Fourth-generation seismic hazard maps for the 2005 national building code of Canada

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The Geological Survey of Canada's new seismic hazard model for Canada will form the basis for the seismic design provisions of the 2005 National Building Code of Canada (NBCC). As such it represents Canada's fourth generation of seismic hazard maps (previous ones were in 1953, 1970, and 1985). The Cornell-McGuire method is used with two complete earthquake source models - historical and regional/geological - to represent the uncertainty in where (and why) earthquakes will happen in the future. Ground motions for a deterministic Cascadia subduction earthquake are computed for southwestern Canada, and probabilistic seismic hazard for the nearly aseismic central part of Canada is assessed based on a global model. A 'robust' method is used to combine the probabilistic hazard estimates (at a probability of 2%/50 years or 0.000404 p.a.) from the four source models: the mapped value is the largest of the values. Products will include seismic hazard maps, tabulated values, uniform hazard spectra (UHS), plots of deaggregated hazard and documentation. For the seismic provisions of the 2005 National Building Code of Canada the median ground motion on firm soil sites for spectral acceleration at periods of 0.2, 0.5, 1.0 and 2.0 seconds and peak acceleration will be used. The four spectral parameters will allow the construction of approximate UHS for each locality, and hence improve earthquake-resistant design.