DOGAMI Open-File Report Series

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Open-File Report O-20-14, Earthquake and tsunami impact analysis for coastal Tillamook County, Oregon, by Jonathan C. Allan, Fletcher E. O’Brien, John M. Bauer, and Matthew C. Williams; 121 p. report, including community-specific profiles for Manzanita, Nehalem Bay State Park, Nehalem, Wheeler, Rockaway Beach, Barview, Garibaldi, Bay City, Tillamook, Cape Meares, Oceanside, Netarts, Cape Lookout Sate Park, Sand Lake Recreation Area, Tierra Del Mar, Pacific City, and Neskowin; data tables spreadsheet.

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 Tillamook 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.

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EXECUTIVE SUMMARY

This report provides an evaluation of the potential impacts of a Cascadia earthquake and accompanying tsunami in coastal Tillamook 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). Furthermore, our analyses evaluate 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 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 Tillamook 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 Tillamook 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.