Seattle's Seismic Design Category, explained

Under the seismic model IBC and ASCE 7 use for new construction, Seattle is Category D. High seismic hazard - this is the category most of coastal California, the Pacific Northwest, and other active fault regions fall into. Code mandates significant seismic detailing and restricts irregular structural configurations. This is the category the Brace + Bolt scope (cripple-wall bracing, foundation bolting) is built for. Nationally, Seattle ranks above 92% of the 4,875 cities in this dataset for seismic hazard - the 92th percentile.

How Seattle compares

USGS's underlying values for Seattle: 0.59g peak ground acceleration, 1.385g at short period, 0.483g at 1 second. Within Washington alone, Seattle ranks 23 of 125 cities by seismic hazard - the 82th percentile in-state. Seattle has a population of about 780,995.

What a retrofit costs in Seattle

A full earthquake retrofit typically runs $5,000-$10,000 nationally (around $7,000 typical), driven mainly by house size and foundation type, not by Washington specifically. California's Earthquake Brace + Bolt grant, which covers a large share of this cost, is a California-only program and does not apply in Washington.

What this means for insurance

A Seattle homeowner cannot buy a standalone earthquake policy in most cases - it is added to an existing homeowners policy as an endorsement, so the place to start is a regular home-insurance quote.

Where Seattle's figures come from

Seattle's Category D and every number above trace to USGS's own ASCE 7-16 Design Maps service - see the methodology guide. See the category explainer for what Category D does and doesn't tell you about Seattle.