Glen Carbon's Seismic Design Category, explained

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Glen Carbon 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. Nationally, Glen Carbon ranks above 84% of the 4,875 cities in this dataset for seismic hazard - the 84th percentile.

Where Glen Carbon sits in Illinois

The raw figures: peak ground acceleration 0.25g, short-period spectral response 0.436g, 1-second spectral response 0.156g. Among 330 Illinois cities in this dataset, Glen Carbon ranks 33 for seismic hazard, the 90th percentile within the state. About 13,883 people live in Glen Carbon, Illinois.

Bracing and bolting: the actual cost

Outside California, no state-level retrofit grant equivalent to Brace + Bolt could be found for Illinois. 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 Glen Carbon address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced Glen Carbon'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.