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Open-File Report O-20-03, Analysis of earthquake and tsunami impacts for people and structures inside the tsunami zone for five Oregon coastal communities: Gearhart, Rockaway Beach, Lincoln City, Newport, and Port Orford,
by John M. Bauer, Jonathan C. Allan, Laura L. S. Gabel, Fletcher E. O’Brien, and Jed T. Roberts; 185 p. report, 1 Excel file.

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What's in This Report?

This report evaluates the effects of a great (Mw 9.0) earthquake and tsunami on the Cascadia Subduction Zone for five Oregon coast communities, in order to understand the degree of potential destruction, including: potential building losses, debris generated, fatalities and injuries, and estimated numbers of the displaced populations. The goal is to help coastal communities prepare.

Executive Summary:

This report provides an evaluation of the potential impacts of a Cascadia earthquake and tsunami on five Oregon coastal communities — Gearhart, Rockaway Beach, Lincoln City, Newport, and Port Orford. Each community was selected based on discussions with the Oregon Department of Land Conservation and Development (DLCD) and the respective communities, which were interested to receive tsunami evacuation modeling and Hazus results in order to guide community-based tsunami planning efforts. The analyses include an assessment of the numbers of people, businesses, and critical facilities located in the maximum-considered XXL1 Cascadia tsunami inundation zone; in a few areas we evaluated the L1 tsunami scenario. Importantly, this report evaluates population demographics in each community in order to better understand potential evacuation challenges that could affect different population groups, as well as socioeconomic impacts associated with a Cascadia subduction zone (CSZ) earthquake and resultant tsunami. The results and analyses presented here reflect a comprehensive effort to document the likely effects the next great earthquake and tsunami will have on coastal communities in the state of Oregon.

We used previously developed physical models of a CSZ earthquake and resultant tsunami, previous and concurrent “Beat the Wave” tsunami evacuation modeling, and the recently published FEMA Hazus Tsunami Model to develop standardized loss estimates for each community: injuries, fatalities, and building damage. From the latter we estimated the amount of debris generated from the building damage. To more efficiently quantify and visualize the tsunami evacuation challenges and options for mitigation, we developed an independent tool (Excel spreadsheet) that implements the FEMA Hazus Tsunami casualty model. The tool is included with this report.

Our study is the first structure-level analysis of tsunami impacts in Oregon using the FEMA Hazus methods. Accordingly, much of this report is given to documenting our methods, including the development of population models. Our devised population model improves upon previous studies by providing spatially detailed estimates of permanent and temporary populations — the latter quantifying numbers of visitors and second-home owners, which varies widely throughout the calendar year. The tsunami injury and fatality modeling evaluates a nighttime (2 AM) evacuation scenario, quantifying impacts to permanent and temporary residents. We analyzed two daytime (2 PM) evacuation scenarios, for two settings: a popular state park beach, and the efficacy of the tsunami vertical evacuation structure (TVES) at the Hatfield Marine Science Center in Newport. Results are summarized as follows:

For better adaptation into community planning and for communicating more directly with community members, this report contains detailed, individual community profiles. Each community profile is composed of estimates on numbers of people and buildings within the tsunami zone, injuries and fatalities from both the earthquake and tsunami, number of people who successfully escaped the tsunami in need of short-term shelter, and social characteristics of people in the tsunami zone that can better inform planning for tsunamis. Community profiles conclude with tailored recommendations for education, mitigation, response, and recovery options. Although each community in this report has unique circumstances and challenges, as supported by the results of this study, in all communities injuries and fatalities from a tsunami can be minimized if people evacuate on foot toward safety as soon as possible and travel as fast as possible.