Gravity method

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undergraduate gravity lecture

undergraduate gravity lecture

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  • 1. Gravity Method By Dr. Amin E. Khalil
  • 2. 2 21 r MM GF
  • 3. gMF 2 21 2 r MM GgM 2 r M Gg
  • 4. R = radius of the earth Earth is considered as sphere and hence radius is constant.
  • 5. Earth is not sphere and hence radius is not constant. Hence correction must be applied
  • 6. Because many factors affect the value of g. As an example: •Earth flattening. •Surface relief. • anomalous masses inside the earth
  • 7. What is geoid? It is equipotential surface where the g is always constant. The equipotential surface is usually taken as the sea level. However, due to some heterogeneity in the earth Geoid may differ slightly from Sea level.
  • 8. Reduction is carried out to correct for: •Latitude •Elevation •Excess mass •Terrain •Drift •Isostacy •Earth’s rotation
  • 9. The earth is flattened, i.e the radius at the equator is longer than at the poles. gn = 978031.85 (1.0 + 0.005278895 sin2(lat) + 0.000023462 sin4(lat)) (mGal)
  • 10. geoid
  • 11. gb = gobs - gn + 0.3086h - 0.04193r h (mGal)