Sensitivity Analysis of Fire-Following Earthquake Models

Abstract eng:
Fire-Following Earthquake (FFEQ) is a secondary disaster to earthquakes which can cause significant losses and, in some cases, may comprise a large portion of the total loss by developing into large conflagrations (e.g., 1906 San Francisco earthquake). In order to estimate fire losses, conditioned on the occurrence of an earthquake, a probabilistic conflagration model is required. Such a model predicts the burnt areas based on the three-phases of the FFEQ process: fire ignition, fire spread and fire suppression. The first phase, fire ignition, estimates the number of fires that can occur in the aftermath of an earthquake and is a function of the intensity and time of occurrence of the earthquake, the square footage of the buildings in the impacted region, and the mix of construction and occupancy classes. The second phase, fire spread, estimates the propagation of each of the initial fires within a building, to other buildings, and among city blocks. This process is in general a function of building construction material and footprint size, separation between buildings and city blocks, wind speed and other modeling parameters. Lastly, fire suppression attempts at modeling all the activities associated with extinguishing a fire, beginning with its discovery, reporting, arrival of fire units, and fire control. This study adopts a simulation-based framework by dividing the area of interest into grid cells and carrying out the time-stepping analysis of all three phases of the fire process into a conflagration model. There is, however, a significant uncertainty in the parameters required for performing the simulation. Hence, each of these parameters is characterized by a proper probability distribution function and a Monte Carlo simulation approach is then used to characterize the probability distribution of the output variables of interest such as the number of initial fire ignitions and final burnt area. This study presents the sensitivity of the fire loss results for 24 metropolitan areas to different ignition and conflagration model parameters. Results of the sensitivity analysis show that FFEQ results are more sensitive to the density of fire stations, builtupness of the area, average PGA of earthquake footprint, wind speed and percentage of wood construction compared to the other input parameters.

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