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Summary
Summary
This is the first textbook to cover the essential aspects of the topic at a level accessible to students. While focusing on applications in solid earth geophysics, the book also includes excursions into helioseismology, thereby highlighting the strong affinity between the two fields. The book provides a comprehensive introduction to seismic tomography, including the basic theory of wave propagation, the ray and Born approximations required for interpretation of amplitudes, and travel times and phases. It considers observational features while also providing practical recommendations for implementing numerical models. Written by one of the leaders in the field, and containing numerous student exercises, this textbook is appropriate for advanced undergraduate and graduate courses. It is also an invaluable guide for seismology research practitioners in geophysics and astronomy. Solutions to the exercises and accompanying tomographic software and documentation can be accessed online from www.cambridge.org/9780521882446.
Table of Contents
Preface | p. xi |
1 Introduction | p. 1 |
1.1 Early efforts at seismic tomography | p. 2 |
1.2 Ocean acoustic tomography | p. 3 |
1.3 Global tomography | p. 3 |
1.4 Some major discoveries | p. 4 |
1.5 Helioseismology | p. 7 |
1.6 Finite-frequency tomography | p. 8 |
2 Ray theory for seismic waves | p. 11 |
2.1 The stress tensor | p. 11 |
2.2 Forces in continuous media | p. 12 |
2.3 Newton's law and the elastodynamic equations | p. 13 |
2.4 The acoustic wave equation | p. 16 |
2.5 The ray approximation | p. 20 |
2.6 Ray solutions in layered and spherical systems | p. 22 |
2.7 Geometrical spreading | p. 25 |
2.8 Rays in an isotropic, elastic Earth | p. 26 |
2.9 Fermat's Principle | p. 29 |
2.10 Huygens, Fresnel and Green | p. 30 |
2.11 Flow: solar p-waves or ocean acoustic waves | p. 34 |
2.12 Appendix A: Some elements of Fourier analysis | p. 36 |
3 Ray tracing | p. 40 |
3.1 The shooting method | p. 40 |
3.2 Ray bending | p. 42 |
3.3 Other raytracing algorithms for 3D media | p. 46 |
3.4 Ray-centred coordinates | p. 49 |
3.5 Dynamic ray tracing | p. 50 |
3.6 Ray tracing on the sphere | p. 53 |
3.7 Computational aspects | p. 54 |
4 Wave scattering | p. 58 |
4.1 The acoustic Green's function | p. 60 |
4.2 An acoustic point scatterer | p. 62 |
4.3 Green's functions for elastic waves | p. 63 |
4.4 Green's functions in the ray approximation | p. 68 |
4.5 The Born approximation | p. 70 |
4.6 Scattering of a plane wave | p. 73 |
4.7 The scattering matrix | p. 77 |
4.8 Appendix B: The impulse response | p. 79 |
5 Body wave amplitudes: theory | p. 82 |
5.1 Geometrical spreading | p. 82 |
5.2 The quality factor Q | p. 84 |
5.3 The correspondence principle | p. 86 |
5.4 Attenuating body waves | p. 88 |
5.5 Scattering | p. 91 |
6 Travel times: observations | p. 93 |
6.1 Phase picks | p. 96 |
6.2 Matched filters | p. 100 |
6.3 Wavelet estimation | p. 103 |
6.4 Differential times | p. 107 |
6.5 Signal and noise | p. 109 |
6.6 Time-distance analysis in helioseismology | p. 110 |
7 Travel times: interpretation | p. 116 |
7.1 The ray theoretical interpretation | p. 116 |
7.2 Cross-correlation of seismic arrivals | p. 121 |
7.3 Forward scattering | p. 125 |
7.4 Finite frequency sensitivity: a simple example | p. 126 |
7.5 Finite frequency kernels: general | p. 129 |
7.6 Alternative arrival time measurements | p. 135 |
7.7 Alternative methods for kernel computation | p. 138 |
7.8 Computational aspects | p. 139 |
8 Body wave amplitudes: observation and interpretation | p. 145 |
8.1 Amplitude observations | p. 146 |
8.2 t* observations | p. 149 |
8.3 Amplitude healing | p. 151 |
8.4 Boundary topography | p. 152 |
8.5 Finite-frequency Q tomography | p. 154 |
9 Nomal modes | p. 158 |
9.1 The discrete spectrum | p. 159 |
9.2 Rayleigh's Principle | p. 166 |
9.3 Mode splitting | p. 168 |
9.4 Observations of mode splits | p. 174 |
10 Surface wave interpretation: ray theory | p. 178 |
10.1 The theory of surface waves | p. 180 |
10.2 Love and Rayleigh waves | p. 182 |
10.3 Measuring fundamental mode dispersion | p. 187 |
10.4 Measuring higher mode dispersion | p. 190 |
10.5 Waveform fitting | p. 192 |
10.6 Partitioned waveform inversion (PWI) | p. 194 |
10.7 Appendix C: Asymptotic theory | p. 197 |
11 Surface waves: finite-frequency theory | p. 208 |
11.1 Phase and amplitude perturbations | p. 209 |
11.2 Practical considerations | p. 214 |
11.3 Phase velocity maps: an incompatibility | p. 217 |
12 Model parametrization | p. 219 |
12.1 Global parametrization | p. 220 |
12.2 Local parametrization | p. 222 |
12.3 Numerical considerations | p. 228 |
12.4 Spectral analysis and model correlations | p. 229 |
13 Common corrections | p. 233 |
13.1 Ellipticity corrections | p. 233 |
13.2 Topographic and bathymetric time corrections | p. 238 |
13.3 Crustal time corrections | p. 240 |
13.4 Surface wave corrections | p. 243 |
13.5 Source corrections | p. 245 |
13.6 Amplitude corrections for body waves | p. 247 |
13.7 Dispersion corrections | p. 249 |
13.8 Instrument response | p. 250 |
13.9 Clock corrections | p. 253 |
14 Linear inversion | p. 255 |
14.1 Maximum likelihood estimation and least squares | p. 256 |
14.2 Alternatives to least squares | p. 260 |
14.3 Singular value decomposition | p. 261 |
14.4 Tikhonov regularization | p. 265 |
14.5 Bayesian inference | p. 266 |
14.6 Information theory | p. 270 |
14.7 Numerical considerations | p. 272 |
14.8 Appendix D: Some concepts of probability theory and statistics | p. 275 |
15 Resolution and error analysis | p. 277 |
15.1 Resolution matrix | p. 277 |
15.2 Backus-Gilbert theory | p. 281 |
15.3 Sensitivity tests | p. 285 |
16 Anisotropy | p. 289 |
16.1 The elasticity tensor | p. 290 |
16.2 Waves in homogeneous anisotropic media | p. 295 |
16.3 S-wave splitting | p. 296 |
16.4 Surface wave anisotropy | p. 301 |
17 Future directions | p. 306 |
17.1 Beyond Born | p. 306 |
17.2 Adjoint methods | p. 307 |
17.3 Global coverage of seismic sensors | p. 310 |
17.4 Helioseismology and astroseismology | p. 312 |
References | p. 313 |
Author index | p. 334 |
General index | p. 339 |