Does Antioch, IL need an earthquake retrofit?

Under the seismic model IBC and ASCE 7 use for new construction, Antioch is Category B. Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. That puts Antioch in the 29th percentile nationally for seismic hazard - higher than 29% of the 4,875 US cities USGS was checked against here.

How Antioch compares

The raw figures: peak ground acceleration 0.048g, short-period spectral response 0.096g, 1-second spectral response 0.055g. Among 330 Illinois cities in this dataset, Antioch ranks 322 for seismic hazard, the 2th percentile within the state. About 15,108 people live in Antioch, 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 Antioch address.

More on how this number was built

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