DOGAMI Open-File Report Series

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Open-File Report O-21-02, Earthquake and tsunami impact analysis for coastal Lincoln County, Oregon, by Jonathan C. Allan and Fletcher E. O’Brien; 117 p. report, including community-specific profiles for Lincoln City, Gleneden Beach, Lincoln Beach, Depoe Bay, Otter Rock, Beverly Beach State Park, Newport, South Beach State Park, Toledo, Seal Rock, Bayshore, Waldport, Beachside State Recreation Site, Tillicum Beach Campground, and Yachats; data tables spreadsheet.

This report evaluates a Cascadia subduction zone earthquake (Mw 9.0) and tsunami (M1, L1, and XXL1 scenarios) affecting coastal Lincoln County, Oregon, in order 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.



This report provides an evaluation of the potential impacts of a Cascadia earthquake and accompanying tsunami in coastal Lincoln County. The analyses presented here include an assessment of the numbers 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) inundation zones reflect earthquake and tsunami scenarios that are more likely to occur than XXL1 but are characterized with less slip on the subduction zone (critical for tsunami generation) and thus carry more risk because they are less conservative. L1 captures 95% of the uncertainty in tsunami modeling (there is a ~5% chance that the tsunami could exceed the L1 scenario), while the M1 scenario captures 78% of the uncertainty (there is a ~22% chance that the tsunami could exceed the M1 inundation zone).

A major focus of this study has been to provide improved evaluations of local 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 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 Lincoln County.

We used previously developed physical models of a CSZ earthquake and tsunami, "Beat the Wave" tsunami evacuation modeling, and the recently published FEMA Hazus Tsunami Model to develop standardized loss estimates for each community, including injuries, fatalities, and building damage. From the latter we estimated the amount of debris generated from the building damage. Our 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 vary widely throughout the calendar year. The tsunami injury and fatality modeling evaluates a nighttime (2 AM) evacuation scenario (maximizing visitor occupancy), quantifying impacts to permanent and temporary residents.

Although each community in coastal Lincoln County has unique circumstances and challenges, as supported by the results of this study, 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.