Analytical Tsunami Fragility Modelling for Building Classes Using Tsunami Time-History Simulations

Tsunami fragility curves for building classes are essential tools for portfolio risk assessment of tsunami-prone regions. However, existing fragility data comprises mainly empirical fragility curves, which reflect the vulnerability of local building classes based on observed damage data. While useful, these empirical curves have limited applicability in regions with no recorded tsunami events or insufficient damage data. This highlights the need to expand the database with analytical fragility curves, particularly for areas lacking empirical damage records. To fill this gap, this study proposes a comprehensive framework for developing analytical tsunami fragility curves for building classes in tsunami-prone regions. The framework integrates simulation of tsunami time-history scenarios with random selection of case study buildings from identified tsunami hotspots. Fragility curves are then derived using Modified Cloud Analysis (MCA), which employs logarithmic regression of structural response estimated from high-fidelity finite-element modelling of structural response (e.g., demand to capacity ratios for different damage levels) versus tsunami intensity (e.g., flow depth, momentum flux) for a set of tsunami time histories. To illustrate the framework, a case study is presented focusing on the low-rise residential reinforced concrete (RC) buildings along the east coast of Sicily, Italy, within the Plain of Catania. An extensive set of tsunami inundation scenarios was simulated for the Catania Plain, which includes tsunamis generated by earthquakes in the Mediterranean Sea with following features: i) near- and far-field earthquakes; ii) crustal and subduction earthquakes; and iii) earthquakes with moment magnitudes from 6.0 to 9.0. For each scenario, locations with the most significant flow depths, i.e. tsunami hotspots, were identified and one building was then selected from each tsunami hotspot for structural simulation under tsunami loading. Details of the selected building structures were generated via the simulated design tools provided by EUCENTRE, which does automatic identification of possible structural design, considering both the variations of structural configuration and material properties. Finally, the resulting fragility curves for RC buildings were derived using the MCA approach and hierarchical fragility modelling for a 5-tier damage scale based on EMS 98 definition and with relative confidence intervals, providing valuable information of building vulnerability in that region.