Spatiotemporal seismic hazard and risk assessment of M9.0 megathrust earthquake sequences of wood-frame houses in Victoria, British Columbia, Canada

Megathrust earthquake sequences, comprising mainshocks and triggered aftershocks along the subduction interface and in the overriding crust, can impact multiple buildings and infrastructure in a city. The time between the mainshocks and aftershocks usually is too short to retrofit the structures; therefore, moderate-size aftershocks can cause additional damage. To have a better understanding of the impact of aftershocks on city-wide seismic risk assessment, a new simulation framework of spatiotemporal seismic hazard and risk assessment of future M9.0 sequences in the Cascadia subduction zone is developed. The simulation framework consists of an Epidemic Type Aftershock Sequence (ETAS) model, ground-motion model, and state-dependent seismic fragility model. The spatiotemporal ETAS model is modified to characterise aftershocks of large and anisotropic M9.0 mainshock ruptures. To account for damage accumulation of wood-frame houses due to aftershocks in Victoria, British Columbia, Canada, state-dependent fragility curves are implemented. The new simulation framework can be used for quasi-real-time aftershock hazard and risk assessments and city-wide post-event risk management.