Does Riverdale, IL need an earthquake retrofit?

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Riverdale in Seismic Design Category B: Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. That puts Riverdale in the 38th percentile nationally for seismic hazard - higher than 38% of the 4,875 US cities USGS was checked against here.

Where Riverdale sits in Illinois

The raw figures: peak ground acceleration 0.061g, short-period spectral response 0.122g, 1-second spectral response 0.066g. Among 330 Illinois cities in this dataset, Riverdale ranks 229 for seismic hazard, the 31th percentile within the state. About 10,299 people live in Riverdale, 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.

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 Riverdale address.

More on how this number was built

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