Effects of simulated magnitude 9 earthquake motions on structures in the Pacific Northwest

The Cascadia Subduction Zone (CSZ) produces long-duration, large-magnitude earthquakes that could severely affect structures in the Pacific Northwest (PNW). The impact of synthetic M9.0 CSZ earthquakes on buildings in the Pacific Northwest is studied using eight reinforced concrete wall archetypes that range from 4 to 40 stories. These archetypes were subjected to an ensemble of simulated ground-motions from 30 M9 earthquakes for a location in Seattle that overlies a ~8km deep sedimentary basin and an equivalent location outside the basin. Long-period (1-7s) ground motions are strongly amplified in the CSZ synthetics within the Seattle Basin, leading to a 6-fold increase in deformation demand (inter-story drift) compared to an equivalent out of basin site. The variability in demand was also found to be much larger inside the basin than outside the basin.