Cohesion, permeability, and slope failure dynamics: Implications for failure morphology and tsunamigenesis from benchtop flume experiments
Cohesion, permeability, and slope failure dynamics: Implications for failure morphology and tsunamigenesis from benchtop flume experiments
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DOI：
10.1016/j.margeo.2023.107079
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发表时间：
2023-08
期刊：
影响因子：
2.9
通讯作者：
M. Silver;B. Dugan
中科院分区：
文献类型：
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作者：
M. Silver;B. Dugan
海底斜坡失稳能够破坏海底基础设施并引发海啸，从而对沿海社区构成危害。海底斜坡破坏发生在世界各地的沿着大陆边缘，但我们的了解海底斜坡破坏的演变和海啸的潜力是有限的。超压已被认为是引发和预处理边坡破坏的机制，但对它在边坡破坏中的作用的理解是有限的。在这项研究中，我们调查了超压引起的边坡失稳与不同的沉积物成分和性质的海洋环境中常见的。研究了沉积物渗透性和粘聚力与边坡破坏所需的超压和破坏行为的关系。我们研究了失败的台式水槽实验中使用的混合物细颗粒石英砂和粘性蒙脱石粘土或细颗粒石英砂和非粘性粘土大小的石英。在高渗透性、富砂系统（0-5重量%蒙脱石）中，引起失效所需的超压与蒙脱石含量直接相关（R2为0.89）。在蒙脱石浓度为25wt%或更高时，诱导边坡破坏所需的标准化超压（λ*）保持恒定，λ*= 1.52 ± 0.55。在25%蒙皂石时，失效行为也发生了变化。在富砂系统中，即使在持续或增加的超压下也会发生单一故障事件。蒙脱石或粘土大小的石英浓度为25重量%或更高，发生了一系列的边坡破坏。蒙脱石浓度≥25%也会产生更大和更脆的破坏变形特征（例如，张裂和地下裂缝）。我们的结论是，低渗透率系统有可能发生更大的破坏，粘性沉积物混合物是产生脆性破坏特征所必需的（例如，张裂、地下裂缝、筏状块体等）。实验使用25，75，和90重量%的蒙皂石产生筏状沉积物块分离的母坡。然而，即使坡度相对较陡（19°），实验也没有调动任何完整的块体。观察到的实验失效变形特征（例如，泥火山作用、张裂、富含粘土的趾状沉积物等）与自然海洋环境中观察到的现象相匹配。从我们的实验中，我们解释在低渗透性，高凝聚力的沉积物的存在下，超压可以产生非海啸海底边坡故障和海啸故障的先决条件斜坡。因此，我们的工作证明了沉积物性质和成分与所产生的故障类型相关的重要性，并强调了多个因素的必要性（例如，过大的水头加上地震震动），以调动大型筏式块体下坡，这对改善海岸灾害评估有直接影响。
Submarine slope failures pose hazards to coastal communities through their ability to damage seafloor infrastructure and generate tsunamis. Submarine slope failures occur along continental margins worldwide, yet our understanding of submarine slope failure evolution and tsunamigenic potential is limited. Overpressure has been a proposed mechanism for initiating and preconditioning for slope failures, but understanding of its role in slope failures is limited. In this study, we investigate overpressure-induced slope failures with different sediment compositions and properties common in the marine environment. Overpressure required for slope failure and failure behavior were investigated in relation to sediment permeability and cohesion. We investigated failures in benchtop flume experiments using mixtures of fine-grained quartz sand and cohesive smectite clay or fine-grained quartz sand and non-cohesive clay-sized quartz. In high-permeability, sand-rich systems (0–5 wt% smectite), overpressure required to induce failure directly related to smectite content (R2of 0.89). At smectite concentrations of 25 wt% or greater, normalized overpressure (λ*) required to induce slope failure remained constant atλ*= 1.52 ± 0.55. Failure behavior also changed at 25% smectite. In sand-rich systems, a single failure event occurred even with sustained or increased overpressure. With smectite or clay-sized quartz concentrations of 25 wt% or higher, a series of slope failures occurred. Concentrations of smectite ≥25% also produced larger and more brittle failure deformation features (e.g., tension cracks and subsurface fissures). We conclude that lower permeability systems have the potential for larger failures and cohesive sediment mixtures are necessary for producing brittle failure features (e.g., tension cracks, subsurface fissures, rafted blocks, etc.). Experiments using 25, 75, and 90 wt% smectite produced rafted sediment blocks separated from the parent slope. However, experiments did not mobilize any intact blocks downslope even with a relatively steep (19°) slope. Observed experiment failure deformation features (e.g., mud-volcanism, tension cracks, clay-enriched toe deposits, etc.) match observed phenomenon in natural marine environments. From our experiments, we interpret in the presence of low-permeability, high-cohesion sediments, overpressure can produce non-tsunamigenic submarine slope failures and precondition slopes for tsunamigenic failure. Thus, our work demonstrates the importance of sediment properties and composition in relation to the types of failures produced and additionally emphasize the need for multiple factors (e.g., excess head plus seismic shaking) to mobilize large, rafted blocks downslope which has direct impact in improving coastal hazard assessment.