Mercer Island's Seismic Design Category, explained

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Mercer Island in Seismic Design 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. Rank it against the rest of the country and Mercer Island sits at the 93th percentile for seismic hazard among 4,875 US cities.

How Mercer Island compares

USGS's underlying values for Mercer Island: 0.615g peak ground acceleration, 1.437g at short period, 0.499g at 1 second. Within Washington alone, Mercer Island ranks 13 of 125 cities by seismic hazard - the 90th percentile in-state. Mercer Island has a population of about 25,302.

Bracing and bolting: the actual cost

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.

Earthquake insurance for a Mercer Island home

A Mercer Island 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 Mercer Island's figures come from

Mercer Island'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 Mercer Island.