P. Schmoldt, PhD - MTNet - DIAS

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Depth (km) Depth (km) 10. Data inversion (a) (b) 0 30 60 90 120 150 180 0 30 60 90 120 150 180 pic020 pic019 pic017 pic015 pic013 pic011 pic009 pic007 pic005 pic004 pic003 pic002 pic001 S N W E Horizontal -100 -50 0 50 100 -20 0 20 Distance from centre of profile (km) Distance (km) pic020 pic019 pic017 pic015 pic013 pic011 pic009 pic007 pic005 pic004 pic003 pic002 pic001 -100 -50 0 50 100 Distance from centre of profile (km) Depth (km) Depth (km) 0 30 60 90 120 150 180 0 30 60 90 120 150 180 -20 0 20 Distance (km) Distance (km) 100 50 0 -50 100 N -20 0 20 Distance (km) S N W E Horizontal pic0XX pic0XX Distance (km) 100 50 0 -50 100 N -20 0 20 Distance (km) Overview X, Y, Z: 0, 0, -50 Resistivity log 10 (Wm) Fig. 10.24.: Results of the initial 3D inversion sequence using (a) a halfspace starting model and (b) a layered starting model. The two inversion models on display possess the minimum RMS misfit for the respective starting model, i.e. 2.05 (a) and 2.35 (b); cf. Fig. 10.23. Models are displayed, from left to right, by a vertical slice parallel to the N-S axis, i.e. approximately parallel to the PICASSO Phase I profile (left-hand plot); a vertical slice through the central area of the profile, parallel to the E-W axis (middle plot); and a horizontal slice through the model at 50 km depth (right-hand plot); relative positions of the slices are indicated in the overview plot at the top-right of this Figure. along the whole length of the PICASSO Phase I profile (labelled ‘a’ in Figure 10.6) is discontinuous in the 3D inversion models. Also, the crustal region is more resistive in the isotropic 3D inversion (for both starting models) than in the isotropic 2D inversion; i.e. in the order of a few hundreds to a thousand of Ωm’s in contrast to the few tens of Ωm’s in the 2D inversion. Model features from this initial inversion sequence, however, are not to be over-interpreted and additional iterations are required to enhance the model. Based on its overall lowest RMS misfit, the model obtained through inversion with a halfspace starting model and a model roughness of 10 (model ‘a’ in Figure 10.24) is used as starting model for an additional inversion sequence of ten iterations. After eight inversion steps the RMS misfit is reduce to 1.5 with subsequent inversion steps exhibiting higher misfits; indicating that a misfit minimum is reached (cf. Fig. 10.25). A comparison between observed and calculated responses for the minimum misfit model of the second 3D inversion sequence (labelled ‘a’ in Figure 10.27) is displayed in Figure 10.26; figures 264 N 3 2 1 0 S
RMS−misfit 3.0 2.5 2.0 1.5 1.0 0.1 1 10 100 Roughness(1/τ) 10.2. Inversion for mantle structures Iteration 0 Iteration 1 Iteration 2 Iteration 3 Iteration 4 Iteration 5 Iteration 6 Iteration 7 Iteration 8 Iteration 9 Iteration 10 Fig. 10.25.: RMS misfit for isotropic 3D inversion models at different iteration steps of the second inversion sequence using the lowest misfit model of the initial inversion sequence as starting model; i.e. the model obtained from the fifth iteration with a halfspace starting model and a model roughness of 10 (cf. Fig. 10.23). The RMS misfits for the fifth iteration of the initial sequence are indicated by markers connected with the dashed black line. The wsinv3d algorithm [Siripunvaraporn et al., 2005a] determined up to four models at each iteration step and uses the lowest misfit model as starting model for the following inversions (cf. Sec. 6.3). The overall lowest RMS misfit is obtained during the second inversion sequence after eight iterations (purple markers). Results are plotted in terms of RMS misfit versus roughness 6 for all models at each iteration step. displaying individual misfits for each station are moved to the Appendix (Sec. A.4.2). It is possible that the model of the eighth iteration step represents a local, rather than the global, minimum (cf. Sec. 6.3), but owing to the considerably low misfit of this model the second inversion sequence is terminated after ten iterations (resulting in a total of 15 iteration steps). Results of the second 3D inversion sequence are presented in terms of the lowest misfit model with the highest model roughness (RMS = 1.50, 1/τ = 10), the model with the lowest misfit for a slightly lower roughness (RMS = 1.59, 1/τ = 3.16), and the lowest roughness model (RMS = 1.75, 1/τ = 0.32); labelled ‘a’, ‘b’, and ‘c’ in Figure 10.27, respectively. The three models exhibit a strong mutual similarity, i.e. all models comprise a relatively conductive region ≤100 Ωm in the centre of the PICASSO Phase I profile at a depth range associated with the lithospheric-mantle beneath the Tajo Basin (i.e. 30 – 110 km). For the Earth’s lithospheric-mantle usually electric resistivities in the range of 1000 Ωm or greater are determined (cf. Sec. 5.2.2). A reduction in the order of one magnitude in electric resistivity implies an unusual geological setting of the lithospheric-mantle, e.g. significantly increased temperatures or well-connected networks of conducting constituents (cf. Sec. 5.1). Ten additional iterations are carried out to ensure that the relatively low electric resistivity of the lithospheric-mantle in the centre of the profile is not the result of smoothing constraints used during the inversion process in combination with low sensitivity of the PICASSO Phase I dataset to the lithospheric-mantle. Therein, a layered a priori model containing a 100 Ωm crust (≤31 km), a 1000 Ωm lithospheric-mantle (31 – 110 km), and 100 Ωm sublithospheric mantle is used, which enforces a more resistive lithosphericmantle. Inversion models obtained using the layered a priori model exhibit a more re- 265
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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
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Regularisation order Smoothing para
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S N 1% 0 Depth (km) 3% Depth (km) 1
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9.1. Profile location Data collecti
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Location (degrees) Recording period
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Geological region Stations Geologic
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9.4. Segregation of data acquired w
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Phase (degrees) 135 90 45 0 Z xy -4
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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 290 and 291: 10. Data inversion isotropic 2D lay
Page 292 and 293: 10. Data inversion Depth (km) Depth
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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
Page 310 and 311: 10. Data inversion 10.3. Summary an
Page 312 and 313: 10. Data inversion owing to availab
Page 315 and 316: 11 Summary and conclusions The key
Page 317 and 318: 11.2. PICASSO Phase I investigation
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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
Page 334 and 335: 298 07-centre profile The profile 0
Page 336 and 337: 300 3D-crust profile The profile 3D
Page 338 and 339: 302 J-centre profile The J-centre p
Page 340 and 341: A. Appendix Anisotropy Resistivity
Page 348 and 349: 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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P. Schmoldt, PhD - MTNet - DIAS

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