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Addressing Challenges in Regional Seismic Risk Assessments in British Columbia: M9 Cascadia Subduction Zone Earthquakes, Deep Sedimentary Basin Amplification and Non-Ductile Reinforced Concrete Shear Wall Buildings

Description: 

This presentation aims to address some of the challenges associated with conducting regional seismic risk assessments in Southwest British Columbia: (1) the lack of ground motion recordings of M9 Cascadia Subduction Zone (CSZ) earthquakes; (2) the presence of the Georgia sedimentary basin, which can amplify ground motion shaking, particularly in the medium-to-long period range, and is not accounted for in current building codes; and (3) the large concentration of tall nonductile reinforced concrete shear wall (RCSW) buildings constructed prior to the 1980s, which are of special concern because they predate modern seismic codes and are clustered in densely populated areas, raising concerns about the risks to life, property, and recovery from large earthquakes.

Physics-based ground motion simulations of 30 plausible M9 CSZ earthquakes, which explicitly consider basin effects, are benchmarked against existing ground motion models to develop site-specific and period-dependent basin amplification factors. A framework to incorporate these factors into uniform hazard spectra (UHS) calculations, to enable the inclusion of these effects in the design and assessment of buildings, is proposed.

The collapse risk of older tall RCSW buildings is assessed via nonlinear response history analysis of 3D numerical models of 25 representative archetypes generated by means of a predictive model that leverages a detailed inventory of such buildings. Collapse risk is quantified using hazard estimates of Canada’s national seismic hazard model, which neglects basin effects, and a “hybrid” hazard model that considers basin amplification. A scenario-based seismic performance assessment, under the M9 CSZ earthquakes previously introduced, to quantify economic losses and recovery times in these buildings, is also carried out.

The results aim to inform seismic policy development in British Columbia, in particular, ongoing efforts by the City of Vancouver to address seismic risks in its aging building infrastructure.

Session: Regional-Scale Hazard, Risk and Loss Assessments - II

Type: Oral

Date: 5/2/2024

Presentation Time: 02:45 PM (local time)

Presenting Author: Carlos

Student Presenter: No

Invited Presentation: Yes

Authors