Modelling the role of material depletion, grain coarsening and revegetation in debris flow occurrences after the 2008 Wenchuan earthquake
Modelling the role of material depletion, grain coarsening and revegetation in debris flow occurrences after the 2008 Wenchuan earthquake
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DOI：
10.1016/j.enggeo.2019.01.010
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发表时间：
2019-02-21
影响因子：
7.4
通讯作者：
Hales, Tristram C.
中科院分区：
文献类型：
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作者：
Domenech, Guillem;Fan, Xuanmei;Hales, Tristram C.
2008年汶川7.9级地震伴生的同震质量浪费产生了大量的岩屑。山坡上大量的这种松散物质导致了更频繁的泥石流，这是由较弱和/或较短的降雨引发的。然而，在过去十年中，触发降雨和泥石流频率似乎都逐渐正常化。虽然在几次大地震后记录了震后泥石流降雨阈值的变化，但控制这些变化的因素仍然知之甚少。通过虚拟实验，研究了同震碎屑的物质耗竭、颗粒粗化和植被恢复对径流泥石流传播和沉积的影响，以及它们对触发降雨阈值的影响。我们采用基于地理信息系统（GIS）的径流侵蚀引发泥石流的模拟，我们首先对2010年8月14日发生在汶川地震震中附近的洪春沟事件进行了校准。通过调查上述过程中的每一个，我们获得了给定泥石流跳动距离的临界降雨强度-持续时间阈值的变化。颗粒粗化似乎起了主要作用，这与已发表的实验室实验结果一致，而物质消耗和植被恢复似乎不能单独解释泥石流频率的实际快速衰减。虽然虚拟实验已证明在确定对这种衰减的一阶控制方面是有用的，但需要对多个集水区进行模型改进和验证，以使结果在危害评估中有用。
A large amount of debris was generated by the co-seismic mass wasting associated with the 2008 M-w 7.9 Wenchuan earthquake. The abundance of this loose material along the slopes caused more frequent debris flows, triggered by less intense and/or shorter rainfalls. However, both the triggering rainfall and the debris flow frequency seem to have normalised progressively during the past decade. Although changes of rainfall thresholds for post-seismic debris flows were recorded after several major earthquakes, the factors controlling these changes remain poorly constrained. With the aid of a virtual experiment, we investigate the roles of material depletion, grain coarsening and revegetation of the co-seismic debris on the propagation and deposition of debris flows initiated by runoff, as well as their influence on the triggering rainfall thresholds. We employ a Geographic Information System (GIS)-based simulation of debris flow initiation by runoff erosion, which we first calibrate on the 14th August 2010 Hongchun gully event that occurred near the Wenchuan earthquake epicentre. We obtain, by investigating each of the aforementioned processes, changing critical rainfall intensity-duration thresholds for given debris flow runout distances. Grain coarsening appears to play a major role, which is consistent with published laboratory experiments, while material depletion and revegetation do not seem able to account alone for the actual quick decay of debris flow frequency. While the virtual experiment has proven useful in identifying the first-order controls on this decay, model improvements and verification over multiple catchments are needed to make the results useful in hazard assessments.