Submarine sediment failures or landslides triggered by storm waves in river delta areas pose a significant risk to coastal infrastructure. Due to the limitations of in situ monitoring technology, existing investigations are mostly carried out with geophysical techniques to provide some basic characteristics (e.g. location, size, runout distance, volume, and potential triggers) of existing submarine landslides. However, it is of equal importance to identify the starting criterion and the in situ evolutionary process of the initial stage of seafloor instabilities—sediment failure, which naturally relies heavily on long-term field observations. A field monitoring system was developed for observing sediment failure, which successfully recorded the wave-induced seabed deformation in the subaqueous Yellow River Delta for the first time. Once sediment failure is initiated, the shallow soil undergoes periodic and reciprocating oscillations under alternating action of wave crests and troughs. The evolution of the maximum deformation depth interface moves from shallow to deep, and then migrates upward from deep to shallow layers (the shallow-deep-shallow pattern), which indicates a stability recovery process following the wave-induced seabed failure, and these processes were found to occur multiple times within one storm event. Laboratory wave flume experimental results reproduced and verified the field observations, while also providing pore pressure data which explains the initiation of sediment failure and the deformation process. Finally, a development pattern of the seafloor instabilities in the subaqueous Yellow River Delta is proposed. The in situ observation methods proposed and the knowledge acquired by field monitoring and flume testing could benefit the investigation of costal seafloor instabilities.

中文翻译：

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黄河三角洲水下波浪引起的海底不稳定性——沉积物破坏的发生和过程

河流三角洲地区的风暴波引发的海底沉积物破坏或山体滑坡对沿海基础设施构成了重大风险。由于原位监测技术的局限性，现有的调查大多采用地球物理技术进行，以提供现有海底滑坡的一些基本特征（例如位置、大小、跳动距离、体积和潜在触发因素）。然而，确定海底不稳定初始阶段——沉积物破坏的起始标准和原位演化过程同样重要，这自然很大程度上依赖于长期的野外观测。开发了用于观察沉积物破坏的现场监测系统，首次成功记录了黄河三角洲水下海床的波浪诱发海床变形。一旦沉积物破坏开始，浅层土壤在波峰和波谷的交替作用下经历周期性的往复振荡。最大变形深度界面的演化由浅到深，然后由深到浅层向上迁移（浅-深-浅模式），表明海床破坏后的稳定性恢复过程，以及这些过程发现在一次风暴事件中多次发生。实验室波浪水槽实验结果再现并验证了现场观测结果，同时还提供了解释沉积物破坏和变形过程的孔隙压力数据。最后，提出了黄河三角洲水下海底不稳定的发展模式。