Description of folds
Matlab project
Ana Isabel Martínez Poza
The classification of the folds is important because the
structure produced by experimental models on deformed
layered can be compared with the theoretical models of
rock deformation and hence with the results on the
geological processes.
The following classification (Ramsay, 1967) offers a very
sensitive method for determining slight changes in the fold
geometry from layer to layer in a fold structure.
The geometrical classification of 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 axial
surface.
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 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 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 isogons. 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 consider
fundamental classes.
• Their definition is based on the comparison of curvature
changes on adjacent surfaces in the folded layer:
Class 1: Folds 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 2: Folds with parallel
isogons. Curvature of the
inner and outer arcs are
equal.
Class 3: Folds with divergent isogons.
Curvature of the inner fold arc is
always less than that of the outer arc
t’= tα / to
α= angle of inclination
tα= proportional thickness
to= thickness of the hinge of
the fold
T’= Tα/To
Tα= thickness of the fold in the
parallel direction if the axis of the
fold.
T0= thickness of the hinge of the
fold
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
Objetive: Anaylize this image and specially the folds marked in
green.
Matlab approach
• Using the edge-based approach and the morphological approach to
decide which develop the best structure of the folds.
Edge-based
Morphological
•Different filters to
enhance the folds edges.
Best result:
Bottom hat
Skeleton
Image after
several
filters
Inverted image
Further 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.
Bibliography
• Folding and fracturing of rocks. John G. Ramsay (1967).
• Matlab image tool box guide.