Istanbul, a megacity of over 16 million people, is located adjacent to the North Anatolian Fault Zone, a major strike-slip fault system and one of the most seismically active tectonic boundaries in the world. While much of the city’s disaster planning focuses on its urban core, peripheral districts such as Şile, situated along the Black Sea coast, have gained increasing strategic relevance. Perceived as a low-risk, low-density zone, Şile has been designated as a primary post-disaster assembly and sheltering area due to its open spaces and geographic separation. However, this role is complicated by its seasonal transformation, with the population swelling from 50,000 to over 2 million in summer months due to tourism. This paper presents findings from a scenario-based risk analysis workshop conducted in Şile in June 2025. The workshop employed participatory approach to evaluate the district’s disaster preparedness under varying hazard conditions. A worst-case scenario, a major earthquake (Mw > 7.0) occurring during peak tourist season, revealed critical vulnerabilities, including overwhelmed infrastructure, limited emergency capacity, and high flood risk. The results emphasize the importance of integrating seasonal population dynamics and multi-hazard interactions into Istanbul’s disaster risk reduction strategies. Moreover, the methodology developed through this study offers a transferable framework for assessing preparedness in other peri-urban areas with similar compound risk profiles and strategic emergency roles.