Numerical modelling of coastal inundation from Cascadia Subduction Zone tsunamis and implications for coastal communities on western Vancouver Island, Canada

In the present study, numerical simulations were conducted to estimate the spatio-temporal characteristics of tsunami inundation for municipalities on Vancouver Island, Canada, as a result of various potential Cascadia Subduction Zone earthquake deterministic scenarios. By varying the earthquake magnitude and associated slip distance, the influence of these parameters on the tsunami wave propagation, inundation, and the possible damage on infrastructure and buildings was investigated. A numerical tsunami inundation model based on nonlinear shallow water equations was constructed using publically available bathymetric and topographic data and applied to three study areas: the City of Port Alberni, the District of Ucluelet, and the District of Tofino. The numerical results obtained in this study show that the maximum tsunami inundation depth and spatial extent of inundation are sensitive to the earthquake magnitude, whereas the tsunami arrival time is not. For the worst-case earthquake scenario investigated (MW 9.3), all of the three study areas were extensively inundated. Results of tsunami wave amplitude and overland inundation depth, flow velocity, hydrodynamic force, and depth–velocity product are analysed in detail to assess the impacts of the tsunami on inland buildings. The potential damage was estimated with previously proposed fragility curves for wood, reinforced concrete, and steel frame buildings. In conjunction with a site reconnaissance visit by the authors for better understanding the general characteristics of these areas, model results suggest that significant damage to buildings would occur, especially to wooden constructions, with considerable risk of loss of human life.