Physical modelling of plausible earthquake-induced tsunami scenarios and risk assessment at urban scale: a case study in Northeastern Italy

Physical modelling of earthquakes and cascading hazards, such as tsunamis or landslides, provides the basis for defining plausible (yet unobserved) multi-hazard and risk scenarios. The developed scenarios supply
a systematic method for exploring how the complex interplay between hazards and urban systems may impact a society, and can be applied to support and rationalise decision making and inform preparedness for multi-risks management and mitigation (e.g. Strong, Carpenter and Ralph, 2020. Cambridge Centre for Risk Studies).

Significant earthquake-induced tsunamis in the Northern Adriatic are rare, with most historical events reported along the central and southern coasts, hence related risk awareness is limited. Although a tsunami alert system has been established for the Mediterranean region and connected seas, a detailed understanding of the potential impacts of tsunami waves on coastal areas is still lacking for many sites. Here we consider hazard scenarios associated with potential tsunamis generated by offshore earthquakes to contribute to tsunami risk assessments for urban areas along the Northeastern Adriatic coasts (Peresan and Hassan, MEGR 2024). Tsunami modelling is conducted using the NAMI DANCE software (Yalciner et al. 2014 and references therein), which accounts for seismic source properties, bathymetry, topography and non-linear effects in wave propagation. Earthquake induced hazard scenarios are developed for selected coastal areas of Northeastern Italy, focusing on selected cities such as Trieste and Lignano. The modelling considers a wide set of potential earthquake-induced tsunami scenarios, with sources defined based on historical tsunami catalogues and active fault databases. Existing bathymetry and topography datasets are refined to incorporate high-resolution data (25-meter and 10-meter resolutions) and to better capture small-scale coastal features that influence tsunami inundation. The modelling provides a set of tsunami hazard-related parameters, such as arrival times and inundation maps, which are critical for planning emergency and mitigation actions in these areas.

For effective multi-hazard disaster risk reduction and mitigation, high-resolution exposure models are needed at the local scale, especially for hazards like tsunamis and flooding, which exhibit high spatial variability. We consider here a methodology for developing high-resolution exposure models for population and residential buildings to support local multi-hazard risk assessments. Tested and validated for a coastal area in the Northeastern Adriatic, the methodology combines global population density data with national census data for greater accuracy. Building census data is enhanced with exposure indicators, such as built area, replacement cost, height, and plan regularity, derived from digital building footprints. The final exposure layers are created at 100-meter and 30-meter resolutions and also at the census unit level. These high-resolution exposure models, integrated with tsunami hazard maps, allow improving the resolution of risk and damage assessments.

Finally, the possibility is explored to use the resulting risk scenarios for developing plausible storylines to enhance urban planning, preparedness, response, and mitigation efforts for coastal hazards in the Northeastern Adriatic.

This research is a contribution to the RETURN Extended Partnership (European Union Next-Generation EU—National Recovery and Resilience Plan—NRRP, Mission 4, Component 2, Investment 1.3—D.D. 1243 2/8/2022, PE0000005).