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

Abstract

<title>Abstract</title> <p> 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: ( <italic>i</italic> ) Damage Ratio Index to quantify seismic structural risk per neighborhood, ( <italic>ii</italic> ) 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. </p>