Probabilistic Seismic Loss Estimation for Vulnerable Water System Components in Kashan, Iran through Fragility Functions

Abstract

Water systems are indispensable for effective crisis management; however, they are highly vulnerable to the devastating impacts of earthquakes. This study assesses the seismic vulnerability of critical water system components in Kashan, Iran, including wells, storage tanks (ground supported and elevated), and pump stations, and provides quantitative loss estimates for two earthquake scenarios: Design Basis Earthquake and Maximum Considered Earthquake. Field surveys characterized the spatial distribution, capacity, classification, and operational status of all components. Direct physical damages were quantified using empirical HAZUS fragility functions for most components and analytical functions for elevated tanks. The risk analysis incorporates crucial modification factors accounting for seismic design levels and observed asset degradation, integrating probabilistic ground motion fields to generate loss maps. Key findings reveal that elevated tanks are the most vulnerable, with their Compounded Damage Ratio rising from 0.421 under DBE to 0.680 under MCE, and complete damage probability reaching 32.1%. MCE events mainly cause severe structural damage, while DBE events typically result in slight to moderate damage. On ground tanks, pump stations, and wells have DRc values of 53.3%, 50.2%, and 29.2% under MCE, respectively. The significant vulnerability of unanchored components and aging infrastructure underscores the urgent need for targeted mitigation measures, including seismic anchorage, retrofitting, or complete reconstruction where necessary. These recommendations offer actionable and practical guidance for enhancing the safety, reliability, and overall resilience of water systems in earthquake prone regions, contributing to improved disaster preparedness and response capabilities.