Gravity anomaly

A gravity anomaly is the difference between measured gravitational acceleration and a specified reference value. It reflects both variations in Earth's mass distribution and the chosen reference model.

Free-air anomaly: A gravity anomaly corrected for elevation using the free-air gradient, without accounting for the mass between the station and a reference datum. It isolates elevation effects while retaining the gravitational attraction of terrain and subsurface masses.
Gravity gradiometry: Measurement of spatial variations in the gravity field, including gradients between nearby locations. Gradiometers map short-wavelength anomalies that ordinary gravity surveys may blur.
Gravitational acceleration: The acceleration experienced by a body in a gravitational field, commonly measured in metres per second squared. Gravity anomalies quantify differences in this acceleration from a reference.
Bouguer gravity map: A map of Bouguer gravity anomalies across a region. Regional maps connect corrected measurements to major crustal structures.
Bouguer anomaly: A gravity anomaly corrected for elevation and the attraction of rock between the measurement station and a reference datum. Its terrain and slab corrections help reveal subsurface density variations.
Satellite gravimetry: Measurement of Earth's gravity field from satellite motion or onboard instruments. Satellite data reveal broad anomaly patterns over oceans and inaccessible regions.
Gravimeter: An instrument that measures gravitational acceleration or changes in it. Its precision and calibration set the quality of observed anomaly values.
Mid-ocean ridge: A continuous underwater mountain system where tectonic plates diverge and new oceanic crust forms. Ridge-associated gravity patterns reflect crustal thickness, heat, and seafloor relief.
Isostatic anomaly: A gravity anomaly corrected for the gravitational effects of topography and its assumed compensating mass at depth. It tests whether topographic loads are balanced by subsurface compensation.
Geodesy: The science of measuring Earth's shape, orientation, gravity field, and changes over time. Gravity anomalies are observations used to refine Earth's geodetic models.

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