An alternative approach to site factors for NBCC 2015.

The site amplification factors in the 2015 edition of the National Building Code of Canada (NBCC 2015) for South Western British Columbia (SWBC) were developed using only the single site term associated with the ground motion prediction equation (GMPE) for crustal sources. The seismic hazard in SWBC is derived from three source types; crustal, subduction intraplate, and subduction interface sources. Therefore site factors based only on a crustal site term are approximate. This study was conducted to assess the degree of approximation. Alternative site amplification factors for Vancouver and Victoria, British Columbia were calculated using site specific look-up tables incorporating all the GMPEs associated with each seismic source type and their associated site terms. The alternative site factors are significantly greater than those given in NBCC 2015 for periods 0.3 s, 0.5 s, and 1.0 s. These results suggest that the process for calculating site amplification factors should be reassessed by the committee currently reviewing seismic hazard for NBCC 2020. [ABSTRACT FROM AUTHOR]