The Cascadia earthquake: power for months, not days

What it is, and the odds

The Cascadia Subduction Zone is a 700-mile fault 70 to 100 miles off the coast, from northern California to British Columbia. A full rupture would be a magnitude 9 or larger, with five to seven minutes of shaking on the coast and a tsunami that could reach 100 feet (Oregon OEM).

The last one struck on January 26, 1700. The odds in the next 50 years, from Oregon's geology agency (DOGAMI):

7–12% for a rupture along the whole fault
16–22% for one hitting the Oregon and northern California coast
37–43% for a smaller one along southern Oregon and northern California

How long things stay broken

Oregon's own Resilience Plan estimated how long services would take to come back under present conditions (Oregon Resilience Plan):

Service	Willamette Valley	Coast
Electricity	1 to 3 months	3 to 6 months
Drinking water and sewer	1 month to 1 year	1 to 3 years

The same plan asked Oregon to change its advice from 72 hours of supplies to a minimum of two weeks, and possibly more. That's now "Be 2 Weeks Ready" in both Oregon and Washington (Oregon OEM, Washington EMD).

The run above uses two months as the usual case, the middle of the Valley estimate, and six months as the worst, the coast. It runs in your darkest month, because it can happen any time.

What it means for you

Power for months beats fuel for days. No one stores six months of generator fuel. A solar and battery system sized for your darkest month keeps refilling itself, as long as it can run without the grid (why that matters).
Water is the long pole. With water service out for months to years, a well with power for its pump, or a filter and a water source, is worth more than a bigger stockpile. Store two weeks to start: a gallon per person per day (FEMA, where to start).
Strap things down. The Earthquake Country Alliance's first step is to secure the water heater to wall studs with two metal straps, and top-heavy furniture and appliances to studs too (ECA). Treat a battery rack the same way.

Common questions

How long would the power be out after a Cascadia earthquake?

Oregon's Resilience Plan estimates 1 to 3 months in the Willamette Valley and 3 to 6 months on the coast, under present conditions. Drinking water and sewer take longer: 1 month to a year in the Valley, 1 to 3 years on the coast.

What are the odds of a Cascadia earthquake?

For the next 50 years, Oregon's geology agency (DOGAMI) gives 7–12% for a full-length rupture, 16–22% for one that hits the Oregon and northern California coast, and 37–43% for a smaller one along southern Oregon and northern California. The last one struck on January 26, 1700.

Is two weeks of supplies enough?

It's the minimum Oregon and Washington ask everyone to have, up from the old 72 hours. With power out for months in many places, a way to make your own power and get your own water matters more than a bigger stockpile.