UBC Faculty Research and Publications

A Framework to Incorporate Basin Amplification Factors in the Calculation of Uniform Hazard Spectra for Canada Kakoty, Preetish; Molina Hutt, Carlos; Ghofrani, H.; Molnar, S.


Canada’s 2020 national seismic hazard model (CSHM 2020) provides hazard estimates for interface Cascadia Subduction Zone (CSZ) earthquakes in southwestern Canada using four ground motion models (GMMs) with equal weights. Two out of the four GMMs were derived from data primarily from subduction earthquakes in Japan so their use in Canada’s national seismic hazard model includes a “Japan-to-Cascadia” factor to account for local site conditions. Despite this regional factor, the GMMs do not explicitly consider basin amplification effects from the Georgia sedimentary basin beneath Metro Vancouver. This study benchmarks ground motion shaking from a suite of 30 physics-based simulations of M9 CSZ earthquake scenarios, which explicitly account for the basin effects by means of a 3D velocity model, to corresponding estimates from CSHM 2020. Using this comparison, this study proposes site-specific and period-dependent basin amplification factors for a range of sites located within the Georgia sedimentary basin. A framework to incorporate the basin amplification factors in uniform hazard spectra (UHS) is also proposed. The modified UHS estimates are approximately 13% and 23% higher in the 1-5s period range, with respect to reference sites located in the basin-edge and outside of the basin, respectively, when compared to non-basin UHS.

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