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Open-File Report O-22-06, Earthquake and tsunami impact analysis for coastal Lane, Douglas, and Coos Counties, Oregon, by Jonathan C. Allan and Fletcher E. O’Brien; 124 p. report, including data tables and community-specific profiles.

WHAT'S IN THIS REPORT?
This report evaluates a Cascadia Subduction Zone earthquake (MW 9.0) and tsunami (M1, L1, and XXL1 scenarios) affecting coastal Lane, Douglas, and Coos counties, Oregon, to understand the degree of potential destruction, including building losses, debris generated, fatalities and injuries, and estimated numbers of the displaced populations. The goal is to help coastal communities prepare for this inevitable disaster.

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EXECUTIVE SUMMARY

This report provides an evaluation of the potential impacts of a Cascadia earthquake and accompanying tsunami in coastal Lane, Douglas, and Coos counties. The analyses presented here include an assessment of the number of people, businesses, and critical facilities located in three Cascadia tsunami inundation zones (M1, L1, and XXL1). XXL1 represents the maximum-considered inundation scenario given our knowledge of the Cascadia Subduction Zone (CSZ). Large (L1) and Medium (M1) tsunami zones reflect smaller earthquake and tsunami scenarios that are more likely to occur than XXL1. L1 captures 95% of the uncertainty in tsunami modeling (there is a ~5% chance that the tsunami could exceed the L1 tsunami zone), whereas the M1 scenario captures 78% of the uncertainty (there is a ~22% chance that the tsunami could exceed the M1 tsunami zone).

A major focus of this study is to provide improved estimates of local population demographics in each community to better understand evacuation challenges that could affect different population groups, as well as socioeconomic impacts associated with a CSZ earthquake and 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 all three counties.

We used previously developed physical models of a CSZ earthquake and tsunami, “Beat the Wave” tsunami evacuation modeling, and the recently published Federal Emergency Management Agency (FEMA) Hazus Tsunami Model to develop standardized damage loss estimates for each community, as well as estimates of injuries, fatalities, and displaced population. From the building damage losses, we estimated the amount of debris generated. Our population model improves upon previous studies by providing spatially detailed estimates of permanent and temporary populations — the latter quantifying numbers of visitors, which vary widely throughout the calendar year. The tsunami injury and fatality modeling evaluates a nighttime (2 AM) evacuation scenario, which assumes people are in their homes/hotels/campgrounds at the time of the event (as opposed to on the beach or walking around town). We also maximize visitor occupancy by assuming all hotels/second homes/campgrounds are at capacity, to fully quantify potential impacts to permanent and temporary residents. Our major findings include the following:

The large loss estimates for Coos County can be attributed to the effects of liquefaction (and lateral spreading) that are particularly damaging to bayfront infrastructure. Earthquake damage losses in the communities of Coos Bay and North Bend are substantial and are estimated to reach ~$1.8 billion. Nevertheless, the largest earthquake losses fall within the “other” category (~$1.9 billion) in Coos County, which reflect those buildings located throughout unincorporated Coos County.

Although each community in coastal Lane, Douglas, and Coos counties has unique circumstances and challenges, our results unequivocally demonstrate that in every community, 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.