Rapid 3D inversion of gravity and gravity gradient data to test geologic hypotheses

84d34651c3931a54310a57484a109821?s=47 Leonardo Uieda
October 15, 2012

Rapid 3D inversion of gravity and gravity gradient data to test geologic hypotheses

84d34651c3931a54310a57484a109821?s=128

Leonardo Uieda

October 15, 2012
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  1. Rapid 3D inversion of gravity and gravity gradient data to

    test geologic hypotheses Leonardo Uieda Valéria C. F. Barbosa Observatório Nacional Rio de Janeiro, Brazil GGHS2012 S7-044
  2. Forward modeling

  3. Observed Predicted Model

  4. ✔ Control ✔ Prior information ✔ Speed ✗ Tedious ✗

    Gravity + gradients ✗ 3D
  5. Geophysical inversion

  6. Inversion Observed data 3D model

  7. Prior information Regularization: • Damping • Smoothness Inversion Observed data

    3D model
  8. ✔ Automatic fit ✔ Gravity + gradients ✔ 3D ✗

    Control ✗ Prior information ✗ Speed
  9. Source http://xkcd.com/747 Something in the middle

  10. Planting anomalous densities Uieda and Barbosa (2012), Geophysics

  11. Observed data Mesh

  12. Zero density contrast

  13. Seeds (user specified) Predicted data

  14. Neighbors

  15. The best New predicted data

  16. The best New predicted data

  17. None
  18. None
  19. None
  20. None
  21. None
  22. None
  23. None
  24. None
  25. Fit!

  26. Seeds = Skeleton Source http://www.sciencebuzz.org

  27. Inversion Body Source http://dinocrisis.wikia.com

  28. ✔ Control ✔ Prior information ✔ Speed ✔ Automatic fit

    ✔ Gravity + Gradients ✔ 3D (only need skeleton) Seeds
  29. Example applications

  30. Redenção granite

  31. Outcrop

  32. Oliveira et al. (2008)

  33. Seed Density contrast = -0.09 g.cm-3

  34. None
  35. Quadrilátero Ferrífero

  36. Complex geology and topography

  37. Complex geology and topography Iron ore deposits

  38. Seeds

  39. None
  40. Hypothesis testing Registro do Araguaia intrusion

  41. Registro do araguaia • Not outcropping • Alkaline intrusion •

    Density contrast ≈0.3 g.cm-3
  42. After Dutra et al. (2012)

  43. After Dutra et al. (2012)

  44. 3D gravity inversion (Dutra et al., 2012) Bottom = 18

    km
  45. Hypothesis 1

  46. 18 km

  47. None
  48. None
  49. Hypothesis 1

  50. Hypothesis 1 X

  51. Hypothesis 2

  52. 18 km 5 km

  53. None
  54. None
  55. Hypothesis 2

  56. Hypothesis 2 X

  57. Hypothesis 3

  58. 5 km

  59. None
  60. None
  61. Outcropping

  62. Hypothesis 3

  63. Hypothesis 3 X

  64. Hypothesis 4

  65. 5 km

  66. Density 0.5 g.cm-3

  67. None
  68. Not outcropping

  69. Not outcropping

  70. Hypothesis 4

  71. Hypothesis 4 V

  72. Conclusion • 3D forward modeling = difficult • Traditional 3D

    inversion = not flexible • Planting densities = fast + flexible