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How do gravity anomalies reveal differences in density within Earth?

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Diagram showing the deflection of the vertical from the geoid to the ellipsoid or spheroid, with labeled lines for geoid, spheroid, rock surface, ocean, and geoid height in a geology context. — geoid Deflection of the vertical from the geoid to the spheroid.

A gravity anomaly is the difference between the locally observed value of gravity and the theoretically calculated value for a specific location. These anomalies occur because Earth’s internal composition is not uniform; rather, it contains heterogeneities in density that influence the gravitational field.123

Geophysicists use gravimeters to measure these variations, which are essential for interpreting subsurface geologic structures. By correcting for factors such as elevation, latitude, and topography, researchers can isolate the gravitational effects caused by underground density distributions.43

These anomalies reveal specific geologic features:
* Positive anomalies: Often caused by uplifts that bring denser rocks closer to the surface.4
* Negative anomalies: Frequently associated with salt domes or subterranean cavities, as these materials are less dense than the surrounding rock.4

Because the geoid is an equipotential surface of the gravitational field, its shape is directly influenced by these same internal density variations. Consequently, mapping gravity anomalies provides critical insights into Earth's subsurface, aiding in petroleum exploration and the identification of mineral deposits.24