The gravity method involves measuring the acceleration due to the earth's gravitational field. A gravity meter or gravimeter measures the variations in the earth's gravitational field. The variations in gravity are due to lateral changes in the density of the subsurface rocks in the vicinity of the measuring point. Because the the density variations are very small and uniform, the gravimeters are very sensitive and they measure one part in 100 million of the earth's gravity field (980 gals or 980,000 milligals) in units of milligals or microgals. Gravity Surveys are used for modeling the earth's crustal structure, for locating bedrock fractures, buried topographic valleys, subsurface voids such as abandoned mines, caverns, and sinkholes, and for determining overburden thickness and depth to bedrock.
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