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.