The Effect of Forearc Mantle Serpentinization on Ground Motions from Megathrust and Intraslab Events in the Cascadia Subduction Zone

There is now growing evidence that large-magnitude earthquakes have occurred and could occur again along the Cascadia subduction zone located west of Vancouver Island, Bristish Columbia. Numerical simulations indicate that these earthquakes would produce long-duration ground motions and would thus be capable of inducing a large number of reversals of inelastic deformations in engineered structures. Efforts have now been undertaken to account for this damage potential in building codes. In this paper, inelastic design spectra are developed for Cascadia subduction earthquakes for four sites in British Columbia. These spectra are compared with elastic design spectra that have been developed recently for the same sites based on empirical attenuation relationships for Cascadia events. The approach used to develop the inelastic spectra aims at providing the same level of protection against structural failure for both subduction events and crustal or subcrustal earthquakes. Force modification factors are first determined for structures exhibiting various failure modes and ductility levels when subjected to representative crustal and subcrustal earthquake ground motions. Thereafter, design spectra are developed for the same structures to prevent structural collapse under simulated Cascadia subduction ground motions. The study reveals that the elastic spectra do not reflect adequately the damage potential of Cascadia earthquakes. These elastic spectra generally are unconservative for Tofino and Victoria. For Vancouver and Prince George, the elastic spectra overestimate the demand, especially for short-period structures.Key words: collapse, crustal earthquakes, damage index, design spectrum, ductility, duration, ground motion, subduction zone.

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Estimation of strong ground motions from hypothetical earthquakes on the Cascadia subduction zone, Pacific Northwest

Open-File Report ◽

10.3133/ofr86328 ◽

1986 ◽

Cited By ~ 2

Author(s):

T.H. Heaton ◽

S.H. Hartzell

Keyword(s):

Subduction Zone ◽

Pacific Northwest ◽

Ground Motions ◽

Cascadia Subduction Zone ◽

Strong Ground Motions ◽

Strong Ground

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Modeling the Effects of Source and Path Heterogeneity on Ground Motions of Great Earthquakes on the Cascadia Subduction Zone Using 3D Simulations

Bulletin of the Seismological Society of America ◽

10.1785/0120130181 ◽

2014 ◽

Vol 104 (3) ◽

pp. 1430-1446 ◽

Cited By ~ 5

Author(s):

A. A. Delorey ◽

A. D. Frankel ◽

P. Liu ◽

W. J. Stephenson

Keyword(s):

Subduction Zone ◽

Ground Motions ◽

Cascadia Subduction Zone ◽

3D Simulations ◽

Great Earthquakes

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Impacts of Simulated M9 Cascadia Subduction Zone Motions on Idealized Systems

Earthquake Spectra ◽

10.1193/052418eqs123m ◽

2019 ◽

Vol 35 (3) ◽

pp. 1261-1287 ◽

Cited By ~ 9

Author(s):

Nasser A. Marafi ◽

Marc O. Eberhard ◽

Jeffrey W. Berman ◽

Erin A. Wirth ◽

Arthur D. Frankel

Keyword(s):

Subduction Zone ◽

Ground Motions ◽

High Strength ◽

Sedimentary Basins ◽

Cascadia Subduction Zone ◽

Seismic Resistance ◽

Spectral Acceleration ◽

Single Degree Of Freedom ◽

Conditional Mean ◽

Subduction Zone Earthquake

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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