GRAVIMETRY

Equipment: Gravimeter (Scintrex CG-5)

Gravity is the attraction between bodies that have mass. In geophysics, gravimetric methods allow the determination of the density distribution of subsurface materials. Each type of material (soils, rocks, cavities, etc.) has a distinct characteristic density, enabling subsurface modeling based on detailed readings of gravitational attraction within a given study area.

Across a study area, gravitational acceleration undergoes very slight variations (positive or negative) due to changes in the density of buried masses beneath the surface. These small variations are superimposed on known and quantifiable effects caused by the total mass of the Earth (and, to a lesser extent, the Moon and the Sun). Gravimetric surveys employ instruments capable of detecting these minute differences in gravitational acceleration, which can reveal, for example, subsurface mass deficiencies associated with natural or artificial cavities, and geological structures of engineering interest.

Measurements are taken at points or stations, typically spaced between 1 and 50 meters apart, depending on the objectives of the study. Once the necessary corrections (latitude, free-air, Bouguer, and topographic) are applied, local anomaly maps (residual anomalies) are generated, representing density variations beneath the study area.

Residual anomaly values along a profile or grid are then used as reference data to construct density models. From these gravimetric anomaly distributions, subsurface density contrast models are created, whose gravitational response is compared against observed values.