Presentation given at the 2012 International Symposium on Gravity, Geoid and Height System in Venice, Italy.

1. GGHS2012
S7-044
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

2. Forward modeling

3. Predicted
Observed
Model

4. ✔ Control
✔ Prior information
✔ Speed
✗ Tedious
✗ Gravity + gradients
✗ 3D

5. Geophysical inversion

6. Observed data
Inv
er
sio
n
3D model

7. Observed data
Inv
er
sio
n
3D model
Prior information
Regularization:
●
Damping
●
Smoothness

8. ✔ Automatic fit
✔ Gravity + gradients
✔ 3D
✗ Control
✗ Prior information
✗ Speed

9. Something in the middle
Source http://xkcd.com/747

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

11. Observed data
Mesh

12. Zero
density contrast

13. Predicted data
Seeds
(user specified)

14. Neighbors

15. New predicted data
The best

16. New predicted data
The best

25. Fit!

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

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

28. ✔ Control Seeds
✔ Prior information
✔ Speed
✔ Automatic fit
✔ Gravity + Gradients
✔ 3D (only need skeleton)

29. Example
applications

30. Redenção granite

31. Outcrop

32. Oliveira et al. (2008)

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

35. Quadrilátero Ferrífero

36. Complex geology and
topography

37. Complex geology and
topography
Iron ore
deposits

38. Seeds

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

49. Hypothesis 1

50. X
Hypothesis 1

51. Hypothesis 2

52. 18 km 5 km

55. Hypothesis 2

56. X
Hypothesis 2

57. Hypothesis 3

58. 5 km

61. Outcropping

62. Hypothesis 3

63. X
Hypothesis 3

64. Hypothesis 4

65. 5 km

66. -3
Density 0.5 g.cm

68. Not
outcropping

69. Not
outcropping

70. Hypothesis 4

71. V
Hypothesis 4

72. Conclusion
● 3D forward modeling = difficult
● Traditional 3D inversion = not flexible
● Planting densities = fast + flexible