The chemical and process industries are increasingly concerned about NaTech events, technological disasters that occur after natural calamity such as earthquakes, floods or hurricanes. In this context, some of the most damaged equipment are the storage tanks, which are affected by high seismic vulnerability and containment of hazardous materials. In this regard, their failure often leads to the loss of containment (LOC) of the substances stored inside, triggering domino effects such as explosions, environmental pollution, operational disruption, and business interruption.

A review of past seismic events reveals that some of the most common damage modes affecting unanchored tanks are elephant foot buckling, uplifting, and sliding. Particular attention is given to the latter, due to the notable lack of effort dedicated to understanding and modelling this specific failure mechanism, which is strongly associated with the relative displacement between the equipment and the ground.  Based On these premises, this study proposes a fragility analysis focused on LOC scenarios triggered by seismic action specifically associated with the sliding mechanism of unanchored storage tanks. A simplified probabilistic approach is adopted, where the engineering demand parameter (EDP) is the relative displacement of the tank with respect to the ground, which is then correlated to different levels of liquid release. Fragility curves are developed in terms of the probability of leakage as a function of seismic intensity measure, such as the Peak Ground Acceleration (PGA). This methodology provides a practical tool for quantifying the seismic risk of sliding-induced LOC events, supporting their integration into Quantitative Risk Assessment (QRA) frameworks.