Changes

==What is residual?==

==What is residual?==

Residual is what remains after regional magnetic trends are removed from the total intensity Residual maps show local magnetic variations, which may have exploration significance. The regional trend of the total intensity can be calculated using a number of techniques, including running averages, polynomials, low-pass filters, or upward continuation techniques. The figure below shows magnetic profiles of total intensity, regional trend, and residual.

Residual is what remains after regional magnetic trends are removed from the total intensity Residual maps show local magnetic variations, which may have exploration significance. The regional trend of the total intensity can be calculated using a number of techniques, including running averages, polynomials, low-pass filters, or upward continuation techniques. [[:file:using-magnetics-in-petroleum-exploration_fig14-2.png|Figure 1]] shows magnetic profiles of total intensity, regional trend, and residual.

[[file:using-magnetics-in-petroleum-exploration_fig14-2.png|thumb|{{figure number|14-2}}After .<ref name=ch14r7>Nettleton, 1962, Elementary Gravity and [[Magnetics]] for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series 1, 121 p.</ref> Copyright: Society of Exploration Geophysicists.]]

[[file:using-magnetics-in-petroleum-exploration_fig14-2.png|thumb|{{figure number|1}}After .<ref name=ch14r7>Nettleton, 1962, Elementary Gravity and [[Magnetics]] for Geologists and Seismologists: Society of Exploration Geophysicists Monograph Series 1, 121 p.</ref> Copyright: Society of Exploration Geophysicists.]]

==Total intensity and residual map example==

==Total intensity and residual map example==

The maps below are examples of a residual map (A) that was calculated from the total intensity magnetic map (B). The grid and small circles on the total intensity map are the flight path lines [approximately [[length::2 km]] (1.2 mi) apart] and location points for the flight lines. The total intensity map strikingly does not resemble the residual map and would be of limited value for delineating basement fault blocks.

The maps in [[:file:using-magnetics-in-petroleum-exploration_fig14-3.png|Figure 2]] are examples of a residual map (A) that was calculated from the total intensity magnetic map (B). The grid and small circles on the total intensity map are the flight path lines [approximately [[length::2 km]] (1.2 mi) apart] and location points for the flight lines. The total intensity map strikingly does not resemble the residual map and would be of limited value for delineating basement fault blocks.

Total intensity [[magnetics]] responds to rock types over broad areas as well as those deep within the crust. We can see by a careful examination of map B, however, that many of the features shown by the residual map are vaguely apparent in the total intensity data. Fortunately, we no longer have to interpret such total intensity maps in petroleum basins because many enhancement techniques employing residuals, derivatives, polynomials, or downward continuation exist to reveal the subtle magnetic anomalies that result from the changes in rock type across basement block boundaries.

Total intensity [[magnetics]] responds to rock types over broad areas as well as those deep within the crust. We can see by a careful examination of map B, however, that many of the features shown by the residual map are vaguely apparent in the total intensity data. Fortunately, we no longer have to interpret such total intensity maps in petroleum basins because many enhancement techniques employing residuals, derivatives, polynomials, or downward continuation exist to reveal the subtle magnetic anomalies that result from the changes in rock type across basement block boundaries.

[[file:using-magnetics-in-petroleum-exploration_fig14-3.png|thumb|{{figure number|14-3}}. Copyright: Gay, 1995; courtesy International Basement Tectonics Assoc.]]

[[file:using-magnetics-in-petroleum-exploration_fig14-3.png|thumb|{{figure number|2}}. Copyright: Gay, 1995; courtesy International Basement Tectonics Assoc.]]

==See also==

==See also==