Gravitational Anomalies

the difference between the observed force of gravity and its theoretical (normal) value at the same point, to which a correction is introduced allowing for the dependence of the force of gravity on the height of the observation point. Depending on the corrections introduced, several types of anomalies are distinguished. If the decrease in the force of gravity with height in free space is considered, with an average gradient taken over the entire earth of 0.3086 milligal/m (1 milligal = 10^-3 cm/sec²), then the anomaly is called a gravitational anomaly in free air (or Faye anomaly); these anomalies are used in studying the earth’s figure in geodetic gravimetry. If, in addition, the attraction exerted by a uniform layer of mass between the level of the observation point and sea level is considered, the gravitational anomaly is called a Bouguer anomaly. Since Bouguer anomalies reflect the nonuniform density of rock in the earth’s topmost layer, they are employed in the solution of geological prospecting problems.