Black Diamond's Seismic Design Category, explained

Black Diamond carries Seismic Design Category D under USGS's ASCE 7-16 model. 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, Black Diamond ranks above 90% of the 4,875 cities in this dataset for seismic hazard - the 90th percentile.

How Black Diamond compares

USGS's underlying values for Black Diamond: 0.497g peak ground acceleration, 1.175g at short period, 0.403g at 1 second. Within Washington alone, Black Diamond ranks 69 of 125 cities by seismic hazard - the 45th percentile in-state. Black Diamond has a population of about 6,787.

Retrofit economics for Black Diamond

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 Black Diamond 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 Black Diamond's figures come from

Black Diamond'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 Black Diamond.