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How do gravimeters detect tiny differences in Earth’s gravitational acceleration?

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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.

Gravimeters are highly sensitive instruments designed to detect minute variations in the Earth’s gravitational field, often with an accuracy of one part in 100,000,000.12

The core mechanism typically involves a weight suspended from a spring. As gravitational acceleration changes, the weight causes the spring to stretch or contract. Because these physical deflections are extremely small, the devices employ sophisticated mechanical and optical schemes to measure the displacement.12

In geological and geophysical applications, these instruments are used to identify gravity anomalies caused by local density variations in the subsurface, such as salt domes, faults, or mineral deposits. To isolate these geological signals, researchers must correct raw readings for external factors, including:2

Elevation: Adjustments for the distance from the Earth's center.23
Latitude: Accounting for variations in centrifugal force and the Earth's shape.3
Topography: Compensating for the gravitational attraction of surface relief.3
Tidal effects: Correcting for periodic gravitational influences.3

By accounting for these variables, geophysicists can interpret the remaining anomalies to map subsurface structures.3