Seismic cycles, earthquakes, landslides and sediment fluxes: Linking tectonics to surface processes using a reduced-complexity model
Seismic cycles, earthquakes, landslides and sediment fluxes: Linking tectonics to surface processes using a reduced-complexity model
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DOI：
10.1016/j.geomorph.2019.04.017
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发表时间：
2019-08-15
期刊：
影响因子：
3.9
通讯作者：
Hilton, Robert G.
中科院分区：
文献类型：
--
作者：
Croissant, Thomas;Steer, Philippe;Hilton, Robert G.
在构造活跃的山脉中，地震引发的山体滑坡会动员大量的沉积物，影响河流的动态。这种沉积物输送可能导致下游河流几何形状和运输能力的变化，影响河流将沉积物输出震中区域的效率。滑坡沉积物在河流网络中的后续传播对下游灾害管理和多个地震周期内地形的长期演变具有影响。然而，对地震后河流清除滑坡沉积物的过程和时间尺度仍然缺乏充分的了解。在这里，我们提出了一个嵌套的数值方法来调查的过程中控制地震后的沉积物疏散在山脉规模，从到达尺度模型的结果通知。首先，我们探讨了河流地貌动力响应的滑坡级联在达到规模使用的二维建模方法。结果，然后用经验来描述疏散的滑坡体，避免使用一个计算广泛的模型，在集水区，可能有成千上万的同震滑坡。其次，我们提出了一个降低复杂性的模型，以量化疏散时间的地震引发的滑坡集群规模的山脉，检查假设的情况下，M-W 7.9地震及其余震发生在阿尔卑斯山断层，新西兰。我们的方法结合了地震滑坡群的经验描述与沉积物输出过程中涉及的震后阶段。我们的研究结果表明，地震间的山脉疏散同震沉积物的能力是至关重要的，以评估大地震的沉积物预算，在一个到几个地震周期。我们发现，泥沙疏散是由两个时间尺度，1。材料从山坡到渠道的转移时间; 2.滑坡沉积物到达河流网络后的疏散时间反过来，地震后的沉积物疏散可以是连通性有限的，当沉积物沿沿着山坡输送是主要限制过程时，或者是运输有限的，当河流运输是限制过程时。尽管径流值很高，我们认为，新西兰南阿尔卑斯山很可能是在连通性有限的条件下，连接速度2米。年（-1）足以让大多数同震沉积物被动员，并可能在不到一个地震周期的范围内输出。由于不良约束率的沉积物转移沿着山坡，我们的研究结果可能会提出的问题，同震沉积物积累山脉内的几个地震周期和构造输入和沉积物输出之间的不平衡。因此，我们呼吁重新开展观测工作，以更好地描述和量化导致滑坡疤痕和沉积物重新分配和动员的物理过程。(C)2019爱思唯尔B. V.保留所有权利。
In tectonically active mountain ranges, landslides triggered by earthquakes mobilise large volumes of sediment that affect river dynamics. This sediment delivery can cause downstream changes in river geometry and transport capacity that affect the river efficiency to export this sediment out of the epicentre area. The subsequent propagation of landslide deposits in the fluvial network has implications for the management of hazards downstream and for the long-term evolution of topography over multiple seismic cycles. A full understanding of the processes and time scales associated with the removal of landslide sediment by rivers following earthquakes however, is still lacking. Here, we propose a nested numerical approach to investigate the processes controlling the post-seismic sediment evacuation at the mountain range scale, informed by results from a reach scale model. First, we explore the river morphodynamic response to a landslide cascade at the reach-scale using a 2D modelling approach. The results are then used to describe empirically the evacuation of a landslide volume which avoids using a computationally extensive model in catchments which may have thousands of co-seismic landslides. Second, we propose a reduced-complexity model to quantify evacuation times of earthquake-triggered landslide clusters at the scale of a mountain range, examining the hypothetical case of a M-w 7.9 earthquake and its aftershocks occurring on the Alpine Fault, New Zealand. Our approach combines an empirical description of co-seismic landslide clusters with the sediment export processes involved during the post-seismic phase. Our results show that the inter-seismic capacity of the mountain range to evacuate co-seismic sediment is critical to assess the sediment budget of large earthquakes, over one to several seismic cycles. We show that sediment evacuation is controlled by two timescales, 1. the transfer time of material from hillslopes to channels and 2. the evacuation time of the landslide deposits once it has reached the fluvial network In turn, post-seismic sediment evacuation can either be connectivity-limited, when sediment delivery along hillslopes is the main limiting process, or transport-limited, when the transport by rivers is the limiting process. Despite high values of runoff, we suggest that the Southern Alps of New Zealand are likely to be in connectivity-limited conditions, for connection velocities 2 m.yr(-1) are sufficient to allow most of co-seismic sediments to be mobilised and potentially exported out of the range within less than one seismic cycle. Because of the poorly-constrained rate of sediment transfer along hillslopes, our results potentially raise the issue of co-seismic sediment accumulation within mountain ranges over several seismic cycles and of the imbalance between tectonic inputs and sediment export. We, therefore, call for renewed observational efforts to better describe and quantify the physical processes responsible for the redistribution and mobilization of sediment from landslide scars and deposits. (C) 2019 Elsevier B.V. All rights reserved.