Does Rock Falls, IL need an earthquake retrofit?

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Rock Falls in Seismic Design Category B: Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. That puts Rock Falls in the 36th percentile nationally for seismic hazard - higher than 36% of the 4,875 US cities USGS was checked against here.

How Rock Falls compares

The raw figures: peak ground acceleration 0.059g, short-period spectral response 0.117g, 1-second spectral response 0.065g. Among 330 Illinois cities in this dataset, Rock Falls ranks 254 for seismic hazard, the 23th percentile within the state. About 8,614 people live in Rock Falls, Illinois.

What a retrofit costs in Rock Falls

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.

Insuring against this, not just retrofitting

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 Rock Falls address.

More on how this number was built

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