Numerical Modelling of a Tsunami impinging Verde Lago, Algarve

This work aims to contribute to a better understanding of tsunamigenic events in Iberiaby enriching the discussion about seismic sources based on a combine approachusing sedimentological and numerical approaches. In Verde Lago (eastern Algarve, south Portugal), a tsunami deposit was identifiedconsisting primarily of sand and shell fragments, with a strong erosive base. To ascribe its potential source four tsunami-earthquake sources were simulated (i.e. GorringeBank, the Horseshoe Fault, the Marquês de Pombal Fault and a combined scenario derived from the combination of the Gorringe and Horseshoe Faults) using Delft3DFlow. Field data was gathered to validate the numerical modelling results including sediment samples collected in eight trenches and three cores retrieved within the Late Holocene stratigraphic sequence, textural analysis and age-estimation of the main lithostratigraphic units. Within this sequence a tsunami-related depositional unit wastentatively identified based on features commonly associates with tsunami sedimentological imprints (e.g. coarser unit, thinning inland; erosional contact). Despiteage-estimation uncertainties, this unit was dated to ca. 4000 years BP which very broadly could overlap with the 3600 yrs BP tsunami event recently described onoffshore cores retrieved from the shallow Algarve shelf. The results of this study show that for this specific location the Horseshoe Fault seismic source presents a better agreement with the deposits observed on the alluvial plain in the vicinity of Verde Lago and the predicted erosional/depositional patterns. This work reinforces the need for further efforts in tsunami geosciences both in the field, recognizing evidence of past events, as well as with numerical approaches to better define tsunami and seismic hazard for any given region.本研究旨在通过结合沉积学与数值模拟方法，深化对伊比利亚（Iberia）地区海啸触发事件的认知，以此丰富有关地震震源的探讨。在葡萄牙南部阿尔加维（Algarve）东部的韦德拉戈湖（Verde Lago）区域，研究人员识别出一处以砂与贝壳碎屑为主要组分、底部具有强烈侵蚀特征的海啸沉积层。为探明该沉积层的潜在震源，研究团队借助Delft3D Flow数值模型，对四类海啸-地震震源开展模拟：分别为戈兰奇海岭（Gorringe Bank）、马蹄形断层（Horseshoe Fault）、蓬巴尔侯爵断层（Marquês de Pombal Fault），以及由戈兰奇海岭与马蹄形断层组合而成的联合情景。为验证数值模拟结果，研究团队采集了多组野外实测数据：包括在晚全新世（Late Holocene）地层序列中挖掘的8个探槽与3个岩芯所获取的沉积样品，以及对主要岩石地层单元开展的粒度分析与年代估算工作。在该地层序列中，研究人员基于海啸沉积的典型标识特征（如粒度较粗的层位、向内陆方向厚度逐渐减薄、存在侵蚀接触界面等），初步识别出一处与海啸相关的沉积单元。尽管年代估算存在一定不确定性，但该沉积单元的年代约为距今4000年（BP），其时间范围大致可与近期在阿尔加维浅海大陆架获取的近海岩芯中记录的距今3600年BP的海啸事件相重合。本研究结果表明，针对该特定区域，马蹄形断层作为震源，与韦德拉戈湖附近冲积平原上观测到的沉积层以及模拟得到的侵蚀/沉积模式吻合度更高。本研究进一步凸显了在海啸地球科学领域开展更多研究的必要性：既要通过野外工作识别过往海啸事件的相关证据，也要借助数值模拟方法，以更精准地界定任意区域的海啸与地震灾害风险。