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Practical Magnetotellurics
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 (ISBN-13: 9780511079191)

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Index

Bold entries are defined in the glossary. Italic page numbers refer to a figure.

active induction technique, 5, 191–192

   and source-field geometry, 191

   use in static shift correction, 111–112, 192

A/D converter, 43, 43–45

   calibration of, 62

   for fluxgate magnetometer, 43–44

   for induction coil magnetometer, 44–45

   resolution, 43, 43–45

adjustment length see horizontal adjustment length

aliasing, 214

   in frequency domain, 62

   in time domain, 42–43, 43, 45

   Nyquist frequency, 42–43, 43, 45

   spatial, 47–48, 48, 78

Ampère’s law, 18

anti-alias filter, 46

anisotropy, 80, 91, 107, 165

   and array data, 48, 183

   and decomposition model, 93–94, 95

   and electromagnetic strike, 93–94, 108–109, 165, 171

   and impedance phase splitting, 93–94, 95, 107, 109, 128

   and inversion, 131, 137–140, 139

   and mantle conductivity, 168–169, 171

   and percolation theory, 160–161

   and 2-D modelling, 128, 131, 133, 137–140, 139, 144–145

   and skew, 108, 108–109

   case studies, 168–169

   distinguishing from lateral heterogeneity (hypothesis testing), 107, 110, 183, 183

   equivalence of macroscopic and microscopic, 107–108, 108

   hydrogen diffusivity, 10, 168, 170–172

   of graphite, 149

   of KTB core samples, 154

   of mylonites, 148

   scale dependence, 154

apparent resistivity, 214

   and three-dimensional induction, 98–101, 105

   and 2-D inversion, 131, 140, 140–141, 144

   and vertical contact, 30, 74

   comparison of thick vs. thin layers on, 127, 127–128, 129

   definition of, 2

   of the layered half-space, 23–27, 27

   pseudosection, 76, 78

   single-site display of, 74–75

   static shift of, 79, 80–81, 92, 111, 114, 114–115

   static shift correction of, 111–115

Archie’s law, 152–153

array studies, 133, 182–183

   anisotropy test with, 183

artefacts, 76, 100–101, 137–141, 139, 140

asthenosphere, 167, 168

audiomagnetotellurics (AMT), 41, 45

aurora australis, 5, 214

aurora borealis, 5

auroral electrojet see polar electrojet

backing-off, 44

basalt

   conductivity of, 157

Berdichevsky average, 159, 214

bivariate linear regression, 66

   and noise, 65–66

   coherence, 206

   implementation, 205–206

borehole magnetometer, 190

B-polarisation, 28, 28–31, 30, 80, 98–101, 99, 104, 128, 136, 140, 215

   pseudosection, 76, 76–78

bulk conductivity, 6, 157, 215

   versus direction-dependent conductivity, 159

calibration, 45–46, 215

   as part of data processing, 61–62

   of A/D converter, 62

   of sensors, 61

carbon see graphite

coherence, 215

   and bivariate regression, 206

   and noise, 52–53

   and robust processing, 70

   definition of, 52

   versus degrees of freedom, and confidence intervals, 52–53, 53

colour scale, 75, 75, 143

compensation, 44, 215

   of the geomagnetic main field at the field site, 57

complex Fourier coefficients, 60, 209–211, 215

complex number, 49, 88, 215

composite media, 155–159

conductance, 25, 127–128

   anisotropy of, 160

   delta functions, 133, 133–134

conduction, 5–10, 16, 152–154, 216

   composite media and mixing laws, 155–159

   geoelectrics, 5

   interconnectivity, 6, 152

   mechanisms, 5–6, 148, 170–172

      electrolytic, 6, 150

      hydrogen diffusivity, 150, 170–171

      metallic, 5–6

      semi-conduction, 6, 153

      surface, 7

   pressure dependence of, 148–149

   random media and percolation theory, 163–164

   temperature dependence of, 153

conductivity, 16

   average, of Earth, 13

   as a model parameter

   distribution in Earth models, 19

   laboratory measurements, 10, 147, 148, 149, 150, 151, 157

   mid-mantle transition zones, 10, 151

   of commonly occurring earth materials, 10, 148

   of mantle, 9–10, 11, 114, 150, 150–151

   of seawater, 8

confidence interval, 49, 118, 169, 216

   and coherence, 52–53

   and degrees of freedom, 52–53, 53, 63, 205

   and Fisher F-distribution, 205

   and Gaussian distribution, 220

   and model misfits, 123–125

   estimation from measured data, 68

   implementation, 206–207

continental mantle

   conductivity of, 173

cosine bell, 60, 63, 216

   implementation, 211

C-response, 216

   and impedance tensor, equivalence relationship, 113, 187–188, 195–198, 219

   definition in the wavenumber-frequency domain, 196

   from internal: external part separation in the wavenumber-frequency domain, 198

   from magnetotellurics in the wavenumber-frequency domain, 197

   from Z/H technique and magnetic daily variation, 183–187

   from Z/H technique in the wavenumber-frequency domain, 198

   in spherical co-ordinates, 184, 185

   of the layered half-space, 23–27

   of the sandwich model, 27, 38

   use in static shift correction, 113–114

crustal studies, 170

   current channelling, 115–116

   equipment for, 37, 40

   geotherms, 153, 153

   graphite, 170

   hypothesis testing, 155, 160, 161

   multi-disciplinary, 166–167

   period range, 38

   saline fluids, 6, 170

   sandwich model, 27

   thick vs. thin conductors, 127–128, 155–159

current channelling, 50, 115–116

data-acquisition system, 42–47

   datalogger, 42–47, 54

   for induction coils, 47

data processing, 60–64, 63–64, 71

   calibration, 61–62

   confidence intervals, 68

   cosine bell, 60, 63, 211, 216

   decimation, 70, 216

   degrees of freedom, 64–65

   discrete Fourier transform (DFT), 60–61, 209–211, 217

   estimation of impedance tensor elements from measured data, 65–74

   evaluation frequencies, 62–63

   least-square processing, 66

   remote reference processing, 66–67, 225

   robust processing, 58, 66, 225

   spectral matrix, 64

   spectral window, 63, 226

   stacking, 65, 221

data quality

   and decomposition, 79

   and duration of a campaign, 49

   and economic considerations, 54

   in dead-band, 3

dead-band, 3, 3, 5, 216

decimation, 70, 216

   and Nyquist frequency, 70

declination, 13, 216

decompose, 216

decomposition model (hypothesis), 217

   and anisotropy, 93–94, 95

   as an hypothesis test, 101–102, 105

   Bahr model, 87, 88–90

   Groom–Bailey model, 90–93, 92

   Larsen model, 86–88, 87

   of tipper vector, 116

deep-crustal conductivity, 8, 11, 165

   and anisotropy, 93–94, 95, 107

   and mixing laws, 146

   case studies, 93–94, 140–141, 166–167

   comparison of field and laboratory measurements, 148

   fluids vs. graphite, 8, 9, 146, 149, 160, 161, 166–167, 170

   graphite, 8, 148–149

   transfer function, 27

degrees of freedom, 49, 87, 201, 217

   and confidence intervals, 52–53, 53, 63, 207

   estimation during processing, 64–65

   of chi-squared distribution function, 201

   of Fisher F-distribution function, 202

   reduction of the number of in robust processing, 69

   vs. coherence, and confidence intervals, 52–53, 53

delta (δ) technique, 89–90, 217

determinant average, 159, 217

differential equation modelling methods, 119–120, 120–121

diffusion equation, 5, 15, 23, 81, 195, 217

   and MT as volume sounding, 174

   in the wavenumber-frequency domain, 196

dipping interface, 109, 110, 140

discontinuity

   and induction vectors, 33

   and Maxwell’s equations, 28–31

   and static shift, 80, 80–81

   E- and B-polarisation transfer functions, 30, 76

discrete Fourier transformation (DFT), 60–61, 217

   implementation, 209–211

distortion matrix, 86, 217

   resistor network model of, 156–157

diurnal variation, 10, 13

D+model, 133–134, 217

downwards-biased impedance, 71–74

duration of a field campaign, 49–50

   for mantle studies, 49

   with induction coil magnetometers, 50

earthquakes, 166, 180

Earth response function, 218

effective conductivity, 156, 218

effective conductance, 161

effective porosity, 161

electrical conductivity, 1

   in relation to electromagnetic skin depth, 2

electrical permittivities, 16, 19

electrodes, 41–42

   non-polarisable, 41, 41

   set up at field site, 55–57

electrojet see equatorial electrojet and polar electrojet

electromagnetic array profiling (EMAP), 218

electromagnetic skin depth, 2, 218

   and galvanic effects, 35, 85–86, 86

   and penetration depth, 2

   and rules for designing a model grid, 122–123

   and thin-sheet modelling, 121

   and 3-D induction, 36

   and transfer function, 22

electromagnetic strike, 79–80, 218

   90° ambiguity of, 85

   and anisotropy, 93–94, 108–109, 165, 171

   and geodynamics, 165, 171, 175, 180

      as a tool for decoupling regional structures, 100–101, 101, 102–105, 140–141

   from decomposition model, 86, 89–90, 90–93, 94–98, 103

   of the, 28–29, 35, 84–85(Swift) model, 35

E-polarisation, 28, 28–31, 30, 80–81, 98–101, 99, 104, 128, 218

   pseudosection, 76, 76–78

equatorial electrojet, 16, 17

   and Z/H technique, 187–188, 189

equinoxes, 186

equivalence relationship, 113, 187–188, 195–198, 219

error propagation

   Swift skew and strike, 85, 97, 98

   in phase-sensitive skew and strike, 94–98, 97, 98

evaluation frequencies, 62–63

   and resolution, 63

Faraday’s law, 176

fast Fourier transformation (FFT), 219

Fourier transformation, 60–61, 208–209, 219

finite difference modelling, 120–121

finite element modelling, 120

fluids

   effects of salinity, temperature and pressure on resistivities of, 7, 7–8

   interconnectivity of, 6, 7

   resistivity of seawater, 8

   results from boreholes, 150

   vs. graphite discussion, 8, 9, 146, 149, 160, 161, 166–167, 170

fluxgate magnetometer, 37, 39, 39–40, 219

   and A/D converter, 43–44

   sensitivity of, 40, 222

forward modelling, 117–128, 131, 132

   advantages and disadvantages of compared to inversion, 118, 142–143

   and galvanic effects, 127

   and non-uniqueness, 131

   avoiding common mistakes, 126–128

   calculating transfer functions from fields, 125–126

   choosing the appropriate algorithm, 118–119

   differential equation methods, 119–120, 120–121

   integral equation methods, 120

   thick vs. thin conductors, 127, 127–128

   with inhomogeneous source fields, 189–190

gabbro

   conductivity of, 157

galvanic effects, 79, 81, 219

   and electromagnetic skin depth, 35, 85–86, 86

   and forward modelling, 127

   and impedance phase mixing, 81, 88–89

   and superimposition (decomposition) models, 85–98

Gaussian distribution, 219, 220

   departure from, and robust processing, 69

   errors and misfits, 134

   of static shift factor, 113

Gauss separation, 10–13, 220

geodynamics, 170–172, 180

   and electromagnetic strike P9.2, 165, 171, 175, 180

geoelectrics, 5

geotherms, 153, 170

geothermal studies, 166, 177, 178

geomagnetic depth sounding (GDS), 1, 48, 183

grain-boundary films, 7

granite

   conductivity of, 157

graphite, 6, 8–9, 148–149

   genesis, 8–9, 153–154, 170

   grain-boundary films, 8

   in shear zones, 169

   interconnectivity of, 9

   laboratory measurements, 153–154

   KTB, 8, 149, 149

   resistivity of, 11, 149

   vs. fluids, discussion, 8, 9, 146, 149, 160, 161, 166–167, 170

   xenoliths, 8

gridding rules, 119, 122–123

   example grid, 123, 124

groundwater, 177, 178–179, 179–180

half-space, 19, 21, 133, 220

   apparent resistivity, 2

   homogeneous, and transfer function, 21–22

Hashin-Shtrikman upper and lower bounds, 11, 156, 220

horizontal adjustment length, 31–32, 220

   and impedance phase, 31, 32

   and oceanic mantle, 32

horizontal gradient technique, 188–190

horizontal wavenumber, 196, 198

host rock, 143

hydrogen diffusivity, 9, 10, 150, 169, 170–172

   anisotropy, 10, 168, 170–172

   conduction, 150, 170–171

hypothesis testing, 15, 125, 142, 155, 161, 220

   anisotropy model, 107, 110, 183, 183

   decomposition model, 101–102, 105

   fluids vs. graphite, discussion, 146, 149, 160, 161, 166–167, 170

H+model, 134

impedance phase, 15, 221

   and determination of electromagnetic strike, 89–90

   and horizontal adjustment length, 31, 32

   and static shift, 79, 81, 92, 112, 113, 114, 114–115, 127

   and 3-D induction, 105

   and 2-D inversion, 131, 140–141, 144

   and vertical contact, 30, 74

   comparison of thick vs. thin layers on, 127, 127–128, 129

   mixing due to galvanic effects, 81, 88–89

   of impedance tensor elements, 34, 88

   of layered half-space, 25–27, 27

   pseudosection, 76, 76–78

   single-site display of, 74–75

   splitting of, and anisotropy, 93–94, 95, 107, 109, 128

   splitting of, and stability of phase-sensitive strike, 94–98

impedance spectroscopy, 147

impedance tensor, 34, 83–93, 126–128, 141, 221

   and C-response, equivalence relationship, 113, 187–188, 195–198, 219

   calculating from modelled fields, 125–126

   classification of, 93, 94

   decomposition of, 86, 88–90, 90–93, 93–94

   definition of, 34, 83

   estimation from measured data, 65–74

   layered-Earth model, 83

   mathematical rotation of, 81–83

   phase-sensitive skew of, 90

   2-D model, 83–84

   “upwards”- and “downwards”- biased estimates of the elements, 71–74

inclination, 12–13, 221

induction arrows, 32–34, 33, 103, 103, 105, 107, 128, 221

   decomposition of, 116

   discontinuity, 33

induction coil, 37, 39, 40, 221

   and A/D converter, 44–45

   data-acquisition system for, 47

   sensitivity of, 40

   site occupation with, 50

inductive scale length, C, 221

   and dimensionality, 35

   and galvanic distortion, 35, 86, 86, 88

   and impedance tensor, equivalence relationship, 113, 187–188, 195–198, 219

insurance industry, 180

integral equation modelling methods, 120

interconnectivity, 164

   conduction, 6, 152

inversion, 130–145

   and anisotropy, 131, 137–140, 139

   and apparent resistivity, 131, 140–141, 144

   and a priori information, 142

   artefacts of, 137–141

   avoiding common mistakes, 131, 143–145

   model roughness, 135, 143

   layered models, 134

   steps involved in, 138, 139

   vs. forward modelling, 142–143

ionosphere, 3, 4–5, 13, 14, 20, 113, 179

   current vortices associated with magnetic daily variation, 183–187

island effects, 122, 174–175

Kenya rift, 102–105, 103, 105, 106

Kramers–Kroenig relationship (see also Weidelt’s dispersion relation), 25

KTB borehole

   anisotropy of core samples, 154

   fluids, 150

   graphite, 8, 149, 149

   vertical gradient technique, 190

laboratory conductivity measurements, 146, 147, 147, 148, 149, 151, 157

   comparison with field measurements, 146, 148, 151, 151

   graphite, 153–154

   mantle, 146, 150

   melts, 150

   transition zones, 151, 154

Larsen’s (1975) model, 86–88

   misfit measure, 88

layered half-space, 23, 23–27, 83, 195

   apparent resistivity, 23–27, 27

layered models, 134

least count, 43, 44, 221

least-square processing, 66, 221

   bivariate, 205–206

   confidence intervals of regression parameter, 205, 206–207

   univariate, 204

least-structure model, 130–131, 133, 135–137, 137–141, 138, 139, 142, 143, 222

   examples of artefacts in, 139, 140

lithology, 6–7

lithosphere-asthenosphere boundary, 135, 168, 171

local response, 84, 86, 87, 88–89, 91–92, 102, 222

low-pass filter, 34

   ocean as, 45, 173

lower mantle, 188

magnesiowüstite, 151

magnetic daily variation, 10, 13, 183–187, 195, 222

   and estimation of C-responses, 183–187

   data-acquisition system for, 47

   ionospheric current vortices, 183–187, 184

magnetic distortion, 81, 115–116

magnetic permeability, 2

magnetic storms, 4, 5, 43, 179, 222

   and failure of the plane-wave assumption, 69

magnetohydrodynamic process, 3

magnetopause, 4, 4, 222

magnetosphere, 4, 4–5, 14, 179, 222

magnetotail, 4, 222

magnetovariational study, 182–183

   anisotropy test with, 183

mantle conductivity, 9–10, 11, 114, 150–151

   and anisotropy, 168–169, 171

   and hydrogen diffusion, 170–172

   comparison of field and laboratory measurements, 146, 151, 151

   heterogeneous mantle models, 187–188

   laboratory measurements, 150–151

   continental vs. oceanic, 173

mantle convection, 172

mantle flow, 10, 102, 168, 170–171

mantle plume, 169, 170, 175

mantle studies, 167–170, 170–171, 173

   period range, 38

   sensors, 40

Maxwell’s equations, 15, 16, 18–19, 117, 120–121

   discontinuity, 28–31

microcracks, 7

misfit measures, 83

   and numerical modelling, 123–125, 125, 131–132, 134, 143–144

   Groom–Bailey model, 92–93

   Larsen’s model, 88

   model misfit and confidence intervals of measured data, 123–125

   one-dimensionality (D+ model), 134

   phase-sensitive skew, 90, 106–107

   Swift skew, 85, 106

mixing laws, 155–159

   and deep-crustal studies, 146

   and fluids vs. graphite, discussion, 146, 160–161

   effective medium theory, 156–157

   Hashin–Shtrikman upper and lower bounds, 11, 156, 156–157, 220

   minimum energy theorems, 155

   percolation theory, 158–159, 163–164

   Waff (1974) model, 156

Monte-Carlo technique, 130, 131–132, 222

MTnet, 14

Nernst–Einstein equation, 170–171

nodes, 120–121, 122–123, 135, 162

noise, 50–53, 65

   and biased estimates of the impedance tensor elements, 72–73

   and coherence, 52–53

   and remote-reference processing method, 67

   cultural, 50–51

   electrical, 45

   meteorological, 51

   non-uniqueness, 127–128, 131, 142, 143, 145

   of magnetic sensors, 40, 44, 51

   representation in the bivariate linear regression, 65–66

normal distribution, 199–200, 219

northern lights, 5

numerical modelling, 14

   and a priori information, 142

   and current channelling, 115

   and misfit measures, 123–125, 125, 131–132, 134, 143–144

   and static shift, 127

   avoiding common mistakes, 126–128, 131

   case studies

      2-D, 140–141

      2-D, and anisotropy, 128, 131, 133, 137–140, 139, 144–145

      3-D, 102–105, 105, 106, 141

   designing a grid, 122–123, 124, 144

   forward modelling vs. inversion, 142–143

   rough vs. smooth models, 130–131, 142

   steps involved in inversion, 138, 139

   thin-sheet, 121, 121, 174–175

Nyquist frequency, 42–43, 60, 223

   and decimation, 70

Nyquist period, 43, 45, 46, 210, 223

Occam inversion, 135–137, 223

   and static shift correction, 112–113

ocean bottom studies, 172–176, 177

   and vertical gradient technique, 190–191

   instrumentation, 45, 172, 173, 178

oceanic mantle

   and adjustment length, 32

   conductivity of, 173

oceanography, 176

olivine, 9, 10, 170–171

   alignment of, 148, 165, 168

   phase transitions, 151

ore body, 143, 177, 179

outliers, 58, 69, 69, 223

   and time window length, 70

oxygen fugacity, 150–151

Parkinson convention, 33, 33, 223

partial melt, 6, 9, 168, 169–170, 171, 173

   comparison of field and laboratory measurements, 150

penetration depth, 1, 2, 10, 79

   and electromagnetic skin depth, 2

   and galvanic effects, 86

   and horizontal adjustment length, 31–32, 32

   and modelling, 144

   and static shift, 80–81

   and transfer function, 21–22

   in thermal diffusion, 15, 42

   of the layered half-space, 25–27

percolation theory, 158–159

   and anisotropy, 160–161

   and resistor networks, 163–164

   conduction, 163–164

percolation threshold, 163–164, 164, 223

period band, 44, 47, 223

permeability, 5, 6–7, 39, 223

perovskite, 151

petroleum industry, 166, 177, 178

petrology, 170

phase lag, 34

phase transitions, 10, 114

   and conductivity increases, 151

   olivine to wadsleyite, 10

   ringwoodite to perovskite + magnesiowüstite, 10

   wadsleyite to ringwoodite, 10

phase-sensitive skew, 90, 106–107, 220, 223

   error of, 95–96, 169

   3-D modelling of, 105, 105, 107

phase-sensitive strike, 89–90, 224

   error of, 94–98

   3-D modelling of, 105, 105, 107, 128

plane wave, 16–17, 224

   assumption, 14, 16–17, 20, 65

   departure from plane wave source field in the daily variation, 184, 185

   departure from plane wave source field in the electrojet, 16, 189

   failure of the assumption during magnetic storms, 69

polar electrojet, 16, 17, 189, 190

porosity, 5, 6–7, 179, 224

   and Archie’s law, 152–153

   sedimentary rocks, 6–7

   volcanic rocks, 7

power spectrum, 3

   dead-band, 3

   practical implementation, 60–64, 63–64

   source field, 3–5

   theoretical, 212

probability distributions, 199–202

   chi-squared, 201

   Fisher, 201–202

   Fisher and confidence intervals of bivariate linear regression, 206–207

   Fisher and confidence interval of univariate linear regression, 205

   normal, 199–200

pseudosection, 75, 76, 76–78, 103, 224

   E-polarisation, 76, 76–78

   B-polarisation, 76, 76–78

pyroxene, 151

random media, 163–164

rapid relaxation (RRI) inversion, 135–137, 224

raw spectra, 61, 224

recursion formula, 24, 224

regional response, 84, 86, 102, 116, 224

   Bahr’s model, 88–89

   Groom–Bailey model, 91–92

   Larsen’s model, 86–87

regularisation mesh, 136, 225

remote-reference processing (method), 66–67, 225

   and noise, 67

resistivity, of

   commonly occurring Earth materials, 10, 11

   dry olivine, 9, 11

   dry rocks, 157

   graphite, 11, 149

   partial melt, 9, 11

   saline fluids, 7, 11

resistor networks, 158, 160

   and percolation theory, 163–164

   and static shift factor determination, 161–162

resolution

   and evaluation frequencies, 63

   and modelling of MT data, 127, 129, 130, 143

   of A/D converter, 43, 43–45

   of E- and B-polarisation, 76

   in ocean studies, 173

ringwoodite, 151

robust processing, 58, 66, 225

   and coherence, 70

   and degrees of freedom, 69

rotating a tensor, 81–83

rotational (rotationally) invariant, 83, 225

   misfit measure of Larsen’s model, 88

   phase-sensitive skew, 90

   Swift skew, 85

roughness (function), 225

salt domes, 166, 178

sampling theorem, 42–43, 225

scale dependence

   of anisotropy, 154

   of dimensionality, 35, 86

Schmucker-Weidelt transfer function, 22, 117, 174, 225

   from Z/H technique and magnetic daily variation, 183–187

   in wavenumber-frequency domain

      definition, 196

      from internal: external part separation in the wavenumber-frequency domain, 198

      from magnetotellurics in the wavenumber-frequency domain, 197

      from Z/H technique in the wavenumber-frequency domain, 198

   in spherical co-ordinates, 184, 185

   of the layered half space, 23–27

   of the sandwich model, 27, 38

seafloor studies see ocean-bottom studies

secular variation, 188

seismic

   and MT studies, 166–167

   low-velocity zones, 167, 168

   reflection, 166–167

   refraction, 103

seismology, 165

   and MT studies, 167–170

   composite media, 155

   mid-mantle transition zones, 10

   shear wave splitting, 169

   surface-wave studies, 165, 168, 169

   tomography, 169

semi-conduction, 153

   Arrhenius equation, 153

sensitivity, 225

   in forward modelling/inversion, 117, 144

   of induction coil magnetometers, 39

   of sensors, use during processing, 61

sensors, 37, 39–42

   calibration of, 61

   set up at field site, 54–57

sferics, 3–4

signal-to-noise ratio, 49, 51

site layout, 54–57, 55

skew, 106–109

   in presence of anisotropy, 108, 108–109

   in presence of three-dimensionality, 105, 106, 107

skin depth, 22

solar flare, 179, 180

solar quiet (Sq), 113, 226

   ionospheric current vortices, 183–187, 184

   spectral lines, 3, 187

solar wind, 4, 4–5, 179

sounding volume, 31, 86

southern lights, 5

source field, 3, 16, 18

   active induction techniques, 191

   dipole, 10–12, 12

   internal and external parts, 1, 10–13, 198

   magnetic daily variation, 183–187, 184

   ring current, 10–12, 12

   sferics, 3–4

space weather, 179

spatial aliasing, 47–48, 78, 226

spectral lines, 3, 61, 113, 187, 226

spectral matrix, 64, 226

spectral window, 63, 226

stacking (stacked), 65, 226

static shift, 16, 25, 79, 80–81, 87, 111–115, 167, 217, 226

   and forward modelling, 127

   causes of, 81

   effect on apparent resistivity curves, 79, 80–81, 92, 111

   effect on resistivity-depth models, 111

   examples of, 80, 114, 114–115

   identification of, 81, 111

   under-parameterisation of decomposition model, 92

static shift corrections, 111–115

   and mid-mantle transition zones, 114

   and Occam inversion, 112–113

   averaging techniques, 112–113, 137

   EMAP, 112

   resistor networks, 161–162

   target depth dependence, 114–115, 162–163

   using C-response or geomagnetic transfer functions, 113–114

   using TEM/DC data, 111–112, 192

static shift factor, 92, 111, 112–113, 114, 227

strike see electromagnetic strike

subduction, 171

superimposition model see decomposition model

swift model, 84–85, 88, 227

Swift skew, 85, 95, 106, 106, 107, 107, 227

   error of, 85, 96

Swift strike, 84–85, 95, 227

   error of, 85, 96

Tahiti hotspot, 175, 175

   and transition zone, 175

thermal conductivity, 15, 42

thin-sheet modelling, 121, 121, 174–175

three-dimensional induction, 98–101, 99

   and skew values, 105, 106, 107

tides, 176, 177

time series, 42–43, 59, 227

   and Fourier transformation, 208–209

   examples of, 59, 180, 186

time window, 59, 60, 63, 227

   length of, and outliers, 70

tipper vectors, 33, 33

   decomposition of, 116

   from modelled fields, 125–126

transfer function, 15, 21–22, 58, 79

   and electromagnetic skin depth, 22

   and model misfits, 123–125

   and Sq source field, 113

   confidence intervals of, 52–53

   estimation from measured data, 65–74

   equivalence relationship, 113, 187–188, 195–198, 219

   from anisotropic models, 107–108, 131

   from forward modelling, 117–128

   geomagnetic, 113, 183

   of the layered half-space, 23–27

   period dependence in the presence of a, 36

   single-site display of, 74–75

   scale dependence of dimensionality of, 35, 86

transient electromagnetic sounding (TEM), 191–192, 227

   use in static shift correction, 111–112

transition zones, 10, 38, 135, 168, 228

   and static shift correction, 80–81, 114

   and Tahiti hotspot, 175

   comparison of field and laboratory measurements, 146, 151, 151, 154

   magnetic daily variation, 13, 187–188

transverse electric (TE) mode see E-polarisation

transverse magnetic (TM) mode see B-polarisation

trend removal, 60, 228

   implementation, 210

two-phase medium, 7

univariate linear regression, 203

“upwards”-biased impedance, 71–74

vector calculus, 18, 228

vertical gradient techniques, 190–191

   and seafloor studies, 175, 190–191

vertical magnetic field, 33

wadsleyite, 151

Wait algorithm, 24

wave equation, 21, 228

Weidelt’s dispersion relation, 25, 62

weighted stacking, 60, 228

Wiese convention, 33, 228

Z/Htechnique, 198, 228

   and equatorial electrojet, 187–188, 189

   and magnetic daily variation, 183–187

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