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Lecture 14 Tomography

Lecture 14 Tomography. Body waves In the interior Of the Earth’s body. P is direct P wave in mantle PcP is a reflection from the core Angle of incidence = Angle of reflection. P arrives at about 7.7 minutes after the origin of the earthquake PcP arrives at 9.7 minutes.

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Lecture 14 Tomography

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  1. Lecture 14 Tomography

  2. Body waves In the interior Of the Earth’s body P is direct P wave in mantle PcP is a reflection from the core Angle of incidence = Angle of reflection

  3. P arrives at about 7.7 minutes after the origin of the earthquake PcP arrives at 9.7 minutes

  4. P shadow and S shadow were the original evidence for a liquid outer core. P wave gets refracted downwards because of low P velocity in core. S has zero velocity in outer core.

  5. Tomography Positron emission tomography (PET scan) MRI (magnetic resonance imaging) CAT Scan [computerized axial tomography (CAT) scan. A CT scanner directs a series of X-ray pulses through the body. ]

  6. MRI 20 Tesla (Earth’s field 50000 nT

  7. Travel time= distanc/velocity

  8. Theoretical Tomography The Radon transform is an integral transform whose inverse is used to reconstruct images from medical CT scans.

  9. Seismic tomography uses earthquakes (or shots) to image lateral heterogeneity in the Earth’s interior.

  10. Tomography beneath Yellowstone Caldera

  11. Tomography shows shallow asthenosphere beneath Kenya dome on east African Rift

  12. (from John Woodhouse) (from Adam Dziewonski) Tomography of the mantle and inner core. Note Africa and Pacific Super Plumes

  13. Tomography

  14. UCSD Global Tomographic models

  15. Slab graveyard 100-200 ma

  16. Laboratory Experiments • Lava Lamp • Shows plumes rising

  17. Two deep plumes Two shallow plumes Montelli et al., Science 2004

  18. Deep plumes

  19. Shallow plumes

  20. Plumes from Montelli et al., 2004

  21. http://www.mala.bc.ca/~earles/mantle-plume-depths-jan04.htm

  22. From Albarede and VanderHilst

  23. Tomography of Furnace Creek Fault zone Steps: 1. Pick 48x48 arrivals using RAS24.exe Save as ascii 2. Use linear velocity background model V=a+bz analytic solutions for T, X 3. Find average a b that fit data 4. Find nearest node points on 5 m grid for rays 5. Back project residuals along rays to form tomogram

  24. Fit of background model

  25. Rays One shot Analytic for V=a+bz=1200+45z m/s

  26. Shot at 12 th geophone 55 m.

  27. Rays from all 48 shots

  28. Rays interpolated onto 48x48 5 meter grid

  29. Hit count at each grid node

  30. Tomogram

  31. Tomogram after stacking travel times Note loader.m shows velocities

  32. Axis (no vertical exaggeration) image view of tomogram 65m

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