First remote sensing of turbidity currents via seismic signals: how much can we learn about the longest sediment flows on Earth?

浊流将全球大量的沉积物和有机碳输送到深海，并对海底基础设施构成相当大的危害。尽管技术不断进步，但由于其相对难以接近的位置和经常不可预测的发生，浊度流很难监测。最重要的是，它们强大的特性经常会损坏放置在其路径上的仪器。过去5年的开创性工作表明，利用系泊监测浊度流是可能的。最近的一次是在2020年1月，从刚果河口流出的流量达到了12200公里；这是迄今为止地球上测量到的最长的沉积物流。然而，系泊测量既昂贵又困难。此外，它们位于浊度流内，因此处于危险之中。这些挑战意味着只有少数现场可以研究，但我们需要研究浊度流在世界各地的位置，以了解其控制。因此，我们需要浊度电流的传感系统，它位于远离危险的地方。令人兴奋的是，最近从西非近海刚果峡谷获得的海底地震仪（OBS）数据表明，浊流发出独特的地震信号。这些新识别的地震信号现在可以通过位于事件外部的遥感系统监测大范围的事件。为了在理解浊度流及其更广泛的影响方面做出一步改变，我建议开发全球适用的方法，利用来自刚果峡谷的OBS数据远程监测浊度流，那里已知会发生强大的浊度流。为了做到这一点，OBS的结果将与相邻系泊所提供的关于流动及其时间的独立信息进行比较。这将有助于理解地震信号不仅可以告诉我们浊流发生的时间，还可以告诉我们内部流动结构及其演变，甚至侵蚀速率。海底地震仪调查很有可能成为未来海底灾害监测的重要支柱。这个项目的结果将成为今后这种调查分析的基础。

Turbidity currents transport globally significant volumes of sediment and organic carbon into the deep-sea and pose a considerable hazard to sea floor infrastructure. Despite advances in technology, turbidity currents are notoriously difficult to monitor due to their relatively inaccessible location and often unpredictable occurrence. Most importantly, their powerful nature often damages instruments placed in their path. Pioneering work in the last 5 years has shown it was possible to monitor turbidity currents using moorings. Most recently, this included a flow that ran out for >1,200 km from the Congo River mouth in Jan. 2020; the longest sediment flow (of any type) yet measured on Earth. Mooring measurements, however, are expensive and logistically difficult. In addition, they are located within turbidity currents, and thus in harm’s way. These challenges mean that only a few field sites can ever be studied, yet we need to study turbidity currents at locations worldwide to understand their controls. We therefore need sensing systems for turbidity currents, which are located out of harm’s way. Excitingly, recently acquired ocean bottom seismometer (OBS) data from the Congo Canyon offshore West Africa suggest that turbidity currents emit distinctive seismic signals. These newly-recognised seismic signals now enable monitoring events across large areas via remote sensing systems located outside the event. To make a step change in understanding turbidity currents and their wider impacts, I propose to develop globally applicable methods to remotely monitor turbidity currents using OBS data from the Congo Canyon, where powerful turbidity currents are known to occur. To do this, the OBS results will be compared to independent information provided by adjacent moorings on the flows and their timing. This will help to understand what seismic signals can tell us about not only when turbidity currents occur, but also the internal flow structure and its evolution and even erosion rates. OBS surveys have a high potential of constituting an important pillar of sea floor hazard monitoring in the future. The results of this project will form the basis of the analyses of such future surveys.