Processes beneath the Great Wave: improved understanding of tsunami geohazards using advances in deep-sea sedimentology

海啸对沿海社区和基础设施构成非常严重的危害，2004年影响印度洋和2011年影响日本的大地震引发的海啸就是明证。最近，汤加火山Hunga Tonga-Hunga Ha'apai在2022年初的爆发也导致了具有局部和远场影响的破坏性海啸。对这种海啸的理解是复杂的，因为它们非常罕见和非常高的震级，这使得测量它们的波浪非常困难。我们的大部分知识仅限于对古代海啸沉积物的认识，主要基于它们的运行（内陆的最大距离）和运行（达到的最大高度）。这些矿床的沉积学资料主要限于其矿床的总体粒度。大部分关于海啸波本质的证据都被锁定在这些沉积物中，然而直到最近我们才具备能够解读这些信息的知识。在这里，我们将采用一种新的方法，利用最近在理解深海流动方面取得的巨大进展，纯粹基于它们的沉积物。深海沉积物似乎不太可能成为海啸研究的起点，但它们有许多令人惊讶的相似之处。沙级（和较大）物质在深海的沉积主要是一类流动的结果，包括浊流和碎屑流，统称为沉积物重力流。深海中的这种水流非常罕见，而且非常强大，因此我们对实际水流的测量非常少，即使是这些测量也几乎完全限于斜坡，而不是盆地底部。即使对于这些流动，我们对速度分布的了解也比对泥沙浓度、垂直分层和泥沙成分的了解要好得多。因此，我们对这些强大的水下流的知识主要是从它们的沉积物中获得的。在过去的10-15年里，我们对这些SGF沉积物的理解发生了革命性的变化，并认识到它们不仅仅是低浓度的湍流或高浓度的粘性泥石流。我们现在认识到，有一个完整的频谱的流量在浓度，内聚强度，与大范围的“过渡流”，和个别的流动事件可以显示出戏剧性的变化，在流动性质的纵向，并随着时间的推移在一个给定的点。最近，我们已经开发出能够识别这些不同的流动状态，并评估其流动演变的方法。监督团队一直处于深水沉积学进步的前沿，并了解过渡和高浓度流动的动力学。最近，我们对海啸沉积物进行了概念验证研究，以检查这些深水方法的适用性。在这个研究项目中，学生将在日本和苏格兰对已知的海啸沉积物进行采样。我们的目标还包括从其他例子中整合海洋和陆地岩心以及一些浅水多波束数据集。这些数据集将用于记录沉积记录的特征（颗粒大小、形状、矿物学），使用利兹大学沉积物、土壤和污染物分析实验室的先进设备，以便更好地了解海啸下的形成过程。有巨大的潜力，重新审视海啸沉积物的沉积学，以解决相关的地质灾害，并提高沿海社区和基础设施的恢复能力。拟议的博士项目的主要目的是提高与海啸相关的地质灾害的认识，利用新的沉积学的理解，从深海沉积物中开发的概念。

Tsunami pose a very significant hazard to coastal communities and infrastructure, as seen in the giant earthquake-generated tsunami that affected the Indian Ocean in 2004, and Japan in 2011. More recently, the eruption of the Tongan volcano Hunga Tonga-Hunga Ha'apai in early 2022 also led to a destructive tsunami with both local and far field effects. Understanding of such tsunami is complicated by their great rarity and very high magnitude, which makes measurements of their waves exceptionally problematic. Much of our knowledge is limited to the recognition of ancient tsunami deposits, based primarily on their run-in (maximum distance inland) and run-up (maximum height reached). Sedimentological information from such deposits is largely restricted to the overall grain-size of their deposits. Much of the evidence for the nature of tsunami waves is locked in these deposits, and yet we have lacked the knowledge to be able to read this until recently. Here we will adopt a new approach that utilises the huge recent advances in understanding of flows in the deep oceans, based purely on their deposits.Deep-sea deposits may seem an unlikely starting point for the study of tsunami, yet there are many surprising similarities. Sedimentation of sand-sized (and larger) material in the deep-sea is primarily the result of a class of flows that include turbidity currents and debris flows, collectively known as sediment gravity flows (SGFs). Such flows in the deep-sea are highly infrequent and very powerful, and thus we have very few measurements of actual currents, and even these are almost entirely restricted to the slope, rather than the basin floor. Even for these flows, we have a much better idea on velocity distributions than we do sediment concentrations, stratification in the vertical, and sediment composition. Consequently, our knowledge of these powerful underwater flows is dominantly obtained from their deposits. Over the past 10-15 years there has been a revolution in our understanding of these SGF deposits, and a realisation that they are not solely low-concentration, turbulent currents or high-concentration cohesive debris flows. We now recognise that there is a full spectrum of flows in terms of concentration, and cohesive strength, with a large range of 'transitional flows', and that individual flow events can show dramatic changes in flow properties both longitudinally, and over time at a given point. More recently, we have developed methods to be able to identify these different flow states, and to assess their flow evolution. The supervisory team have been at the forefront of these advances in deepwater sedimentology, and understanding the dynamics of transitional and high concentration flows. More recently we have undertaken a proof-of-concept study on tsunami deposits to examine the applicability of these deepwater approaches. In this research project, the student will sample known tsunami deposits in Japan and Scotland. We also aim to integrate both marine and terrestrial cores, as well as some shallow water multibeam datasets, from additional examples. These datasets will be used to document the character of the sedimentary record (particle size, shape, mineralogy) using the cutting edge equipment in the Sediment, Soil, and Pollutant Analysis Laboratory at the University of Leeds, to better understand the formative processes under the tsunami. There is huge potential to re-examine the sedimentology of tsunami deposits to tackle the associated geohazards, and improve the resilience of coastal communities and infrastructure.The principal aim of the proposed PhD project is to improve understanding of the geohazards associated with tsunami utilising new sedimentological understanding derived from concepts developed in deep-marine sediments.