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Seismic waves and 3D structure

Seismic waves and 3D structure. Barbara Romanowicz UC Berkeley CIDER’04/KITP 07/21/04. Body waves : ray theory Surface waves : path average approximation (PAVA) “Infinite frequency approximations”. Vasco and Johnson, 1998. Van der Hilst et al., 1998. Montelli et al., 2004.

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Seismic waves and 3D structure

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  1. Seismic waves and 3D structure Barbara Romanowicz UC Berkeley CIDER’04/KITP 07/21/04

  2. Body waves: ray theory Surface waves: path average approximation (PAVA) “Infinite frequency approximations”

  3. Vasco and Johnson, 1998

  4. Van der Hilst et al., 1998

  5. Montelli et al., 2004

  6. Fukao et al., 2001

  7. Surface waves P S

  8. observed Synthetic (PREM)

  9. “Fresnel zone” l = wavelength Df < p 2(r-z)<l/2

  10. Yoshizawa and Kennett, 2004

  11. Marquering et al. 1999

  12. How can we model full waveforms, i.e. body waves (including diffracted waves), AND surface waves (fundamental mode and overtones), in a realistic 3D earth • with “accurate” broadband kernels • and reasonable computation time for global tomographic inversions ?

  13. Path AVerage Approximation • 1D kernels • Along branch coupling • zeroth order asymptotics • NACT • 2D kernels (in vertical plane) • across branch coupling • zeroth order asymptotics • NACT + focusing • 2.5D kernels (off plane effects included) • order 1/l asymptotics • Full 1st order Born Approximation • 3D kernels • single scattering

  14. Synthetic seismogram comparison • Reference : “Exact numerical ”: • Spectral Element Method (SEM) • Compare differences between synthetics computed in PREM (1D) and synthetics computed in simple 3D models

  15. SS Sdiff PAVA NACT Li and Romanowicz , 1995

  16. PAVA NACT

  17. Global S velocity models

  18. Top trace: observed (80-300sec); Bottom trace: PREM predictions

  19. Motivation for seismic Q tomography: Faul and Jackson, in prep.

  20. Long period waveforms Upper Mantle Q models Depth = 160 km Rayleigh waves Spectral ratios, P,PP

  21. Hotspot distribution QRLW8 Weighted by buoyancy flux

  22. Depth = 450 km Depth = 600 km Degree 8 no focusing Degree 12 with foc. Degree 16 with foc. -50 0 dln(1/Q)(%) 50

  23. QRLW8 QRLf12 SAW24B16 Pacific “superplume”

  24. Modeling short scale heterogeneity

  25. Sharp boundary of the African Superplume Ni et al., 2002

  26. Bréger and Romanowicz, 1998

  27. Toh et al. 2004

  28. Coupled SEM/modes (Capdeville et al., 2002, 2003)

  29. CSEM Synthetics Toh et al. 2004

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