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| Titel |
Hanging-wall deformation above a normal fault: sequential limit analyses |
| VerfasserIn |
Xiaoping Yuan, Yves M. Leroy, Bertrand Maillot |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107506
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| Publikation (Nr.) |
 EGU/EGU2015-7209.pdf |
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| Zusammenfassung |
| The deformation in the hanging wall above a segmented normal fault is analysed with the
sequential limit analysis (SLA). The method combines some predictions on the dip and
position of the active fault and axial surface, with geometrical evolution à la Suppe
(Groshong, 1989). Two problems are considered. The first followed the prototype proposed
by Patton (2005) with a pre-defined convex, segmented fault. The orientation of the upper
segment of the normal fault is an unknown in the second problem. The loading in both
problems consists of the retreat of the back wall and the sedimentation. This sedimentation
starts from the lowest point of the topography and acts at the rate rs relative to the wall retreat
rate.
For the first problem, the normal fault either has a zero friction or a friction value set to
25o or 30o to fit the experimental results (Patton, 2005). In the zero friction case, a hanging
wall anticline develops much like in the experiments. In the 25o friction case, slip on the
upper segment is accompanied by rotation of the axial plane producing a broad shear zone
rooted at the fault bend. The same observation is made in the 30o case, but without slip on the
upper segment. Experimental outcomes show a behaviour in between these two latter
cases.
For the second problem, mechanics predicts a concave fault bend with an upper segment
dip decreasing during extension. The axial surface rooting at the normal fault bend sees its
dips increasing during extension resulting in a curved roll-over. Softening on the normal fault
leads to a stepwise rotation responsible for strain partitioning into small blocks in the hanging
wall. The rotation is due to the subsidence of the topography above the hanging wall.
Sedimentation in the lowest region thus reduces the rotations. Note that these rotations
predicted by mechanics are not accounted for in most geometrical approaches (Xiao and
Suppe, 1992) and are observed in sand box experiments (Egholm et al., 2007, referring to
Dahl, 1987).
References:
Egholm, D. L., M. Sandiford, O. R. Clausen, and S. B. Nielsen (2007), A new strategy for
discrete element numerical models: 2. sandbox applications, Journal of Geophysical
Research, 112 (B05204), doi:10.1029/2006JB004558.
Groshong, R. H. (1989), Half-graben structures: Balanced models of extensional
fault-bend folds, Geological Society of America Bulletin, 101 (1), 96-105.
Patton, T. L. (2005), Sandbox models of downward-steepening normal faults, AAPG
Bulletin, 89 (6), 781-797.
Xiao, H.-B., and J. Suppe (1992), Orgin of rollover, AAPG Bulletin, 76 (4), 509-529. |
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