The precise location of the seismic source of Great Lisbon Earthquake is still uncertain. The aim of this work is to use the an onland sedimentary record in southern Portugal to test and validate seismic sources of the AD 1755 earthquake. To achieve this, tsunami deposit thicknesses from over 150 cores retrieved from Salgados (Portugal) were compared to the results of a tsunami sediment transport model (Delft3D-FLOW) which simulates tsunami propagation, inundation, erosion, and deposition. Seven different hypothetical seismic sources and varying bed roughness coefficients were used to determine which modeled sources better reproduce observed patterns of tsunami deposit thicknesses and also dune erosion at the studied site in southern Portugal. Modeled and observed historical tsunami arrival times were also used to test different earthquake sources. Based on these comparisons, four modeled earthquake sources were unable to reproduce the observed physical data, suggesting they should be disregarded as likely sources of the AD 1755 earthquake.