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USGS Tsunami Sources Powell Center Working Group on Tsunami Sources: Probabilistic Tsunami Hazard Assessment for the Cascadia Subduction Zone

Description: 

U.S. states and territories adjacent to the Pacific Ocean are subject to tsunami generated from the surrounding subduction zones. Probabilistic Tsunami Hazard Analysis (PTHA) is adopted as a process that helps society mitigate impacts along coastlines through improved products for decision making for evacuation planning and through informed engineering approaches for structural design in tsunami hazard areas. The PTHA process includes four basic steps: source characterization, logic tree development (e.g., source rate distribution), tsunami modeling, and tsunami hazard mapping.

The U.S. Geological Survey (USGS) John Wesley Powell Center’s working group on tsunami sources hosted a week-long meeting in May 2022 that focused on the characterization of the Cascadia subduction zone (CSZ), a primary disaggregated contributor for tsunami hazard along the west coast of the continental U.S. Meeting participants included subject matter experts from academia, private industry, and state and national government agencies. A major goal for the meeting was to draft a logic tree for CSZ tsunami sources based solely on peer reviewed literature.

We present a summary of the meeting that included presentations on how subduction zones slip and deform during earthquakes (rupture dynamics), the structural evidences that may reveal how the CSZ may coseismically deform (informed by estimates of variation in megathrust seismogenic locking, the potential for splay faulting, etc.), and the spatiotemporal variation of prehistoric earthquakes along the margin. Together these informed the design of a draft logic tree with branches representing the range of possibilities, from known to unknown instances of CSZ tsunamigenesis. Where there was not consensus, participants assigned branch weights via an anonymous online poll. Parts of the logic tree are aligned with the USGS National Seismic Hazard Model. Future work will include developing guidance for probabilistic tsunami hazard and risk assessments.

Session: Constraining Seismic Hazard in the Cascadia Subduction Zone

Type: Oral

Date: 4/20/2023

Presentation Time: 04:45 PM (local time)

Presenting Author: Jason R. Patton

Student Presenter: No

Invited Presentation: 

Authors