Description of foldsDescription of folds

Matlab projectMatlab project

Ana Isabel Martínez Poza

The classification of the folds is important because thestructure produced by experimental models on

deformedlayered can be compared with the theoretical models ofrock deformation and hence with the results on thegeological processes.

The following classification (Ramsay, 1967) offers a verysensitive method for determining slight changes in the

foldgeometry from layer to layer in a fold structure.

The geometrical classification The geometrical classification of foldsof folds

• This classification depends on the shape of the profile section of the folded layers.

• The form of any one layer in the structure depends on the relationship of the bounding surfaces of the layer, and in particular, the relative rates of change of the inclination of these bounding surfaces.

• There are several ways in which we can measure these relatives rates of change and hence describe the shape of the folded layer.

• The successive positions of the fold hinges form an important curved or plane surface known as the

axialaxial surfacesurface..

In each fold we can determinate various parameters of amplitude, wavelength,

rates of curvature and the size and curvature of the hinge zone for each surface. So

we could make a complete and systematic description of the fold.

Orthogonal thicknessOrthogonal thickness.. In a cross section of any fold we can determine the thickness t∞ of the material between two folded surfaces by constructing tangents to each surface making an angle of 900-α with tha axial trace of the fold.t0= hinge zone of the fold.

Thickness parallel to the axial Thickness parallel to the axial surfaces,surfaces, T. Describes the variation in thickness of the folded layers records the distance between the bounding the bounding surfaces measured in a direction parallel to the axial surface of the fold.Lines of equal dip, or dip Lines of equal dip, or dip isogonsisogons. On the profile section of the fold it is possible to determine points on the folded surface which have the same slope. By joining points of the same slope on adjacent surfaces, we obtain lines of equal slope known as dip isogons.

• There are three types of fold which we can considerfundamental classes. • Their definition is based on the comparison of curvaturechanges on adjacent surfaces in the folded layer:Class 1Class 1: Folds with convergent dip isogonsFolds with convergent dip isogons. Curvature of

the inner fold arc always exceeds that of the outer arc. Subclass 1A: Folds with strongly convergent dip isogons. Subclass 1B: Parallel folds. Subclass 1C: Folds with weakly convergent isogons.

Class 2Class 2: Folds with parallelFolds with parallel

isogonsisogons. Curvature of theinner and outer arcs areequal.

Class 3Class 3: Folds with divergent Folds with divergent isogonsisogons. Curvature of the inner fold arc is always less than that of the outer arc

t’= tα / to T’= Tα/To

α= angle of inclination

tα= proportional thickness

to= thickness of the hinge of the fold

Tα= thickness of the fold in the parallel direction if the axis of the fold.

T0= thickness of the hinge of the fold

Objetive:Objetive: Anaylize this image and specially the folds marked ingreen.

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Matlab approachMatlab approach• Using the edge-based approachedge-based approach and the

morphological approachmorphological approach to decide which develop the best structure of the folds.

Edge-based

Morphological

•Different filters to enhance the folds edges.

Best result:Best result:

Bottom hat Skeleton

Inverted imageInverted image

Image after several filters

Further codingFurther coding

• Get the axial plane of the fold.

• Get the tangent lines of the fold.

• Get the thickness of the fold, tα, to, Tα and T0.

• Get the inclination α.

In order to define the fold type.

BibliographyBibliography

• Folding and fracturing of rocks. John G. Ramsay (1967).

• Matlab image tool box guide.