Seismological ground-motion models for generic hard-rock site condition in Western Canada

We develop ground-motion models (GMMs) to characterize the Fourier amplitude spectrum (FAS) for earthquakes in British Columbia (B.C.), Canada. GMMs developed for FAS are useful for understanding the underlying seismological parameters and can be transformed into GMMs for response spectral values for other applications (e.g., probabilistic seismic hazard analysis [PSHA]). The GMMs are calibrated using a compiled FAS database, referenced to a B.C. generic hard-rock site condition (shear-wave velocity approximately 2285 m/s). The GMMs are developed separately for crustal, in-slab, transition, offshore, and Haida Gwaii events. The GMMs are calibrated using data mostly from M 2.5 to 5.5 earthquakes recorded at rupture distances of approximately 50 to 500 km. Outside this range, the models are constrained by a seismological model supplemented with sparse observational data. The amplitude decay rate for crustal earthquakes in B.C. is very similar to that given by the empirical model of Bayless and Abrahamson (2018; hereafter, BA18), developed from California data on soil sites. However, we observe magnitude- and frequency-dependent differences between the models for ground-motion amplitude levels. We attribute these to (1) the different reference-site conditions of the models, with the B.C. GMMs being referenced to hard rock, and (2) steeper magnitude scaling at small-to-moderate magnitudes for events in B.C. in comparison to the BA18 model.