Magellan
A forward marine magnetic modeling program

Contamination Coefficient

Magnetic data, collected over slow spreading ridges, often lack fine scale charecteristics because the spreading is too slow to resolve some of the short reversal periods. To better the magnetic model for slow spreading anomalies the method of the contamination coeffient has been implemented into Magellan.

This method involves making the magnetic blocks narrower prior to calculating the model. For each point on the profile, where the model is calculated, the blocks are made less wide by a factor of c. If the original width of a a magnetized block is z it is reduced to z*c after the method has been applied. The value of c is between 0 and 1 and if the method is not used c=1 (the blocks retain their original width).

Fig 1. Graphical explanation of the contamination coefficient. See text for details.

The method is described graphically in Figure 1. Let P be an arbitrary point on the profile. The blue paralellepiped in Figure 1a represents the first normal stripes which run paralell to the strike of the ridge. The flowline of the ridge is perpendicular to its strike and Figure 1b shows a crossection through the flowline. Each box represents a magnetized block with a finite width, z. Point P, at which the model is being calculated, can be thought of as the center of a moving coordinate system (which is not to be confused with the fixed coordinate system where the ridge axis is at x=0). The upper set of blocks represents the magnetized blocks prior to narrowing and the lower set of blocks represents the magnetized blocks after narrowing. Notice that the blocks are narrowed toward point P, where the model is being calculated, independent of the position of the ridge axis. The width of the block is narrowed from z to z*c, where c is the contamination coefficient.