Hydrodynamic Modeling of the CE1755 Tsunami along the Western Algarve (Portugal)

To implement effective mitigation strategies and coastal planning, it is crucial to understand the hydrodynamics of Extreme Wave Events (EWE) including major storms, hurricanes or tsunamis. One of such examples is the CE1755 tsunami that affected the shores of several regions around the Atlantic. Despite its magnitude, the exact seismogenic source of this event is still an open discussion, with hypotheses ranging form the Horseshoe Fault (HSF) and the Marques de Pombal Fault (MPF) to the Gorringe Bank (GB) and the Cadiz Accretionary Wedge (CAW).

This study specifically focused on the embayments of Martinhal, Boca do Rio and Lagos (along the southern coast of Portugal, immediately to the east of Sagres) where detailed geological and historical records are available facilitating ground truth on the adopted modelling approach.

Hydrodynamic modeling was made using Delft3D-FLOW to simulate wave generation, propagation and inundation. Five potential tectonic scenarios were tested: the four singular faults mentioned above and a combined “Scenario 1” (HSF+GB). To ensure accuracy in the nearshore interactions, high-resolution nested grids were generated, refining the spatial resolution down to 50 meters.

The model outputs were validated by cross-referencing reported wave heights (e.g., ~6.6m at Martinhal, ~11-13m at Boca do Rio) and arrival times. The comparative analysis reveals that the Horseshoe Fault (HSF) and the combined faults (Scenario 1) provided the best fit with historical accounts and geological evidence. Contrarily, the Cadiz Accretionary Wedge scenario produced wave heights significantly lower than those historically reported, making it an unlikely source. These findings contribute to the ongoing effort to better understand EWE impacts along the Iberian coasts.

This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020 , UID/50019/2025 and  https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025. Finally, this work is a contribution to project iCoast (project 14796 COMPETE2030-FEDER-00930000).