1. n. [Geophysics]

The magnetic field associated with the Earth’s crust arises from induced and remanent magnetism. The crustal field—also referred to as the anomaly field—varies in direction and strength when measured over the Earth’s surface. It is relatively strong in the vicinity of ferrous and magnetic materials, such as in the oceanic crust and near concentrations of metal ores, and is a focus of geophysical mineral exploration.

See: main magnetic field,  external disturbance field,  local magnetic interference