Natech Risk Assessment Based on the Istanbul Earthquake Scenario at Neighborhood Level

Natural hazards, particularly earthquakes, can trigger technological accidents in industrial facilities, known as Natech events, leading to cascading secondary hazards. This paper focuses on Istanbul, a densely populated megacity situated in a high seismic activity zone. Past devastating earthquakes in Türkiye, such as Kocaeli (1999) and Kahramanmaraş (2023), have demonstrated the potential for catastrophic Natech events. This study presents neighborhood-level assessment of potential Natech risks in Istanbul specifically under the scenario of the probable earthquake, analyzing the spatial intersection of structural vulnerability and hazardous industrial/economic activities. The methodology integrates seismic structural damage estimations for 939 neighborhoods using geocoded data on over 500,000 businesses, based on workplace hazard classification. Three indices were introduced: ( i ) Damage Ratio Index to quantify seismic structural risk per neighborhood, ( ii ) Natech Concentration Index to assess the concentration of very hazardous business activities, and Integrated Natech Risk Assesment to combine structural risk and Natech-risk. The analysis identifies 8,785 businesses engaged in activities posing significant Natech risks, 4,843 chemical leakage and 3,942 fire/explosion. Findings indicated that neighborhoods classified with high structural vulnerability combined with a high concentration of hazardous activities represent critical hotspots, with approximately 17% of Istanbul's neighborhoods falling into the highest risk category, encompassing 31% of the city's population, 25% of the total businesses and 24% of the Natech-risky businesses. These findings highlight the critical necessity of integrating seismic hazard assessments with industrial risk management and targeted land-use planning to enhance urban resilience and mitigate potentially devastating consequences from Natech events triggered by the seismic events.