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[[file:using-magnetics-in-petroleum-exploration_fig14-5.png|300px|thumb|{{figure number|1}}Geologic map of an area of crystalline basement in central Wisconsin on the southern edge of the Canadian Shield. From LaBerge, 1976; courtesy International Basement Tectonics Assoc.]]

[[file:using-magnetics-in-petroleum-exploration_fig14-5.png|300px|thumb|{{figure number|1}}Geologic map of an area of crystalline basement in central Wisconsin on the southern edge of the Canadian Shield. From LaBerge;<ref=LaBerge, G. L., 1976, Major structural lineaments in the Precambrian of central Wisconsin: Proceedings of the First International Conference on the New Basement Tectonics, Utah Geological Assoc., p. 508–518.> courtesy International Basement Tectonics Assoc.]]

A major pitfall in interpreting magnetic residual maps is assuming that magnetic highs and lows are caused by elevation changes on basement rocks in a sedimentary basin. To the contrary, most magnetic anomalies are caused by lithologic changes and the corresponding changes in susceptibility. As shown in [[:file:using-magnetics-in-petroleum-exploration_fig14-5.png|Figure 1]], the basement is of complex lithology and is highly fractured. The fractures divide the basement into blocks and are zones of weakness along which faults occur. The most important and most reliable information obtainable from aeromagnetic maps is the configuration (in plan view) of the underlying basement fault block pattern.

A major pitfall in interpreting magnetic residual maps is assuming that magnetic highs and lows are caused by elevation changes on basement rocks in a sedimentary basin. To the contrary, most magnetic anomalies are caused by lithologic changes and the corresponding changes in susceptibility. As shown in [[:file:using-magnetics-in-petroleum-exploration_fig14-5.png|Figure 1]], the basement is of complex lithology and is highly fractured. The fractures divide the basement into blocks and are zones of weakness along which faults occur. The most important and most reliable information obtainable from aeromagnetic maps is the configuration (in plan view) of the underlying basement fault block pattern.

==Interpreting depth to basement==

==Interpreting depth to basement==

It is futile to attempt to define accurately the vertical dimension, Z, of adjacent source bodies with [[magnetics]] because of the inherent ambiguity of potential field methods in determining Z (see, e.g. .<ref name=ch14r8>Skeels, D., C., 1947, Ambiguity in gravity interpretation: Geophysics, vol. 12, p. 43–56., 10., 1190/1., 1437295</ref> Furthermore, seismic and subsurface methods measure depth so much more accurately than magnetics that it is unwise to try to compete with these excellent techniques. This is not to say, however, that we should not use magnetics to estimate the approximate thickness of the sedimentary section in a new basin, i.e., in determining whether it is 2, 5, or [[length::10 km]] thick, for example, to a usual accuracy of about ±15% under favorable conditions.

It is futile to attempt to define accurately the vertical dimension, Z, of adjacent source bodies with [[magnetics]] because of the inherent ambiguity of potential field methods in determining Z (see, e.g. .<ref name=ch14r8>Skeels, D. C., 1947, Ambiguity in gravity interpretation: Geophysics, vol. 12, p. 43–56., 10., 1190/1., 1437295</ref> Furthermore, seismic and subsurface methods measure depth so much more accurately than magnetics that it is unwise to try to compete with these excellent techniques. This is not to say, however, that we should not use magnetics to estimate the approximate thickness of the sedimentary section in a new basin, i.e., in determining whether it is 2, 5, or [[length::10 km]] thick, for example, to a usual accuracy of about ±15% under favorable conditions.

==Interpreting fault throw==

==Interpreting fault throw==