Automated modelling of folds from structural data

Lachlan Grose and Laurent Ailleres and Laurent Gautier. ( 2016 )
in: 2016 RING Meeting, ASGA

Abstract

Folds present a challenge for 3D modelling because the geometry of the fold is not explicitly contained in individual observations of the folded surface. The interpolation algorithms at the base of structural modelling fit surfaces with minimal curvature to structural observations. Folds typically produce patterns of localised variation in curvature. To obtain folded geometries the geologist is required to draw fold shapes or add interpretive constraints to control the fold geometry. This is a subjective process and means that the models are generally not reproducible. A new method for modelling folds uses a fold frame with coordinates based on the structural geology of folds: fold axis direction, fold axial surface and stretching lineation. The fold geometry can be characterised by rotating the fold axis direction field and fold axial surface field to give the final orientation of the folded surface. These rotations angles can be expressed as 1D functions of the fold frame coordinates. In this contribution we present methods for extracting and automatically modelling the fold geometries from structural data. The fold rotation angles used for characterising the fold geometry can be calculated locally from structural observations. The fold rotation angles incorporate the structural geology of the fold and allow for individual structural measurements to be viewed in the context of the folded structure. To filter out the effects of later folding the fold rotation angles are plotted against the coordinates of the fold frame. Using these plots the geometry of the folds can be interpolated directly from structural data where we use a combination of radial basis function and harmonic analysis to interpolate and extrapolate the fold geometry. This technique is applied to two natural case studies, an outcrop of an asymmetrical fold within the Lachlan Fold belt at Cape Conran, Victoria, Australia and a fold interference pattern from the Pilbara, Western Australia.

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BibTeX Reference

@INPROCEEDINGS{,
    author = { Grose, Lachlan and Ailleres, Laurent and Gautier, Laurent },
     title = { Automated modelling of folds from structural data },
 booktitle = { 2016 RING Meeting },
      year = { 2016 },
 publisher = { ASGA },
  abstract = { Folds present a challenge for 3D modelling because the geometry of the fold is not explicitly
contained in individual observations of the folded surface. The interpolation algorithms at the
base of structural modelling fit surfaces with minimal curvature to structural observations. Folds
typically produce patterns of localised variation in curvature. To obtain folded geometries the
geologist is required to draw fold shapes or add interpretive constraints to control the fold geometry.
This is a subjective process and means that the models are generally not reproducible. A new
method for modelling folds uses a fold frame with coordinates based on the structural geology of
folds: fold axis direction, fold axial surface and stretching lineation. The fold geometry can be
characterised by rotating the fold axis direction field and fold axial surface field to give the final
orientation of the folded surface. These rotations angles can be expressed as 1D functions of the
fold frame coordinates. In this contribution we present methods for extracting and automatically
modelling the fold geometries from structural data. The fold rotation angles used for characterising
the fold geometry can be calculated locally from structural observations. The fold rotation angles
incorporate the structural geology of the fold and allow for individual structural measurements
to be viewed in the context of the folded structure. To filter out the effects of later folding the
fold rotation angles are plotted against the coordinates of the fold frame. Using these plots the
geometry of the folds can be interpolated directly from structural data where we use a combination
of radial basis function and harmonic analysis to interpolate and extrapolate the fold geometry.
This technique is applied to two natural case studies, an outcrop of an asymmetrical fold within
the Lachlan Fold belt at Cape Conran, Victoria, Australia and a fold interference pattern from the
Pilbara, Western Australia. }
}