St. Clair's Seismic Design Category, explained

Under the seismic model IBC and ASCE 7 use for new construction, St. Clair is Category A. Lowest seismic design category. Building code requires no seismic-specific detailing here beyond ordinary construction practice. Rank it against the rest of the country and St. Clair sits at the 14th percentile for seismic hazard among 4,875 US cities.

St. Clair by the numbers

The raw figures: peak ground acceleration 0.042g, short-period spectral response 0.086g, 1-second spectral response 0.041g. Among 153 Michigan cities in this dataset, St. Clair ranks 122 for seismic hazard, the 20th percentile within the state. About 5,824 people live in St. Clair, Michigan.

What a retrofit costs in St. Clair

Outside California, no state-level retrofit grant equivalent to Brace + Bolt could be found for Michigan. A typical retrofit still runs $5,000-$10,000 nationally, about $7,000 for a common single-family job.

What this means for insurance

Outside California, earthquake coverage is typically sold as an endorsement added to a standard homeowners policy, not a separate product - worth asking about directly when getting a home-insurance quote for a St. Clair address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced St. Clair's numbers. The guide to what a Seismic Design Category actually means covers why a category is never a substitute for an engineer's assessment of one specific house.