P. Schmoldt, PhD - MTNet - DIAS

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10. Data inversion TM+TE Depth (km) 0 50 100 150 200 250 300 TE-only 0 Depth (km) S N Campo de Montiel M.P. Loranca Basin 50 100 150 200 250 300 TM-only 0 Depth (km) 50 100 150 200 250 300 TM+TE: 4.51 TE-only: 4.57 TM-only: 2.95 Error floor: r a=10%, f=5% pic020 pic019 pic011 pic009 pic007 pic005 pic004 pic003 pic002 pic001 0 20 40 60 80 100 120 140 Distance (km) log 10 (Wm) 5 Fig. 10.14.: Results of initial isotropic 2D smooth inversion for the Tajo Basin subsurface; using data from both MT modes (‘TM+TE’, uppermost plot), only from the TE mode (‘TE-only’, middle plot), and only from the TM mode (‘TM-only’, bottom plot). Shaded areas indicate regions with low resolution (see text for details), dotted grey lines denote the Niblett-Bostick depth (Sec. 6.3.1) for the longest period of each mode at the respective MT recording station, and the dashed white line in the TM-only inversion model plot indicates a potential location of the electric lithosphere-asthenosphere boundary (LAB) that would be in agreement with previous estimates of the seismic and thermal LAB depth for the Tajo Basin subsurface (cf. Sec. 7.3.2). Location of stations is indicated on the top of the figure, together with labels denoting regions within the Tajo Basin (M.P.: Manchega Plain). Also shown on the top of this figure is the average RMS misfit of the stations with colours denoting values for each of the three datasets. depths can be inferred, indicating a depth extent of approximately 100 km and 300 km for the TE-only and combined-mode inversion models, respectively (cf. Fig. 10.14). A vast extent of the conductive feature, as modelled for TE-only and combined-mode data, is unlikely as it would require an extraordinary geological setting. The purpose of this initial inversion sequence is not to provide a final concluding model though, but to identify contributions of the two modes to the combined mode model. The RMS misfit of the TM-only model is generally lower than the misfit of TE-only and combined-mode models; however, the distribution of the three inversions (TE-only, TM-only, TM+TE) is similar (cf. plot on the top of Figure 10.14). A significant difference between misfits of the three inversion models is observable at stations pic001, pic004, and pic005, for which TE mode data are poorly fit by the best-fitting models derived by the inversion program. The increased misfit, as well as the increased electric conductivity 248 4 3 2 1 0
10.2. Inversion for mantle structures of the TE mode model, may be a result of galvanic distortion by small-scale off-profile features or crustal structures which remain in the dataset despite decomposition of the impedance tensor and cannot be adequately modelled with 2D inversion. The TE mode is usually more affected by small-scale off-profile features than the TM mode (cf. Sec. 6.3); therefore, the TE mode is often down-weighted in cases where effects of 3D structures are assumed. In this initial inversion procedure, error floors of apparent resistivity and impedance phase for both modes are set to 10 % and 5 %, respectively. Modification of error floors in the combined-mode inversion can later be used to weigh the two modes, through that controlling their influence on the resulting inversion search for the best-fitting model. Such weighting of the modes will be carried out in subsequent inversion sequences of this work. A remarkable feature of this initial inversion step is the transition from the resistive uppermost mantle (10 3 – 10 4 Ωm) to the more conductive region below (≈ 10 2 Ωm). For the northern and central part of the TM-only model and the southern part of the combinedmode model, the transition is modelled at a depth of approximately 100 – 150 km, which is consistent with LAB depth estimates for the Tajo Basin region in proximity of the PICASSO Phase I profile by other investigations (cf. Sec. 7). The upward extension of the more conductive region in the south-central area of the TM-only model coincides to some degree with the location of a low velocity region determined in seismic tomography studies (cf. Fig. 7.24). The vast downward extension of the resistor at the southern edge of the TM-only model (indicated by the dashed areas), on the other hand, does not seem plausible and is most likely an inversion artefact. Owing to the low validity of the isotropic 2D inversion results when using a homogeneous crust, the investigation is extended by using projected results of the crustal inversion model (cf. Sec. 10.1.5) as starting model in the inversion for mantle structures. The starting model is augmented by assigning resistivity values of 100 Ωm to cells below the crustal model. Inversion is carried out like the previous inversions at the beginning of this Section, following the Jones Catechism (Sec. A.2.3), using data of periods greater 100 s to minimise contribution of crustal structures, and examining results for each of the modes individually and in combination (Fig. 10.15). Therein, structures at crustal depths (above 30 km) are kept fixed. Data for the TE mode can only be fit poorly by the isotropic 2D inversion models; i.e. despite (unduly) high levels for related error floors of 20% (ρa) and 10% (φ), an unacceptable RMS misfit of 4.01 prevails. Likewise, the misfit for the inversion model using both modes is exceedingly high (RMS misfit = 3.39). Thus, isotropic 2D inversion models are not adequately representing the Tajo Basin subsurface but can only be used to examine characteristics of the models. As for the inversion with a homogeneous crust (Fig. 10.14), models for the three datasets (only TE mode, only TM mode, both modes) differ significantly. At greater depth (>100 km) the TE mode inversion model exhibits a highly conductive region, whereas TM mode inversion yields a highly resistive region. Different characteristics may in parts be related to the limited depth of induction for the TE mode (indicated by the grey lines in Figure 10.15, denoting Niblett-Bostick depth (Sec. 6.3.1) estimates for the longest period 249
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Multidimensional isotropic and anis
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Contents 2.3. Deviation from plane
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Contents 8.3. Inversion of 3D model
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List of Figures 2.1. Amplitude of t
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List of Figures 4.17. Visual repres
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List of Figures 8.2. Ambient noise
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List of Figures 10.10.RMS misfit va
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List of Figures A.15.Result of anis
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List of Tables xviii 5.5. Parameter
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List of Acronyms FE finite element
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List of Symbols Below is a list of
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Symbol SI unit Denotation φ · pha
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Abstract The Tajo Basin and Betic C
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Publications Poster presentations x
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Acknowledgements Team, namely Colin
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Introduction 1 The Iberian Peninsul
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ections from enhanced one-dimension
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Part I Theoretical background of ma
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2. Sources for magnetotelluric reco
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Mathematical description of electro
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yields 3.2. Deriving magnetotelluri
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3.2. Deriving magnetotelluric param
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3.3. Magnetotelluric induction area
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Depth d s d 1 d 2 d n-2 d n-1 t 1 t
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3.4. Boundary conditions materials
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3.5. The influence of electric perm
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Distortion of magnetotelluric data
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4.1. Types of distortion Fig. 4.1.:
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J s 0 s 0 4.1. Types of distortion
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Scale Type Terminology Example Atom
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4.1. Types of distortion the use of
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4.2. Dimensionality Fig. 4.12.: The
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1D 2D local 3D/1D 3D/2D regional 4.
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4.3. General mathematical represent
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4.4. Removal of distortion effects
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Parameter Geoelectrical application
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4.4.5. Caldwell-Bibby-Brown phase t
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Method Applicability Swift angle 2D
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5. Earth’s properties observable
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6. Using magnetotellurics to gain i
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Part II Geology of the study area I
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7. Geology of the Iberian Peninsula
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Recovering a synthetic 3D subsurfac
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direction direction Depth: 12 - 30
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8.2. Generating synthetic 3D model
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Distance from the centre of the mes
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3D N45W 3D-crust TE Rho TE Phi Peri
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8.3. Inversion of 3D model data sch
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Model variation RMS misfit Optimal
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Profile: 3D-crust (TM-only) Depth (
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Parameter Value 8.3. Inversion of 3
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Depth (km) 10 -2 10 -1 10 0 10 1 10
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Depth (km) 10 -2 10 -1 10 0 10 1 10
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Step 1: Isotropic 2D inversion Step
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8.3. Inversion of 3D model data par
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8.4. Summary and conclusions bution
Page 233 and 234: Regularisation order Smoothing para
Page 235 and 236: S N 1% 0 Depth (km) 3% Depth (km) 1
Page 237 and 238: 9.1. Profile location Data collecti
Page 239 and 240: Location (degrees) Recording period
Page 241 and 242: Geological region Stations Geologic
Page 243 and 244: 9.4. Segregation of data acquired w
Page 245 and 246: Phase (degrees) 135 90 45 0 Z xy -4
Page 247 and 248: 0 km 10 km 30 km 100 km 300 km Dept
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Page 257 and 258: 9.8. Analysis of vertical magnetic
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Page 262 and 263: 10. Data inversion WinGLink softwar
Page 264 and 265: a (horizontal smoothing) 10. Data i
Page 266 and 267: 10. Data inversion Short period ran
Page 268 and 269: 10. Data inversion TM+TE Depth (km)
Page 270 and 271: 10. Data inversion (a) Constrained
Page 272 and 273: 10. Data inversion the model into u
Page 274 and 275: 10. Data inversion Depth (km) S N 0
Page 276 and 277: Depth (km) 10. Data inversion S N 0
Page 278 and 279: 10. Data inversion Group velocity m
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Page 282 and 283: 10. Data inversion Shtrikman upper
Page 286 and 287: 10. Data inversion TM+TE Depth (km)
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Page 292 and 293: 10. Data inversion Depth (km) Depth
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Page 300 and 301: Depth (km) Depth (km) 10. Data inve
Page 302 and 303: Modelled Observed Modelled Observed
Page 304 and 305: Depth (km) 10. Data inversion 0 30
Page 306 and 307: 10. Data inversion Depth off LAB (k
Page 308 and 309: 10. Data inversion Depth (km) S 0 5
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Page 315 and 316: 11 Summary and conclusions The key
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Page 324 and 325: A. Appendix Eocene 54 Ma 42 Ma 36 M
Page 326 and 327: A. Appendix A.2. Auxiliary informat
Page 328 and 329: A. Appendix 292 Fig. A.3.: Issues i
Page 330 and 331: A. Appendix A.2.4. Computation time
Page 332 and 333: 296 3D-mantle profile Inversion res
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298 07-centre profile The profile 0
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300 3D-crust profile The profile 3D
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302 J-centre profile The J-centre p
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A. Appendix Anisotropy Resistivity
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A. Appendix A.4. Auxiliary figures
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A. Appendix 314 ρ TE(Ω−m) φ T
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A. Appendix 320 pic003 (off-diagona
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A. Appendix 322 pic013 (off-diagona
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Bibliography Abalos, B., J. Carrera
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Bibliography Artemieva, I. M. (2006
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Bibliography Berdichevsky, M., V. D
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Bibliography Cebriá, J.-M., and J.
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Bibliography de Vicente, G., J. Gin
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Bibliography Egbert, G. D., and J.
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Bibliography Ganapathy, R., and E.
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Bibliography Haak, V., and R. Hutto
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Bibliography Hutton, R. (1972), Som
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Bibliography Jones, A. G., and R. W
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Bibliography Kurtz, R. D., J. A. Cr
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Bibliography Lviv Centre of Institu
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Bibliography Merrill, R. T., and M.
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Bibliography Newman, G., and G. Hoh
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Bibliography Pádua, M. B., A. L. P
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Bibliography Prácser, E., and L. S
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Bibliography Ritter, J. R. R., M. J
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Bibliography Serson, P. H. (1973),
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Bibliography Spitzer, K. (2006), Ma
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Bibliography Tikhonov, A. N., and V
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Bibliography Wanamaker, B. J., and
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Bibliography Xu, Y., C. McCammon, a
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