Introduction: A Region That Practices the Worst Case
Puget Sound is the rare American metro whose defining disaster has a name, a date, and a rehearsal schedule. The Cascadia Subduction Zone, offshore from northern California to Vancouver Island, last ruptured on January 26, 1700, in an earthquake estimated at magnitude 9.0. The region’s planners do not debate whether it will happen again; they run exercises about it. Cascadia Rising, the multi-state exercise series built on the magnitude-9 scenario, put more than 20,000 participants through four days of play in June 2016 alone.
This is a local-resilience audit for Seattle–Tacoma healthcare operators: the seismic stack the region actually faces, the access problem the region has already lived in peacetime — a major hospital catchment severed by one bridge — and what a continuity program here must contain that a generic one does not.
The Seismic Stack: Three Fault Systems, One Planning Scenario
The subduction zone is the headline, but the planning picture has three layers. The Cascadia Subduction Zone sits roughly 100 miles off the coast and, on the geological record, ruptures at intervals of roughly 300 to 500 years — the 1700 event is more than three centuries past. University of Washington researchers working the standard M9 planning scenario put a full-zone rupture at magnitude 8.7 to 9.2, with an estimated 7 to 12 percent chance of occurring in the next 50 years, and minutes — not seconds — of strong shaking. Layered under the metro itself are crustal faults: the Seattle Fault, running east–west directly beneath the city; the Tacoma Fault; and the South Whidbey Island Fault, each assessed as capable of producing an earthquake of magnitude 7.0 or greater, at much shallower depth and therefore with intense local shaking.
For facility planning, the layers differ in kind. A Cascadia event is a regional catastrophe: the exercise scenario assumes bridges down, freeways cut, power and communications grids dark, and help arriving from across the country over days to weeks — the planning consequence is extended self-sufficiency. A Seattle Fault event is a local catastrophe with a functioning region around it: the planning consequence is surge, mutual aid, and patient movement. A continuity program that conflates the two will mis-size both. The federal floor remains the CMS Emergency Preparedness Rule, covered in our guide to the rule’s four core components; the Puget Sound addition is that the hazard analysis must carry both scenarios separately, with different resource assumptions for each.
The region’s exercise program has played the hospital layer specifically. The Washington Military Department’s Cascadia Rising account describes, among dozens of missions, a water-purification system established at St. Clare Hospital in Lakewood and hoist training with an air support squadron at Grays Harbor Community Hospital — because in the scenario, some patients will have to be evacuated by helicopter when roads are cut. Those two details are the audit in miniature: water independence and vertical evacuation are not abstractions here; they are rehearsed tasks.
The One-Bridge Problem: Access as a Continuity Asset
Seismic planning in Puget Sound is usually framed as a future risk. The access half of it has already happened, in peacetime, for two and a half years. In March 2020, the Seattle Department of Transportation closed the West Seattle Bridge — the high-rise crossing that is the West Seattle peninsula’s fast route to the rest of the city — after inspectors found cracks growing rapidly in the 40-year-old structure. The bridge did not reopen until September 17, 2022, a closure of 908 days.
What replaced it is the continuity case study. The lower Spokane Street Swing Bridge became the peninsula’s lifeline, and the city rationed it: during daytime hours it was restricted to emergency vehicles, transit, and freight. As the closure wore on, the city granted conditional access to additional categories — a City Council account of the program lists on-call medical workers and people traveling for lifesaving medical treatments among those authorized, alongside maritime and industrial users. In other words, for 908 days, one swing bridge’s access list functioned as a de facto healthcare-continuity instrument for a peninsula of more than 100,000 people: ambulance routing, staff commuting, and patient access to the region’s hospitals all ran through a permit decision at a transportation department.
West Seattle is the famous case, not the only geometry. The Tacoma Narrows crossing is the single road route between the Gig Harbor and Key Peninsula communities and the hospital concentration in Tacoma. Vashon Island’s surface access is ferry-only — which is why Cascadia Rising play included Army landing craft delivering support to the island when ferry terminals were assumed inoperable. The audit principle generalizes: for every campus, the continuity question is not only “what is our alternate site” but “by which named crossings do patients, staff, fuel, and supplies reach us — and what is the plan for the day one of those crossings is the thing that failed.” A destination without a route is a line in a plan, not a capability. Patient-movement, staffing, and supply assumptions should each be written against primary and alternate routes, and re-validated whenever the region’s bridge program changes — bridge closures for repair are announced years in advance and still routinely absent from hospital continuity files.
What the Exercises Already Taught
Cascadia Rising 2016 ran four days in June 2016 across Washington, Oregon, and Idaho, with more than 20,000 participants from over 100 federal, state, county, local, and tribal agencies, built on the magnitude-9.0 scenario: up to five minutes of shaking, a destructive tsunami on the coast, aftershocks, and lifelines dark. Its published priority areas — operational communications and public health and medical services among the top six — read as a list of what the region’s own planners judge most likely to fail first. Communications failure is the recurring exercise finding everywhere, but in the Cascadia scenario it has a specific shape: the systems that survive must work across a region where the wired infrastructure is assumed down and the receiving facilities for mutual aid are themselves managing damage.
For an individual facility, the exercise program’s value is that it prices assumptions. A plan that assumes staff will report assumes those staff can cross the region; a plan that assumes resupply in 72 hours assumes a logistics chain the scenario explicitly breaks; a plan that assumes helicopter evacuation assumes landing zones, hoist-capable partners, and weather. Facilities that play in the regional exercises learn which of their assumptions are regional fictions. Facilities that do not play should at least borrow the scenario: our disaster recovery plan testing guide covers exercise design and after-action discipline, and our healthcare continuity compliance guide covers the regulatory frame the exercise results feed back into.
The Continuity Audit: Seismic Plus Access
Nonstructural mitigation, inventoried. In earthquakes, hospitals most often lose function to nonstructural failure — toppled equipment, broken piping, fallen ceilings, jammed doors — rather than structural collapse. The audit: anchoring and bracing status for critical equipment, flexible connections on medical gas, water, and fuel lines, and a post-event building assessment protocol that can clear or condemn space in hours, because the first operational question after shaking stops is which rooms are usable.
Self-sufficiency sized to the scenario, not the slogan. The Cascadia planning assumption is regional isolation measured in days to weeks, not the conventional 72 hours. State the facility’s position honestly in hours and days: generator fuel under load, potable water, food for patients and ride-in staff, and pharmaceuticals — and reconcile it with the exercise record, which assumes resupply arrives by air and sea before it arrives by road.
Staff as residents first. Every exercise account of Cascadia makes the same point: the workforce is drawn from the affected population. Staff-family support provisions, on-site sheltering, and reporting expectations graded to a region where some staff physically cannot arrive are operational controls, not kindnesses — they determine the staffing denominator on day two. The financial exposure of the long tail — a region rebuilding for years — belongs in the same conversation as business interruption coverage.
The route map. For each campus: primary and alternate road routes for ambulances, staff, and freight, named by crossing; the permit or priority-access arrangement, if any, that governs the alternate in an emergency (the West Seattle precedent — a city-issued access list that included medical travel — now exists as a model to negotiate before the event, not during it); helicopter landing capability and its limits; and the trigger points at which patient movement shifts from road to air or water. Review the map whenever the regional bridge and ferry program changes.
Frequently Asked Questions
What is Cascadia Rising?
A multi-state exercise series built on a magnitude-9.0 Cascadia Subduction Zone earthquake and tsunami scenario. The 2016 iteration ran four days across Washington, Oregon, and Idaho with more than 20,000 participants from over 100 agencies; hospital-specific play included establishing a water-purification system at St. Clare Hospital in Lakewood and helicopter hoist training for patient evacuation at Grays Harbor Community Hospital.
How likely is the magnitude-9 earthquake, and how long would shaking last?
The zone last ruptured on January 26, 1700, and historically recurs at roughly 300-to-500-year intervals. University of Washington researchers estimate a 7 to 12 percent chance of a magnitude 8.7–9.2 event in the next 50 years. The planning scenario assumes up to about five minutes of strong shaking — far longer than a typical crustal earthquake — which is why nonstructural damage and lifeline failure, rather than building collapse alone, dominate the planning.
What did the West Seattle Bridge closure teach hospitals?
That access is a continuity asset that can fail without any disaster. The bridge closed in March 2020 over rapidly growing cracks and stayed closed for 908 days; the low bridge that replaced it was rationed, with emergency vehicles prioritized and conditional access later extended to on-call medical workers and people traveling for lifesaving treatment. Hospital catchments across Puget Sound sit behind single crossings — the Tacoma Narrows route to Gig Harbor and the Key Peninsula, ferry-only Vashon Island — and continuity plans should map those routes by name.
What is the difference between planning for Cascadia and planning for the Seattle Fault?
Scale and self-sufficiency. A Seattle Fault earthquake (magnitude 7+) is a severe local event inside a functioning region — mutual aid, surge, and patient movement dominate. A Cascadia rupture is a regional catastrophe in which the exercise scenario assumes bridges down, grids dark, and outside help arriving over days to weeks — extended self-sufficiency in fuel, water, food, and communications dominates. The hazard analysis should carry them as separate scenarios with separate resource assumptions.
Continuity Hub’s metro series audits local resilience the way the national guides audit frameworks. The companion pieces cover New York City and Houston.