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Challenges in Assessing Site-Specific Seismic Hazards in Cascadia

Description: 

In site-specific seismic hazard analyses, a more rigorous approach to addressing epistemic uncertainties in seismic source and ground motion characterization needs to be taken than for large-scale assessments such as the USGS National Seismic Hazard Maps. Although originally developed for the nuclear industry, the principles behind Senior Seismic Hazard Analysis Committee (SSHAC) guidance have been applied to a wider range of critical and important infrastructures. This has been the case particularly in the Pacific Northwest, where it has been applied to numerous dams. As emphasized in the SSHAC guidance, analyses need to address the “center, body, and range of technically-defensible interpretations”. Despite the incredible advances that have been made in our understanding of earthquake hazards in the Pacific Northwest, many significant challenges in site-specific seismic hazard analyses remain. Although the Cascadia megathrust controls the hazard for much of the Pacific Northwest, particularly at long periods, crustal faults can still dominate the probabilistic hazard if the site is sufficiently close. Given that there remain significant uncertainties in the characterization of Quaternary faults in the Pacific Northwest, and the fact that Quaternary faults continue to be identified and characterized, site-specific seismic hazard analyses need to incorporate these rapid changes in our state of knowledge. Three case histories will be presented where recently recognized Quaternary faults - the Spencer Canyon fault (Sherrod et al., 2021), Mt. Hood fault zone (Madin et al., 2021), and Canyon River-Saddle Mountain fault zone (Bennett et al., 2017) - have resulted in the need to re-evaluate several high hazard dams due to their proximity to these faults and local communities. Hence, these faults and their significant associated epistemic uncertainties need to be characterized for seismic hazard analyses. None of these faults are included in the 2018 National Seismic Hazard Maps.

Session: Constraining Seismic Hazard in the Cascadia Subduction Zone

Type: Oral

Date: 4/20/2023

Presentation Time: 05:30 PM (local time)

Presenting Author: Ivan G. Wong

Student Presenter: No

Invited Presentation: 

Authors