A Localized Probabilistic Risk Framework Integrating Seismic Damage-Induced Fire Degradation for Dense Informal Historic Districts Under Earthquake and Post-Earthquake Fire

Earthquake and post-earthquake fire cascading hazards impose disproportionate risks on dense informal historic districts across South Asia. Conventional multi-hazard evaluation methodologies fail to accommodate non-engineered mixed-use constructions and ultra-compact unplanned urban morphologies prevalent in regional megacities, owing to two inherent limitations: decoupled quantification of seismic deterioration and structural fire performance, and fire spread parameters calibrated for regular Western urban grids rather than narrow, congested historic streetscapes. This work develops a localized probabilistic risk framework integrating seismic damage-induced fire degradation, and advances two dedicated methodological improvements to address the identified research voids. Seismic damage-dependent fire resistance reduction coefficients are embedded within cellular automaton iterations to dynamically modulate effective burnout durations of seismically compromised buildings; urban morphological correction factors are further incorporated to refine inter-building fire propagation probabilities tailored to compact informal settlements. Field inventories, nonlinear pushover finite element analysis, morphology-modified fire simulation and large-sample Monte Carlo stochastic sampling are integrated to execute full-process quantitative risk assessment, with model calibration and validation conducted against field survey data and the 2019 Chawkbazar chemical fire archive in Dhaka. The empirically validated framework (note: the validation primarily applies to the fire spread submodel; the coupled seismic–fire mechanism is supported by numerical simulation rather than empirical observation) delivers transferable quantitative benchmarks for multi-hazard governance of analogous South Asian historic agglomerations, and provides actionable technical evidence to inform targeted urban renewal schemes and the formulation of earthquake-fire coupled design specifications within Bangladesh’s national building regulatory codes.