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

Transcript

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

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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