Difference between revisions of "The role of surface displacement in landscape evolution"

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'''The influence of crustal strength fields on the patterns and rates of fluvial incision'''
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The objective of this project is to study the effects of 3D fault slip on landscape evolution. Specifically, there can be implications for the steepness of rivers and the evolution of drainage network patterns when considering the full 3D solution for fault slip. Our method is to apply kinematic conditions to points on a model landscape surface, representing tectonic motion, and allow for surface processes to erode the surface. Additionally we include rock damage associated with shear strain as an influence on rock erodibility surrounding the fault. Results suggest that the lateral motion attributed to slip along a fault plane can drastically increase channel slope in reverse thrust regimes and decrease slope in normal rift regimes, however, this depends on the dip angle of the primary slip surface.
  
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S.G. Roy a,*, P.O. Koons a, P. Upton b,a, G.E. Tucker c
 
  
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a ''Earth and Climate Sciences, University of Maine, 111 Bryand Global Sci. Ctr., Orono ME 04469''
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Model results suggest three major ways in which rivers will align to fault structures:
  
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b ''GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand''
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1. Kinematic: Strike-slip motion displaces rivers that cross the primary slip surface, extending their reach along strike. The magnitude of this extension depends on the slip rate after a pseudo-steady-state is reached.
  
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c ''Cooperative Institute for Research in Environmental Sciences (CIRES) and Department of Geological Sciences, University of Colorado, UCB 399 Boulder, CO 80309-0399''
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2. Kinematic: Dip-slip convergence advects channel sections toward the primary slip surface. Because the hanging wall is eroded before it can cross the current exposure of the fault strike, rivers continue to follow these channel sections that have been transferred to the primary slip surface.
  
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'''Abstract'''
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3. Damage/Erosion: Local reductions in rock strength associated with continued shear abrasion enhances erodibility along fault strike, lading to rapid erosion rates and alignment of large channels to the primary slip surface.
  
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Gradients in the bedrock strength field are increasingly recognized as integral to the rates and patterns of landscape evolution. To explore this influence, we incorporate data from fault strength profiles into a landscape evolution model, under the assumption that erodibility of rock is proportional to the inverse square root of cohesion for bedrock rivers incised by bedload abrasion. Our model calculations illustrate how patterns in the crustal strength field can play a dominant role in local fluvial erosion rates and consequently the development of fluvial network patterns. Fluvial incision within weak zones can be orders of magnitude faster than for resistant bedrock. The large difference in erosion rate leads to the formation of a straight, high order channel with short, orthogonal tributaries of low order. In comparison, channels incising into homogeneous strength fields produce dendritic drainage patterns with no directional dependence associated with erodibility gradients. Channels that cross the strength gradient experience local variations in knickpoint migration rate and the development of stationary knickpoints. Structurally confined channels can shift laterally if they incise into weak zones with a shallow dip angle, and this effect is strongly dependent on the magnitude of the strength difference, the dip angle, and the symmetry and thickness of the weak zone. The influence of the strength field on drainage network patterns becomes less apparent for erodibility gradients that approach homogeneity. There are multiple natural examples with drainage network patterns similar to those seen in our numerical experiments.
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Future work: This sensitivity analysis uses 3D kinematic solutions to predict what may happen under dynamic situations of tectonic deformation.  
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{| class="wikitable"
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|-
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! style="width:500px" | [[File:kin_slope-v-area.jpg|500px|thumb|Experimental models used to determine influence of lateral surface motion on surface slopes. (A) Block uplift, no lateral motion (black); (B) reverse dip-slip (red); (C) normal dip-slip (blue). (D) E-W topographic profiles. (E) Slope versus area log-log plots]]
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|-
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! style="width:500px" | [[File:kinematic-01.png|500px|thumb|left|Reverse dip-slip faulting]]
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! {{#ev:youtube|epZmuzxnGk8}}
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|-
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! style="width:500px" | [[File:kinematic-02.png|500px|thumb|left|Normal dip-slip faulting]]
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! {{#ev:youtube|V5803fcKFpY}}
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|-
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! style="width:500px" | [[File:kinematic-03.png|500px|thumb|left|Left-lateral strike-slip faulting]]
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! {{#ev:youtube|U-7Ex4wSmmw}}
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|-
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! style="width:500px" | [[File:kinematic-04.png|500px|thumb|left|Reverse oblique-slip faulting]]
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! {{#ev:youtube|XVPzurj9TRE}}
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|}
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</div>
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Images and models produced by Sam Roy

Latest revision as of 00:50, 18 February 2016

The objective of this project is to study the effects of 3D fault slip on landscape evolution. Specifically, there can be implications for the steepness of rivers and the evolution of drainage network patterns when considering the full 3D solution for fault slip. Our method is to apply kinematic conditions to points on a model landscape surface, representing tectonic motion, and allow for surface processes to erode the surface. Additionally we include rock damage associated with shear strain as an influence on rock erodibility surrounding the fault. Results suggest that the lateral motion attributed to slip along a fault plane can drastically increase channel slope in reverse thrust regimes and decrease slope in normal rift regimes, however, this depends on the dip angle of the primary slip surface.


Model results suggest three major ways in which rivers will align to fault structures:

1. Kinematic: Strike-slip motion displaces rivers that cross the primary slip surface, extending their reach along strike. The magnitude of this extension depends on the slip rate after a pseudo-steady-state is reached.

2. Kinematic: Dip-slip convergence advects channel sections toward the primary slip surface. Because the hanging wall is eroded before it can cross the current exposure of the fault strike, rivers continue to follow these channel sections that have been transferred to the primary slip surface.

3. Damage/Erosion: Local reductions in rock strength associated with continued shear abrasion enhances erodibility along fault strike, lading to rapid erosion rates and alignment of large channels to the primary slip surface.

Future work: This sensitivity analysis uses 3D kinematic solutions to predict what may happen under dynamic situations of tectonic deformation.

Experimental models used to determine influence of lateral surface motion on surface slopes. (A) Block uplift, no lateral motion (black); (B) reverse dip-slip (red); (C) normal dip-slip (blue). (D) E-W topographic profiles. (E) Slope versus area log-log plots
Reverse dip-slip faulting
Normal dip-slip faulting
Left-lateral strike-slip faulting
Reverse oblique-slip faulting

Images and models produced by Sam Roy

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