1. Variation of G with latitude
gp =983.2 Gal ge = Gal
Radius gprad-gerad = 6.6 Gal
Excess mass gpem-geem = -4.8 Gal
Rotation gprot-gerot = 3,4 Gal

2. Variation of G with latitude
In the long-term, the earth behaves like a fluid
Reference ellipsoid (approximation to geoid)
The scalar potential verifies the Laplace equation and the solution can be expanded on Legendre polynomials
degree degree rotation

3. Variation of G with latitude
We then get for the normal gravity (uniform density) due to position only
We are interested in the gravity anomaly gobs -gn

4. Variation of G with latitude

5. Free air correction At the Earth’s surface
z is the elevation from sea level. The gravity anomaly is then
(brings gravity to sea level)
Units: mGal, m

6. Bouguer correction
We also need to correct for the mass between sea level and
elevation z. Bouguer assumes an infinite slab of density ρ and
thickness z
Units: mGal, m, g/cm3

7. Bouguer correction
The difficulty is to choose the right density ρ (average crustal
rock has a density of 2.67

8. Terrain correction

9. Terrain correction (hammer)

10. Terrain correction (laborious)

11. other corrections and precautions
Isostatic correction: due to deeper sources regional trend  correct or filter
Tidal correction  correct or drift if short time sales
Elevation
Latitude
Drift
Base

12. Gravity of simple shapes

13. Gravity of simple shapes

14. Gravity of simple shapes
Bedrock density 2.3, ore density 3.0, half cylinder at depth 100m
radius for precision 0.1 mGal?

15. Gravity of simple shapes

16. Regionals and residuals

17. Regionals and residuals

18. Regionals and residuals geological knowledge and experience

19. Regionals and residuals trend surfaces

20. Regionals and residuals trend surfaces

21. Regionals and residuals trend surfaces

22. Regionals and residuals upward continuation

23. Regionals and residuals second derivatives

24. Regionals and residuals second derivatives

25. Gravity interpretation half-maximum technique

26. Gravity interpretation half-maximum technique

27. Gravity interpretation 2nd derivatives technique

28. Gravity interpretation 2nd derivatives technique

29. Gravity interpretation 2nd derivatives technique

30. Detection of cavities

31. Bedrock depths