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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.

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 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.

PUBLICATION DOWNLOADS

• Report and appendix (117 p., 95 MB PDF), including an appendix of 45 tabloid-page-size 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
• Report only (72 p., 8.3 MB PDF)
• Appendix community profile sheets only (45 p., 87 MB PDF)
• Spreadsheet only (Excel spreadsheet, 750 KB) - contains all the data that are the basis for this report’s tables and figures
• Publication bundle (report, appendix, spreadsheet; 179 MB .zip file)
  
  

EXECUTIVE SUMMARY

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.

• The total permanent resident population present on the Lincoln County coastline within a tsunami zone ranges from ~4,220 (M1) to ~11,470 (XXL1). If the temporary population is included, the local population could increase to ~16,700 (M1) to ~42,000 (XXL1) assuming 100% occupancy;
• The fraction of the total permanent resident population within the three tsunami zones varies widely between communities.
  • The communities of Gleneden Beach, Bayshore, Yachats, and to a lesser extent Waldport each have relatively large numbers of people located in the XXL1 tsunami zone; respectively 75%, 74%, 77%, and 53%;
  • Within the L1 zone, Yachats has 60% of its population in the tsunami zone, Bayshore (58%), and Waldport (44%);
  • For the M1 scenario, communities with the largest number of people in the tsunami zone include Bayshore (44%), Waldport (37%), and Yachats (27%);
  • The communities of Newport, Depoe Bay, and especially Otter Rock have relatively few people in the various tsunami zones due to all three communities being largely perched on marine terraces; and,
  • These findings reflect contrasting patterns in the general shape and elevation of the Lincoln County coastline, whether it is open coast versus up an estuary; tsunami travel; dispersion (loss of energy) and inundation extents between the communities; and the distribution of permanent residents within the communities;
    
    
• Beachside State Recreation Area and Beverly Beach State Park are mostly (>88%) located in the M1 tsunami zone, and 100% within the L1 and XXL1 tsunami zones; South Beach State Park and Tillicum campground are also 100% within the L1 and XXL1 tsunami zones;
• All major Lincoln County coastal communities can experience significant influxes of visitors, well exceeding their local resident populations. Of note, the community of Gleneden Beach can swell by ~760% to 600% (M1 to XXL1), Lincoln City by ~400% (M1 to XXL1), Yachats by ~660% to 420% (M1 to XXL1), and Newport by ~300% (M1 to XXL1). These results demonstrate the importance of these communities as major tourist destinations with potentially large numbers of visitors located in the tsunami zones. The popularity of these communities as centers of tourism presents challenges associated with preparing such a large transient population for a CSZ earthquake and tsunami;
• Analyses of Lincoln County population demographics indicate that the countywide resident population of ≥65 years of age is ~29-30% of the total population for all three tsunami zones; this reflects about 1,280, 1,930, and 3,620 residents in the M1, L1, and XXL1 zones who are ≥65 years of age. Nevertheless, two communities have significantly more people ≥65 years of age: Gleneden Beach (52%), followed by Lincoln Beach (~40%); Seal Rock has 45% of people ≥65 in the L1 and XXL1 tsunami zones. Variations in demographics will likely impact ability to evacuate from the tsunami zone;
• The number of buildings located in a tsunami zone are greatest in Lincoln City, Gleneden Beach, Newport, and to a lesser degree Waldport. Nevertheless, the largest number of buildings across the entire county falls within the "other" category (~3,570). The bulk of this latter group reflect residential buildings established along the open coast outside of community boundaries, as well as along the shores of each of the estuaries. Exposure to the tsunami hazard is highest in Waldport and at Bayshore. This is because both communities are significantly exposed to all three tsunami inundation scenarios;
• Building damage caused by earthquake shaking is estimated to range from $621 million in Newport to a low of tens of thousands in the various campgrounds. The large losses estimated for Newport can be attributed to the effects of liquefaction (and lateral spreading) along the Newport bayfront and building engineering. Earthquake damage losses in Lincoln City are also substantial and are estimated to reach $396 million. Countywide damage losses caused by the earthquake alone are expected to exceed $2.1 billion;
• Incorporating damage caused by the tsunami results in destruction levels for an M1 event that range from ~20% (Lincoln Beach) to ~75% damage at Depoe Bay and 91% damage in Waldport; for an XXL1 event our analyses indicate >70% destruction in most communities, including Lincoln City, Gleneden Beach, Newport, Seal Rock, Bayshore, Waldport, and Yachats; complete destruction will occur at all four campgrounds. These findings can be attributed to the powerful hydraulic forces associated with the tsunami and the prevalence of light-frame construction material (i.e., wood frame) on the Oregon coast;
• Combined earthquake and tsunami damage for each tsunami zone indicates losses that range from ~$2.4 billion for an M1 size event, $2.8 billion for an L1 size event, and $3.5 billion for an XXL1 size event. These estimates reflect community-wide losses associated with the earthquake, combined with destruction caused by the tsunami. Note that these estimates exclude building content losses, such that the numbers may be viewed as minimal estimates;
• The destruction of buildings in coastal Lincoln county is expected to generate ~239,000 tons (M1) to ~705,000 tons (XXL1) of debris. This equates to ~23,900 dump trucks for M1 to as much as 70,500 dump trucks for an XXL1 event (assuming dump truck capacity of ~10 yd3). These estimates are almost certainly on the low end, as they do not include debris associated with content from buildings (personal items, business equipment, etc.), road rip-ups, vehicles, and vegetation;
• Modeled tsunami casualties (injuries and fatalities) vary widely between communities. This is due to many factors, but most important is the relative distance to high ground.
  • For the M1 scenario, estimated fatalities are confined mainly to the communities of Lincoln City (~80 resident/110 visitor), and Gleneden Beach (~25 resident/180 visitor) with few fatalities in the remaining communities. Low casualties associated with the M1 scenario in the majority of the communities is indicative of the fact that high ground is located close to the population centers, allowing for quick access to high ground, or the tsunami simply does not reach them;
• For the maximum-considered XXL1 tsunami scenario, the number of fatalities increases and ranges from very few (e.g., Lincoln Beach, Depoe Bay, Otter Rock, Siletz, Toledo, Seal Rock and Yachats) to ~620 at South Beach State Park in Newport, followed by Gleneden Beach (~480), Bayshore (~450), and Beverly Beach State Park (~390). Overall, the bulk of the fatalities (79%) are likely to be from the temporary visitor population;
• High casualties associated with the temporary visitor population is predicated on the assumption that these facilities are at 100% occupancy.
• The large number of potential fatalities at South Beach State Park and Gleneden Beach is entirely due to the significant travel distances required to reach high ground.
• These results demonstrate a need to evaluate alternative forms of high ground (e.g., vertical evacuation structures), and/or retrofitting bridges to withstand the earthquake shaking, thereby allowing for faster evacuation;
• Following the effects of the earthquake and accompanying tsunami, communities can expect to have to deal with many hundreds to potentially thousands of displaced people requiring immediate short-term shelter and care (~days to a few weeks), after which many people are likely to be evacuated from the coast. Hazus modeling indicates that the numbers of displaced increase significantly as one progresses from M1 (~16,260) to XXL1 (~38,580). We expect these challenges to be especially difficult in the following communities: Lincoln City, Newport, Gleneden Beach and Yachats. Furthermore, an estimated 7,770 people outside of UGB and community boundaries will require shelter and care; and
• Compared with fatalities, injuries from the earthquake and XXL1 tsunami were found to be relatively low. Overall, our combined earthquake and tsunami Hazus modeling indicates ~350 critically injured (Levels 2 and 3 in Table 2-2) for the M1 scenario, ~400 for L1, and ~530 for XXL1 in Lincoln County.

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.