Seismic vulnerability assessment of victoria, british columbia, canada: impact of long duration subduction zone ground motion

The City of Victoria, British Columbia, one of the oldest cities in Western Canada, has a current population of 80,000 people in just 19.5 km. The City of Victoria is located on the southern tip of Vancouver Island off Canada’s Pacific coast which happens to be in the Cascadia Subduction earthquake zone. Major subduction megathrust events and smaller, more frequent earthquakes can occur in the Cascadia Subduction zone, both of which pose a constant threat to the infrastructure and population of the city. The combination of a large, dense urban population, an aging building stock, and its location put Victoria at a high seismic risk. Accordingly, in 2017, the authors performed a seismic assessment for the City of Victoria in order to identify the city’s most atrisk buildings and to facilitate the development of a seismic resiliency plan. In this paper the results of the City of Victoria study, obtained using FEMA’s HAZUS framework, are compared to those obtained through the OpenQuake software. OpenQuake is a software package developed by Global Earthquake Model (GEM) for disaster risk reduction and combines probabilistic seismic hazard analysis with physical risk analysis to efficiently assess the seismic risk of a building or region. In this study, damage is calculated at a building-by-building level, based on a comprehensive database of building types, properties, and locations in Victoria. Results between the two frameworks are compared using individual building types and shaking levels, as well as general trends over large areas. Only damage probabilities are considered in this study; other loss metrics, such as cost or casualties are not considered, however, these measures are directly related to expected damage. HAZUS uses displacement-based structural fragility curves and obtains displacement estimates from static nonlinear analyses. The static nonlinear analysis procedure used in HAZUS can account for ground motion duration, as well as intensity. OpenQuake is a platform that allows the user to employ intensity-based fragility curves, which depend on the expected level of shaking. Part of this work was to compare the results of the two methodologies under moderate and long duration motions and to compare the differences in how they can account for ground motion duration. For this, the current fragility curves developed by GEM for use in OpenQuake for Canadian structures were employed.