Seismic facies analysis is the most widely used method to identify event deposits from subaqueous environments. However, the internal structures of a chaotic or transparent seismic unit that represent event deposits are usually poorly imaged. This is primarily due to the limited resolution (usually <10 m) of commonly available multi-channel seismic reflection data. As a consequence, potential (sub)meter-thick, interbedded background sediments that may divide the chaotic layer cannot be discerned on such a seismic profile. The result of this, is that a complex of multiple moderate-thickness event layers can be misinterpreted as a single, thick event layer and this can greatly impact age-depth model reconstruction and geohazard assessment. One approach to resolve the problem is to correlate seismic data with high-resolution sediment core analysis. To address the problem in the South China Sea, we combine multiple methods to identify event deposits in the IODP holes U1499A and U1432C. Our dataset reveals that: (1) the previously interpreted ∼50 m-thick slumping unit in the region is a complex of multiple moderately sized units; (2) the slumping events are clustered between 0.6 and 0.4 Ma. Using our new understanding of event emplacement, we define event-free age models for mass wasting on the margin of the South China Sea, improving our understanding of local geohazards. Our methods here represent a sedimentological approach which could be used in other subaqueous environments to reconstruct event-free age models and geohazard histories.

中文翻译：

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南海北部集群状下降：对年代学和地质灾害的影响


地震相分析是从水下环境中识别事件沉积物的最广泛使用的方法。然而，代表事件沉积物的混沌或透明地震单元的内部结构通常成像不佳。这主要是由于常用的多通道地震反射数据的分辨率有限（通常为 <10 m）。因此，在这样的地震剖面上无法辨别可能划分混沌层的潜在（亚）米厚的互层背景沉积物。其结果是，多个中等厚度事件层的复合体可能会被误解为单个较厚的事件层，这会极大地影响年龄深度模型重建和地质灾害评估。解决此问题的一种方法是将地震数据与高分辨率沉积物岩芯分析相关联。为了解决南海的问题，我们结合了多种方法来识别 IODP 钻孔 U1499A 和 U1432C 中的事件矿床。我们的数据集显示：（1） 先前解释的该地区 ∼50 m 厚的坍落单元是多个中等尺寸单元的复合体;（2） 坍塌事件集中在 0.6 和 0.4 马 之间。利用我们对事件安置的新理解，我们为南海边缘的大规模浪费定义了无事件年龄模型，从而提高了我们对当地地质灾害的理解。我们这里的方法代表了一种沉积学方法，可用于其他水下环境，以重建无事件的年龄模型和地质灾害历史。