Sensitivity Analysis of FEMAHAZUSEarthquake Model: Case Study from King County, Washington

Hazards U.S. Multi-Hazard Maintenance Release 4 (HAZUS-MH MR4) is damage- and loss-estimation software developed by FEMA to estimate potential losses from natural disasters. Federal, state, regional, and local governments use the HAZUS earthquake model for earthquake risk mitigation, preparedness, response, and recovery planning. This paper examines earthquake model input parameters for earthquake source, including epicenter location, hypocentral depth, magnitude, and fault-plane dimensions, orientation, and dip, as well as geologic site conditions, to show how modifying the user-supplied settings affect ground-motion analysis, seismic risk assessment, and earthquake loss estimates. HAZUS calculates ground motion and resulting ground failure to estimate direct physical damage for general building stock, essential facilities, and lifelines, including transportation systems and utility systems. Earthquake losses in HAZUS are expressed in building-damage, economic, and social terms; this paper focuses on monetary building damages, which are predicted by building type and occupancy classification (building use). This analysis centers on both shallow crustal and deep intraslab events that affect King County, Washington, in the Pacific Northwest; however, the methods and results of this paper may help to assess the accuracy of HAZUS estimates more generally for seismically active regions. The results show that the estimated economic building damage varies by a factor of 14, on average, when using more accurate user-supplied source and site parameters rather than default values. In extreme cases, the estimated economic building damage varies by a factor of more than 500. The results also show that HAZUS scenarios for King County are more sensitive to changes in source parameters than site conditions. The considerable variability in the estimated economic building damage can have a dramatic impact on both hazard-mitigation plans and initial postevent assessments used by emergency managers.