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  1. A departure from the expected or normal. AGI
  2. The difference between an observed value and the corresponding computed value. AGI
  3. A geological feature, esp. in the subsurface, distinguished by geological, geophysical, or geochemical means, which is different from the general surroundings and is often of potential economic value; e.g., a magnetic anomaly. AGI
  4. Any deviation from conformity or regularity. A distinctive local feature in a geophysical, geological, or geochemical survey over a larger area. An area or a restricted portion of a geophysical survey, such as a magnetic survey or a gravity survey, that differs from the rest of the survey in general. The anomaly might be associated with petroleum, natural gas, or mineral deposits, or provide a key to interpreting the underlying geologic structure. Drilling for economic mineral deposits might be conducted in the area of a geophysical anomaly. In seismic usage, anomaly is generally synonymous with subsurface structure or material properties, but it is also used for spurious or unexplainable seismic events or for local deviations of observed signals which cannot be conclusively attributed to a unique cause. See also: hydrochemical anomaly AGI
  5. A gravity anomaly is the difference between the theoretical calculated gravity and the observed terrestrial gravity. In comparing any set of observed data with a computed theoretical curve, the difference of an observed value and the corresponding computed value, or the observed minus the computed value. Excess observed gravity is a positive anomaly, and a deficiency is a negative anomaly. See also: Bouguer anomaly; free-air anomaly; isostatic anomaly. AGI
  6. A crystallographic anomaly is the lack of agreement between the apparent external symmetry of a crystal and the observed optical properties. Schieferdecker
  7. Any departure from the normal magnetic field of the Earth is a magnetic anomaly. It may be a high or a low, subcircular, ridgelike or valleylike, or linear and dikelike. AGI
    Source: Dictionary of Mining, Mineral, and Related Terms

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