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.

6. 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. ]
CT was discovered independently by a British engineer named Sir Godfrey Hounsfield and Dr. Alan Cormack. It has become a mainstay for diagnosing medical diseases. For their work, Hounsfield and Cormack were jointly awarded the Nobel Prize in 1979.
Positron emission tomography (PET) is a nuclear medicine medical imaging technique which produces a three-dimensional image or map of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radioisotope, which is introduced into the body on a metabolically active molecule.

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

8. Travel time= distanc/velocity

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

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

11. Tomography beneath Yellowstone Caldera

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

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

14. Tomography

15. Major curculation in the mantle

16. UCSD Global
Tomographic models

20. Slab graveyard ma

22. Laboratory Experiments
Lava Lamp
Shows plumes rising

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

25. Deep plumes

27. Shallow plumes

28. Plumes from Montelli et al., 2004

30. From Albarede and VanderHilst

32. 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

33. Fit of background model

34. Rays One shot
Analytic for V=a+bz= z m/s

35. Shot at 12 th geophone 55 m.

36. Rays from all 48 shots

37. Rays interpolated onto 48x48 5 meter grid

38. Hit count at each grid node

39. Tomogram

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

41. Axis (no vertical exaggeration) image view of tomogram