Plotting folded surfaces with parasitic folds

This section describes how the default script can be easily modified to plot folded surfaces exhibting parasitic folds. Parasitic folding can be plotted using simplified Fourier series (similar to that used for the box and chevron folds) using the series:





where b₁ and b₅ are Fourier coefficients that determine the fold shape and w is the wavelength. The first coefficient modifies the amplitude of the first order fold, whereas the fifth the amplitude of the second order folds. A chart of parasitic fold shapes that were plotted using the above equation is shown below.



To plot parasitic folds and their structure contours open the file structure_contours_folds.m in Matlab. In the Matlab editor select the menu ‘debug’ and ‘run’. In the Matlab command window the following text appears:

Please choose topography

valley (enter 1) or ridge (enter 2) or both (enter 3)?

Type 1, 2 or 3 and press the return key. Then the following text appears:

Please choose geological structure

Box- and Chevron folds (enter 1) or parasitic folds (enter 2)?

Type 2 and press the return key. Then the following text appears:

plunge of fold:

Type the plunge of the fold (in degrees) and press the return key. Then you are asked the following:

Please enter harmonic coefficients, b1 and b5

b1:

b5:

Type in the coefficients (some guidelines are given in the diagram above) and press return. The Matlab diagrams shown below give some examples with non-plunging (top) and 10 degree plunging parasitic folds that were created with this script. The Fourier coefficients b₁ and b₅ are 1.0 and 0.5, respectively.

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