Gravitational Attraction of Buried Bodies
Every subsurface mass anomaly perturbs Earth's gravitational field. The gravity anomaly measured at the surface depends on the density contrast between the body and surrounding rock, the body's size and shape, and its depth. For a buried sphere, the vertical component of gravitational attraction follows an inverse-square law with depth, making it a fundamental model in gravity exploration.
Gravity Data Processing
Raw gravity measurements require several corrections before geological interpretation. The free-air correction accounts for elevation above the reference ellipsoid. The Bouguer correction removes the effect of rock mass between the station and sea level. Terrain corrections handle irregular topography. The resulting Bouguer anomaly map reveals subsurface density variations.
Anomaly Interpretation
The shape of a gravity anomaly profile constrains the depth, size, and density contrast of the causative body. The half-width (distance from peak to half-maximum) is proportional to depth for standard geometric models. However, interpretation is inherently non-unique: many different mass distributions can produce the same surface anomaly, requiring integration with geological and other geophysical data.
Applications in Exploration
Gravity surveys are used extensively in mineral exploration (detecting dense ore bodies), petroleum exploration (mapping sedimentary basins and salt structures), engineering geology (locating voids and faults), and regional tectonics (mapping crustal thickness variations). Satellite gravity missions like GRACE and GOCE now provide global gravity fields at scales from continental to 100 km resolution.