Effects of the Georgia Sedimentary Basin on the Response of Modern Tall RC Shear-Wall Buildings to M9 Cascadia Subduction Zone Earthquakes

Abstract

Tall residential RC shear wall buildings (RCSW), which are predominant in Metro Vancouver, have the potential to experience large magnitude earthquakes generated by the Cascadia Subduction Zone (CSZ). Furthermore, the region lies above the Georgia sedimentary basin, which can amplify the intensity of ground motions at medium to long periods and the resulting damage in tall structures. This study provides insights into the effects of the Georgia sedimentary basin amplification on (1) spectral accelerations associated with magnitude 9 (M9) CSZ earthquakes, (2) resulting force- and deformation-controlled actions in modern tall RCSW buildings, and (3) ensuing earthquake-induced repair costs and times. To this end, we leveraged a suite of physics-based ground motion simulations of a range of M9 CSZ earthquake scenarios, which explicitly consider basin effects, and benchmarked these scenarios against a range of seismic hazard intensities, which neglects basin effects. While the M9 simulations have an estimated 500-year return period, at deep basin sites their spectra exceed the 2,475-year hazard in the 1–3 s period range. Nonlinear dynamic analysis results under probabilistic seismic hazard estimates result in negligible collapse risk. In contrast, collapse risk conditioned on the occurrence of the M9 motions results in probabilities as high as 15%. Additionally, seismic demands from the M9 simulations at deep basin sites result in earthquake-induced repair costs and times that exceed those associated with the 2,475-year hazard level.