The Evolution and Variability in Structural Style of Normal Fault Zones: Comparing Field Observations with Numerical Models
Abstract
Integration of high quality 3D seismic data from the North Sea, exceptional exposures of syn-rift stratigraphy and fault zones and 2D discrete element modelling provides information on the variability of structural style around segmented normal fault zones and the resultant changes due to fault growth and segment linkage. Using the geometry of syn-rift stratigraphy as an aid to reconstructing structural style, we focus on the 3D geometry of normal faults and associated structures during the rift initiation phase, prior to strain localisation on major tilt-block bounding fault zones. Early syn-rift stratigraphy indicates that surface deformation is initially characterised by a fault-parallel monocline above a blind fault tip that is often replaced, with increasing slip, by a through-going fault. Localisation onto a single fault produces fault-parallel hangingwall synclines and footwall anticlines as a result of breaching of the earlier monocline. This does not represent 'drag' against the fault. Secondary structures are common above the fault tip and comprise both synthetic and antithetic normal and reverse faults. Simultaneous faulting of competent materials and flow of weaker materials can lead to complex structural relationships. Faults in the cover can die out up and down section and do not necessarily link to the basement fault at depth. Similarly, complex ductile characteristics such as footwall thinning and hangingwall thickening can be juxtaposed against simple brittle fault cut-offs. Along-strike displacement gradients produce broad open folds and faults at high angles to the trace of the normal fault segment. These secondary structures show systematic decrease in amplitude and displacement into both hangingwall and footwall. 2D Discrete Element models are employed to examine the effect of heterogeneity in the cover on fold development and fault propagation. Experiments using a number of mechanically multi-layered cover sequences cause the distribution and timing of fractures and folds to vary dramatically.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.T43A1630G
- Keywords:
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- 8109 Continental tectonics: extensional (0905)