Impacts of simulated M9 Cascadia Subduction Zone motions on idealized systems

Earthquake Spectra
By: , and 



Ground motions have been simulated for a magnitude 9 (M9) Cascadia Subduction Zone earthquake, which will affect the Puget Lowland region, including cities underlain by the Seattle, Everett, and Tacoma sedimentary basins. The current national seismic maps do not account for the effects of these basins on the risk-targeted Maximum Considered Earthquake (MCER). The simulated motions for Seattle had large spectral accelerations (at a period of 2 s, 43% of simulated M9 motions exceeded the MCER), damaging spectral shapes (particularly at periods near 1 s), and long durations (5%–95% significant durations near 110 s). For periods of 1 s or longer, the resulting deformation demands and collapse likelihood for four sets of single-degree-of-freedom systems exceeded the corresponding values for motions consistent with the conditional mean spectra at the MCER intensity (MCER). The regional variation of damage was estimated by combining probabilistic characterizations of the seismic resistance of structures and of the effective spectral acceleration, Sa,eff, which accounts for the effects of spectral acceleration, spectral shape, and ground-motion duration. For high-strength, low-ductility systems located above deep basins (Z2.5 > 6 km), the likelihood of collapse during an M9 earthquake averaged 13% and 18% at 1.0 s and 2.0 s periods, respectively. For low-strength, high-ductility systems, the corresponding likelihoods of collapse averaged 18% and 7%.

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Publication type Article
Publication Subtype Journal Article
Title Impacts of simulated M9 Cascadia Subduction Zone motions on idealized systems
Series title Earthquake Spectra
DOI 10.1193/052418EQS123M
Volume 35
Issue 3
Year Published 2019
Language English
Publisher Earthquake Engineering Research Institute
Contributing office(s) Earthquake Science Center
Description 27 p.
First page 1261
Last page 1287
Country United States
State Washington
Other Geospatial Puget Lowland region
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