic003<br />

pic004<br />

pic005<br />

pic007<br />

pic009<br />

pic011<br />

pic013<br />

pic015<br />

pic017<br />

pic019<br />

pic020<br />

a<br />

0<br />

log10(r) Wm<br />

3.5<br />

Upper Intermed. Lower<br />

c<br />

b2<br />

b1<br />

6<br />

12<br />

Depth (km)<br />

2.5<br />

Crust Mantle<br />

f<br />

18<br />

1.5<br />

24<br />

e<br />

d<br />

10.1. Inversion for crustal structures<br />

30<br />

0.5<br />

36<br />

0 15 30 45 60 75 90 105 120 135<br />

Distance (km)<br />

Fig. 10.6.: Final model of the electric resistivity distribution at crustal depth beneath the Tajo Basin, derived through inversions of the magnetotelluric PICASSO Phase I profile data in the<br />

period range 10−2 – 103 s; see Figure 7.1 for the profile location. Also shown are the geological regions of the Tajo Basin (based on the USGS EnVision map for Europe, Figure 9.1), cross-over<br />

point locations of faults with the PICASSO Phase I profile (dotted black lines, cf. Sec. 7.3.1), different crustal and mantle layers derived by seismic studies in this region (thin white horizontal<br />

dashed lines, cf. Sec. 7.3.2), and regions of low resolution (shaded). A discussion of model features is given in subsection 10.1.5 (page 239)<br />

237

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