UBC Theses and Dissertations
Effect of subduction ground motions on regional seismic risk assessment in selected localities in British Columbia Abraham, Ann
In this thesis, the effect of subduction ground motions on Regional Seismic Risk Assessment (RSRA) in British Columbia (BC), is studied. The primary objective of this study is to measure the increase in RSRA results when explicitly accounting for risk from the subduction events within the RSRA. Separate crustal and subduction fragility and vulnerability functions are introduced in RSRA to estimate risk from different seismic sources in 10 selected localities in BC, with varying subduction hazard. The resulting collapse and loss exceedance curves, average annual collapse fraction, average annual loss and loss ratios are used to measure the effect of subduction ground motions on RSRA. Fragility and vulnerability functions are developed for predominant building typologies in BC (wood and concrete shear wall (C2)), for crustal and subduction events, using single-degree-of-freedom models that represent BC construction. New typologies are introduced to better classify BC wood buildings. Scenario risk analyses are done for Vancouver using these functions to determine the effect of the changes made, as compared to functions currently used to develop the first generation Canadian Seismic Risk Model (CanSRM1), before they are used to perform RSRA. Most BC building typologies are weaker than the corresponding typologies used to develop the CanSRM1, implying that damage and loss estimates are higher when using BC-specific functions. Long duration effects of the subduction ground motions influence the fragility and vulnerability functions of newer constructions more, due to their larger inherent ductility. Subfloors and cripple walls increase the loss and damage estimates in low-rise residential wood construction. Scenario loss analyses in Vancouver shows that largest individual asset losses are from C2, multi-family residential and commercial wood construction, while most of the total damage and loss comes from low-rise residential wood constructions. RSRAs demonstrate that as the relative contribution of subduction hazard to total seismic hazard increases, generally, the influence of subduction ground motions on regional risk becomes significant. Therefore, using crustal functions alone for RSRA in sites within mainland BC will provide a good estimate of seismic risk, while it will be severely underestimated in sites on the islands off the mainland coast of BC.
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