Spectral acceleration basin amplification factors for interface Cascadia Subduction Zone earthquakes in Canada’s 2020 national seismic hazard model

Canada’s 2020 national seismic hazard model (CSHM 2020) provides estimates for interface Cascadia Subduction Zone (CSZ) earthquakes in southwestern Canada using four ground motion models (GMMs) with equal weights. Two out of the GMMs were derived data primarily from subduction Japan so their use CSHM includes a “Japan-to-Cascadia” factor to account local site conditions. Despite this regional factor, do not explicitly consider amplification effects Georgia sedimentary basin below Metro Vancouver. This study benchmarks shaking suite 30 physics-based simulations M9 CSZ earthquakes, which periods exceeding 1 s, corresponding 2020. Using comparison, proposes site-specific and period-dependent factors range sites located within basin. The average at deepest location reach values as high 2.24 6.29 2 s period respect basin-edge outside-basin reference locations, respectively. We evaluate proposed by comparing them against long-period amplifications observed empirical strong recordings 2001 M6.8 Nisqually earthquake. A framework incorporate calculation uniform spectra (UHS) is also proposed. modified UHS ordinates that are 58% 271% higher, period, than non-basin when calculated