A report for the Oregon Health Authority provides a glimpse of the potential loss of life from a Cascadia Subduction Zone tsunami — an event whose precursor hundreds of thousands of Oregonians will rehearse for during an annual self-led drill Oct. 21.
According to the website for the Great Oregon Shakeout, held along with other Shakeout events around the world on the third Thursday of October, 520,000 in the state plan to participate. And so on 10/21, at 10:21 a.m., they will practice the “drop, cover, hold on” protective response to a quake. The event also encourages disaster preparedness, like having at least 72 hours’ worth of food and water, plus a flashlight, batteries, medicine and other supplies.
The greatest danger of a major earthquake in the Cascadia Subduction Zone, where the Juan de Fuca Plate slips under the North American Plate, will come as soon as 10 or 15 minutes after the shaking ends — the first of multiple waves in an inundating tsunami.
Casualties in the last big Cascadia quake, Jan. 26, 1700, are unknown, but most estimates of fatalities from the tsunami waves that followed a 8-9 magnitude tremor range in the hundreds in villages on the Oregon coast, at a time when the area was sparsely populated.
The Cascadia Tsunami Casualty Estimates Report, prepared for the Oregon Health Authority’s Health Preparedness Program in May, is meant as a disaster planning tool for hospitals and emergency departments, and it notes, “Estimates are not a prediction for an actual Cascadia earthquake event and the actual number of casualties will be different.” But it does give a rough idea of the scope of the immediate loss of life.
The report assumes a magnitude 9 earthquake at 2 a.m. during the summer. It’s not a worst-case scenario — the authors also assume “that all persons are quick to evacuate by foot using the most optimal tsunami evacuation route.”
Most people who are unable to escape will be killed rather than just injured, the authors’ research found, with total loss of life on the Oregon coast at more than 18,000, and 819 injured. Fatalities will be highest in the north due to “the extensive low-lying coastal plains on the north coast and the development patterns that expose many people to tsunami hazards.”
The report, by Sustainable Living Solutions, of Portland, relies on prior research by the Oregon Department of Geology and Mineral Industries and others, and it uses different data sources for northern counties than south.
An estimated 12,090 would die in Clatsop County, 4,786 in Tillamook County, 1,015 in Lincoln, 43 in Lane, 352 in Coos and 382 in Curry. The report estimates zero deaths in Douglas County but notes this is likely an underestimate.
Included are those dead in the tsunami and in the hours immediately after, not those who might later succumb to wounds or conditions like “tsunami lung,” a severe, chronic pneumonia that can result from near-drowning. Estimates do not include potential casualties from the earthquake itself.
In Lincoln County, Bayshore is estimated to see the highest number of fatalities — 302, followed by Lincoln City (236), Gleneden Beach (224) and Beverly Beach (143). The report estimates 49 would die in Newport.
A study cited in the report, which examines potential tsunami impacts in Rockaway Beach, Gearhart, Port Orford, Lincoln City and Newport, notes that the latter two and Rockaway Beach can experience daytime population increases of up to 700 percent of their full-time residents, which would multiply potential casualties.
That study found people in the two Lincoln County cities would have advantages over others in terms of accessibility of evacuation points, and both have fewer homes and rental lodging located in tsunami zones. Its worst-case scenario estimate was 750 deaths in Newport and 6,600 in Gearhart, attributing the high number in the latter to “the significant travel distances required in order to reach high ground in the eastern foothills.”
The report for the health authority estimated 100 injuries in Lincoln County, who could arrive en masse at the two local hospitals.
Speaking to the Lincoln County Board of Commissioners in September in the context of the COVID-19 pandemic, Dr. Lesley Ogden, chief executive officer of Samaritan Pacific Communities and Samaritan North Lincoln hospitals, said overwhelming demand would prompt activation of hospital incident command and a shift to surge mode.
This could enable the Newport hospital to treat as many as 150 patients, Ogden said, with all available space and staff rededicated from non-emergent surgery and clinics. Health care facility capacity could be reduced due to earthquake damage, the report notes. The main facilities on both of Lincoln County’s hospital campuses are recently constructed to modern seismic standards.
Detailed evacuation maps for Lincoln County can be found online at tinyurl.com/wcczunmb. Survivors are likely to be stranded with no outside aid for weeks or months — damage to roads and bridges could even isolate people between neighborhoods — which is why emergency management officials put such a heavy emphasis on preparation.
Disaster caches are located throughout the county, stocked with provisions for nearby residents (and students, in the case of the disaster caches at each area school). None of those can come close to accommodating all the additional tourists between Yachats and Roads End at 2 p.m. on a Saturday in July.
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