Probabilistic Landslide Susceptibility Offshore South West Iberian Margin-Paper

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The study evaluates probabilistic maps of earthquake-triggered submarine landslide susceptibility along the tectonically active South-West Iberian margin, an area where landslides could generate tsunamis. It examines three well-documented events—Marquês de Pombal, South Gorringe and Portimão Bank—to assess whether regional model outputs can help identify landslide source areas.<br /><br />The displacement-based method combines estimates of seabed slope, earthquake ground motion and sediment geotechnical properties, accounting for uncertainty through probabilistic simulations. A predicted permanent displacement of 11 cm was used as the failure threshold. The authors also applied a minimum slope criterion to distinguish likely source areas from flatter deposits.<br /><br />The approach identified plausible source areas for the Marquês de Pombal and South Gorringe landslides. It classified 84% of mapped Marquês de Pombal cells and 41% of South Gorringe cells as potentially unstable; slope filtering helped separate potential source areas from deposits. Results for Portimão Bank were less convincing, particularly for its complex debris-flow deposits, likely because their material behavior is not well represented by the model’s simplified slope-stability assumptions.<br /><br />The findings suggest that probabilistic susceptibility maps are useful for preliminary screening of unstable offshore areas and may support tsunami-hazard analysis. However, their reliability depends on landslide type, available geotechnical data and the limitations of applying a regional-scale model to complex failures.

Keywords

submarine landslide

earthquake-triggered

probabilistic susceptibility

South-West Iberian margin

tsunami hazard

Marquês de Pombal

South Gorringe

Portimão Bank

seabed slope

ground motion