Calculated intensity of the magnetic anomaly is shown by the colored iso-shells, orange indicating large positive values and purple showing negative values. The colored iso-shells are cut to reveal the 3D structure of the magnetic anomaly. The 3D structure of magnetic fields causes ambiguity in the interpretation of 1D and 2D surveys. For example, in aeromagnetic surveys at a single flight elevation will intersect part of the anomaly associated with the buried prism, but miss a great deal of the anomaly's structure. Small variations in flight line elevation will create more ambiguity, because the different flight lines will intersect the anomaly at different levels.
Similar problems occur in ground magnetic surveys, especially in areas with steep topography.
Such ambiguity is often ignored in the interpretation of magnetic data. With improved data acquisition and interpretation techniques, however, the 3D structure of magnetic fields can be exploited to better model geologic structures and related phenomena. As an example of the power of 3D surveys, consider the following figures in which the magnetic field is calculated over a buried steeply dipping fault that is approximated as a semi-infinite horizontal slab. The magnetic field is calculated from 0 to 200 m above the ground surface and for 300 m horizontal distance on either side of the top edge of the buried slab. The dip of the fault, depth to the top and bottom of the buried slab, and the intensity of magnetization are identical for the two figures.