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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Feb 2019

Research article | 14 Feb 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).

Statistical modelling of co-seismic knickpoint formation and river response to fault slip

Philippe Steer1, Thomas Croissant1,a, Edwin Baynes1,b, and Dimitri Lague1 Philippe Steer et al.
  • 1Univ Rennes, CNRS, Géosciences Rennes – UMR 6118, F-35000 Rennes, France
  • anow at: Department of Geography, Durham University, Durham, UK
  • bnow at: Department of Civil and Environmental Engineering, University of Auckland, Auckland, New Zealand

Abstract. Most landscape evolution models adopt the paradigm of constant and uniform uplift. It results that the role of fault activity and earthquakes on landscape building is understood under simplistic boundary conditions. Here, we develop a numerical model to investigate river profile development subjected to fault displacement by earthquakes and erosion. The model generates earthquakes, including mainshocks and aftershocks, that respect the classical scaling laws observed for earthquakes. The distribution of seismic and aseismic slip can be partitioned following a spatial distribution of mainshocks along the fault plane. Slope patches, such as knickpoints, induced by fault slip are then migrated at a constant rate upstream a river crossing the fault. A major result is that this new model produces co-seismic knickpoints with a uniform height distribution for a fully coupled fault, i.e. with only co-seismic slip. Increasing aseismic slip at shallow depths, and decreasing shallow seismicity, censors the range magnitude of earthquakes cutting the river towards large magnitudes and leads to less frequent but higher amplitude knickpoints, on average. Inter-knickpoint distance or time between successive knickpoints follows an exponential decay law. Using classical rates for fault slip, 15 mm.yr−1 and knickpoint retreat, 0.1 m.yr−1, leads to high spatial densities of knickpoints requiring sub-metric spatial resolution to distinguish them. The correlation between the topographic profiles of successive parallel rivers cutting the fault remains positive for distance along the fault of less than half the maximum earthquake rupture length. This suggests that river topography can be used for paleo-seismological analysis and to assess fault slip partitioning between aseismic and seismic slip. Yet, considering simple scenarios of fault burial by intermittent sediment cover, driven by climatic changes or linked to earthquake occurrence, leads to knickpoint distributions and river profiles markedly different from the case with no sediment cover. This highlights the potential role of sediments in modulating and potentially altering the expression of tectonic activity in river profiles and surface topography.

Philippe Steer et al.
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Philippe Steer et al.
Philippe Steer et al.
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Publications Copernicus
Short summary
We use a statistical earthquake generator to investigate the influence of fault activity on river profile development and on the formation of co-seismic knickpoints. We find that the height distribution of knickpoints resulting from a purely seismic fault is homogeneous. Shallow aseismic slip favors knickpoints generated by large magnitude earthquakes nucleating at depth. Accounting for fault burial by alluvial cover can modulate the topographic expression of earthquakes and fault activity.
We use a statistical earthquake generator to investigate the influence of fault activity on...