Silvis's Seismic Design Category, explained

Under the seismic model IBC and ASCE 7 use for new construction, Silvis is Category B. Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. Nationally, Silvis ranks above 27% of the 4,875 cities in this dataset for seismic hazard - the 27th percentile.

Silvis by the numbers

The raw figures: peak ground acceleration 0.047g, short-period spectral response 0.098g, 1-second spectral response 0.065g. Among 330 Illinois cities in this dataset, Silvis ranks 326 for seismic hazard, the 1th percentile within the state. About 8,003 people live in Silvis, Illinois.

What a retrofit costs in Silvis

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 Silvis address.

More on how this number was built

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